Electrolyte flow control method for all-vanadium redox flow battery

Abstract

The invention discloses an all-vanadium redox flow battery electrolyte flow control method, which comprises the following steps: step 1, establishing a hybrid model of an all-vanadium redox flow battery system and an all-vanadium redox flow battery system efficiency calculation model, the hybrid model comprising an electrochemical model, a fluid mechanics model and an equivalent loss circuit model of the all-vanadium redox flow battery system, the system efficiency calculation model calculates the system efficiency according to the battery rated power and the pump loss power; step 2, performing a simulation experiment on the hybrid model and the system efficiency calculation model established in the step 1 to obtain the electrolyte flow under different SOC states when the system efficiency is the highest, namely the optimal flow; and step 3, controlling a variable frequency pump of the all-vanadium redox flow battery system to work according to the optimal flow under different SOC states obtained in the step 2. According to the method, the working characteristics of the battery can be intuitively reflected, the system efficiency can be accurately calculated, rapid switching among the optimal flow intervals can be realized, and the working stability is improved.

Description

Technical Field

[0001] The present invention relates to the field of all-vanadium redox flow battery control methods, and particularly to an all-vanadium redox flow battery electrolyte flow control method. Background Art

[0002] An all-vanadium redox flow battery system (VRB) mainly consists of a stack, an electrolyte storage tank, an electrolyte delivery module, and a control module. The electrolyte delivery module includes pumps, pipelines, valves, etc., which are responsible for transporting the electrolyte from the storage tank to the stack and then back to the storage tank after the reaction. When the electrolyte flows through the pipeline, the stack electrode, and the stack flow channel, a flow pressure drop will occur, resulting in pump power loss. As the scale of the all-vanadium redox flow battery energy storage system increases to the MW level, the proportion of pump power loss in the total system loss becomes larger and cannot be ignored.

[0003] Since the pump power loss is mainly related to the electrolyte flow rate, how to control the flow rate during charge and discharge to make the system most efficient and improve the system stability is an important issue currently faced. Summary of the Invention

[0004] The present invention provides an all-vanadium redox flow battery electrolyte flow control method to solve the problem of poor system working stability caused by neglecting pump power loss in the existing all-vanadium redox flow battery system.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] An all-vanadium redox flow battery electrolyte flow control method includes the following steps:

[0007] Step 1, establish a hybrid model of the all-vanadium redox flow battery system and a calculation model of the all-vanadium redox flow battery system efficiency.

[0008] The hybrid model includes an electrochemical model, a fluid mechanics model, and an equivalent loss circuit model of the all-vanadium redox flow battery system, where:

[0009] The electrochemical model is used to calculate the real-time concentration of various valence vanadium ions, calculate the SOC value according to the vanadium ion concentration in the storage tank, and calculate the single-cell open-circuit voltage U according to the vanadium ion concentration in the stack through the Nernst equation. cell Then, combined with the single-cell open-circuit voltage U cell and the number of single cells N, calculate the stack voltage U s ;

[0010] The fluid mechanics model calculates the electrode pressure drop ΔP electrode caused by the circulation pump, the stack pressure drop ΔP stack and the pipeline pressure drop ΔP pipe, and then calculate the total pressure drop ΔP; then calculate the pump loss power P according to the total pressure drop ΔP, the flow rate Q, and the pump efficiency η p ; then, according to the stack voltage U s calculate the pump loss current I p ;

[0011] The equivalent loss circuit model uses the stack voltage U calculated by the electrochemical model s as the controlled voltage source, and the pump loss current I calculated by the hydrodynamic model p as the controlled current source, and equivalent other losses in the all-vanadium redox flow battery system to resistances, including the internal resistance and the fixed parasitic resistance. The internal resistance includes the ohmic internal resistance R b generated by battery materials (ion exchange membrane, electrode, bipolar plate, electrolyte, etc.) and the reaction internal resistance R a caused by the redox reaction of the battery. The fixed parasitic resistance R f is the loss internal resistance caused by the system controller and the stack bypass current. The electrode capacitance C e mainly reflects the transient reaction performance during the operation of the battery, and its value is related to the vanadium ion concentration. Combining the controlled voltage source U s , the controlled current source I p , calculate the values of each parameter in the equivalent circuit. The values of each parameter are the capacitive current I e , the parasitic current I f , the stack current I s , the electrode capacitance U e , and thus obtain the charge-discharge voltage U d ;

[0012] In the calculation model of the all-vanadium redox flow battery system efficiency, calculate the charging power P s and the pump loss power P p to calculate the charging power P charge and the discharging power P discharge , and then calculate the system efficiency η s ;

[0013] Step 2: Conduct a simulation experiment on the hybrid model and the system efficiency calculation model of the all-vanadium redox flow battery system established in Step 1. Through the model, simulate the relationship between the system charging power P charge and the SOC under different flow rates. According to the lowest value of the charging power, roughly confirm the optimal flow rate range, and then evenly divide the optimal flow rate range. Simulate the relationship between the system discharging power P discharge and the SOC within each range respectively. According to the highest value of the discharging power, further refine to obtain the optimal flow rate.

[0014] Step 3: Operate the variable-frequency pump of the optimal flow control all-vanadium redox flow battery system under different SOC states obtained in Step 2, so that the variable-frequency pump outputs the electrolyte at the optimal flow rate under different SOC states.

[0015] Further, in Step 1, the electrochemical model includes the dynamic differential equations of the concentrations of various valence vanadium ions in the liquid storage tank and the stack, and the Nernst equation for calculating the open-circuit cell voltage U cell of each monomer; calculate the real-time concentration of various valence vanadium ions through the dynamic differential equations, calculate the SOC value according to the vanadium ion concentration in the liquid storage tank obtained therefrom, and calculate the open-circuit voltage U of the monomer according to the vanadium ion concentration in the stack through the Nernst equation cell , and then combine the open-circuit voltage U of the monomer cell and the number of monomers N to calculate the stack voltage U s .

[0016] Further, in Step 1, the hydrodynamic model includes the calculation equations of the electrode pressure drop ΔP caused by the circulation pump established according to Darcy's theorem electrode , the calculation equation of the stack pressure drop ΔP stack , the calculation equation of the pipeline pressure drop ΔP pipe , respectively calculate the electrode pressure drop ΔP caused by the circulation pump through each calculation equation electrode , the stack pressure drop ΔP stack , the pipeline pressure drop ΔP pipe , and then obtain the total pressure drop ΔP; then calculate the pump loss power P according to the total pressure drop ΔP, the flow rate Q and the pump efficiency η p , and calculate the pump loss current I according to the stack voltage U s ; then consider the terminal voltage fed back by the all-vanadium redox flow battery system to calculate the pump loss current I p ; p .

[0017] Further, in Step 1, in the equivalent loss circuit model, other losses in the all-vanadium redox flow battery system are equivalent to the internal resistance and the parasitic resistance. The internal resistance includes the ohmic internal resistance R generated by battery materials (ion exchange membrane, electrode, bipolar plate, electrolyte, etc.) b and the reaction internal resistance R caused by the redox reaction of the battery a , and the fixed parasitic resistance R f is the loss internal resistance caused by the system controller and the stack bypass current.

[0018] Further, in Step 2, first set the battery parameters, respectively simulate the battery in the open-circuit state and the charge and discharge states, draw the corresponding curves of ion concentration, stack voltage and SOC change, and verify the accuracy of the model; secondly, simulate the system charging power P under different flow rates through the model chargeThe relationship with the SOC is used to roughly confirm the optimal flow rate range according to the lowest value of the charging power; then the optimal flow rate range is evenly divided, and the discharge power P of the simulation system is calculated within each range respectively. discharge The relationship with the SOC is used to further refine the optimal flow rate range according to the highest value of the discharge power.

[0019] Furthermore, in step 3, the M-PID multi-modal control strategy is adopted to control the efficient switching of the variable-frequency pump of the all-vanadium redox flow battery system between the optimal flow rates in different SOC states, so that the variable-frequency pump outputs the electrolyte at the optimal flow rate in different SOC states.

[0020] Compared with the prior art, the advantages of the present invention are as follows:

[0021] 1. In the present invention, the hybrid model of the all-vanadium redox flow battery system couples each model with each other, can intuitively reflect the working characteristics of the all-vanadium redox flow battery, comprehensively observe the operating state of the system, and accurately calculate the system efficiency. The high efficiency and accuracy of the model are helpful for further understanding the influence of various parameters on the system and expanding the scale of the all-vanadium redox flow battery energy storage system.

[0022] 2. The hybrid model adopts a modular design, which is divided into an electrochemical model, a fluid mechanics model, and an equivalent loss circuit model. It is convenient to carry out modular design and debugging of each part of the all-vanadium redox flow battery system on MATLAB / Simulink.

[0023] 3. Through MATLAB / Simulink modeling and simulation, it is possible to analyze the influence of the flow rate on the performance of the all-vanadium redox flow battery system, and it is possible to analyze that the optimal flow rate during the current charge and discharge period is a function of the state of charge, so as to obtain the optimal flow rate under different SOC states and improve the working stability of the battery system.

[0024] 4. Adopting a segmented variable flow rate control strategy, compared with constant flow rate operation, it reduces the pump power loss and improves the system efficiency.

[0025] 5. Adopting the M-PID multi-modal control strategy, for the flow rate intervals in different segments during the charge and discharge states, corresponding control strategies are adopted to control the variable-frequency pump, so as to change the electrolyte flow rate, which can realize the rapid switching between the optimal flow rate intervals, make up for the hysteresis of the flow rate change, reduce the overshoot, improve the subsequent working stability, and improve the system efficiency. Description of the Drawings

[0026] Figure 1 It is a diagram of the equivalent loss circuit model established in the embodiment of the present invention.

[0027] Figure 2 It is a diagram of the hybrid model established in the embodiment of the present invention.

[0028] Figure 3 It is the MATLAB / Simulink simulation diagram in the embodiment of the present invention.

[0029] Figure 4 It is the block diagram of the M-PID structure in the embodiment of the present invention.

[0030] Figure 5 It is the control flow chart of M-PID in the embodiment of the present invention. Specific implementation manners

[0031] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0032] This embodiment discloses a method for controlling the electrolyte flow rate of a vanadium redox flow battery, including the following steps:

[0033] Step 1, establish a hybrid model of the vanadium redox flow battery system (VRB) and a calculation model of the efficiency of the vanadium redox flow battery system.

[0034] In this embodiment, the hybrid model includes an electrochemical model, a hydrodynamics model, and an equivalent loss circuit model of the vanadium redox flow battery system, and the specific description is as follows:

[0035] (1) Electrochemical model

[0036] The electrochemical model considers the influencing factors of vanadium ions in the storage tank and the stack, quantifies the transfer of vanadium ions through the membrane, and establishes a mass balance equation in combination with the charge-discharge redox reaction, cross self-discharge reaction, and Fick's law. It is known that the stack voltage is related to the number of monomers and the equilibrium potential, and is established by combining the mass balance equation with the circuit model.

[0037] The dynamic differential equations of the concentrations of various valence vanadium ions in the stack and the storage tank are shown in equations (1)-(2):

[0038]

[0039]

[0040] In the formula: V s and V t are the volumes of the electrolyte in the stack and the storage tank; C si and C ti (i = 2, 3, 4, 5) are the concentrations of the i-valent vanadium ions in the stack and the storage tank; k i is the transmembrane diffusion coefficient of the i-valent vanadium ions; F is the Faraday constant; z is the electron transfer coefficient; d is the thickness of the ion membrane; S is the area of the ion membrane; Q is the flow rate of the electrolyte flowing into the stack; I d represents the magnitude of the charge and discharge of the current; N is the number of monomers.

[0041] According to the concentration of vanadium ions with different valences, the open-circuit cell voltage U of each monomer can be obtained using the Nernst equation cell , assuming that the properties of each monomer are the same, the stack voltage U can be calculated based on the monomer voltage s , as shown in formula (3):

[0042]

[0043] In the formula: U eq is the standard electrode potential of the positive and negative electrodes of the VRB during the electrochemical reaction at a temperature of 298K, that is, 1.259V; R is the universal gas constant; T represents the influence of temperature on the operation of the battery; N is the number of monomers

[0044] (2) Hydrodynamics model

[0045] The hydrodynamics model considers that the electrolyte will generate a flow pressure drop when flowing through the pipeline, the stack electrodes and the stack flow channels, and then generate pump power loss. The pump power loss mainly includes the flow loss generated when the electrolyte flows through the internal electrodes, the pipeline friction loss generated when the electrolyte flows through the external pipeline, and the flow loss generated when the electrolyte flows through the stack channels. According to Darcy's theorem, the electrode pressure drop ΔP electrode , the pipeline pressure drop ΔP pipe , and the stack pressure drop ΔP stack are calculated as follows:

[0046]

[0047] ΔP stack =Q·R e (6)

[0048] The total flow pressure drop ΔP is calculated based on the flow pressure drops of each part:

[0049] ΔP = ΔP electrode +ΔP pipe +ΔP stack (7)

[0050] The pump loss power P is calculated based on the total pressure drop, flow rate and pump efficiency p :

[0051]

[0052] The pump loss current I is calculated based on the pump power loss and the stack voltage p :

[0053]

[0054] In the formula: μ is the electrolyte viscosity; L e is the electrode length; A cs is the electrode cross-sectional area; Ke is the electrolyte permeability; f d is the Darcy friction factor; L n is the pipe length; D h is the hydraulic diameter of the pipe; ρ is the density of the fluid; v is the flow velocity of the electrolyte; R e is the flow resistance of the battery; η is the pump efficiency.

[0055] (3) Equivalent loss circuit model

[0056] As Figure 1 shown, the equivalent loss circuit model of the all-vanadium redox flow battery system reflects the electrical relationships of various components during battery operation. The currents mainly include the charge-discharge current I d , the stack current I s , the capacitance current I e , the parasitic current I f and the pump loss current I p caused by the circulation pump. The other losses in the system are equivalent to resistors, including the internal resistance and the fixed parasitic resistance. The internal resistance includes the ohmic internal resistance R b generated by battery materials (ion exchange membrane, electrode, bipolar plate, electrolyte, etc.) and the reaction internal resistance R a caused by the redox reaction of the battery. The fixed parasitic resistance R f is the loss internal resistance caused by the system controller and the stack bypass current. U s is the stack voltage, U e is the capacitance voltage, U d is the charge-discharge voltage. The electrode capacitance C e mainly reflects the transient reaction performance during battery operation, and its value is related to the vanadium ion concentration.

[0057] The electrical relationships between the parameters of the equivalent loss model are as follows:

[0058]

[0059] As Figure 2 shown, the VRB hybrid model established in this embodiment is composed of three sub-models, namely the equivalent loss circuit model, the electrochemical model, and the pump loss model.

[0060] In the electrochemical model, the charge-discharge current magnitude I d , the VRB system parameters, the electrolyte flow rate Q, and the initial concentrations of various valence ions are used as the inputs of the electrochemical model; the real-time concentrations of various valence vanadium ions are obtained through the dynamic differential equations of the electrochemical reaction, formulas (1)-(2). The SOC value is calculated based on the vanadium ion concentration in the storage tank obtained therefrom, and the open-circuit voltage U cell; Then, knowing that the properties of each monomer are the same, and based on the open-circuit voltage U of the monomer cell and the number of monomers N, calculate the stack voltage U s , U s is used as the controlled voltage source in the equivalent loss circuit model.

[0061] In the hydrodynamic model, according to the flow rate of the circulation pump and the basic characteristics of the all-vanadium redox flow battery hydraulic circuit, calculate the electrode pressure drop ΔP caused by the circulation pump electrode , the stack pressure drop ΔP stack and the pipeline pressure drop ΔP pipe , calculate the total pressure drop ΔP; then, based on the total pressure drop ΔP, the flow rate Q and the pump efficiency η, obtain the pump loss power P p ; then, according to the stack voltage U s calculate the pump loss current I p ; Take I p as the controlled current source in the equivalent loss circuit model.

[0062] The equivalent loss circuit model uses the stack voltage U calculated by the electrochemical model s as the controlled voltage source, and the pump loss current I calculated by the hydrodynamic model p as the controlled current source, and equivalent other losses in the all-vanadium redox flow battery system to resistors, including internal resistance and fixed parasitic resistance. The internal resistance includes the ohmic internal resistance R b generated by battery materials (ion exchange membrane, electrode, bipolar plate, electrolyte, etc.) and the reaction internal resistance R a caused by the battery redox reaction. The fixed parasitic resistance R f is the loss internal resistance caused by the system controller and the stack bypass current. The electrode capacitance C e mainly reflects the transient reaction performance during the battery operation, and its value is related to the vanadium ion concentration. Combining the controlled voltage source U s , the controlled current source I p , calculate the values of each parameter in the equivalent circuit (capacitor current I e , parasitic current I f , stack current I s , electrode capacitance U e ), and then the charge and discharge current U d can be obtained;

[0063] In this embodiment, the calculation model of the all-vanadium redox flow battery system efficiency calculates the system efficiency η s based on the stack power P p and the pump loss power P s . The system efficiency reflects the input-output ability of the system, and the calculation formula is as follows:

[0064]

[0065] Where: P discharge is the power of the discharge system; P charge is the power of the charging system; P s is the power of the stack; P p is the pump loss power.

[0066] According to the working principle and equivalent circuit model analysis of VRB, when the charge-discharge current I d is constant, the larger the flow rate Q, the greater the pump loss power P p increases, and the larger I p is, the smaller the stack current I s is, thus reducing the power of the stack P s ; while when Q is too small, it cannot transport enough electrolyte for reaction, thereby affecting I s and P s . Therefore, during the charge-discharge process of the battery, with the change of SOC, there must be a corresponding optimal flow rate, making the system power P charge smaller during the charging process and the system power P discharge larger during the discharging process, that is, the system efficiency of the battery is higher.

[0067] Step 2: As Figure 3 shown, by building a platform on MATLAB / Simulink, a simulation experiment is carried out on the hybrid model and system efficiency calculation model of the all-vanadium redox flow battery system established in Step 1.

[0068] First, set the battery parameters, and respectively simulate the battery in the open-circuit state and the charge-discharge state, draw the corresponding ion concentration, stack voltage, and SOC change curves to verify the accuracy of the model. Secondly, through the model, simulate the relationship between the system charging power P charge and SOC under different flow rates, and roughly confirm the optimal flow rate range according to the lowest value of the charging power. Then, evenly divide the flow rate range, and respectively simulate the relationship between the system discharging power P discharge and SOC within each range, and further refine to obtain the optimal flow rate according to the highest value of the discharging power. Finally, organize and summarize the optimal flow rate values at each SOC obtained from the simulation, and the results are shown in Table 1. It can be seen from Table 1 that as the charging progresses, SOC increases continuously, and the optimal flow rate shows a trend of decreasing first and then increasing. Table 1 is as follows:

[0069] Table 1 Relationship between Optimal Flow Rate and SOC

[0070]

[0071] Step 3: In step 3, the M-PID multimodal control strategy is adopted to control the efficient switching of the variable-frequency pump of the all-vanadium redox flow battery system among the optimal flows in different SOC states, so that the variable-frequency pump outputs the electrolyte at the optimal flow in different SOC states.

[0072] The entire control process of the traditional controller is divided into three stages, namely, acceleration start control, forced braking control, and position learning control.

[0073] 1. Acceleration start control (ASC): It is a control action that causes the controlled variable to start from the steady state at the previous moment and change in an accelerating manner. Its action direction is to try to eliminate the deviation or deviation trend that has already occurred between the controlled variable and the reference input. The purpose is to force the controlled quantity to track the change of the reference input as quickly as possible or to eliminate the influence of interference on the system.

[0074] 2. Forced braking control (FDC): This is a control action that is closely related to the acceleration start control, but its nature and function are completely opposite. It forces the controlled variable to decelerate rapidly to deal with the energy storage effect of the multi-capacity object. Compared with the method of increasing the system damping, FDC has the strongest ability to suppress overshoot and the least impact on the response rapidity.

[0075] 3. Position learning control (PLC): When the system response enters the steady state, the output of the controller - the control action should maintain the current value, that is, the current position where the actuator stays. Since this position is obtained through online learning of the system response, it is called position learning control.

[0076] In addition, an ideal control strategy, in addition to including three control factors of ASC, FDC, and PLC, also needs to meet the following basic conditions:

[0077] 1. The three control actions of ASC, FDC, and PLC must independently and without interference fully exert their respective functions, that is, when one of the control functions needs to play a role, the other two control functions do not play a role or do not affect the exertion of this control function, and more importantly, they cannot produce opposite control effects. Only in this way can the mutual cancellation and weakening between the three control actions of ASC, FDC, and PLC be avoided, so that they can fully display their respective capabilities within the specific sections where they need to play a role in the system response process.

[0078] 2. The three control actions of ASC, FDC, and PLC not only require no interference with each other, but also require them to coordinate and cooperate with each other. This is because there are close qualitative and quantitative relationships among the three, especially between ASC and FDC. When selecting the parameters of the three control actions and the sections where they play a role, the objective qualitative and quantitative relationships existing among them must be fully considered.

[0079] The M-PID multi-modal control strategy adds a decision-making mechanism DE and a virtual sampling switch VSS on the basis of the conventional PID control. The decision-making mechanism is used to determine whether the three basic controls of the proportional-integral-differential of the controller act on the controlled object, so as to achieve the control principle that the three control actions do not interfere with each other, are independent of each other, and coordinate with each other, in order to improve the control effect of the controller.

[0080] Compared with the traditional PID control, the structural block diagram of the M-PID multi-modal control strategy is as Figure 4 shown. It introduces a decision-making mechanism (DE, Decision Element) and a virtual sampling switch (VSS, Visual Sampling Switch). The decision-making mechanism is used to determine whether the three basic controls of the proportional-integral-differential of the controller act on the controlled object, so as to achieve the control principle that the three control actions do not interfere with each other, are independent of each other, and coordinate with each other, in order to improve the control effect of the controller.

[0081] Compared with the traditional PID, the multi-modal PID controller adds a decision-making mechanism. By judging the change rate d|e|dt of the absolute value of the deviation and its second derivative d 2 |e|dt 2 value, it decides the on-off of the three links. Its basic control strategy is as follows:

[0082] (1) When the change rate d|e|dt of the absolute value of the deviation ≥ 0, the controller adopts proportional plus integral control. At this time, the system is in the accelerating start control state.

[0083] (2) When the change rate d|e|dt of the absolute value of the deviation < 0, and the second derivative value d 2 |e|dt 2 > 0 of the absolute value of the deviation, the system adopts integral plus differential control. At this time, the system is in the forced braking control state.

[0084] (3) When the change rate d|e|dt of the absolute value of the deviation < 0, and the second derivative value d 2 |e|dt 2 < 0 of the absolute value of the deviation, the system adopts integral control. At this time, the system is in the position learning control state.

[0085] The control flow chart of the M-PID multi-modal control strategy is as Figure 5 shown. Using the M-PID multi-modal control strategy to control the variable frequency pump of the all-vanadium redox flow battery system, thereby changing the electrolyte flow rate, can achieve a rapid switch between each optimal flow rate interval, make up for the lag of the flow rate change, reduce the overshoot, and improve the subsequent stable process.

[0086] In this embodiment, a Siemens smart 200 controller is selected, and the M-PID is programmed with ladder diagrams on the STEP 7-MicroWIN SMART software, thereby implementing the M-PID multi-modal control strategy. The modbus RTU communication protocol is adopted, and the frequency converter is communicated with through the 485 interface to control the pump speed and realize the switching of the optimal flow range. The upper computer uses the MCGS touch screen as the monitoring and display interface to display the parameters of the system in real time.

[0087] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. The embodiments described in the present invention are only descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention. Among the various specific technical features described in the above specific embodiments, they can be combined in any suitable manner without contradiction. As long as such a combination does not violate the idea of the present invention, it should also be regarded as the content disclosed in the present disclosure. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0088] The present invention is not limited to the specific details in the above embodiments. Without departing from the technical concept of the present invention and within the scope of the design idea of the present invention, various modifications and improvements made by those skilled in the art to the technical solution of the present invention shall fall within the protection scope of the present invention. The technical content requested to be protected by the present invention has been fully recorded in the claims.

Claims

1. A method for controlling the electrolyte flow rate of an all-vanadium redox flow battery, characterized in that, Including the following steps: Step 1, establish a hybrid model of the all-vanadium redox flow battery system and a calculation model of the efficiency of the all-vanadium redox flow battery system, The hybrid model includes an electrochemical model, a hydrodynamics model, and an equivalent loss circuit model of the all-vanadium redox flow battery system, where: The electrochemical model is used to calculate the real-time concentration of vanadium ions with various valences, and calculate SOC value, and calculate the open-circuit voltage of a single cell according to the vanadium ion concentration in the stack through the Nernst equation U cell Then, combined with the open-circuit voltage of a single cell U cell and the number of single cells N calculate the stack voltage U s ; The hydrodynamic model calculates the electrode pressure drop Δ P electrode , the stack pressure drop Δ P stack and the pipeline pressure drop Δ P pipe according to the flow rate of the circulation pump in combination with the basic characteristics of the hydraulic circuit of the all-vanadium redox flow battery system, and then calculates the total pressure drop Δ P ; Then, based on the total pressure drop Δ P , the flow rate Q and the pump efficiency η , the pump loss power P p is calculated; Then, based on the stack voltage U s , the pump loss current I p is calculated; The equivalent loss circuit model uses the stack voltage calculated by the electrochemical model U s as a controlled voltage source, and the pump loss current calculated by the hydrodynamic model I p as a controlled current source, and other losses in the all-vanadium redox flow battery system are equivalent to resistances, including the internal resistance and fixed parasitic resistance. The internal resistance includes the ohmic internal resistance generated by battery materials (ion exchange membrane, electrode, bipolar plate, electrolyte, etc.) R b and the reaction internal resistance caused by the battery redox reaction R a , and the fixed parasitic resistance R f is the loss internal resistance caused by the system controller and stack bypass current. The electrode capacitance C e mainly reflects the transient reaction performance during the battery operation, and its value is related to the vanadium ion concentration. Combining the controlled voltage source U s , the controlled current source I p , calculate the values of each parameter in the equivalent circuit. The values of each parameter are the capacitive current I e , the parasitic current I f , the stack current I s , the electrode capacitance U e , and thus obtain the charge-discharge voltage U d ; In the calculation model of the efficiency of the all-vanadium redox flow battery system, according to the stack power P s and the pump loss power P p calculate the charging power P charge and the discharging power P discharge , and then calculate the system efficiency η s ; Step 2: Conduct a simulation experiment on the hybrid model and system efficiency calculation model of the all-vanadium redox flow battery system established in Step 1, and simulate the system charging power at different flow rates through the model P charge and SOC the relationship between them. Based on the lowest value of the charging power, roughly confirm the optimal flow rate range, and then evenly divide the optimal flow rate range. Simulate the system discharge power within each range respectively P discharge and SOC the relationship between them. Based on the highest value of the discharge power, further refine to obtain the optimal flow rate; Step 3: Operate the variable-frequency pump of the optimal flow control all-vanadium redox flow battery system obtained in Step 2, so that the variable-frequency pump outputs the electrolyte at the optimal flow rate under different SOC conditions. SOC Output the electrolyte at the optimal flow rate under different conditions.

2. The method for controlling the electrolyte flow rate of an all-vanadium redox flow battery according to claim 1, wherein In Step 1, the electrochemical model includes the dynamic differential equations of the concentrations of various valence vanadium ions in the storage tank and the stack, as well as the Nernst equation for calculating the open-circuit cell voltage of each monomer. U cell The real-time concentrations of various valence vanadium ions are calculated through the dynamic differential equations, and the SOC value is calculated based on the vanadium ion concentration in the storage tank obtained therefrom. The open-circuit voltage of the monomer is calculated through the Nernst equation based on the vanadium ion concentration in the stack. U cell Then, combined with the open-circuit voltage of the monomer U cell and the number of monomers N the stack voltage U s is calculated.

3. A method for controlling the electrolyte flow rate of an all-vanadium redox flow battery according to claim 1, characterized in that, In Step 1, the hydrodynamic model includes the calculation equation of the electrode pressure drop Δ P electrode caused by the circulation pump established according to Darcy's theorem, the calculation equation of the stack pressure drop Δ P stack and the calculation equation of the pipeline pressure drop Δ P pipe . The electrode pressure drop Δ P electrode caused by the circulation pump, the stack pressure drop Δ P stack and the pipeline pressure drop Δ P pipe are respectively calculated through each calculation equation, and then the total pressure drop Δ P is obtained; then, the pump loss power P is calculated according to the total pressure drop Δ Q , the flow rate η and the pump efficiency P p , and the pump loss current U s is calculated according to the stack voltage I p ; furthermore, the pump loss current I p is calculated by considering the terminal voltage fed back by the all-vanadium redox flow battery system.

4. A method for controlling the electrolyte flow rate of an all-vanadium redox flow battery according to claim 1, characterized in that, In Step 1, in the equivalent loss circuit model, other losses in the all-vanadium redox flow battery system are equivalent to internal resistance and parasitic resistance, where the internal resistance includes ohmic internal resistance generated by battery materials (ion exchange membrane, electrode, bipolar plate, electrolyte, etc.) R b and reaction internal resistance caused by the oxidation-reduction reaction of the battery R a , and the fixed parasitic resistance R f is the loss internal resistance caused by the system controller and the stack bypass current.

5. A method for controlling the electrolyte flow rate of an all-vanadium redox flow battery according to claim 1, characterized in that, In Step 2, first set the battery parameters, and respectively simulate the battery in the open circuit state and the charge and discharge states, draw the corresponding ion concentration, stack voltage, and SOC variation curves to verify the accuracy of the model; secondly, simulate the system charging power at different flow rates through the model P charge and SOC the relationship between them, and roughly confirm the optimal flow rate range according to the lowest value of the charging power; then evenly divide the optimal flow rate range, and simulate the system discharge power in each range respectively P discharge and SOC the relationship between them, and further refine the optimal flow rate range according to the highest value of the discharge power.

6. The method for controlling the electrolyte flow rate of an all-vanadium redox flow battery according to claim 1, wherein, In step 3, the M-PID multimodal control strategy is adopted to control the high-efficiency switching of the variable-frequency pump of the all-vanadium redox flow battery system among the optimal flows in different SOC states, so that the variable-frequency pump outputs the electrolyte at the optimal flow in different SOC states.

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