A control method and flow battery system for discharging a flow battery

Abstract

This application relates to a control method and system for discharging a flow battery. The system mainly includes: adjusting the power of a first stack to above its rated power and adjusting the pump frequency of the first stack's circulation pump to above the standard pump frequency corresponding to the adjusted power; adjusting the power of a second stack to below its rated power and adjusting the pump frequency of the second stack's circulation pump to above the standard pump frequency corresponding to the rated power; adjusting the power of the second stack to above its rated power and adjusting the pump frequency of the second stack's circulation pump to above the standard pump frequency corresponding to the adjusted power; adjusting the power of the first stack to below its rated power and adjusting the pump frequency of the first stack's circulation pump to above the standard pump frequency corresponding to the rated power. This application can effectively reduce the influence of mass transfer polarization during flow battery stack discharge, restore stack performance online, and enable the stack to continuously perform constant power discharge, meeting the usage requirements of full-power operation of the flow battery system.

Description

Technical Field

[0001] This application relates to the field of flow battery technology, and in particular to a control method and a flow battery system for discharging a flow battery. Background Technology

[0002] With the booming development of the new energy storage industry, the advantages of flow battery energy storage are becoming increasingly prominent, especially in the long-term and ultra-long-term applications. Its safety, recoverable capacity, and customizable power-capacity decoupling characteristics make it a promising sector. State of Charge (SOC) is a core parameter that measures the ratio of a flow battery's remaining usable capacity to its fully charged capacity, with a value ranging from 0 to 1 (equivalent to 0%-100%).

[0003] Currently, during the use of flow batteries, especially during discharge, constant power mode is used for both charging and discharging to meet the needs of grid dispatch. To reduce the impact of mass transfer polarization at the end of discharge and to prevent the stack voltage from exceeding the set voltage range, a constant voltage model, i.e., power reduction mode, is generally adopted when the discharge SOC value is below 30%. At this time, for the demand side, the full power usage requirement cannot be met after the SOC value is below 30%.

[0004] Therefore, how to overcome the problem that flow battery systems cannot operate at full power at the end of discharge in the existing technology is a problem to be solved in this technical field. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, and in order to solve the problem that the existing flow battery system cannot operate at full power at the end of the discharge, this application provides a control method and flow battery system for discharge of flow battery. It can effectively reduce the influence of mass transfer polarization during the discharge of flow battery stack, restore the stack performance online, and enable the stack to continuously perform constant power discharge, so as to meet the usage requirements of flow battery system to operate at full power at any stage.

[0006] The embodiments of this application adopt the following technical solutions:

[0007] In a first aspect, this application provides a control method for discharging a flow battery, comprising:

[0008] Set up at least two sets of fuel cells. When the fuel cell voltage is lower than a preset threshold, detect the SOC value of the two sets of fuel cells. The one with the higher SOC value is the first set of fuel cells, and the one with the lower SOC value is the second set of fuel cells.

[0009] Adjust the power of the first stack to be higher than the rated power, and adjust the pump frequency of the circulation pump of the first stack to be higher than the standard pump frequency corresponding to the adjusted power; adjust the power of the second stack to be lower than the rated power, and adjust the pump frequency of the circulation pump of the second stack to be higher than the standard pump frequency corresponding to the rated power; continue discharging for the first preset time;

[0010] Adjust the power of the second stack to be higher than the rated power, and adjust the pump frequency of the circulation pump of the second stack to be higher than the standard pump frequency corresponding to the adjusted power; adjust the power of the first stack to be lower than the rated power, and adjust the pump frequency of the circulation pump of the first stack to be higher than the standard pump frequency corresponding to the rated power; continue discharging for the second preset time;

[0011] Adjust the power of the first and second fuel cells back to their rated power and discharge them in constant power mode. Stop discharging once the SOC setting value is reached.

[0012] By adopting the above technical solution, at least two sets of fuel cell stacks are set up. At the end of the system discharge, the stack with the higher SOC value is subjected to increased power load and flow rate; the stack with the lower SOC value is deloaded while the flow rate is increased. This operation can quickly reduce the impact of mass transfer polarization in the low-power stack. Furthermore, after discharging for a certain period based on the aforementioned adjustments, the power and flow rate adjustments for the two stacks are reversed to further rapidly reduce the impact of mass transfer polarization, effectively mitigating the voltage drop trend of the stacks. After this operation, full-power discharge is performed until the SOC cutoff threshold is reached. This solution can effectively reduce the impact of mass transfer polarization during flow battery stack discharge, restore stack performance online, and enable the stack to continuously perform constant-power discharge, meeting the requirement for the flow battery system to operate at full power at any stage.

[0013] In some embodiments, when detecting the SOC values ​​of the two sets of fuel cells, if the SOC values ​​of the two sets of fuel cells are the same, one set of fuel cells may be selected as the first set of fuel cells, and the other set of fuel cells may be selected as the second set of fuel cells.

[0014] By adopting the above technical solution, when the SOC values ​​of the two sets of fuel cells are the same, one set of fuel cells can be loaded first and the other set can be unloaded first. Then, the opposite operation can be performed on the two sets of fuel cells. This can also quickly reduce the influence of mass transfer polarization and enable the fuel cells to continuously discharge at constant power to meet the usage requirements.

[0015] In some embodiments, adjusting the power of the first group of fuel cells to a level higher than the rated power and adjusting the pump frequency of the circulation pump of the first group of fuel cells to a level higher than the standard pump frequency corresponding to the adjusted power; adjusting the power of the second group of fuel cells to a level lower than the rated power and adjusting the pump frequency of the circulation pump of the second group of fuel cells to a level higher than the standard pump frequency corresponding to the rated power specifically includes:

[0016] Adjust the power of the first fuel cell stack to 110%-130% of the rated power, and adjust the pump frequency of the circulating pump of the first fuel cell stack to 105%-115% of the standard pump frequency corresponding to the adjusted power.

[0017] Adjust the power of the second fuel cell stack to 70%-90% of the rated power, and adjust the pump frequency of the circulating pump of the second fuel cell stack to 105%-115% of the standard pump frequency corresponding to the rated power.

[0018] By adopting the above technical solution, the power of the first stack can be increased to 110%-130% of the rated power, for example, 120%, and the pump frequency of the circulating pump can be increased accordingly; the power of the second stack can be reduced to 70%-90% of the rated power, for example, 80%, and the pump frequency of the circulating pump can be increased accordingly, which can quickly reduce the influence of mass transfer polarization of the second stack.

[0019] In some embodiments, the first preset time is 4 min to 6 min.

[0020] By adopting the above technical solution, and discharging for 4-6 minutes, such as 5 minutes, on the basis of the above adjustments, the purpose of rapidly reducing the mass transfer polarization effect of the second stack can be effectively achieved.

[0021] In some embodiments, adjusting the power of the second stack to a level higher than the rated power and adjusting the pump frequency of the circulation pump of the second stack to a level higher than the standard pump frequency corresponding to the adjusted power; adjusting the power of the first stack to a level lower than the rated power and adjusting the pump frequency of the circulation pump of the first stack to a level higher than the standard pump frequency corresponding to the rated power specifically includes:

[0022] Adjust the power of the second fuel cell stack to 110%-130% of the rated power, and adjust the pump frequency of the circulation pump of the second fuel cell stack to 105%-115% of the standard pump frequency corresponding to the adjusted power.

[0023] Adjust the power of the first fuel cell stack to 70%-90% of the rated power, and adjust the pump frequency of the circulating pump of the first fuel cell stack to 105%-115% of the standard pump frequency corresponding to the rated power.

[0024] By adopting the above technical solution, the power of the second stack can be increased to 110%-130% of the rated power, for example, 120%, and the pump frequency of the circulating pump can be increased accordingly; the power of the first stack can be reduced to 70%-90% of the rated power, for example, 80%, and the pump frequency of the circulating pump can be increased accordingly, which can quickly reduce the influence of mass transfer polarization of the first stack.

[0025] In some embodiments, the second preset time is 4 min to 6 min.

[0026] By adopting the above technical solution and discharging for 4-6 minutes, such as 5 minutes, on the basis of the above adjustments, the purpose of rapidly reducing the mass transfer polarization effect of the first group of fuel cells can be effectively achieved.

[0027] In some embodiments, during the process of adjusting the power of the first group of fuel cells and the power of the second group of fuel cells back to their rated power and discharging in constant power mode, a SOC balancing strategy is activated to maintain a balance in the SOC values ​​of the first group of fuel cells and the second group of fuel cells; the SOC balancing strategy includes:

[0028] Based on the different differences between the SOC values ​​of the first group of fuel cells and the SOC values ​​of the second group of fuel cells, the pump frequency of the circulating pump of the fuel cell group with the lower SOC value is increased; wherein, the greater the difference between the SOC values ​​of the two groups of fuel cells, the greater the increase in the pump frequency of the circulating pump of the fuel cell group with the lower SOC value.

[0029] When the difference between the SOC values ​​of the two sets of fuel cells is less than the preset difference, the SOC balancing strategy is stopped.

[0030] By adopting the above technical solution, the pump frequency of the circulating pump in the low SOC stack group is increased according to the different SOC differences, the influence of mass transfer polarization is reduced, and the SOC values ​​between different stack groups are balanced.

[0031] In some embodiments, when the difference in SOC values ​​between the two stacks is 0.5%-1.5%, the circulation pump frequency of the stack with the lower SOC value increases by 3%; when the difference in SOC values ​​between the two stacks is 1.5%-2.5%, the circulation pump frequency of the stack with the lower SOC value increases by 5%; when the difference in SOC values ​​between the two stacks is 2.5%-3.5%, the circulation pump frequency of the stack with the lower SOC value increases by 8%; and when the difference in SOC values ​​between the two stacks is greater than 3.5%, the circulation pump frequency of the stack with the lower SOC value increases by 10%.

[0032] By adopting the above technical solution, the equalization strategy is stopped when the SOC difference is less than 0.5%. The upper limit of the pump frequency adjustment in the equalization strategy is 10%.

[0033] Secondly, this application provides a flow battery system that applies the control method for flow battery discharge as described in the first aspect, including an electrical module, a battery control system, and at least two sets of battery stacks. Each set of battery stacks is connected to a set of positive and negative electrolyte tanks via a set of positive and negative electrolyte circulation pumps. Both sets of battery stacks are connected to the electrical module, which is connected to the battery control system. The electrical module is used to realize different power outputs for different sets of battery stacks and to realize AC / DC conversion. The battery control system is used to judge various parameters and issue start-up and shutdown commands, circulation pump frequency adjustment commands, and charge / discharge power adjustment commands.

[0034] By adopting the above technical solution, when the flow battery stack is discharging, the power of the stack and the pump frequency of the circulation pump can be adjusted through the electrical module and the positive and negative electrolyte circulation pumps, under the adjustment command of the battery control system. This effectively reduces the influence of mass transfer polarization, restores the stack performance online, and enables the stack to continuously discharge at constant power, meeting the usage requirements of the flow battery system to operate at full power at any stage.

[0035] In summary, this application includes at least the following beneficial technical effects:

[0036] 1. Set up at least two sets of fuel cell stacks. At the end of the system discharge, increase the power load and flow rate of the stack with the higher SOC value; decrease the load and flow rate of the stack with the lower SOC value. This operation can quickly reduce the impact of mass transfer polarization in the low-power stack. Furthermore, after discharging for a certain period based on the above adjustments, reverse the power and flow rate adjustments for both stacks to further rapidly reduce the impact of mass transfer polarization, effectively mitigating the voltage drop trend of the stacks. After this operation, perform full-power discharge until the SOC cutoff threshold is reached. This scheme can effectively reduce the impact of mass transfer polarization during flow battery stack discharge, restore stack performance online, and enable the stack to continuously perform constant-power discharge, meeting the requirement for the flow battery system to operate at full power at any stage.

[0037] 2. Based on the different SOC differences, increase the pump frequency of the circulating pump in the low SOC stack group to reduce the impact of mass transfer polarization and balance the SOC values ​​between different stack groups. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A flowchart of a control method for discharging a flow battery provided in this application embodiment;

[0040] Figure 2 A structural block diagram of a flow battery system provided in this application embodiment;

[0041] Figure 3 This is a schematic diagram of the working process of the flow battery system provided in the embodiments of this application. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. Furthermore, the technical features involved in the various embodiments described below can be combined with each other as long as they do not conflict with each other.

[0043] The purpose of this application is to solve the problem that flow battery systems cannot operate at full power at the end of the discharge period. Through control strategies, without adding additional hardware facilities, the influence of mass transfer polarization is effectively reduced, so that the stack can continuously discharge at constant power to meet the usage requirements.

[0044] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Example 1

[0045] Embodiment 1 of this application provides a control method for the discharge of a flow battery. While maintaining a constant system power, it effectively reduces the impact of mass transfer polarization at the end of the discharge, achieving constant power discharge from 100% to 0% SOC. This method is applicable to flow battery systems containing at least two stacks. At the end of the system discharge, one stack is subjected to increased power and flow rate; the other stack is deloaded and flow rate is increased; after a certain period, the two stacks are subjected to the opposite operation. This operation can quickly reduce mass transfer polarization in the low-power stack, effectively mitigating the voltage drop trend. After this operation, active SOC balancing is performed on the different stacks, followed by full-power discharge until the SOC cutoff threshold is reached.

[0046] like Figure 1 As shown, the above-mentioned control method for discharging a flow battery includes the following steps.

[0047] Step 101: When the battery stack voltage is lower than a preset threshold, the SOC values ​​of the two battery stacks are detected. The battery stack with the higher SOC value is designated as the first battery stack, and the battery stack with the lower SOC value is designated as the second battery stack. For this step, during the discharge process, the battery stack voltage is set as the judgment threshold (usually set to a single-cell voltage of 1.28V). When the single-cell voltage is lower than the preset threshold (e.g., 1.28V), the SOC values ​​of the two battery stacks are detected. In some embodiments, when detecting the SOC values ​​of the two battery stacks, if the SOC values ​​of the two battery stacks are the same, one battery stack is randomly selected as the first battery stack, and the other battery stack is selected as the second battery stack.

[0048] Step 102: Adjust the power of the first group of fuel cells to above the rated power, and adjust the pump frequency of the circulation pump of the first group of fuel cells to above the standard pump frequency corresponding to the adjusted power; adjust the power of the second group of fuel cells to below the rated power, and adjust the pump frequency of the circulation pump of the second group of fuel cells to above the standard pump frequency corresponding to the rated power; continue discharging for a first preset time. For this step, the power of the first group of fuel cells can be adjusted to 110%-130% of the rated power, and the pump frequency of the circulation pump of the first group of fuel cells can be adjusted to 105%-115% of the standard pump frequency corresponding to the adjusted power; the power of the second group of fuel cells can be adjusted to 70%-90% of the rated power, and the pump frequency of the circulation pump of the second group of fuel cells can be adjusted to 105%-115% of the standard pump frequency corresponding to the rated power. By using the above scheme, the power of the first stack is increased to 110%-130% of the rated power, for example, 120%, and the pump frequency of the circulating pump is increased accordingly; the power of the second stack is reduced to 70%-90% of the rated power, for example, 80%, and the pump frequency of the circulating pump is increased accordingly; and the second stack is discharged for 4-6 minutes, for example, 5 minutes, based on the above adjustments, which can effectively achieve the goal of rapidly reducing the mass transfer polarization effect of the second stack.

[0049] Step 103: Adjust the power of the second stack to above the rated power, and adjust the pump frequency of the second stack's circulation pump to above the standard pump frequency corresponding to the adjusted power; adjust the power of the first stack to below the rated power, and adjust the pump frequency of the first stack's circulation pump to above the standard pump frequency corresponding to the rated power; continue discharging for the second preset time. For this step, the power of the second stack can be adjusted to 110%-130% of the rated power, and the pump frequency of the second stack's circulation pump can be adjusted to 105%-115% of the standard pump frequency corresponding to the adjusted power; the power of the first stack can be adjusted to 70%-90% of the rated power, and the pump frequency of the first stack's circulation pump can be adjusted to 105%-115% of the standard pump frequency corresponding to the rated power. By using the above scheme, the power of the second stack is increased to 110%-130% of the rated power, for example, 120%, and the pump frequency of the circulating pump is increased accordingly; the power of the first stack is reduced to 70%-90% of the rated power, for example, 80%, and the pump frequency of the circulating pump is increased accordingly; and the first stack is discharged for 4-6 minutes, for example, 5 minutes, based on the above adjustments, which can effectively achieve the goal of rapidly reducing the mass transfer polarization effect of the first stack.

[0050] Examples of power adjustment and pump frequency adjustment values ​​are shown in Table 1 below.

[0051] Table 1:

[0052]

[0053] In Table 1, Pe represents the rated power, set at 40kW. When the power of the first fuel cell stack is adjusted to 120%Pe (i.e., 48kW), the standard pump frequency corresponding to 120%Pe should be 28Hz. Therefore, the pump frequency of the circulating pump corresponding to the first fuel cell stack should be adjusted to 28Hz * 110% = 30.8Hz. When the power of the first fuel cell stack is adjusted to 80%Pe (i.e., 32kW), the standard pump frequency corresponding to 80%Pe should be 24Hz. Since the power is less than the rated power, the pump frequency adjustment should not be based on the standard pump frequency corresponding to 80%Pe, but rather on the standard pump frequency corresponding to the rated power (26Hz). Therefore, the pump frequency of the circulating pump corresponding to the first fuel cell stack should be adjusted to 26Hz * 110% = 28.6Hz. The adjustment of the second fuel cell stack is similar and will not be elaborated here.

[0054] Through steps 102 and 103 above, the effect of mass transfer polarization can be significantly reduced, and the stack voltage will be significantly restored and improved.

[0055] Step 104: Adjust the power of the first and second fuel cell stacks back to their rated power and discharge in constant power mode. Stop discharging after the SOC setting value is reached. The SOC setting value, i.e., the SOC cutoff threshold, can be set to 0 or 10%, depending on the requirements. During this step, while adjusting the power of the first and second fuel cell stacks back to their rated power and discharging in constant power mode, a SOC balancing strategy is activated to maintain a balance between the SOC values ​​of the first and second fuel cell stacks. The SOC balancing strategy includes: increasing the pump frequency of the circulating pump in the fuel cell stack with the lower SOC value based on the difference between their SOC values; the larger the difference in SOC values ​​between the two stacks, the greater the increase in the pump frequency of the circulating pump in the fuel cell stack with the lower SOC value; when the difference in SOC values ​​between the two stacks is less than a preset difference, the SOC balancing strategy is stopped. The SOC balancing strategy implemented through the above scheme is achieved by increasing the flow rate of low-SOC stacks. An example of parameter settings is as follows: Based on different SOC differences, the pump frequency of the circulating pump in the low-SOC stack group is increased to reduce the impact of mass transfer polarization and balance the SOC values ​​between different stack groups. The balancing strategy stops when the SOC difference is less than 0.5%. The upper limit for pump frequency adjustment in this balancing strategy is typically set to 10%.

[0056] Specifically, examples of SOC difference and pump frequency increase are shown in Table 2 below.

[0057] Table 2:

[0058]

[0059] In Table 2, when the difference in SOC values ​​between the two groups of fuel cell stacks is 0.5%-1.5%, the pump frequency of the circulating pump in the fuel cell stack with the lower SOC value increases by 3%; when the difference in SOC values ​​between the two groups of fuel cell stacks is 1.5%-2.5%, the pump frequency of the circulating pump in the fuel cell stack with the lower SOC value increases by 5%; when the difference in SOC values ​​between the two groups of fuel cell stacks is 2.5%-3.5%, the pump frequency of the circulating pump in the fuel cell stack with the lower SOC value increases by 8%; and when the difference in SOC values ​​between the two groups of fuel cell stacks is greater than 3.5%, the pump frequency of the circulating pump in the fuel cell stack with the lower SOC value increases by 10%.

[0060] The above scheme involves setting up at least two sets of fuel cell stacks. At the end of the system discharge phase, the stack with the higher State of Charge (SOC) is subjected to increased power and flow rate; the stack with the lower SOC is deloaded while the flow rate is increased. This operation quickly reduces the impact of mass transfer polarization in the low-power stack. Furthermore, after discharging for a certain period based on the aforementioned adjustments, the power and flow rate adjustments for the two stacks are reversed to further rapidly reduce the impact of mass transfer polarization, effectively mitigating the voltage drop trend of the stacks. After this operation, full-power discharge is performed, and active SOC balancing of different stack groups begins until the SOC cutoff threshold is reached. This scheme effectively reduces the impact of mass transfer polarization during flow battery stack discharge, restores stack performance online, and allows the stack to continuously perform constant-power discharge, meeting the requirement for full-power operation of the flow battery system at any stage. Example 2

[0061] Based on the control method for discharging a flow battery provided in Example 1, this Example 2 provides a flow battery system that applies the control method for discharging a flow battery as described in Example 1.

[0062] refer to Figure 2 As shown, the flow battery system includes a positive electrolyte tank (electrolyte tank+), a negative electrolyte tank (electrolyte tank-), a fuel cell stack, an electrical module, a battery control system, a positive electrolyte circulation pump (Pump+), and a negative electrolyte circulation pump (Pump-); wherein, at least two fuel cell stacks are provided. Figure 2 Taking two groups as an example, each group of battery stacks is connected to a set of positive and negative electrolyte tanks through a set of positive and negative electrolyte circulation pumps. Both groups of battery stacks are connected to an electrical module, which is connected to the battery control system. The electrical module is used to realize different power outputs for different groups of battery stacks and to realize AC / DC conversion. The battery control system is used to judge various parameters and issue start-up and shutdown commands, circulation pump frequency adjustment commands, and charge / discharge power adjustment commands.

[0063] Specifically, the electrical module includes several DC / DC sub-modules and one DC / AC sub-module. Each DC / DC sub-module is connected to a corresponding fuel cell stack, and each DC / DC sub-module is connected to a DC bus. The DC bus ends in a DC / AC sub-module, which is connected to the AC power grid. The electrical module has the following functions: responsible for DC load application to the fuel cell stack and voltage conversion and adjustment; enabling different power outputs for different fuel cell stacks; and realizing AC / DC power conversion.

[0064] The battery control system includes a detection module, a judgment module, and a control unit. The judgment module includes judgment module 1 and judgment module 2, and the control unit includes control unit 1, control unit 2, and control unit 3. The battery control system is responsible for managing the overall battery system status. The detection module detects battery system parameters (voltage, SOC, etc.), judgment module 1 judges the voltage, and judgment module 2 judges the SOC. Control unit 1 issues battery system power-on / off commands, control unit 2 issues commands to adjust the electrolyte circulation pump frequency, and control unit 3 issues commands to request charging / discharging power adjustment.

[0065] The above scheme allows for the adjustment of the stack power and circulation pump frequency via electrical modules and positive and negative electrolyte circulation pumps, under the control of the battery control system during the discharge of the flow battery stack. This effectively reduces the impact of mass transfer polarization, restores the stack performance online, and enables the stack to continuously discharge at constant power, meeting the usage requirements of the flow battery system to operate at full power at any stage.

[0066] refer to Figure 3 Based on the above system, its overall workflow is as follows.

[0067] Step 1 (Start): The battery control system receives the power demand and issues a constant power discharge command to the flow battery system.

[0068] Step 2 (Discharge at rated power): The battery control system issues a command, and the electrical module begins constant power discharge in constant power mode.

[0069] Step 3 (Detecting whether the stack voltage has reached the set threshold): The detection module of the battery control system detects the stack voltage. If the judgment module 1 determines that the voltage of a single cell of the stack is lower than 1.28V, it starts to execute step 4; otherwise, it continues to execute constant power discharge.

[0070] Step 4 (Determine the SOC of different battery stacks): The judgment module 2 in the battery control system judges the SOC of the battery stacks and identifies battery stacks with high SOC and battery stacks with low SOC.

[0071] Step 5: The control unit in the battery control system issues the following command:

[0072] (1) The output power of the fuel cell stack with high SOC is increased to 120%, and the pump frequency of the circulating pump is increased to 110% of the standard value under this power;

[0073] (2) The output power of the fuel cell stack with low SOC is reduced to 80%, and the pump frequency of the circulating pump is increased to 110% of the standard value under rated power;

[0074] (3) Maintain this state for 5 minutes;

[0075] If the two sets of fuel cells have the same SOC, then the following scheme will be implemented:

[0076] (1) The output power of any fuel cell stack is increased by 120%, and the pump frequency of the circulating pump is increased to 110% of the standard value of that power;

[0077] (2) The output power of another fuel cell stack is reduced to 80%, and the pump frequency of the circulating pump is increased to 110% of the standard value under the rated power;

[0078] (3) Keep running in this state for 5 minutes.

[0079] Step 6: Perform the reverse operation on the two sets of fuel cells in Step 5, specifically:

[0080] (1) The load of the fuel cell stack that was deloaded in step 5 is increased to 120%, and the pump frequency of the circulating pump is increased to 110% of the standard value of that power.

[0081] (2) Reduce the load of the fuel cell stack that was increased in step 5 to 80%, and increase the pump frequency of the circulating pump to 110% of the standard value under rated power;

[0082] (3) Keep running in this state for 5 minutes.

[0083] Step 7: The battery control unit controls the following operating modes:

[0084] (1) Resume constant power discharge: The flow battery system operates in constant power mode;

[0085] (2) SOC balancing strategy: The flow battery system performs active SOC balancing according to the balancing strategy in Example 1.

[0086] Step 8 (Determine if SOC has reached the set threshold): The judgment unit 2 of the battery control system determines whether SOC has reached the set discharge cutoff threshold. If it has reached the set threshold, proceed to step 9; otherwise, return to step 2 and continue constant power discharge.

[0087] Step 9 (End): The control unit issues a shutdown command to shut down the flow battery system.

[0088] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A control method for discharging a flow battery, characterized by, The method comprises the following steps: Setting at least two groups of stacks, detecting the SOC values of the two groups of stacks when the stack voltage is lower than a preset threshold value, taking the group of stacks with a higher SOC value as a first group of stacks, and taking the group of stacks with a lower SOC value as a second group of stacks; Adjusting the power of the first group of stacks to be higher than the rated power, adjusting the circulating pump frequency of the first group of stacks to be higher than the standard pump frequency corresponding to the adjusted power; adjusting the power of the second group of stacks to be lower than the rated power, adjusting the circulating pump frequency of the second group of stacks to be higher than the standard pump frequency corresponding to the rated power; continuing to discharge for a first preset time; specifically, adjusting the power of the first group of stacks to be 110%-130% of the rated power, adjusting the circulating pump frequency of the first group of stacks to be 105%-115% of the standard pump frequency corresponding to the adjusted power; adjusting the power of the second group of stacks to be 70%-90% of the rated power, adjusting the circulating pump frequency of the second group of stacks to be 105%-115% of the standard pump frequency corresponding to the rated power; the first preset time is 4-6 min; Adjusting the power of the second group of stacks to be higher than the rated power, adjusting the circulating pump frequency of the second group of stacks to be higher than the standard pump frequency corresponding to the adjusted power; adjusting the power of the first group of stacks to be lower than the rated power, adjusting the circulating pump frequency of the first group of stacks to be higher than the standard pump frequency corresponding to the rated power; continuing to discharge for a second preset time; specifically, adjusting the power of the second group of stacks to be 110%-130% of the rated power, adjusting the circulating pump frequency of the second group of stacks to be 105%-115% of the standard pump frequency corresponding to the adjusted power; adjusting the power of the first group of stacks to be 70%-90% of the rated power, adjusting the circulating pump frequency of the first group of stacks to be 105%-115% of the standard pump frequency corresponding to the rated power; the second preset time is 4-6 min; Adjusting the power of the first group of stacks and the power of the second group of stacks back to the rated power and discharging in a constant power mode, and stopping discharging when the SOC set value is reached.

2. The control method for discharging a liquid flow battery according to claim 1, wherein, When the SOC values of the two groups of stacks are detected, if the SOC values of the two groups of stacks are the same, one group of stacks is optionally taken as the first group of stacks, and the other group of stacks is taken as the second group of stacks.

3. The control method for discharging a liquid flow battery according to claim 1, wherein In the process of adjusting the power of the first group of stacks and the power of the second group of stacks back to the rated power and discharging in a constant power mode, a SOC balancing strategy is started to keep the SOC values of the first group of stacks and the second group of stacks balanced; The SOC balancing strategy comprises: According to the different difference between the first group of stacks SOC value and the second group of stacks SOC value, the circulating pump frequency of the group of stacks with a lower SOC value is increased; wherein the greater the difference between the two groups of stacks SOC values, the greater the circulating pump frequency of the group of stacks with a lower SOC value is increased; When the difference between the two groups of stacks SOC values is less than a preset difference, the SOC balancing strategy is stopped.

4. The control method for discharging a liquid flow battery according to claim 3, wherein When the difference between the SOC values of the two groups of stacks is 0.5%-1.5%, the circulating pump frequency of the stack group with the lower SOC value is increased by 3%; when the difference between the SOC values of the two groups of stacks is 1.5%-2.5%, the circulating pump frequency of the stack group with the lower SOC value is increased by 5%; when the difference between the SOC values of the two groups of stacks is 2.5%-3.5%, the circulating pump frequency of the stack group with the lower SOC value is increased by 8%; and when the difference between the SOC values of the two groups of stacks is greater than 3.5%, the circulating pump frequency of the stack group with the lower SOC value is increased by 10%.

5. A flow battery system applying the control method for discharging a flow battery as claimed in any one of claims 1 to 4, characterized in that, The battery system comprises an electrical module, a battery control system and at least two groups of stacks, each group of stacks is connected to a group of positive and negative electrolyte tanks through a group of positive and negative electrolyte circulating pumps, the two groups of stacks are connected to the electrical module, and the electrical module is connected to the battery control system; wherein the electrical module is used to realize the output of different powers of different groups of stacks and realize the conversion between AC and DC; and the battery control system is used to judge various parameters and issue switch-on / off instructions, circulating pump frequency size adjustment instructions and charge / discharge power size adjustment instructions.

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