Online evaluation method and system for state of health of vanadium redox flow battery

Abstract

The invention relates to an online evaluation method and system for the state of health of a vanadium redox flow battery. The method mainly comprises the following steps: in a calibration stage, current integration is carried out in an interval from a first voltage to a second voltage of a reference battery to obtain a reference capacity integral, and a function relationship between positive and negative voltage change and capacity change is established; in the subsequent operation stage, current integration is carried out in the interval from the first voltage to the second voltage of the reference battery to obtain the current capacity integration, and the current positive and negative pole capacity change is obtained according to the current positive and negative pole voltage change based on the function relation between the positive and negative pole voltage change and the capacity change established in the calibration stage; and taking the ratio of the current capacity integral to the reference capacity integral as the health state of the whole current system, taking the difference value of the current positive and negative pole capacity changes as irreversible capacity, and taking the rest as reversible capacity. According to the method, the online health state of the all-vanadium redox flow battery system can be accurately evaluated, and the reversible capacity and the irreversible capacity can be distinguished.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vanadium flow battery, in particular to a method and system for online evaluation of health state of vanadium flow battery. BACKGROUND

[0002] Vanadium redox flow battery (VRFB) as a new type of large-scale energy storage technology is widely used in grid frequency modulation, peak shaving and distributed energy storage scenarios due to its advantages of recyclable electrolyte, high safety and long service life.

[0003] However, with the increase of running time, the battery system will have different degrees of performance degradation, showing capacity decline, voltage efficiency reduction, ion cross intensification, liquid level imbalance, etc. Based on this, accurate evaluation of the health state (SOH) of the battery is an important link to ensure stable operation of the system. The current general definition of SOH of the battery is the ratio of the maximum available capacity to the nominal capacity of the system: SOH= (system current maximum available capacity / system nominal capacity) x 100%.

[0004] The existing estimation of SOH mainly based on the following methods: 1. Equivalent circuit model (ECM) method: the SOH is inferred by measuring the internal resistance and polarization voltage change, but the model is simplified and cannot reflect the complex electrochemical reaction characteristics.

[0005] 2. Electrochemical model method: relying on concentration difference and reaction kinetics equation for parameter inversion, but the parameters are many, the calculation is complex and sensitive to the running environment.

[0006] 3. Incremental capacity analysis (ICA) or differential voltage analysis (DVA) method: the capacity change characteristics are calculated through charge and discharge data, which is more commonly used in lithium battery systems. Because the positive and negative vanadium ions of the flow battery are seriously intermixed, offline / on-line mixed liquid is needed for real-time balance, and the ICA / DVA method brings larger error in the flow system.

[0007] The above methods have the following problems: the online health state evaluation of the vanadium flow battery system is not accurate enough, and the reversible capacity and irreversible capacity cannot be distinguished.

[0008] Therefore, how to overcome the problem that the existing technology cannot accurately evaluate the online health status of the all-vanadium redox flow battery system and cannot distinguish between reversible capacity and irreversible capacity is a difficult problem to be solved in the technical field. SUMMARY

[0009] In view of the above defects or improvement needs of the prior art, in order to solve the problem that the existing online health status evaluation of the all-vanadium redox flow battery system is not accurate and cannot distinguish between reversible capacity and irreversible capacity, the present application provides an online evaluation method and system for the health status of a vanadium redox flow battery. By setting a reference battery, an auxiliary positive electrode and an auxiliary negative electrode, a function relationship between reference capacity integration, positive and negative electrode voltage change and capacity change is established in the calibration stage. After obtaining the current capacity integration in the subsequent operation stage, the health status of the current system as a whole can be directly calculated. After obtaining the current positive and negative electrode voltage change, the current positive and negative electrode capacity change can be obtained according to the function relationship between the positive and negative electrode voltage change and the capacity change, and then the irreversible capacity and the reversible capacity can be calculated according to the current positive and negative electrode capacity change. The above scheme can accurately evaluate the online health status of the all-vanadium redox flow battery system and can distinguish between reversible capacity and irreversible capacity.

[0010] The embodiment of the present application adopts the following technical scheme: In a first aspect, the present application provides an online evaluation method for the health status of a vanadium redox flow battery, comprising: A reference battery, an auxiliary positive electrode and an auxiliary negative electrode are set. The reference battery is connected in parallel with the main stack, and the auxiliary positive electrode and the auxiliary negative electrode are respectively connected with the positive and negative electrodes of the reference battery. In the calibration stage, the current is integrated to obtain reference capacity integration in the first voltage to second voltage interval of the reference battery, and a function relationship between positive and negative electrode voltage change and capacity change is established. In the subsequent operation stage, the current is integrated to obtain current capacity integration in the first voltage to second voltage interval of the reference battery, and based on the function relationship between positive and negative electrode voltage change and capacity change established in the calibration stage, the current positive and negative electrode capacity change is obtained according to the current positive and negative electrode voltage change. The ratio of the current capacity integration to the reference capacity integration is taken as the health status of the current system as a whole, and the difference between the current positive and negative electrode capacity change is taken as the irreversible capacity, and the rest is the reversible capacity.

[0011] By adopting the technical scheme, the reference battery, the auxiliary electrode positive electrode and the auxiliary electrode negative electrode are arranged, the function relationship between the reference capacity integral, the positive and negative electrode voltage change and the capacity change is established in the calibration stage, the current system overall health state can be directly calculated after the current capacity integral is obtained in the subsequent operation stage, the current positive and negative electrode capacity change can be obtained according to the function relationship between the positive and negative electrode voltage change and the capacity change after the current positive and negative electrode voltage change is obtained, and then the irreversible capacity and the reversible capacity are calculated according to the current positive and negative electrode capacity change. The above scheme can realize accurate evaluation of the online health state of the all-vanadium redox flow battery system, and can distinguish the irreversible capacity and the reversible capacity.

[0012] In some embodiments, the first voltage and the second voltage are voltages between positive and negative electrodes of the reference battery.

[0013] By adopting the technical scheme, the first voltage and the second voltage of the reference battery form a whole measurement range standard, in the calibration stage, the capacity increment obtained by integrating the current in the range can be used as the reference capacity integral when SOH=100%, and a reference benchmark is provided for subsequent SOH estimation.

[0014] In some embodiments, the function relationship between the positive and negative electrode voltage change and the capacity change specifically includes: establishing a function relationship between the positive electrode voltage change and the capacity change; wherein the positive electrode voltage change is a voltage change between the reference battery positive electrode and the auxiliary electrode positive electrode; establishing a function relationship between the negative electrode voltage change and the capacity change; wherein the negative electrode voltage change is a voltage change between the reference battery negative electrode and the auxiliary electrode negative electrode.

[0015] By adopting the technical scheme, the function relationship between the voltage change and the capacity change between the reference battery positive electrode and the auxiliary electrode positive electrode, and the function relationship between the voltage change and the capacity change between the reference battery negative electrode and the auxiliary electrode negative electrode are established, respectively, the capacity change between the positive and negative electrodes can be distinguished, and a basis is provided for subsequent judgment of the irreversible capacity and the reversible capacity.

[0016] In some embodiments, the function relationship between the positive electrode voltage change and the capacity change specifically includes: The voltage signal between the reference battery positive electrode and the auxiliary electrode positive electrode at the time point when the reference battery reaches the first voltage is collected and recorded as V11, the voltage signal between the reference battery positive electrode and the auxiliary electrode positive electrode at the time point when the reference battery reaches the second voltage is collected and recorded as V11', and the corresponding voltage V1 11 , V1 12 , V1 13 ……V1 1n is recorded every certain current integral capacity dQ in the process; wherein V111 =V11, V1 1n =V11'; A function relationship between the positive electrode voltage change and the capacity change is established: dq1=f(dv1)=a*(dv1) 2 +b*(dv1)+c; where dv1 is a sequence of V1 12 -V1 11 , V1 13 -V1 11 … V1 1n -V1 11 , and dq1 is a sequence of dQ, 2dQ, 3dQ, …, (n-1)*dQ; a, b, and c are parameters to be identified, and the parameters are identified by the least square method.

[0017] By adopting the above technical solution, the function relationship between the voltage change and the capacity change between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode can be established, and subsequently the function relationship can be used to obtain the positive electrode capacity change after the corresponding positive electrode voltage change is directly substituted into the function.

[0018] In some embodiments, the function relationship between the negative electrode voltage change and the capacity change specifically includes: A voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode is collected at a time point when the reference battery reaches a first voltage, denoted as V21; a voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode is collected at a time point when the reference battery reaches a second voltage, denoted as V21'; and a corresponding voltage V2 11 , V2 12 , V2 13 … V2 1n is recorded every certain current integral capacity dQ in the process; where V2 11 =V21, V2 1n =V21'; A function relationship between the negative electrode voltage change and the capacity change is established: dq2=g(dv2)=d*(dv2) 2 +e*(dv2)+f; where dv2 is a sequence of V2 12 -V2 11 , V2 13 -V2 11 … V2 1n -V2 11 , and dq2 is a sequence of dQ, 2dQ, 3dQ, …, (n-1)*dQ; d, e, and f are parameters to be identified, and the parameters are identified by the least square method.

[0019] By adopting the technical scheme, the function relationship between the voltage change and the capacity change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode can be established, and the function relationship can be used to obtain the capacity change of the negative electrode side after the corresponding voltage change of the negative electrode side is directly substituted into the function.

[0020] In some embodiments, the function relationship between the voltage change and the capacity change of the positive electrode and the negative electrode established in the calibration stage comprises: obtaining the voltage signals V12 and V12' between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode when the reference battery reaches the first voltage and the second voltage respectively in the current cycle; calculating the current positive electrode voltage change ΔV12=V12-V12'; substituting ΔV12 into the function dq1=f(dv1) to obtain the current positive electrode capacity change ΔQ pos =f(ΔV12); obtaining the voltage signals V22 and V22' between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode when the reference battery reaches the first voltage and the second voltage respectively in the current cycle; calculating the current negative electrode voltage change ΔV22=V22-V22'; substituting ΔV22 into the function dq2=g(dv2) to obtain the current negative electrode capacity change ΔQ neg =g(ΔV22); The difference between the current positive electrode capacity change and the current negative electrode capacity change is used as the irreversible capacity, specifically comprising: irreversible capacity DQ irrev =|(|ΔQ pos |−|ΔQ neg |)|。

[0021] By adopting the technical scheme, based on the voltage signal change between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode, the current positive electrode capacity change of the positive electrode side can be obtained based on the foregoing function; similarly, based on the voltage signal change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode, the current negative electrode capacity change of the negative electrode side can be obtained based on the foregoing function; and then the irreversible capacity is obtained by the difference between the current positive electrode capacity change and the current negative electrode capacity change, so as to realize the differentiation of the irreversible capacity and the reversible capacity.

[0022] In some embodiments, the calibration stage and the subsequent running stage are re-performed after the mixing or refilling operation is performed.

[0023] By adopting the technical scheme, when the system recovers the valence balance and concentration uniformity of the electrolyte through the mixed liquid or the liquid refilling operation, the previously identified characteristic functions f(dv1) and g(dv2) may deviate from the actual function of the voltage and the capacity, the reference capacity also changes, and therefore, the parameter self-correction process needs to be performed, the calibration phase is re-performed, and a new round of parameters are obtained to ensure the accuracy and continuity of the SOH estimation.

[0024] In some embodiments, further comprising: In the calibration phase, the voltage V41 between the auxiliary electrode positive electrode and the auxiliary electrode negative electrode is collected; In the subsequent operation phase, the voltage V4 between the auxiliary electrode positive electrode and the auxiliary electrode negative electrode is periodically collected n ; ΔV4=|V4 n -V41|, when ΔV4 exceeds a preset threshold, an alarm is issued, and the voltage V4 is restored to the V41 state through external operation. n

[0025] By adopting the technical scheme, although the data collection is performed for a short time at a specific sampling time, the potential of the auxiliary electrode positive electrode and the auxiliary electrode negative electrode may drift due to ion migration or local concentration difference in long-term operation, thereby affecting the subsequent voltage sampling accuracy and SOH estimation stability. Therefore, the state monitoring and self-maintenance mechanism of the auxiliary electrode positive electrode and the auxiliary electrode negative electrode is introduced, and after the voltage change value between the auxiliary electrode positive electrode and the auxiliary electrode negative electrode exceeds a preset threshold, the voltage between the auxiliary electrode positive electrode and the auxiliary electrode negative electrode is restored through manual electrolyte supplement or oxidation-reduction.

[0026] In a second aspect, the application provides an online evaluation system for the health state of a vanadium flow battery, which applies the online evaluation method for the health state of the vanadium flow battery as described in the first aspect, and includes a main stack, a reference battery, an auxiliary electrode positive electrode, an auxiliary electrode negative electrode, and a control and calculation module, wherein: The positive electrode of the reference battery is connected to the positive electrode of the main stack through a liquid path, and the negative electrode of the reference battery is connected to the negative electrode of the main stack through a liquid path; The auxiliary electrode positive electrode is connected to the positive electrode of the reference battery through a liquid path, and a first electromagnetic valve is arranged on the liquid path; the auxiliary electrode negative electrode is connected to the negative electrode of the reference battery through a liquid path, and a second electromagnetic valve is arranged on the liquid path; the auxiliary electrode positive electrode is connected to the auxiliary electrode negative electrode through a liquid path, and a third electromagnetic valve is arranged on the liquid path; The control and calculation module is used for controlling the instantaneous opening and closing of each electromagnetic valve, collecting the voltage between the liquid paths at the corresponding time, calculating the health state through the voltage change and the capacity increment, and distinguishing the reversible capacity and the irreversible capacity.​

[0027] By adopting the technical scheme, the main stack, the reference battery, the auxiliary electrode positive electrode and the auxiliary electrode negative electrode are connected based on the liquid path, the opening and closing of each liquid path are controlled through the electromagnetic valve arranged on the liquid path, the instantaneous opening and closing of each electromagnetic valve are realized through the control and calculation module to collect corresponding data, and then the health state of the whole system is calculated through the collected data and the reversible capacity and the irreversible capacity are distinguished.

[0028] In some embodiments, the auxiliary electrode positive electrode and the auxiliary electrode negative electrode are both half cells, and the positive electrode chamber of the auxiliary electrode positive electrode and the negative electrode chamber of the auxiliary electrode negative electrode are both arranged with corresponding electrolyte.

[0029] By adopting the technical scheme, the positive and negative electrode chambers of the auxiliary electrode positive electrode and the auxiliary electrode negative electrode store electrolyte corresponding to the determined SOC, for example, the positive electrode stores VO2 + and the negative electrode stores V 2+ and the negative electrode stores V 3+ and the negative electrode stores V 2+ .

[0030] In summary, the present application at least includes the following beneficial technical effects: 1. The reference battery, the auxiliary electrode positive electrode and the auxiliary electrode negative electrode are arranged, the function relationship between the reference capacity integral, the voltage change of the positive and negative electrodes and the capacity change is established in the calibration stage, the health state of the whole system at present can be directly calculated after the current capacity integral is obtained in the subsequent running stage, the current capacity change of the positive and negative electrodes can be obtained according to the function relationship between the voltage change of the positive and negative electrodes and the capacity change in advance, and then the irreversible capacity and the reversible capacity are calculated according to the current capacity change of the positive and negative electrodes. The above scheme can realize accurate evaluation of the online health state of the all-vanadium redox flow battery system, and can distinguish the reversible capacity and the irreversible capacity.

[0031] 2. When the system restores the valence balance and the concentration uniformity of the electrolyte through the mixed liquid or the liquid refilling operation, the characteristic functions f(dv1) and g(dv2) identified in advance may have deviation from the actual function of the voltage to the capacity, including the reference capacity will also change, so the parameter self-correction process needs to be performed, the calibration stage is re-performed, and a new round of parameters are obtained to ensure the accuracy and continuity of the SOH estimation.

[0032] 3. Although data collection is performed for a short time at a specific sampling time, potential drift of the positive auxiliary electrode and the negative auxiliary electrode due to ion migration or local concentration difference in long-term operation may affect the accuracy of subsequent voltage sampling and the stability of SOH estimation; therefore, a state monitoring and self-maintenance mechanism of the positive auxiliary electrode and the negative auxiliary electrode is introduced, and after the voltage change value between the positive auxiliary electrode and the negative auxiliary electrode exceeds a preset threshold, electrolyte is supplemented or redox is performed to restore the voltage between the positive auxiliary electrode and the negative auxiliary electrode. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0034] Figure 1 A flow chart of a vanadium flow battery health state online evaluation method provided by the embodiments of the present application; Figure 2 An extended flow chart of step 102 provided by the embodiments of the present application; Figure 3 An architecture diagram of a vanadium flow battery health state online evaluation system provided by the embodiments of the present application; Figure 4 A running flow chart of a control and calculation module provided by the embodiments of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other. The present application will be described in detail below with reference to the drawings and embodiments. Embodiment 1

[0036] As shown in Figure 1 , the embodiments of the present application provide a vanadium flow battery health state online evaluation method, and the specific steps are as follows.

[0037] Step 101: setting a reference battery, an auxiliary electrode positive electrode and an auxiliary electrode negative electrode; wherein the reference battery is connected in parallel with the main stack, the auxiliary electrode positive electrode and the auxiliary electrode negative electrode are connected with the positive and negative electrodes of the reference battery respectively, the auxiliary electrode positive electrode and the auxiliary electrode negative electrode are connected between them, and each connection is a liquid connection, and an electromagnetic valve is arranged on the liquid path for on-off control.

[0038] Step 102: calibration stage, the reference capacity integral is obtained by integrating the current in the first voltage to the second voltage interval of the reference battery, and the function relationship between the positive and negative electrode voltage change and the capacity change is established. Wherein, the first voltage and the second voltage are the voltages between the positive and negative electrodes of the reference battery, and the first voltage and the second voltage of the reference battery form a whole measurement range standard. In the calibration stage, the capacity increment obtained by integrating the current in the range can be used as the reference capacity integral when SOH=100%, which provides a reference for subsequent SOH estimation.

[0039] Reference Figure 2 As shown in the above step 102, the function relationship between the positive and negative electrode voltage change and the capacity change includes the following steps.

[0040] Step 1021: establishing a function relationship between the positive electrode voltage change and the capacity change; wherein the positive electrode voltage change is the voltage change between the positive electrode of the reference battery and the auxiliary electrode positive electrode. Specifically, the voltage signal between the positive electrode of the reference battery and the auxiliary electrode positive electrode is collected at the time point when the reference battery reaches the first voltage, which is recorded as V11; the voltage signal between the positive electrode of the reference battery and the auxiliary electrode positive electrode is collected at the time point when the reference battery reaches the second voltage, which is recorded as V11'; and at the same time, the corresponding voltage V1 11 , V1 12 , V1 13 ……V1 1n is recorded every certain current integral capacity dQ in the process; wherein V1 11 =V11, V1 1n =V11'; the function relationship between the positive electrode voltage change and the capacity change is established: dq1=f(dv1)=a*(dv1) 2 +b*(dv1)+c; wherein dv1 is a sequence of V1 12 -V1 11 , V1 13 -V1 11 ……V1 1n -V1 11, dq1 series are dQ, 2dQ, 3dQ, (n-1)*dQ; a, b, c are parameters to be identified, and the parameters are identified by the least square method. Through the above technical scheme, the function relationship between the voltage change and the capacity change between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode can be established, and the function relationship can be used to obtain the capacity change of the positive electrode side after the corresponding voltage change.

[0041] Step 1022: Establish a function relationship between the negative electrode voltage change and the capacity change; wherein the negative electrode voltage change is the voltage change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode. Specifically, the voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode is collected at the time point when the reference battery reaches the first voltage, denoted as V21; the voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode is collected at the time point when the reference battery reaches the second voltage, denoted as V21'; and the corresponding voltage V2 is recorded every certain current integral capacity dQ in the process 11 , V2 12 , V2 13 ……V2 1n ; wherein V2 11 =V21, V2 1n =V21'; a function relationship between the negative electrode voltage change and the capacity change is established: dq2=g(dv2)=d*(dv2) 2 +e*(dv2)+f; wherein dv2 series are V2 12 -V2 11 , V2 13 -V2 11 ……V2 1n -V2 11 , dq2 series are dQ, 2dQ, 3dQ, (n-1)*dQ; d, e, f are parameters to be identified, and the parameters are identified by the least square method. Through the above technical scheme, the function relationship between the voltage change and the capacity change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode can be established, and the function relationship can be used to obtain the capacity change of the negative electrode side after the corresponding voltage change.

[0042] Through steps 1021 and 1022, the function relationships between the voltage change and the capacity change between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode and between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode are established, respectively, which can distinguish the capacity change between the positive electrode and the negative electrode, and provide a basis for subsequent judgment of irreversible capacity and reversible capacity.

[0043] Step 103: in a subsequent running stage, a current capacity integral is obtained by integrating the current in the first voltage-second voltage interval of the reference battery, and based on the function relationship between the voltage change of the positive and negative electrodes and the capacity change established in the calibration stage, the current positive and negative electrode capacity change is obtained according to the current positive and negative electrode voltage change. Specifically, the voltage signals V12, V12' between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode when the reference battery reaches the first voltage and the second voltage in the current cycle are obtained; the current positive electrode voltage change AV12 = V12-V12' is calculated; AV12 is substituted into the function dq1 = f(dv1) to obtain the current positive electrode capacity change AQ pos =f(ΔV12); the voltage signals V22, V22' between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode when the reference battery reaches the first voltage and the second voltage in the current cycle are obtained; the current negative electrode voltage change AV22 = V22-V22' is calculated; AV22 is substituted into the function dq2 = g(dv2) to obtain the current negative electrode capacity change AQ neg =g(ΔV22).

[0044] Step 104: the ratio of the current capacity integral to the reference capacity integral is taken as the health state of the current system as a whole, and the difference between the current positive and negative electrode capacity changes is taken as the irreversible capacity, and the rest is reversible capacity. Specifically, the difference between the current positive and negative electrode capacity changes is taken as the irreversible capacity DQ irrev =|(|ΔQ pos |−|ΔQ neg |)|.

[0045] Through steps 103 and 104, based on the voltage signal change between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode, the current positive electrode capacity change on the positive electrode side can be obtained based on the foregoing function; similarly, based on the voltage signal change between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode, the current negative electrode capacity change on the negative electrode side can be obtained based on the foregoing function; and then the irreversible capacity is obtained by the difference between the current positive electrode capacity change and the current negative electrode capacity change, realizing the distinction between the irreversible capacity and the reversible capacity.

[0046] By adopting the above technical solution, the reference battery, the positive electrode of the auxiliary electrode and the negative electrode of the auxiliary electrode are set, the reference capacity integral and the function relationship between the voltage change of the positive and negative electrodes and the capacity change are established in the calibration stage; after obtaining the current capacity integral in the subsequent running stage, the health state of the current system as a whole can be directly calculated, and after obtaining the current positive and negative electrode voltage change, the current positive and negative electrode capacity change can be obtained according to the function relationship between the voltage change of the positive and negative electrodes and the capacity change in the foregoing, and then the irreversible capacity and the reversible capacity are calculated according to the current positive and negative electrode capacity change. The above scheme can realize accurate evaluation of the online health state of the all-vanadium redox flow battery system, and can distinguish the reversible capacity and the irreversible capacity.

[0047] In some embodiments, further comprising: after the mixing or refilling operation, re-performing the calibration phase and the subsequent running phase. Through the above technical solution, when the system restores the valence balance and concentration uniformity of the electrolyte through the mixing or refilling operation, the previously identified characteristic functions f(dv1) and g(dv2) may deviate from the actual function of voltage versus capacity, including the reference capacity will also change, so the parameter self-correction process needs to be performed, the calibration phase is re-performed, and a new round of parameters are obtained to ensure the accuracy and continuity of the SOH estimation.

[0048] In some embodiments, further comprising: in the calibration phase, collecting the voltage V41 between the auxiliary electrode positive electrode and the auxiliary electrode negative electrode; in the subsequent running phase, periodically collecting the voltage V4 n ; ΔV4 = |V4 n -V41|, when ΔV4 exceeds the preset threshold, an alarm is issued, and the voltage V4 n is restored to the V41 state through external operation. Through the above technical solution, although data collection is performed for a short time at a specific sampling time, the potential of the auxiliary electrode positive electrode and the auxiliary electrode negative electrode may still drift due to ion migration or local concentration difference in long-term operation, thereby affecting the subsequent voltage sampling accuracy and SOH estimation stability; therefore, the state monitoring and self-maintenance mechanism of the auxiliary electrode positive electrode and the auxiliary electrode negative electrode is introduced, and after the voltage change value between the auxiliary electrode positive electrode and the auxiliary electrode negative electrode exceeds the preset threshold, the voltage between the auxiliary electrode positive electrode and the auxiliary electrode negative electrode is restored through manual electrolyte supplement or oxidation-reduction. Embodiment 2

[0049] Based on the online evaluation method of the health state of the vanadium flow battery provided in embodiment 1, the online evaluation system of the health state of the vanadium flow battery is provided in this embodiment 2, and the online evaluation method of the health state of the vanadium flow battery is applied as described in embodiment 1.

[0050] Reference Figure 3 As shown in the figure, the online evaluation system of the health state of the vanadium flow battery of the present application includes a main stack, a reference battery, an auxiliary electrode positive electrode, an auxiliary electrode negative electrode, and a control and calculation module.

[0051] Among them, the main stack is a full vanadium flow battery stack, which includes a positive electrode chamber and a negative electrode chamber, and is connected with positive and negative electrolyte circulation systems respectively. Specifically, the main stack positive electrode is connected with the positive electrolyte tank, and the main stack negative electrode is connected with the negative electrolyte tank.

[0052] The reference battery is a complete full battery, and the corresponding liquid path is connected in parallel with the liquid path of the positive and negative electrolyte of the main stack. Specifically, the positive electrode of the reference battery is connected to the positive electrode of the main stack through a liquid path, and the negative electrode of the reference battery is connected to the negative electrode of the main stack through a liquid path.

[0053] The auxiliary electrode positive electrode and the auxiliary electrode negative electrode are two half batteries, and the liquid paths thereof are connected to the positive and negative electrode liquid paths of the reference battery through electromagnetic valves, and the positive and negative electrode chambers store electrolyte corresponding to a certain SOC, for example, the positive electrode stores VO2 + and V 2+ electrolyte, and the negative electrode stores V 3+ and V 2+ electrolyte. Specifically, the auxiliary electrode positive electrode is connected to the positive electrode of the reference battery through a liquid path, and a first electromagnetic valve is arranged on the liquid path; the auxiliary electrode negative electrode is connected to the negative electrode of the reference battery through a liquid path, and a second electromagnetic valve is arranged on the liquid path; the auxiliary electrode positive electrode is connected to the auxiliary electrode negative electrode through a liquid path, and a third electromagnetic valve is arranged on the liquid path.

[0054] For the above-mentioned liquid path connection and electromagnetic valve control structure, the reference battery and the auxiliary electrode are connected through a controllable liquid path, which specifically includes the following liquid paths. Reference positive electrode liquid path: the positive electrode of the reference battery is connected to the positive electrode of the main stack through a liquid path; at the same time, the positive electrode of the reference battery is connected to the positive electrode of the auxiliary electrode through a liquid path, and a first electromagnetic valve S1 is arranged on the liquid path for controlling the on-off. Reference negative electrode liquid path: the negative electrode of the reference battery is connected to the negative electrode of the main stack through a liquid path, and at the same time, the negative electrode of the reference battery is connected to the negative electrode of the auxiliary electrode through a liquid path, and a second electromagnetic valve S2 is arranged on the liquid path for controlling the on-off. Auxiliary electrode mutual liquid path: the positive electrode of the auxiliary electrode and the negative electrode of the auxiliary electrode are provided with a mutual liquid path, and a third electromagnetic valve S3 is arranged on the liquid path for controlling the on-off of the electrolyte channel between the two auxiliary electrodes. The liquid path pipes of the positive electrode of the reference battery and the positive electrode of the auxiliary electrode, the pipes connected between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode, and the auxiliary electrode mutual liquid path can be designed by using ion communication U-shaped pipes to minimize the ion mutual interference during voltage sampling when the electromagnetic valve is turned on.

[0055] The control and calculation module is used for controlling the instantaneous switching of each electromagnetic valve and collecting the voltage between each liquid path at the corresponding time, and calculating the health state and distinguishing the reversible capacity and the irreversible capacity through the voltage change and the capacity increment. Specifically, the control and calculation module is used for collecting the following signals: the voltage V1 between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode; the voltage V2 between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode; the voltage V3 between the positive electrode and the negative electrode of the reference battery; and the voltage V4 between the positive electrode of the auxiliary electrode and the negative electrode of the auxiliary electrode. The control and calculation module collects the system current, calculates the charge integral, and controls the switching time sequence of each electromagnetic valve according to the set strategy, opens the electromagnetic valve to establish the instantaneous ion channel at the specified sampling time, closes immediately after collecting the voltage, and operates the voltage change and the capacity increment to calculate the SOH.

[0056] Through the above technical solution, the main electric pile, the reference battery, the positive electrode of the auxiliary electrode and the negative electrode of the auxiliary electrode are connected through the liquid path, the switching of each liquid path is controlled through the electromagnetic valve arranged on the liquid path, the instantaneous switching of each electromagnetic valve is realized through the control and calculation module to collect the corresponding data, and then the health state of the whole system is calculated through the collected data and the reversible capacity and the irreversible capacity are distinguished.

[0057] Reference Figure 4 As shown in the figure, the specific operation process of the control and calculation module includes the following steps.

[0058] (1) System initialization and SOH = 100% reference establishment.

[0059] In the initial running or offline calibration stage of the system (which can be understood as the state of SOH = 100%), within the specified temperature and flow range, in the set voltage interval (the overall voltage of the reference battery changes from V3 to V3'), the charging or discharging process is carried out, and the following steps are sequentially performed in this process: 1. Open the electromagnetic valve S1 between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode on the liquid path at the time point when the corresponding reference battery reaches the voltage V3, collect the voltage signal V11 between them, and close the electromagnetic valve S1 after the collection is completed, open the electromagnetic valve S1 between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode on the liquid path again at the time point when the corresponding reference battery reaches the voltage V3', collect the voltage V11' between them, and close the electromagnetic valve S1 after the collection is completed, and obtain the corresponding pressure difference AV11 = V11-V11', and at the same time, every certain current integral capacity dQ (dQ is as small as possible, which is determined according to the ability of the control and calculation module and the actual current integral interval, or the entire interval can be equally divided according to experience) is recorded during the process. The corresponding voltage V1 11 , V1 12 , V1 13 ……V1 1n ; wherein, V1 11=V11, V1 1n =V11'.

[0060] 2. Open the electromagnetic valve S2 between the reference battery negative electrode and the auxiliary electrode negative electrode at the corresponding time point of the previous step, collect the corresponding voltage signals V21 and V21', and obtain the corresponding pressure difference AV21 = V21 - V21' and the corresponding dq voltage point V2 11 , V2 12 , V2 13 … V2 1n ; wherein V2 11 = V21, V2 1n = V21'.

[0061] 3. After the system is running normally and in the subsequent periodic cycles, open the electromagnetic valve S3 between the auxiliary electrode positive electrode and the auxiliary electrode negative electrode, and collect the voltage signals V41 between the two.

[0062] In the above process, the corresponding electromagnetic valve should be closed immediately after the voltage collection is completed to isolate the ion channel and avoid electrochemical interference between different half-cells. The control and calculation module obtains the capacity increment DQ 100 by integrating the current in the voltage V3 and V3' interval, which is the reference capacity integral when SOH = 100%. The reference capacity contains reversible (recoverable) capacity and irreversible (lost) capacity, which provides a reference for subsequent SOH estimation. In order to reduce the calculation error, the interval of V3 and V3' can be appropriately expanded, for example, the voltage range interval corresponding to 50% capacity and 100% capacity.

[0063] (2) Parameter identification of voltage to capacity change.

[0064] The parameter identification of the function relationship between the changes of V1 1n and V2 1n and the capacity is as follows: dq1 = f (dv1) = a * (dv1) 2 + b * (dv1) + c; wherein dv1 is a sequence of V1 12 - V1 11 , V1 13 - V1 11 … V1 1n - V1 11 , and dq1 is a sequence of dQ, 2dQ, 3dQ … (n-1) * dQ; a, b, c are parameters to be identified, which can be identified by the least square method.

[0065] Similarly, the Q2 function can be identified: dq2 = g(dv2) = d*(dv2) + e*(dv2) + f; wherein dv2 is a sequence of V2 2 + e*(dv2) + f; wherein dv2 is a sequence of V2 12 -V2 11 , V2 13 -V2 11 … V2 1n -V2 11 , dq2 is a sequence of dQ, 2dQ, 3dQ, …, (n-1)*dQ; d, e, f are parameters to be identified, and the parameters are identified by the least square method.

[0066] (3) SOH estimation in the running stage.

[0067] In each subsequent charging and discharging process of the system, when the reference battery voltage reaches the V3 to V3' point, and the operating conditions (temperature, flow, etc.) meet the same flow and temperature range as the initial collection, control the electromagnetic valve to periodically open and close according to the steps and collect the voltage at each point: 1. Open and close the reference battery positive electrode and auxiliary electrode positive electrode liquid road electromagnetic valve S1, collect the corresponding voltage V12 and V12', and calculate the voltage change AV12 = V12-V12' in this interval; 2. Open and close the reference battery negative electrode and auxiliary electrode negative electrode liquid road electromagnetic valve S2, collect the corresponding voltage V22 and V22', and calculate the voltage change AV22 = V22-V22' in this interval; 3. Open and close the auxiliary electrode liquid road electromagnetic valve S3, collect the voltage V4; 4. Synchronously collect the current in the voltage range of the reference battery voltage V3 to V3' and perform capacity integration to obtain the capacity increment DQ corresponding to this cycle n . Take the ratio of the current capacity integration DQ n to the reference capacity integration DQ 100 as the current system SOH total : SOH total = DQ n / DQ 100 x 100%; SOH total = SOH reversible + SOH irreversible ; Wherein SOH total contains two parts, one part is the reversible (recoverable) capacity SOH reversible , which can be recovered by mixing the positive and negative electrode electrolyte, and the other part is the irreversible (non-recoverable) capacity SOH irreversible, the part capacity can not be restored by mixing liquid, etc., and needs to be restored to the initial state by re-supplementing vanadium ions.

[0068] (4) Calculation of reversible capacity and irreversible capacity.

[0069] The reversible part of the capacity is caused by the energy mutual series of the positive and negative electrolyte. If there is no loss of vanadium ions, the change of the concentration of vanadium ions at one pole must be symmetrical to the change of the concentration of vanadium ions at the other pole, and then reflected in the change of the available capacity. The mapping functions f(dv) and g(dv) identified before are used to calculate the respective capacity changes of the positive and negative electrodes: ΔQ pos =f(ΔV12); ΔQ neg =g(ΔV22); If |ΔQ pos |≈|ΔQ neg |, it indicates that the concentration changes of vanadium ions on both sides are relatively consistent, and the change of the system capacity is mainly caused by the migration of vanadium ions, which are all reversible capacity.

[0070] If |ΔQ pos | and |ΔQ neg | differ greatly (the difference threshold can be determined by the maximum error of the identified functions f() and g() and the actual test quantity), there is a loss of irreversible part, and the capacity loss of the irreversible part can be calculated by the following formula: DQ irrev =|(|ΔQ pos |−|ΔQ neg |)|; SOH irreversible =DQ irrev / DQ 100 ×100%; In this way, the total SOH, reversible SOH and irreversible SOH of the current battery are calculated in real time during the operation of the system. Thus, the system provides a reference for maintenance schemes such as mixing liquid or gradient utilization, electrolyte supplement, etc.

[0071] (5) Self-correction scheme after mixing or refilling.

[0072] When the system restores the valence balance and concentration uniformity of the electrolyte by mixing or refilling, the characteristic functions f(dv1) and g(dv2) identified before may have deviated from the actual function of voltage to capacity, including the initial capacity DQ 100The values ​​can also change, so a parameter self-correction process needs to be performed to ensure the accuracy and continuity of the SOH estimation. For example, initialize the SOH to 100%, and re-acquire data according to step (1), and perform parameter identification according to step (2).

[0073] (6) Auxiliary reference electrode status monitoring and self-maintenance mechanism.

[0074] Although the solenoid valve only opens briefly at specific sampling moments, potential drift at the positive and negative electrodes of the auxiliary electrode can still occur during long-term operation due to ion migration or local concentration differences, thus affecting the accuracy of subsequent voltage sampling and the stability of SOH estimation. Therefore, this application introduces a state monitoring and self-maintenance mechanism for the positive and negative electrodes of the auxiliary electrode, as follows: The voltage V41 collected in step (1) should remain stable for a period of time; during system operation, the voltage state V4 between the positive and negative electrodes of the auxiliary electrode should be collected periodically (e.g., every few cycles or after each mixing). n And compared with V41, ΔV4=|V4 n -V41|, when ΔV4 exceeds a preset threshold (e.g., 10mV~20mV, specifically determined based on the SOC-OCV data and allowable error), it is determined that the auxiliary reference electrode has significant ion crosstalk or concentration imbalance. When the above phenomenon occurs, it can be restored by manually replenishing the electrolyte or by redox reactions, so that the sampling voltage value of V4 returns to the V41 state.

[0075] In summary, this application achieves accurate state of health (SOH) determination and dynamic correction of vanadium redox flow batteries in different operating cycles by introducing an auxiliary reference electrode system, capacity integration benchmark calibration, and reversible / irreversible capacity separation and correction algorithm, which has the following beneficial effects.

[0076] 1. This application establishes an adaptive benchmark of steady-state SOH=100% through capacity integration, realizing a unified health assessment standard under different cyclic conditions.

[0077] 2. By establishing a mathematical function for voltage range and capacity change through the dv–dq relationship, the reversible and irreversible capacities of the vanadium redox flow battery can be accurately separated and determined.

[0078] 3. By recalibrating the dv–dq parameters after mixing or refilling, the algorithm can adaptively correct the function parameters and maintain the accuracy of SOH calculation.

[0079] 4. By monitoring the voltage drift of the positive and negative electrodes of the auxiliary electrode and performing liquid replenishment or redox maintenance, the stability of the auxiliary reference electrode potential and the accuracy of the measurement are ensured.

[0080] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. An online method for evaluating the state of health of a vanadium flow battery, characterized in that, The method comprises the following steps: setting a reference battery, an auxiliary electrode positive electrode and an auxiliary electrode negative electrode; wherein the reference battery is connected in parallel with the main stack, and the auxiliary electrode positive electrode and the auxiliary electrode negative electrode are connected with the positive and negative electrodes of the reference battery, respectively; in the calibration stage, the current is integrated to obtain a reference capacity integral in the first voltage to the second voltage interval of the reference battery, and a function relationship between the positive and negative electrode voltage changes and the capacity changes is established; in the subsequent operation stage, the current is integrated to obtain a current capacity integral in the first voltage to the second voltage interval of the reference battery, and based on the function relationship between the positive and negative electrode voltage changes and the capacity changes established in the calibration stage, the current positive and negative electrode capacity changes are obtained according to the current positive and negative electrode voltage changes; the ratio of the current capacity integral to the reference capacity integral is taken as the health state of the current system as a whole, and the difference between the current positive and negative electrode capacity changes is taken as the irreversible capacity, and the rest is reversible capacity.

2. The method for on-line evaluation of the state of health of a vanadium flow battery according to claim 1, characterized in that, The first voltage and the second voltage are the voltages between the positive and negative electrodes of the reference battery.

3. The method for on-line evaluation of the state of health of a vanadium flow battery according to claim 1, characterized in that, The establishment of the function relationship between the positive and negative electrode voltage changes and the capacity changes specifically comprises: establishing a function relationship between the positive electrode voltage change and the capacity change; wherein the positive electrode voltage change is the voltage change between the positive electrode of the reference battery and the auxiliary electrode positive electrode; establishing a function relationship between the negative electrode voltage change and the capacity change; wherein the negative electrode voltage change is the voltage change between the negative electrode of the reference battery and the auxiliary electrode negative electrode.

4. The method for on-line evaluation of the state of health of a vanadium flow battery according to claim 3, characterized in that, The establishment of the function relationship between the positive electrode voltage change and the capacity change specifically comprises: The voltage signal between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode is collected at the time point when the reference battery reaches the first voltage, denoted as V11; the voltage signal between the positive electrode of the reference battery and the positive electrode of the auxiliary electrode is collected at the time point when the reference battery reaches the second voltage, denoted as V11'; and the corresponding voltage V1 is recorded every certain current integral capacity dQ in the process 11 , V1 12 , V1 13 ……V1 1n ; wherein V1 11 = V11, V1 1n = V11'. establishing a function relationship between the positive electrode voltage change and the capacity change: dq1 = f (dv1) = a * (dv1) + b * (dv1) + c; wherein dv1 is a sequence of V1 2 + b * (dv1) + c; wherein dv1 is a sequence of V1 12 - V1 11 , V1 13 - V1 11 ... V1 1n - V1 11 , dq1 is a sequence of dQ, 2dQ, 3dQ,... (n-1) * dQ; a, b, c are parameters to be identified, and the parameters are identified by a least square method.

5. The method for on-line evaluation of the state of health of a vanadium flow battery according to claim 4, characterized in that, The establishment of the function relationship between the negative electrode voltage change and the capacity change specifically comprises: The voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode at the time point when the reference battery reaches the first voltage is collected and recorded as V21; the voltage signal between the negative electrode of the reference battery and the negative electrode of the auxiliary electrode at the time point when the reference battery reaches the second voltage is collected and recorded as V21'; and the corresponding voltage V2 is recorded every certain current integral capacity dQ in the process 11 , V2 12 , V2 13 ……V2 1n ; wherein V2 11 = V21, V2 1n = V21'. establishing a function relationship between the negative electrode voltage change and the capacity change: dq2 = g(dv2) = d*(dv2) + e*(dv2) + f; wherein dv2 is a sequence of V2 2 + e*(dv2) + f; wherein dv2 is a sequence of V2 12 - V2 11 , V2 13 - V2 11 ... V2 1n - V2 11 , dq2 is a sequence of dQ, 2dQ, 3dQ,... (n-1)*dQ; d, e, f are parameters to be identified, and the parameters are identified by a least square method.

6. The method for on-line evaluation of the state of health of a vanadium flow battery according to claim 5, characterized in that, The establishment of the function relationship between the positive and negative electrode voltage changes and the capacity changes based on the calibration stage, and the current positive and negative electrode capacity changes obtained according to the current positive and negative electrode voltage changes specifically comprise: obtaining the voltage signals V12, V12' between the positive electrode of the reference battery and the auxiliary electrode positive electrode when the reference battery reaches the first voltage and the second voltage in the current cycle, respectively; The current positive electrode voltage change AV12 = V12 - V12' is calculated; AV12 is substituted into the function of dq1 = f(dv1) to obtain the current positive electrode capacity change AQ pos = f(AV12). obtaining the voltage signals V22, V22' between the negative electrode of the reference battery and the auxiliary electrode negative electrode when the reference battery reaches the first voltage and the second voltage in the current cycle, respectively; The current negative electrode voltage change AV22 = V22 - V22' is calculated; AV22 is substituted into the function of dq2 = g(dv2) to obtain the current negative electrode capacity change AQ neg = g(AV22). The difference between the current positive and negative capacity changes as the irreversible capacity specifically includes: irreversible capacity DQ irrev = | ( | ΔQ pos | - | ΔQ neg | ) |.

7. The method for on-line evaluation of the state of health of a vanadium flow battery according to any of claims 1 to 6, characterized in that Further comprising: After the mixing or refilling operation is performed, the calibration stage and the subsequent operation stage are performed again.

8. The method for on-line evaluation of the state of health of a vanadium flow battery according to any of claims 1 to 6, characterized in that Further comprising: In the calibration stage, the voltage V41 between the auxiliary electrode positive electrode and the auxiliary electrode negative electrode is collected. In a subsequent operating phase, the voltage V4 between the auxiliary electrode positive and the auxiliary electrode negative is periodically acquired n ; AV4 = |V4 n - V41, when AV4 exceeds a preset threshold, an alarm is issued, and the voltage V4 n is restored to the V41 state by external operation.

9. An online evaluation system of the state of health of a vanadium flow battery, applying the online evaluation method of the state of health of a vanadium flow battery according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: The positive electrode of the reference battery is connected with the positive electrode of the main stack through a liquid path, and the negative electrode of the reference battery is connected with the negative electrode of the main stack through a liquid path; The auxiliary electrode positive electrode is connected with the positive electrode of the reference battery through a liquid path, and a first electromagnetic valve is arranged on the liquid path; the auxiliary electrode negative electrode is connected with the negative electrode of the reference battery through a liquid path, and a second electromagnetic valve is arranged on the liquid path; the auxiliary electrode positive electrode is connected with the auxiliary electrode negative electrode through a liquid path, and a third electromagnetic valve is arranged on the liquid path; The control and calculation module is used for controlling the instantaneous switching of each electromagnetic valve and collecting the voltage between each liquid path at the corresponding time, and calculating the health state and distinguishing the reversible capacity and the irreversible capacity through the voltage change and the capacity increment.

10. The system for online assessment of state of health of a vanadium flow battery of claim 9, wherein, The auxiliary electrode positive electrode and the auxiliary electrode negative electrode are both half batteries, and corresponding electrolytes are arranged in the positive electrode chamber of the auxiliary electrode positive electrode and the negative electrode chamber of the auxiliary electrode negative electrode.

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