A method and system for state-of-charge equalization control of a series energy storage system

Abstract

This invention relates to the field of energy storage technology and provides a method and system for state-of-charge (SOC) balancing control of a series energy storage system. The method includes: acquiring the real-time output voltage, real-time output current, and SOC value of the energy storage battery from the inverter module of the series energy storage system; obtaining the actual output power, local SOC value, and average SOC value of the inverter module based on the acquired data; obtaining the desired balancing output angular frequency of the inverter module based on the obtained actual output power, local SOC value, average SOC value, reference active power of the inverter module, and reference angular frequency of the inverter module; and obtaining the balancing control pulse signal of the inverter module by combining the desired balancing output angular frequency, desired balancing output voltage, real-time output voltage, and current in the series inductor within the inverter module. SOC balancing can be achieved using only the SOC information of neighboring systems, enabling synchronization in grid-connected mode and realizing SOC balancing of the series energy storage system.

Description

Technical Field

[0001] This invention belongs to the field of energy storage technology, and specifically relates to a method and system for state-of-charge balancing control of a series energy storage system. Background Technology

[0002] Energy storage systems (ESS), composed of power electronic devices, play a crucial role in renewable energy integration. They effectively suppress power fluctuations caused by the intermittency and randomness of renewable energy sources such as solar and wind power. However, the output voltage of traditional ESS structures cannot meet the power system's requirements for high power and high voltage levels. Connecting multiple inverters in series can increase voltage and power levels without requiring additional transformers. Series-type energy storage systems (SESS) employ a series inverter topology and can be applied to large-capacity energy storage integration. SESS is considered to have broader prospects in microgrids and large-scale renewable energy integration.

[0003] Synchronization of series inverters is a core issue in their control. Traditional control methods typically rely on a central controller and a global communication network to obtain all necessary information, including frequency, voltage phase angle, and other essential data. As series inverter systems scale up, high-bandwidth communication increases costs. Furthermore, communication delays and failures negatively impact system reliability. State of Charge (SOC) is another crucial indicator for Series-Electronic System (SESS). In SESS, the initial SOC and output power of each module differ, leading to SOC imbalance and consequently overcharging and over-discharging issues. Clearly, SOC imbalance reduces SESS lifespan. Existing control schemes rely on centralized control, placing high demands on communication; therefore, a low-bandwidth-dependent SOC balancing control scheme is urgently needed. Summary of the Invention

[0004] To address the above problems, this invention discloses a method for state-of-charge (POC) balancing control of a series energy storage system, the method comprising: Collect the real-time output voltage, real-time output current, and SOC value of the inverter module of the series energy storage system; The actual output power, local SOC value, and average SOC value of the inverter module can be obtained based on the collected real-time output voltage, real-time output current, and energy storage battery SOC value. The desired balanced output angular frequency of the inverter module is obtained based on the actual output power, local SOC value, average SOC value, reference active power of the inverter module, and reference angular frequency of the inverter module. By combining the desired balanced output angular frequency and desired balanced output voltage of the inverter module, as well as the real-time output voltage and the current in the series inductor within the inverter module, the balanced control pulse signal of the inverter module is obtained.

[0005] Furthermore, the calculation of the average SOC value requires obtaining the local SOC value and the neighboring SOC values ​​of the other inverter modules.

[0006] Furthermore, the algorithm for the average SOC value is as follows:

[0007] in, For the first series energy storage system The state of charge (SOC) value of the energy storage battery of each inverter module; and These are the average state of charge (SOC) values ​​of the energy storage batteries in the i-th and j-th inverter modules of the series energy storage system, respectively; N i a represents the set of adjacent nodes i; ij Let a represent the communication weight of node i that receives data from node j, where if there is an edge connecting node i to node j, then a ij =1, where if there is no edge connecting node i to node j, then a ij =0.

[0008] Furthermore, the algorithm for the average SOC value is set based on a dynamic consistency control protocol.

[0009] Furthermore, the desired balanced output angular frequency and desired balanced output voltage are calculated using a series energy storage system equalization control model, which is as follows:

[0010] Where, ω ω is the reference angular frequency for each inverter module in a series energy storage system. i The desired balanced output angular frequency for each inverter module in a series energy storage system; P and P i Let represent the reference active power and the actual output power of the i-th series energy storage system inverter module, respectively. For the first series energy storage system The state of charge (SOC) value of the energy storage battery of each inverter module. V represents the average state of charge (SOC) of the energy storage battery in the i-th inverter module of the series energy storage system. and V iLet represent the reference voltage and the desired balanced output voltage of the i-th series energy storage system inverter module, respectively; m is the active power-frequency proportional control coefficient of the i-th series energy storage system inverter module; k is the SOC balanced control coefficient of the i-th series energy storage system inverter module; and N is the number of inverter modules in the series energy storage system.

[0011] Furthermore, the average SOC value of all inverter modules in the series energy storage system is dynamically represented in matrix form, resulting in:

[0012] Where I is the unit diagonal matrix, H is the transfer function of the average SOC estimator, L is the Laplacian matrix carrying communication graph information, and s is the Laplacian operator. The matrix formed by the estimated SOC values, The matrix formed by the actual SOC values.

[0013] Furthermore, if the Laplace matrix L is equilibrium, we obtain:

[0014] in, , ...... The values ​​are the average state of charge (SOC) values ​​of the energy storage batteries in the first to Nth inverter modules of the series energy storage system, respectively. For the first series energy storage system The state of charge (SOC) value of the inverter module's energy storage battery; N is the number of inverter module energy storage batteries in the series energy storage system.

[0015] Furthermore, all series-connected energy storage system inverter modules use a distributed communication topology to transmit angular frequency and estimated SOC values.

[0016] Furthermore, the state-of-charge (POC) balancing control method is used to achieve POC balancing among the inverter modules of the series energy storage system. In charging mode, the power absorbed by an inverter module with a higher SOC value is less than that absorbed by an inverter module with a lower SOC value. In discharge mode, the output power of an inverter module with a larger SOC value is greater than that of an inverter module with a smaller SOC value. Under steady-state conditions, the SOC values ​​of each inverter module in SESS tend to be consistent.

[0017] In another aspect, the present invention also discloses a state-of-charge (POC) balancing control system for a series energy storage system, the balancing control system comprising: The data acquisition unit is used to acquire the real-time output voltage, real-time output current, and SOC value of the energy storage battery of the inverter module of the series energy storage system. The power calculation unit is used to obtain the actual output power of the inverter module based on the collected real-time output voltage and real-time output current. The SOC estimation unit is used to obtain the local SOC value and the average SOC value based on the actual output power of the inverter module and the SOC value of the energy storage battery. The SOC equalization control unit is used to obtain the desired equalization output angular frequency of the inverter module based on the actual output power, local SOC value, average SOC value, reference active power of the inverter module, and reference angular frequency of the inverter module. The closed-loop control unit is used to combine the desired balanced output angular frequency and desired balanced output voltage of the inverter module, as well as the real-time output voltage and the current on the series inductor in the inverter module, to obtain the balanced control pulse signal of the inverter module.

[0018] Furthermore, the SOC estimation unit includes a local SOC estimation subunit and an average SOC estimator; The local SOC estimation subunit is used to obtain the local SOC value based on the actual output power of the inverter module and the SOC value of the energy storage battery. The average SOC estimator is used to obtain an average SOC value based on the local SOC value and the neighboring SOC values ​​of the other inverter modules.

[0019] Furthermore, the algorithm for the average SOC value is as follows:

[0020] in, For the first series energy storage system The state of charge (SOC) value of the energy storage battery of each inverter module; and These are the average state of charge (SOC) values ​​of the energy storage batteries in the i-th and j-th inverter modules of the series energy storage system, respectively; N i a represents the set of adjacent nodes i; ij Let a represent the communication weight of node i that receives data from node j, where if there is an edge connecting node i to node j, then a ij =1, where if there is no edge connecting node i to node j, then a ij =0.

[0021] Furthermore, the desired balanced output angular frequency and desired balanced output voltage are calculated using a series energy storage system equalization control model, which is as follows:

[0022] Where, ω ω is the reference angular frequency for each inverter module in a series energy storage system. i The desired balanced output angular frequency for each inverter module in a series energy storage system; P and P i Let represent the reference active power and the actual output power of the i-th series energy storage system inverter module, respectively. For the first series energy storage system The state of charge (SOC) value of the energy storage battery of each inverter module. V represents the average state of charge (SOC) of the energy storage battery in the i-th inverter module of the series energy storage system. and V i Let represent the reference voltage and the desired balanced output voltage of the i-th series energy storage system inverter module, respectively; m is the active power-frequency proportional control coefficient of the i-th series energy storage system inverter module; k is the SOC balanced control coefficient of the i-th series energy storage system inverter module; and N is the number of inverter modules in the series energy storage system.

[0023] Furthermore, the average SOC value of all inverter modules in the series energy storage system is dynamically represented in matrix form, resulting in:

[0024] Where I is the unit diagonal matrix, H is the transfer function of the average SOC estimator, L is the Laplacian matrix carrying communication graph information, and s is the Laplacian operator. The matrix formed by the estimated SOC values, The matrix formed by the actual SOC values.

[0025] Furthermore, if the Laplace matrix L is equilibrium, we obtain:

[0026] in, , ...... The values ​​are the average state of charge (SOC) values ​​of the energy storage batteries in the first to Nth inverter modules of the series energy storage system, respectively. For the first series energy storage system The state of charge (SOC) value of the inverter module's energy storage battery; N is the number of inverter module energy storage batteries in the series energy storage system.

[0027] Furthermore, the equalization control system also includes a communication unit, which is used to transmit and communicate the angular frequency and the estimated SOC value between each inverter module using a distributed communication topology.

[0028] Compared with the prior art, the present invention has the following beneficial effects: Distributed communication is a decentralized communication method that eliminates the need for a centralized controller. Instead, each subsystem communicates point-to-point to acquire global information. It only requires the SOC information of its neighbors to achieve SOC balancing, enabling synchronization in grid-connected mode and resolving the SOC imbalance problem in series energy storage systems. This effectively prevents overcharging and over-discharging of modules during charging and discharging operations, thus avoiding degradation of battery life. Because SOC regulation has a longer timescale, the requirements for distributed communication are lower. It maintains good control performance even under communication delays and single-link communication failures. Compared to centralized control schemes, this method, using distributed communication, improves system reliability.

[0029] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 A flowchart of the present invention for implementing a SOC equalization control system for a series energy storage system is shown; Figure 2 This diagram illustrates the structure of the SOC equalization control system of the present invention, which can be used to realize a series energy storage system. Figure 3 The flowchart of the SOC equalization control method of the present invention for a series energy storage system is shown. Figure 4 The diagram shows the waveforms of the output active power and SOC value of the inverter module control in the series energy storage system under charge and discharge modes according to the present invention. Figure 5 The diagram shows the waveforms of the output active power and SOC value of the inverter module in the series energy storage system during the switching from charging mode to discharging mode.

[0032] Figure 6 The diagram shows the waveforms of the active power and SOC value output by the inverter module of the series energy storage system under charging and discharging modes with a communication delay of 50ms. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Figure 1 The diagram illustrates a flowchart of the SOC (State of Charge) balancing control system for a series energy storage system, as described in this invention. The left side of the diagram shows the framework of the series energy storage system, which includes the AC grid side, line impedance, and multiple modules. The balancing control process for one of the modules is explained in detail below. Figure 1 On the right side, the data acquisition unit first obtains the initial SOC value of the inverter module in the series energy storage system and the series inductor current i of the i-th inverter. L Inverter module real-time output current i o and real-time output voltage u o Then, the power calculation unit calculates the actual output power P of the inverter module of the series energy storage system. i Then, the local SOC estimation subunit calculates the local SOC value, and the average SOC estimator calculates the average SOC value. The obtained data is then sent to the SOC balancing control unit, which simultaneously obtains the reference active power P of the i-th series energy storage system inverter module. and the reference angular frequency ω of each series energy storage system inverter module The expected equalization output angular frequency ω of each inverter module in the series energy storage system was calculated. i For the desired equalized output angular frequency ω i Conduct the points-based process ( Figure 1 The calculation (where 1 / s represents the integral stage) is combined with the desired balanced output voltage V of the inverter module of the series energy storage system. i After processing by the closed-loop control unit, pulse signals are obtained to control the inverter modules, adjusting them to achieve a balanced state of charge (SOC) of the energy storage batteries in each inverter module of the series energy storage system in grid-connected operation mode. Additionally, the balancing control system includes a communication unit used to transmit angular frequency and estimated SOC values ​​between the inverter modules using a distributed communication topology.

[0035] Figure 2 This invention illustrates a schematic diagram of a SOC (State of Charge) equalization control system for a series energy storage system, comprising: The data acquisition unit is used to acquire the real-time output voltage, real-time output current, output angular frequency, and SOC value of the energy storage battery of the inverter module of the series energy storage system (the SOC value acquired for the first time is the initial SOC value). The power calculation unit is used to obtain the actual output power of the inverter module based on the collected real-time output voltage and real-time output current. The SOC estimation unit is used to obtain the local SOC value and the average SOC value based on the actual output power of the inverter module and the SOC value of the energy storage battery. The SOC equalization control unit is used to obtain the desired equalization output angular frequency of the inverter module based on the actual output power, local SOC value, average SOC value, reference active power of the inverter module, and reference angular frequency of the inverter module. The closed-loop control unit is used to combine the desired balanced output angular frequency and desired balanced output voltage of the inverter module, as well as the real-time output voltage and the current on the series inductor in the inverter module, to obtain the balanced control pulse signal of the inverter module.

[0036] The SOC estimation unit includes a local SOC estimation subunit and an average SOC estimator. The local SOC estimation subunit is used to obtain the local SOC value based on the actual output power of the inverter module and the SOC value of the energy storage battery. The average SOC estimator is used to obtain an average SOC value based on the local SOC value and the neighboring SOC values ​​of the other inverter modules.

[0037] Figure 3 The flowchart of the present invention for implementing the SOC equalization control method of a series energy storage system is shown. The specific SOC equalization control method for a series energy storage system includes: First, the real-time output voltage, real-time output current, and SOC value of the energy storage battery of the inverter module of the series energy storage system are collected. The actual output power, local SOC value, and average SOC value of the inverter module can be obtained based on the collected real-time output voltage, real-time output current, and energy storage battery SOC value. The desired balanced output angular frequency of the inverter module is obtained based on the actual output power, local SOC value, average SOC value, reference active power of the inverter module, and reference angular frequency of the inverter module. By combining the desired balanced output angular frequency and desired balanced output voltage of the inverter module, as well as the real-time output voltage and the current in the series inductor within the inverter module, the balanced control pulse signal of the inverter module is obtained.

[0038] The desired balanced output angular frequency and desired balanced output voltage are calculated using a series energy storage system equalization control model, which is as follows: (1) Where, ω ω is the reference angular frequency for each inverter module in a series energy storage system. i P is the desired balanced output angular frequency for each inverter module in a series energy storage system. and P i Let represent the reference active power and the actual output power of the i-th series energy storage system inverter module, respectively. For the first series energy storage system The state of charge (SOC) value of the energy storage battery of each inverter module. V represents the average state of charge (SOC) of the energy storage battery in the i-th inverter module of the series energy storage system. and V i Let represent the reference voltage and the desired balanced output voltage of the i-th series energy storage system inverter module, respectively; m is the active power-frequency proportional control coefficient of the i-th series energy storage system inverter module; k is the SOC balanced control coefficient of the i-th series energy storage system inverter module; and N is the number of inverter modules in the series energy storage system.

[0039] Secondly, when calculating the average SOC value, the average SOC value estimated by the neighbors can be obtained by using the distributed communication topology (i.e., the average SOC value of each inverter module other than the local SOC).

[0040] Design an average SOC estimation algorithm based on dynamic consensus control protocol: (2) in, For the first series energy storage system The state of charge (SOC) value of the energy storage battery of each inverter module; and These are the average state of charge (SOC) values ​​of the energy storage batteries in the i-th and j-th inverter modules of the series energy storage system, respectively; N i a represents the set of adjacent nodes i; ij Let a represent the communication weight of node i that receives data from node j, where if there is an edge connecting node i to node j, then a ij =1, where if there is no edge connecting node i to node j, then a ij =0.

[0041] The following further explains the calculation process of the average SOC value based on the principle of the constructed SOC equalization control algorithm of this invention: The average SOC value of all inverter modules in the series energy storage system is dynamically represented in matrix form, resulting in: (3) Where I is the unit diagonal matrix, H is the transfer function of the average SOC estimator, L is the Laplacian matrix carrying communication graph information, and s is the Laplacian operator. The matrix formed by the estimated SOC values, The matrix formed by the actual SOC values.

[0042] If the Laplace matrix L is equilibrium, then: (4) in, , ...... The values ​​are the average state of charge (SOC) values ​​of the energy storage batteries in the first to Nth inverter modules of the series energy storage system, respectively. For the first series energy storage system The state of charge (SOC) value of the inverter module's energy storage battery; N is the number of inverter module energy storage batteries in the series energy storage system.

[0043] SOC balancing can be achieved by utilizing the output power of the i-th inverter module and the j-th inverter module. When At that time, P i Larger, and P j Lower. In charging mode, the power absorbed by the inverter module with the larger SOC value is less than that absorbed by the inverter module with the smaller SOC value; in discharging mode, the output power of the inverter module with the larger SOC value is greater than that of the inverter module with the smaller SOC value; in steady state, the SOC values ​​of the inverter modules in SESS tend to be consistent.

[0044] To more clearly verify the effect of this invention in achieving SOC equalization, a comparative case simulation analysis is presented here. The simulation system is actually a series energy storage system composed of three inverter modules. The storage unit (energy storage battery) has a capacity of 3Ah. Figure 4 , Figure 5 and Figure 6 In the diagram, curves #1, #2, and #3 represent the changes in the SOC value or active power of the three inverter modules, respectively. Three case studies, A, B, and C, were conducted.

[0045] In Case A, the simulation results are as follows: Figure 4 As shown. We considered different initial SOC values ​​for each module. For example... Figure 4 a. In charging mode, SOC1, SOC2, and SOC3 are 16%, 20%, and 24% respectively. Figure 4 b. In discharge mode, SOC1, SOC2, and SOC3 are 92%, 88%, and 82%, respectively. We can observe that in charging mode, as... Figure 4 a and 4c, as the system enters steady state (ΔSOC=SOC) max -SOC min ΔP=P max -P min ), the deviation from ΔSOC and ΔP gradually decreases to zero; in discharge mode, such as Figure 4 For b and 4d, as the system enters steady state, the deviations from ΔSOC and ΔP gradually decrease to zero. The results show that this method can achieve SOC equilibrium.

[0046] In Case B, the simulation results are as follows: Figure 5 As shown, the mode transitions from charging mode to discharging mode, and we verify the proposed method. Figure 5 a. The initial SOC values ​​of each module are 44%, 45%, and 46%, respectively. In charging mode, the maximum SOC deviation decreases to 0.2% within 150 seconds. Then, the mode is switched to discharging mode, and the output power switch changes from negative to positive, but the SOC deviation gradually decreases until it reaches zero. Additionally, as... Figure 5 As shown in b, during the mode transition from charging mode to discharging mode, the deviation of active power between modules gradually decreases over time until ΔP is reduced to zero. Therefore, the proposed SOC equalization method remains effective during the mode transition from charging mode to discharging mode.

[0047] In Case C, the simulation results are as follows: Figure 6 As shown in the figure. In this case, the impact of time delay on the equalization control method was studied. Considering a communication time delay of 50ms, the simulation results are as follows. Figure 6 As shown. With a communication delay of 50ms, the SOC values ​​and active power of each inverter module in Case C show the same trend as those in Case A. In charging mode, as... Figure 6 a and 6c, as the system enters steady state, the deviations from ΔSOC and ΔP gradually decrease to zero; in discharge mode, such as Figure 6 For values ​​b and 6d, as the system enters steady state, the deviations from ΔSOC and ΔP gradually decrease to zero. Analysis shows that the 50ms communication delay has little impact on performance. This is mainly because the SOC value is on a long time scale. Since the SOC changes over a long period, the communication delay is short. Therefore, the delay does not affect SOC equalization. However, due to the impact of the communication delay, the estimation of the average SOC value will have a steady-state error, resulting in the output power being lower than the rated power. Through reasonable control parameter design, the steady-state error can be controlled within an acceptable range.

[0048] Distributed communication is a decentralized communication method that eliminates the need for a centralized controller. Instead, each subsystem acquires global information through point-to-point communication. It achieves SOC balancing using only neighboring SOC information, enabling synchronization in grid-connected mode and resolving SOC imbalance issues in series energy storage systems. This effectively prevents overcharging and over-discharging of modules during charging and discharging operations, thus avoiding battery life degradation. Due to the longer timescale of SOC regulation, the requirements for distributed communication are lower. It maintains good control performance even under communication delays and single-link communication failures. Compared to centralized control schemes, this method, employing distributed communication, improves system reliability.

[0049] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for state-of-charge (POC) balancing control of a series energy storage system, characterized in that, The method includes: Collect the real-time output voltage, real-time output current, and SOC value of the inverter module of the series energy storage system; The actual output power, local SOC value, and average SOC value of the inverter module can be obtained based on the collected real-time output voltage, real-time output current, and energy storage battery SOC value. The desired balanced output angular frequency of the inverter module is obtained based on the actual output power, local SOC value, average SOC value, reference active power of the inverter module, and reference angular frequency of the inverter module. By combining the desired balanced output angular frequency and desired balanced output voltage of the inverter module, as well as the real-time output voltage and the current on the series inductor inside the inverter module, the equalization control pulse signal of the inverter module is obtained. The desired balanced output angular frequency and desired balanced output voltage are calculated using a series energy storage system equalization control model, which is as follows: Where, ω ω is the reference angular frequency for each inverter module in a series energy storage system. i The desired balanced output angular frequency for each inverter module in a series energy storage system; and P i Let represent the reference active power and the actual output power of the i-th series energy storage system inverter module, respectively. For the first series energy storage system The state of charge (SOC) value of the energy storage battery of each inverter module. V represents the average state of charge (SOC) of the energy storage battery in the i-th inverter module of the series energy storage system. and V i Let represent the reference voltage and the desired balanced output voltage of the i-th series energy storage system inverter module, respectively; m is the active power-frequency proportional control coefficient of the i-th series energy storage system inverter module; k is the SOC balanced control coefficient of the i-th series energy storage system inverter module; and N is the number of inverter modules in the series energy storage system.

2. The method for state-of-charge equalization control of a series energy storage system according to claim 1, characterized in that, The calculation of the average SOC value requires obtaining the local SOC value and the neighboring SOC values ​​of the other inverter modules.

3. The method for state-of-charge balancing control of a series energy storage system according to claim 1, characterized in that, The algorithm for the average SOC value is as follows: in, For the first series energy storage system The state of charge (SOC) value of the energy storage battery of each inverter module; and These are the average state of charge (SOC) values ​​of the energy storage batteries in the i-th and j-th inverter modules of the series energy storage system, respectively; N i a represents the set of adjacent nodes i; ij Let a represent the communication weight of node i that receives data from node j, where if there is an edge connecting node i to node j, then a ij =1, where if there is no edge connecting node i to node j, then a ij =0.

4. The method for state-of-charge equalization control of a series energy storage system according to claim 3, characterized in that, The algorithm for the average SOC value is set based on a dynamic consistency control protocol.

5. The method for state-of-charge equalization control of a series energy storage system according to claim 1, characterized in that, The average SOC value of all inverter modules in the series energy storage system is dynamically represented in matrix form, resulting in: Where I is the unit diagonal matrix, H is the transfer function of the average SOC estimator, L is the Laplacian matrix carrying communication graph information, and s is the Laplacian operator. The matrix formed by the estimated SOC values, The matrix formed by the actual SOC values.

6. The method for state-of-charge equalization control of a series energy storage system according to claim 5, characterized in that, If the Laplace matrix L is equilibrium, then: in, , ...... The values ​​are the average state of charge (SOC) values ​​of the energy storage batteries in the first to Nth inverter modules of the series energy storage system, respectively. For the first series energy storage system The state of charge (SOC) value of the inverter module's energy storage battery; N is the number of inverter module energy storage batteries in the series energy storage system.

7. The method for state-of-charge equalization control of a series energy storage system according to claim 1, characterized in that, All inverter modules in the series energy storage system communicate with each other using a distributed communication topology to transmit angular frequency and estimated SOC values.

8. The method for state-of-charge equalization control of a series energy storage system according to any one of claims 1-7, characterized in that, The state-of-charge equalization control method is used to achieve state-of-charge equalization among inverter modules in a series energy storage system. In charging mode, the power absorbed by an inverter module with a higher SOC value is less than that absorbed by an inverter module with a lower SOC value. In discharge mode, the output power of an inverter module with a larger SOC value is greater than that of an inverter module with a smaller SOC value. Under steady-state conditions, the SOC values ​​of each inverter module in SESS tend to be consistent.

9. A state-of-charge (POC) balancing control system for a series energy storage system, characterized in that, The equalization control system includes: The data acquisition unit is used to acquire the real-time output voltage, real-time output current, and SOC value of the energy storage battery of the inverter module of the series energy storage system. The power calculation unit is used to obtain the actual output power of the inverter module based on the collected real-time output voltage and real-time output current. The SOC estimation unit is used to obtain the local SOC value and the average SOC value based on the actual output power of the inverter module and the SOC value of the energy storage battery. The SOC equalization control unit is used to obtain the desired equalization output angular frequency of the inverter module based on the actual output power, local SOC value, average SOC value, reference active power of the inverter module, and reference angular frequency of the inverter module. The closed-loop control unit is used to combine the desired balanced output angular frequency and desired balanced output voltage of the inverter module, as well as the real-time output voltage and the current on the series inductor in the inverter module, to obtain the equalization control pulse signal of the inverter module. The desired balanced output angular frequency and desired balanced output voltage are calculated using a series energy storage system equalization control model, which is as follows: Where, ω ω is the reference angular frequency for each inverter module in a series energy storage system. i The desired balanced output angular frequency for each inverter module in a series energy storage system; and P i Let represent the reference active power and the actual output power of the i-th series energy storage system inverter module, respectively. For the first series energy storage system The state of charge (SOC) value of the energy storage battery of each inverter module. V represents the average state of charge (SOC) of the energy storage battery in the i-th inverter module of the series energy storage system. and V i Let represent the reference voltage and the desired balanced output voltage of the i-th series energy storage system inverter module, respectively; m is the active power-frequency proportional control coefficient of the i-th series energy storage system inverter module; k is the SOC balanced control coefficient of the i-th series energy storage system inverter module; and N is the number of inverter modules in the series energy storage system.

10. The state-of-charge (POC) balancing control system for a series energy storage system according to claim 9, characterized in that, The SOC estimation unit includes a local SOC estimation subunit and an average SOC estimator; The local SOC estimation subunit is used to obtain the local SOC value based on the actual output power of the inverter module and the SOC value of the energy storage battery. The average SOC estimator is used to obtain an average SOC value based on the local SOC value and the neighboring SOC values ​​of the other inverter modules.

11. The state-of-charge (POC) balancing control system for a series energy storage system according to claim 9, characterized in that, The algorithm for the average SOC value is as follows: in, For the first series energy storage system The state of charge (SOC) value of the energy storage battery of each inverter module; and These are the average state of charge (SOC) values ​​of the energy storage batteries in the i-th and j-th inverter modules of the series energy storage system, respectively; N i a represents the set of adjacent nodes i; ij Let a represent the communication weight of node i that receives data from node j, where if there is an edge connecting node i to node j, then a ij =1, where if there is no edge connecting node i to node j, then a ij =0.

12. The state-of-charge (POC) balancing control system for a series energy storage system according to claim 9, characterized in that, The average SOC value of all inverter modules in the series energy storage system is dynamically represented in matrix form, resulting in: Where I is the unit diagonal matrix, H is the transfer function of the average SOC estimator, L is the Laplacian matrix carrying communication graph information, and s is the Laplacian operator. The matrix formed by the estimated SOC values, The matrix formed by the actual SOC values.

13. The state-of-charge (POC) balancing control system for a series energy storage system according to claim 12, characterized in that, If the Laplace matrix L is equilibrium, then: in, , ...... The values ​​are the average state of charge (SOC) values ​​of the energy storage batteries in the first to Nth inverter modules of the series energy storage system, respectively. For the first series energy storage system The state of charge (SOC) value of the inverter module's energy storage battery; N is the number of inverter module energy storage batteries in the series energy storage system.

14. The state-of-charge (POC) balancing control system for a series energy storage system according to any one of claims 10-13, characterized in that, The equalization control system also includes a communication unit, which is used to transmit and communicate the angular frequency and the estimated SOC value between each inverter module using a distributed communication topology.

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