A current-sharing control method and system for energy storage systems operating in parallel

Abstract

The application discloses a current sharing control method and system for a multi-machine parallel operation energy storage system, comprising: collecting three-phase voltage and AC side synchronous phase angle of the energy storage system; through positive sequence d-q transformation of the three-phase voltage, and according to the AC side synchronous phase angle, an output control phase angle of the energy storage system in off-grid operation is obtained to control the energy storage system to start; based on the obtained active power and reactive power of the energy storage system, after comparison according to average power output by the energy storage system, the output voltage of the energy storage system is corrected by obtaining the output of the power outer ring of the energy storage system, to inhibit the circulating current between the converters of the energy storage system; the application can inhibit the circulating current between the converters, ensure stable operation of the energy storage system, and overcome the defects of unstable system operation caused by unbalanced load by judging the balance of the load, thereby providing technical support for safe operation of the multi-machine parallel energy storage system.

Description

Technical Field

[0001] This invention relates to the field of current sharing control technology for multi-stage parallel energy storage systems, and more specifically, to a current sharing control method and system for energy storage systems operating in parallel with multiple units. Background Technology

[0002] The distributed energy storage converter is synchronized through the virtual synchronous generator (VSG) control strategy in the energy storage system, so that when the energy storage system is inverted and discharged, it can not only provide power to the grid, but also provide a certain amount of inertial support.

[0003] To improve the capacity and reliability of energy storage systems, multiple energy storage devices are typically connected in parallel. This parallel connection enables high-capacity and redundant power supply, significantly enhancing system reliability. However, in practical applications, the output voltage amplitude and phase angle of each energy storage device are unlikely to be perfectly equal, and the output line impedance may also differ. Consequently, when multiple energy storage devices operate in parallel, circulating currents inevitably occur. This prevents the load from being evenly distributed among the devices, causing some devices to operate under overload conditions and potentially leading to system failure. Therefore, a current-sharing control method and system for multi-device parallel operation is urgently needed. By incorporating parallel control suppression into the off-grid control of the energy storage devices, circulating currents between the converters can be suppressed, ensuring that each energy storage device operates normally with even load distribution. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a current sharing control method and system for energy storage systems operating in parallel with multiple units, thereby meeting the operational requirements of such systems.

[0005] To achieve the above technical objectives, this application provides a current sharing control method for an energy storage system operating in parallel with multiple energy storage devices. The energy storage system consists of multiple energy storage devices connected in parallel, and includes the following steps:

[0006] Collect the three-phase voltage and AC-side synchronization phase angle of the energy storage system;

[0007] By performing positive-sequence dq transformation on the three-phase voltage and obtaining the output control phase angle of the energy storage system during off-grid operation based on the AC side synchronization phase angle, the energy storage system can be started.

[0008] Based on the acquired active and reactive power of the energy storage system, and after comparing the average output power of the energy storage system, the output voltage of the energy storage system is corrected by acquiring the output of the outer power loop of the energy storage system, in order to suppress the circulating current between the converters of the energy storage system.

[0009] Preferably, during the positive-sequence dq transformation of the three-phase voltage, the d-axis voltage component and the q-axis voltage component are generated through the positive-sequence dq transformation, and the reactive power is obtained based on the d-axis voltage component and the active power is obtained based on the q-axis voltage component.

[0010] Preferably, in the process of obtaining the output control phase angle, the output control phase angle is obtained by adding the initial phase angle of the off-grid phase generator to the synchronous phase angle of the AC side.

[0011] Preferably, during the startup process of the energy storage system, the startup of the energy storage system is controlled by keeping the q-axis voltage component constant to zero based on the output control phase angle.

[0012] Preferably, after the energy storage system is started, the negative sequence output impedance and positive sequence output impedance of the system are calculated by obtaining the power balance of the load connected to the energy storage system, and then the energy storage system is controlled to operate.

[0013] Preferably, during the control of the energy storage system operation, the negative sequence components of the output voltage and output current of the energy storage system are obtained, and a negative sequence compensation function is added to obtain the negative sequence output impedance. At the same time, the positive sequence component of the output current is obtained, and the positive sequence output impedance is obtained according to the Thevenin equivalent model of the inverter output voltage. The operation of the energy storage system is controlled according to the negative sequence output impedance and the positive sequence output impedance.

[0014] Preferably, after the energy storage system is started, by obtaining the power imbalance of the load connected to the energy storage system, the average power output of the energy storage system is obtained by calculating the reactive power and active power, and compared with it. Then, the output of the outer power loop of the energy storage system is obtained according to PI control, and the output voltage of the energy storage system is corrected.

[0015] This invention discloses a current sharing control system for multi-unit parallel operation of an energy storage system, comprising:

[0016] The data acquisition module is used to acquire the three-phase voltage and AC-side synchronization phase angle of the energy storage system.

[0017] The startup module is used to control the startup of the energy storage system by performing positive-sequence dq conversion on the three-phase voltage and obtaining the output control phase angle of the energy storage system during off-grid operation based on the AC side synchronization phase angle.

[0018] The correction module is used to correct the output voltage of the energy storage system based on the acquired active and reactive power of the energy storage system, after comparing it with the average output power of the energy storage system, and by acquiring the output of the outer power loop of the energy storage system, in order to suppress the circulating current between the converters of the energy storage system.

[0019] The present invention discloses the following technical effects:

[0020] This invention ensures the stable operation of the energy storage system by suppressing the circulating current between each converter, and overcomes the shortcomings of system instability caused by unbalanced loads by judging the load balance, thus providing technical support for the safe operation of multi-machine parallel energy storage systems. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating the method described in this invention;

[0023] Figure 2 This is the control block diagram of the multi-machine parallel converter described in this invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0025] like Figure 1-2 As shown, this invention provides a current sharing control method for an energy storage system operating in parallel with multiple energy storage devices. The energy storage system consists of multiple energy storage devices connected in parallel, and includes the following steps:

[0026] Collect the three-phase voltage and AC-side synchronization phase angle of the energy storage system;

[0027] By performing positive-sequence dq transformation on the three-phase voltage and obtaining the output control phase angle of the energy storage system during off-grid operation based on the AC side synchronization phase angle, the energy storage system can be started.

[0028] Based on the acquired active and reactive power of the energy storage system, and after comparing the average output power of the energy storage system, the output voltage of the energy storage system is corrected by acquiring the output of the outer power loop of the energy storage system, in order to suppress the circulating current between the converters of the energy storage system.

[0029] When designing a multi-unit parallel energy storage system for startup, the sequential startup of each device is inevitably a concern. Therefore, the synchronization of internal voltages must be considered; otherwise, large inrush currents can easily occur, affecting system stability. This invention is primarily based on the fundamental theory of droop control. It obtains the upper and lower limits of the on-grid frequency protection as the frequency setpoint limits under off-grid conditions. Through droop control, the frequency modulation setpoints of the three phases after passing the limit are obtained. A synchronous frequency modulation control method is then used to adjust the output frequency of each phase. Synchronous frequency modulation is an open-loop frequency modulation method, directly adjusting the output frequency by changing the triangular carrier frequency, resulting in a faster response speed during parallel operation.

[0030] More preferably, in the process of performing positive-sequence dq transformation on three-phase voltage, the present invention generates d-axis voltage components and q-axis voltage components through positive-sequence dq transformation, and obtains reactive power based on d-axis voltage components and active power based on q-axis voltage components.

[0031] More preferably, in the process of obtaining the output control phase angle, the present invention obtains the output control phase angle by adding the initial phase angle of the off-grid phase generator to the synchronous phase angle of the AC side.

[0032] More preferably, in the process of controlling the start-up of the energy storage system, based on the output control phase angle, the present invention controls the start-up of the energy storage system by keeping the q-axis voltage component constant to zero.

[0033] This invention addresses the issue of load imbalance in a multi-machine parallel system after synchronous startup. Load imbalance leads to output voltage imbalance, causing problems such as system overheating, vibration, and over / under voltage. While existing technologies offer numerous solutions for suppressing output voltage imbalance, research on this issue during parallel operation is scarce. This invention derives the positive and negative sequence output impedance characteristics of the energy storage inverter and analyzes the imbalance between output impedance, circulating current, and voltage control. On one hand, it introduces negative sequence compensation to reduce output impedance, thereby suppressing output voltage imbalance. On the other hand, it introduces virtual impedance to enhance circulating current suppression, achieving balanced control of circulating current and voltage. Simulation experiments demonstrate the high stability of this process.

[0034] When the load of a multi-unit parallel energy storage system is balanced, the output power balancing problem of the parallel system needs to be considered. By introducing the concept of average power sharing, the relationship between the output active and reactive power and their average power is calculated. The output of the power outer loop is obtained through PI control, and then superimposed on the converter output voltage command as a correction to suppress the circulating current between converters in the multi-stage parallel energy storage system. The power balancing scheme designed in this invention, after simulation analysis using Matlab / Simulink software, shows that it can play a good role in suppressing current under both no-load and load operation, thereby realizing the current sharing operation of multiple parallel energy storage systems. It has good current sharing effect, high stability, and strong anti-disturbance capability.

[0035] More preferably, after the energy storage system is started, the present invention controls the operation of the energy storage system by obtaining the power balance of the load connected to the energy storage system, calculating the negative sequence output impedance and positive sequence output impedance of the system respectively.

[0036] More preferably, in the process of controlling the operation of the energy storage system, the present invention obtains the negative sequence components of the output voltage and output current of the energy storage system, and obtains the negative sequence output impedance by adding a negative sequence compensation function. At the same time, it obtains the positive sequence component of the output current and obtains the positive sequence output impedance according to the Thevenin equivalent model of the inverter output voltage. The energy storage system is controlled to operate based on the negative sequence output impedance and the positive sequence output impedance.

[0037] More preferably, after the energy storage system is started, the present invention obtains the power imbalance of the load connected to the energy storage system, obtains the average power output of the energy storage system calculated based on reactive power and active power, compares it with the output of the outer power loop of the energy storage system according to PI control, and corrects the output voltage of the energy storage system.

[0038] This invention discloses a current sharing control system for multi-unit parallel operation of an energy storage system, comprising:

[0039] The data acquisition module is used to acquire the three-phase voltage and AC-side synchronization phase angle of the energy storage system.

[0040] The startup module is used to control the startup of the energy storage system by performing positive-sequence dq conversion on the three-phase voltage and obtaining the output control phase angle of the energy storage system during off-grid operation based on the AC side synchronization phase angle.

[0041] The correction module is used to correct the output voltage of the energy storage system based on the acquired active and reactive power of the energy storage system, after comparing it with the average output power of the energy storage system, and by acquiring the output of the outer power loop of the energy storage system, in order to suppress the circulating current between the converters of the energy storage system.

[0042] This invention also discloses a computing program and a portable storage device. The invention implements the logical relationships of a current sharing control method through a computer program, thereby forming an executable program that runs in the current sharing control system or on other intelligent terminals, achieving intelligent control of a multi-unit parallel energy storage system. The portable storage device is used to carry the current sharing control system formed by the current sharing control method, or to carry the computer program implementing the current sharing control method, and is installed in a microgrid with a multi-unit parallel energy storage system. By collecting data from the load, energy storage system, bus, etc., it enables intelligent control of the multi-unit parallel energy storage system.

[0043] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0044] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0045] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A current sharing control method for an energy storage system operating in parallel with multiple units, characterized in that, The energy storage system consists of multiple energy storage devices connected in parallel, and includes the following steps: Collect the three-phase voltage and AC-side synchronization phase angle of the energy storage system; By performing positive-sequence dq transformation on the three-phase voltage and obtaining the output control phase angle of the energy storage system during off-grid operation based on the AC side synchronization phase angle, the energy storage system is controlled to start. Based on the obtained active and reactive power of the energy storage system, and after comparing it with the average output power of the energy storage system, the output voltage of the energy storage system is corrected by obtaining the output of the outer power loop of the energy storage system, in order to suppress the circulating current between the converters of the energy storage system. In the process of performing positive-sequence dq transformation on three-phase voltage, d-axis voltage component and q-axis voltage component are generated through the positive-sequence dq transformation, and reactive power is obtained based on the d-axis voltage component and active power is obtained based on the q-axis voltage component. In the process of obtaining the output control phase angle, the initial phase angle of the off-grid phase generator is obtained and the synchronous phase angle of the AC side is added to obtain the output control phase angle; During the startup process of the energy storage system, based on the output control phase angle, the q-axis voltage component is kept constant at zero to control the startup of the energy storage system.

2. The current sharing control method for an energy storage system operating in parallel with multiple units as described in claim 1, characterized in that: After the energy storage system is started, the negative sequence output impedance and positive sequence output impedance of the system are calculated by obtaining the power balance of the load connected to the energy storage system, and then the energy storage system is controlled to operate.

3. The current sharing control method for an energy storage system operating in parallel with multiple units as described in claim 2, characterized in that: During the operation of the energy storage system, the negative-sequence components of the output voltage and output current of the energy storage system are obtained, and a negative-sequence compensation function is added to obtain the negative-sequence output impedance. At the same time, the positive-sequence component of the output current is obtained, and the positive-sequence output impedance is obtained according to the Thevenin equivalent model of the inverter output voltage. The operation of the energy storage system is controlled based on the negative-sequence output impedance and the positive-sequence output impedance.

4. The current sharing control method for an energy storage system operating in parallel with multiple units as described in claim 1, characterized in that: After the energy storage system is started, by obtaining the power imbalance of the load connected to the energy storage system, the average power output of the energy storage system is obtained by calculating the reactive power and the active power and comparing them. Then, the output of the outer power loop of the energy storage system is obtained according to PI control, and the output voltage of the energy storage system is corrected.

5. A current sharing control system for multi-unit parallel operation of an energy storage system, used to execute the current sharing control method for multi-unit parallel operation of an energy storage system as described in claim 1, characterized in that, include: The data acquisition module is used to acquire the three-phase voltage and AC-side synchronization phase angle of the energy storage system. The startup module is used to control the energy storage system to start by performing positive-sequence dq transformation on the three-phase voltage and obtaining the output control phase angle of the energy storage system when it is running off-grid based on the AC side synchronization phase angle. The correction module is used to correct the output voltage of the energy storage system based on the acquired active power and reactive power of the energy storage system, after comparing it with the average output power of the energy storage system, by acquiring the output of the outer power loop of the energy storage system, in order to suppress the circulating current between the converters of the energy storage system.

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