A method and system for controlling SOC balance within a phase of a chain energy storage system

Abstract

A method and system for controlling the SOC balance within a phase of a chain energy storage system, wherein the chain energy storage system includes three-phase circuits A, B, and C, with multiple power submodules connected in series on each phase circuit. The method includes the following steps: collecting the SOC and voltage of the batteries in all power submodules in a single phase, and judging whether to activate the SOC balance control method within the phase based on the SOC and voltage; if the SOC balance control method within the phase is activated, judging the charge and discharge state of the bridge arm based on the direction of the bridge arm current and the direction of the modulation wave; sorting the power submodules from small to large according to the SOC of the batteries, and calculating the mean SOC of the batteries in all power submodules; when the bridge arm is in a discharging state, putting kN modules with the largest SOCs and (1‑k)N power submodules closest to the mean SOC into operation. The present invention can take into account both the modulation wave quality and the balancing speed during the intra-phase balancing process.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical energy storage and power electronics, and more specifically, relates to a method for controlling the intra-phase SOC (State of Charge) of a chain energy storage system based on an NLM (Nearest Level modulation) modulation mode. Background Art

[0002] With the advancement and expansion of renewable energy generation technologies, renewable energy is increasingly accounting for a larger share of traditional power grids. However, the volatility and randomness of its generation also pose significant challenges to the safe operation of the grid. As a crucial component of stable grid operation, renewable energy storage stations, with their flexible charging and discharging capabilities and rapid response speeds, effectively balance the instability of renewable energy generation. Recent advances in power electronics technology have enabled modular multi-level energy storage technology to play a key role in renewable energy storage.

[0003] Energy storage systems based on a cascaded power submodule topology can guarantee output voltage levels, even reaching 10kV and 35kV, by cascading multiple submodules, meeting the voltage requirements for direct grid access. The modular structure allows for relatively independent control of the battery packs within each module, while also facilitating system expansion. This gives chain-type energy storage systems significant advantages in renewable energy grid integration. Furthermore, because NLM modulation does not require a carrier wave and directly controls the power submodules by calculating the required duty cycle of the switching devices, it can be flexibly and digitally implemented in multiple connected devices, making it widely used in modular chain-type energy storage technology.

[0004] However, in engineering practice, due to factors such as the battery manufacturing process and the working environment, the SOC of batteries in different modules within the same phase may be different during the operation of the chain energy storage device. If not controlled, the SOC deviation of batteries in each module within the phase will gradually increase, reducing the normal charging and discharging operation time of the energy storage system, and reducing the battery utilization rate and the overall service life of the device. Summary of the Invention

[0005] In order to solve the deficiencies in the prior art, the purpose of the present invention is to solve the problem of gradually increasing SOC deviation of each module battery in a phase and then propose a phase SOC balancing control method for a chain energy storage system.

[0006] The present invention adopts the following technical solutions.

[0007] A method for controlling SOC balancing within a phase of a chain energy storage system, wherein the chain energy storage system includes three-phase circuits A, B, and C, and each phase circuit is connected in series with multiple power submodules. The method comprises the following steps:

[0008] Step 1: Collect the SOC and voltage of the batteries in all power submodules in the single-phase circuit of the chain energy storage system, and determine whether to start the intra-phase SOC balancing control method based on the SOC and voltage, wherein the single phase is any one of the three phases A, B or C;

[0009] Step 2: If the intra-phase SOC balancing control method is started, the charge and discharge state of the bridge arm is determined according to the direction of the bridge arm current and the direction of the modulation wave. The bridge arm is the part of each phase power submodule connected to the grid through the reactor;

[0010] Step 3: Sort the power submodules in ascending order according to the SOC of the batteries, and calculate the average SOC of the batteries in all power submodules;

[0011] Step 4: When the bridge arm is in the discharge state, kN power submodules with the largest SOC and N-kN power submodules closest to the average SOC are put into operation, where k is a preset value and N is the number of power submodules put into charge and discharge under the NLM modulation method determined according to the size of the modulation wave;

[0012] Step 5: When the bridge arm is in the charging state, kN modules with the largest SOC and N-kN power sub-modules closest to the average SOC are put into operation.

[0013] Furthermore, step 1 also includes:

[0014] If the maximum SOC deviation is greater than the preset SOC ERRSTART And the maximum voltage deviation is greater than the preset V ERRSTART , then the intra-phase SOC balancing control method is started; otherwise, the intra-phase SOC balancing control method is not started; the maximum SOC deviation is the difference between the maximum SOC and the minimum SOC in the power submodule, the maximum voltage deviation is the difference between the maximum voltage and the minimum voltage in the power submodule, SOC ERRSTART With V ERRSTART is the default value.

[0015] Furthermore, the method further comprises:

[0016] Step 6: If the maximum SOC deviation is less than the preset SOC ERREND , and the maximum voltage deviation is less than the preset V ERREND , it is considered that the SOC in the phase has been balanced and the SOC balancing procedure ends; otherwise, the SOC of all power submodules is collected again and the process goes to step 2, where SOC ERREND With V ERREND All are preset values ​​and meet SOC ERREND <SOC ERRSTART , V ERREND <V ERRSTART .

[0017] Furthermore, SOC ERRSTART With V ERRSTART Set according to the requirements of battery management system accuracy and engineering accuracy.

[0018] Furthermore, the method further comprises:

[0019] Step 7: After an interval of time T, return to and execute step 1, where T is a preset value.

[0020] Furthermore, T is set according to the need of engineering accuracy.

[0021] Furthermore, N=NLM modulation wave amplitude / power submodule average voltage, where N is rounded up.

[0022] A chain energy storage system intra-phase SOC balancing control system, comprising: a battery management module and a logic judgment module;

[0023] The battery management module is used to collect the SOC and voltage of the batteries in all power submodules in a single phase;

[0024] The logic judgment module is used to determine whether to start the intra-phase SOC balance control method and to determine the charge and discharge status of the bridge arm;

[0025] The energy storage system changes the trigger pulses of the IGBTs in the modules to put into operation kN modules with the largest SOCs and (1-k)N power submodules with the SOCs closest to the average.

[0026] Furthermore, the logic judgment module is also used to adjust k according to the requirements of the SOC balancing effect and the output current quality.

[0027] Furthermore, the system also includes a timer for automatically returning to and executing step 1 in claim 1 after an interval T.

[0028] The beneficial effects of the present invention are that, compared with the prior art, the present invention has the following advantages:

[0029] (1) In general SOC balancing algorithms, although selecting submodules with larger or smaller SOC to participate in charging and discharging can also play a balancing role, the SOC deviation will also lead to voltage deviation. The modulation waves generated by these submodules with larger SOC deviations will be more distorted than the command values, and the quality of the modulation waves cannot be guaranteed. The SOC balancing method proposed in this patent sorts the power submodules according to the difference with the average SOC value in the process of selecting power submodules to generate modulation waves, and selects the proportion of submodules with larger SOC deviations in the participating power submodules by setting the parameter k, so that the modulation wave quality and the balancing speed can be taken into account during the intra-phase balancing process.

[0030] (2) Design the SOC detection interval to reduce the frequent sorting of sub-modules.

[0031] (3) Hysteresis is introduced by setting different start and end conditions to prevent the SOC phase balancing program from being started frequently. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the topological structure of the energy storage system according to the embodiment of the present disclosure.

[0033] Figure 2 This is the topological structure of the power submodule according to the embodiment of the present disclosure.

[0034] Figure 3 This is a flow chart of a method for controlling SOC balancing within a phase of a chain energy storage system according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0035] The present application will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present application.

[0036] To address the problem of uneven SOC of submodule batteries within a phase of a chain energy storage system, the present invention utilizes the relatively independent characteristics of the modular topology to control the working state of the power submodules, so that submodules with different battery SOCs are connected to the bridge arm at different times during the charging and discharging process, thereby achieving the purpose of balancing the SOC of the submodule batteries within the phase. The specific steps are as follows:

[0037] Step 1: Using a battery management system, collect the SOC and voltage of batteries in all power submodules in a single phase, where the single phase can be any one of the three phases A, B, or C.

[0038] Preferably, after step 1 is completed, it can be determined whether to enable the intra-phase SOC balance control: if the maximum SOC deviation is greater than the set SOC ERRSTART And the maximum voltage deviation is greater than V ERRSTART , then start SOC balancing control and go to step 3; otherwise, do not enable intra-phase SOC balancing control and end. Among them, the maximum SOC deviation is the difference between the maximum SOC and the minimum SOC in the power submodule, the maximum voltage deviation is the difference between the maximum voltage and the minimum voltage in the power submodule, and the SOC ERRSTART With V ERRSTART The threshold is preset to meet the needs of comprehensive battery management system accuracy and engineering accuracy.

[0039] Step 2: Determine the charge and discharge state of the bridge arm according to the direction of the bridge arm current and the direction of the modulation wave, wherein the bridge arm is the part where each phase power submodule is connected to the grid through the reactor;

[0040] Step 3: sort the power submodules in ascending order according to the SOC of the batteries.

[0041] Step 4, when the bridge arm is in the discharge state, kN modules with the largest SOC and (1-k)N power sub-modules closest to the average SOC are put into operation. Preferably, N = NLM modulation wave amplitude / average voltage of the power sub-module, and N is rounded up. It should be noted that k is a preset value, and the value range of k is 1≥k>0. The larger k is, the faster the SOC balancing speed is, but the greater the difference between the output waveform and the command value is. The smaller k is, the slower the SOC balancing speed is, but the smaller the difference between the output waveform and the command value is. The k value can be dynamically adjusted to meet the requirements of SOC balancing effect and output current quality.

[0042] Step 5: When the bridge arm is in the charging state, kN modules with the largest SOC and (1-k)N power submodules closest to the average SOC are put into operation;

[0043] Step 6: After the interval T, return to step 1. Wherein, T is a preset value according to the need of engineering accuracy. Preferably, after executing step 5, if the maximum SOC deviation is less than the preset SOC ERREND (SOC ERREND <SOC ERRSTART ) and the maximum voltage deviation is less than the preset V ERREND (V ERREND <V ERRSTART ), it is considered that the SOC in the phase has been balanced and the SOC balancing procedure ends; otherwise, jump to step 2 and continue to perform the phase balance. It should be noted that by setting the hysteresis, the starting condition is looser than the termination condition, that is, SOC ERRSTART >SOC ERREND , V ERRSTART >V ERREND By setting the hysteresis, the SOC state standard can be higher than the condition for starting SOC balancing after the cycle ends. This can prevent the balancing program from being frequently started because the balancing has just ended and the balancing start is triggered soon.

[0044] In order to execute the above method, the present invention also discloses a chain energy storage system intra-phase SOC balancing control system, comprising: a battery management module and a logic judgment module;

[0045] The battery management module is used to collect the SOC and voltage of the batteries in all power submodules in a single phase;

[0046] The logic judgment module is used to determine whether to start the intra-phase SOC balance control method and to determine the charge and discharge status of the bridge arm;

[0047] In addition, the energy storage system changes the trigger pulse of the IGBT in the module to put into operation kN modules with the largest SOC and (1-k)N power sub-modules with the SOC values ​​closest to the average.

[0048] The above steps are further explained below in conjunction with specific embodiments.

[0049] The implemented energy storage system topology is as follows Figure 1 As shown, the energy storage system adopts a chain star connection and includes three phases. Each phase includes 20 power sub-modules. The battery pack voltage of the power sub-module is 700V to 800V. The power sub-modules are cascaded to increase the output voltage level. After passing through the filter, each phase can be directly connected to the 10kV voltage level grid, or connected to other voltage level grids through a transformer.

[0050] Power submodules such as Figure 2 A power submodule may include: an H-bridge circuit, a pre-charge circuit, and an energy storage battery pack.

[0051] Combine Figure 1 In the scenario described above, the parameters of the energy storage system and the accuracy of the battery management system, the specific parameters of the intra-phase SOC balancing control method can be set as shown in Table 1:

[0052] Table 1: Case parameters

[0053]

[0054]

[0055] Figure 2 Various working states of the power sub-module

[0056] Table 2: Submodule operation status table

[0057]

[0058] During normal system operation, the submodule's operating state switches only between forward input, reverse input, and bypass, and the locked state only occurs during fault ride-through and submodule pre-start charging.

[0059] According to the parameter settings, such as Figure 3 As shown, the steps of SOC phase balancing control in this case are as follows:

[0060] Step 1: The battery management system obtains the SOC and voltage status of all 20 power submodules in a single phase, and determines whether the SOC difference between the submodule with the maximum and minimum SOC is greater than 5% and the voltage difference is greater than 10V. If both the SOC and voltage threshold requirements are met, control is initiated.

[0061] Step 2: Calculate the difference between the average voltage of the submodules and the SOC of each module and the average SOC of the submodules.

[0062] Step 3: According to NLM modulation, calculate the number of sub-modules N that need to be invested.

[0063] Step 4: Check the direction of the bridge arm current and the submodule voltage to determine the charge and discharge status of the submodule. If the submodule is in the discharge state, 0.2N submodules with the largest SOC and 0.8N submodules closest to the average SOC of the submodules are put into discharge, and the remaining (20-N) submodules are bypassed. If the submodule is in the charging state, 0.2N submodules with the smallest SOC and 0.8N submodules closest to the average SOC of the submodules are put into discharge, and the remaining (20-N) submodules are bypassed. Then return to step 3.

[0064] Step 5: Check the SOC status of all submodules every 1 minute. If the SOC difference between the maximum and minimum modules is less than 3% and the voltage difference is less than 5V, the SOC of the submodules in the current phase is considered to be balanced, and the balancing process ends.

[0065] The applicant of the present invention has made a detailed explanation and description of the implementation examples of the present invention in conjunction with the drawings in the specification. However, those skilled in the art should understand that the above implementation examples are only preferred implementation plans of the present invention, and the detailed description is only to help readers better understand the spirit of the present invention, and is not a limitation on the scope of protection of the present invention. On the contrary, any improvements or modifications based on the inventive spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for controlling SOC balance within a phase of a chain energy storage system, wherein: The chain energy storage system includes three-phase circuits A, B, and C, and multiple power sub-modules are connected in series on each phase circuit. The method includes the following steps: Step 1: Collect the SOC and voltage of the batteries in all power submodules in the single-phase circuit of the chain energy storage system, and determine whether to start the intra-phase SOC balancing control method based on the SOC and voltage, wherein the single phase is any one of the three phases A, B or C; Step 2: If the intra-phase SOC balancing control method is started, the charge and discharge state of the bridge arm is determined according to the direction of the bridge arm current and the direction of the modulation wave. The bridge arm is the part of each phase power submodule connected to the grid through the reactor; Step 3: Sort the power submodules in ascending order according to the SOC of the batteries, and calculate the average SOC of the batteries in all power submodules; Step 4: When the bridge arm is in the discharge state, kN power submodules with the largest SOC and N-kN power submodules closest to the average SOC are put into operation, where k is a preset value and N is the number of power submodules put into charge and discharge under the NLM modulation method determined according to the size of the modulation wave; Step 5: When the bridge arm is in the charging state, kN modules with the smallest SOC and N-kN power sub-modules closest to the average SOC are put into operation.

2. A method for controlling SOC balance within a phase of a chain energy storage system according to claim 1, characterized in that: The step 1 further comprises: If the maximum SOC deviation is greater than the preset SOC ERRSTART And the maximum voltage deviation is greater than the preset V ERRSTART , then the intra-phase SOC balancing control method is started; otherwise, the intra-phase SOC balancing control method is not started; the maximum SOC deviation is the difference between the maximum SOC and the minimum SOC in the power submodule, the maximum voltage deviation is the difference between the maximum voltage and the minimum voltage in the power submodule, SOC ERRSTART With V ERRSTART is the default value.

3. The method for controlling SOC balance within a phase of a chain energy storage system according to claim 2, characterized in that: The method further comprises: Step 6: If the maximum SOC deviation is less than the preset SOC ERREND , and the maximum voltage deviation is less than the preset V ERREND , it is considered that the SOC in the phase has been balanced and the SOC balancing procedure ends; otherwise, the SOC of all power submodules is collected again and the process goes to step 2, where SOC ERREND With V ERREND All are preset values ​​and meet SOC ERREND <SOC ERRSTART , V ERREND <V ERRSTART .

4. The method for controlling SOC balance within a phase of a chain energy storage system according to claim 2, characterized in that: The SOC ERRSTART With V ERRSTART Set according to the requirements of battery management system accuracy and engineering accuracy.

5. The method for controlling SOC balance within a phase of a chain energy storage system according to claim 1, characterized in that: The method further comprises: Step 7: After an interval of time T, return to and execute step 1, where T is a preset value.

6. A method for controlling SOC balance within a phase of a chain energy storage system according to claim 5, characterized in that: The T is set according to the requirements of engineering accuracy.

7. The method for controlling SOC balance within a phase of a chain energy storage system according to claim 1, characterized in that: N = NLM modulation wave amplitude / power submodule average voltage, N is rounded up.

8. A chain energy storage system intra-phase SOC balancing control system, used to execute the method according to claim 1, characterized in that: The system includes: a battery management module and a logic judgment module; The battery management module is used to collect the SOC and voltage of the batteries in all power submodules in a single phase; The logic judgment module is used to determine whether to start the intra-phase SOC balance control method and to determine the charge and discharge status of the bridge arm; The energy storage system changes the trigger pulses of the IGBTs in the modules to put into operation kN modules with the largest or smallest SOCs and (1-k)N power submodules with the SOCs closest to the average.

9. The intra-phase SOC balancing control system of a chain energy storage system according to claim 8, characterized in that: The logic judgment module is further configured to adjust k according to requirements of the SOC balancing effect and the output current quality.

10. The intra-phase SOC balancing control system of a chain energy storage system according to claim 8, characterized in that: The system further comprises a timer for automatically returning to and executing step 1 in claim 1 after an interval T.

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