JP2006114360A - Method for operating redox flow battery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for operating a redox flow battery system that can fully secure a battery capacity for emergency without increasing the amount of an electrolyte excessively. <P>SOLUTION: In the operation method of the redox flow battery system for discharging by supplying an electrolyte to a cell, a computer is allowed to perform: a step for controlling the stop of discharge for securing a capacity for emergency, a step for measuring a cell terminal voltage, an open voltage, and a load current (1), a step for computing the voltage difference between the terminal voltage and the open voltage (2), a step for computing cell resistance based on the computed voltage difference and a load current (3), a step for determining the lower-limit value of the open voltage for securing the capacity for emergency based on the computed cell resistance (4), and a step for continuing discharge when the measured open voltage is equal to or higher than the lower-limit value and stopping discharge when it is less than the lower-limit value by comparing the lower-limit value of the determined open voltage with the measured open voltage (5). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for operating a redox flow battery system in which an electrolytic solution is supplied to a cell for discharging. In particular, the present invention relates to a method for operating a redox flow battery system capable of sufficiently securing an emergency battery capacity without excessively increasing the amount of electrolyte.

The redox flow battery is conventionally used as a load leveling or a voltage drop countermeasure. FIG. 3 is an explanatory diagram showing the operating principle of the redox flow battery. This battery includes a cell 100 separated into a positive electrode cell 100A and a negative electrode cell 100B by a diaphragm 101 made of an ion exchange membrane. The positive electrode cell 100A and the negative electrode cell 100B each incorporate a positive electrode 102 and a negative electrode 103. Connected to the positive electrode cell 100A is a positive electrode electrolyte tank 104A that stores the positive electrode electrolyte that is supplied to the positive electrode 102 and discharged from the positive electrode 102 via a conduit 106A that serves as a transport path for the electrolyte. . The negative electrode cell 100B is connected to a negative electrode electrolyte tank 104B that stores the negative electrode electrolyte that is supplied to the negative electrode 103 and discharged from the negative electrode 103 via a conduit 106B that serves as an electrolyte transport path. . An aqueous solution of ions such as vanadium ions whose valence changes is used for each electrode electrolyte, and is circulated by pumps 105A and 105B, and charging and discharging are performed in accordance with the valence change reaction of the positive electrode 102 and the negative electrode 103. For example, when an electrolytic solution containing vanadium ions is used, the reaction that occurs during charging and discharging in the cell is as follows.
The positive ^{electrode: V 4+ → V 5+ + e} - ( ^{charging) V 4+ ← V 5+ + e} - ( discharge)
The negative ^{electrode: V 3+ + e - → V} 2+ ( ^{charging) V 3+ + e - ← V} 2+ ( discharge)

The above redox flow battery system is connected to an AC / DC converter and connected to a charging power source such as a power plant or a discharge target such as a consumer via the AC / DC converter. I do. In the case of a redox flow battery for load leveling, a charging time band, a discharging time band, and a standby time band are determined in advance, and charging, discharging, and standby are repeated. In such a redox flow battery system, an emergency battery intended for supply to a fire extinguishing load (fire extinguishing equipment) in the event of a fire always ensures a certain battery capacity so that sufficient power can be supplied in an emergency. It is necessary to keep. Therefore, as shown in the graph of FIG. 4, the terminal voltage v ₁ (or open circuit voltage v ₂ ) that can maintain the emergency capacity is set in advance, and the cell terminal voltage (or open circuit voltage) is constantly monitored to discharge the battery. When the terminal voltage (or open circuit voltage) reaches the set voltage v ₁ (or voltage v ₂ ), the discharge is stopped (or put into a standby state). In addition, Patent Document 1 includes an emergency tank that stores an electrolyte solution with a high charging depth separately from a tank that stores an electrolyte solution used for normal operation, and is charged by switching to an emergency tank in an emergency such as a fire. The battery system which supplies electric power to load using the electrolyte solution with a high depth is disclosed.

JP 2002-329522 A

However, the above conventional technique has a problem that the battery system is increased in size and cost.
Even if the terminal voltage is the same, the dischargeable battery capacity varies depending on the internal resistance of the cell. The change in the internal resistance of the cell is caused by temperature change or aging deterioration. Therefore, the voltage that determines when the discharge is stopped is sufficiently high so that an emergency capacity can be secured even under the worst conditions where the internal resistance of the cell has increased, assuming temperature changes and deterioration over time. The electrolyte was increased to increase the time capacity by setting to. However, by increasing the amount of electrolyte, the tank to be stored has to be enlarged, leading to an increase in the size of the battery system. In addition, the worst condition under which the internal resistance of the cell has increased is rare, and since the discharge is normally performed under good conditions with little internal resistance of the cell, it is excessive for most of the operation time. It was designed. In addition, most of the operation time is operated with an extra capacity remaining, and improvement in battery efficiency is desired.

  On the other hand, Patent Document 1 includes an emergency tank that stores an electrolytic solution having a high charging depth, so the tank storing the electrolytic solution used for normal operation need not be large, but a separate emergency tank The increase in the size of the battery system is caused by the provision of.

  Therefore, a main object of the present invention is to provide a method for operating a redox flow battery system that can reliably maintain an emergency capacity without increasing the size of the battery system.

  The present invention achieves the above object by always detecting the internal resistance of the cell during discharge and changing the discharge stop timing according to the internal resistance.

That is, the present invention is a method for operating a redox flow battery system in which an electrolytic solution is supplied to a cell to perform discharge, and the computer performs the following steps to stop the discharge in order to ensure an emergency capacity. It is characterized by controlling.
1. Measuring cell terminal voltage, open circuit voltage and load current
2. Step to calculate voltage difference between terminal voltage and open circuit voltage
3. Step of calculating cell resistance based on calculated voltage difference and load current
4. Based on the calculated cell resistance, the step to determine the lower limit of the open circuit voltage that can secure the emergency capacity
5. Comparing the lower limit value of the determined open-circuit voltage with the measured open-circuit voltage, and if the measured open-circuit voltage is greater than or equal to the lower-limit value, continue the discharge, and if less than the lower-limit value, stop the discharge

Hereinafter, the present invention will be described in more detail.
The redox flow battery system used in the operation method of the present invention is a cell for a redox flow battery (main cell) that is connected to a load for charging and discharging, a tank for storing an electrolyte solution supplied / discharged to the cell, The structure which comprises the transport path of the electrolyte solution which connects a cell and a tank is mentioned. You may provide the pump so that electrolyte solution may be easily supplied to a cell from a tank. Examples of the battery cell include a configuration including a positive electrode cell and a negative electrode cell through a diaphragm. As the electrolyte, 1. High electromotive force 2. High energy density 3. Since the electrolyte is a single element system, it can be regenerated by charging even if the cathode electrolyte and anode electrolyte are mixed Vanadium ion solutions having many advantages such as being possible are preferred. As a transportation path for the electrolytic solution, a pipe (pipe) formed of an insulating material may be used so that an accident such as a short circuit does not occur even when the electrolytic solution contacts. In addition, in the present invention, in order to measure the open circuit voltage (voltage during non-energization) during normal operation, in particular during discharge, the voltage in the non-energized state can be measured even in the energized state. Specifically, it is possible to provide a monitor cell for measuring an open-circuit voltage separately from the main cell connected to a load for charging and discharging. A monitor cell having the same configuration as that of the main cell may be used. A known redox flow battery system may be used. A redox flow battery system having the above configuration is connected to an AC / DC converter and connected to the system (charging power source such as a power plant, discharge target (load) such as a consumer) via the AC / DC converter. To charge and discharge.

In the present invention, the discharge stop timing is controlled using a computer capable of performing various processes such as storage, calculation, and determination. Specifically, a predetermined control program shown below is input to a computer in advance, and discharging is continued or stopped according to a computer command.
(1) Step of measuring cell terminal voltage, open circuit voltage, and load current
(2) Step of calculating cell resistance based on measured terminal voltage, open circuit voltage, and load current
(3) Step of determining the lower limit value of the open-circuit voltage that can secure the emergency capacity based on the calculated cell resistance, and comparing the determined lower limit value with the measured open-circuit voltage to determine the continuation / stop of discharge

  In performing the first step, terminal voltage measuring means, open-circuit voltage measuring means, and load current measuring means are provided. An AC / DC converter having means for measuring terminal voltage and load current may be used. Any open-circuit voltage measuring means may be used as long as it can measure the voltage. These measurement means and the computer are connected via a wiring for transmitting a measurement result (electric signal). Further, the processing means is configured so that an electric signal from each measuring means is input to the signal receiving unit.

  In performing the second step, the computing means included in the computer obtains the difference between the terminal voltage and the open circuit voltage and divides this voltage difference by the load current to obtain the cell resistance.

  In performing the third step, the relationship between the cell resistance and the open-circuit voltage that can secure the emergency capacity is obtained in advance, and this relationship value data is input in advance to the storage means of the computer. A plurality of desired emergency capacities may be provided, and relation value data may be created for each of these capacities so that the desired value of the related capacity data can be appropriately selected. Then, the collation determining means included in the computer compares the cell resistance obtained from the computing means with the relational value data called from the storage means so as to obtain the lower limit value of the open-circuit voltage that can secure the emergency capacity. Keep it. Next, the determination means of the computer calls the measured open circuit voltage from the storage means, and determines the magnitude relationship between the measured value and the lower limit value. Specifically, when the measured value is equal to or higher than the lower limit value, the emergency capacity can be sufficiently secured, so that it is determined that the operation (discharge) is continued as it is. On the other hand, if the measured value is less than the lower limit value, it is determined that the operation (discharge) is to be stopped (or shifted to the standby state) because the emergency capacity cannot be secured if the discharge is continued. In addition to the computer, a processing device that can perform various processes such as storage, calculation, and determination as described above may be used.

  The operation method of the present invention having the above-described configuration ensures that the emergency capacity is secured because the voltage for determining the discharge stop timing is not a fixed value but is changed according to the cell resistance in order to secure the emergency capacity. The size of the battery system is not increased without increasing the size of the tank of the electrolyte or providing an emergency tank. For this reason, even a small battery system or a battery system of the same size as the conventional one can sufficiently secure an emergency capacity, and does not leave an excessive capacity and operates efficiently. It can be carried out.

  Embodiments of the present invention will be described below.

  FIG. 1 is a schematic configuration diagram of a redox flow battery system to which the operation method of the present invention is applied. This redox flow battery system 1 stores a cell stack 2, a positive electrolyte tank 3a for storing a positive electrolyte supplied / discharged to the cell stack 2, and a negative electrolyte supplied / discharged to the cell stack 2. A negative electrode electrolyte tank 3b, and pipes 4a, 4b, 5a, and 5b serving as electrolyte transport paths connecting the cell stack 2 and the tanks 3a and 3b are provided. Further, the supply pipes 4a and 4b are respectively provided with pumps 6a and 6b so that the electrolyte can be easily supplied to the cell stack 2.

  The cell stack 2 has a stacked structure in which a plurality of cells for redox flow batteries are stacked, and includes a main cell 2a used for normal operation and a monitor cell 2b for measuring an open circuit voltage. The main cell 2a is connected to an AC / DC converter 11, and is connected via the AC / DC converter 11 to a system such as a charging power source such as a power plant or a discharge target such as a consumer. The monitor cell 2b is a cell through which the electrolyte solution of each electrode is transported in common with the main cell 2a, and is not connected to the system and is not used for charging / discharging. That is, the monitor cell 2b is always in a non-energized state. The cell stack 2 and the positive electrode electrolyte tank 3a and the pipes 4a and 5a constitute the positive electrode electrolyte circuit, and the cell stack 2 and the negative electrode electrolyte tank 3b and the pipes 4b and 5b form the negative electrode circuit. Constitute.

The basic structure of the cells constituting the main cell 2a and the monitor cell 2b is the same as that of the cell 100 shown in FIG. 3, and is separated into a positive electrode cell and a negative electrode cell by an ion exchange membrane (diaphragm). A negative electrode is built in the negative electrode cell, and a positive electrode electrolyte and a negative electrode electrolyte are supplied to each electrode. In this example, a solution containing V ⁵⁺ was used as the positive electrode electrolyte, and a solution containing V ²⁺ was used as the negative electrode electrolyte.

  The AC / DC converter 11 is provided with measuring means (not shown) capable of measuring the terminal voltage A (V) and load current C (A) of the main cell 2a, and measured from each measuring means. The result is connected to the computer 20 via wiring so that the result is transmitted to the computer 20. A voltage measuring means 12 is connected to the monitor cell 2b to measure the open circuit voltage, and the voltage measuring means 12 is connected to the computer 20 via wiring so that the measurement result is transmitted to the computer 20. In this example, the computer 20 controls the AC / DC converter 11 to control external charging and external discharging. The pumps 6a and 6b are also connected to the computer 20 via wiring, and the computer 20 controls the driving of the pumps 6a and 6b. In this example, a known computer that can perform various processes such as storage, calculation, and determination is used as the computer 20.

  In the redox flow battery system having the above-described configuration, the operation method of the present invention for controlling the discharge stop timing in order to secure an emergency battery capacity such as supplying power to a fire extinguishing facility will be specifically described. . FIG. 2 is a flowchart showing a control procedure of the operation method of the redox flow battery system of the present invention. In this example, during discharge, the terminal voltage A (V) and the load current C (A) are constantly measured by the measuring means included in the AC / DC converter, and the open circuit voltage B (V) is constantly measured by the voltage measuring means. The computer is configured to be input.

  In the operation method of the present invention, first, the terminal voltage A (V) and the load current C (A) are measured by the measuring means of the AC / DC converter (step S1), and the open voltage B (V) is measured by the voltage measuring means. (Step S2). The measurement result (electrical signal) is input to the signal receiver of the computer. At this time, the computer reads the input electrical signals as terminal voltage A (V), open circuit voltage B (V), and load current C (A), respectively, and temporarily stores them in the storage means.

  Next, the computing means of the computer calculates the difference E (V) = AB between the measured terminal voltage A (V) and the open circuit voltage B (V) (step S3), and measures this voltage difference E (V) The cell resistance F (Ω) = E / C is calculated by dividing by the load current C (A) (step S4). Then, the computer verification determining means calls the relation value data between the cell resistance and the open voltage stored in the storage means, and compares the cell resistance F (Ω) with the lower limit of the open voltage that can secure the emergency capacity. A value G (V) is determined (step S5). In this example, when performing step S5, a plurality of emergency capacitors are set in advance so as to be able to cope with various requested emergency capacitors, and the relationship between the cell resistance and the open circuit voltage for each emergency capacitor. Value data is created and input to a computer, and desired value data of emergency capacity is selected.

  Next, the determination means of the computer determines the magnitude relationship between the determined lower limit value G (V) of the open-circuit voltage and the measured open-circuit voltage B (V) (step S6). When the measured open circuit voltage B (V) is equal to or higher than the lower limit G (V), the redox flow battery system can sufficiently maintain the emergency capacity. Therefore, since it is not necessary to stop the discharge, the determination means of the computer determines that the discharge is continued (step S7). Thereafter, in this example, the procedure after step S1 is repeated in order to control the discharge stop during the discharge. On the other hand, if the measured open circuit voltage B (V) is less than the lower limit G (V), the emergency capacity cannot be secured if the discharge is continued as it is. Therefore, the determination means of the computer determines that the discharge is stopped (step S8), and ends the control. When the discharge is finished, it is preferable to set it to stand by, and then to perform each operation when each preset operation time band (charge, discharge, standby) is reached. Then, when discharging is performed, the discharge stop is controlled.

  The present invention having the above configuration changes the voltage at which discharge stops according to the internal resistance of the cell, so that even if the dischargeable battery capacity changes due to the cell resistance, sufficient emergency capacity can be secured. it can. In addition, when applied to a conventional redox flow battery system without excessive design, more efficient operation can be performed.

  The present invention is particularly suitable for use in the operation of an emergency redox flow battery system for the purpose of supplying to a fire extinguishing load in a fire in addition to a load leveling application.

It is a schematic block diagram of the redox flow battery system to which the operation method of the redox flow battery system of the present invention is applied. It is a flowchart which shows the operation procedure of the operating method of this invention redox flow battery system. It is explanatory drawing which shows the operating principle of a vanadium redox flow battery system. It is a graph which shows the relationship between battery capacity and voltage.

Explanation of symbols

1 Redox flow battery system 2 Cell stack 2a Main cell
2b Monitor cell 3a Positive electrolyte tank 3b Negative electrolyte tank
4a, 4b, 5a, 5b Piping 6a, 6b Pump
11 AC / DC converter 12 Voltage measurement means 20 Computer
100 cells 100A positive electrode cell 100B negative electrode cell 101 diaphragm 102 positive electrode
103 Negative electrode 104A Positive electrolyte tank 104B Negative electrolyte tank
105A, 105B Pump 106A, 106B Conduit

Claims (1)

A method of operating a redox flow battery system that discharges by supplying an electrolytic solution to a cell,
A method for operating a redox flow battery system, comprising: causing a computer to perform the following steps to control stop of discharge in order to ensure an emergency capacity.
1. Measuring cell terminal voltage, open circuit voltage and load current
2. Step to calculate voltage difference between terminal voltage and open circuit voltage
3. Step of calculating cell resistance based on calculated voltage difference and load current
4. Based on the calculated cell resistance, the step to determine the lower limit of the open circuit voltage that can secure the emergency capacity
5. Comparing the lower limit value of the determined open-circuit voltage with the measured open-circuit voltage, and if the measured open-circuit voltage is greater than or equal to the lower-limit value, continue the discharge, and if less than the lower-limit value, stop the discharge

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