RU2818206C1 - Autonomous combined power supply system with renewable power sources and frequency-phase control of flexibility - Google Patents

Abstract

FIELD: electric power industry.

SUBSTANCE: technical result is achieved due to the fact that autonomous combined power supply system (ACPSS) with renewable energy sources (RES) and frequency-phase control of flexibility contains AC busbar (2), sectioned for each RES, to which renewable sources of electric power (1) and support terminals with flexible communication (6) are connected. Terminals 6 contain booster phase regulators (5) for connecting sections to each other and controlling power flows between them, bidirectional power electronic converters (3) operating according to the concept of a virtual synchronous generator with connected electric energy accumulators (4) to maintain voltage and frequency on each section, and active rectifiers (8) for connection of other sources of electric energy (7) and electric receiving installations (load) (9).

EFFECT: improving reliability, controllability of the system and efficiency of extraction of maximum power from renewable sources of electric energy.

1 cl, 3 dwg

Description

The invention relates to the field of electrical power engineering, namely to power supply systems for consumers of autonomous (isolated) electrical power networks with renewable energy sources and electrochemical energy storage devices of various types and purposes. The invention has a block-transportable (container) design and can be used as a complex for field mobile or stationary power supply to facilities of the Ministry of Defense of the Russian Federation, as well as weapons, military and special equipment (VVST).

State of the art

Effective use of renewable energy resources in isolated power systems requires special approaches to their design and management.

There is a known method for organizing parallel operation of renewable energy sources [CN110429649A, IPC H02J 3/38, published 2019-11-08]. The invention discloses a method for separating renewable energy sources (RES) into highly permeable clusters while taking into account flexibility. The method involves creating a flexible supply and demand model based on the characteristics of flexibility balance, supply and demand balance, cluster flexibility and cluster structure characteristics, taking into account the dynamic characteristics of the cluster flexibility balance. Despite the obvious advantages of the method under consideration, the optimal division of RES sources into clusters, regulation of the flexibility resources of the initial network load and, as a result, reducing the need for flexibility of clusters, increasing the speed and accuracy of operation and regulating the electricity distribution system against the backdrop of increasing access to complex highly permeable renewable energy ,This approach involves extensive research for the ,planning and operation of RES clusters, loads and requires ,control of the system through an upper level. This approach is not possible for use in autonomous isolated systems due to limited load resources for flexibility, they are not comparable to the grid and low predictability of wind energy potential.

There are three main types of connection diagrams for RES inverter generators in autonomous combined power supply systems (ACPS):

1. Parallel operation of RES inverter generators as current sources for the busbar.

2. Parallel operation of RES inverter generators as voltage sources with static.

3. Parallel operation of RES inverter generators as voltage sources for the busbar.

For example, in terms of parallel operation of renewable energy sources as a current source to the busbar, an autonomous power supply system with a combined energy storage device is known [RU 2726735 C1, IPC H02J 7/34, H02J 3/38 (2006.01), published: 07/15/2020, Bulletin . No. 20], containing two wind power plants, two current sensors, two maximum power take-off controllers, a diesel generator set, three controlled rectifiers, two batteries, an autonomous inverter, an AC electrical load, a ballast load, a ballast load regulator, a DC bus, wherein the output of the first wind power plant is connected to the input of the first rectifier, the output of which is connected to the DC bus, the first current sensor is installed on a line between the first wind power plant and the first rectifier, the output of the first current sensor is connected to the input of the first maximum power take-off controller, the output of which is connected to control circuit of the first rectifier, the output of the second wind power plant is connected to the input of the second rectifier connected to the DC bus, the second current sensor is installed on the line between the output of the second wind power plant and the second rectifier, the output of the second current sensor is connected to the input of the second maximum power take-off controller, the output which is connected to the control circuit of the second rectifier, the diesel generator set is connected to the input of the third rectifier connected to the DC bus, the AC electrical load is connected from a stand-alone inverter connected to the DC bus, the ballast load is connected to the ballast load regulator, which is connected to the bus DC, characterized in that it contains an energy storage device in the form of a battery of supercapacitors connected directly to the DC bus, and also contains two matching charge-discharge devices based on bidirectional pulse step-up and step-down DC converters, the inputs of which are connected to the DC bus, and the outputs are connected to a corresponding battery.

In terms of the parallel operation of renewable energy sources as voltage sources with static, a method of operating a wind farm is known [RU 2727939 C1, IPC H02J 3/38(2006.01), convention priority: 06/07/2017 DE 102017112491.8, published: 07/15/2020, Bull. No. 20] A described method of operating a wind power plant (100) or a wind park (112) with multiple wind power plants (100) for exchanging electrical power between the wind farm and the power grid, each wind power plant (100) having one or more power supply devices (808, 810), and the wind power plant (100) or wind farm (112) is connected via a network connection point (118) to the power supply network (120), and power is exchanged through the network connection point (118), wherein one or more power supply devices (808, 810) operate as voltage generating units (808) and one or more power supply devices (808, 810) operate as current generating units (810), wherein, in particular, it is provided that the voltage generating units ( 808) and current-forming blocks (810) worked, generating voltage or generating current, respectively, also in trouble-free network operation mode.

The first type of circuit solutions refers to the simplest organization of systems, which has the lowest reliability with a single point of failure.

The second type has significant limitations on the dynamic stability of the system.

In addition, the solutions discussed above with a group primary flexibility regulator do not ensure the achievement of local maxima in the installed capacity utilization factor (IUR) of individual wind power plants (WPPs) due to the imbalance of their real dynamics and, therefore, are limited in achieving high efficiency of the scheme as a whole. With an increase in the number of wind turbines connected to a common bus, this disadvantage of the device increases, which limits the scalability of such systems. In addition, the presence of one failure point in the primary flexibility control significantly reduces the reliability of such a system.

The third type of connection scheme does not have the disadvantages of the first two, but is limited in scaling due to the difficulty in organizing parallel operation of reference generators.

There is a known method for controlling a distributed power converter in a microgrid to ensure parallel operation of more than one power source [CN106877387A, IPC H02J 3/38, published 2017-06-20]. Compared with the traditional control strategy of a grid-connected inverter, the control strategy of a distributed power inverter in a microgrid is obviously more complex. The traditional grid-connected inverter has the output characteristic of a current source and is only responsible for providing power to the grid, but the off-grid microgrid inverter must provide stable voltage and maintain frequency, so the power converter must have the output characteristics of a voltage source. In a microgrid with distributed power supplies, it is often necessary to use multiple power supplies in parallel to share the load, overall voltage and frequency stability in the microgrid.

The microgrid distributed power converter control method includes three parts: active power control - frequency droop characteristic, reactive power control - amplitude droop characteristic, and seamless circuit switching control. By controlling the frequency decay characteristics of active power, the power angle is indirectly controlled by adjusting the phase angle of the voltage, thereby realizing the control of the output power of the converter.

By controlling the characteristics of the decay of the reactive power amplitude, the output reactive power of the converter is controlled by regulating the magnitude of the voltage phase.

The microgrid control system coordinates the control and transfer of power to multiple parallel operating converters in the microgrid.

The disadvantage of this method of controlling a distributed power converter in a microgrid to ensure parallel operation of several frequency power sources is the low speed of system control and the limit for reactive power compensation, which leads to a significant limitation in the speed of the system as a whole and ineffective operational control at short, fast time intervals.

There is a known method for connecting one AC power network to a second AC power network, or microgrid control [WO2016023574A1, IPC H02J 3/06, H02J 3/08, H02J 3/40, H02J 3/42 (2006.01), published 2016-02- 18]. The method is as follows: when the first micro-grid is disconnected from the second micro-grid, control of the AC frequency (f1) of the first micro-grid is performed based on the AC frequency (f2) of the second micro-grid to ensure that when the first and second micro-grids of the network are connected, energy will flow from the first micro-grid and the second micro-grid, having a higher frequency, to the power network of the first and second micro-grid, having a lower frequency. The method also includes, after control, connecting (3) the first micro-grid to the second micro-grid, wherein power at the time of connection flows from the first micro-grid and the second micro-grid having a higher frequency to the first micro-grid and the second micro-grid having a lower frequency.

The disadvantage of this device and the frequency control method, known as droop control, of interconnected microenergy networks is the inability to maintain the dynamic stability of the system as a whole due to the limited range of reactive power compensation and low performance. Despite the ability to restore the original or close to the original mode of operation of a microenergy system after a small disturbance or slow changes in the mode parameters, that is, over long, hourly intervals of operation, this method does not allow taking into account large disturbances and rapid changes in the operation of microenergy systems with renewable energy sources, and, as a consequence, , is not capable of maximally accepting power from renewable energy sources into the system.

The closest technical solutions for organizing and constructing autonomous combined power supply systems with renewable energy sources (prototypes) are presented in the draft standard of the US Department of Defense “Tactical microgrid communications and control” (Control and communications in tactical microgrids), published on April 19, 2021, project number “TBD”, index MIL-STD-XXX DRAFT [https://docs.bidfortune.com/documents/bidfortune/bids/1946/2021/07/09/13926947775391631275/Draft%20Tactical%20Microgrid%20Standard%20-%20Tactical %20Ground%20Power%20TMS-TGP%20MIL-STD-XXX19%20April%202021_Approved%20fbr%20Public%20Release.pdf], which defines the architecture for control and communication of the tactical network. By definition, a tactical microgrid is a controlled power system consisting of a mobile group of interconnected sources of energy generation, distribution, energy storage and electrical receivers.

The following draft standard identifies the following types of equipment:

1) Electricity sources

Designed for the production of electricity, capable of operating as individual power supplies or synchronized in a group and controlled to turn on and off depending on the load. This type of equipment includes typical diesel generator sets, alternative energy sources such as solar, wind, fuel cells and hybrids.

2) Energy accumulation and storage systems

Designed to provide stability during transitions and smooth out peaks. Energy storage systems must provide electricity during periods when additional power is needed but no energy source has been added to the grid. In addition, energy storage systems must function as an uninterruptible power supply or as a hybrid when coupled to a power supply for individual loads.

3) Connection systems

Connection systems are distribution equipment that provides the interface or connection points to the system for other types of microgrid equipment. Connectivity systems define the microgrid itself. These can be added or subtracted to determine the electrical bus needed to supply power to loads directly or through distribution systems. They can also provide energy conversion from power supplies to the microgrid or loads from the microgrid. Feeder systems must include the ability to control the circuits through independent control or control system equipment.

4) Distribution systems

Distribution systems provide power from the microgrid through connection systems to loads that require separate circuits for standard lighting and standard duplex receptacles. Distribution systems must include the ability to control circuits either through independent control or through a control system. Distribution systems must have built-in measurement and monitoring systems for manual and automatic system control.

5) Control systems

Control systems provide power management to the microgrid. Control systems monitor various microgrid parameters, such as current, and add or subtract power generation sources and/or add or subtract loads to ensure energy availability. Control systems must monitor and protect the system in the event of overload or faults. Control systems must be located as a separate element or integrated into various types of microgrid equipment.

6) Electrical receiving installations

Electrical receiving installations consume the power provided by the microgrid. Standard loads consume power but do not interact with the microgrid. Smart loads also consume power but can communicate with the control system to protect the microgrid. Smart loads allow the microgrid controller to monitor its loads to prevent grid overload. In addition, smart loads can notify the microgrid controller of the expected activation. This notification will allow the microgrid controller to provide sufficient power for the additional load.

7) Energy conversion systems

Energy conversion systems allow power supplies and energy storage systems to connect to the connectivity system. These systems convert source/storage power into microgrid common bus AC voltage. These systems may be separate elements or may be integrated into the source/storage systems they support.

The disadvantages of this prototype are the system architecture and the lack of installations that do not allow for maximum power take-off from renewable energy sources, in particular:

When designing a system, the selection of equipment is carried out taking into account the static characteristics, when the power of the power plant directly depends on the speed of the wind flow or solar insolation.

An equally important parameter that ensures maximum use of wind energy potential or solar insolation is the rate of change of this flow. Taking into account the dynamics of changes in wind flow speed, which can manifest themselves over short time intervals, it is possible to make maximum use of existing distributed resources, especially in areas with an unstable energy-climatic factor. Otherwise this energy will be lost. This point determines the use of technical solutions to obtain the full spectrum of wind power in this range.

A significant part of the oscillation energy of renewable energy sources is in the high-frequency region, in the range of seconds, tens of seconds. The prototype under consideration does not include power plants capable of using these spectra.

The system architecture does not have a solution for using high-frequency wind spectra and does not ensure complete power take-off from renewable energy sources. This leads to the need to increase the power of the RES generator to capture these dynamic characteristics.

Also, the circuit design of a tactical microsystem involves assembling the system onto a busbar with the allocation of one reference source of electrical energy to maintain the frequency voltage, while other sources are connected, each with its own static. Parallel operation of sources in a system with one reference node, especially independent renewable energy sources connected with their own statism, leads to ensuring static stability of the system, but does not take into account the dynamic characteristics and, as a result, does not ensure the operation of sources in optimal modes.

The proposed technical solution is aimed at solving this problem.

Disclosure of the invention

The technical result of the claimed invention is to increase the reliability, controllability of the system and the efficiency of maximum power extraction from renewable energy sources.

To achieve a technical result, it is proposed to introduce another type in addition to the listed seven types of equipment: “Support terminals with flexible communication”, ensuring the dynamic stability of the ACPS modes in terms of the selection of maximum power from renewable energy sources in a wide range of fluctuations in the energy of the primary renewable resource (frequency regulation) and flexible power exchange between reference nodes in order to ensure stability of the network of reference nodes (phase regulation).

The system design is organized in such a way that the assembly of ACS with RES is carried out on an AC bus. An electrical energy storage device is connected to this bus through an electrical energy converter operating as a virtual synchronous machine, which together implements the functionality of the system busbar while maintaining voltage and frequency. Depending on the types and number of electrical energy sources in the system or components, the design of the system may differ, but the stability of the system is ensured through a fast dynamic source of electrical energy, be it a storage device or a multi-mode diesel power plant, connected to the busbar through an electrical energy converter.

According to the requirements for the design of this type of energy systems, the converter and electrical energy storage device in question must have a pie chart of active and reactive power that is capable of providing all possible states of the energy system. This approach allows us to ensure a static balance of the system.

Thus, the frequency of the current and the voltage of the busbar are formed by an electrochemical energy storage system operating in a “grid-forming” mode, known in the sources as “grid forming”. Power semiconductor inverters of wind turbines operate as virtual synchronous generators with full power delivery from the wind turbine to the system through the busbar (see Fig. 1).

ACS with RES in Fig. 1 represents the parallel operation of renewable energy sources (1) as voltage sources to the AC busbar (2), where maintaining the frequency voltage on the busbar is provided by an electrical energy storage device (4) connected through a bidirectional power electronic converter (3), where :

P _W1 , P _W2 , P _W3 - power flows from wind turbines;

P _F - power flow in the reference node of the system;

P _L - load power flow.

The non-stationary nature of wind turbine power requires ACSE to demonstrate flexibility in terms of ensuring power balance in the system and the ability to operate all wind turbines at points of maximum generation (MPPT, maximum power point tracking (OTMM, maximum power point tracking)).

Flexibility is the ability of ACSE to ensure the dynamic stability of maximum power take-off modes of renewable energy sources in a wide range of energy fluctuations of the primary renewable resource.

The system demonstrates stability if a change in the power balance has an equivalent response in the reference node of the system, corresponding to the change in active and reactive power.

Essentially, if the energy system under consideration has the ability to adaptively respond to changes in the power balance, such a system is stable and has the required flexibility property, reflecting the dynamics of the power balance in the system.

The relationship between active power flow (P) and reactive power flow (Q) and the resulting changes in P and Q depends on where the system in question is located.

Thus, the dynamics equation describing the behavior of the system can be represented in the state space of active and reactive power flows in the reference electrical energy storage device:

Where:

P - state parameter, active power flow;

- state parameter, reactive power flow;

a ₁₁ - coefficient of the equation of system state parameters;

a ₁₂ is the coefficient of the equation of system state parameters;

R _P - active power ramp;

a ₂₁ is the coefficient of the equation of system state parameters;

a ₂₂ is the coefficient of the equation of system state parameters;

R _Q - reactive power ramp.

The equation matrix for system state parameters is presented below:

Thus, the design of the system makes it possible to obtain static and dynamic stability of the system both in P and Q, while the system participants gather in a common group and there is no need to monitor their local parameters.

However, known solutions with parallel operation of RES inverter generators as voltage sources for the busbar, corresponding to Fig. 1 with a group primary flexibility regulator do not ensure the achievement of local maxima in the installed power utilization factor (IUR) of individual wind turbines due to the imbalance of their real dynamics and, therefore, are limited in achieving high efficiency of the circuit as a whole. With an increase in the number of wind turbines connected to a common bus, this disadvantage of the device increases, which limits the scalability of such systems. In addition, the presence of one failure point in the primary flexibility control significantly reduces the reliability of such a system.

Group regulation of power flows from wind turbines by one reference node has significant limitations, since the sum of all changes in power flows arriving at the busbar is not equal to the power flow in the system reference node, which leads to losses and output from the MPRT of individual wind turbines or the system as a whole .

The proposed technical solution and control of ACS with RES is free of these disadvantages, but requires stable parallel operation of two independent primary regulators. The solution to this problem is achieved by connecting busbar sections through a booster phase regulator.

To increase the efficiency and reliability of the system, it is proposed to partition the system into several subsystems, where each renewable energy source will have its own reference terminal with flexible communication.

The essence of the proposed technical solution is illustrated in Fig. 2, which shows an ACPS with RES with an AC busbar, where the AC busbar (2) with parallel operating RES (1), as voltage sources, is sectioned into several subsystems and connected to each other through a booster phase regulator (5) , representing, together with a bidirectional power electronic converter (3) and an electrical energy storage device (4), a reference terminal with flexible communication (6). Maintaining the frequency voltage on the AC busbar (2) is ensured by an electrical energy storage device (4) connected through a bidirectional power electronic converter (3).

Thus, the ACPS with RES forms the static stability of the system, which is ensured by a circular PQ diagram, through a network-forming SNE, which allows balancing all possible states of the active and reactive power of the MRRT wind turbines and electrical receiving installations (loads).

Also, ACS with RES implements the dynamic stability of the system, which is ensured by balancing the dynamic characteristics of all power generating and power receiving installations with a network-forming electrical energy storage device as the primary regulator of flexibility.

Also, ACS with RES ensures scaling of the system with the inclusion of new RES by partitioning the busbar, allocating a reference terminal with flexible communication for each RES and regulating power flows between the allocated sections using a booster phase regulator.

Brief description of the drawings

The essence of the invention is illustrated with the help of drawings, which show diagrams for connecting ACS with RES.

In fig. Figure 1 shows an ACSE device in network-forming mode.

In fig. Figure 2 shows an ACSE device with partitioning of the system into several subsystems.

In fig. Figure 3 shows a diagram of an ACSE with support terminals with flexible communication.

In the figures the following positions are indicated by numbers:

1 - renewable energy source (RES);

2 - AC busbar;

3 - bidirectional power electronic converter;

4 - electrical energy storage;

5 - booster phase regulator;

6 - support terminal with flexible connection;

7 - source of electrical energy;

8 - active rectifier;

9 - electrical receiving installations (load).

Carrying out the invention

An autonomous combined power supply system with renewable energy sources and frequency-phase control of flexibility is carried out in the form of a block-transportable (container) complex of a mobile or stationary type. All types (modules) of equipment are placed in containers and connected by a complete cable network when deploying the ACSE at the facility. Power and low-current communication between block containers is carried out through support terminals with flexible connections. The control system is peer-to-peer using the publisher-subscriber protocol. Schematically the ACS with RES is shown in Fig. 3.

Autonomous combined power supply system with renewable electricity sources and frequency-phase control of flexibility, including electrical energy sources, electrical energy accumulation and storage systems, connection systems, distribution systems, control systems, power receiving installations, electrical energy conversion systems and support terminals with flexible communication, contains at least two renewable energy sources (1), which are wind power or photovoltaic installations, connected to an AC busbar (2), which is sectioned for each renewable electrical energy source, with connected support terminals with flexible communication (6) as part of a booster phase regulator (5) for connecting sections to each other and controlling power flows between them, bidirectional power electronic converters (3) operating on the concept of virtual synchronous generators with connected electrical energy storage devices (4) to maintain voltage and frequency in each section busbar, active rectifier (8) for connecting other known sources of electrical energy (7) and electrical receiving installations (load) (9).

An autonomous combined power supply system with renewable energy sources and frequency-phase flexibility control works as follows.

Renewable energy sources (1), being at their optimal operating points, depending on the wind flow, provide the maximum possible electrical power to the AC busbar (2), sectioned for each renewable source of electrical energy. The connection of the sections of the busbar (2) with each other while maintaining static and dynamic stability in each section is provided by a support terminal with flexible connection (6), which includes: a booster phase regulator (5), an electrical energy storage device (4), a bidirectional power electronic converter (3) and active rectifier (8). Other known sources of electrical energy (7), connected through the active rectifier (8) of the reference terminal with a flexible connection (6) to the sections of the AC busbar (2) provide electrical power for selection by power receiving units (load) (9). Static and dynamic stability on each section of the busbar (2) is provided by electrical energy storage devices (4), which generate voltage and frequency on them through bidirectional power electronic converters (3). In this case, the state of charge/discharge of electrical energy storage devices (4) characterizes an excess of power in the system or a deficit. Taking into account the wide range of fluctuations in wind speed and the generally non-stationary nature of the operation of renewable energy sources (1), electrical energy storage devices (4) in conjunction with bidirectional power electronic converters (3) provide primary rapid regulation of the dynamic power balance, each for its own section of the collection tires (2), thereby showing technological adaptability and flexibility, adapting to the operation of renewable energy sources (1). In the case of an increase in the charge of the electrical energy storage device (4) on the busbar section (2), a surplus of power appears from the renewable energy source (1), and in the opposite situation, when the electrical energy storage device (4) is discharged, there is a corresponding shortage of power supplied from the renewable energy source. energy source (1). To further maintain static and dynamic stability, an adjustable bidirectional power flow is carried out on each section of the busbar (2) through a booster phase regulator (5). Thus, the section of the busbar (2), where there is a power deficit, receives the necessary power from another section of the busbar (2) through the booster phase regulator (5) and outputs power in the opposite direction when a surplus occurs.

Thus, the architecture of an autonomous combined power supply system with renewable electricity sources and frequency-phase control of flexibility is distinguished by the fact that:

the system is assembled on an AC busbar, sectioned for each RES source;

the connection of the busbar sections to each other with the maintenance of static and dynamic stability on each section is provided by a support terminal with flexible coupling through voltage booster phase regulation and primary regulation discussed above;

the voltage and frequency of each section of the AC busbar is generated by an electrical energy storage device and a bidirectional power electronic converter;

primary regulation of the static and dynamic power balance on each section of the AC busbar is carried out by an electrical energy storage device and is adjusted by monitoring its state;

distributed decentralized control between reference terminals with flexible communication and local power plant controllers does not require an upper level.

This circuit design solution for the construction of autonomous combined power supply systems with renewable electricity sources and frequency-phase regulation of flexibility ensures maximum power take-off from parallel operating renewable energy sources without their leaving optimal operating modes, and also allows you to deploy and freely scale such systems, while maintaining optimal operating modes of all power plants, static and dynamic stability of the system, increases the reliability and controllability of systems in the system.

Claims (1)

Autonomous combined power supply system (ACPS) with renewable electricity sources (RES) and frequency-phase control of flexibility, including electricity sources, energy accumulation and storage systems, connection systems, distribution systems, control systems, electrical receiving installations, electrical energy conversion systems, characterized by , that in order to increase the efficiency and reliability of the selection of maximum power from renewable energy sources, support terminals with flexible communication have been introduced into the ACSE, ensuring, through built-in electrical energy storage systems and bidirectional power electronic converters, maintaining a stable frequency and voltage on the busbar, sectioned for each renewable source of electrical energy , and due to voltage booster phase control devices and active rectifiers - stability of parallel operation and distributed decentralized control between support terminals with flexible communication on bus sections, which does not require an upper level of control, as well as the ability to scale the ACSE.

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