Patent Description:
Patent Literature <NUM> discloses a redox flow battery system including a cell that performs charging and discharging between the cell and a power system, a tank that stores an electrolyte supplied to the cell, a circulation pump that circulates the electrolyte between the cell and the tank, and a power converter (alternating current/direct current converter) disposed between the cell and the power system. <CIT>, forming the basis for the preamble of claim <NUM>, relates to a redox flow battery system and a method of operating a redox flow battery system. <CIT> relates to an operation method of a redox flow battery. <CIT> relates to a gravity feed flow battery system and method.

A redox flow battery system according to the present invention is according to claim <NUM>.

A method for operating a redox flow battery system according to the present invention is according to claim <NUM>.

Although a redox flow battery system is used as countermeasures against momentary voltage drop and the like, the redox flow battery system cannot perform discharging to a power system on its own if power failure occurs in the power system. This is because, when circulation pumps that circulate electrolytes in a cell stop, the redox flow battery system cannot continuously perform charging and discharging. As a countermeasure against this, in Patent Literature <NUM>, an uninterruptible power supply (UPS) that drives circulation pumps during power failure in a power system is provided. However, since the size of the UPS for securing the power for operating the circulation pumps is increased in accordance with the battery capacity of a redox flow battery, a large installation space and a high installation cost are necessary.

Accordingly, an object of the present disclosure is to provide a redox flow battery system capable of performing discharging to a power system on its own during power failure in the power system. Another object of the present disclosure is to provide a method for operating a redox flow battery system, the method being capable of restarting a redox flow battery system on its own during power failure in a power system.

The redox flow battery system according to the present disclosure is capable of operating a circulation pump on its own during power failure in a power system.

According to the method for operating a redox flow battery system of the present disclosure, a redox flow battery system can restart on its own during power failure in a power system.

First, the contents of embodiment according to the present invention will be listed and described.

A redox flow battery system according to an embodiment is according to claim <NUM>.

According to the above configuration, during power failure in the power system, the circulation pump can be operated by using the power of the electrolyte remaining in the cell. Once the circulation pump can be operated, power of the electrolyte stored in the tank can be drawn, and the operation of the circulation pump can be further continued by the power. As a result, the power of the electrolyte in the tank can be discharged to the power system. Thus, the redox flow battery system according to the embodiment can perform discharging to the power system on its own.

The redox flow battery system according to the embodiment, the redox flow battery system being capable of performing discharging on its own during power failure in the power system, does not require an UPS. Since no UPS is necessary, for example, the following advantages can be achieved.

In the redox flow battery system according to claim <NUM>,
the redox flow battery system includes a valve provided in a pipe that extends from the circulation pump toward the cell.

When circulation of the electrolyte is stopped, the charge/discharge control unit closes the valve to cause the electrolyte to remain in the cell.

In the redox flow battery system, in some cases, the circulation pump may be stopped during the operation of the system to stop circulation of the electrolyte to the cell. In such a case, the valve provided in the pipe that extends from the circulation pump toward the cell is closed so that the electrolyte remains in the cell. Accordingly, even if power failure in the power system occurs while the circulation pump is stopped, the redox flow battery system according to the embodiment can perform discharging to the power system on its own because the electrolyte remains in the cell.

In an exemplary embodiment of the redox flow battery system according to an embodiment described herein but not according to the present invention,
the tank is positioned such that a liquid level of the electrolyte stored in the tank is higher than an upper end of the cell.

With the above configuration, even if power failure in the power system occurs while the circulation pump is stopped, the redox flow battery system according to the embodiment can perform discharging to the power system on its own because the electrolyte remains in the cell. This is because since the liquid level of the electrolyte in the tank is located at a position higher than the upper end of the cell, a state where the electrolyte remains in the cell is provided by the gravity even when the circulation pump is stopped.

According to the method for operating a redox flow battery system, the redox flow battery system can perform discharging to a power system on its own. This is because during power failure in the power system, the circulation pump can be operated by using power of the electrolyte remaining in the cell. Once the circulation pump can be
operated, power of the electrolyte stored in the tank can be drawn, and the operation of the circulation pump can be further continued by the power.

In an exemplary embodiment of the method for operating a redox flow battery system according to the embodiment,
during a period with no power failure in the power system, charging and discharging of the cell are performed such that power of the electrolyte in the cell is not lower than power necessary for resuming circulation of the electrolyte by the circulation pump.

During a period with no power failure in the power system, charging and discharging of the cell are performed such that the power of the electrolyte remaining in the cell is not lower than power necessary for restarting the circulation pump, and consequently, during power failure in the power system, the circulation pump can be reliably operated.

Hereafter, a redox flow battery system and a method for operating the redox flow battery system according to embodiments of the present disclosure will be described.

Prior to a description of a redox flow battery system according to an embodiment, a basic configuration of a redox flow battery (hereinafter, RF battery) will be described with reference to <FIG>.

An RF battery <NUM> is one of electrolyte-circulating storage batteries and is used for, for example, storage of electricity of new energy from solar photovoltaic power generation or wind power generation. An operating principle of the RF battery <NUM> will be described with reference to <FIG>. The RF battery <NUM> is a battery that performs charging and discharging using the difference between an oxidation-reduction potential of active material ions contained in a positive electrolyte and an oxidation-reduction potential of active material ions contained in a negative electrolyte. The RF battery <NUM> is connected through a power converter <NUM> to a transformer facility <NUM> in a power system <NUM> and performs charging and discharging between the RF battery <NUM> and the power system <NUM>. The power system <NUM> of this example is a power system that performs alternating-current power transmission, and the power converter <NUM> is an alternating current/direct current converter. The power system may be a power system that performs direct-current power transmission. In such a case, the power converter is a direct current/direct current converter. The RF battery <NUM> includes a cell <NUM> divided into a positive electrode cell <NUM> and a negative electrode cell <NUM> by a membrane <NUM> that allows hydrogen ions to permeate therethrough.

The positive electrode cell <NUM> includes a positive electrode <NUM>. A positive electrolyte tank <NUM> that stores a positive electrolyte is connected through pipes <NUM> and <NUM> to the positive electrode cell <NUM>. The pipe <NUM> is provided with a circulation pump <NUM>. These components <NUM>, <NUM>, <NUM>, and <NUM> form a positive electrolyte circulation mechanism 100P that circulates the positive electrolyte. Similarly, the negative electrode cell <NUM> includes a negative electrode <NUM>. A negative electrolyte tank <NUM> that stores a negative electrolyte is connected through pipes <NUM> and <NUM> to the negative electrode cell <NUM>. The pipe <NUM> is provided with a circulation pump <NUM>. These components <NUM>, <NUM>, <NUM>, and <NUM> form a negative electrolyte circulation mechanism 100N that circulates the negative electrolyte. During charging and discharging, the electrolytes stored in the tanks <NUM> and <NUM> are circulated in the cells <NUM> and <NUM> by the circulation pumps <NUM> and <NUM>, respectively. When charging and discharging are not performed, the circulation pumps <NUM> and <NUM> are stopped and the electrolytes are not circulated.

The cell <NUM> is typically formed inside a structure called a cell stack <NUM>, as illustrated in <FIG> and <FIG>. The cell stack <NUM> is formed by sandwiching a layered structure called a substack <NUM> (<FIG>) with two end plates <NUM> and <NUM> on both sides of the layered structure, and then fastening the resulting structure with a fastening mechanism <NUM> (in the configuration illustrated in <FIG>, a plurality of substacks <NUM> are included).

The substack <NUM> (<FIG>) has a configuration in which cell frames <NUM>, positive electrodes <NUM>, membranes <NUM>, and negative electrodes <NUM> are repeatedly stacked and the resulting layered body is sandwiched between supply/drainage plates <NUM> (refer to the lower part of <FIG>, omitted in <FIG>).

A cell frame <NUM> includes a frame body <NUM> having a through-window and a bipolar plate <NUM> that covers the through-window. That is, the frame body <NUM> supports the bipolar plate <NUM> from the outer periphery of the bipolar plate <NUM>. The cell frame <NUM> can be produced by, for example, integrally forming the frame body <NUM> on an outer peripheral portion of the bipolar plate <NUM>. Alternatively, the cell frame <NUM> can be produced by preparing the frame body <NUM> formed to have a thin portion along an outer peripheral edge of the through-window and the bipolar plate <NUM> produced separately from the frame body <NUM>, and subsequently fitting an outer peripheral portion of the bipolar plate <NUM> into the thin portion of the frame body <NUM>. A positive electrode <NUM> is disposed so as to be in contact with one surface of the bipolar plate <NUM> of the cell frame <NUM>, and a negative electrode <NUM> is disposed so as to be in contact with the other surface of the bipolar plate <NUM>. In this configuration, one cell <NUM> is formed between bipolar plates <NUM> fitted in adjacent cell frames <NUM>.

Circulation of electrolytes to the cell <NUM> through the supply/drainage plates <NUM> illustrated in <FIG> is performed by liquid supply manifolds <NUM> and <NUM> and liquid drainage manifolds <NUM> and <NUM> that are formed in each cell frame <NUM>. The positive electrolyte is supplied from the liquid supply manifold <NUM> through an inlet slit (refer to a curved channel indicated by a solid line) formed on one surface side of the cell frame <NUM> (on the front side of the drawing) to the positive electrode <NUM>, and drained through an outlet slit (refer to a curved channel indicated by a solid line) formed in the upper part of the cell frame <NUM> into the liquid drainage manifold <NUM>. Similarly, the negative electrolyte is supplied from the liquid supply manifold <NUM> through an inlet slit (refer to a curved channel indicated by a broken line) formed on the other surface side of the cell frame <NUM> (on the back side of the drawing) to the negative electrode <NUM>, and drained through an outlet slit (refer to a curved channel indicated by a broken line) formed in the upper part of the cell frame <NUM> into the liquid drainage manifold <NUM>. Ring-shaped sealing members <NUM>, such as O-rings or flat gaskets, are disposed between cell frames <NUM> so as to suppress leakage of the electrolytes from the substack <NUM>.

On the basis of the basic configuration of the RF battery <NUM> described above, an RF battery system α according to an embodiment will be described with reference to <FIG>. Although <FIG> illustrates the configuration of a cell <NUM> in a simplified manner, it may be considered that the cell <NUM> has a configuration similar to that in <FIG>. Although <FIG> schematically illustrates an electrolyte <NUM> in the cell <NUM>, a positive electrolyte 8P (refer to the inside of a positive electrolyte tank <NUM>) and a negative electrolyte 8N (refer to the inside of a negative electrolyte tank <NUM>) are not mixed in the cell <NUM>.

The RF battery system α of this example includes an RF battery <NUM> and a charge/discharge control unit <NUM> that controls an operation of a power converter <NUM> to control charging and discharging of the cell <NUM>. The charge/discharge control unit <NUM> of this example is connected to the power converter <NUM>. The charge/discharge control unit <NUM> may be configured so that power is constantly supplied from the cell <NUM>. Alternatively, the charge/discharge control unit <NUM> may be configured so that, during a period with no power failure in a power system <NUM>, power is supplied from the power system <NUM>, and during power failure in the power system <NUM>, power is supplied from the cell <NUM>. The cell <NUM> of the RF battery <NUM> performs charging and discharging between the RF battery <NUM> and the power system <NUM>, as described with reference to <FIG>. The tank <NUM> (<NUM>) of the RF battery <NUM> stores the electrolyte 8P (8N) supplied to the cell <NUM>. A circulation pump <NUM> (<NUM>) of the RF battery <NUM> circulates the electrolyte 8P (8N) through pipes <NUM> and <NUM> (<NUM> and <NUM>) between the cell <NUM> and the tank <NUM> (<NUM>).

The RF battery system α of this example further includes a pump line <NUM> through which power is supplied to the circulation pump <NUM> (<NUM>), a valve 5A (5B) provided in the pipe <NUM> (<NUM>), and a valve line <NUM> through which power is supplied to the valves 5A and 5B. Here, the circulation pumps <NUM> and <NUM> and the valves 5A and 5B used in this example are those operated by an alternating current. When the power system <NUM> is a direct-current power transmission system, circulation pumps and valves that are operated by a direct current are used as the circulation pumps <NUM> and <NUM> and the valves 5A and 5B.

The pump line <NUM> through which power is supplied to the circulation pumps <NUM> and <NUM> extends from the power converter <NUM> to the circulation pumps <NUM> and <NUM>. Unlike the example illustrated in the figure, the pump line <NUM> may be branched from a point between the power converter <NUM> and the power system <NUM> and may extend to the circulation pumps <NUM> and <NUM>. With this configuration, during a period with no power failure in the power system <NUM>, the circulation pumps <NUM> and <NUM> can be operated by the power from the power system <NUM>, and during power failure in the power system <NUM>, the circulation pumps <NUM> and <NUM> can be operated by using the power of the electrolyte <NUM> remaining in the cell <NUM>. The amount of power supplied to the circulation pumps <NUM> and <NUM> is controlled by the charge/discharge control unit <NUM>. Operation signals of the circulation pumps <NUM> and <NUM> of this example are generated from the charge/discharge control unit <NUM> as indicated by the thin-line arrows. The operation signals are signals for switching ON/OFF of the circulation pumps <NUM> and <NUM>.

The valve 5Ais provided at a halfway position of the pipe <NUM> and regulates the amount of the positive electrolyte 8P supplied from the positive electrolyte tank <NUM> to the cell <NUM>. Similarly, the valve 5B is provided at a halfway position of the pipe <NUM> and regulates the amount of the negative electrolyte 8N supplied from the negative electrolyte tank <NUM> to the cell <NUM>. As the valves 5A and 5B, electrically operated valves driven by motors or electromagnetic valves driven by solenoids can be used.

The valve line <NUM> through which power is supplied to the valves 5A and 5B extends from the power converter <NUM> to the valves 5A and 5B. Unlike the example illustrated in the figure, the valve line <NUM> may be branched from a point between the power converter <NUM> and the power system <NUM> and may extend to the valves 5A and 5B. With this configuration, during a period with no power failure in the power system <NUM>, the valves 5A and 5B can be operated by the power from the power system <NUM>, and during power failure in the power system <NUM>, the valves 5A and 5B can be operated by using the power of the electrolyte <NUM> remaining in the cell <NUM>. Operation signals of the valves 5A and 5B of this example are generated from the charge/discharge control unit <NUM> as indicated by the thin-line arrows. The operation signals are signals for switching ON/OFF of the valves 5A and 5B.

The RF battery system α having the configuration described above is operated as follows.

During a normal operation of the RF battery system α (during a period with no power failure), the charge/discharge control unit <NUM> of the RF battery system a, for example, monitors a voltage of the electrolyte <NUM> in the cell <NUM> with a monitor cell (not illustrated) to control charging and discharging of the cell <NUM> such that power of the electrolytes 8P and 8N in the cell <NUM> is not lower than power necessary for resuming circulation of the electrolytes 8P and 8N by the circulation pumps <NUM> and <NUM>.

During the normal operation of the RF battery system a, in some cases, the circulation pumps <NUM> and <NUM> may be stopped to stop the circulation of the electrolytes 8P and 8N to the cell <NUM>. An example of a situation in which the circulation pumps <NUM> and <NUM> are stopped is a case where the RF battery <NUM> is sufficiently charged. In this example, when the circulation of the electrolytes 8P and 8N is stopped, the charge/discharge control unit <NUM> of the RF battery system α closes the valves 5A and 5B to cause the electrolyte <NUM> to remain in the cell <NUM>.

During power failure in the power system <NUM>, the charge/discharge control unit <NUM> of the RF battery system α operates the circulation pumps <NUM> and <NUM> using the power of the electrolyte <NUM> remaining in the cell <NUM> and discharges the power of the electrolytes 8P and 8N in the tanks <NUM> and <NUM> to the power system <NUM>.

Specifically, the charge/discharge control unit <NUM> detects power failure in the power system <NUM> on the basis of a change in the voltage of the power system <NUM>. Upon detection of power failure in the power system <NUM>, in the case where the valves 5A and 5B are opened, the charge/discharge control unit <NUM> closes the valves 5A and 5B to cause the electrolyte <NUM> to remain in the cell <NUM> and then restarts in a dedicated mode during power failure. The power for restarting the charge/discharge control unit <NUM> is provided by the power of the electrolyte <NUM> remaining in the cell <NUM>.

The charge/discharge control unit <NUM> that has started in the dedicated mode during power failure generates alternating-current power having a frequency optimal to operate the circulation pumps <NUM> and <NUM>, operates the circulation pumps <NUM> and <NUM>, and opens the valves 5A and 5B. Once the circulation pumps <NUM> and <NUM> operate, the electrolytes 8P and 8N in the tanks <NUM> and <NUM> are fed to the cell <NUM> and the power of the electrolytes 8P and 8N can also be drawn, and thus the operation of the circulation pumps <NUM> and <NUM> and the valves 5A and 5B can be continued. As a result, the power of the electrolytes 8P and 8N in the tanks <NUM> and <NUM> can be discharged to the power system <NUM>.

As described above, according to the RF battery system α and the method for operating the RF battery system α of this example, since the RF battery system α can perform discharging on its own during power failure in the power system <NUM>, the RF battery system α does not require an UPS. Since no UPS is necessary, the following advantages can be achieved.

In Embodiment <NUM> described herein but not according to the present invention, an RF battery system β which differs from the system in Embodiment <NUM> in configuration for causing the electrolyte <NUM> to remain in the cell <NUM> will be described with reference to <FIG>. Configurations that are the same as those of Embodiment <NUM> are assigned the same reference signs as those in <FIG>, and the description thereof is omitted.

In the configuration of Embodiment <NUM> illustrated in <FIG>, tanks <NUM> and <NUM> are arranged such that liquid levels of electrolytes 8P and 8N in the tanks <NUM> and <NUM> are higher than an upper end of a cell <NUM>. Herein, the upper end of the cell <NUM> is an upper end of a space in which the electrodes <NUM> and <NUM> illustrated in <FIG> and <FIG> are arranged. With this configuration, regardless of operation or stop of circulation pumps <NUM> and <NUM>, a state where an electrolyte <NUM> remains in the cell <NUM> can be provided.

During a normal operation of the RF battery system β, a charge/discharge control unit <NUM> of the RF battery system β also, for example, monitors a voltage of the electrolyte <NUM> in the cell <NUM> with a monitor cell (not illustrated) to control charging and discharging of the cell <NUM> such that power of the electrolytes 8P and 8N in the cell <NUM> is not lower than power necessary for resuming circulation of the electrolytes 8P and 8N by the circulation pumps <NUM> and <NUM>.

During the normal operation of the RF battery system β, in the case where the circulation pumps <NUM> and <NUM> are stopped to stop the circulation of the electrolytes 8P and 8N in the cell <NUM>, the electrolyte <NUM> can be caused to remain in the cell <NUM> by simply stopping the circulation pumps <NUM> and <NUM>. This is because the liquid levels of the electrolytes 8P and 8N in the tanks <NUM> and <NUM> are located higher than the upper end of the cell <NUM>.

During power failure in a power system <NUM>, the charge/discharge control unit <NUM> of the RF battery system β operates the circulation pumps <NUM> and <NUM> using the power of the electrolyte <NUM> remaining in the cell <NUM> and discharges the power of the electrolytes 8P and 8N in the tanks <NUM> and <NUM> to the power system <NUM>, as in the configuration of Embodiment <NUM>.

Specifically, the charge/discharge control unit <NUM> detects power failure in the power system <NUM> from a decrease in the voltage of the power system <NUM>. Upon detection of power failure in the power system <NUM>, the charge/discharge control unit <NUM> restarts in a dedicated mode during power failure. The power for restarting the charge/discharge control unit <NUM> is provided by the power of the electrolyte <NUM> remaining in the cell <NUM>. The charge/discharge control unit <NUM> that has started in the dedicated mode during power failure generates alternating-current power having a frequency optimal to operate the circulation pumps <NUM> and <NUM> and operates the circulation pumps <NUM> and <NUM>. Once the circulation pumps <NUM> and <NUM> operate, the power of the electrolytes 8P and 8N can also be drawn and thus the operation of the circulation pumps <NUM> and <NUM> can be continued. As a result, the power of the electrolytes 8P and 8N in the tanks <NUM> and <NUM> can be discharged to the power system <NUM>.

The configuration of this example also does not require an UPS, and thus advantages that are the same as those in Embodiment <NUM> can be achieved. Furthermore, since the configuration of this example is a simple configuration in which the valves 5A and 5B (refer to <FIG>) of Embodiment <NUM> and control thereof are not necessary, the configuration is easily constructed and has good maintainability.

Claim 1:
A redox flow battery system comprising:
a cell (<NUM>) that performs charging and discharging between the cell (<NUM>) and a power system (<NUM>); a tank (<NUM>, <NUM>) that stores an electrolyte supplied to the cell (<NUM>);
a circulation pump (<NUM>, <NUM>) that circulates the electrolyte between the cell (<NUM>) and the tank (<NUM>, <NUM>);
a power converter (<NUM>) disposed between the cell (<NUM>) and the power system; and
a charge/discharge control unit (<NUM>) that controls an operation of the power converter to control charging and discharging of the cell (<NUM>),
wherein when the charge/discharge control unit (<NUM>) detects power failure in the power system, the charge/discharge control unit (<NUM>) controls the power converter such that power of the electrolyte remaining in the cell is supplied to the circulation pump (<NUM>, <NUM>),
characterized in that:
the redox flow battery system further comprises a valve (5A, 5B) provided in a pipe (<NUM>, <NUM>) that extends from the circulation pump (<NUM>, <NUM>) toward the cell (<NUM>),
wherein when circulation of the electrolyte is stopped, the charge/discharge control unit (<NUM>) closes the valve (5A, 5B) to cause the electrolyte to remain in the cell.