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Energies, Volume 7, Issue 6 (June 2014) – 31 articles , Pages 3512-4053

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4215 KiB  
Article
An Intelligent Fuzzy Logic Controller for Maximum Power Capture of Point Absorbers
by Mohammed Jama, Addy Wahyudie, Ali Assi and Hassan Noura
Energies 2014, 7(6), 4033-4053; https://doi.org/10.3390/en7064033 - 24 Jun 2014
Cited by 25 | Viewed by 7314
Abstract
This article presents an intelligent fuzzy logic controller (FLC) for controlling single-body heaving wave energy converter (WEC) or what is widely known as “Point Absorber”. The controller aims at maximizing the energy captured from the sea waves. The power take-off (PTO) limitations are [...] Read more.
This article presents an intelligent fuzzy logic controller (FLC) for controlling single-body heaving wave energy converter (WEC) or what is widely known as “Point Absorber”. The controller aims at maximizing the energy captured from the sea waves. The power take-off (PTO) limitations are addressed implicitly in the fuzzy inference system (FIS) framework. In order to enhance the WEC power capturing bandwidth and make it less susceptible to wave environment irregularities and the system parametric uncertainties, the controller is built to have a self-configurable capability. This also eliminates the need to repeatedly run in-situ tuning procedure of the fuzzy controller or switch between several controllers based on the operating conditions. The fuzzy membership functions (MFs) are optimally tuned using particle swarm optimization (PSO) algorithm. To alleviate the computational burden associated with performing on-line optimization, the fuzzy controller is tuned at a rate significantly lower than the system sampling time. The suggested PSO-FLC has shown promising results compared with the fixed structure fuzzy logic controller (FS-FLC) and other passive control strategies. Several computer simulations were carried out to evaluate the controller effectiveness by applying different sea-states and analyzing the resultant WEC dynamics. Full article
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<p>Heaving point absorber structure.</p> Full article ">
<p>The Gaussian MFs updating principle.</p> Full article ">
<p>Block diagram of the proposed PSO-FLC controller.</p> Full article ">
<p>The dynamics of the WEC buoy under different controllers (<b>a</b>) wave elevation; (<b>b</b>) buoy displacement; (<b>c</b>) buoy velocity.</p> Full article ">
<p>The instantaneous absorbed power (black) along with the corresponding time-averaged power (grey) (<b>a</b>) PSO-FLC; (<b>b</b>) FS-FLC; (<b>c</b>) PRC.</p> Full article ">
<p>The dynamics of the WEC PTO (<b>a</b>) damping coefficient; (<b>b</b>) stiffness coefficient; (<b>c</b>) PTO control force.</p> Full article ">
<p>Comparison of the controllers performance for sea-states with <span class="html-italic">H<sub>s</sub></span> = 1 m and varying wave frequency (<b>a</b>) average absorbed power; (<b>b</b>) average-to-peak power ratio; (<b>c</b>) normalized PTO damping; (<b>d</b>) normalized PTO stiffness.</p> Full article ">
<p>Comparison of the controllers performance for sea-state with <span class="html-italic">H<sub>s</sub></span> = 3 m and varying wave frequency (<b>a</b>) average absorbed power; (<b>b</b>) average-to-peak power ratio; (<b>c</b>) normalized PTO damping; (<b>d</b>) normalized PTO stiffness.</p> Full article ">
<p>Jonswap wave spectrum of a sea-state with <span class="html-italic">T<sub>p</sub></span>= 11s and <span class="html-italic">H<sub>s</sub></span> = 2.25 m, broad bandwidth (solid) narrow bandwidth (dashed).</p> Full article ">
1237 KiB  
Article
Investigation of Process Variables in the Densification of Corn Stover Briquettes
by Curtis P. Thoreson, Keith E. Webster, Matthew J. Darr and Emily J. Kapler
Energies 2014, 7(6), 4019-4032; https://doi.org/10.3390/en7064019 - 24 Jun 2014
Cited by 22 | Viewed by 7710
Abstract
The bulk density of raw corn stover is a major limitation to its large-scale viability as a biomass feedstock. Raw corn stover has a bulk density of 50 kg/m3, which creates significant transportation costs and limits the optimization of transport logistics. [...] Read more.
The bulk density of raw corn stover is a major limitation to its large-scale viability as a biomass feedstock. Raw corn stover has a bulk density of 50 kg/m3, which creates significant transportation costs and limits the optimization of transport logistics. Producing a densified corn stover product during harvest would reduce harvest and transportation costs, resulting in viable pathways for the use of corn stover as a biomass feedstock. This research investigated the effect of different process variables (compression pressure, moisture content, particle size, and material composition) on a densification method that produces briquettes from raw corn stover. A customized bench-scale densification system was designed to evaluate different corn stover inputs. Quality briquette production was possible using non-reduced particle sizes and low compression pressures achievable in a continuous in-field production system. At optimized bench settings, corn stover was densified to a dry bulk density of 190 kg/m3. Corn stover with a moisture content above 25%wb was not suitable for this method of bulk densification, and greater cob content had a positive effect on product quality. Full article
(This article belongs to the Special Issue Renewable Energy for Agriculture)
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Figure 1

Figure 1
<p>Cross-section of densification region.</p> Full article ">Figure 2
<p>Free body diagram of the die region of the densification system.</p> Full article ">Figure 3
<p>Treatment factor effects on dry particle density. Compression pressure and moisture content are averaged over all particle sizes. Means are represented by the crossed circle and error bars indicate the 95% confidence interval for the mean.</p> Full article ">Figure 4
<p>Qualitative comparison of briquettes produced under varying parameters. All briquettes shown were produced with corn stover (classification 1 in <a href="#sec2dot2-energies-07-04019" class="html-sec">Section 2.2</a>) unless otherwise indicated. (<b>A</b>) “as received” briquette produced under 7.0 MPa in the three-way interaction experiment; (<b>B</b>) “as received” briquette produced under 14.0 MPa in the three-way interaction experiment; (<b>C</b>) “hammer milled” briquette produced in the three-way interaction experiment; (<b>D</b>) briquette produced at 47.6%wb moisture content in the moisture effects experiment; (<b>E</b>) briquette produced using MOG in the material types experiment; (<b>F</b>) briquette produced using pure cubs in the material types experiment.</p> Full article ">Figure 5
<p>Treatment factor effects on dry particle density. Means are represented by the crossed circle and error bars indicate the 95% confidence interval for the mean.</p> Full article ">Figure 6
<p>Moisture content effect on dry particle density averaged over all levels of compression, pressure, and die taper angle. Means are represented by the crossed circle and error bars indicate the 95% confidence interval for the mean.</p> Full article ">Figure 7
<p>Moisture content effects on axial expansion and dry briquette weight. Means are represented by the crossed circle and error bars indicate the 95% confidence interval for the mean.</p> Full article ">Figure 8
<p>Treatment factor effects on dry particle density. Means are represented by the crossed circle and error bars indicate the 95% confidence interval for the mean.</p> Full article ">Figure 9
<p>Material moisture content effect on density. Means are represented by the crossed circle and error bars indicate the 95% confidence interval for the mean.</p> Full article ">
1543 KiB  
Review
Evaluation of the Wave Energy Conversion Efficiency in Various Coastal Environments
by Eugen Rusu
Energies 2014, 7(6), 4002-4018; https://doi.org/10.3390/en7064002 - 24 Jun 2014
Cited by 122 | Viewed by 10810
Abstract
The main objective of the present work was to assess and compare the wave power resources in various offshore and nearshore areas. From this perspective, three different groups of coastal environments were considered: the western Iberian nearshore, islands and an enclosed environment with [...] Read more.
The main objective of the present work was to assess and compare the wave power resources in various offshore and nearshore areas. From this perspective, three different groups of coastal environments were considered: the western Iberian nearshore, islands and an enclosed environment with sea waves, respectively. Some of the most representative existent wave converters were evaluated in the analysis and a second objective was to compare their performances at the considered locations, and in this way to determine which is better suited for potential commercial exploitation. In order to estimate the electric power production expected in a certain location, the bivariate distributions of the occurrences corresponding to the sea states, defined by the significant wave height and the energy period, were constructed in each coastal area. The wave data were provided by hindcast studies performed with numerical wave models or based on measurements. The transformation efficiency of the wave energy into electricity is evaluated via the load factor and also through the capture width, defined as the ratio between the electric power estimated to be produced by each specific wave energy converters (WEC) and the expected wave power corresponding to the location considered. Finally, by evaluating these two different indicators, comparisons of the performances of three WEC types (Aqua Buoy, Pelamis and Wave Dragon) in the three different groups of coastal environments considered have been also carried out. The work provides valuable information related to the effectiveness of various technologies for the wave energy extraction that would operate in different coastal environments. Full article
(This article belongs to the Special Issue Selected Papers from the 1st International e-Conference on Energies — Whither Energy Conversion? Present Trends, Current Problems and Realistic Future Solutions)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>The specific pattern for the west Iberian nearshore, scatter diagrams <span class="html-italic">H</span><sub>s</sub>-<span class="html-italic">T</span><sub>e</sub> as resulted from 41 years (1960–2000) of WAM (acronym for Wave Modeling) simulations (structured in total and winter time, respectively). The color scale is used to represent the contribution of the sea state to the total incident energy, as a percentage. The wave power isolines are also represented.</p> Full article ">Figure 2
<p>.Distribution of the mean relative wave power and the positions of the reference points in the northwest Iberian and Portuguese coastal environments (<b>a</b>) the northwestern Iberian nearshore (denoted as the Spanish nearshore), SWAN simulation corresponding to the time frame 2010/01/16/h18 reflecting high non storm energy conditions, the positions of 12 reference points are also indicated (I-points), the computational domains considered in the Portuguese nearshore are also indicated. The extents of the geographical spaces corresponding to the subsequent northern and central computational domains are also illustrated. (<b>b</b>) and (<b>c</b>) the northern and central domains defined in the Portuguese nearshore, SWAN simulations corresponding to the time frame 2010/04/22/h18 reflecting average wave energy conditions, the positions of 15 reference points are defined in each case (NP and CP-points, respectively).</p> Full article ">Figure 3
<p>(<b>a</b>) Canary Islands (C-points), the map of the area and the positions of the reference points considered. The other data points available are represented by white dots. (<b>b</b>) Distribution of the mean relative wave power in the vicinity of Madeira island (SWAN simulation corresponding to the time frame 2001/03/18/h06, average energetic conditions), the position of the reference point M1 is also represented; (<b>c</b>) Wave energy pattern in the vicinity of Porto Santo island (SWAN simulation corresponding to the time frame 2001/03/18/h06, average energetic conditions), the position of the reference points M2 and M3 are also represented.</p> Full article ">Figure 4
<p>(<b>a</b>) Distribution of the mean relative wave power in the Black Sea (SWAN simulation corresponding to the time frame 1997/01/18/h12, average energetic conditions) and the position of the reference point (B-point); (<b>b</b>) Distribution of the mean relative wave power in the Caspian Sea (SWAN simulation corresponding to the time frame 2009/10/02/h18, winter average energy conditions).</p> Full article ">Figure 5
<p>Expected electric power in various coastal environments. (<b>a</b>) Aqua Buoy; (<b>b</b>) Pelamis; (<b>c</b>) Wave Dragon.</p> Full article ">
589 KiB  
Article
Efficacy and Efficiency of Italian Energy Policy: The Case of PV Systems in Greenhouse Farms
by Filippo Sgroi, Salvatore Tudisca, Anna Maria Di Trapani, Riccardo Testa and Riccardo Squatrito
Energies 2014, 7(6), 3985-4001; https://doi.org/10.3390/en7063985 - 24 Jun 2014
Cited by 65 | Viewed by 8259
Abstract
The production of energy from renewable sources is a form of energy production that has less impact on the environment than the traditional one. For the farmer this new form of production represents an opportunity, especially for the economic benefits that can produce, [...] Read more.
The production of energy from renewable sources is a form of energy production that has less impact on the environment than the traditional one. For the farmer this new form of production represents an opportunity, especially for the economic benefits that can produce, both in terms of the incentives provided by the public operator and for higher revenues, deriving from the sale of energy back to the grid and/or the savings generated by self-consumed energy, that help to increase the farmer’s income. In this paper, we analyzed a case study of a farm that has realized a grid-connected photovoltaic (PV) system on a greenhouse. In particular, firstly the farm profitability has been estimated and subsequently, in order to assess the efficiency of the energy policy adopted by the Second Conto Energia in Italy, the minimum incentive tariff at which the entrepreneur has an economic advantage to realize a PV system has been determined. Results show that PV system relegates to a marginal role the cultivation of agricultural products compared to energy production and that government PV remuneration policies far outweigh the minimum threshold that makes the investment advantageous. Full article
(This article belongs to the Special Issue Energy Transitions and Economic Change)
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Figure 1

Figure 1
<p>Case study.</p> Full article ">Figure 2
<p>Breakeven point determination.</p> Full article ">
3888 KiB  
Article
Investigation of a Five-Phase Dual-Rotor Permanent Magnet Synchronous Motor Used for Electric Vehicles
by Yumeng Li, Jing Zhao, Zhen Chen and Xiangdong Liu
Energies 2014, 7(6), 3955-3984; https://doi.org/10.3390/en7063955 - 24 Jun 2014
Cited by 13 | Viewed by 13376
Abstract
This paper presents a novel five-phase permanent magnet synchronous motor (PMSM), which contains dual rotors and a single stator, equivalent to two five-phase motors working together. Thus, this kind of motor has the potential of good fault tolerant capability and high torque density, [...] Read more.
This paper presents a novel five-phase permanent magnet synchronous motor (PMSM), which contains dual rotors and a single stator, equivalent to two five-phase motors working together. Thus, this kind of motor has the potential of good fault tolerant capability and high torque density, which makes it appropriate for use in electric vehicles. In view of the different connection types, the inside and outside stator windings can be driven in series or parallel, which results in the different performances of the magnetomotive force (MMF) and torque under open-circuit fault conditions. By decomposing the MMF, the reason that torque ripple increases after open-circuit faults is explained, and the relationship between MMF and torque is revealed. Then, the current control strategy is applied to adjust the open-circuit faults, and the electromagnetic analysis and MMF harmonics analysis are performed to interpret the phenomenon that the torque ripple is still larger than in the normal situation. The investigations are verified by finite element analysis results. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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Graphical abstract

Graphical abstract
Full article ">
<p>The Component diagram of five-phase DRPMSM.</p> Full article ">
<p>Finite element model of five-phase DRPMSM.</p> Full article ">
<p>Drive mode of five-phase DRPMSM: (<b>a</b>) series; (<b>b</b>) parallel.</p> Full article ">
<p>Phase “a” winding function.</p> Full article ">
<p>MMF distribution under normal conditions: (<b>a</b>) time-space distribution; (<b>b</b>) space domain projection; (<b>c</b>) time domain projection.</p> Full article ">
<p>MMF distribution under one phase open-circuit fault case a: (<b>a</b>) time-space distribution; (<b>b</b>) space domain projection; (<b>c</b>) time domain projection.</p> Full article ">
<p>MMF distribution under one phase open-circuit fault case b: (<b>a</b>) time-space distribution; (<b>b</b>) space domain projection; (<b>c</b>) time domain projection.</p> Full article ">
<p>MMF distribution under one phase open-circuit fault case c: (<b>a</b>) time-space distribution; (<b>b</b>) space domain projection; (<b>c</b>) time domain projection.</p> Full article ">
<p>Torque comparison under one phase open-circuit fault without adjustment: (<b>a</b>) three fault cases; (<b>b</b>) fault case c equivalent.</p> Full article ">
1895 KiB  
Article
A Systematic Method for Designing a PR Controller and Active Damping of the LCL Filter for Single-Phase Grid-Connected PV Inverters
by Ningyun Zhang, Houjun Tang and Chen Yao
Energies 2014, 7(6), 3934-3954; https://doi.org/10.3390/en7063934 - 24 Jun 2014
Cited by 135 | Viewed by 15450
Abstract
The Proportional Resonant (PR) current controller provides gains at a certain frequency (resonant frequency) and eliminates steady state errors. Therefore, the PR controller can be successfully applied to single grid-connected PV inverter current control. On the contrary, a PI controller has steady-state errors [...] Read more.
The Proportional Resonant (PR) current controller provides gains at a certain frequency (resonant frequency) and eliminates steady state errors. Therefore, the PR controller can be successfully applied to single grid-connected PV inverter current control. On the contrary, a PI controller has steady-state errors and limited disturbance rejection capability. Compared with the L- and LC filters, the LCL filter has excellent harmonic suppression capability, but the inherent resonant peak of the LCL filter may introduce instability in the whole system. Therefore, damping must be introduced to improve the control of the system. Considering the controller and the LCL filter active damping as a whole system makes the controller design method more complex. In fact, their frequency responses may affect each other. The traditional trial-and-error procedure is too time-consuming and the design process is inefficient. This paper provides a detailed analysis of the frequency response influence between the PR controller and the LCL filter regarded as a whole system. In addition, the paper presents a systematic method for designing controller parameters and the capacitor current feedback coefficient factor of LCL filter active-damping. The new method relies on meeting the stable margins of the system. Moreover, the paper also clarifies the impact of the grid on the inverter output current. Numerical simulation and a 3 kW laboratory setup assessed the feasibility and effectiveness of the proposed method. Full article
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<p>Two-stage single-phase grid-connected PV system with LCL filter typical topology.</p> Full article ">
<p>Two-stage single-phase PV system with LCL-filter control scheme.</p> Full article ">
<p>Injected current: control diagram.</p> Full article ">
<p>Equivalent control diagram.</p> Full article ">
<p>Ideal PR controller Bode diagram.</p> Full article ">
<p>Improved PR controller Bode diagram: (<b>a</b>) <span class="html-italic">K<sub>p</sub></span> = 0.4; (<b>b</b>) <span class="html-italic">K<sub>r</sub></span> = 1.</p> Full article ">
<p>LCL, and L filters Bode diagrams.</p> Full article ">
<p>Grid phase diagram.</p> Full article ">
<p>System with no PR controller: Bode diagram.</p> Full article ">
541 KiB  
Article
Effects of Pretreatment Methods on Electrodes and SOFC Performance
by Guo-Bin Jung, Li-Hsing Fang, Min-Jay Chiou, Xuan-Vien Nguyen, Ay Su, Win-Tai Lee, Shu-Wei Chang, I-Cheng Kao and Jyun-Wei Yu
Energies 2014, 7(6), 3922-3933; https://doi.org/10.3390/en7063922 - 23 Jun 2014
Cited by 11 | Viewed by 7008
Abstract
Commercially available tapes (anode, electrolyte) and paste (cathode) were choosen to prepare anode-supported cells for solid oxide fuel cell applications. For both anode-supported cells or electrolyte-supported cells, the anode needs pretreatment to reduce NiO/YSZ to Ni/YSZ to increase its conductivity as well as [...] Read more.
Commercially available tapes (anode, electrolyte) and paste (cathode) were choosen to prepare anode-supported cells for solid oxide fuel cell applications. For both anode-supported cells or electrolyte-supported cells, the anode needs pretreatment to reduce NiO/YSZ to Ni/YSZ to increase its conductivity as well as its catalytic characteristics. In this study, the effects of different pretreatments (open-circuit, closed-circuit) on cathode and anodes as well as SOFC performance are investigated. To investigate the influence of closed-circuit pretreatment on the NiO/YSZ anode alone, a Pt cathode is utilized as reference for comparison with the LSM cathode. The characterization of the electrical resistance, AC impedance, and SOFC performance of the resulting electrodes and/or anode-supported cell were carried out. It’s found that the influence of open-circuit pretreatment on the LSM cathode is limited. However, the influence of closed-circuit pretreatment on both the LSM cathode and NiO/YSZ anode and the resulting SOFC performance is profound. The effect of closed-circuit pretreatment on the NiO/YSZ anode is attributed to its change of electronic/pore structure as well as catalytic characteristics. With closed-circuit pretreatment, the SOFC performance improved greatly from the change of LSM cathode (and Pt reference) compared to the Ni/YSZ anode. Full article
(This article belongs to the Special Issue Reacting Transport Phenomena in Solid Oxide Fuel Cells)
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Figure 1

Figure 1
<p>Anode pretreatments via: (<b>a</b>) open-circuit; (<b>b</b>) closed-circuit proposed by this study.</p> Full article ">Figure 2
<p>Effect of pretreatment method and time on the performance of the supported anode.</p> Full article ">Figure 3
<p>Impedance spectra of anode supported cell with as-prepared, open-circuit and closed-circuit pretreatment: (<b>a</b>) 30 min; (<b>b</b>) 120 min.</p> Full article ">Figure 4
<p>Effect of pretreatment time on the performance of SOFC with Pt cathode: (<b>a</b>) open-circuit; (<b>b</b>) closed-circuit.</p> Full article ">Figure 5
<p>Impedance spectra of anode supported cell with Pt cathode with: (<b>a</b>) open-circuit; (<b>b</b>) closed-circuit pretreatment.</p> Full article ">Figure 6
<p>IV curve of NiO-YSZ/YSZ/LSM and NiO-YSZ/YSZ/Pt: (<b>a</b>) as-prepared; (<b>b</b>) after 2 h closed-circuit pretreatment.</p> Full article ">Figure 7
<p>AC curve of NiO-YSZ/YSZ/LSM and NiO-YSZ/YSZ/Pt.</p> Full article ">
1669 KiB  
Article
Communication Network Architectures for Smart-Wind Power Farms
by Mohamed A. Ahmed and Young-Chon Kim
Energies 2014, 7(6), 3900-3921; https://doi.org/10.3390/en7063900 - 23 Jun 2014
Cited by 28 | Viewed by 12502
Abstract
Developments in the wind power industry have enabled a new generation of wind turbines with longer blades, taller towers, higher efficiency, and lower maintenance costs due to the maturity of related technologies. Nevertheless, wind turbines are still blind machines because the control center [...] Read more.
Developments in the wind power industry have enabled a new generation of wind turbines with longer blades, taller towers, higher efficiency, and lower maintenance costs due to the maturity of related technologies. Nevertheless, wind turbines are still blind machines because the control center is responsible for managing and controlling individual wind turbines that are turned on or off according to demand for electricity. In this paper, we propose a communication network architecture for smart-wind power farms (Smart-WPFs). The proposed architecture is designed for wind turbines to communicate directly and share sensing data in order to maximize power generation, WPF availability, and turbine efficiency. We also designed a sensor data frame structure to carry sensing data from different wind turbine parts such as the rotor, transformer, nacelle, etc. The data frame includes a logical node ID (LNID), sensor node ID (SNID), sensor type (ST), and sensor data based on the International Electrotechnical Commission (IEC) 61400-25 standard. We present an analytical model that describes upstream traffic between the wind turbines and the control center. Using a queueing theory approach, the upstream traffic is evaluated in view of bandwidth utilization and average queuing delay. The performance of the proposed network architectures are evaluated by using analytical and simulation models. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
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Figure 1

Figure 1
<p>Smart-wind power farms’ (Smart-WPFs) domains. SCADA: supervisory control and data acquisition.</p> Full article ">Figure 2
<p>Generated data from sensor nodes (SNs) at the wind turbine side. AP: access point.</p> Full article ">Figure 3
<p>Proposed communication network architecture of Smart-WPFs. AM: analogue measurements; SI: status information; PCI: protection and control information; ONU: optical network unit; and OLT: optical line terminal.</p> Full article ">Figure 4
<p>SCADA system for wind power farm (WPF) and upstream scheduling mechanism: (<b>a</b>) polling scheme; and (<b>b</b>) interleaved polling scheme. ESW: Ethernet switch; and RTU: remote terminal unit.</p> Full article ">Figure 5
<p>Proposed sensor frame structure.</p> Full article ">Figure 6
<p>Queuing model of wind turbine data traffic.</p> Full article ">Figure 7
<p>Turbine area network (TAN).</p> Full article ">Figure 8
<p>Data packet format of SN and relay node (RN).</p> Full article ">Figure 9
<p>Layout of Ormonde offshore WPF (Electric Topology).</p> Full article ">Figure 10
<p>Linear topology configuration. BS: base station.</p> Full article ">Figure 11
<p>Schematic view of proposed Ethernet passive optical network (EPON) communication network for WPF.</p> Full article ">Figure 12
<p>Generated data traffic during 1 s (2 ms/slot).</p> Full article ">Figure 13
<p>Bandwidth utilization of WT-ONU.</p> Full article ">Figure 14
<p>Average queuing delay of WT-ONU.</p> Full article ">Figure 15
<p>Optimized network engineering tool (OPNET) model for meteorological data shared among wind turbines.</p> Full article ">Figure 16
<p><span class="html-italic">ETE</span> delay of sensing data at <span class="html-italic">WT</span> coordinator (8 <span class="html-italic">WT</span>s).</p> Full article ">Figure 17
<p>Transmission time of sensing data packets among <span class="html-italic">WT</span>s.</p> Full article ">
832 KiB  
Article
Gas Hydrate Occurrence Inferred from Dissolved Cl− Concentrations and δ18O Values of Pore Water and Dissolved Sulfate in the Shallow Sediments of the Pockmark Field in Southwestern Xisha Uplift, Northern South China Sea
by Min Luo, Linying Chen, Hongpeng Tong, Wen Yan and Duofu Chen
Energies 2014, 7(6), 3886-3899; https://doi.org/10.3390/en7063886 - 20 Jun 2014
Cited by 16 | Viewed by 42109
Abstract
Deep-water pockmarks are frequently accompanied by the occurrence of massive gas hydrates in shallow sediments. A decline in pore-water Cl− concentration and rise in δ18O value provide compelling evidence for the gas hydrate dissociation. Mega-pockmarks are widely scattered in the [...] Read more.
Deep-water pockmarks are frequently accompanied by the occurrence of massive gas hydrates in shallow sediments. A decline in pore-water Cl− concentration and rise in δ18O value provide compelling evidence for the gas hydrate dissociation. Mega-pockmarks are widely scattered in the southwestern Xisha Uplift, northern South China Sea (SCS). Pore water collected from a gravity-core inside of a mega-pockmark exhibits a downward Cl− concentration decrease concomitant with an increase in δ18O value at the interval of 5.7–6.7 mbsf. Concentrations of Cl−, Na+, and K+ mainly cluster along the seawater freshening line without distinct Na+ enrichment and K+ depletion. Thus, we infer that the pore water anomalies of Cl− concentrations and δ18O values are attributed to gas hydrate dissociation instead of clay mineral dehydration. Moreover, the lower δ18O values of sulfate in the target core (C14) than those in the reference core (C9) may be associated with the equilibrium oxygen fractionation during sulfate reduction between sulfate and the relatively 18O-depleted ambient water resulting from gas hydrate formation. The gas hydrate contents are estimated to be 6%–10% and 7%–15%, respectively, according to the offset of Cl− concentrations and δ18O values from the baselines. This pockmark field in southwestern Xisha Uplift is likely to be a good prospective area for the occurrence of gas hydrate in shallow sediments. Full article
(This article belongs to the Special Issue Coastal Ocean Natural Gas Hydrate 2014)
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Figure 1

Figure 1
<p>Sampling location of sediment cores. The insets are the multibeam bathymetry maps showing sampling sites relative to pockmarks.</p> Full article ">Figure 2
<p>Pore-water concentration profiles of Cl<sup>−</sup> (<b>A</b>), Na<sup>+</sup> (<b>B</b>), and K<sup>+</sup> (<b>C</b>) as well as δ<sup>18</sup>O values (<b>D</b>) for C9 (blue) and C14 (red). The dash line in (<b>D</b>) representing the background trend of δ<sup>18</sup>O values is determined via polynomial fitting using measured pore water δ<sup>18</sup>O values above 5.7 mbsf.</p> Full article ">Figure 3
<p>(<b>A</b>) δ<sup>18</sup>O values of sulfate in C9 (blue) and C14 (red); (<b>B</b>) δ<sup>18</sup>O<sub>SO4</sub> <span class="html-italic">vs.</span> δ<sup>34</sup>S<sub>SO4</sub> data in pore water sulfate of C9 (blue) and C14 (red). δ<sup>34</sup>S<sub>SO4</sub> values were taken from Luo <span class="html-italic">et al.</span> [<a href="#B33-energies-07-03886" class="html-bibr">33</a>].</p> Full article ">Figure 4
<p>Plots of Cl<sup>−</sup> <span class="html-italic">vs.</span> Na<sup>+</sup> (<b>A</b>), K<sup>+</sup> (<b>B</b>), and δ<sup>18</sup>O (<b>C</b>). Solid circles in (<b>A</b>) and (<b>B</b>) indicate seawater values.</p> Full article ">Figure 5
<p>The estimated gas hydrate concentrations below 5.7mbsf. Solid squares and opentriangles represent the results derived from Cl<sup>−</sup> concentrations and δ<sup>18</sup>O values, respectively.</p> Full article ">
431 KiB  
Article
Production of Ethanol and Biomass from Thin Stillage Using Food-Grade Zygomycetes and Ascomycetes Filamentous Fungi
by Jorge A. Ferreira, Patrik R. Lennartsson and Mohammad J. Taherzadeh
Energies 2014, 7(6), 3872-3885; https://doi.org/10.3390/en7063872 - 20 Jun 2014
Cited by 71 | Viewed by 9893 | Correction
Abstract
A starch-based ethanol facility producing 200,000 m3 ethanol/year also produces ca. 2 million m3 thin stillage, which can be used to improve the entire process. In this work, five food-grade filamentous fungi, including a Zygomycete and four Ascomycetes were successfully grown [...] Read more.
A starch-based ethanol facility producing 200,000 m3 ethanol/year also produces ca. 2 million m3 thin stillage, which can be used to improve the entire process. In this work, five food-grade filamentous fungi, including a Zygomycete and four Ascomycetes were successfully grown in thin stillage containing 9% solids. Cultivation with Neurospora intermedia led to the production of ca. 16 g·L−1 biomass containing 56% (w/w) crude protein, a reduction of 34% of the total solids, and 5 g·L−1 additional ethanol. In an industrial ethanol production process (200,000 m3 ethanol/year), this can potentially lead to the production of 11,000 m3 extra ethanol per year. Cultivation with Aspergillus oryzae resulted in 19 g·L−1 biomass containing 48% (w/w) crude protein and the highest reduction of the thin stillage glycerol (54%) among the Ascomycetes. Cultivation with Rhizopus sp. produced up to 15 g·L−1 biomass containing 55% (w/w) crude protein. The spent thin stillage had been reduced up to 85%, 68% and 21% regarding lactic acid, glycerol and total solids, respectively. Therefore, N. intermedia, in particular, has a high potential to improve the ethanol process via production of additional ethanol and high-quality biomass, which can be considered for animal feed applications such as for fish feed. Full article
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<p>General overview of the main starch-based ethanol process pathways leading to the production of ethanol and dry distiller grains with solubles (DDGS).</p> Full article ">Figure 2
<p><span class="html-italic">Rhizopus</span> sp. biomass concentration during cultivation in thin stillage at different temperatures.</p> Full article ">Figure 3
<p>Concentration of lactic acid, glycerol, ethanol, arabinose and xylose during cultivation of <span class="html-italic">Rhizopus</span> sp. in thin stillage at 30 °C (black), 35 °C (grey) and 40 °C (white).</p> Full article ">Figure 4
<p>Produced biomass profiles during cultivation of <span class="html-italic">Ascomycetes</span> filamentous fungi in thin stillage at 30 °C. <span class="html-italic">A. oryzae</span> (circles), <span class="html-italic">N. intermedia</span> (squares), <span class="html-italic">F. venenatum</span> (triangles), <span class="html-italic">M. purpureus</span> (diamonds).</p> Full article ">Figure 5
<p>Concentration profiles of glycerol, ethanol, arabinose and xylose during cultivation of Ascomycetes in thin stillage at 30 °C. <span class="html-italic">A. oryzae</span> (circles), <span class="html-italic">N. intermedia</span> (squares), <span class="html-italic">F. venenatum</span> (triangles), <span class="html-italic">M. purpureus</span> (diamonds).</p> Full article ">
839 KiB  
Article
Aqueous Hybrids of Silica Nanoparticles and Hydrophobically Associating Hydrolyzed Polyacrylamide Used for EOR in High-Temperature and High-Salinity Reservoirs
by Dingwei Zhu, Limin Wei, Biqing Wang and Yujun Feng
Energies 2014, 7(6), 3858-3871; https://doi.org/10.3390/en7063858 - 19 Jun 2014
Cited by 132 | Viewed by 11063
Abstract
Water-soluble polymers are known to be used in chemically enhanced oil recovery (EOR) processes, but their applications are limited in high-temperature and high-salinity oil reservoirs because of their inherent poor salt tolerance and weak thermal stability. Hydrophobic association of partially hydrolyzed polyacryamide (HAHPAM) [...] Read more.
Water-soluble polymers are known to be used in chemically enhanced oil recovery (EOR) processes, but their applications are limited in high-temperature and high-salinity oil reservoirs because of their inherent poor salt tolerance and weak thermal stability. Hydrophobic association of partially hydrolyzed polyacryamide (HAHPAM) complexed with silica nanoparticles to prepare nano-hybrids is reported in this work. The rheological and enhanced oil recovery (EOR) properties of such hybrids were studied in comparison with HAHPAM under simulated high-temperature and high-salinity oil reservoir conditions (T: 85 °C; total dissolved solids: 32,868 mg∙L−1; [Ca2+] + [Mg2+]: 873 mg∙L−1). It was found that the apparent viscosity and elastic modulus of HAHPAM solutions increased with addition of silica nanoparticles, and HAHPAM/silica hybrids exhibit better shear resistance and long-term thermal stability than HAHPAM in synthetic brine. Moreover, core flooding tests show that HAHPAM/silica hybrid has a higher oil recovery factor than HAHPAM solution. Full article
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Figure 1
<p>(<b>A</b>) Apparent viscosity plotted as a function of shear rate for various concentrationsof HAHPAM and (<b>B</b>) zero-shear viscosity (<span class="html-italic">η</span><sub>0</sub>) plotted as a function of polymer concentration for HAHPAM in brine (TDS = 32,868 mg∙L<sup>−1</sup>, [Ca<sup>2+</sup>] + [Mg<sup>2+</sup>] = 873 mg∙L<sup>−1</sup>, <span class="html-italic">T</span> = 85 °C).</p> Full article ">Figure 2
<p>Dependence of apparent viscosity on silica nanoparticle concentration for HAHPAM/silica hybrids in brine and silica suspension (TDS = 32,868 mg∙L<sup>−1</sup>, [Ca<sup>2+</sup>] + [Mg<sup>2+</sup>] = 873 mg∙L<sup>−1</sup>, <span class="html-italic">T</span> = 85 °C, <span class="html-fig-inline" id="energies-07-03858-i001"> <img alt="Energies 07 03858 i001" src="/energies/energies-07-03858/article_deploy/html/images/energies-07-03858-i001.png"/></span> = 10 s<sup>−1</sup>, C<sub>p</sub> = 0.5 wt%).</p> Full article ">Figure 3
<p>Apparent viscosity plotted as a function of shear rate for HAHPAM/silica hybrids in brine with different silica loading (TDS = 32,868 mg∙L<sup>−1</sup>, [Ca<sup>2+</sup>] + [Mg<sup>2+</sup>] = 873 mg∙L<sup>−1</sup>, <span class="html-italic">T</span> = 85 °C, C<sub>p</sub> = 0.5 wt%).</p> Full article ">Figure 4
<p>Comparison of FT-IR spectra of (<b>A</b>) 0.5% HAHPAM and (<b>B</b>) 0.5% HAHPAM/0.5% silica.</p> Full article ">Figure 5
<p>Storage modulus (<span class="html-italic">G′</span>) plotted as a function of angular frequency (<span class="html-italic">ω</span>) for HAHPAM/silica hybrids in brine with different silica loading (TDS = 32,868 mg∙L<sup>−1</sup>, [Ca<sup>2+</sup>] + [Mg<sup>2+</sup>] = 873 mg∙L<sup>−1</sup>, <span class="html-italic">T</span> = 85 °C, C<sub>p</sub> = 0.5 wt%).</p> Full article ">Figure 6
<p>Long-term thermal stability of 0.5% HAHPAM/0.5% silica hybrid in comparison with 0.5% HAHPAM and 0.5% silica (TDS = 32,868 mg∙L<sup>−</sup><sup>1</sup>, [Ca<sup>2+</sup>] + [Mg<sup>2+</sup>] = 873 mg∙L<sup>−</sup><sup>1</sup>, <span class="html-fig-inline" id="energies-07-03858-i001"> <img alt="Energies 07 03858 i001" src="/energies/energies-07-03858/article_deploy/html/images/energies-07-03858-i001.png"/></span> = 10 s<sup>−</sup><sup>1</sup>). Both the aging and measuring temperature is 85 °C.</p> Full article ">Figure 7
<p>Recovery factor, water cut and flooding pressure plotted as a function of injected volume of the samples: (<b>A</b>) 0.5% HAHPAM and (<b>B</b>) 0.5% HAHPAM/0.5% silica hybrid (TDS = 32,868 mg∙L<sup>−</sup><sup>1</sup>, [Ca<sup>2+</sup>] + [Mg<sup>2+</sup>] = 873 mg∙L<sup>−</sup><sup>1</sup>; <span class="html-italic">T</span> = 85 °C; injected volume = 30% PV; injected rate = 0.23 mL∙min<sup>−</sup><sup>1</sup>).</p> Full article ">Figure 8
<p>The molecular structure of HAHPAM (x = 25.0 wt%, y = 74.85 wt%, m = 0.1 wt%, n = 0.05 wt%).</p> Full article ">
1090 KiB  
Article
Batch Growth of Chlorella Vulgaris CCALA 896 versus Semi-Continuous Regimen for Enhancing Oil-Rich Biomass Productivity
by Sigita Vaičiulytė, Giulia Padovani, Jolanta Kostkevičienė and Pietro Carlozzi
Energies 2014, 7(6), 3840-3857; https://doi.org/10.3390/en7063840 - 19 Jun 2014
Cited by 21 | Viewed by 9734
Abstract
The aim of this study was to induce lipid accumulation in Chlorella cells by creating stressful growth conditions. Chlorella vulgaris CCALA 896 was grown under various batch growth modes in basal and modified BG-11 and Kolkwitz culture broths, using a continuous light regimen [...] Read more.
The aim of this study was to induce lipid accumulation in Chlorella cells by creating stressful growth conditions. Chlorella vulgaris CCALA 896 was grown under various batch growth modes in basal and modified BG-11 and Kolkwitz culture broths, using a continuous light regimen of 150 µE/m2/s, at 30 °C. In order to perform the experiments, two indoor photobioreactor shapes were used: a cylindrical glass photobioreactor (CGPBR) with a working volume of 350 mL, and a flat glass photobioreactor (FGPBR) with a working volume of 550 mL. Stress-eliciting conditions, such as nitrogen and phosphorous starvation, were imposed in order to induce lipid accumulation. The results demonstrated that more than 56% of the lipids can be accumulated in Chlorella biomass grown under two-phase batch growth conditions. The highest biomass productivity of 0.30 g/L/d was obtained at the highest nominal dilution rate (0.167 day−1) during a semi-continuous regimen, using a modified Kolkwitz medium. During the pH-stress cycles, the amount of lipids did not increase significantly and a flocculation of Chlorella cells was noted. Full article
(This article belongs to the Special Issue Renewable Energy for Agriculture)
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<p>Batch growth of <span class="html-italic">Chlorella vulgaris</span> CCALA 896 using three different synthetic culture broths: Basal; Kolkwitz and BG-11. All experiments were carried out at 30 °C, and with a light intensity of 150 µE/m<sup>2</sup>/s.</p> Full article ">Figure 2
<p>(<b>a</b>) Changes in Chl-a and (<b>b</b>) cell numbers <span class="html-italic">versus</span> time in <span class="html-italic">Chlorella vulgaris</span> CCALA 896 grown under repetitive batch (<span class="html-italic">i.e.</span>, semi-continuous) regimen conditions. Every 72 h, a culture volume of 175 mL was withdrawn from the C<sub>G</sub>PBR (working volume of 350 mL) and replaced with an equal volume of fresh medium. Experiments were performed by culturing <span class="html-italic">Chlorella</span> in two different culture broths: basal and Kolkwitz.</p> Full article ">Figure 3
<p>Changes in the Chl-a concentration and lipid content <span class="html-italic">versus</span> time, of <span class="html-italic">Chlorella vulgaris</span> CCALA 896 grown under batch growth conditions using the modified BG-11 medium (<b>a</b>) and modified Kolkwitz medium (<b>b</b>). The nitrogen (N) and phosphorus (P) concentrations were checked as well. The lipid content in the <span class="html-italic">Chlorella</span> biomass was checked, starting from the N and P starvation conditions, which are indicated by the arrows.</p> Full article ">Figure 4
<p>Changes in the Chl-a concentration <span class="html-italic">versus</span> time, in <span class="html-italic">Chlorella vulgaris</span> CCALA 896 grown under three different repetitive batch-growth (<span class="html-italic">i.e.</span>, semi-continuous) regimens and using a modified Kolkwitz medium. The <span class="html-italic">Chlorella</span> cultures were diluted by removing half of the reactor working volume: (<b>a</b>) every 3 days (nominal dilution rate = 0.167 day<sup>−1</sup>); (<b>b</b>) every 4 days (nominal dilution rate = 0.125 day<sup>−1</sup>) and (<b>c</b>) every 5 days (nominal dilution rate = 0.100 day<sup>−1</sup>). Arrows indicate when the dilutions were performed.</p> Full article ">Figure 5
<p>Lipid content in the dry-biomass of <span class="html-italic">Chlorella</span> and lipid and biomass productivities. Experiments were performed using a C<sub>G</sub>PBR (working volume of 350 mL). <span class="html-italic">Chlorella vulgaris</span> CCALA 896 was grown by using a modified Kolkwitz medium under three different repetitive batch-growth regimens, as reported in the previous <a href="#energies-07-03840-f004" class="html-fig">Figure 4</a>. The data represent the mean ±SD.</p> Full article ">Figure 6
<p>Changes in the Chl-<span class="html-italic">a</span>, N and P concentrations and lipid content <span class="html-italic">versus</span> time, under two sequential phases (Start-up and Starvation) of <span class="html-italic">Chlorella vulgaris</span> CCALA 896 growth (<b>a</b>); Changes in the pH and O<sub>2</sub> <span class="html-italic">versus</span> time (<b>b</b>); The arrow in Figure (<b>a</b>) indicates the beginning of the N and P starvation condition; the two arrows in Figure (<b>b</b>) indicate a halt into the inflow of CO<sub>2</sub> in the culture; instead, the dotted row indicates the turn on to the inflow of CO<sub>2</sub>. A F<sub>G</sub>PBR with a working volume of 550 mL was used.</p> Full article ">Figure 7
<p>Changes in biomass composition in <span class="html-italic">Chlorella vulgaris</span> CCALA 896 <span class="html-italic">versus</span> time, during the N and P starvation phase. The arrow indicates the beginning of the pH-stressed conditions. A F<sub>G</sub>PBR with a working volume of 550 mL was used. The data represent the mean ± SD.</p> Full article ">
964 KiB  
Article
Optimum Peak Current Hysteresis Control for Energy Recovering Converter in CDI Desalination
by Alberto M. Pernía, Francisco J. Alvarez-González, Juan Díaz, Pedro J. Villegas and Fernando Nuño
Energies 2014, 7(6), 3823-3839; https://doi.org/10.3390/en7063823 - 18 Jun 2014
Cited by 8 | Viewed by 6552
Abstract
Capacitive De-Ionization (CDI) is becoming a suitable alternative for desalination. The low cost of the materials required and its reduced energy consumption can be critical factors for developing this technique. CDI technology does not require a high-pressure system and the energy storage capability [...] Read more.
Capacitive De-Ionization (CDI) is becoming a suitable alternative for desalination. The low cost of the materials required and its reduced energy consumption can be critical factors for developing this technique. CDI technology does not require a high-pressure system and the energy storage capability of CDI cells allows it to be reused in other CDI cells, thus minimizing consumption. The goal of the power stage responsible of the energy recovery is transferring the stored energy from one cell to another with the maximum possible efficiency, thus allowing the desalination process to continue. Assuming hysteresis current control is implemented at the DC/DC (direct current) converter, this paper aims to determine the optimum peak current through the inductor in each switching period with a view to maximizing overall efficiency. The geometrical parameters of the desalination cell and the NaCl concentration modify the cell electrical properties. The peak current control of the power stage should be adapted to the cell characteristics so that the efficiency behavior of the whole CDI system can be improved. The mathematical model defined in this paper allows the CDI plant automation using the peak inductor current as control variable, adapting its value to the salt concentration during the desalination process. Full article
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Full article ">
<p>Ion adsorption during polarization of the plates.</p> Full article ">
<p>Piling of substrates with screen printed active carbon.</p> Full article ">
<p>Electric circuit used for the parasitic determination.</p> Full article ">
<p>Electric charge/discharge test used for the parasitic determination. Top: Current source used, <span class="html-italic">I</span>; Bottom: Voltage across the capacitor, <span class="html-italic">V</span>c.</p> Full article ">
<p>Capacitive De-Ionization (CDI) module prototype.</p> Full article ">
<p>Desalination block diagram with a buck-boost converter for recovering energy process.</p> Full article ">
<p>Proposed System.</p> Full article ">
<p><span class="html-italic">I</span><sub>Lmax</sub> calculation process during the energy transfer.</p> Full article ">
<p>Buck-boost converter.</p> Full article ">
516 KiB  
Article
Hydrodynamic Effects on Spectroscopic Water Detection in Gasoline Pipe Flow
by Jeong Heon Kim and Chang Sik Lee
Energies 2014, 7(6), 3810-3822; https://doi.org/10.3390/en7063810 - 18 Jun 2014
Cited by 2 | Viewed by 5689
Abstract
The hydrodynamic effects on spectroscopic water detection were microscopically investigated in a gasoline pipe flow. The effects of the gasoline flow rate and the water content on the water droplet characteristics were investigated experimentally using a phase Doppler particle measurement system. The characteristics [...] Read more.
The hydrodynamic effects on spectroscopic water detection were microscopically investigated in a gasoline pipe flow. The effects of the gasoline flow rate and the water content on the water droplet characteristics were investigated experimentally using a phase Doppler particle measurement system. The characteristics of spectral absorbance of water and gasoline were measured using a spectrophotometer to determine the optimal wavelength of the incident light for spectroscopic water detection. The effects of the droplet size on the light transmittance characteristics were calculated using the light extinction theory of Mie scattering on polydisperse particles and experimental results on the water droplet size in the gasoline flow. The measurement results of spectral absorbance showed that gasoline was almost transparent at 980 nm wavelength of light while water showed peak absorption at this wavelength, therefore, it was appropriate incident light for spectroscopic water detection. It was found that the flow conditions of the gasoline flow rate and the water content influenced the Sauter mean diameter and the volume concentration of water droplets, which influenced the light transmittance. Full article
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Full article ">Figure 1
<p>Schematic diagram of experimental setup.</p> Full article ">Figure 2
<p>Optical model for spectroscopic water detection.</p> Full article ">Figure 3
<p>Water droplet dispersion visualized through transparent test window 2: (<b>a</b>) <span class="html-italic">Q<sub>g</sub></span> = 1.8 m<sup>3</sup>/h and <span class="html-italic">C<sub>w</sub></span> = 100 ppm; (<b>b</b>) <span class="html-italic">Q<sub>g</sub></span> = 3.6 m<sup>3</sup>/h and <span class="html-italic">C<sub>w</sub></span> = 100 ppm.</p> Full article ">Figure 4
<p>Distribution of arithmetic mean diameter of water droplets along transverse direction of gasoline pipe flow.</p> Full article ">Figure 5
<p>Volume mean diameter and number density of water droplets: (<b>a</b>) volume mean diameter <span class="html-italic">D</span><sub>30</sub>; (<b>b</b>) number density <span class="html-italic">N</span>.</p> Full article ">Figure 6
<p>Distributions of size and cumulative volume of water droplets at <span class="html-italic">Q<sub>g</sub></span> = 1.8 m<sup>3</sup>/h, <span class="html-italic">C<sub>w</sub></span> = 150 ppm and <span class="html-italic">Q</span><span class="html-italic"><sub>g</sub></span> = 3.6 m<sup>3</sup>/h, <span class="html-italic">C<sub>w</sub></span> = 150 ppm: (<b>a</b>) size distribution; (<b>b</b>) cumulative volume distribution.</p> Full article ">Figure 7
<p>Sauter mean diameter of water droplets in gasoline pipe flow.</p> Full article ">Figure 8
<p>Spectral absorbance characteristics of water and gasoline.</p> Full article ">Figure 9
<p>Transmittance characteristics in quiescent gasoline containing monodisperse water droplets: (<b>a</b>) transmittance <span class="html-italic">versus</span> water content; (<b>b</b>) transmittance <span class="html-italic">versus</span> droplet diameter.</p> Full article ">Figure 10
<p>Transmittance characteristics in gasoline pipe flow.</p> Full article ">
527 KiB  
Article
Pitch Based Wind Turbine Intelligent Speed Setpoint Adjustment Algorithms
by Asier González-González, Ismael Etxeberria-Agiriano, Ekaitz Zulueta, Fernando Oterino-Echavarri and Jose Manuel Lopez-Guede
Energies 2014, 7(6), 3793-3809; https://doi.org/10.3390/en7063793 - 18 Jun 2014
Cited by 13 | Viewed by 7338
Abstract
This work is aimed at optimizing the wind turbine rotor speed setpoint algorithm. Several intelligent adjustment strategies have been investigated in order to improve a reward function that takes into account the power captured from the wind and the turbine speed error. After [...] Read more.
This work is aimed at optimizing the wind turbine rotor speed setpoint algorithm. Several intelligent adjustment strategies have been investigated in order to improve a reward function that takes into account the power captured from the wind and the turbine speed error. After different approaches including Reinforcement Learning, the best results were obtained using a Particle Swarm Optimization (PSO)-based wind turbine speed setpoint algorithm. A reward improvement of up to 10.67% has been achieved using PSO compared to a constant approach and 0.48% compared to a conventional approach. We conclude that the pitch angle is the most adequate input variable for the turbine speed setpoint algorithm compared to others such as rotor speed, or rotor angular acceleration. Full article
(This article belongs to the Special Issue Wind Turbines 2014)
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<p>Wind speed realization calculated with TurbSim.</p> Full article ">
<p>Extreme Operation Gust.</p> Full article ">
<p>Torque setpoint <span class="html-italic">vs.</span> rotor speed.</p> Full article ">
<p>Mean Reward <span class="html-italic">vs.</span> optimization parameters.</p> Full article ">
567 KiB  
Article
Solar Air Collectors for Space Heating and Ventilation Applications—Performance and Case Studies under Romanian Climatic Conditions
by Sanda Budea
Energies 2014, 7(6), 3781-3792; https://doi.org/10.3390/en7063781 - 18 Jun 2014
Cited by 20 | Viewed by 7133 | Correction
Abstract
Solar air collectors have various applications: on the one hand, they can be used for air heating in cold seasons; on the other hand they can be used in summer to evacuate the warm and polluted air from residential, offices, industrial, and commercial [...] Read more.
Solar air collectors have various applications: on the one hand, they can be used for air heating in cold seasons; on the other hand they can be used in summer to evacuate the warm and polluted air from residential, offices, industrial, and commercial buildings. The paper presents experimental results of a solar collector air, under the climatic conditions of the Southeastern Europe. The relationships between the direct solar irradiation, the resulting heat flow, the air velocity at the outlet, the air flow rate, the nominal regime of the collector and the efficiency of conversion of solar energy into thermal energy are all highlighted. Thus, it was shown that after a maximum 50 min, solar air collectors, with baffles and double air passage can reach over 50% efficiency for solar irradiation of 900–1000 W/m2. The article also presents a mathematical model and the results of a computational program that allows sizing solar collectors for the transfer of air, with the purpose of improving the natural ventilation of buildings. The article is completed with case studies, sizing the area to be covered with solar collectors, to ensure ventilation of a house with two floors or for an office building. In addition, the ACH (air change per hour) coefficient was calculated and compared. Full article
(This article belongs to the Special Issue Selected Papers from the 1st International e-Conference on Energies — Whither Energy Conversion? Present Trends, Current Problems and Realistic Future Solutions)
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Figure 1

Figure 1
<p>Global solar irradiance on a tilted plane for a clean sky day from January 2009: (<b>a</b>) Proprietery software, <span class="html-italic">T</span>’<sub>a</sub> and <span class="html-italic">I</span>’<sub>g</sub> are interpolated values with sixth degree polynomials; (<b>b</b>) JRC PVGIS application.</p> Full article ">Figure 2
<p>Global solar irradiance on a tilted plane for a partly cloudy sky day from July, 2009: (<b>a</b>) Proprietary software, <span class="html-italic">T</span>’<sub>a</sub> and <span class="html-italic">I</span>’<sub>g</sub> are interpolated values with sixth degree polynomials; (<b>b</b>) JRC PVGIS application.</p> Full article ">Figure 3
<p>(<b>a</b>) Solar collector SH 1500, and system to modify the angle of inclination; (<b>b</b>) Optimal inclination angle for Bucharest [<a href="#B14-energies-07-03781" class="html-bibr">14</a>].</p> Full article ">Figure 4
<p>Heat fluxes and air outlet temperatures variation in times, in July: (<b>a</b>) heating process; (<b>b</b>) cooling process.</p> Full article ">Figure 5
<p>Heat fluxes and air outlet temperatures variation in times, in a sunny day in January: (<b>a</b>) heating process; (<b>b</b>) cooling process.</p> Full article ">Figure 6
<p>Solar global irradiance and the variation of temperature with air velocity.</p> Full article ">Figure 7
<p>Efficiency of solar air collector <span class="html-italic">versus</span> (<b>a</b>) solar radiation <span class="html-italic">I<sub>g</sub></span> (W/m<sup>2</sup>) and (<b>b</b>) time <span class="html-italic">t</span> (min).</p> Full article ">Figure 8
<p>Area of solar air collectors <span class="html-italic">versus</span> solar radiation for three fields of temperature for a family house.</p> Full article ">Figure 9
<p>Area of solar air colectors <span class="html-italic">versus</span> solar radiation for three fields of temperature for an office building.</p> Full article ">
670 KiB  
Article
Production of a Biofuel that Keeps the Glycerol as a Monoglyceride by Using Supported KF as Heterogeneous Catalyst
by Juan Calero, Gema Cumplido, Diego Luna, Enrique D. Sancho, Carlos Luna, Alejandro Posadillo, Felipa M. Bautista, Antonio A. Romero and Cristóbal Verdugo-Escamilla
Energies 2014, 7(6), 3764-3780; https://doi.org/10.3390/en7063764 - 18 Jun 2014
Cited by 12 | Viewed by 8092
Abstract
This study describes the results obtained in the synthesis of a biofuel that avoids the production of glycerol by applying supported KF as alkaline heterogeneous catalyst, to generate two moles of fatty acid methyl esters and one mole of monoglyceride from one mol [...] Read more.
This study describes the results obtained in the synthesis of a biofuel that avoids the production of glycerol by applying supported KF as alkaline heterogeneous catalyst, to generate two moles of fatty acid methyl esters and one mole of monoglyceride from one mol of triglyceride. In this respect, the selective transesterification process of sunflower oil with methanol was carried out with KF (10 wt%) supported on three different solids, Al2O3, ZnO and MgO. The standard experimental conditions employed in the heterogeneous selective methanolysis reaction were: 12 mL of sunflower oil, 2.7 mL of methanol, 0.8 g of catalyst, at 65 °C temperature and one hour of reaction time. In all cases 100% conversion was obtained, with high selectivity values, greater than 90%, and quite suitable viscosity values, 4.5–8.5 cSt. In this way, the best catalytic behavior in the first use was obtained by using Al2O3 as support. However, although in the five consecutive reuses all catalysts exhibited a continuous decrease in their catalytic activities; the lower one was for KF catalyst using MgO as support. In summary, these three KF supported catalysts are very suitable to obtain a new biofuel, similar to conventional biodiesel, applicable to diesel engines. Full article
(This article belongs to the Special Issue Selected Papers from the 1st International e-Conference on Energies — Whither Energy Conversion? Present Trends, Current Problems and Realistic Future Solutions)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Representative scheme of the production of Ecodiesel, a biofuel, by partial methanolysis of sunflower oil.</p> Full article ">Figure 2
<p>(<b>a</b>) Viscosity values and (<b>b</b>) Conversion and Selectivity values, obtained in the heterogeneous selective methanolysis of sunflower oil under standard conditions, with different amounts of KF/Al<sub>2</sub>O<sub>3</sub>, reaction time 60 min, reaction temperature 65 °C, 12 mL of oil and 2.43 mL of methanol.</p> Full article ">Figure 3
<p>(<b>a</b>) Viscosity values and (<b>b</b>) Conversion and Selectivity values, obtained in the heterogeneous selective methanolysis of sunflower oil under standard conditions, with different molar oil/methanol ratios, reaction time 60 min, reaction temperature 65 °C, 12 mL oil and 0.8 g of KF/Al<sub>2</sub>O<sub>3</sub>.</p> Full article ">Figure 4
<p>(<b>a</b>) Viscosity values and (<b>b</b>) Conversion and Selectivity values, obtained in the heterogeneous selective methanolysis of sunflower oil carried out under standard conditions, reaction time 60 min, 0.8 g of KF/Al<sub>2</sub>O<sub>3</sub> catalyst, 12 mL of oil and 2.43 mL of methanol, under different reaction temperatures in the interval 45–65 °C.</p> Full article ">Figure 5
<p>Arrhenius plot (Ln<span class="html-italic">k</span> <span class="html-italic">vs</span>. 1/<span class="html-italic">T</span>) obtained from the evolution of Ln<span class="html-italic">k</span> values with temperature, where <span class="html-italic">k</span> = viscosity<sup>−1</sup>; operating under standard conditions, with 12 mL of oil, 2.43 mL of methanol, 0.8 g of catalyst weight, 60 min reaction time and different reaction temperatures in the interval 25–65 °C.</p> Full article ">Figure 6
<p>(<b>a</b>) Viscosity values obtained in the successive reuses of heterogeneous selective methanolysis of sunflower oil under standard conditions, with 0.8 g of KF/Al<sub>2</sub>O<sub>3</sub>, 65 °C, 12 mL of oil and 2.43 mL methanol. (<b>b</b>) Conversion and Selectivity values obtained with identical conditions.</p> Full article ">Figure 7
<p>(<b>a</b>) Viscosity values obtained in the successive reuses of heterogeneous selective methanolysis of sunflower oil (viscosity 32.0 cSt) under standard conditions, with 0.8 g of KF/ZnO, 65 °C, 12 mL of oil and 2.43 mL methanol. (<b>b</b>) Conversion and Selectivity values obtained with identical conditions.</p> Full article ">Figure 8
<p>(<b>a</b>) Viscosity values obtained in the successive reuses of heterogeneous selective methanolysis of sunflower oil (viscosity 32.0 cSt) under standard conditions, with 0.8 g of KF/MgO, 65 °C, 12 mL of oil and 2.43 mL methanol. (<b>b</b>) Conversion and Selectivity values obtained with identical conditions.</p> Full article ">
402 KiB  
Article
An Acceleration Slip Regulation Strategy for Four-Wheel Drive Electric Vehicles Based on Sliding Mode Control
by Hongwen He, Jiankun Peng, Rui Xiong and Hao Fan
Energies 2014, 7(6), 3748-3763; https://doi.org/10.3390/en7063748 - 17 Jun 2014
Cited by 61 | Viewed by 13844
Abstract
This paper presents an acceleration slip regulation (ASR) system for four-wheel drive (4WD) electric vehicles, which are driven by the front and rear axles simultaneously. The ASR control strategy includes three control modes: average distribution of inter-axle torque, optimal distribution of inter-axle torque [...] Read more.
This paper presents an acceleration slip regulation (ASR) system for four-wheel drive (4WD) electric vehicles, which are driven by the front and rear axles simultaneously. The ASR control strategy includes three control modes: average distribution of inter-axle torque, optimal distribution of inter-axle torque and independent control of optimal slip rate, respectively, which are designed based on the torque adaptive principle of inter-axle differential and sliding mode control theory. Furthermore, in order to accurately describe the longitudinal tyre force characteristic, a slip rate calculation formula in the form of a state equation was used for solving the numerical problem posed by the traditional way. A simulation was carried out with the MATLAB/Simulink software. The simulation results show that the proposed ASR system can fully use the road friction condition, inhibit the drive-wheels from slipping, and improve the vehicle longitudinal driving stability. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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Figure 1
<p>The four-wheel drive (4WD) electric vehicle acceleration slip regulation (ASR) system layout.</p> Full article ">Figure 2
<p>Comparison of two methods for tyre slip rate calculation: (<b>a</b>) Simulation results of Equation (6); (<b>b</b>) Simulation results of Equation (7).</p> Full article ">Figure 3
<p>The modified tyre slip rate at a low vehicle velocity.</p> Full article ">Figure 4
<p>The acceleration slip regulation strategy.</p> Full article ">Figure 5
<p>Simulation results of average distribution of inter-axle torque on good roads: (<b>a</b>) The front and rear axle tyre slip rate; (<b>b</b>) Vehicle acceleration.</p> Full article ">Figure 6
<p>Simulation results of torque distribution by axle load on good roads: (<b>a</b>) The front and rear axle tyre slip rate; (<b>b</b>) Vehicle acceleration.</p> Full article ">Figure 7
<p>Simulation of stepping on the pedal lightly to accelerate on a mid-adhesion road: (<b>a</b>) Optimal torque of inter-axle distribution control; (<b>b</b>) Average torque distribution control; (<b>c</b>) Acceleration under optimal torque of the inter-axle distribution control; (<b>d</b>) Acceleration under the average torque distribution control.</p> Full article ">Figure 8
<p>The change of sliding mode surface and controlled variables in the sliding mode control process: (<b>a</b>) Convergence process of the front and rear axle speed deviation; (<b>b</b>) Output torque of the front and rear axle motor under sliding mode control.</p> Full article ">Figure 9
<p>Simulation results of stepping on the pedal heavily on snowy roads: (<b>a</b>) Independent control of the optimal slip rate; (<b>b</b>) Optimal distribution of inter-axle control; (<b>c</b>) Acceleration under independent control of optimal slip rate control; (<b>d</b>) Acceleration under optimal distribution of inter-axle torque control.</p> Full article ">Figure 10
<p>Front and rear axle input torque under different control modes: (<b>a</b>) Front axle slip rate control deviation; (<b>b</b>) Rear axle slip rate control deviation; (<b>c</b>) Output torque under independent control of the optimal slip rate mode.</p> Full article ">Figure 11
<p>Simulation results of torque distribution on changing roads: (<b>a</b>) Changes of slip rate with light pedal; (<b>b</b>) Changes of slip rate with heavy pedal; (<b>c</b>) Control mode switching; (<b>d</b>) Control mode switching; (<b>e</b>) Vehicle performance under light pedal; (<b>f</b>) Vehicle performance under heavy pedal.</p> Full article ">Figure 12
<p>Simulation results under the same road with the changing driver accelerator pedal: (<b>a</b>) Driver accelerator pedal signal; (<b>b</b>) The change of control mode under inter-axle torque distribution control strategy; (<b>c</b>) Change of slip rate; (<b>d</b>) Vehicle acceleration.</p> Full article ">
808 KiB  
Article
Sensitivity Analyses for Cross-Coupled Parameters in Automotive Powertrain Optimization
by Pongpun Othaganont, Francis Assadian and Daniel Auger
Energies 2014, 7(6), 3733-3747; https://doi.org/10.3390/en7063733 - 17 Jun 2014
Cited by 4 | Viewed by 8262
Abstract
When vehicle manufacturers are developing new hybrid and electric vehicles, modeling and simulation are frequently used to predict the performance of the new vehicles from an early stage in the product lifecycle. Typically, models are used to predict the range, performance and energy [...] Read more.
When vehicle manufacturers are developing new hybrid and electric vehicles, modeling and simulation are frequently used to predict the performance of the new vehicles from an early stage in the product lifecycle. Typically, models are used to predict the range, performance and energy consumption of their future planned production vehicle; they also allow the designer to optimize a vehicle’s configuration. Another use for the models is in performing sensitivity analysis, which helps us understand which parameters have the most influence on model predictions and real-world behaviors. There are various techniques for sensitivity analysis, some are numerical, but the greatest insights are obtained analytically with sensitivity defined in terms of partial derivatives. Existing methods in the literature give us a useful, quantified measure of parameter sensitivity, a first-order effect, but they do not consider second-order effects. Second-order effects could give us additional insights: for example, a first order analysis might tell us that a limiting factor is the efficiency of the vehicle’s prime-mover; our new second order analysis will tell us how quickly the efficiency of the powertrain will become of greater significance. In this paper, we develop a method based on formal optimization mathematics for rapid second-order sensitivity analyses and illustrate these through a case study on a C-segment electric vehicle. Full article
(This article belongs to the Special Issue Advances in Hybrid Vehicles)
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<p>Schematic diagram of (<b>a</b>) vehicle backward-facing modeling and (<b>b</b>) vehicle forward-facing modeling.</p> Full article ">
<p>Schematic diagram of case study vehicle powertrain.</p> Full article ">
<p>Standard test cycle used in this presentation (<b>a</b>) NEDC and (<b>b</b>) Combined Artemis.</p> Full article ">
<p>First-order sensitivity analysis of the nominal vehicle parameters. (<b>a</b>) NEDC and (<b>b</b>) Artemis Cycle.</p> Full article ">
<p>Second-order sensitivity analysis for the nominal vehicle parameters. (<b>a</b>) NEDC and (<b>b</b>) Artemis.</p> Full article ">
<p>Second-order sensitivity analysis results. (<b>a</b>) Coupling between mass and aerodynamic drag area (no coupling); (<b>b</b>) Coupling between mass and rolling resistance (medium coupling); (<b>c</b>) Coupling between mass and gear efficiency (very strong coupling).</p> Full article ">
2452 KiB  
Article
Exponential Smoothing Approaches for Prediction in Real-Time Electricity Markets
by Tryggvi Jónsson, Pierre Pinson, Henrik Aa. Nielsen and Henrik Madsen
Energies 2014, 7(6), 3710-3732; https://doi.org/10.3390/en7063710 - 16 Jun 2014
Cited by 42 | Viewed by 7177
Abstract
The optimal design of offering strategies for wind power producers is commonly based on unconditional (and, hence, constant) expectation values for prices in real-time markets, directly defining their loss function in a stochastic optimization framework. This is why it may certainly be advantageous [...] Read more.
The optimal design of offering strategies for wind power producers is commonly based on unconditional (and, hence, constant) expectation values for prices in real-time markets, directly defining their loss function in a stochastic optimization framework. This is why it may certainly be advantageous to account for the seasonal and dynamic behavior of such prices, hence translating to time-varying loss functions. With that objective in mind, forecasting approaches relying on simple models that accommodate the seasonal and dynamic nature of real-time prices are derived and analyzed. These are all based on the well-known Holt–Winters model with a daily seasonal cycle, either in its conventional form or conditioned upon exogenous variables, such as: (i) day-ahead price; (ii) system load; and (iii) wind power penetration. The superiority of the proposed approach over a number of common benchmarks is subsequently demonstrated through an empirical investigation for the Nord Pool, mimicking practical forecasting for a three-year period over 2008–2011. Full article
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<p>Time series plot of the down- and up-regulation penalties (<b>left</b> and <b>right</b>, respectively) with the excluded observations marked.</p> Full article ">
<p>Exponentially smoothed state probabilities of the observed <b><span class="html-italic">I</span></b><sup>(↑/↓)</sup> (<b>top row</b>) and the simulated <b><span class="html-italic">I</span></b><sup>(↑/↓)</sup> (<b>bottom row</b>) with λ = 0.99 (<b>left column</b>) and λ = 0.999 (<b>right column</b>). The horizontal lines represent the empirical probabilities for the whole period.</p> Full article ">
<p>The intra-day and intra-week variations (<b>left</b> and <b>right</b> columns, respectively) of the imbalance sign (<b>top row</b>) and imbalance penalties (<b>bottom row</b>), with respect to their empirical average.</p> Full article ">
<p>The empirical frequency of each imbalance sign as a function of predicted wind power penetration (<b>top left</b>) and average imbalance penalties as a function of predicted spot price (<b>top right</b>), predicted load (<b>bottom left</b>) and predicted wind power penetration (<b>bottom right</b>).</p> Full article ">
<p>Stacked bar plot showing the posterior imbalance sign probabilities estimated at 10:00 on 12 November 2010, for November 13. The most likely imbalance sign and the observed one are marked.</p> Full article ">
<p>Reliability diagrams for both unconditional (<b>top row</b>) and conditional (<b>bottom row</b>) models with diurnal seasonalities, over both training and test periods (<b>left</b> and <b>right</b> columns, respectively).</p> Full article ">
1268 KiB  
Article
Development of a Digital and Battery-Free Smart Flowmeter
by Wang Song Hao and Ronald Garcia
Energies 2014, 7(6), 3695-3709; https://doi.org/10.3390/en7063695 - 16 Jun 2014
Cited by 16 | Viewed by 8030
Abstract
To effectively manage and save energy and natural resources, the measurement and monitoring of gas/fluid flows play extremely important roles. The objective of this study was to incorporate an efficient power generation and a power management system for a commercial water flow meter [...] Read more.
To effectively manage and save energy and natural resources, the measurement and monitoring of gas/fluid flows play extremely important roles. The objective of this study was to incorporate an efficient power generation and a power management system for a commercial water flow meter thus eliminating the usage of batteries. Three major technologies have made this possible: a low power consumption metering unit, a cog-resistance-free generator with high efficiency; and an effective methodology to extract/store energy. In this system, a new attempt and simple approach was developed to successfully extract a portion of the kinetic energy from the fluid/air, store it in a capacitor and used it efficiently. The resistance to the flow was negligible because of the very low power consumption as well as the application of the coreless generator technology. Feasibility was demonstrated through repeated experiments: for air flowing in an 11 mm diameter pipe, 18 s of energy harvesting at 10 revolution-per-second (RPS) turbine speeds generated enough power for the flowmeter to operate for 720 s with a flowrate of 20 RPS, without battery or any external power. The pipeline monitoring in remote areas such as deep sea oil drilling; geothermal power plants and even nuclear power plants could benefit greatly from this self-power metering system design. Full article
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Graphical abstract
Full article ">Figure 1
<p>Ultralow power metering system designed by EPSON<sup>®</sup> Corporation.</p> Full article ">Figure 2
<p>Block diagram for the metering system.</p> Full article ">Figure 3
<p>Structure of the coreless AFPM generator.</p> Full article ">Figure 4
<p>Axial-Flux-Permanent-Magnet (AFPM) Generator Schematic.</p> Full article ">Figure 5
<p>Prototype of the Rotor and the stator.</p> Full article ">Figure 6
<p>Energy harvesting IC circuit schematic.</p> Full article ">Figure 7
<p>AFPM Generator schematic.</p> Full article ">Figure 8
<p>Schematic of AC to DC conversion and energy storage for a single phase.</p> Full article ">Figure 9
<p>Air-gap flux density using 3-D FEM simulation.</p> Full article ">Figure 10
<p>Induced voltage profile with no-load (600 rpm).</p> Full article ">Figure 11
<p>Induced voltage profile with a heavy-load of 100 Ω/phase (600 rpm).</p> Full article ">Figure 12
<p>Design of the mechanism (left to right): frame, IC circuit and sensor, casing, blades, magnets, coils, and cap.</p> Full article ">Figure 13
<p>Experimental setup.</p> Full article ">Figure 14
<p>Power consumption and storage.</p> Full article ">
426 KiB  
Article
Performance of a 250 kW Organic Rankine Cycle System for Off-Design Heat Source Conditions
by Ben-Ran Fu, Sung-Wei Hsu, Yuh-Ren Lee, Jui-Ching Hsieh, Chia-Ming Chang and Chih-Hsi Liu
Energies 2014, 7(6), 3684-3694; https://doi.org/10.3390/en7063684 - 13 Jun 2014
Cited by 19 | Viewed by 7699
Abstract
An organic Rankine cycle system comprised of a preheater, evaporator, condenser, turbine, generator, and pump was used to study its off-design performance and the operational control strategy. R245fa was used as the working fluid. Under the design conditions, the net power output is [...] Read more.
An organic Rankine cycle system comprised of a preheater, evaporator, condenser, turbine, generator, and pump was used to study its off-design performance and the operational control strategy. R245fa was used as the working fluid. Under the design conditions, the net power output is 243 kW and the system thermal efficiency is 9.5%. For an off-design heat source flow rate (mW), the operating pressure was controlled to meet the condition that the R245fa reached the liquid and vapor saturation states at the outlet of the preheater and the evaporator, respectively. The analytical results demonstrated that the operating pressure increased with increasing mW; a higher mW yielded better heat transfer performance of the preheater and required a smaller evaporator heat capacity, and the net power output and system thermal efficiency increased with increasing mW. For the range of mW studied here, the net power output increased by 64.0% while the total heat transfer rate increased by only 9.2%. In summary, off-design operation of the system was examined for a heat source flow rate which varied by –39.0% to +78.0% from the designed rate, resulting in –29.2% to +16.0% and –25.3% to +12.6% variations in the net power output and system thermal efficiency, respectively. Full article
(This article belongs to the Special Issue Selected Papers from the 1st International e-Conference on Energies — Whither Energy Conversion? Present Trends, Current Problems and Realistic Future Solutions)
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<p>Schematic diagram of the studied ORC system.</p> Full article ">Figure 2
<p>Engineering drawing of the ORC prototype: (<b>a</b>) front view and (<b>b</b>) right view.</p> Full article ">Figure 3
<p><span class="html-italic">T</span>-<span class="html-italic">s</span> diagram of the ORC system.</p> Full article ">Figure 4
<p>Operating pressure and evaporation temperature as a function of the heat source flow rate.</p> Full article ">Figure 5
<p>Temperature distribution of water and R245fa for different heat source flow rates.</p> Full article ">Figure 6
<p>Heat transfer rate as a function of the heat source flow rate.</p> Full article ">Figure 7
<p>Preheater heat transfer coefficient as a function of the heat source flow rate.</p> Full article ">Figure 8
<p>Net power output and system efficiency as a function of the heat source flow rate.</p> Full article ">
238 KiB  
Article
Proof-of-Concept of a Zinc-Silver Battery for the Extraction of Energy from a Concentration Difference
by Massimo Marino, Lorenza Misuri, Andrea Carati and Doriano Brogioli
Energies 2014, 7(6), 3664-3683; https://doi.org/10.3390/en7063664 - 13 Jun 2014
Cited by 44 | Viewed by 9835 | Correction
Abstract
The conversion of heat into current can be obtained by a process with two stages. In the first one, the heat is used for distilling a solution and obtaining two flows with different concentrations. In the second stage, the two flows are sent [...] Read more.
The conversion of heat into current can be obtained by a process with two stages. In the first one, the heat is used for distilling a solution and obtaining two flows with different concentrations. In the second stage, the two flows are sent to an electrochemical cell that produces current by consuming the concentration difference. In this paper, we propose such an electrochemical cell, working with water solutions of zinc chloride. The cell contains two electrodes, made respectively of zinc and silver covered by silver chloride. The operation of the cell is analogous to that of the capacitive mixing and of the “mixing entropy battery”: the electrodes are charged while dipped in the concentrated solution and discharged when dipped in the diluted solution. The cyclic operation allows us to extract a surplus of energy, at the expense of the free energy of the concentration difference. We evaluate the feasibility of such a cell for practical applications and find that a power up to 2 W per m2 of the surface of the electrodes can be achieved. Full article
(This article belongs to the Special Issue Electrochemical Energy Storage—Battery and Capacitor)
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Graphical abstract

Graphical abstract
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<p>Sketch of the heat-to-current converter system. The electrochemical cells consume the concentration difference between two flows, A and B, using the available free energy for producing an electrical current. The concentrations are then restored by means of a distiller, which consumes heat. The system is thus a heat-to-current converter.</p> Full article ">
<p>Cycles of the accumulator mixing (AccMix) technique. The cycle starts with the cell filled with the high concentration solution. The phases are: (1) charge; (2) flow of dilute solution; (3) discharge; (4) flow of concentrated solution.</p> Full article ">
<p>The AccMix cell for zinc chloride. The reactions taking place in the two steps of the AccMix cycle are shown. Legend: <span class="html-fig-inline" id="energies-07-03664i1"> <img alt="Energies 07 03664i1" src="/energies/energies-07-03664/article_deploy/html/images/energies-07-03664i1.png"/></span> Concentrated zinc chloride solution; <span class="html-fig-inline" id="energies-07-03664i2"> <img alt="Energies 07 03664i2" src="/energies/energies-07-03664/article_deploy/html/images/energies-07-03664i2.png"/></span> dilute zinc chloride solution; <span class="html-fig-inline" id="energies-07-03664i3"> <img alt="Energies 07 03664i3" src="/energies/energies-07-03664/article_deploy/html/images/energies-07-03664i3.png"/></span> zinc electrode; <span class="html-fig-inline" id="energies-07-03664i4"> <img alt="Energies 07 03664i4" src="/energies/energies-07-03664/article_deploy/html/images/energies-07-03664i4.png"/></span> porous silver chloride; <span class="html-fig-inline" id="energies-07-03664i5"> <img alt="Energies 07 03664i5" src="/energies/energies-07-03664/article_deploy/html/images/energies-07-03664i5.png"/></span> silver.</p> Full article ">
<p>Boiling point elevation of the ZnCl<sub>2</sub> solutions at 1 atm pressure. Data kindly provided by Italshell [<a href="#b50-energies-07-03664" class="html-bibr">50</a>], obtained by calculation. Some of the values have been also experimentally tested. The concentration is expressed as the ratio between the mass of the solute and the total mass of the solution. The lines are the linear approximation for dilute solutions, for two different values of the van’t Hoff factor. The actual boiling point elevation has an evident deviation from the ideal solution, also at low concentrations. A quite high boiling temperature is observed in concentrated solutions.</p> Full article ">
<p>The available free energy. The graph shows the energy that can be ideally produced by a cell per liter of solvent in the diluted solution, as a function of the concentration of the outgoing diluted solution. The concentrated solution has a mass fraction <span class="html-italic">C<sub>A</sub></span> = 75.5%, considered constant during the cycle, <span class="html-italic">c<sub>D</sub></span> = <span class="html-italic">c<sub>A</sub></span>. The step of the cycle in dilute solution starts with the cell filled with fresh water, <span class="html-italic">c<sub>B</sub></span> = 0, and stops at a concentration <span class="html-italic">c<sub>C</sub></span>.</p> Full article ">
<p>The cell voltage as a function of the concentration. The voltage is measured in an open circuit. Two independent sets of measurements are shown. Four measurements are performed and averaged; the error bars represent the observed standard deviation. The solid line has been obtained from the chemical potential, in turn calculated from the boiling point elevation.</p> Full article ">
<p>Example of the charge–discharge cycle. The cycle is clockwise.</p> Full article ">
<p>The average dissipated power during charge-discharge cycles in ZnCl<sub>2</sub> solutions. The various data sets refer to different concentrations and different electrodes. The size of the electrodes is 1 × 1 cm; in the case of the Ag wool, this is the macroscopic dimension of the felt. The reported power is an average over five consecutive cycles; the standard deviation is less than 6%.</p> Full article ">
<p>The average dissipated power density at the AgCl/Ag electrode. The conditions are the same as <a href="#f8-energies-07-03664" class="html-fig">Figure 8</a>.</p> Full article ">
858 KiB  
Article
Silicon Heterojunction Solar Cells Using AlOx and Plasma-Immersion Ion Implantation
by Yu-Hsien Lin, Yung-Chun Wu, Hsin-Chiang You, Chun-Hao Chen, Ping-Hua Chen, Yi-He Tsai, Yi-Yun Yang and K. S. Chang-Liao
Energies 2014, 7(6), 3653-3663; https://doi.org/10.3390/en7063653 - 13 Jun 2014
Cited by 5 | Viewed by 8054
Abstract
Aluminum oxide (AlOx) and plasma immersion ion implantation (PIII) were studied in relation to passivated silicon heterojunction solar cells. When aluminum oxide (AlOx) was deposited on the surface of a wafer; the electric field near the surface of wafer [...] Read more.
Aluminum oxide (AlOx) and plasma immersion ion implantation (PIII) were studied in relation to passivated silicon heterojunction solar cells. When aluminum oxide (AlOx) was deposited on the surface of a wafer; the electric field near the surface of wafer was enhanced; and the mobility of the carrier was improved; thus reducing carrier traps associated with dangling bonds. Using PIII enabled implanting nitrogen into the device to reduce dangling bonds and achieve the desired passivation effect. Depositing AlOx on the surface of a solar cell increased the short-circuit current density (Jsc); open-circuit voltage (Voc); and conversion efficiency from 27.84 mA/cm2; 0.52 V; and 8.97% to 29.34 mA/cm2; 0.54 V; and 9.68%; respectively. After controlling the depth and concentration of nitrogen by modulating the PIII energy; the ideal PIII condition was determined to be 2 keV and 10 min. As a result; a 15.42% conversion efficiency was thus achieved; and the Jsc; Voc; and fill factor were 37.78 mA/cm2; 0.55 V; and 0.742; respectively. Full article
(This article belongs to the Special Issue Selected Papers from the 2014 International Symposium on Computer, Consumer and Control (IS3C2014))
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<p>Heterojunction solar cell with AlO<span class="html-italic"><sub>x</sub></span> passivation.</p> Full article ">Figure 2
<p>Passivated solar cell by using PIII.</p> Full article ">Figure 3
<p>Basic structure of AlO<span class="html-italic"><sub>x</sub></span>/c-Si capacitance.</p> Full article ">Figure 4
<p>Comparison of without AlO<span class="html-italic"><sub>x</sub></span> and with AlO<span class="html-italic"><sub>x</sub></span> structure.</p> Full article ">Figure 5
<p>The I-V characteristic curve of without AlO<span class="html-italic"><sub>x</sub></span> and with AlO<span class="html-italic"><sub>x</sub></span> samples.</p> Full article ">Figure 6
<p>The I-V characteristic curve of without PIII, PIII 2 Kev, PIII 4 Kev, and PIII 6 Kev homojunction samples.</p> Full article ">Figure 7
<p>(<b>a</b>) The SIMS profiles of PIII 4 KeV sample. (<b>b</b>) The SIMS profiles of PIII 2 KeV sample.</p> Full article ">Figure 8
<p>The reverse dark I-V characteristic curve of solar cell (using heterojunction solar cell with AlO<span class="html-italic"><sub>x</sub></span> passivation).</p> Full article ">Figure 9
<p>The I-V characteristic curve of without PIII, PIII 2 KeV 5 min, PIII 2 KeV 10 min, and PIII 2 KeV 15 min samples.</p> Full article ">Figure 10
<p>The reverse dark I-V characteristic curve of solar cell (using homojunction solar cell with AlO<span class="html-italic"><sub>x</sub></span> passivation).</p> Full article ">Figure 11
<p>The I-V characteristic curve comparison of without PIII &amp; PIII 2 KeV 10 min heterojunction solar cells without AlO<span class="html-italic"><sub>x</sub></span>.</p> Full article ">Figure 12
<p>The reverse dark I-V characteristic curve of solar cell (using heterojunction solar cell without AlO<span class="html-italic"><sub>x</sub></span> passivation).</p> Full article ">
1058 KiB  
Article
Importance of Fuel Cell Tests for Stability Assessment—Suitability of Titanium Diboride as an Alternative Support Material
by Christina Roth, Peter Bleith, Christoph A. Schwöbel, Sebastian Kaserer and Jens Eichler
Energies 2014, 7(6), 3642-3652; https://doi.org/10.3390/en7063642 - 11 Jun 2014
Cited by 11 | Viewed by 9585
Abstract
Carbon corrosion is a severe issue limiting the long-term stability of carbon-supported catalysts, in particular in the highly dynamic conditions of automotive applications. (Doped) oxides have been discussed as suitable alternatives to replace carbon, but often suffer from poor electron conductivity. That is [...] Read more.
Carbon corrosion is a severe issue limiting the long-term stability of carbon-supported catalysts, in particular in the highly dynamic conditions of automotive applications. (Doped) oxides have been discussed as suitable alternatives to replace carbon, but often suffer from poor electron conductivity. That is why non-oxide ceramics, such as tungsten carbide and titanium nitride, have been discussed recently. Titanium diboride has also been proposed, due to its promising activity and stability in an aqueous electrochemical cell. In this work, Pt nanoparticles were deposited onto μm-sized TiB2 particles with improved grain size, manufactured into porous gas diffusion electrodes and tested in a realistic polymer electrolyte membrane (PEM) fuel cell environment. In contrast to the model studies in an aqueous electrochemical cell, in the presence of oxygen and high potentials at the cathode side of a real fuel cell, TiB2 becomes rapidly oxidized as indicated by intensely colored regions in the membrane-electrode assembly (MEA). Moreover, already the electrode manufacturing process led to the formation of titanium oxides, as shown by X-ray diffraction measurements. This demonstrates that Cyclic Voltammetry (CV) measurements in an aqueous electrochemical cell are not sufficient to prove stability of novel materials for fuel cell applications. Full article
(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>X-ray diffraction pattern of Pt nanoparticles supported on TiB<sub>2</sub>. Both measured data and Rietveld refinement are shown. Sharp reflections belong to the support material, broad reflections can be attributed to the Pt nanoparticles. The Pt nanoparticle size is ≈5 nm.</p> Full article ">Figure 2
<p>Transmission electron micrograph of Pt/TiB<sub>2</sub>. Nafion™-stabilized Pt nanoparticles can only be imaged in thinner edge regions, as the μm-sized TiB<sub>2</sub> grains are too thick to let electrons pass through the grain center. The average Pt particle size as <span class="html-italic">ca.</span> 5 nm embedded in a Nafion™ ionomer film.</p> Full article ">Figure 3
<p>(<b>a</b>) Base voltammogram of a Pt/TiB<sub>2</sub> catalyst in 0.1 M perchloric acid showing the prominent Pt characteristics. Different sweeps are presented showing the loss of ECSA with extended cycling up to 100 cycles; (<b>b</b>) cyclic voltammogram of the same Pt/TiB<sub>2</sub> catalyst in 1 M methanol solution as a reliable activity probe (black—second cycle, blue—10th cycle).</p> Full article ">Figure 4
<p>Diffraction patterns of Pt/TiB<sub>2</sub> powder as-synthesized (<b>bottom</b>), after preparation into a porous electrode with no fuel cell operation (<b>middle</b>), after fuel cell operation (<b>top</b>). While the as-synthesized support can be described by pure TiB<sub>2</sub>, the other diffraction patterns display an additional peak of the TiO<sub>2</sub> rutile phase. TiB<sub>2</sub> already starts to oxidize during the electrode fabrication step.</p> Full article ">Figure 5
<p>Decline of power output during fuel cell operation and comparison of the corresponding SEM images before and after operation.</p> Full article ">Figure 6
<p>Photograph of TiB<sub>2</sub> electrode after fuel cell test. Iridescent blue regions close to the oxygen inlet (<b>top left</b>) indicate where titanium diboride has been transformed into titanium oxide. At the oxygen outlet (<b>bottom right</b>), orange colors dominate.</p> Full article ">
3013 KiB  
Article
A Single Phase Doubly Grounded Semi-Z-Source Inverter for Photovoltaic (PV) Systems with Maximum Power Point Tracking (MPPT)
by Tofael Ahmed, Tey Kok Soon and Saad Mekhilef
Energies 2014, 7(6), 3618-3641; https://doi.org/10.3390/en7063618 - 3 Jun 2014
Cited by 21 | Viewed by 10981
Abstract
In this paper, a single phase doubly grounded semi-Z-source inverter with maximum power point tracking (MPPT) is proposed for photovoltaic (PV) systems. This proposed system utilizes a single-ended primary inductor (SEPIC) converter as DC-DC converter to implement the MPPT algorithm for tracking the [...] Read more.
In this paper, a single phase doubly grounded semi-Z-source inverter with maximum power point tracking (MPPT) is proposed for photovoltaic (PV) systems. This proposed system utilizes a single-ended primary inductor (SEPIC) converter as DC-DC converter to implement the MPPT algorithm for tracking the maximum power from a PV array and a single phase semi-Z-source inverter for integrating the PV with AC power utilities. The MPPT controller utilizes a fast-converging algorithm to track the maximum power point (MPP) and the semi-Z-source inverter utilizes a nonlinear SPWM to produce sinusoidal voltage at the output. The proposed system is able to track the MPP of PV arrays and produce an AC voltage at its output by utilizing only three switches. Experimental results show that the fast-converging MPPT algorithm has fast tracking response with appreciable MPP efficiency. In addition, the inverter shows the minimization of common mode leakage current with its ground sharing feature and reduction of the THD as well as DC current components at the output during DC-AC conversion. Full article
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<p>Proposed single phase semi-Z-source inverter with MPPT.</p> Full article ">Figure 2
<p>Load lines on I-V curves for solar irradiation level of 0.4 kW/m<sup>2</sup> and 1.0 kW/m<sup>2</sup>.</p> Full article ">Figure 3
<p>Flow chart of the proposed MPPT algorithm.</p> Full article ">Figure 4
<p>(<b>a</b>) Single phase doubly grounded semi-Z-source inverters, (<b>b</b>) voltage gain of Semi-Z-source inverters.</p> Full article ">Figure 5
<p>Modes of operation of semi-Z-source inverters when <span class="html-italic">D</span> &lt; 0.5: (<b>a</b>) State I; (<b>b</b>) State II.</p> Full article ">Figure 6
<p>Modes of operation of semi-Z-source inverters when <span class="html-italic">D</span> &gt; 0.5: (<b>a</b>) State I; (<b>b</b>) State II.</p> Full article ">Figure 7
<p>(<b>a</b>) Off state voltage across the switch <span class="html-italic">vs</span>. M and ω<span class="html-italic">t</span>, (<b>b</b>) On state current through the switch <span class="html-italic">vs</span>. M and ω<span class="html-italic">t</span>.</p> Full article ">Figure 8
<p>(<b>a</b>) Voltage across capacitor C<sub>1</sub> <span class="html-italic">vs</span>. M and ω<span class="html-italic">t</span>; (<b>b</b>) Current through inductor L<sub>1</sub> <span class="html-italic">vs.</span> M and ω<span class="html-italic">t</span>.</p> Full article ">Figure 9
<p>(<b>a</b>) Voltage ripple capacitor C<sub>1</sub>; (<b>b</b>) Current ripple of inductor L<sub>1</sub>.</p> Full article ">Figure 10
<p>Modulation principle of semi-Z-source inverter.</p> Full article ">Figure 11
<p>(<b>a</b>) Experimental waveforms of gate to source voltage, drain to source voltage, output voltage, output current for R load; (<b>b</b>) zoomed in waveform of (<b>a</b>); (<b>c</b>) experimental waveforms of drain to source voltage of two switches, output voltage, output current for R load; (<b>d</b>) zoomed in waveform of figure (<b>c</b>).</p> Full article ">Figure 12
<p>(<b>a</b>) Experimental waveforms of gate to source voltage, drain to source voltage, output voltage, output current for R-L load; (<b>b</b>) zoomed in waveform of figure (<b>a</b>); (<b>c</b>) experimental waveforms of input DC voltage, capacitor C<sub>1</sub> voltage, output voltage, output current for R load; (<b>d</b>) experimental waveforms of input DC voltage, capacitor C<sub>1</sub> voltage, output voltage, output current for R-L load.</p> Full article ">Figure 13
<p>(<b>a</b>) Experimental waveforms of input DC voltage, capacitor C<sub>1</sub> voltage, output voltage, output current for <span class="html-italic">R</span> load; (<b>b</b>) experimental waveforms of input DC voltage, capacitor C<sub>1</sub> voltage, output voltage, output current for <span class="html-italic">R</span>-<span class="html-italic">L</span> load; (<b>c</b>) THD and Harmonic spectrum of output voltage and current for R load; (<b>d</b>) THD and Harmonic spectrum of output voltage and current for <span class="html-italic">R</span>-<span class="html-italic">L</span> load.</p> Full article ">Figure 14
<p>(<b>a</b>) Waveform of PV module power and duty cycle of proposed algorithm; (<b>b</b>) waveform of PV module power and duty cycle of conventional incremental conductance algorithm; (<b>c</b>) I–V curve and P–V curve; (<b>d</b>) experimental waveforms of MPPT output/inverter input DC voltage, output voltage, output current for R load; (<b>e</b>) experimental waveforms of MPPT output/inverter input DC voltage, output voltage, output current for R-L load.</p> Full article ">
1065 KiB  
Article
Novel Modeling and Control Strategies for a HVAC System Including Carbon Dioxide Control
by Chang-Soon Kang, Jong-Il Park, Mignon Park and Jaeho Baek
Energies 2014, 7(6), 3599-3617; https://doi.org/10.3390/en7063599 - 2 Jun 2014
Cited by 26 | Viewed by 8668
Abstract
Conventional heating, ventilating, and air conditioning (HVAC) systems have traditionally used the temperature and the humidity ratio as the quantitative indices of comfort in a room. Recently, the carbon dioxide (CO2) concentration has also been recognized as having an important contribution [...] Read more.
Conventional heating, ventilating, and air conditioning (HVAC) systems have traditionally used the temperature and the humidity ratio as the quantitative indices of comfort in a room. Recently, the carbon dioxide (CO2) concentration has also been recognized as having an important contribution to room comfort. This paper presents the modeling of an augmented HVAC system including CO2 concentration, and its control strategies. Because the proposed augmented HVAC system is multi-input multi-output (MIMO) and has no relative degree problem, the dynamic extension algorithm can be employed; then, a feedback linearization technique is applied. A linear-quadratic regulator (LQR) is designed to optimize control performance and to stabilize the proposed HVAC system. Simulation results are provided to validate the proposed system model, as well as its linearized control system. Full article
(This article belongs to the Special Issue Energy Efficient Building Design and Operation 2014)
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<p>Model of the representative conventional HVAC system.</p> Full article ">Figure 2
<p>Overall block diagram for controlling the proposed HVAC system.</p> Full article ">Figure 3
<p>Concept of the dynamic extension algorithm [13].</p> Full article ">Figure 4
<p>(<b>a</b>) Temperature response for each pole placement; (<b>b</b>) Humidity ratio response for each pole placement; (<b>c</b>) CO<sub>2</sub> concentration response for each pole placement.</p> Full article ">Figure 5
<p>(<b>a</b>) Temperature response by LQR; (<b>b</b>) Humidity ratio response by LQR; (<b>c</b>) CO<sub>2</sub> concentration response by LQR.</p> Full article ">
466 KiB  
Article
System for Road Vehicle Energy Optimization Using Real Time Road and Traffic Information
by Felipe Jiménez and Wilmar Cabrera-Montiel
Energies 2014, 7(6), 3576-3598; https://doi.org/10.3390/en7063576 - 2 Jun 2014
Cited by 29 | Viewed by 7286 | Correction
Abstract
Nowadays, reducing the energy and fuel consumption of road vehicles is a key issue. Different strategies have been proposed. One of them is to promote Eco-driving behaviour among drivers. Most Eco-driving tips take into account only the road stretch where the vehicle is [...] Read more.
Nowadays, reducing the energy and fuel consumption of road vehicles is a key issue. Different strategies have been proposed. One of them is to promote Eco-driving behaviour among drivers. Most Eco-driving tips take into account only the road stretch where the vehicle is located. However, larger improvements could be achieved if information from subsequent stretches is used. The main objective of this work is to develop a system to warn the driver in real time of the optimal speed that should be maintained on every road segment in order to optimize the energy used and the fuel consumed while observing a time schedule. The system takes into account the road vertical profile, the fixed and variable speed limits and the traffic information retrieved using V2V and V2I communications. The system has been tested on real road sections with satisfactory results in fuel savings. Full article
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<p>Scheme of the optimization process.</p> Full article ">Figure 2
<p>Overlap of the partial speed profiles.</p> Full article ">Figure 3
<p>Operation traffic states when a perturbation appears.</p> Full article ">Figure 4
<p>Road slopes profile.</p> Full article ">Figure 5
<p>Optimal speed profile (only fixed and variable speed limits expected before the trip begins).</p> Full article ">Figure 6
<p>Constant speed profile (unexpected speed restriction).</p> Full article ">Figure 7
<p>Optimal speed profile (unexpected speed restriction).</p> Full article ">
1185 KiB  
Article
Cascaded Position-Flux Controller for an AMB System Operating at Zero Bias
by Rafal P. Jastrzebski, Alexander Smirnov, Arkadiusz Mystkowski and Olli Pyrhönen
Energies 2014, 7(6), 3561-3575; https://doi.org/10.3390/en7063561 - 30 May 2014
Cited by 27 | Viewed by 6350 | Correction
Abstract
The paper reports on the implementation and the design of a controller for a fuel cell blower (FCB) with active magnetic bearings (AMBs). The cascaded position-fluxcentralized controller is comprised of a centralized position control loop and an inner flux control loop. The last [...] Read more.
The paper reports on the implementation and the design of a controller for a fuel cell blower (FCB) with active magnetic bearings (AMBs). The cascaded position-fluxcentralized controller is comprised of a centralized position control loop and an inner flux control loop. The last one is based on state estimation without explicit flux measurements. As the position control is not dependent on the magnetic field nonlinearities, such a control structure enables operation under a zero bias. The practical working implementation of a flux control for the industrial levitated rotor is shown for the first time. The flux control gives better results than current control for both normal and zero bias operation. The system is analyzed fully, combining rotor dynamics and power amplifier analyses simultaneously. The importance of using the coil voltage in addition to current and practical treatment of the flux control is revealed. The centralized position-flux controller is compared with a state-of-the-art cascaded position-current control, which has inner current control loops. The proposed control solution with a zero bias can achieve a dynamic performance comparable that of a controller with the classical bias current. Full article
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<p>Rotor model with locations of radial sensor planes (dashed line with arrows), radial actuator planes (solid line with arrows) and motor (solid line with two arrows) in the active magnetic bearing (AMB) rotor system.</p> Full article ">
<p>Cascaded control diagrams. For current (flux)-controlled AMB, the centralized controller provides a vector of four control currents, <b><span class="html-italic">i</span></b><sub>c</sub> (forces <b><span class="html-italic">f</span></b><sub>c</sub>), and after biasing the vector of eight reference currents, <b><span class="html-italic">i</span></b><sub>r</sub> (forces <b><span class="html-italic">f</span></b><sub>r</sub>), to the inner control loops. Additionally, the inner flux loops require the vector of estimated rotor displacements in bearing planes <b><span class="html-italic">x</span></b><sub>mb</sub>. <b><span class="html-italic">x</span></b><sub>r</sub>, <b><span class="html-italic">i</span></b><sub>m</sub>, <b><span class="html-italic">u</span></b><sub>r</sub>, <b><span class="html-italic">f</span></b> and <b>x</b><sub>m</sub> are vectors of reference positions, measured currents, reference voltages, and bearing force rotor displacements in sensor planes, respectively.</p> Full article ">
<p>Comparison of the force growth for the biased AMB with <span class="html-italic">i</span><sub>0</sub> = 2.5 A and for the zero-bias case when the rotor remains in the central position.</p> Full article ">
<p>Simulated step position reference and disturbance force responses of the selected position and current signals of the centralized radial AMB rotor system. <span class="html-italic">i<sub>x</sub></span><sub>pA</sub> and <span class="html-italic">i<sub>x</sub></span><sub>mA</sub> are the coil currents resulting in the magnetic force generation that acts in the positive and negative direction of the <span class="html-italic">x</span>-axis at the A-end of the rotor. <b>(a)</b> Flux controlled system with zero bias; <b>(b)</b> Flux controlled system with bias; <b>(c)</b> Flux controlled system with bias and gain scheduling in the inner control loops.</p> Full article ">
<p>Measured initial levitation of the rotor from the safety bearings at both rotor ends. <b>(Left)</b> The B-end; <b>(Right)</b> the A-end.</p> Full article ">
<p>Measured step response at the A-end in the <span class="html-italic">y</span>-direction with a 100 μm magnitude at a standstill.</p> Full article ">
<p>Measured maximum singular values for output sensitivity functions at a standstill.</p> Full article ">
<p>Measured maximum singular values for output sensitivity functions at 11, 000 rpm.</p> Full article ">
306 KiB  
Article
The Real-Time Optimisation of DNO Owned Storage Devices on the LV Network for Peak Reduction
by Matthew Rowe, Timur Yunusov, Stephen Haben, William Holderbaum and Ben Potter
Energies 2014, 7(6), 3537-3560; https://doi.org/10.3390/en7063537 - 30 May 2014
Cited by 52 | Viewed by 8639
Abstract
Energy storage is a potential alternative to conventional network reinforcement of the low voltage (LV) distribution network to ensure the grid’s infrastructure remains within its operating constraints. This paper presents a study on the control of such storage devices, owned by distribution network [...] Read more.
Energy storage is a potential alternative to conventional network reinforcement of the low voltage (LV) distribution network to ensure the grid’s infrastructure remains within its operating constraints. This paper presents a study on the control of such storage devices, owned by distribution network operators. A deterministic model predictive control (MPC) controller and a stochastic receding horizon controller (SRHC) are presented, where the objective is to achieve the greatest peak reduction in demand, for a given storage device specification, taking into account the high level of uncertainty in the prediction of LV demand. The algorithms presented in this paper are compared to a standard set-point controller and bench marked against a control algorithm with a perfect forecast. A specific case study, using storage on the LV network, is presented, and the results of each algorithm are compared. A comprehensive analysis is then carried out simulating a large number of LV networks of varying numbers of households. The results show that the performance of each algorithm is dependent on the number of aggregated households. However, on a typical aggregation, the novel SRHC algorithm presented in this paper is shown to outperform each of the comparable storage control techniques. Full article
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<p>Five histograms showing the error distributions between the forecasted and actual demand in demand aggregation sizes of five, 10, 15, 25 and 35 individual demand profiles, respectively (from top to bottom). The forecasting methodology used to produce these errors can be found in the appendix of [<a href="#b6-energies-07-03537" class="html-bibr">6</a>].</p> Full article ">
<p>The model predictive control loop.</p> Full article ">
<p>A scenario tree of five time steps with a varying number of nodes per time step. The probabilities of a specific node occurring are shown, as is the probability of the complete route occurring.</p> Full article ">
<p>A specific example: (<b>a</b>) the actual demand and the stochastic receding horizon controller (SRHC) and MPC controller results; (<b>b</b>) the actual demand and the best possible and set-point controller results.</p> Full article ">
<p>(<b>a</b>) The forecasted and actual demand profiles; (<b>b</b>) the evolution of the state of charge (SOC) across the horizon.</p> Full article ">
<p>(<b>a</b>) The demand profile with and without a storage device; (<b>b</b>) the final SOC of the storage device throughout the day.</p> Full article ">
<p>Algorithm performance <span class="html-italic">vs.</span> horizon size for the SRHC, MPC, MPC with a perfect demand model and the best possible demand reduction given a perfect demand model.</p> Full article ">
<p>Set-point control and MPC performance when varying the number of demand profiles aggregated.</p> Full article ">
<p>Box plots showing the distribution of demand reduction achieved using algorithms (from left to right) MPC, SRHC, best possible demand reduction and set-point control.</p> Full article ">
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