Method and system for equalizing the state of charge of an all-vanadium liquid flow battery energy storage system

Abstract

The present application provides a method and system for balancing the state of charge of an all-vanadium liquid flow battery energy storage system. The method includes starting a liquid mixing program when it is detected that the deviation between the total SOC of the energy storage system at the current moment and the set SOC of the energy storage system is greater than a preset target; wherein the liquid mixing program includes making the backup tanks of the first battery stack and the second battery stack of the energy storage system become working tanks of the corresponding battery stacks respectively; mixing the same-level working tanks of the first battery stack and the second battery stack; after the liquid mixing is completed, the working tanks of the first battery stack and the second battery stack become the backup tanks of the corresponding battery stacks respectively. The method and system of the present application can balance the SOC value by mixing liquid while working without stopping the system, thereby improving the working efficiency of the system.

Description

Technical Field

[0001] The present application relates to, but is not limited to, the field of batteries, and in particular to a method and system for balancing the state of charge of an all-vanadium liquid flow battery energy storage system. Background Art

[0002] At present, large-scale all-vanadium liquid flow battery energy storage systems are usually composed of several stacks connected in series and parallel. Due to the characteristics of the structure of the stack itself, such as the differences in material properties and stack resistance characteristics, the charge in the electrolyte tank of the same level of each stack will deviate, resulting in an unbalanced charge, which makes the state of charge between different stacks unbalanced, and some stacks are overcharged and some stacks are undercharged. During discharge, some battery subsystems are over-discharged, while some battery subsystems are not fully discharged. Due to the short board effect, the entire battery system is unavailable, which directly affects the efficiency of the all-vanadium liquid flow battery. In order to achieve large-scale application of all-vanadium liquid flow battery systems, extend their service life, and improve economic efficiency, it is crucial to solve the problem of how to deal with the consistency of the state of charge of multiple stacks in series. The current solution is to balance the SOC through the liquid circuit. However, the current liquid circuit balancing method requires shutdown maintenance, which is complicated to operate and reduces the utilization rate and efficiency of the system.

[0003] Therefore, there is a need for a method and system for balancing the state of charge of an all-vanadium liquid flow battery energy storage system in a convenient and non-stop manner. Summary of the invention

[0004] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0005] In one aspect, the present application provides a method for balancing the state of charge (SOC) of an all-vanadium liquid flow battery energy storage system, wherein the all-vanadium liquid flow battery energy storage system comprises at least a first battery stack and a second battery stack, wherein the first battery stack and the second battery stack are each equipped with a working tank and at least one backup tank;

[0006] The method comprises detecting the state of charge of the first battery stack and the state of charge of the second battery stack in real time and calculating the total state of charge of the energy storage system at the current moment; starting a liquid mixing procedure when the deviation between the total state of charge of the energy storage system at the current moment and the set state of charge of the energy storage system is greater than a preset target;

[0007] The liquid mixing procedure includes making the spare tank of the first battery stack and the spare tank of the second battery stack become working tanks of corresponding battery stacks respectively; mixing the same-level working tanks of the first battery stack and the second battery stack; after the liquid mixing is completed, the working tank of the first battery stack and the working tank of the second battery stack become spare tanks of corresponding battery stacks respectively.

[0008] In one embodiment, the working tanks of the first battery stack include a first positive electrode electrolyte working tank and a first negative electrode electrolyte working tank, and the spare tanks of the first battery stack include a first positive electrode electrolyte spare tank and a first negative electrode electrolyte spare tank; the working tanks of the second battery stack include a second positive electrode electrolyte working tank and a second negative electrode electrolyte working tank, and the spare tanks of the second battery stack include a second positive electrode electrolyte spare tank and a second negative electrode electrolyte spare tank; mixing the same-level working tanks of the first battery stack and the second battery stack includes simultaneously mixing the first positive electrode electrolyte working tank and the second positive electrode electrolyte working tank for T1 time and mixing the first negative electrode electrolyte working tank and the second negative electrode electrolyte working tank for T2 time.

[0009] In one embodiment, the mixed solution of the first cathode electrolyte working tank and the second cathode electrolyte working tank comprises:

[0010] gradually reducing the flow rate of the positive electrolyte flowing from the first positive electrolyte working tank to the first battery stack, and gradually increasing the flow rate of the positive electrolyte flowing from the first positive electrolyte reserve tank to the first battery stack;

[0011] gradually reducing the flow rate of the positive electrolyte flowing from the second positive electrolyte working tank to the second battery stack, and gradually increasing the flow rate of the positive electrolyte flowing from the second positive electrolyte reserve tank to the second battery stack;

[0012] When the positive electrolyte is stopped from being transported from the first positive electrolyte working tank to the first battery stack and the positive electrolyte is stopped from being transported from the second positive electrolyte working tank to the second battery stack, the first positive electrolyte working tank and the second positive electrolyte working tank are fluidly connected to perform a liquid mixing process.

[0013] In one embodiment, the mixed solution of the first negative electrode electrolyte working tank and the second negative electrode electrolyte working tank comprises:

[0014] The mixing of the negative electrode liquid includes:

[0015] gradually reducing the flow rate of the negative electrode electrolyte flowing from the first negative electrode electrolyte working tank to the first battery stack, and gradually increasing the flow rate of the negative electrode electrolyte flowing from the first negative electrode electrolyte reserve tank to the first battery stack;

[0016] gradually reducing the flow rate of the negative electrode electrolyte flowing from the second negative electrode electrolyte working tank to the second battery stack, and gradually increasing the flow rate of the negative electrode electrolyte flowing from the second negative electrode electrolyte reserve tank to the second battery stack;

[0017] When the negative electrode electrolyte is stopped from being transported from the first negative electrode electrolyte working tank to the first battery stack and the negative electrode electrolyte is stopped from being transported from the second negative electrode electrolyte working tank to the second battery stack, the fluids of the first negative electrode electrolyte working tank and the second negative electrode electrolyte working tank are connected to perform a liquid mixing process.

[0018] In one embodiment, the mixing time T1 of the positive electrolyte is calculated by the following formula:

[0019] T1=(V1+V2) / S1,

[0020] Wherein V1 is the volume of the first positive electrode electrolyte working tank, V2 is the volume of the second positive electrode electrolyte working tank, and S1 is the mixed liquid flow rate of the positive electrode electrolyte.

[0021] In one embodiment, the mixing time T2 of the negative electrolyte is calculated by the following formula:

[0022] T2=(V'1+V'2) / S2,

[0023] Wherein V'1 is the volume of the first negative electrode electrolyte working tank, V'2 is the volume of the second negative electrode electrolyte working tank, and S2 is the mixed liquid flow rate of the negative electrode electrolyte.

[0024] In one embodiment, the preset target is that the total state of charge of the energy storage system at the current moment is greater than or equal to 80% of the set state of charge of the energy storage system.

[0025] On the other hand, the present application provides a system for equalizing the state of charge (SOC) of an all-vanadium liquid flow battery energy storage system, the system comprising:

[0026] A first battery stack, which is equipped with a first positive electrode electrolyte working tank and at least one first positive electrode electrolyte backup tank and a corresponding first negative electrode electrolyte working tank and at least one first negative electrode electrolyte backup tank;

[0027] A second battery stack, which is equipped with a second positive electrode electrolyte working tank and at least one second positive electrode electrolyte standby tank and a corresponding second negative electrode electrolyte working tank and at least one second negative electrode electrolyte standby tank;

[0028] A state of charge detection system, which is used to detect the state of charge of the first battery stack and the state of charge of the second battery stack;

[0029] a liquid level detection system, which is used to detect the liquid level height of the electrolyte in the first positive electrolyte working tank, the first positive electrolyte reserve tank, the first negative electrolyte working tank, the first negative electrolyte reserve tank, the second positive electrolyte working tank, the second positive electrolyte reserve tank, the second negative electrolyte working tank and the second negative electrolyte reserve tank;

[0030] a first positive electrode delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end of which is in fluid communication with the first positive electrode electrolyte working tank;

[0031] a first positive electrode standby delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end of which is in fluid communication with the first positive electrode electrolyte standby tank;

[0032] a second positive electrode delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end of which is in fluid communication with the second positive electrode electrolyte working tank;

[0033] a second positive electrode standby delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end of which is in fluid communication with the second positive electrode electrolyte standby tank;

[0034] a positive electrode interconnecting pipeline, one end of which is in fluid communication with the first positive electrode electrolyte working tank and the other end of which is in fluid communication with the second positive electrode electrolyte working tank;

[0035] a positive electrode standby interconnecting pipeline, one end of which is in fluid communication with the first positive electrode electrolyte standby tank and the other end of which is in fluid communication with the second positive electrode electrolyte standby tank;

[0036] a first negative electrode delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end of which is in fluid communication with the first negative electrode electrolyte working tank;

[0037] a first negative electrode backup delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end of which is in fluid communication with the first negative electrode electrolyte backup tank;

[0038] a second negative electrode delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end of which is in fluid communication with the second negative electrode electrolyte working tank;

[0039] a second negative electrode backup delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end of which is in fluid communication with the second negative electrode electrolyte backup tank;

[0040] a negative electrode interconnecting pipeline, one end of which is in fluid communication with the first negative electrode electrolyte working tank and the other end of which is in fluid communication with the second negative electrode electrolyte working tank;

[0041] a negative electrode standby interconnecting pipeline, one end of which is in fluid communication with the first negative electrode electrolyte standby tank and the other end of which is in fluid communication with the second negative electrode electrolyte standby tank;

[0042] a control system electrically connected to the detection system, the first positive electrode delivery pipeline, the first positive electrode backup delivery pipeline, the second positive electrode delivery pipeline, the second positive electrode backup delivery pipeline, the first negative electrode delivery pipeline, the first negative electrode backup delivery pipeline, the second negative electrode delivery pipeline, the second negative electrode backup delivery pipeline, the positive electrode interconnection pipeline, the positive electrode backup interconnection pipeline, the negative electrode interconnection pipeline, and the negative electrode backup interconnection pipeline;

[0043] When the control system determines, based on the SOC value detected by the detection device, that the deviation between the total SOC of the energy storage system at the current moment and the set SOC of the energy storage system is greater than or equal to a preset target, the mixing program is started, and the mixing program includes simultaneously mixing the first positive electrode electrolyte working tank with the second positive electrode electrolyte working tank for a time T1 and mixing the first negative electrode electrolyte working tank with the second negative electrode electrolyte working tank for a time T2.

[0044] In one embodiment, the control system performs the mixing of the positive electrode liquid, including:

[0045] The control system gradually reduces the flow rate of the positive electrolyte flowing from the first positive electrolyte working tank to the first fuel cell stack, and gradually increases the flow rate of the positive electrolyte flowing from the first positive electrolyte reserve tank to the first fuel cell stack;

[0046] The control system gradually reduces the flow rate of the positive electrolyte flowing from the second positive electrolyte working tank to the second battery stack, and gradually increases the flow rate of the positive electrolyte flowing from the second positive electrolyte reserve tank to the second battery stack;

[0047] When the control system stops delivering positive electrolyte to the first battery stack via the first positive electrode delivery pipeline and stops delivering positive electrolyte to the second battery stack via the second positive electrode delivery pipeline, the positive electrode interconnecting pipeline is opened to allow the first positive electrode electrolyte working tank and the second positive electrode electrolyte working tank to mix.

[0048] In one embodiment, the control system performs the mixing of the negative electrode solution, including:

[0049] The control system gradually reduces the flow rate of the negative electrode electrolyte flowing from the first negative electrode electrolyte working tank to the first battery stack, and gradually increases the flow rate of the negative electrode electrolyte flowing from the first negative electrode electrolyte reserve tank to the first battery stack;

[0050] The control system gradually reduces the flow rate of the negative electrode electrolyte flowing from the second negative electrode electrolyte working tank to the second battery stack, and gradually increases the flow rate of the negative electrode electrolyte flowing from the second negative electrode electrolyte reserve tank to the second battery stack;

[0051] When the control system stops delivering negative electrode electrolyte to the first battery stack via the first negative electrode delivery pipeline and stops delivering negative electrode electrolyte to the second battery stack via the second negative electrode delivery pipeline, the negative electrode interconnecting pipeline is opened to allow the first negative electrode electrolyte working tank and the second negative electrode electrolyte working tank to mix.

[0052] The method and system of the present application can balance the SOC value by mixing liquid while working without stopping the system, can respond to the power grid and perform charging and discharging in a timely manner, and greatly improve the working efficiency of the system.

[0053] The present application controls the electrolyte of different electrode storage tanks of the same level in real time, thereby maintaining the SOC balance between the battery stacks, thereby extending the service life of the liquid flow battery energy storage system and improving its utilization efficiency.

[0054] This application is aimed at adjusting the SOC balance between different electrode liquid tanks of the same level in a liquid flow battery energy storage system. The method and system of this application can not only greatly shorten the corresponding time in the grid dispatching process, but also reduce the number of shutdowns and the duration of liquid mixing, and can avoid the power reduction of the liquid flow energy storage system due to excessive SOC differences between liquid flow units.

[0055] Other features and advantages of the present application will be described in the following description, and partly become apparent from the description, or be understood by implementing the present application. Other advantages of the present application can be invented and obtained by the schemes described in the description. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The accompanying drawings are used to provide an understanding of the technical solution of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present application and do not constitute a limitation on the technical solution of the present application.

[0057] Figure 1 A schematic diagram of a system for equalizing the state of charge of an all-vanadium liquid flow battery energy storage system provided for an exemplary embodiment of the present disclosure;

[0058] Figure 2 A schematic flow chart of a method for equalizing the state of charge of an all-vanadium liquid flow battery energy storage system is provided for an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solution and advantages of the present application more clear, the embodiments of the present application are described in detail below. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other arbitrarily without conflict.

[0060] The present application provides a method for balancing the state of charge of an all-vanadium liquid flow battery energy storage system, wherein the all-vanadium liquid flow battery energy storage system comprises at least a first battery stack and a second battery stack, wherein the first battery stack and the second battery stack are respectively equipped with a working tank and at least one backup tank; wherein the method comprises detecting the state of charge of the first battery stack and the state of charge of the second battery stack in real time and calculating the total state of charge of the energy storage system at the current moment; when the deviation between the total state of charge of the energy storage system at the current moment and the set state of charge of the energy storage system is greater than a preset target, starting a liquid mixing program; wherein the liquid mixing program comprises making the backup tank of the first battery stack and the backup tank of the second battery stack become working tanks of the corresponding battery stacks respectively; mixing the same-level working tanks of the first battery stack and the second battery stack; after the liquid mixing is completed, the working tank of the first battery stack and the working tank of the second battery stack become the backup tanks of the corresponding battery stacks respectively.

[0061] Specifically, the method for balancing the state of charge of the all-vanadium liquid flow battery energy storage system provided in the present application may include real-time detection of the SOC of the first battery stack 100 and the SOC of the second battery stack 200 and calculation of the total SOC of the energy storage system at the current moment; starting a liquid mixing program when the deviation between the total SOC of the energy storage system at the current moment and the set SOC is greater than a preset target; connecting the spare tanks of each battery stack to the corresponding battery stack to become their respective working tanks; when it is monitored that the liquid level of the initial working tank reaches the initial height, disconnecting each initial working tank from the corresponding battery stack fluid (that is, the electrolyte in each initial working tank no longer flows into the corresponding battery stack); mixing the initial working tanks of the same level of each battery stack; and making the initial working tank of each battery stack the spare tank of the corresponding battery stack.

[0062] The present application also provides a system for balancing the state of charge of an all-vanadium liquid flow battery energy storage system, comprising: a first battery stack, which is equipped with a first positive electrode electrolyte working tank and at least one first positive electrode electrolyte backup tank and a corresponding first negative electrode electrolyte working tank and at least one first negative electrode electrolyte backup tank; a second battery stack, which is equipped with a second positive electrode electrolyte working tank and at least one second positive electrode electrolyte backup tank and a corresponding second negative electrode electrolyte working tank and at least one second negative electrode electrolyte backup tank; a state of charge detection system, which is used to detect the state of charge of the first battery stack and the state of charge of the second battery stack; a liquid level detection system, which is used to detect the first positive electrode electrolyte working tank, the first positive electrode electrolyte backup tank, the first negative electrode electrolyte The liquid levels of the electrolytes in the working tank, the first negative electrode electrolyte reserve tank, the second positive electrode electrolyte working tank, the second positive electrode electrolyte reserve tank, the second negative electrode electrolyte working tank and the second negative electrode electrolyte reserve tank; the first positive electrode delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end is in fluid communication with the first positive electrode electrolyte working tank; the first positive electrode reserve delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end is in fluid communication with the first positive electrode electrolyte reserve tank; the second positive electrode delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end is in fluid communication with the second positive electrode electrolyte working tank; the second positive electrode reserve delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end is in fluid communication with the second positive electrode electrolyte reserve tank; a first cathode intercommunication pipeline, one end of which is in fluid communication with the first cathode electrolyte working tank and the other end of which is in fluid communication with the second cathode electrolyte working tank; a first cathode standby intercommunication pipeline, one end of which is in fluid communication with the first cathode electrolyte standby tank and the other end of which is in fluid communication with the second cathode electrolyte standby tank; a first cathode delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end of which is in fluid communication with the first cathode electrolyte working tank; a first cathode standby delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end of which is in fluid communication with the first cathode electrolyte standby tank; a second cathode delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end of which is in fluid communication with the second cathode electrolyte working tank; a second cathode standby delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end is in fluid communication with the second negative electrode electrolyte reserve tank; a negative electrode interconnecting pipeline, one end of which is in fluid communication with the first negative electrode electrolyte working tank and the other end is in fluid communication with the second negative electrode electrolyte working tank; a negative electrode spare interconnecting pipeline, one end of which is in fluid communication with the first negative electrode electrolyte reserve tank and the other end is in fluid communication with the second negative electrode electrolyte reserve tank; a control system, which is electrically connected to the detection system, the first positive electrode delivery pipeline, the first positive electrode spare delivery pipeline, the second positive electrode delivery pipeline, the second positive electrode spare delivery pipeline, the first negative electrode delivery pipeline, the first negative electrode spare delivery pipeline, the second negative electrode delivery pipeline, the second negative electrode spare delivery pipeline, the positive electrode interconnecting pipeline, the positive electrode spare interconnecting pipeline, the negative electrode interconnecting pipeline and the negative electrode spare interconnecting pipeline;When the control system determines that the total state of charge of the energy storage system at the current moment deviates from the set state of charge of the energy storage system by a value of the state of charge detected by the detection device and is greater than or equal to a preset target, the liquid mixing program is started, and the liquid mixing program includes simultaneously mixing the first positive electrode electrolyte working tank with the second positive electrode electrolyte working tank for a time of T1 and mixing the first negative electrode electrolyte working tank with the second negative electrode electrolyte working tank for a time of T2. ;

[0063] Reference below Figure 1 and Figure 2 A method and system for equalizing the state of charge of an all-vanadium liquid flow battery energy storage system is described in detail.

[0064] The SOC of the first battery stack 100 and the SOC of the second battery stack 200 are monitored in real time, and the total SOC of the energy storage system at the current moment is calculated; when it is detected that the deviation between the total SOC of the energy storage system at the current moment and the set SOC of the energy storage system is greater than a preset target (the preset target may be that the total state of charge of the energy storage system at the current moment is greater than or equal to 80% of the set state of charge of the energy storage system, for example, the preset target may be that the total state of charge of the energy storage system at the current moment is 80% or 90% of the set state of charge of the energy storage system, or the preset target is a deviation less than or equal to 20%, that is, the deviation between the two may be 10% or 20%), the mixing instruction is started, i.e., the mixing program is entered.

[0065] The SOC value can be obtained by conventional methods in the art, such as by the ampere-hour integration method.

[0066]

[0067] Among them, SOC0 is the initial state of charge, I is the current charge and discharge current, t is the time, and C is the total capacity of the battery.

[0068] The change in battery capacity during this period of time is obtained by integrating the current and time, and divided by the total capacity to obtain the percentage of capacity change. The current SOC value is obtained by subtracting the capacity change percentage from the initial SOC value.

[0069] The mixing instruction may include gradually closing the positive electrode three-way valves 9, 10 and the negative electrode three-way valves 12, 13 that are fluidically connected to the first battery stack 100 (i.e., gradually disconnecting the fluid); gradually closing the positive electrode three-way valves 11, 20 and the negative electrode three-way valves 14, 15 that are fluidically connected to the second battery stack 200 (i.e., gradually disconnecting the fluid); a pressure sensor (not shown) monitors the pressure of the pipeline, at which time the circulation pump 1 that is fluidically connected to the first positive electrode electrolyte and the circulation pump 3 that is fluidically connected to the first negative electrode electrolyte will gradually reduce the frequency to maintain the pressure of the pipeline, and at this time the positive and negative circulation pumps 5, 6, 7, 8 on the other side will slowly increase the speed to maintain the flow and pressure stability in the pipeline.

[0070] The liquid levels of the first positive electrolyte working tank 110 and the second positive electrolyte working tank 210 and the first negative electrolyte working tank 120 and the second negative electrolyte working tank 220 are monitored (eg, by liquid level sensors).

[0071] In this application, it can be assumed that the volume of electrolyte corresponding to a 1MW device is V, so a 200kW device requires an electrolyte volume of V / 5. Figure 1 , the first positive electrolyte working tank 110 and the second positive electrolyte working tank 210 of the energy storage system; the first positive electrolyte reserve tank 130 and the second positive electrolyte reserve tank 230; the first negative electrolyte working tank 120 and the second negative electrolyte working tank 220; and the first negative electrolyte reserve tank 140 and the second negative electrolyte reserve tank 240 can be respectively provided with a volume of electrolyte of V / 5 (taking 200 kilowatts as an example). At this time, the bottom area of ​​the tank is known to be S, and S×h=V 罐 The relationship between the initial liquid level h of the electrolyte in the tank is obtained and used as a reference. When the battery stack starts working, the liquid levels of the first positive electrode electrolyte working tank 110 and the second positive electrode electrolyte working tank 210 and the first negative electrode electrolyte working tank 120 and the second negative electrode electrolyte working tank 220, which are in fluid communication with the first battery stack 100 and the second battery stack 200, will gradually decrease. After the mixing of the liquids begins, the liquid level of the working tank will gradually return to the initial height.

[0072] When the liquid level height of the first positive electrode electrolyte working tank 110 and the second positive electrode electrolyte working tank 210 is restored or close to the initial liquid level height h by means of the liquid level sensor 300, the three-way valves 9, 10, 20, 11, 12, 13, 14, 15 are completely closed, and the electric ball valves 16, 22, 30, 34, 19, 21, 31, 33 are closed. That is, the first positive electrode electrolyte reserve tank 130 and the second positive electrode electrolyte reserve tank 230 are completely connected to the first battery stack 100 and the second battery stack 200 (that is, they are completely fluid-connected), and become the positive electrode working tanks of each battery stack.

[0073] Next, the positive electrode interconnecting pipeline is opened to mix the positive electrode electrolytes in the first positive electrode electrolyte working tank 110 and the second positive electrode electrolyte working tank 210 . The mixing time is T1 .

[0074] The positive electrode liquid mixing process may include completely extracting the electrolyte in the second positive electrode electrolyte working tank 210 and entering the first positive electrode electrolyte working tank 110 by means of a liquid mixing pump, and then returning the electrolyte in the first positive electrode electrolyte working tank 110 to the second positive electrode electrolyte working tank 210 to achieve the positive electrode liquid mixing process. This liquid mixing method can achieve full mixing and minimize the impact on the working system.

[0075] Similarly, the negative electrode mixing process may include completely extracting the electrolyte in the second negative electrode electrolyte working tank 220 into the first negative electrode electrolyte working tank 120 with the help of a mixing pump, and then returning the electrolyte in the first negative electrode electrolyte working tank 120 to the second negative electrode electrolyte working tank 220 to realize the negative electrode mixing process.

[0076] The mixing time T1 of the positive electrolyte is calculated by the following formula:

[0077] T1=(V1+V2) / S1,

[0078] Wherein V1 is the volume of the first positive electrode electrolyte working tank, V2 is the volume of the second positive electrode electrolyte working tank, and S1 is the mixed liquid flow rate of the positive electrode electrolyte.

[0079] The mixing time T2 of the negative electrode electrolyte is calculated by the following formula:

[0080] T2=(V'1+V'2) / S2,

[0081] Wherein V'1 is the volume of the first negative electrode electrolyte working tank, V'2 is the volume of the second negative electrode electrolyte working tank, and S2 is the mixed liquid flow rate of the negative electrode electrolyte.

[0082] According to different working conditions, the volumes of the storage tanks can be the same, the flow rates of the positive and negative electrode mixed liquids can be the same, and then the mixing time T1 of the positive electrode electrolyte and the mixing time T2 of the negative electrode electrolyte can also be the same.

[0083] Generally, the mixing process can be considered complete if the calculated mixing time T1 and T2 is extended by 1 to 4 hours.

[0084] In addition, when the three-way valve opening reaches two-thirds, the electric ball valves 16, 22, 30, and 34 are opened. The purpose is that as the circulating pump gradually decreases in frequency and the standby circulating pump gradually increases in frequency, the flows in the two pipes will have an impact, increasing the loss of the circulating pump with reduced frequency. Therefore, the electric valve is opened to bypass it, and the liquid can be mixed quickly. The water pump supply ports 17, 18, 23, 24, 27, 29, 35, and 36 are single-way check valves. The purpose is to prevent the electrolyte from refluxing at the moment when the water pump stops and during the process of reducing the frequency of the water pump. At this time, part of the flow will enter the respective storage tanks through the bypass pipeline.

[0085] A flow meter is provided in the positive electrode interconnection pipeline to monitor the flow of the mixed liquid. The valve mainly controls the opening of the pipeline and replaces the pipeline. At this time, the tanks of the same level will reach a balance, and the first positive electrode electrolyte working tank 110 and the second positive electrode electrolyte working tank 210 will become the backup tanks of the first battery stack 100 and the second battery stack 200 respectively, and can be ready to be reconnected to the first battery stack and the second battery stack for work at any time.

[0086] The length of the positive electrode interconnection pipeline needs to be calculated based on the potential difference u between the first positive electrode electrolyte working tank and the second positive electrode electrolyte working tank, the current I, and the resistance R, R = pL / s, p is the resistivity of the pipeline, L is the length of the tube, and s is the cross-sectional area of ​​the pipeline. Use Ohm's law to calculate the length of the pipeline without breakdown.

[0087] In addition, during the process of issuing the mixing command, the SOC of the fuel cell stack is monitored for a delay of T+1. At this time, the fuel cell stack works based on the backup tanks of the positive and negative electrolytes.

[0088] If a deviation in the SOC value is detected at this time, the first battery stack and the second battery stack are respectively connected to the first positive electrode electrolyte working tank 110 and the second positive electrode electrolyte working tank 210 that have completed the mixing process, and the first positive electrode electrolyte working tank and the second positive electrode electrolyte working tank can become working tanks again.

[0089] On the contrary, the first positive electrode electrolyte backup tank 130 and the second positive electrode electrolyte backup tank 230 that are in operation can gradually separate from the first battery stack 100 and the second battery stack 200, and the mixing instruction is turned on the first positive electrode electrolyte backup tank 130 and the second positive electrode electrolyte backup tank 230 to perform the mixing process, so that the first positive electrode electrolyte backup tank 130 and the second positive electrode electrolyte backup tank 230 can become backup working tanks again.

[0090] Similarly, the negative electrode is mixed in the same way. For example, the working first negative electrode electrolyte backup tank 140 and the second negative electrode electrolyte backup tank 240 are gradually separated from the first battery stack 100 and the second battery stack 200. The mixing instruction is turned on the first negative electrode electrolyte backup tank 140 and the second negative electrode electrolyte backup tank 240 to perform the mixing process, so that the first negative electrode electrolyte backup tank 140 and the second negative electrode electrolyte backup tank 240 become backup working tanks again, so as to ensure that there is no shutdown during the mixing process.

[0091] Although the embodiments disclosed in this application are as above, the contents are only embodiments adopted to facilitate understanding of this application and are not intended to limit this application. Any technician in the field to which this application belongs can make any modifications and changes in the form and details of implementation without departing from the spirit and scope disclosed in this application, but the scope of protection of this application shall still be based on the scope defined by the attached claims.

Claims

1. A method for balancing the state of charge of an all-vanadium liquid flow battery energy storage system, characterized in that: The all-vanadium liquid flow battery energy storage system comprises at least a first battery stack and a second battery stack, wherein the first battery stack and the second battery stack are each equipped with a working tank and at least one backup tank; The method comprises detecting the state of charge of the first battery stack and the state of charge of the second battery stack in real time and calculating the total state of charge of the energy storage system at the current moment; starting a liquid mixing procedure when the deviation between the total state of charge of the energy storage system at the current moment and the set state of charge of the energy storage system is greater than a preset target; The liquid mixing procedure includes making the spare tank of the first battery stack and the spare tank of the second battery stack become working tanks of corresponding battery stacks respectively; mixing the same-level working tanks of the first battery stack and the second battery stack; after the liquid mixing is completed, the working tank of the first battery stack and the working tank of the second battery stack become spare tanks of corresponding battery stacks respectively.

2. The method according to claim 1, characterized in that: The working tanks of the first battery stack include a first positive electrode electrolyte working tank and a first negative electrode electrolyte working tank, and the spare tanks of the first battery stack include a first positive electrode electrolyte spare tank and a first negative electrode electrolyte spare tank; the working tanks of the second battery stack include a second positive electrode electrolyte working tank and a second negative electrode electrolyte working tank, and the spare tanks of the second battery stack include a second positive electrode electrolyte spare tank and a second negative electrode electrolyte spare tank; mixing the same-level working tanks of the first battery stack and the second battery stack includes simultaneously mixing the first positive electrode electrolyte working tank and the second positive electrode electrolyte working tank for T1 time and mixing the first negative electrode electrolyte working tank and the second negative electrode electrolyte working tank for T2 time.

3. The method according to claim 2, characterized in that The mixed liquid of the first positive electrode electrolyte working tank and the second positive electrode electrolyte working tank comprises: gradually reducing the flow rate of the positive electrolyte flowing from the first positive electrolyte working tank to the first battery stack, and gradually increasing the flow rate of the positive electrolyte flowing from the first positive electrolyte reserve tank to the first battery stack; gradually reducing the flow rate of the positive electrolyte flowing from the second positive electrolyte working tank to the second battery stack, and gradually increasing the flow rate of the positive electrolyte flowing from the second positive electrolyte reserve tank to the second battery stack; When the positive electrolyte is stopped from being transported from the first positive electrolyte working tank to the first battery stack and the positive electrolyte is stopped from being transported from the second positive electrolyte working tank to the second battery stack, the first positive electrolyte working tank and the second positive electrolyte working tank are fluidly connected to perform a liquid mixing process.

4. The method according to claim 2, characterized in that: The mixed liquid of the first negative electrode electrolyte working tank and the second negative electrode electrolyte working tank comprises: gradually reducing the flow rate of the negative electrode electrolyte flowing from the first negative electrode electrolyte working tank to the first battery stack, and gradually increasing the flow rate of the negative electrode electrolyte flowing from the first negative electrode electrolyte reserve tank to the first battery stack; gradually reducing the flow rate of the negative electrode electrolyte flowing from the second negative electrode electrolyte working tank to the second battery stack, and gradually increasing the flow rate of the negative electrode electrolyte flowing from the second negative electrode electrolyte reserve tank to the second battery stack; When the negative electrode electrolyte is stopped from being transported from the first negative electrode electrolyte working tank to the first battery stack and the negative electrode electrolyte is stopped from being transported from the second negative electrode electrolyte working tank to the second battery stack, the fluids of the first negative electrode electrolyte working tank and the second negative electrode electrolyte working tank are connected to perform a liquid mixing process.

5. The method according to claim 2, characterized in that: The mixing time T1 of the positive electrolyte is calculated by the following formula: T1=(V1+V2) / S1, Wherein V1 is the volume of the first positive electrode electrolyte working tank, V2 is the volume of the second positive electrode electrolyte working tank, and S1 is the mixed liquid flow rate of the positive electrode electrolyte.

6. The method according to claim 2, characterized in that The mixing time T2 of the negative electrode electrolyte is calculated by the following formula: T2=(V'1+V'2) / S2, Wherein V'1 is the volume of the first negative electrode electrolyte working tank, V'2 is the volume of the second negative electrode electrolyte working tank, and S2 is the mixed liquid flow rate of the negative electrode electrolyte.

7. The method according to any one of claims 1 to 6, characterized in that The preset target is that the total state of charge of the energy storage system at the current moment is greater than or equal to 80% of the set state of charge of the energy storage system.

8. A system for balancing the state of charge of an all-vanadium liquid flow battery energy storage system, characterized in that: The system comprises: A first battery stack, which is equipped with a first positive electrode electrolyte working tank and at least one first positive electrode electrolyte backup tank and a corresponding first negative electrode electrolyte working tank and at least one first negative electrode electrolyte backup tank; A second battery stack, which is equipped with a second positive electrode electrolyte working tank and at least one second positive electrode electrolyte standby tank and a corresponding second negative electrode electrolyte working tank and at least one second negative electrode electrolyte standby tank; A state of charge detection system, which is used to detect the state of charge of the first battery stack and the state of charge of the second battery stack; a liquid level detection system, which is used to detect the liquid level height of the electrolyte in the first positive electrolyte working tank, the first positive electrolyte reserve tank, the first negative electrolyte working tank, the first negative electrolyte reserve tank, the second positive electrolyte working tank, the second positive electrolyte reserve tank, the second negative electrolyte working tank and the second negative electrolyte reserve tank; a first positive electrode delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end of which is in fluid communication with the first positive electrode electrolyte working tank; a first positive electrode standby delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end of which is in fluid communication with the first positive electrode electrolyte standby tank; a second positive electrode delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end of which is in fluid communication with the second positive electrode electrolyte working tank; a second positive electrode standby delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end of which is in fluid communication with the second positive electrode electrolyte standby tank; a positive electrode interconnecting pipeline, one end of which is in fluid communication with the first positive electrode electrolyte working tank and the other end of which is in fluid communication with the second positive electrode electrolyte working tank; a positive electrode standby interconnecting pipeline, one end of which is in fluid communication with the first positive electrode electrolyte standby tank and the other end of which is in fluid communication with the second positive electrode electrolyte standby tank; a first negative electrode delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end of which is in fluid communication with the first negative electrode electrolyte working tank; a first negative electrode backup delivery pipeline, one end of which is in fluid communication with the first battery stack and the other end of which is in fluid communication with the first negative electrode electrolyte backup tank; a second negative electrode delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end of which is in fluid communication with the second negative electrode electrolyte working tank; a second negative electrode backup delivery pipeline, one end of which is in fluid communication with the second battery stack and the other end of which is in fluid communication with the second negative electrode electrolyte backup tank; a negative electrode interconnecting pipeline, one end of which is in fluid communication with the first negative electrode electrolyte working tank and the other end of which is in fluid communication with the second negative electrode electrolyte working tank; a negative electrode standby interconnecting pipeline, one end of which is in fluid communication with the first negative electrode electrolyte standby tank and the other end of which is in fluid communication with the second negative electrode electrolyte standby tank; a control system, which is electrically connected to the state of charge detection system, the liquid level detection system, the first positive electrode delivery pipeline, the first positive electrode backup delivery pipeline, the second positive electrode delivery pipeline, the second positive electrode backup delivery pipeline, the first negative electrode delivery pipeline, the first negative electrode backup delivery pipeline, the second negative electrode delivery pipeline, the second negative electrode backup delivery pipeline, the positive electrode interconnection pipeline, the positive electrode backup interconnection pipeline, the negative electrode interconnection pipeline, and the negative electrode backup interconnection pipeline; When the control system determines, based on the state of charge value detected by the state of charge detection system, that the deviation between the total state of charge of the energy storage system at the current moment and the set state of charge of the energy storage system is greater than or equal to a preset target, the mixing program is started, and the mixing program includes simultaneously mixing the first positive electrode electrolyte working tank with the second positive electrode electrolyte working tank for a time T1 and mixing the first negative electrode electrolyte working tank with the second negative electrode electrolyte working tank for a time T2.

9. The system according to claim 8, characterized in that The control system performs mixing of the positive electrolyte, including: The control system gradually reduces the flow rate of the positive electrolyte flowing from the first positive electrolyte working tank to the first fuel cell stack, and gradually increases the flow rate of the positive electrolyte flowing from the first positive electrolyte reserve tank to the first fuel cell stack; The control system gradually reduces the flow rate of the positive electrolyte flowing from the second positive electrolyte working tank to the second battery stack, and gradually increases the flow rate of the positive electrolyte flowing from the second positive electrolyte reserve tank to the second battery stack; When the control system stops delivering positive electrolyte to the first battery stack via the first positive electrode delivery pipeline and stops delivering positive electrolyte to the second battery stack via the second positive electrode delivery pipeline, the positive electrode interconnecting pipeline is opened to allow the first positive electrode electrolyte working tank and the second positive electrode electrolyte working tank to mix.

10. The system according to claim 8, characterized in that The control system performs mixing of the negative electrode electrolyte, including: The control system gradually reduces the flow rate of the negative electrode electrolyte flowing from the first negative electrode electrolyte working tank to the first battery stack, and gradually increases the flow rate of the negative electrode electrolyte flowing from the first negative electrode electrolyte reserve tank to the first battery stack; The control system gradually reduces the flow rate of the negative electrode electrolyte flowing from the second negative electrode electrolyte working tank to the second battery stack, and gradually increases the flow rate of the negative electrode electrolyte flowing from the second negative electrode electrolyte reserve tank to the second battery stack; When the control system stops delivering negative electrode electrolyte to the first fuel cell stack via the first negative electrode delivery pipeline and When the negative electrode electrolyte is stopped from being transported to the second stack via the second negative electrode transport pipeline, the negative electrode interconnecting pipeline is opened. The first negative electrode electrolyte working tank and the second negative electrode electrolyte working tank are mixed.

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