Redox flow battery system and method for operating the redox flow battery system

Abstract

To provide a redox flow battery system and an operation method for the redox flow battery system, capable of implementing stable operation.SOLUTION: A redox flow battery system 10 comprises a battery cell 100, a circulation unit 300, an open voltage measurement unit 500, and a control unit 600. The battery cell 100 includes: a positive electrode chamber 110a in which a positive electrode 105a is disposed; a negative electrode chamber 110c in which a negative electrode 105c is disposed; and a diaphragm 120 that separates the positive electrode chamber 110a and the negative electrode chamber 110c. The circulation unit 300 makes a positive electrode electrolyte PL circulate in the positive electrode chamber 110a and makes a negative electrode electrolyte NL circulate in the negative electrode chamber 110c. The open voltage measurement unit 500 measures open voltage of the battery cell 100. The control unit 600 calculates a moving average value of the open voltage measured by the open voltage measurement unit 500 depending on charge depth of the positive electrode electrolyte PL and the negative electrode electrolyte NL and, on the basis of the calculated moving average value of the open voltage, controls charging / discharging of the positive electrode electrolyte PL and the negative electrode electrolyte NL.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a redox flow battery system and a method of operating a redox flow battery system. [Background technology]

[0002] Redox flow batteries are known as large-capacity storage batteries. Redox flow batteries are charged and discharged by circulating a positive electrode electrolyte and a negative electrode electrolyte in a battery cell with an ion exchange membrane between the positive and negative electrodes. Solutions containing metals whose valence changes due to oxidation-reduction reactions are used as the positive and negative electrode electrolytes, and electrolytes containing vanadium as the active material are widely used.

[0003] In order to achieve stable operation of a redox flow battery, the charging and discharging are controlled by determining the state of charge (SOC) of the electrolyte. For example, in Patent Document 1, at least one of charging and discharging of the battery is stopped based on the open-circuit voltage obtained from an auxiliary cell used to measure the state of charge of the electrolyte. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-317788 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, the depth of charge of the electrolyte is determined from the measured value of the open-circuit voltage of the auxiliary cell (i.e., the instantaneous open-circuit voltage). When measuring the open-circuit voltage of the auxiliary cell, variations in the measured value can occur due to factors such as the route the electrolyte passes through in the auxiliary cell, variations in the valence of the active material in the electrolyte, and bubbles generated in the electrolyte, and abnormal values can also be measured. Therefore, the operating method of Patent Document 1 may not allow the redox flow battery to be operated in a sufficiently stable state.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a redox flow battery system and an operating method for a redox flow battery system that can achieve stable operation. [Means for solving the problem]

[0007] In order to achieve the above object, a redox flow battery system according to a first aspect of the present disclosure includes: a battery cell having a positive electrode chamber in which a positive electrode is placed, a negative electrode chamber in which a negative electrode is placed, and a diaphragm separating the positive electrode chamber from the negative electrode chamber; a circulation unit that circulates a positive electrode electrolyte in the positive electrode chamber and a negative electrode electrolyte in the negative electrode chamber; an open circuit voltage measurement unit that measures the open circuit voltage of the battery cell; A moving average value of the open-circuit voltage measured by the open-circuit voltage measurement unit is calculated according to the depth of charge of the positive electrode electrolyte and the negative electrode electrolyte, and based on the calculated moving average value of the open-circuit voltage, By controlling the flow rates of the positive electrode electrolyte and the negative electrode electrolyte, a control unit that controls charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte, 、 The control unit calculating a moving average value of the open-circuit voltage in a predetermined first period and a moving average value of the open-circuit voltage in a predetermined third period that is longer than the predetermined first period; controlling the flow rates of the positive electrode electrolyte and the negative electrode electrolyte to a predetermined first flow rate when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are within a predetermined range and a difference between a moving average value of the open-circuit voltage in the predetermined third period and a moving average value of the open-circuit voltage in the predetermined first period is outside a predetermined first range; When the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are within the predetermined range, and a difference between the moving average value of the open-circuit voltage in the predetermined third period and the moving average value of the open-circuit voltage in the predetermined first period is within the predetermined first range, the flow rates of the positive electrode electrolyte and the negative electrode electrolyte are controlled to flow rates smaller than the predetermined first flow rate. A redox flow battery system according to a second aspect of the present disclosure includes: a battery cell having a positive electrode chamber in which a positive electrode is placed, a negative electrode chamber in which a negative electrode is placed, and a diaphragm separating the positive electrode chamber from the negative electrode chamber; a circulation unit that circulates a positive electrode electrolyte in the positive electrode chamber and a negative electrode electrolyte in the negative electrode chamber; an open circuit voltage measurement unit that measures the open circuit voltage of the battery cell; a control unit that calculates a moving average value of the open-circuit voltage measured by the open-circuit voltage measurement unit in accordance with a depth of charge of the positive electrode electrolyte and the negative electrode electrolyte, and controls the flow rates of the positive electrode electrolyte and the negative electrode electrolyte based on the calculated moving average value of the open-circuit voltage, thereby controlling charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte, The control unit acquiring the amount of power generated by a renewable energy power plant connected to the battery cell, and calculating a moving average value of the amount of power generated; When the acquired amount of power generation is greater than the moving average value of the calculated amount of power generation, charging the positive electrode electrolyte and the negative electrode electrolyte; When the acquired amount of power generation is smaller than the moving average value of the calculated amount of power generation, the positive electrode electrolyte and the negative electrode electrolyte are discharged, When the acquired amount of power generation is the same as the calculated moving average value of the amount of power generation, charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte are not performed.

[0008] The present disclosure 3 The method for operating a redox flow battery system according to the above aspect includes: a measuring step of measuring an open circuit voltage of the battery cell; a calculating step of calculating a moving average value of the open-circuit voltage based on the measured open-circuit voltage in accordance with the depth of charge of the positive electrode electrolyte supplied to the positive electrode chamber of the battery cell and the negative electrode electrolyte supplied to the negative electrode chamber of the battery cell; Based on the obtained moving average value of the open circuit voltage, By controlling the flow rates of the positive electrode electrolyte and the negative electrode electrolyte, and a control step of controlling the charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte. fruit, In the calculation step, a moving average value of the open-circuit voltage in a predetermined first period and a moving average value of the open-circuit voltage in a predetermined third period longer than the predetermined first period are calculated, In the control step, when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are within a predetermined range and a difference between the moving average value of the open-circuit voltage in the predetermined third period and the moving average value of the open-circuit voltage in the predetermined first period is outside a predetermined first range, the flow rates of the positive electrode electrolyte and the negative electrode electrolyte are controlled to a predetermined first flow rate, and when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are within the predetermined range and a difference between the moving average value of the open-circuit voltage in the predetermined third period and the moving average value of the open-circuit voltage in the predetermined first period is within the predetermined first range, the flow rates of the positive electrode electrolyte and the negative electrode electrolyte are controlled to a flow rate smaller than the predetermined first flow rate. A method for operating a redox flow battery system according to a fourth aspect of the present disclosure includes: a measuring step of measuring an open circuit voltage of the battery cell; a calculation step of calculating a moving average value of the open-circuit voltage based on the measured open-circuit voltage and according to the depth of charge of the positive electrode electrolyte supplied to the positive electrode chamber of the battery cell and the negative electrode electrolyte supplied to the negative electrode chamber of the battery cell, and acquiring the amount of power generated by a renewable energy power plant connected to the battery cell to calculate the moving average value of the amount of power generated; a control step of controlling the flow rates of the positive electrode electrolyte and the negative electrode electrolyte based on the obtained moving average value of the open-circuit voltage, thereby controlling charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte; In the control step, When the acquired amount of power generation is greater than the moving average value of the calculated amount of power generation, charging the positive electrode electrolyte and the negative electrode electrolyte; When the acquired amount of power generation is smaller than the moving average value of the calculated amount of power generation, the positive electrode electrolyte and the negative electrode electrolyte are discharged, When the acquired amount of power generation is the same as the calculated moving average value of the amount of power generation, charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte are not performed. [Effects of the Invention]

[0009] According to the present disclosure, the charge and discharge of the positive electrode electrolyte and the negative electrode electrolyte are controlled based on the moving average value of the open-circuit voltage calculated according to the depth of charge of the positive electrode electrolyte and the negative electrode electrolyte, thereby achieving stable operation. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a redox flow battery system according to a first embodiment. [Figure 2]4 is a graph showing the relationship between the depth of charge and the open-circuit voltage of the electrolyte solution according to the first embodiment. FIG. [Figure 3] FIG. 2 is a block diagram showing a control unit according to the first embodiment. [Figure 4] 4 is a diagram showing measured values of open-circuit voltage and moving average values of open-circuit voltage according to the first embodiment. FIG. [Figure 5] FIG. 2 is a diagram illustrating a hardware configuration of a control unit according to the first embodiment. [Figure 6] 1 is a flowchart showing a method for operating the redox flow battery system according to the first embodiment. [Figure 7] FIG. 10 is a diagram showing an example of the relationship between the amount of solar power generation, charge / discharge power from the redox flow battery system, and the solar power generation output after charge / discharge control according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a redox flow battery system according to an embodiment will be described with reference to the drawings.

[0012] <Embodiment 1> A redox flow battery system 10 according to this embodiment will be described with reference to FIGS. 1 to 6.

[0013] As shown in Fig. 1, the redox flow battery system 10 includes a battery cell 100 and a circulation unit 300 that circulates a positive electrode electrolyte PL and a negative electrode electrolyte NL through the battery cell 100. The redox flow battery system 10 further includes an open circuit voltage measurement unit 500 that measures the open circuit voltage (OCV) of the battery cell 100, and a control unit 600 that controls the charging and discharging of the positive electrode electrolyte PL and the negative electrode electrolyte NL. In this embodiment, a redox flow battery that uses vanadium ions as the active material of the positive electrode electrolyte PL and the negative electrode electrolyte NL will be described as an example. The positive electrode electrolyte PL and the negative electrode electrolyte NL will also be collectively referred to as electrolytes.

[0014] The redox flow battery system 10 is connected between a power plant and a load via a power converter 610 of a control unit 600. The power plant is, for example, a renewable energy power plant such as a solar power plant or a wind power plant. The load is a power grid or a power consumer. The redox flow battery system 10 charges the power supplied from the power plant. The redox flow battery system 10 also supplies the charged power to the load.

[0015] First, a specific configuration of the battery cell 100 of the redox flow battery system 10 will be described. The battery cell 100 has a positive electrode 105a, a positive electrode chamber 110a, a negative electrode 105c, a negative electrode chamber 110c, and a diaphragm 120.

[0016] The positive electrode 105a of the battery cell 100 is, for example, a carbon fiber electrode. The positive electrode 105a is disposed in the positive electrode chamber 110a of the battery cell 100. The positive electrode chamber 110a of the battery cell 100 contains the positive electrode 105a and is separated from the negative electrode chamber 110c by a diaphragm 120. A positive electrode electrolyte PL circulates through the positive electrode chamber 110a. During charging, tetravalent vanadium ions in the positive electrode electrolyte PL are oxidized to pentavalent vanadium ions. During discharging, the pentavalent vanadium ions in the positive electrode electrolyte PL are reduced to tetravalent vanadium ions.

[0017] The negative electrode 105c of the battery cell 100 is, for example, a carbon fiber electrode. The negative electrode 105c is disposed in the negative electrode chamber 110c of the battery cell 100. The negative electrode chamber 110c of the battery cell 100 contains the negative electrode 105c and is separated from the positive electrode chamber 110a by a diaphragm 120. A negative electrode electrolyte NL circulates through the negative electrode chamber 110c. During charging, trivalent vanadium ions in the negative electrode electrolyte NL are reduced to divalent vanadium ions. During discharging, divalent vanadium ions in the negative electrode electrolyte NL are oxidized to trivalent vanadium ions.

[0018] The diaphragm 120 of the battery cell 100 is an ion exchange membrane. The diaphragm 120 separates the positive electrode chamber 110a and the negative electrode chamber 110c, and allows specific ions to pass through.

[0019] The battery cell 100 is used in the form of a cell stack in which multiple battery cells 100 are stacked. The cell stack is configured, for example, by stacking a cell frame provided with a bipolar plate, a positive electrode 105a, a diaphragm 120, and a negative electrode 105c. The positive electrode 105a is disposed on one side of the bipolar plate, and the negative electrode 105c is disposed on the other side of the bipolar plate, thereby forming a battery cell 100 between adjacent cell frames. The positive electrode electrolyte PL and the negative electrode electrolyte NL circulate through manifolds formed in the frame of the cell frame, the frame supporting the positive electrode 105a, the frame supporting the negative electrode 105c, etc. Note that the battery cell 100 can be configured in any known manner as appropriate.

[0020] As shown in FIG. 1 , the circulation unit 300 of the redox flow battery system 10 has a positive electrode circulation unit 300a and a negative electrode circulation unit 300c. The positive electrode circulation unit 300a of the circulation unit 300 circulates the positive electrode electrolyte PL to the positive electrode chamber 110a of the battery cell 100. The positive electrode circulation unit 300a also circulates the positive electrode electrolyte PL to a monitor cell 510 of the open-circuit voltage measurement unit 500, which will be described later. The negative electrode circulation unit 300c of the circulation unit 300 circulates the negative electrode electrolyte NL to the negative electrode chamber 110c of the battery cell 100. The negative electrode circulation unit 300c also circulates the negative electrode electrolyte NL to the monitor cell 510. The flow rates of the positive electrode electrolyte PL and the negative electrode electrolyte NL are controlled by a control unit 600.

[0021] Positive electrode circulation section 300a of circulation section 300 has a positive electrode electrolyte storage tank 310a, a positive electrode pump 320a, a positive electrode supply pipe 322a, a supply branch pipe 324a, a first positive electrode return pipe 326a, and a second positive electrode return pipe 328a. Positive electrode electrolyte storage tank 310a of positive electrode circulation section 300a stores positive electrode electrolyte PL. Positive electrode electrolyte storage tank 310a is connected to positive electrode pump 320a, first positive electrode return pipe 326a, and second positive electrode return pipe 328a.

[0022] Positive electrode pump 320a of positive electrode circulation unit 300a is a pump that circulates positive electrode electrolyte PL. Positive electrode pump 320a is connected to positive electrode electrolyte reservoir 310a and positive electrode supply pipe 322a. Positive electrode pump 320a is controlled by control unit 600 to control the flow rate of positive electrode electrolyte PL circulating between positive electrode chamber 110a of battery cell 100 and the positive electrode chamber of monitor cell 510.

[0023] The positive electrode supply pipe 322a of the positive electrode circulation unit 300a connects the positive electrode pump 320a and the positive electrode chamber 110a of the battery cell 100, and supplies the positive electrode electrolyte PL to the positive electrode chamber 110a. The supply branch pipe 324a of the positive electrode circulation unit 300a branches off from the positive electrode supply pipe 322a, and supplies the positive electrode electrolyte PL to the positive electrode chamber of the monitor cell 510.

[0024] The first positive electrode return pipe 326a of the positive electrode circulation unit 300a connects the positive electrode chamber 110a and the positive electrode electrolyte reservoir 310a of the battery cell 100. The first positive electrode return pipe 326a returns the positive electrode electrolyte PL, which has been supplied to the positive electrode chamber 110a, from the positive electrode chamber 110a to the positive electrode electrolyte reservoir 310a.

[0025] The second positive electrode recovery pipe 328a of the positive electrode circulation unit 300a connects the positive electrode chamber of the monitor cell 510 and the positive electrode electrolyte reservoir 310a. The second positive electrode recovery pipe 328a returns the positive electrode electrolyte PL, which has been supplied to the positive electrode chamber of the monitor cell 510, from the positive electrode chamber of the monitor cell 510 to the positive electrode electrolyte reservoir 310a.

[0026] The negative electrode circulation unit 300c of the circulation unit 300 has a negative electrode electrolyte storage tank 310c, a negative electrode pump 320c, a negative electrode supply pipe 322c, a supply branch pipe 324c, a first negative electrode recovery pipe 326c, and a second negative electrode recovery pipe 328c. The negative electrode electrolyte storage tank 310c of the negative electrode circulation unit 300c stores the negative electrode electrolyte NL. The negative electrode electrolyte storage tank 310c is connected to the negative electrode pump 320c, the first negative electrode recovery pipe 326c, and the second negative electrode recovery pipe 328c.

[0027] The negative electrode pump 320c of the negative electrode circulation unit 300c is a pump that circulates the negative electrode electrolyte NL. The negative electrode pump 320c is controlled by the control unit 600 to control the flow rate of the positive electrode electrolyte PL that circulates between the negative electrode chamber 110c of the battery cell 100 and the negative electrode chamber of the monitor cell 510.

[0028] The negative electrode supply pipe 322c of the negative electrode circulation unit 300c is connected to the negative electrode pump 320c and supplies the negative electrode electrolyte NL to the negative electrode chamber 110c of the battery cell 100. The supply branch pipe 324c of the negative electrode circulation unit 300c branches off from the negative electrode supply pipe 322c and supplies the negative electrode electrolyte NL to the negative electrode chamber of the monitor cell 510.

[0029] The first negative electrode recovery pipe 326c of the negative electrode circulation unit 300c returns the negative electrode electrolyte NL supplied to the negative electrode chamber 110c from the negative electrode chamber 110c to the negative electrode electrolyte reservoir 310c. The second negative electrode recovery pipe 328c of the negative electrode circulation unit 300c returns the negative electrode electrolyte NL supplied to the negative electrode chamber of the monitor cell 510 from the negative electrode chamber of the monitor cell 510 to the negative electrode electrolyte reservoir 310c.

[0030] The open-circuit voltage measuring unit 500 of the redox flow battery system 10 measures the open-circuit voltage that indicates the charge state of the electrolyte. The open-circuit voltage measuring unit 500 has a monitor cell 510 and a measuring unit 520, as shown in FIG.

[0031] The monitor cell 510 has a similar configuration to the battery cell 100 and is a single redox flow battery cell that does not contribute to charging or discharging. The positive electrode chamber of the monitor cell 510 is supplied with the positive electrode electrolyte PL stored in the positive electrode electrolyte reservoir 310a, similar to the positive electrode chamber 110a of the battery cell 100. The negative electrode chamber of the monitor cell 510 is supplied with the negative electrode electrolyte NL stored in the negative electrode electrolyte reservoir 310c, similar to the negative electrode chamber 110c of the battery cell 100.

[0032] The measuring unit 520 is a voltmeter that measures the potential difference (i.e., open-circuit voltage) between the positive electrode electrolyte PL and the negative electrode electrolyte NL in the monitor cell 510. Similar to the positive electrode chamber 110a and the negative electrode chamber 110c flowing in the battery cell 100, the positive electrode electrolyte PL and the negative electrode electrolyte NL are supplied to the positive electrode chamber and the negative electrode chamber, respectively, of the monitor cell 510, and therefore the open-circuit voltage of the battery cell 100 can be measured by measuring the open-circuit voltage of the monitor cell 510. In this embodiment, the measuring unit 520 measures the open-circuit voltage on the supply side of the positive electrode electrolyte PL and the negative electrode electrolyte NL. In addition, the measuring unit 520 measures the open-circuit voltage at 1-second intervals (measurement interval Δt0 = 1 sec).

[0033] There is a correlation between the depth of charge of the electrolytes (positive electrode electrolyte PL and negative electrode electrolyte NL) and the open-circuit voltage of the monitor cell 510, and the depth of charge of the electrolytes can be obtained from the open-circuit voltage of the monitor cell 510. For example, there is a relationship as shown in FIG. 2 between the depth of charge of the electrolytes and the open-circuit voltage of the monitor cell 510. Furthermore, the depth of charge (SOC) of the electrolyte is simply expressed by the following formula (1) using the open-circuit voltage (OCV) of the monitor cell 510. Here, F is the Faraday constant, R is the gas constant, T is the absolute temperature, and OCVe is the open-circuit voltage when the concentrations of oxides and reduced products are equal.

[0034]

number

[0035] The control unit 600 of the redox flow battery system 10 calculates a moving average value of the open-circuit voltage according to the state of charge of the positive electrode electrolyte PL and the negative electrode electrolyte NL. The control unit 600 controls the charging and discharging of the positive electrode electrolyte PL and the negative electrode electrolyte NL based on the calculated moving average value of the open-circuit voltage. As shown in FIG. 3 , the control unit 600 has an acquiring unit 620, a memory unit 630, a setting unit 640, a calculating unit 650, a determining unit 660, a flow rate control unit 670, and a charging and discharging control unit 680.

[0036] Acquisition unit 620 of control unit 600 acquires the measurement value of the open-circuit voltage measured by measurement unit 520 of open-circuit voltage measurement unit 500. Acquisition unit 620 transmits a signal representing the acquired measurement value of the open-circuit voltage to storage unit 630 and calculation unit 650. The storage unit 630 of the control unit 600 stores programs, data, open circuit voltage measurement values, and the like.

[0037] The setting unit 640 of the control unit 600 sets conditions for the calculation unit 650 to calculate the moving average value of the open-circuit voltage. Specifically, the setting unit 640 sets an interval Δt1 and a period S (S=n×Δt1: n is a natural number of 2 or more) for calculating the moving average value of the open-circuit voltage.

[0038] In this embodiment, the interval Δt1 for calculating the moving average value of the open-circuit voltage is set to 1 second (Δt1 = 1 sec). Furthermore, when the state of charge of the electrolyte is within a predetermined range, the setting unit 640 sets the period S for calculating the moving average value of the open-circuit voltage to a predetermined first period S1 = 60 seconds (S1 = 60 × Δt1, n = 60). The predetermined range of the state of charge of the electrolyte is preferably a range in which the correlation between the open-circuit voltage and the state of charge of the electrolyte can be considered to be proportional. In this embodiment, the predetermined range of the state of charge of the electrolyte is set to a state of charge of the electrolyte of 10% or more and 90% or less.

[0039] Furthermore, when the SOC of the electrolyte is smaller than a predetermined range (when the SOC of the electrolyte is less than 10%) or larger than the predetermined range (when the SOC of the electrolyte is larger than 90%), the setting unit 640 sets the period S for calculating the moving average value of the open-circuit voltage to a predetermined second period S2 = 5 seconds (S2 = 5 × Δt1, n = 5) that is shorter than the predetermined first period S1. In this embodiment, when the SOC of the electrolyte is smaller than or larger than the predetermined range, which causes a sudden change in the correlation between the open-circuit voltage and the SOC of the electrolyte, the setting unit 640 shortens the period S for calculating the moving average value of the open-circuit voltage. This allows the control unit 600 to quickly respond to changes in the SOC of the electrolyte, thereby achieving stable operation of the redox flow battery system 10. The setting unit 640 transmits a signal representing the set condition to the calculation unit 650 .

[0040] The calculation unit 650 of the control unit 600 calculates the moving average value OCV(t) of the open circuit voltage at time t from the measured value of the open circuit voltage acquired by the acquisition unit 620 based on the conditions set by the setting unit 640. Specifically, the moving average value OCV(t) of the open circuit voltage at time t is calculated by the following formula (2), and the moving average value OCV(t+Δt1) of the open circuit voltage at time t+Δt1 is calculated by the following formula (3). Here, OCV n+1 ~OCV1 is the measured open circuit voltage.

[0041]

number

number

[0042] 4 shows the measured open-circuit voltage and the moving average value OCV(t) of the open-circuit voltage during the first period S1. As shown in FIG. 4, by calculating the moving average value OCV(t) of the open-circuit voltage, the variation in the measured open-circuit voltage can be corrected.

[0043] Furthermore, the calculation unit 650 calculates the state of charge SOC(t) of the electrolyte at time t based on the moving average value OCV(t) of the open-circuit voltage. The state of charge SOC(t) of the electrolyte at time t can be calculated, for example, from equation (1). The state of charge SOC(t) of the electrolyte at time t may also be calculated from the correlation between the state of charge and the open-circuit voltage of the electrolyte, as shown in FIG. 2. The correlation between the state of charge and the open-circuit voltage of the electrolyte can be obtained in advance through experiments. In this embodiment, the state of charge SOC(t) of the electrolyte is calculated from the consistent moving average value OCV(t) of the open-circuit voltage, so the state of charge of the electrolyte can be accurately determined. The calculation unit 650 transmits a signal representing the calculated state of charge SOC(t) of the electrolyte to the setting unit 640 and the determination unit 660.

[0044] The determination unit 660 of the control unit 600 determines the state of charge of the electrolyte from the state of charge SOC(t) of the electrolyte at time t. For example, if the state of charge SOC(t) of the electrolyte is within a predetermined range (10% or more and 90% or less), the determination unit 660 determines that the state of charge of the electrolyte is a normal state. If the state of charge SOC(t) of the electrolyte is smaller than the predetermined range (less than 10%), the determination unit 660 determines that the state of charge of the electrolyte is a highly discharged state. If the state of charge SOC(t) of the electrolyte is, for example, 5% or less, the determination unit 660 determines that the state of charge of the electrolyte is a terminal discharge state. On the other hand, if the state of charge SOC(t) of the electrolyte is larger than the predetermined range (greater than 90%), the determination unit 660 determines that the state of charge of the electrolyte is a highly charged state. Furthermore, if the state of charge SOC(t) of the electrolyte is, for example, 95% or more, the determining unit 660 determines that the state of charge of the electrolyte is in the terminal charging state. The determination unit 660 transmits a signal indicating the charge state of the electrolyte to the flow rate control unit 670 and the charge / discharge control unit 680 .

[0045] The flow rate control unit 670 of the control unit 600 controls the flow rates of the positive electrode pump 320a of the positive electrode circulation unit 300a and the negative electrode pump 320c of the negative electrode circulation unit 300c based on the state of charge of the electrolyte. If the state of charge of the electrolyte is determined to be normal, the flow rate control unit 670 controls the flow rates of the positive electrode pump 320a and the negative electrode pump 320c to a predetermined first flow rate. If the state of charge of the electrolyte is determined to be either a highly discharged state or a highly charged state, the flow rate control unit 670 controls the flow rates of the positive electrode pump 320a and the negative electrode pump 320c to a second flow rate that is greater than the first flow rate. If the state of charge of the electrolyte is determined to be either an end-of-discharge state or an end-of-charge state, the flow rate control unit 670 controls the flow rates of the positive electrode pump 320a and the negative electrode pump 320c to a third flow rate that is even greater than the second flow rate. By controlling the flow rates of the positive electrode pump 320a and the negative electrode pump 320c, it is possible to prevent the electrolyte from being overcharged and overdischarged.

[0046] The charge / discharge control unit 680 of the control unit 600 controls the charging and discharging of power between the redox flow battery system 10 (i.e., the electrolyte of the redox flow battery system 10), the power plant, and the load. For example, if the charge / discharge control unit 680 determines that the charge state of the electrolyte is in an end-of-discharge state, it disconnects the redox flow battery system 10 from the load. Also, if the charge / discharge control unit 680 determines that the charge state of the electrolyte is in an end-of-charge state, it disconnects the redox flow battery system 10 from the power plant. These controls make it possible to prevent the electrolyte from being overcharged and overdischarged.

[0047] 5 shows the hardware configuration of the control unit 600. The control unit 600 is composed of a CPU (Central Processing Unit) 602, a ROM (Read Only Memory) 604, a RAM (Random Access Memory) 606, an input / output interface 608, and a power converter 610. The CPU 602 executes a program stored in the ROM 604. The ROM 604 stores programs, data, signals, etc. The RAM 606 stores data. The input / output interface 608 inputs and outputs signals between each unit. The power converter 610 includes an AC / DC converter, a switch that connects the redox flow battery system 10 to a load, a switch that connects the redox flow battery system 10 to a power plant, etc. The functions of the control unit 600 are realized by the execution of the program by the CPU 602 and the functions of the power converter 610.

[0048] Next, a method for operating the redox flow battery system 10 will be described. Fig. 6 is a flowchart showing the method for operating the redox flow battery system 10. The method for operating the redox flow battery system 10 includes a measurement step (step S100) for measuring the open-circuit voltage of the battery cell 100, a calculation step (step S200) for calculating a moving average value of the open-circuit voltage from the measured open-circuit voltage, and a control step (step S300) for controlling charging and discharging of the electrolyte based on the calculated moving average value of the open-circuit voltage. Here, a case will be described in which, as an initial state, the storage state of the electrolyte is normal (i.e., the state of charge (SOC) is within a predetermined range) and the redox flow battery system 10 is connected to a power plant and a load.

[0049] In step S100, the measurement unit 520 of the open-circuit voltage measurement unit 500 measures the open-circuit voltage of the monitor cell 510 of the open-circuit voltage measurement unit 500, thereby measuring the open-circuit voltage of the battery cell 100, which indicates the charge state of the electrolyte. In this embodiment, the open-circuit voltage is measured at intervals of 1 second (measurement interval Δt1 = 1 sec).

[0050] Step S200 includes a process of acquiring a measured value of the open circuit voltage (step S210), a process of calculating a moving average value OCV(t) of the open circuit voltage at time t from the measured value of the open circuit voltage (step S220), and a process of calculating a state of charge SOC(t) of the electrolyte at time t from the calculated moving average value OCV(t) of the open circuit voltage (step S230).

[0051] In step S210, acquisition unit 620 of control unit 600 acquires the measured value of the open-circuit voltage from measurement unit 520. Then, acquisition unit 620 transmits a signal representing the measured value of the open-circuit voltage to storage unit 630 and calculation unit 650 of control unit 600.

[0052] In step S220, the calculation unit 650 of the control unit 600 calculates the moving average value OCV(t) of the open-circuit voltage at time t from the measured open-circuit voltage value based on the conditions set by the setting unit 640 of the control unit 600. In this embodiment, the initial state is that the state of charge of the electrolyte is normal (the state of charge SOC is within a predetermined range), so the setting unit 640 sets the period S for calculating the moving average value of the open-circuit voltage to a first period S1 (S1=60×Δt1, Δt1=1 sec). Therefore, the calculation unit 650 calculates the moving average value OCV(t) of the open-circuit voltage at time t under the conditions of the first period S1. By calculating the moving average value OCV(t) of the open-circuit voltage, variations in the measured open-circuit voltage value can be corrected.

[0053] In step S230, the calculation unit 650 calculates the state of charge SOC(t) of the electrolyte at time t based on the moving average value OCV(t) of the open-circuit voltage. For example, the state of charge SOC(t) of the electrolyte can be calculated from the correlation between the state of charge and the open-circuit voltage of the electrolyte. In this embodiment, the state of charge SOC(t) of the electrolyte can be calculated from the consistent moving average value OCV(t) of the open-circuit voltage, so the state of charge of the electrolyte can be accurately determined. The calculation unit 650 transmits a signal representing the calculated state of charge SOC(t) of the electrolyte to the setting unit 640 and the determination unit 660.

[0054] The setting unit 640 sets the period S for calculating the moving average value of the open-circuit voltage based on the signal representing the state-of-charge SOC(t) of the electrolyte. That is, when the received state-of-charge SOC(t) of the electrolyte is within a predetermined range, the setting unit 640 sets the period S for calculating the moving average value OCV(t) of the open-circuit voltage to a first period S1 as a condition for calculating the next moving average value OCV(t) of the open-circuit voltage. When the state-of-charge SOC(t) of the electrolyte is smaller than the predetermined range or when the received state-of-charge SOC(t) of the electrolyte is larger than the predetermined range, for example, the setting unit 640 sets the period S for calculating the moving average value OCV(t) of the open-circuit voltage to a second period S2 (S2=5×Δt1, Δt1=1 sec). When the depth of charge of the electrolyte is smaller than a predetermined range or larger than a predetermined range, the setting unit 640 shortens the period S for calculating the moving average value of the open-circuit voltage. This allows the control unit 600 to quickly respond to changes in the depth of charge of the electrolyte, thereby achieving stable operation of the redox flow battery system 10.

[0055] Step S300 includes a step of determining the charge state of the electrolyte (step S310), and a step of controlling the flow rate of the electrolyte and the charge / discharge between the power plant and the load (step S320).

[0056] In step S310, the determination unit 660 of the control unit 600 determines the state of charge of the electrolyte from the state of charge (SOC(t)) of the electrolyte calculated based on the moving average value OCV(t) of the open circuit voltage. In this embodiment, as described above, the determination unit 660 determines the state of charge of the electrolyte as one of the following: a normal state (SOC(t): 10% or more and 90% or less), a highly discharged state (SOC(t): less than 10%), an end-of-discharge state (SOC(t): 5% or less), a highly charged state (SOC(t): greater than 90%), or an end-of-charge state (SOC(t): 95% or more). The determination unit 660 transmits a signal indicating the state of charge of the electrolyte to the flow rate control unit 670 and the charge / discharge control unit 680 of the control unit 600.

[0057] In step S320, the flow rate control unit 670 of the control unit 600 controls the flow rates of the positive electrode pump 320a and the negative electrode pump 320c based on the charge state of the electrolyte. Also, the charge / discharge control unit 680 of the control unit 600 controls charging / discharging between the redox flow battery system 10, the power plant, and the load based on the charge state of the electrolyte.

[0058] Specifically, when the charge state of the electrolyte is normal, the flow rate control unit 670 controls the flow rates of the cathode pump 320a and the anode pump 320c to a predetermined first flow rate, and the connection control unit 680 maintains the operation states of the redox flow battery system 10, the power plant, and the load. When the charge state of the electrolyte is either a highly discharged state or a highly charged state, the flow rate control unit 670 controls the flow rates of the cathode pump 320a and the anode pump 320c to a second flow rate greater than the first flow rate, and the charge / discharge control unit 680 maintains the operation states of the redox flow battery system 10, the power plant, and the load. When the charge state of the electrolyte is in an end-of-discharge state, the flow rate control unit 670 controls the flow rates of the cathode pump 320a and the anode pump 320c to a third flow rate greater than the second flow rate, and the charge / discharge control unit 680 disconnects the connection between the redox flow battery system 10 and the load. Furthermore, when the charge state of the electrolyte is in the final stage of charging, the flow rate control unit 670 controls the flow rates of the positive electrode pump 320a and the negative electrode pump 320c to a third flow rate that is greater than the second flow rate, and the charge / discharge control unit 680 disconnects the redox flow battery system 10 from the power plant. These controls make it possible to prevent the electrolyte from being overcharged and overdischarged.

[0059] After step S320, if an operation stop command is not input to the control unit 600 (step S322: NO), the operation of the redox flow battery system 10 returns to step S100. If an operation stop command is input to the control unit 600 (step S322: YES), the operation of the redox flow battery system 10 ends.

[0060] As described above, by calculating the moving average value of the open-circuit voltage, it is possible to correct for variations in the measured open-circuit voltage values and accurately grasp the state of charge of the electrolyte. The control unit 600 calculates the moving average value of the open-circuit voltage according to the state of charge of the electrolyte and controls the charging and discharging of the electrolyte based on the calculated moving average value of the open-circuit voltage, thereby enabling a rapid response to changes in the state of charge of the electrolyte and achieving stable operation of the redox flow battery system 10.

[0061] Furthermore, accurate knowledge of the electrolyte's depth of charge can help to level out fluctuations in power output at renewable energy power plants. Accurate knowledge of the electrolyte's depth of charge also makes it easy to estimate the optimal capacity when increasing the electrolyte capacity, and also makes it easy to control the distribution of power according to load priority in the event of a disaster.

[0062] <Embodiment 2> In the first embodiment, the charging and discharging of the electrolyte is controlled based on the moving average value of the open-circuit voltage, but the charging and discharging of the electrolyte may also be controlled based on the moving average value of the open-circuit voltage and the moving average value of the power generation amount of a renewable energy power plant. Since the configurations of the battery cell 100, circulation unit 300, and open-circuit voltage measurement unit 500 of the redox flow battery system 10 of this embodiment are the same as those of the first embodiment, only the control unit 600 of the redox flow battery system 10 will be described here. The control unit 600 of this embodiment, like the control unit 600 of embodiment 1, has an acquisition unit 620, a memory unit 630, a setting unit 640, a calculation unit 650, a determination unit 660, a flow rate control unit 670, and a charge / discharge control unit 680.

[0063] The acquisition unit 620 of this embodiment acquires the measured value of the open-circuit voltage measured by the measurement unit 520 of the open-circuit voltage measurement unit 500, similar to the acquisition unit 620 of embodiment 1. The acquisition unit 620 of this embodiment also acquires the amount of power generation from the renewable energy power plant. The acquisition unit 620 of this embodiment transmits a signal representing the acquired measured value of the open-circuit voltage and a signal representing the acquired amount of power generation to the storage unit 630 and the calculation unit 650. The storage unit 630 of this embodiment stores programs, data, open circuit voltage measurement values, and the like, similar to the storage unit 630 of the first embodiment.

[0064] The setting unit 640 of this embodiment sets the conditions under which the calculation unit 650 calculates the moving average value of the open-circuit voltage and the moving average value of the power generation amount. In this embodiment, as in the first embodiment, the interval Δt1 for calculating the moving average value is 1 second (Δt1 = 1 sec). Furthermore, when the state of charge of the electrolyte is within a predetermined range, the setting unit 640 of this embodiment sets the period S for calculating the moving average value to a predetermined first period S1 = 60 seconds. When the state of charge of the electrolyte is smaller than the predetermined range or when the state of charge of the electrolyte is larger than the predetermined range, the setting unit 640 of this embodiment sets the period S for calculating the moving average value to a predetermined second period S2 = 5 seconds, which is shorter than the first period S1 (S2 = 5 × Δt1, n = 5). The setting unit 640 of this embodiment sends a signal indicating the set conditions to the calculation unit 650.

[0065] The calculation unit 650 of this embodiment calculates the moving average value OCV(t) of the open-circuit voltage at time t and the state of charge SOC(t) of the electrolyte at time t from the measured value of the open-circuit voltage based on the conditions set by the setting unit 640. The moving average value OCV(t) of the open-circuit voltage and the state of charge SOC(t) of the electrolyte are calculated in the same manner as in embodiment 1. The calculation unit 650 of this embodiment transmits a signal representing the calculated state of charge SOC(t) of the electrolyte to the setting unit 640 and the determination unit 660.

[0066] Furthermore, the calculation unit 650 of this embodiment calculates a moving average value REP(t) of the amount of power generation at time t from the acquired amount of power generation based on the conditions set by the setting unit 640, and calculates a difference Δp between the acquired amount of power generation and the calculated moving average value REP(t) of the amount of power generation. The moving average value REP(t) of the amount of power generation at time t is calculated in the same way as the moving average value OCV(t) of the open circuit voltage. The calculation unit 650 of this embodiment transmits a signal representing the calculated difference Δp to the charge / discharge control unit 680.

[0067] The determination unit 660 of this embodiment determines the state of charge of the electrolyte based on the state of charge SOC(t) of the electrolyte at time t, similar to the determination unit 660 of embodiment 1. Furthermore, the determination unit 660 of this embodiment transmits a signal representing the state of charge of the electrolyte to the flow rate control unit 670 and the charge / discharge control unit 680.

[0068] The flow rate control unit 670 of this embodiment controls the flow rates of the positive electrode pump 320a of the positive electrode circulation unit 300a and the negative electrode pump 320c of the negative electrode circulation unit 300c based on the charge state of the electrolyte, similar to the flow rate control unit 670 of embodiment 1. The control of the flow rates of the positive electrode pump 320a and the negative electrode pump 320c is similar to the control in embodiment 1.

[0069] The charge / discharge control unit 680 of this embodiment controls the charging and discharging of power between the redox flow battery system 10, the power plant, and the load, similarly to the charge / discharge control unit 680 of embodiment 1. The control of charging and discharging of power is similar to the control of embodiment 1.

[0070] Furthermore, the charge / discharge control unit 680 of this embodiment controls the charging / discharging of the electrolyte based on the calculated moving average value REP(t) of the amount of power generation. Specifically, if the difference Δp between the amount of power generation and the moving average value REP(t) of the amount of power generation is positive (i.e., if the amount of power generation is greater than the moving average value REP(t) of the amount of power generation), the charge / discharge control unit 680 of this embodiment charges the electrolyte with the difference Δp of the amount of power generation at the power plant. On the other hand, if the difference Δp between the amount of power generation and the moving average value REP(t) of the amount of power generation is negative (i.e., if the amount of power generation is smaller than the moving average value REP(t) of the amount of power generation), the charge / discharge control unit 680 of this embodiment discharges the difference Δp from the electrolyte. Furthermore, if the difference Δp between the amount of power generation and the moving average value REP(t) of the amount of power generation is zero, the charge / discharge control unit 680 of this embodiment neither charges nor discharges. This allows the instantaneous output fluctuations of renewable energy power generation, which are influenced by nature, to be absorbed. Figure 7 shows an example of the relationship between the amount of solar power generation, the charge / discharge power from the redox flow battery system 10, and the solar power generation output after charge / discharge control (results of absorbing fluctuations in the amount of solar power generation). In Figure 7, the moving average value REP(t) of the amount of solar power generation is temporarily set to 3 kW. As shown in Figure 7, by controlling the charge / discharge of the redox flow battery system 10 (the electrolyte of the redox flow battery system 10) based on the moving average value REP(t) of the amount of power generation, it is possible to level out fluctuations in power generation at renewable energy power plants in real time.

[0071] In this embodiment, the charge / discharge control unit 680 controls the charging / discharging of the electrolyte based on the moving average value of the power generation amount, and the flow rate control unit 670 controls the flow rates of the positive electrode pump 320a and the negative electrode pump 320c based on the moving average value of the open circuit voltage. The moving average value of the power generation amount of a renewable energy power plant represents the short-term or long-term trend of the power generation amount at the renewable energy power plant, so the redox flow battery system 10 can smooth out power generation fluctuations at the renewable energy power plant in real time. Furthermore, as in the first embodiment, overcharging of the electrolyte and overdischarging of the electrolyte can be suppressed, and changes in the state of charge of the electrolyte can be quickly responded to, thereby realizing stable operation of the redox flow battery system 10.

[0072] <Modification> Although the embodiments have been described above, the present disclosure can be modified in various ways without departing from the gist of the present disclosure.

[0073] For example, the active materials of the positive electrode electrolyte PL and the negative electrode electrolyte NL are not limited to vanadium ions, but may be iron ions and chromium ions, respectively.

[0074] In the first embodiment, the setting unit 640 sets the period S for calculating the moving average value of the open-circuit voltage to a predetermined first period S1 when the state of charge of the electrolyte is within a predetermined range, and sets the period S for calculating the moving average value of the open-circuit voltage to a predetermined second period S2 that is shorter than the predetermined first period S1 when the state of charge of the electrolyte is outside the predetermined range. The setting unit 640 may also set the period S for calculating the moving average value of the open-circuit voltage to a third period S3 (e.g., S3=120×Δt1, n=120) that is longer than the predetermined first period S1.

[0075] For example, if the SOC of the electrolyte is within a predetermined range, the setting unit 640 sets the period S for calculating the moving average value of the open-circuit voltage to a predetermined first period S1 and a predetermined third period S3. The calculation unit 650 calculates the moving average value of the open-circuit voltage for the first period S1 and the third period S3, and further calculates the SOC of the electrolyte for the first period S1 and the third period S3. If the difference between the SOC of the electrolyte for the first period S1 and the SOC of the electrolyte for the third period S3 is within a predetermined range, the determination unit 660 determines that the storage state of the electrolyte is stable. If the storage state of the electrolyte is determined to be stable, the flow control unit 670 controls the flow rates of the positive electrode pump 320a and the negative electrode pump 320c to a third flow rate that is smaller than the predetermined first flow rate. This enables the redox flow battery system 10 to operate with reduced power consumption.

[0076] The interval (Δt0) for measuring the open-circuit voltage of the battery cell 100, the interval (Δt1) for calculating the moving average value of the open-circuit voltage, and the period S (S1 to S3) for calculating the moving average value of the open-circuit voltage are arbitrary.

[0077] In the first and second embodiments, the determination unit 640 determines the state of charge of the electrolyte from the state of charge SOC(t) of the electrolyte calculated based on the moving average value OCV(t) of the open-circuit voltage. The determination unit 640 may determine the state of charge of the electrolyte directly from the moving average value OCV(t) of the open-circuit voltage without using the state of charge SOC(t) of the electrolyte. Because there is a correlation between the state of charge of the electrolyte and the open-circuit voltage of the battery cell 100, the determination unit 640 may determine the state of charge of the electrolyte from the moving average value OCV(t) of the open-circuit voltage based on a previously obtained correlation. In this case, the calculation unit 650 does not need to calculate the state of charge SOC(t) of the electrolyte. Furthermore, the setting unit 640 sets conditions for calculating the moving average value based on the calculated moving average value OCV(t) of the open-circuit voltage.

[0078] In the second embodiment, the moving average value of the open circuit voltage OCV(t) and the moving average value of the power generation amount REP(t) are calculated. The period S for calculating the moving average value of the open circuit voltage OCV(t) and the moving average value of the power generation amount REP(t) is preferably equal.

[0079] The control unit 600 may include dedicated hardware such as an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a control circuit. In this case, each process may be executed by separate hardware. Alternatively, each process may be executed collectively by a single piece of hardware. Some of the processes may be executed by dedicated hardware, and other parts of the processes may be executed by software or firmware. [Explanation of symbols]

[0080] 10 redox flow battery system, 100 battery cell, 105a positive electrode, 105c negative electrode, 110a positive electrode chamber, 110c negative electrode chamber, 120 diaphragm, 300 circulation section, 300a positive electrode circulation section, 300c negative electrode circulation section, 310a positive electrode electrolyte reservoir, 320a positive electrode pump, 322a positive electrode supply pipe, 324a supply branch pipe, 326a first positive electrode recovery pipe, 328a second positive electrode recovery pipe, 310c negative electrode electrolyte reservoir, 320c negative electrode pump, 322c negative electrode supply pipe, 324c supply branch pipe, 326c first negative electrode recovery pipe, 328c second negative electrode recovery pipe, 500 open circuit voltage measurement section, 510 monitor cell, 520 measurement section, 600 control section, 602 CPU, 604 ROM, 606 RAM, 608 input / output interface, 610 power converter, 620 acquisition unit, 630 memory unit, 640 setting unit, 650 calculation unit, 660 determination unit, 670 flow rate control unit, 680 charge / discharge control unit, PL positive electrode electrolyte, NL negative electrode electrolyte

Claims

1. a battery cell having a positive electrode chamber in which a positive electrode is placed, a negative electrode chamber in which a negative electrode is placed, and a diaphragm separating the positive electrode chamber from the negative electrode chamber; a circulation unit that circulates a positive electrode electrolyte in the positive electrode chamber and a negative electrode electrolyte in the negative electrode chamber; an open circuit voltage measurement unit that measures the open circuit voltage of the battery cell; a control unit that calculates a moving average value of the open-circuit voltage measured by the open-circuit voltage measurement unit in accordance with a depth of charge of the positive electrode electrolyte and the negative electrode electrolyte, and controls the flow rates of the positive electrode electrolyte and the negative electrode electrolyte based on the calculated moving average value of the open-circuit voltage, thereby controlling charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte, The control unit calculating a moving average value of the open-circuit voltage during a predetermined first period and a moving average value of the open-circuit voltage during a predetermined third period that is longer than the predetermined first period; controlling the flow rates of the positive electrode electrolyte and the negative electrode electrolyte to a predetermined first flow rate when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are within a predetermined range and a difference between a moving average value of the open-circuit voltage in the predetermined third period and a moving average value of the open-circuit voltage in the predetermined first period is outside a predetermined first range; when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are within the predetermined ranges and a difference between a moving average value of the open-circuit voltage in the predetermined third period and a moving average value of the open-circuit voltage in the predetermined first period is within the predetermined first range, controlling the flow rates of the positive electrode electrolyte and the negative electrode electrolyte to flow rates smaller than the predetermined first flow rate; Redox flow battery system.

2. the control unit calculates a moving average value of the open-circuit voltage during a predetermined second period that is shorter than the predetermined first period; when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are smaller than the predetermined range and when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are larger than the predetermined range, the control unit controls charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte based on a moving average value of the open-circuit voltage during the predetermined second period. The redox flow battery system according to claim 1 .

3. the control unit acquires the amount of power generated by a renewable energy power plant connected to the battery cell, calculates a moving average value of the amount of power generated, and controls charging and discharging operations of the positive electrode electrolyte and the negative electrode electrolyte based on the calculated moving average value of the amount of power generated. The redox flow battery system according to claim 1 or 2.

4. a battery cell having a positive electrode chamber in which a positive electrode is placed, a negative electrode chamber in which a negative electrode is placed, and a diaphragm separating the positive electrode chamber from the negative electrode chamber; a circulation unit that circulates a positive electrode electrolyte in the positive electrode chamber and a negative electrode electrolyte in the negative electrode chamber; an open circuit voltage measurement unit that measures the open circuit voltage of the battery cell; a control unit that calculates a moving average value of the open-circuit voltage measured by the open-circuit voltage measurement unit in accordance with a depth of charge of the positive electrode electrolyte and the negative electrode electrolyte, and controls the flow rates of the positive electrode electrolyte and the negative electrode electrolyte based on the calculated moving average value of the open-circuit voltage, thereby controlling charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte, The control unit acquiring the amount of power generated by a renewable energy power plant connected to the battery cell, and calculating a moving average value of the amount of power generated; When the acquired amount of power generation is greater than the moving average value of the calculated amount of power generation, charging the positive electrode electrolyte and the negative electrode electrolyte; When the acquired amount of power generation is smaller than the moving average value of the calculated amount of power generation, the positive electrode electrolyte and the negative electrode electrolyte are discharged, When the acquired amount of power generation is the same as the moving average value of the calculated amount of power generation, charging / discharging of the positive electrode electrolyte and the negative electrode electrolyte is not performed. Redox flow battery system.

5. the control unit calculates a moving average value of the open-circuit voltage during a predetermined first period and a moving average value of the open-circuit voltage during a predetermined second period that is shorter than the predetermined first period; when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are within a predetermined range, the control unit controls charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte based on a moving average value of the open-circuit voltage during the predetermined first period; when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are smaller than the predetermined range and when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are larger than the predetermined range, the control unit controls charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte based on a moving average value of the open-circuit voltage during the predetermined second period. The redox flow battery system according to claim 4.

6. the control unit calculates a moving average value of the open-circuit voltage for a predetermined third period that is longer than the predetermined first period, and controls charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte based on a difference between the moving average value of the open-circuit voltage for the predetermined third period and the moving average value of the open-circuit voltage for the predetermined first period. The redox flow battery system according to claim 5 .

7. a measuring step of measuring an open circuit voltage of the battery cell; a calculating step of calculating a moving average value of the open-circuit voltage based on the measured open-circuit voltage in accordance with the depth of charge of the positive electrode electrolyte supplied to the positive electrode chamber of the battery cell and the negative electrode electrolyte supplied to the negative electrode chamber of the battery cell; a control step of controlling the flow rates of the positive electrode electrolyte and the negative electrode electrolyte based on the obtained moving average value of the open-circuit voltage, thereby controlling charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte; In the calculation step, a moving average value of the open-circuit voltage in a predetermined first period and a moving average value of the open-circuit voltage in a predetermined third period longer than the predetermined first period are calculated, in the control step, when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are within a predetermined range and a difference between the moving average value of the open-circuit voltage in the predetermined third period and the moving average value of the open-circuit voltage in the predetermined first period is outside a predetermined first range, the flow rates of the positive electrode electrolyte and the negative electrode electrolyte are controlled to a predetermined first flow rate, and when the depths of charge of the positive electrode electrolyte and the negative electrode electrolyte are within the predetermined range and a difference between the moving average value of the open-circuit voltage in the predetermined third period and the moving average value of the open-circuit voltage in the predetermined first period is within the predetermined first range, the flow rates of the positive electrode electrolyte and the negative electrode electrolyte are controlled to a flow rate smaller than the predetermined first flow rate. A method for operating a redox flow battery system.

8. a measuring step of measuring an open circuit voltage of the battery cell; a calculation step of calculating a moving average value of the open-circuit voltage based on the measured open-circuit voltage and according to the depth of charge of the positive electrode electrolyte supplied to the positive electrode chamber of the battery cell and the negative electrode electrolyte supplied to the negative electrode chamber of the battery cell, and acquiring the amount of power generated by a renewable energy power plant connected to the battery cell to calculate the moving average value of the amount of power generated; a control step of controlling the flow rates of the positive electrode electrolyte and the negative electrode electrolyte based on the obtained moving average value of the open-circuit voltage, thereby controlling charging and discharging of the positive electrode electrolyte and the negative electrode electrolyte; In the control step, When the acquired amount of power generation is greater than the moving average value of the calculated amount of power generation, charging the positive electrode electrolyte and the negative electrode electrolyte; When the acquired amount of power generation is smaller than the moving average value of the calculated amount of power generation, the positive electrode electrolyte and the negative electrode electrolyte are discharged, When the acquired amount of power generation is the same as the moving average value of the calculated amount of power generation, charging / discharging of the positive electrode electrolyte and the negative electrode electrolyte is not performed. A method for operating a redox flow battery system.

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