Energies

1 pages, 157 KiB

Open AccessCorrection

Correction: Arshad A.; et al. An Analysis of Photo-Voltaic Hosting Capacity in Finnish Low Voltage Distribution Networks. Energies 2017, 10, 1702

by Ammar Arshad, Martin Lindner and Matti Lehtonen

Energies 2018, 11(3), 689; https://doi.org/10.3390/en11030689 - 20 Mar 2018

Viewed by 3363

Abstract

The authors would like to correct following errors[...] Full article

(This article belongs to the Section F: Electrical Engineering)

11 pages, 3781 KiB

Open AccessArticle

A Fast-Transient Output Capacitor-Less Low-Dropout Regulator Using Active-Feedback and Current-Reuse Feedforward Compensation

by Eun-Taek Sung, Sangyong Park and Donghyun Baek

Energies 2018, 11(3), 688; https://doi.org/10.3390/en11030688 - 19 Mar 2018

Cited by 10 | Viewed by 9065

Abstract

In this paper, output capacitor-less low-dropout (LDO) regulator using active-feedback and current-reuse feedforward compensation (AFCFC) is presented. The open-loop transfer function was obtained using small-signal modeling. The stability of the proposed LDO was analyzed using pole-zero plots, and it was confirmed by simulations [...] Read more.

In this paper, output capacitor-less low-dropout (LDO) regulator using active-feedback and current-reuse feedforward compensation (AFCFC) is presented. The open-loop transfer function was obtained using small-signal modeling. The stability of the proposed LDO was analyzed using pole-zero plots, and it was confirmed by simulations that the stability was ensured under the load current of 50 mA. The proposed compensation method increases gain-bandwidth product (GBW) and reduces the on-chip compensation capacitor. The proposed AFCFC technique was applied to a three-stage output capacitor-less LDO. The LDO has a GBW of 5.6 MHz with a small on-chip capacitor of 2.6 pF. Fast-transient time of 450 ns with low quiescent current of 65.8 μA was achieved. The LDO was fabricated in 130 nm CMOS process consuming 180 × 140 μm² of the silicon area. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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20 pages, 2509 KiB

Open AccessArticle

The Energy Cost Analysis of Hybrid Systems and Diesel Generators in Powering Selected Base Transceiver Station Locations in Nigeria

by Peter Ozaveshe Oviroh and Tien-Chien Jen

Energies 2018, 11(3), 687; https://doi.org/10.3390/en11030687 - 19 Mar 2018

Cited by 73 | Viewed by 8719

Abstract

As more locations gain access to telecommunication, there is a growing demand to provide energy in a reliable, efficient and environmentally friendly manner while effectively addressing growing energy needs. Erratic power supply and rising operation costs (OPEX) in Nigeria have increased the need [...] Read more.

As more locations gain access to telecommunication, there is a growing demand to provide energy in a reliable, efficient and environmentally friendly manner while effectively addressing growing energy needs. Erratic power supply and rising operation costs (OPEX) in Nigeria have increased the need to harness local renewable energy sources. Thus, identifying the right generator schedule with the renewable system to reduce OPEX is a priority for operators and vendors. This study evaluates the energy costs of hybrid systems with different generator schedules in powering base transceiver stations in Nigeria using the Hybrid Optimization Model for Electric Renewable (HOMER). A load range of 4 kW to 8 kW was considered using: (i) an optimised generator schedule; (ii) forced-on generator schedule and (iii) the generator-only schedule. The results showed an optimal LCOE range between averages of USD 0.156/kWh to 0.172/kWh for the 8 kW load. The percent energy contribution by generator ranges from 52.80% to 60.90%, and by the solar PV system, 39.10% to 47.20%. Excess energy ranges from 0.03% to 14.98%. The optimised generator schedule has the highest solar PV penetration of 56.8%. The OPEX savings on fuel ranges from 41.68% to 47% for the different load schedules and carbon emission savings of 4222 kg to 31,428.36 kg. The simulation results shows that powering base stations using the optimised hybrid system schedule would be a better option for the telecom industry. Full article

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21 pages, 3958 KiB

Open AccessArticle

Research on Economic Comprehensive Control Strategies of Tractor-Planter Combinations in Planting, Including Gear-Shift and Cruise Control

by Baogang Li, Dongye Sun, Minghui Hu and Junlong Liu

Energies 2018, 11(3), 686; https://doi.org/10.3390/en11030686 - 19 Mar 2018

Cited by 22 | Viewed by 5061

Abstract

An automatic control strategy for forward speed in the planting process is proposed to improve the fuel economy and reduce the labor intensity of drivers. Models of tractors with power-shift transmission (PST) and a precise pneumatic planter with an electric-driven seed metering device [...] Read more.

An automatic control strategy for forward speed in the planting process is proposed to improve the fuel economy and reduce the labor intensity of drivers. Models of tractors with power-shift transmission (PST) and a precise pneumatic planter with an electric-driven seed metering device are built as research objects and simulated using Matlab with Simulink. The economic comprehensive control strategies for forward speed, including gear-shift schedule and cruise control strategy, are developed. Four levels control mode with different fuel economy performances are implemented to meet different driver or operation condition requirements. In addition, the control strategy is developed for the seed-metering device motor to maintain the required seed spacing in planting. Finally, the fuel economy and effectiveness of the control strategies for forward speed and planting quality are verified by simulations with Matlab/Simulink and Matlab/Stateflow. The simulation results verify the satisfactory performance of the proposed control strategies. The error of seed spacing is less than 3% when planting with speed fluctuation. Under the premise of ensuring planting quality and driver’s demands, the cruise control strategies for forward speed have more significant effects on the fuel economy than previous cruise control strategies. Furthermore, the control mode with higher level has better fuel economy and a larger speed deviation range. Full article

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17 pages, 7015 KiB

Open AccessArticle

Hydrodynamic Performance of an Array of Wave Energy Converters Integrated with a Pontoon-Type Breakwater

by De Zhi Ning, Xuan Lie Zhao, Li Fen Chen and Ming Zhao

Energies 2018, 11(3), 685; https://doi.org/10.3390/en11030685 - 18 Mar 2018

Cited by 41 | Viewed by 5444

Abstract

The cost of wave energy converters (WECs) can be reduced significantly by integrating WECs into other marine facilities, especially in sea areas with a mild wave climate. To reduce the cost and increase the efficiency, a hybrid WEC system, comprising a linear array [...] Read more.

The cost of wave energy converters (WECs) can be reduced significantly by integrating WECs into other marine facilities, especially in sea areas with a mild wave climate. To reduce the cost and increase the efficiency, a hybrid WEC system, comprising a linear array (medium farm) of oscillating buoy-type WECs attached to the weather side of a fixed-type floating pontoon as the base structure is proposed. The performance of the WEC array is investigated numerically using a boundary element method (BEM) based on the linear potential flow theory. The linear power take-off (PTO) damping model is used to calculate the output power of the WEC array. The performance of the WEC array and each individual WEC device is balanced by using the mean interaction factor and the individual interaction factor. To quantify the effect of the pontoon, the hydrodynamic results of the WEC arrays with and without a pontoon are compared with each other. Detailed investigations on the influence of the structural and PTO parameters are performed in a wide wave frequency range. Results show that the energy conversion efficiency of a WEC array with a properly designed pontoon is much higher than that without a pontoon. This integration scheme can achieve the efficiency improvement and construction-cost reduction of the wave energy converters. Full article

(This article belongs to the Special Issue Wave Energy Potential, Behavior and Extraction)

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9 pages, 2974 KiB

Open AccessArticle

Assessment of the Induced Electric Fields in a Carbon-Fiber Electrical Vehicle Equipped with a Wireless Power Transfer System

by Valerio De Santis, Tommaso Campi, Silvano Cruciani, Ilkka Laakso and Mauro Feliziani

Energies 2018, 11(3), 684; https://doi.org/10.3390/en11030684 - 18 Mar 2018

Cited by 37 | Viewed by 5522

Abstract

In this study, the electric field induced inside two realistic anatomical models placed near or inside an electric vehicle made of carbon-fiber composite while charging its battery with a wireless power transfer (WPT) system has been investigated. The WPT source consists of two [...] Read more.

In this study, the electric field induced inside two realistic anatomical models placed near or inside an electric vehicle made of carbon-fiber composite while charging its battery with a wireless power transfer (WPT) system has been investigated. The WPT source consists of two parallel inductive coils operating with a power output of 7.7 kW at two different frequencies of 85 and 150 kHz. Since a misalignment between the primary and the secondary coil creates higher induced fields, a misalignment of 20 cm is also considered as the worst-case exposure condition. The analysis of the obtained results shows that the International Commission on Non-Ionizing Radiation Protection (ICNIRP) basic restrictions are exceeded by 1.3 dB and 4.8 dB for the aligned and misaligned coil positions, respectively. This exceedance is however confined only in a small area of the driver’s foot. Full article

(This article belongs to the Section F: Electrical Engineering)

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WPT coil configuration (primary coil on the road and secondary coil below the car platform) (a). WPT equivalent circuit (b). Full article ">Figure 2
Configuration of Duke and Fats placed near and inside an EV chassis. (a) Aligned and (b) misaligned coils. The red box is the computational domain for dosimetry assessment. Full article ">Figure 3
Magnetic flux density distribution for the misaligned coil position. (a) Steel chassis; (b) aluminum chassis. The yellow line represents the ICNIRP limit (RL = 27 µT = 28.63 dBµT). Full article ">Figure 4
Magnetic flux density distribution for the aligned (a) and misaligned (b) coil positions in the case of CF composite chassis. The yellow line represents the ICNIRP limit (RL = 27 µT = 28.63 dBµT). Full article ">Figure 5
Induced electric field inside Duke and Fats for the aligned coil position. E-field normalized to the peak value of 13.3 V/m. BR = 11.48 V/m ≈ −1.3 dBV/m (green area is the portion where the BR is exceeded). Full article ">Figure 6
Induced electric field inside Duke and Fats for the misaligned coil position. E-field normalized to the peak value of 19.9 V/m. BR = 11.48 V/m ≈ −4.8 dBV/m (green area is the portion where the BR is exceeded). Full article ">

19 pages, 3094 KiB

Open AccessEditor’s ChoiceArticle

Big Data Analytics for Discovering Electricity Consumption Patterns in Smart Cities

by Rubén Pérez-Chacón, José M. Luna-Romera, Alicia Troncoso, Francisco Martínez-Álvarez and José C. Riquelme

Energies 2018, 11(3), 683; https://doi.org/10.3390/en11030683 - 18 Mar 2018

Cited by 83 | Viewed by 10821

Abstract

New technologies such as sensor networks have been incorporated into the management of buildings for organizations and cities. Sensor networks have led to an exponential increase in the volume of data available in recent years, which can be used to extract consumption patterns [...] Read more.

New technologies such as sensor networks have been incorporated into the management of buildings for organizations and cities. Sensor networks have led to an exponential increase in the volume of data available in recent years, which can be used to extract consumption patterns for the purposes of energy and monetary savings. For this reason, new approaches and strategies are needed to analyze information in big data environments. This paper proposes a methodology to extract electric energy consumption patterns in big data time series, so that very valuable conclusions can be made for managers and governments. The methodology is based on the study of four clustering validity indices in their parallelized versions along with the application of a clustering technique. In particular, this work uses a voting system to choose an optimal number of clusters from the results of the indices, as well as the application of the distributed version of the k-means algorithm included in Apache Spark’s Machine Learning Library. The results, using electricity consumption for the years 2011–2017 for eight buildings of a public university, are presented and discussed. In addition, the performance of the proposed methodology is evaluated using synthetic big data, which cab represent thousands of buildings in a smart city. Finally, policies derived from the patterns discovered are proposed to optimize energy usage across the university campus. Full article

(This article belongs to the Special Issue Data Science and Big Data in Energy Forecasting)

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24 pages, 10793 KiB

Open AccessArticle

Experimental and Numerical Analyses of the Sloshing in a Fuel Tank

by Emma Frosina, Adolfo Senatore, Assunta Andreozzi, Francesco Fortunato and Pino Giliberti

Energies 2018, 11(3), 682; https://doi.org/10.3390/en11030682 - 17 Mar 2018

Cited by 19 | Viewed by 8150

Abstract

The sloshing of fuel inside the tank is an important issue in aerospace and automotive applications. This phenomenon, in fact, can cause various issues related to vehicle stability and safety, to component fatigue, audible noise, vibrations and to the level measurement of the [...] Read more.

The sloshing of fuel inside the tank is an important issue in aerospace and automotive applications. This phenomenon, in fact, can cause various issues related to vehicle stability and safety, to component fatigue, audible noise, vibrations and to the level measurement of the fuel itself. The sloshing phenomenon can be defined as a highly nonlinear oscillatory movement of the free-surface of liquid inside a container, such as a fuel tank, under the effect of continuous or instantaneous forces. This paper is the result of a research collaboration between the Industrial Engineering Department of the University of Naples “Federico II” and the R&D department of Fiat Chrysler Automobiles (F.C.A.) The activity is focused on the study of the sloshing in the fuel tank of vehicles. The goal is the optimization of the tank geometry in order to allow, for example, the correct fuel suction under all driving conditions and to prevent undesired noise and vibrations. This paper shows results obtained on a reference tank filled by water tinted with a dark blue food colorant. The geometry has been tested on a test bench designed by Moog Inc. on specification from Fiat Chrysler Automobiles with harmonic excitation of a 2D tank slice along one degree of freedom. The test bench consists of a hexapod with six independent actuators connecting the base to the top platform, allowing all six Degrees of Freedom (DOFs). On the top platform there are other two additional actuators to extend pitch and roll envelope, thus the name of “8-DOF bench”. The designed tank has been studied with a three-dimensional Computational Fluid Dynamics (CFD) modeling approach, too. By the end, the numerical and experimental data have been compared with a post-processing analysis by means of Matlab^® software. For this reason, the images have been reduced in two dimensions. In particular, the percentage gaps of the free surfaces and the center of gravity have been compared each other. The comparison, for the three different levels of liquid tested, has shown a good agreement with a discrepancy always less than 3%. Full article

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21 pages, 6637 KiB

Open AccessArticle

Algorithm for Fast and Efficient Detection and Reaction to Angle Instability Conditions Using Phasor Measurement Unit Data

by Igor Ivanković, Igor Kuzle and Ninoslav Holjevac

Energies 2018, 11(3), 681; https://doi.org/10.3390/en11030681 - 17 Mar 2018

Cited by 12 | Viewed by 4796

Abstract

In wide area monitoring, protection, and control (WAMPAC) systems, angle stability of transmission network is monitored using data from phasor measurement units (PMU) placed on transmission lines. Based on this PMU data stream advanced algorithm for out-of-step condition detection and early warning issuing [...] Read more.

In wide area monitoring, protection, and control (WAMPAC) systems, angle stability of transmission network is monitored using data from phasor measurement units (PMU) placed on transmission lines. Based on this PMU data stream advanced algorithm for out-of-step condition detection and early warning issuing is developed. The algorithm based on theoretical background described in this paper is backed up by the data and results from corresponding simulations done in Matlab environment. Presented results aim to provide the insights of the potential benefits, such as fast and efficient detection and reaction to angle instability, this algorithm can have on the improvement of the power system protection. Accordingly, suggestion is given how the developed algorithm can be implemented in protection segments of the WAMPAC systems in the transmission system operator control centers. Full article

(This article belongs to the Special Issue 17TH International Conference on Environment and Electrical Engineering)

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26 pages, 14014 KiB

Open AccessArticle

An Artificially Intelligent Technique to Generate Synthetic Geomechanical Well Logs for the Bakken Formation

by George Parapuram, Mehdi Mokhtari and Jalel Ben Hmida

Energies 2018, 11(3), 680; https://doi.org/10.3390/en11030680 - 17 Mar 2018

Cited by 21 | Viewed by 5934

Abstract

Artificially intelligent and predictive modelling of geomechanical properties is performed by creating supervised machine learning data models utilizing artificial neural networks (ANN) and will predict geomechanical properties from basic and commonly used conventional well logs such as gamma ray, and bulk density. The [...] Read more.

Artificially intelligent and predictive modelling of geomechanical properties is performed by creating supervised machine learning data models utilizing artificial neural networks (ANN) and will predict geomechanical properties from basic and commonly used conventional well logs such as gamma ray, and bulk density. The predictive models were created by following the approach on a large volume of data acquired from 112 wells containing the Bakken Formation in North Dakota. The studied wells cover a large surface area of the formation containing the five main producing counties in North Dakota: Burke, Mountrail, McKenzie, Dunn, and Williams. Thus, with a large surface area being analyzed in this research, there is confidence with a high degree of certainty that an extensive representation of the Bakken Formation is modelled, by training neural networks to work on varying properties from the different counties containing the Bakken Formation in North Dakota. Shear wave velocity of 112 wells is also analyzed by regression methods and neural networks, and a new correlation is proposed for the Bakken Formation. The final goal of the research is to achieve supervised artificial neural network models that predict geomechanical properties of future wells with an accuracy of at least 90% for the Upper and Middle Bakken Formation. Thus, obtaining these logs by generating it from statistical and artificially intelligent methods shows a potential for significant improvements in performance, efficiency, and profitability for oil and gas operators. Full article

(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries 2018)

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11 pages, 2932 KiB

Open AccessArticle

Thermal Performance of Microencapsulated Phase Change Material (mPCM) in Roof Modules during Daily Operation

by Qi Zhou, Pin-Feng Liu, Chun-Ta Tzeng and Chi-Ming Lai

Energies 2018, 11(3), 679; https://doi.org/10.3390/en11030679 - 17 Mar 2018

Cited by 13 | Viewed by 4010

Abstract

This study combines microencapsulated phase change materials (mPCMs) (core material: paraffin; melting points: 37 and 43 °C) and aluminum honeycomb boards (8 mm core cell) to form mPCM roof modules and investigates their heat absorption and release performances, as well as their impact [...] Read more.

This study combines microencapsulated phase change materials (mPCMs) (core material: paraffin; melting points: 37 and 43 °C) and aluminum honeycomb boards (8 mm core cell) to form mPCM roof modules and investigates their heat absorption and release performances, as well as their impact on indoor heat gain by conducting experiments over a 24-h period, subject to representative weather. The outdoor boundary conditions of the module are hourly sunlight and nighttime natural cooling; on the indoor side of the module, the conditions are daytime air conditioning and nighttime natural cooling. The results indicate that compared to a roof module with a 43 °C melting point mPCM, the roof module with a 37 °C melting point mPCM had improved peak load-shifting capacity, but had a slightly increased indoor heat gain. The mPCMs in both roof modules were successfully cooled during the night, returning to their initial state, to begin a new thermal cycle the next day. Full article

(This article belongs to the Section D: Energy Storage and Application)

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11 pages, 2325 KiB

Open AccessArticle

Stochastic Stability Analysis of the Power System with Losses

by Hongyu Li, Ping Ju, Chun Gan, Feng Wu, Yichen Zhou and Zhe Dong

Energies 2018, 11(3), 678; https://doi.org/10.3390/en11030678 - 17 Mar 2018

Cited by 2 | Viewed by 3675

Abstract

Renewable energy and electric vehicles have become involved in power systems, which has attracted researchers to stochastic continuous disturbances (SDEs). This paper addresses stochastic analysis issues for the stability of a power system with losses under SDEs. Firstly, the quasi-Hamiltonian models of power [...] Read more.

Renewable energy and electric vehicles have become involved in power systems, which has attracted researchers to stochastic continuous disturbances (SDEs). This paper addresses stochastic analysis issues for the stability of a power system with losses under SDEs. Firstly, the quasi-Hamiltonian models of power systems with losses under SDEs are given. Secondly, a novel analytical method is proposed to analyze the stability of the power system with losses under SDEs based on the stochastic averaging method. Thirdly, comparisons of stability probability under different parameters are performed, from which insights to improve the stability probability of power systems with losses under SDEs can be obtained. Even though it is challenging to assess the stability of a power system with losses under SDEs, the proposed method in this paper could serve well in this regard. Full article

(This article belongs to the Section F: Electrical Engineering)

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The procedure of the proposed stochastic stability analysis method. SCD: stochastic disturbance. Full article ">Figure 2
Potential energy curve near the stable point. Full article ">Figure 3
The coefficients of the equivalent Itō stochastic differential equation for the system energy: (a) the drift coefficient <math display="inline"> <semantics> <mrow> <mover accent="true"> <mi>m</mi> <mo stretchy="false">¯</mo> </mover> </mrow> </semantics> </math>(H); (b) the diffusion coefficient <math display="inline"> <semantics> <mrow> <mover accent="true"> <mi>σ</mi> <mo stretchy="false">¯</mo> </mover> </mrow> </semantics> </math> (H). Full article ">Figure 4
Stability probability of power system with losses under stochastic continuous disturbances. Full article ">Figure 5
Stability probability of power system with losses under stochastic continuous disturbances: (a) damping coefficient; (b) intensity of stochastic continuous disturbances; (c) mechanical power. Full article ">Figure 5 Cont.
Stability probability of power system with losses under stochastic continuous disturbances: (a) damping coefficient; (b) intensity of stochastic continuous disturbances; (c) mechanical power. Full article ">

17 pages, 3425 KiB

Open AccessArticle

Research on Improved VSG Control Algorithm Based on Capacity-Limited Energy Storage System

by Yanfeng Ma, Zijian Lin, Rennan Yu and Shuqiang Zhao

Energies 2018, 11(3), 677; https://doi.org/10.3390/en11030677 - 16 Mar 2018

Cited by 13 | Viewed by 3737

Abstract

A large scale of renewable energy employing grid connected electronic inverters fail to contribute inertia or damping to power systems, and, therefore, may bring negative effects to the stability of power system. As a solution, an advanced Virtual Synchronous Generator (VSG) control technology [...] Read more.

A large scale of renewable energy employing grid connected electronic inverters fail to contribute inertia or damping to power systems, and, therefore, may bring negative effects to the stability of power system. As a solution, an advanced Virtual Synchronous Generator (VSG) control technology based on Hamilton approach is introduced in this paper firstly to support the frequency and enhance the suitability and robustness of the system. The charge and discharge process of power storage devices forms the virtual inertia and damping of VSG, and, therefore, limits on storage capacity may change the coefficients of VSG. To provide a method in keeping system output in an acceptable level with the capacity restriction in a transient period, an energy control algorithm is designed for VSG adaptive control. Finally, simulations are conducted in DIgSILENT to demonstrate the correctness of the algorithm. The demonstration shows: (1) the proposed control model aims at better system robustness and stability; and (2) the model performs in the environment closer to practical engineering by fitting the operation state of storage system. Full article

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8 pages, 5965 KiB

Open AccessArticle

A Hybrid Excited Machine with Flux Barriers and Magnetic Bridges

by Marcin Wardach, Piotr Paplicki and Ryszard Palka

Energies 2018, 11(3), 676; https://doi.org/10.3390/en11030676 - 16 Mar 2018

Cited by 24 | Viewed by 4219

Abstract

In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic [...] Read more.

In this paper, an U-shape flux barrier rotor concept for a hybrid excited synchronous machine with flux magnetic bridges fixed on the rotor is presented. Using 3D finite element analysis, the influence of axial flux bridges on the field-weakening and -strengthening characteristics, electromagnetic torque, no-load magnetic flux linkage, rotor iron losses and back electromotive force is shown. Three different rotor designs are analyzed. Furthermore, the field control characteristics depending on additional DC control coil currents are shown. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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3D-FEA model (a); stack of axial bridge lamination using in a machine prototype (b). Full article ">Figure 2
Three concepts of magnetic active parts of rotor of the electric controlled permanent magnet synchronous (ECPMS) machine: UB1 concept (a); UB concept (b); U concept (c). Full article ">Figure 3
No-load magnetic flux distribution for the rotor UB1 concept. Full article ">Figure 4
Characteristics of magnetic flux linkage Ψs versus DC field excitation. Full article ">Figure 5
Back-EMF waveforms at different DC field excitation for the UB1 rotor concept. Full article ">Figure 6
Torque ripple at AC 30Arms at different DC field excitations for the UB1 rotor concept. Full article ">Figure 7
Cogging torque versus the rotor position at different DC field excitations for the UB1 rotor concept. Full article ">Figure 8
Losses of M400-50A lamination. Full article ">Figure 9
The B–H curve of M400-50A lamination. Full article ">Figure 10
Mean values of rotor iron losses of UB1, UB, and U rotor concepts. Full article ">

19 pages, 2100 KiB

Open AccessArticle

Life Cycle Performance of Hydrogen Production via Agro-Industrial Residue Gasification—A Small Scale Power Plant Study

by Sara Rajabi Hamedani, Mauro Villarini, Andrea Colantoni, Michele Moretti and Enrico Bocci

Energies 2018, 11(3), 675; https://doi.org/10.3390/en11030675 - 16 Mar 2018

Cited by 29 | Viewed by 5722

Abstract

This study evaluates the environmental profile of a real biomass-based hydrogen production small-scale (1 MW_th) system composed of catalytic candle indirectly heated steam gasifier coupled with zinc oxide (ZnO) guard bed, water gas shift (WGS) and pressure swing absorber (PSA) reactors. [...] Read more.

This study evaluates the environmental profile of a real biomass-based hydrogen production small-scale (1 MW_th) system composed of catalytic candle indirectly heated steam gasifier coupled with zinc oxide (ZnO) guard bed, water gas shift (WGS) and pressure swing absorber (PSA) reactors. Environmental performance from cradle-to-gate was investigated by life cycle assessment (LCA) methodology. Biomass production shows high influence over all impact categories. In the syngas production process, the main impacts observed are global warming potential (GWP) and acidification potential (AP). Flue gas emission from gasifier burner has the largest proportion of total GWP. The residual off gas use in internal combustion engine (ICE) leads to important environmental savings for all categories. Hydrogen renewability score is computed as 90% due to over 100% decline in non-renewable energy demand. Sensitivity analysis shows that increase in hydrogen production efficiency does not necessarily result in decrease in environmental impacts. In addition, economic allocation of environmental charges increases all impact categories, especially AP and photochemical oxidation (POFP). Full article

(This article belongs to the Special Issue BioEnergy and BioChemicals Production from Biomass and Residual Resources)

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12 pages, 3810 KiB

Open AccessArticle

Properties of Hydrochar as Function of Feedstock, Reaction Conditions and Post-Treatment

by Andrea Kruse and Thomas A. Zevaco

Energies 2018, 11(3), 674; https://doi.org/10.3390/en11030674 - 16 Mar 2018

Cited by 61 | Viewed by 7439

Abstract

Hydrothermal carbonization (HTC) is a promising technology to convert wet biomass into carbon-rich materials. Until now, the chemical processes occurring and their influence on the product properties are not well understood. Therefore, a target-oriented production of materials with defined properties is difficult, if [...] Read more.

Hydrothermal carbonization (HTC) is a promising technology to convert wet biomass into carbon-rich materials. Until now, the chemical processes occurring and their influence on the product properties are not well understood. Therefore, a target-oriented production of materials with defined properties is difficult, if not impossible. Here, model compounds such as cellulose and lignin, as well as different definite biomasses such as straw and beech wood are converted by hydrothermal carbonization. Following this, thermogravimetic (TGA) and FTIR measurements are used to get information about chemical structure and thermal properties of the related hydrochars. Some of the isolated materials are thermally post-treated (490 °C and 700 °C) and analyzed. The results show that at “mild” HTC conversion, the cellulose part in a lignocellulose matrix is not completely carbonized and there is still cellulose present. Thermal post-treatment makes the properties of product materials more similar and shows complete carbonization with increase aromatic cross-linking, proven by TGA and FTIR results. Full article

(This article belongs to the Special Issue Thermo Fluid Conversion of Biomass)

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13 pages, 4658 KiB

Open AccessArticle

A Three-Coil Inductively Power Transfer System with Constant Voltage Output

by Ruikun Mai, Youyuan Zhang, Ruimin Dai, Yang Chen and Zhengyou He

Energies 2018, 11(3), 673; https://doi.org/10.3390/en11030673 - 16 Mar 2018

Cited by 10 | Viewed by 4633

Abstract

For a traditional 2-coil system outputting constant voltage (CV), the transfer efficiency decreases drastically as transfer distance increases. To solve this problem, this essay proposes a 3-coil system which could achieve CV output and Zero Phase Angle (ZPA) conditions with specific parameter values. [...] Read more.

For a traditional 2-coil system outputting constant voltage (CV), the transfer efficiency decreases drastically as transfer distance increases. To solve this problem, this essay proposes a 3-coil system which could achieve CV output and Zero Phase Angle (ZPA) conditions with specific parameter values. This 3-coil system could partly relief transfer efficiency fall at a long transfer distance, without any complicated controls. In order to achieve CV and ZPA condition, this essay devises the parameter values based on the decoupling 3-coil model, and a prototype is designed accordingly to verify these characteristics. With 10 cm transfer distance, output voltage deviation is 5.5% as the load varies from 12 Ω to 200 Ω, proving that the output voltage almost keeps constant with load change. Furthermore, with software simulation, a comparison experiment between the proposed 3-coil system and a Series-Inductor-Capacitor-Inductor (S-LCL) compensated 2-coil system is built to verify the efficiency improvement. The transfer distance change leads to the differentiation of voltage gain for both 2-coil and 3-coil systems. So, the input voltage for both systems and the compensated capacitor in receiver loop of the 3-coil system are manipulated for keeping 60 V output voltage on the 12 Ω load. With distance increasing from 10 cm to 20 cm, transfer efficiency varies from 92.61 to 48.9% for the 2-coil system, and from 92.89 to 84.26% for the 3-coil system, effectively proving the efficiency improvement. The experiment and simulation results prove the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Wireless Power Transfer 2018)

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13 pages, 4252 KiB

Open AccessFeature PaperArticle

Solar Cell Capacitance Determination Based on an RLC Resonant Circuit

by Petru Adrian Cotfas, Daniel Tudor Cotfas, Paul Nicolae Borza, Dezso Sera and Remus Teodorescu

Energies 2018, 11(3), 672; https://doi.org/10.3390/en11030672 - 16 Mar 2018

Cited by 21 | Viewed by 9539

Abstract

The capacitance is one of the key dynamic parameters of solar cells, which can provide essential information regarding the quality and health state of the cell. However, the measurement of this parameter is not a trivial task, as it typically requires high accuracy [...] Read more.

The capacitance is one of the key dynamic parameters of solar cells, which can provide essential information regarding the quality and health state of the cell. However, the measurement of this parameter is not a trivial task, as it typically requires high accuracy instruments using, e.g., electrical impedance spectroscopy (IS). This paper introduces a simple and effective method to determine the electric capacitance of the solar cells. An RLC (Resistor Inductance Capacitor) circuit is formed by using an inductor as a load for the solar cell. The capacitance of the solar cell is found by measuring the frequency of the damped oscillation that occurs at the moment of connecting the inductor to the solar cell. The study is performed through simulation based on National Instruments (NI) Multisim application as SPICE simulation software and through experimental capacitance measurements of a monocrystalline silicon commercial solar cell and a photovoltaic panel using the proposed method. The results were validated using impedance spectroscopy. The differences between the capacitance values obtained by the two methods are of 1% for the solar cells and of 9.6% for the PV panel. The irradiance level effect upon the solar cell capacitance was studied obtaining an increase in the capacitance in function of the irradiance. By connecting different inductors to the solar cell, the frequency effect upon the solar cell capacitance was studied noticing a very small decrease in the capacitance with the frequency. Additionally, the temperature effect over the solar cell capacitance was studied achieving an increase in capacitance with temperature. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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16 pages, 5169 KiB

Open AccessArticle

Numerical Study on Heat Transfer to an Arc Absorber Designed for a Waste Heat Recovery System around a Cement Kiln

by Mojtaba Mirhosseini, Alireza Rezaniakolaei and Lasse Rosendahl

Energies 2018, 11(3), 671; https://doi.org/10.3390/en11030671 - 16 Mar 2018

Cited by 15 | Viewed by 4129

Abstract

A numerical study on combined free convection, forced convection, and radiation heat transfers from an industrial isothermal rotating cylinder (cement kiln) is carried out in this work. The investigation is done by the study of two-dimensional (2D) incompressible turbulent flow around the kiln [...] Read more.

A numerical study on combined free convection, forced convection, and radiation heat transfers from an industrial isothermal rotating cylinder (cement kiln) is carried out in this work. The investigation is done by the study of two-dimensional (2D) incompressible turbulent flow around the kiln under steady- and unsteady-state solutions. The results of this study show that the average Reynolds and Rayleigh numbers around the cylindrical kiln are 647,812.1 and 1.75986 × 10¹¹, respectively. A heat absorber is specifically designed around the kiln, according to the available space around the kiln, in a sample cement factory. The study investigates the effect of an added absorber on the heat transfer features, for both constant heat flux and constant temperature, on the kiln. The temperature distribution along the absorber circumference is obtained for designing an efficient thermoelectric waste heat recovery system as a future study. It is observed that the contribution of the radiative heat transfer is significant in the total heat transferred from the kiln to the absorber. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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16 pages, 9762 KiB

Open AccessArticle

Comparison of the Net Work Output between Stirling and Ericsson Cycles

by Rui F. Costa and Brendan D. MacDonald

Energies 2018, 11(3), 670; https://doi.org/10.3390/en11030670 - 16 Mar 2018

Cited by 5 | Viewed by 5814

Abstract

In this paper, we compare Stirling and Ericsson cycles to determine which engine produces greater net work output for various situations. Both cycles are for external heat engines that utilize regenerators, where the difference is the nature of the regeneration process, which is [...] Read more.

In this paper, we compare Stirling and Ericsson cycles to determine which engine produces greater net work output for various situations. Both cycles are for external heat engines that utilize regenerators, where the difference is the nature of the regeneration process, which is constant volume for Stirling and constant pressure for Ericsson. This difference alters the performance characteristics of the two engines drastically, and our comparison reveals which one produces greater net work output based on the thermodynamic parameters. The net work output equations are derived and analysed for three different scenarios: (i) equal mass and temperature limits; (ii) equal mass and pressure or volume; and (iii) equal temperature and pressure or volume limits. The comparison is performed by calculating when both cycles produce equal net work output and then analysing which one produces greater net work output based on how the parameters are varied. In general, the results demonstrate that Stirling engines produce more net work output at higher pressures and lower volumes, and Ericsson engines produce more net work output at lower pressures and higher volumes. For certain scenarios, threshold values are calculated to illustrate precisely when one cycle produces more net work output than the other. This paper can be used to inform the design of the engines and to determine when a Stirling or Ericsson engine should be selected for a particular application. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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P-V diagram of the Stirling cycle and T-s diagram (inset). Full article ">Figure 2
P-V diagram of the Ericsson cycle and T-s diagram (inset). Full article ">Figure 3
(a) Pressure ratio relationship and (b) volume ratio relationship between Stirling and Ericsson cycles, where the solid lines indicate equal net work output for equivalent mass and temperature limits. Full article ">Figure 4
P-V diagrams of Stirling and Ericsson cycles for fixed mass and temperature limits with (a) fixed maximum pressure and volume and (b) fixed minimum pressure and volume. Full article ">Figure 5
(a) High temperature relationship between Stirling and Ericsson cycles for fixed pressure ratios and <math display="inline"> <semantics> <mrow> <msub> <mi>T</mi> <mi>L</mi> </msub> <mo>=</mo> <mn>25</mn> <msup> <mspace width="0.166667em"/> <mo>∘</mo> </msup> </mrow> </semantics> </math>C, with solid lines denoting equal net work output; and (b) P-V diagrams of Stirling and Ericsson cycles for fixed mass, pressure limits and low temperature for equal net work output. Full article ">Figure 6
(a) High temperature relationship between Stirling and Ericsson cycles for fixed volume ratios and <math display="inline"> <semantics> <mrow> <msub> <mi>T</mi> <mi>L</mi> </msub> <mo>=</mo> <mn>25</mn> <msup> <mspace width="0.166667em"/> <mo>∘</mo> </msup> </mrow> </semantics> </math>C, with solid lines denoting equal net work output; (b) P-V diagrams of Stirling and Ericsson cycles for fixed mass, volume limits and low temperature for equal net work output. Full article ">Figure 7
(a) Relationship between pressure and temperature ratio for equal net work output and P-V diagram of Stirling and Ericsson cycles for fixed temperature and pressure limits and maximum volume for equal net work output (inset); (b) non-dimensional net work as a function of pressure ratio and temperature ratio (inset). Full article ">Figure 8
(a) Relationship between volume and temperature ratio for equal net work output and P-V diagram of Stirling and Ericsson cycles for fixed temperature and volume limits and maximum pressure for equal net work output (inset); (b) non-dimensional net work as a function of volume ratio and temperature ratio (inset). Full article ">

23 pages, 2463 KiB

Open AccessFeature PaperArticle

Comparative Study of Energy Performance between Chip and Inlet Temperature-Aware Workload Allocation in Air-Cooled Data Center

by Yan Bai, Lijun Gu and Xiao Qi

Energies 2018, 11(3), 669; https://doi.org/10.3390/en11030669 - 16 Mar 2018

Cited by 15 | Viewed by 4001

Abstract

Improving the energy efficiency of data center has become a research focus in recent years. Previous works commonly adopted the inlet temperature constraint to optimize the thermal environment in the data center. However, the inlet temperature-aware method cannot prevent the servers from over-cooling. [...] Read more.

Improving the energy efficiency of data center has become a research focus in recent years. Previous works commonly adopted the inlet temperature constraint to optimize the thermal environment in the data center. However, the inlet temperature-aware method cannot prevent the servers from over-cooling. To cope with this issue, we propose a thermal-aware workload allocation strategy with respect to the chip temperature constraint. In this paper, we conducted a comparative evaluation of the performance between the chip and inlet temperature-aware workload allocation strategies. The workload allocation strategies adopt a POD-based heat recirculation model to characterize the thermal environment in data center. The contribution of the temperature-dependent leakage power to server power consumption is also considered. We adopted a sample data center under constant-flow and variable-flow cooling air supply to evaluate the performance of these two different workload allocation strategies. The comparison results show that the chip temperature-aware workload allocation strategy prevents the servers from over-cooling and significantly improves the energy efficiency of data center, especially for the case of variable-flow cooling air supply. Full article

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22 pages, 966 KiB

Open AccessArticle

Availability of Ambient RF Energy in d-Dimensional Wireless Networks

by Hongxing Xia, Yongzhao Li, Hailin Zhang and Balasubramaniam Natarajan

Energies 2018, 11(3), 668; https://doi.org/10.3390/en11030668 - 15 Mar 2018

Cited by 1 | Viewed by 2962

Abstract

Radio frequency (RF) enabled energy harvesting has garnered increasingly broad applications in energy-constrained wireless networks. In this context, the actual available energy is constrained by the harvesting threshold of RF harvesters. In this paper, we first propose two new metrics, effective energy harvesting [...] Read more.

Radio frequency (RF) enabled energy harvesting has garnered increasingly broad applications in energy-constrained wireless networks. In this context, the actual available energy is constrained by the harvesting threshold of RF harvesters. In this paper, we first propose two new metrics, effective energy harvesting probability (EEHP) and spatial mean harvestable energy (SMHE) to characterize the availability of ambient RF energy. Assuming that the transmitters are spatially distributed according to a d-dimensional homogeneous Poisson point process (HPPP), we derive the distributions of the ambient RF energy for networks, from the perspective of information receivers, with and without interference control (IC). The corresponding EEHP and SMHE are given in integral forms for the case with IC and inverse Laplace transform form for the case without IC, respectively. For a special case where the dimension to path loss ratio equals 0.5, closed-form exact/approximate expressions for EEHP and SMHE are derived. Analytical results are validated by Monte Carlo simulations. Numerical results with distinct network parameters indicate that the harvesting threshold always has a significant effect on the EEHP, while the impact on SMHE can be ignored as the transmitter density increases. The general unified framework considered in this paper expands the applicability of the derived results to arbitrary dimensional networks. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 2222 KiB

Open AccessArticle

Building Automation and Control Systems and Electrical Distribution Grids: A Study on the Effects of Loads Control Logics on Power Losses and Peaks

by Salvatore Favuzza, Mariano Giuseppe Ippolito, Fabio Massaro, Rossano Musca, Eleonora Riva Sanseverino, Giuseppe Schillaci and Gaetano Zizzo

Energies 2018, 11(3), 667; https://doi.org/10.3390/en11030667 - 15 Mar 2018

Cited by 11 | Viewed by 4262

Abstract

Growing home comfort is causing increasing energy consumption in residential buildings and a consequent stress in urban medium and low voltage distribution networks. Therefore, distribution system operators are obliged to manage problems related to the reliability of the electricity system and, above all, [...] Read more.

Growing home comfort is causing increasing energy consumption in residential buildings and a consequent stress in urban medium and low voltage distribution networks. Therefore, distribution system operators are obliged to manage problems related to the reliability of the electricity system and, above all, they must consider investments for enhancing the electrical infrastructure. The purpose of this paper is to assess how the reduction of building electricity consumption and the modification of the building load profile, due to load automation, combined with suitable load control programs, can improve network reliability and distribution efficiency. This paper proposes an extensive study on this issue, considering various operating scenarios with four load control programs with different purposes, the presence/absence of local generation connected to the buildings and different external thermal conditions. The study also highlights how different climatic conditions can influence the effects of the load control logics. Full article

(This article belongs to the Section F: Electrical Engineering)

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22 pages, 4490 KiB

Open AccessArticle

Research on Optimal Wind Power Penetration Ratio and the Effects of a Wind-Thermal-Bundled System under the Constraint of Rotor Angle Transient Stability

by Ming Ding, Yan Zhang, Pingping Han, Yuying Bao and Haitian Zhang

Energies 2018, 11(3), 666; https://doi.org/10.3390/en11030666 - 15 Mar 2018

Cited by 6 | Viewed by 3562

Abstract

Large-scale wind-thermal-bundled power that is transmitted by mixed ultra-high voltage direct current (UHVDC)/ultra-high voltage alternating current (UHVAC) systems has become crucial for large-scale wind farms in China. Equations describing the electromagnetic power characteristics under short circuits for UHVAC lines and UHVDC blocks are [...] Read more.

Large-scale wind-thermal-bundled power that is transmitted by mixed ultra-high voltage direct current (UHVDC)/ultra-high voltage alternating current (UHVAC) systems has become crucial for large-scale wind farms in China. Equations describing the electromagnetic power characteristics under short circuits for UHVAC lines and UHVDC blocks are derived based on an analysis of the external characteristics of a doubly fed wind farm and UHVDC systems. The effect of wind power penetration ratio on rotor angle transient stability is analysed, and the optimal wind power penetration ratio under the constraint of rotor angle transient stability is determined. The effects of system parameters, such as the UHVDC transmission capacity and the reactance of UHVAC lines on the optimal wind power penetration ratio are discussed. The trend of rotor angle stability varies from a monotonic deterioration to concave, and the optimal wind power penetration ratio increases from 0 to 30% under an UHVDC block when the reactance of UHVAC lines increases from 0.005 to 0.02. The optimal wind power penetration ratio under a short circuit increases from 40% to 60% when the reactance of UHVAC lines decreases from 0.02 to 0.006 and decreases from 40% to 30% when the capacity of UHVDC decreases from 3200 MW to 1600 MW. The analysis is verified by simulating an actual system in China’s Northwest Power Grid. Full article

(This article belongs to the Section F: Electrical Engineering)

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24 pages, 6515 KiB

Open AccessArticle

A New Analytical Wake Model for Yawed Wind Turbines

by Guo-Wei Qian and Takeshi Ishihara

Energies 2018, 11(3), 665; https://doi.org/10.3390/en11030665 - 15 Mar 2018

Cited by 105 | Viewed by 10170

Abstract

A new analytical wake model for wind turbines, considering ambient turbulence intensity, thrust coefficient and yaw angle effects, is proposed from numerical and analytical studies. First, eight simulations by the Reynolds Stress Model are conducted for different thrust coefficients, yaw angles and ambient [...] Read more.

A new analytical wake model for wind turbines, considering ambient turbulence intensity, thrust coefficient and yaw angle effects, is proposed from numerical and analytical studies. First, eight simulations by the Reynolds Stress Model are conducted for different thrust coefficients, yaw angles and ambient turbulence intensities. The wake deflection, mean velocity and turbulence intensity in the wakes are systematically investigated. A new wake deflection model is then proposed to analytically predict the wake center trajectory in the yawed condition. Finally, the effects of yaw angle are incorporated in the Gaussian-based wake model. The wake deflection, velocity deficit and added turbulence intensity in the wake predicted by the proposed model show good agreement with the numerical results. The model parameters are determined as the function of ambient turbulence intensity and thrust coefficient, which enables the model to have good applicability under various conditions. Full article

(This article belongs to the Collection Wind Turbines)

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30 pages, 899 KiB

Open AccessReview

Algal Biomass from Wastewater and Flue Gases as a Source of Bioenergy

by Sandra Lage, Zivan Gojkovic, Christiane Funk and Francesco G. Gentili

Energies 2018, 11(3), 664; https://doi.org/10.3390/en11030664 - 15 Mar 2018

Cited by 74 | Viewed by 9658

Abstract

Algae are without doubt the most productive photosynthetic organisms on Earth; they are highly efficient in converting CO₂ and nutrients into biomass. These abilities can be exploited by culturing microalgae from wastewater and flue gases for effective wastewater reclamation. Algae are known [...] Read more.

Algae are without doubt the most productive photosynthetic organisms on Earth; they are highly efficient in converting CO₂ and nutrients into biomass. These abilities can be exploited by culturing microalgae from wastewater and flue gases for effective wastewater reclamation. Algae are known to remove nitrogen and phosphorus as well as several organic contaminants including pharmaceuticals from wastewater. Biomass production can even be enhanced by the addition of CO₂ originating from flue gases. The algal biomass can then be used as a raw material to produce bioenergy; depending on its composition, various types of biofuels such as biodiesel, biogas, bioethanol, biobutanol or biohydrogen can be obtained. However, algal biomass generated in wastewater and flue gases also contains contaminants which, if not degraded, will end up in the ashes. In this review, the current knowledge on algal biomass production in wastewater and flue gases is summarized; special focus is given to the algal capacity to remove contaminants from wastewater and flue gases, and the consequences when converting this biomass into different types of biofuels. Full article

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25 pages, 5550 KiB

Open AccessArticle

A New Exact Mathematical Approach for Studying Bifurcation in DCM Operated dc-dc Switching Converters

by Mircea Gurbina, Aurel Ciresan, Dan Lascu, Septimiu Lica and Ioana-Monica Pop-Calimanu

Energies 2018, 11(3), 663; https://doi.org/10.3390/en11030663 - 15 Mar 2018

Cited by 5 | Viewed by 6778

Abstract

A bifurcation study for dc-dc converters operated in DCM is performed using an accurate method. When applying classical techniques significant difficulties are encountered in the calculations. For example, using the averaging method the validity of the result is limited to half the switching [...] Read more.

A bifurcation study for dc-dc converters operated in DCM is performed using an accurate method. When applying classical techniques significant difficulties are encountered in the calculations. For example, using the averaging method the validity of the result is limited to half the switching frequency and higher order effects are neglected Another approach is to perform a Taylor expansion of the state transition matrices. However, this is somehow also an averaging but the fact that the Taylor series is truncated leads to unacceptable inaccuracy. A new mathematical technique for discontinuous conduction mode (DCM) analysis of dc-dc switching converters is proposed in order to predict bifurcation and chaos. The proposed technique is based on exact calculation of the state transition matrices and of the Jacobian thus providing higher accuracy of the results compared to other previously reported approaches. Beside the fact the new technique allows for exact diagnosis of instability, it is also highly general, in the sense that it can be applied to any dc-dc DCM operated converter employing any type of control. The good agreement between theoretical, simulation and experimental results, with an error lower than 0.94%, confirms the validity of the proposed method. Full article

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31 pages, 14908 KiB

Open AccessFeature PaperArticle

On-Line Detection of Coil Inter-Turn Short Circuit Faults in Dual-Redundancy Permanent Magnet Synchronous Motors

by Yiguang Chen, Xuemin Chen and Yonghuan Shen

Energies 2018, 11(3), 662; https://doi.org/10.3390/en11030662 - 15 Mar 2018

Cited by 12 | Viewed by 5024

Abstract

In the aerospace and military fields, with high reliability requirements, the dual-redundancy permanent magnet synchronous motor (DRPMSM) with weak thermal coupling and no electromagnetic coupling is needed. A common fault in the DRPMSM is the inter-turn short circuit fault (ISCF). However, research on [...] Read more.

In the aerospace and military fields, with high reliability requirements, the dual-redundancy permanent magnet synchronous motor (DRPMSM) with weak thermal coupling and no electromagnetic coupling is needed. A common fault in the DRPMSM is the inter-turn short circuit fault (ISCF). However, research on how to diagnose ISCF and the set of faulty windings in the DRPMSM is lacking. In this paper, the structure of the DRPMSM is analyzed and mathematical models of the motor under normal and faulty conditions are established. Then an on-line ISCF detection scheme, which depends on the running modes of the DRPMSM and the average values for the difference of the d-axis voltages between two sets of windings in the latest 20 sampling periods, is proposed. The main contributions of this paper are to analyze the calculation for the inductance of each part of the stator windings and propose the on-line diagnosis method of the ISCF under various operating conditions. The simulation and experimental results show that the proposed method can quickly and effectively diagnose ISCF and determine the set of faulty windings of the DRPMSM. Full article

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22 pages, 18250 KiB

Open AccessArticle

Visual Investigation of the Occurrence Characteristics of Multi-Type Formation Water in a Fracture–Cavity Carbonate Gas Reservoir

by Lu Wang, Shenglai Yang, Xian Peng, Hui Deng, Yi Liao, Yicheng Liu, Wei Xu and Youjun Yan

Energies 2018, 11(3), 661; https://doi.org/10.3390/en11030661 - 15 Mar 2018

Cited by 24 | Viewed by 4286

Abstract

It is difficult to investigate the formation process and occurrence states of water in multi-type reservoirs, due to the strong heterogeneity and complex microstructure of the fracture–cavity carbonate gas reservoirs. To date, there is no systematic study on the occurrence characteristics of multi-type [...] Read more.

It is difficult to investigate the formation process and occurrence states of water in multi-type reservoirs, due to the strong heterogeneity and complex microstructure of the fracture–cavity carbonate gas reservoirs. To date, there is no systematic study on the occurrence characteristics of multi-type formation water, especially through visual observation experiments. In this paper, a new creation method for visual micromodels based on CT scan images and microelectronic photolithography techniques was described. Subsequently, a gas–drive–water visual experiment was conducted to intuitively study the formation mechanism and the occurrence states of formation water. Then, the ImageJ gray analysis method was utilized to quantitatively investigate the gas-water saturation and the proportion of residual water film. Finally, the occurrence characteristics of formation water and its effects on gas seepage flow were comprehensively analyzed. Visual experimental results showed that: the migration processes of natural gas in different types of reservoirs are different; the water in multiple media consists of native movable water and residual water, and residual water is composed of secondary movable water and irreducible water; the residual water mainly occurs in different locations of different reservoirs with the forms of “water film”, “water mass”, “water column” and “water droplets”; the main influencing factors are capillary force, surface tension, displacement pressure and channel connectivity. Quantitative results reflect that the saturation of movable water and residual water are the parameters related directly to reservoir physical properties, pore structure and displacement pressure—the smaller the size of flow channel, the larger the space occupied by water film; the thickness proportion of water film is increasing exponentially with the channel size; the thickness proportion of water film decreases as the increase of displacement pressure; the thickness proportion of water film is essentially constant when the displacement pressure increases to a certain extent. The conducted visual investigation not only improves our intuitive understanding of the occurrence characteristics of formation water, but also provides a theoretical basis for the efficient development of fracture-cavity gas reservoirs. Full article

(This article belongs to the Section L: Energy Sources)

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21 pages, 1953 KiB

Open AccessArticle

Multi-Model Prediction for Demand Forecast in Water Distribution Networks

by Rodrigo Lopez Farias, Vicenç Puig, Hector Rodriguez Rangel and Juan J. Flores

Energies 2018, 11(3), 660; https://doi.org/10.3390/en11030660 - 15 Mar 2018

Cited by 25 | Viewed by 4864

Abstract

This paper presents a multi-model predictor called Qualitative Multi-Model Predictor Plus (QMMP+) for demand forecast in water distribution networks. QMMP+ is based on the decomposition of the quantitative and qualitative information of the time-series. The quantitative component (i.e., the daily consumption prediction) is [...] Read more.

This paper presents a multi-model predictor called Qualitative Multi-Model Predictor Plus (QMMP+) for demand forecast in water distribution networks. QMMP+ is based on the decomposition of the quantitative and qualitative information of the time-series. The quantitative component (i.e., the daily consumption prediction) is forecasted and the pattern mode estimated using a Nearest Neighbor (NN) classifier and a Calendar. The patterns are updated via a simple Moving Average scheme. The NN classifier and the Calendar are executed simultaneously every period and the most suited model for prediction is selected using a probabilistic approach. The proposed solution for water demand forecast is compared against Radial Basis Function Artificial Neural Networks (RBF-ANN), the statistical Autoregressive Integrated Moving Average (ARIMA), and Double Seasonal Holt-Winters (DSHW) approaches, providing the best results when applied to real demand of the Barcelona Water Distribution Network. QMMP+ has demonstrated that the special modelling treatment of water consumption patterns improves the forecasting accuracy. Full article

(This article belongs to the Special Issue Smart Water Networks in Urban Environments)

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Qualitative-quantitative multi-model architecture. Full article ">Figure 2
Hourly prediction of water consumption using a sliding window of width h. Full article ">Figure 3
Nearest Neighbor Rule with the current observations. Full article ">Figure 4
Euclidean distance of <math display="inline"> <semantics> <msup> <mi mathvariant="bold">Y</mi> <mo>′</mo> </msup> </semantics> </math> along the time compared with <math display="inline"> <semantics> <msub> <mi>P</mi> <mn>1</mn> </msub> </semantics> </math> and <math display="inline"> <semantics> <msub> <mi>P</mi> <mn>2</mn> </msub> </semantics> </math>. Full article ">Figure 5
Barcelona drinking water transport network. Full article ">Figure 6
Silhouette coefficient obtained by running k-Means with different <math display="inline"> <semantics> <mrow> <mi>k</mi> <mo>∈</mo> <mrow> <mn>1</mn> <mo>,</mo> <mo>⋯</mo> <mo>,</mo> <mn>7</mn> </mrow> </mrow> </semantics> </math>, for each of the seven water distribution sectors. Full article ">Figure 7
Initial patterns <math display="inline"> <semantics> <mi mathvariant="bold">P</mi> </semantics> </math> of sectors 1 to 4. Full article ">Figure 8
Initial patterns <math display="inline"> <semantics> <mi mathvariant="bold">P</mi> </semantics> </math> of sectors 5 to 7. Full article ">

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Energies, Volume 11, Issue 3 (March 2018) – 217 articles

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