FUEL CELL SYSTEM

A fuel cell system according to an embodiment includes: a fuel cell that is supplied with a fuel gas to generate electric power; a determination unit that determines a mixing ratio of inert gas in the fuel gas to be supplied to the fuel cell; and an operation control unit that changes an operation condition of the fuel cell system, based on the mixing ratio of inert gas determined by the determination unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2023-040015, filed Mar. 14, 2023; the entire contents of which are incorporated herein by reference.

FIELD

This embodiment relates to a fuel cell system.

BACKGROUND

A fuel cell system comprises a fuel cell with an electrolyte membrane interposed between a fuel electrode and an oxidant electrode. In the fuel cell, a fuel gas supplied to the fuel electrode and an oxidant gas supplied to the oxidant electrode react electrochemically through the electrolyte membrane. Thus, the fuel cell is a power generation device that converts chemical energy into electric energy. The fuel gas is, for example, a hydrogen gas, and the oxidant gas is, for example, air.

A fuel tank that stores a fuel gas to be supplied to the fuel electrode is connected to the fuel cell system. During normal operation, the fuel gas is supplied from the fuel tank to the fuel electrode, and the fuel cell generates electric power. The fuel tank stores a high-pressure hydrogen gas or liquid hydrogen.

When the fuel tank is replenished with fuel, a separate replenishment tank is connected to the fuel tank through a replenishment channel such as a pipe. The replenishment channel is purged with an inert gas such as a nitrogen gas or a helium gas, and then the fuel in a gaseous state or a liquid state is supplied from the replenishment tank to the fuel tank.

The fuel thus stored in the fuel tank may contain the inert gas. If the fuel gas containing the inert gas is supplied to the fuel electrode, the inert gas tends to accumulate inside the fuel electrode in the fuel cell system. In addition, during the normal operation of the fuel cell, the inert gas contained in the oxidant electrode may move to the fuel electrode through the electrolyte membrane inside the fuel cell.

If the inert gas accumulates inside the fuel electrode in this way, a fuel gas concentration in the fuel electrode may decrease. This may impair a fuel cell performance, resulting in suspension of operation of the fuel cell.

The fuel cell system is sometimes equipped with a fuel-gas circulation channel that returns the fuel gas discharged from the fuel cell to the fuel cell. In this case, a degassing line including a degassing valve is connected to the fuel-gas circulation channel. Such a fuel cell system allows the inert gas in the fuel electrode to be released from the degassing value, so as to recover the fuel gas concentration. However, if the inert gas, an amount of which exceeds an amount of inert gas that can be released by a normal degassing operation, is supplied to the fuel electrode, a concentration of the inert gas in the fuel electrode may increase. This may impair a fuel cell performance, resulting in suspension of operation of the fuel cell.

DETAILED DESCRIPTION

A fuel cell system according to an embodiment comprises: a fuel cell that is supplied with a fuel gas to generate electric power; a determination unit that determines a mixing ratio of inert gas in the fuel gas to be supplied to the fuel cell; and an operation control unit that changes an operation condition of the fuel cell system, based on the mixing ratio of inert gas determined by the determination unit.

A fuel cell system according to an embodiment comprises: a fuel cell that is supplied with a fuel gas to generate electric power; a fuel-gas circulation channel that returns the fuel gas discharged from the fuel cell to the fuel cell; a third pressure gauge that measures a pressure value of the fuel gas in the fuel-gas circulation channel; a degassing channel that discharges outside the fuel gas from the fuel-gas circulation channel; a degassing valve provided on the degassing channel; and an operation control unit that changes an operation condition of the fuel cell system, based on the pressure value measured by the third pressure gauge.

A fuel cell system according to an embodiment comprises: a fuel cell that is supplied with a fuel gas to generate electric power; and an operation control unit that changes an operation condition of the fuel cell system, based on information stored in a superordinate control system of the fuel cell system.

The embodiments are described below with reference to the drawings.

First Embodiment

A fuel cell system1according to a first embodiment is described first usingFIG.1. The fuel cell system1according to this embodiment may be installed in a building or mounted on a mobile body. Examples of buildings include condominiums, office buildings, factories, commercial facilities, etc. In this case, electric power generated by the fuel cell system1may be used to drive elevators, to light and/or air condition the inside of the building. Examples of mobile bodies include ships, automobiles, railcars, etc. In this case, electric power generated by the fuel cell system1may be used to drive the mobile body, to light and/or air condition the inside of the mobile body.

As shown inFIG.1, the fuel cell system1comprises a fuel cell2, a fuel tank3, a fuel-gas supply channel4, an oxidant-gas supply unit5, an oxidant-gas supply channel6, an oxidant-gas discharge channel8, a fuel-gas circulation channel9, a degassing channel10, a power converter11, and a controller30.

The fuel cell2is configured to be capable of generating electric power. The fuel cell2is a power generation device that generates electric power by using a fuel gas supplied from the fuel tank3and an oxidant gas supplied from the oxidant-gas supply unit5. The fuel gas may be a hydrogen gas, or a mixed gas containing a hydrogen gas, etc. The oxidant gas may be air, etc. More specifically, the fuel cell2includes, although not shown, a fuel electrode (anode), an oxidant electrode (cathode), and an electrolyte membrane interposed between the fuel electrode and the oxidant electrode. The fuel gas supplied to the fuel electrode and the oxidant gas supplied to the oxidant electrode react electrochemically through the electrolyte membrane. Thus, chemical energy is converted into electric energy, so that the fuel cell2can generate electric power.

The fuel tank3is an example of a fuel supply unit. The fuel tank3is configured to store the fuel gas to be supplied to the fuel electrode. The fuel tank3stores a high-pressure hydrogen gas or liquid hydrogen.

The fuel-gas supply channel4supplies the fuel gas stored in the fuel tank3to the fuel electrode of the fuel cell2. The fuel-gas supply channel4may be provided with a fuel-gas supply valve12, a flow-rate regulation valve13, a first pressure gauge14, and a second pressure gauge15. The fuel-gas supply valve12is a valve that controls supply of the fuel gas from the fuel tank3to the fuel electrode. The fuel-gas supply valve12is opened upon operation of the fuel cell system1to supply the fuel gas to the fuel electrode. The fuel-gas supply valve12may be controlled by the controller30.

The flow-rate regulation valve13is a valve that regulates a supply flow rate of the fuel gas to the fuel electrode of the fuel cell2. An opening degree of the flow-rate regulation valve13is regulated based on a command of the controller30. Opening degree values commanded by the controller30are stored in the controller30. The flow-rate regulation valve13may be provided downstream of the fuel-gas supply valve12. The flow-rate regulation valve13may be an injector, a proportional solenoid valve or a proportional electric valve whose opening degree can be controlled.

The first pressure gauge14is configured to measure a pressure value P1 of the fuel gas flowing into the flow-rate regulation valve13in the fuel-gas supply channel4. The pressure value P1 corresponds to an inlet pressure value of the flow-rate regulation valve13. The first pressure gauge14is provided upstream of the flow-rate regulation valve13in the fuel-gas supply channel4. The first pressure gauge14may be provided between the fuel-gas supply valve12and the flow-rate regulation valve13. The pressure value P1 measured by the first pressure gauge14is transmitted to the controller30.

The second pressure gauge15is configured to measure a pressure value P2 of the fuel gas flowing out from the flow-rate regulation valve13in the fuel-gas supply channel4. The pressure value P2 corresponds to an outlet pressure value of the flow-rate regulation valve13. The second pressure gauge15is provided downstream of the flow-rate regulation valve13in the fuel-gas supply channel4. The second pressure gauge15may be provided between the flow-rate regulation valve13and the fuel cell2. The pressure value P2 measured by the second pressure gauge15is transmitted to the controller30.

The oxidant-gas supply unit5is configured to supply the oxidant gas to the oxidant electrode. The oxidant-gas supply unit5may be, for example, a blower or a compressor.

The oxidant-gas supply channel6supplies the oxidant gas from the oxidant-gas supply unit5to the oxidant electrode of the fuel cell2. The oxidant-gas supply unit6may be provided with an oxidant gas supply valve16. The oxidant gas supply valve16is a valve that controls supply of the oxidant gas from the oxidant-gas supply unit5to the oxidant electrode. The oxidant gas supply valve16is opened upon operation of the fuel cell system1to supply the oxidant gas to the oxidant electrode. The oxidant gas supply valve16may be controlled by the controller30.

The oxidant-gas discharge channel8discharges outside the oxidant gas discharged from the oxidant electrode of the fuel cell2. The oxidant-gas discharge channel8may be provided with an oxidant-gas discharge valve18. The oxidant-gas discharge valve18is a valve that controls discharge of the oxidant gas from the oxidant electrode to the outside. The oxidant-gas discharge valve18is opened upon operation of the fuel cell system1to discharge the oxidant gas from the oxidant electrode. The oxidant-gas discharge valve18may be controlled by the controller30.

The fuel-gas circulation channel9is configured to return the fuel gas discharged from the fuel electrode of the fuel cell2to the fuel cell2. An upstream end of the fuel-gas circulation channel9may be connected to the aforementioned fuel electrode of the fuel cell2, and a downstream end of the fuel-gas circulation channel9may be connected to the aforementioned fuel-gas supply channel4. In this case, the fuel gas discharged from the fuel electrode can be supplied to the fuel-gas supply channel4to recycle the fuel gas. The fuel-gas circulation channel9may be provided with a circulation blower19. The circulation blower19draws the fuel gas from the fuel electrode and feeds the fuel gas to the fuel-gas supply channel4.

The degassing channel10is configured to discharge outside the fuel gas from the fuel-gas circulation channel9. The degassing channel10may be provided with a degassing valve20.

The degassing valve20is a valve that is provided on the fuel-gas circulation channel9to control discharge of the fuel gas from the fuel-gas circulation channel9to the outside. As shown inFIG.2, in the degassing valve20, a closed state which is maintained at a predetermined time interval t1, and an open state which is maintained at a predetermined time interval t2 may be alternated.

As shown inFIG.1, the power converter11is a device for converting an electric voltage and an electric current of the electric power generated by the fuel cell2. The electric power converted by the power converter11is supplied to an external load. The power converter11may be a DC/DC converter or an inverter. The power converter11is connected to the fuel cell2through an output line21. The output line21is provided with an ammeter22. The ammeter22is configured to measure an electric current value of the generated electric power outputted from the fuel cell2.

The controller30may include a determination unit31and an operation control unit32. The controller30is configured to control the aforementioned fuel-gas supply valve12, the flow-rate regulation valve13, the oxidant gas supply valve16, the oxidant-gas discharge valve18, the degassing valve20, and the power generator11.

The determination unit31is configured to determine a mixing ratio of inert gas in the fuel gas to be supplied to the fuel cell2. The determination unit31according to this embodiment determines the mixing ratio of inert gas based on a fuel gas supply amount to the fuel cell2, and a fuel gas consumption amount in the fuel cell2.

More specifically, the determination unit31calculates a fuel gas supply amount which is an amount of the fuel gas supplied to the fuel electrode, and a fuel gas consumption amount which is an amount of the fuel gas consumed in the fuel cell2. The fuel gas supply amount is calculated based on the pressure value P1 measured by the first pressure gauge14, the pressure value P2 measured by the second pressure gauge15, and the opening degree 0 of the flow-rate regulation valve13. The fuel gas supply amount Qinmay be calculated by the following equation (1):

wherein G represents a specific gravity of the fuel gas, T represents a temperature of the fuel gas, and Cvrepresents a capacity factor of the flow-rate regulation valve13.

The fuel gas consumption amount is calculated based on an electric current value measured by the ammeter22. The fuel gas consumption amount is proportional to an electric current value of the generated electric power. The fuel gas consumption amount Qcomay be calculated by the following equation (2):

wherein I represents a generated electric current of the fuel cell2, N represents the number of cells in a cell stack of the fuel cell2, and F represents the Faraday number.

The determination unit31calculates a difference between the fuel gas supply amount and the fuel gas consumption amount that are calculated as above. When the difference is greater than a predetermined threshold value, it may be determined that the mixing ratio of inert gas has increased.

As the mixing ratio of inert gas in the fuel gas increases, the fuel gas supply amount may increase. More specifically, a molecular weight of the inert gas, such as a nitrogen gas or a helium gas, is greater than a molecular weight of a hydrogen gas. Thus, as the mixing ratio of inert gas in the fuel gas increases, the specific gravity of the fuel gas increases. In this case, pressure loss of the fuel gas increases, so that the flow rate of the fuel gas passing through the flow-rate regulation valve13decreases whereby the pressure value P1 decreases. When the controller30detects the decrease in pressure value P1, it increases the opening degree of the flow rate regulation value13in order to increase the flow rate of the fuel gas. As a result, the fuel gas supply amount Qinshown in the equation (1) increases.

In this way, the difference between the fuel gas supply amount and the fuel gas consumption amount increases. The mixing ratio of inert gas in the fuel gas can be determined based on the difference. The operation condition of the fuel cell system1is changed based on the determination by the determination unit31, in order to continue the operation of the fuel cell system1.

The operation control unit32changes the operation condition of the fuel cell system1based on the mixing ratio of inert gas determined by the determination unit31. For example, the operation control unit32may regulate an upper limit value of a generated electric current of the fuel cell2and may regulate a fuel supply amount, based on the mixing ratio of inert gas. The operation control unit32may control the aforementioned power converter11such that the upper limit value of the generated electric current of the fuel cell2is decreased, when the mixing ratio of inert gas increases. In addition, the operation control unit32may control the flow-rate regulation valve13such that the fuel gas supply amount is decreased, when the mixing ratio of inert gas increases.

Next, an operation method of the fuel cell system1according to the embodiment as structured above is described.

Prior to staring operation of the fuel cell system1, the fuel tank3is replenished with fuel. For example, as shown inFIG.1, one end of a replenishment channel40, such as a pipe, is first connected to the fuel tank3. The replenishment channel40is then purged with the inert gas such as a nitrogen gas. Thereafter, a replenishment tank41is connected to the other end of the replenishment channel40so that the fuel tank3is replenished with the fuel from the replenishment tank41. The inert gas may remain in the fuel supplied to the fuel tank3. The fuel replenished to the fuel tank3from the replenishment tank41may be either the fuel in a liquid state or the fuel in a gaseous state. After completion of the replenishment of fuel, the replenishment channel40and the replenishment tank41are detached from the fuel tank3.

After the replenishment of fuel has been completed, the fuel cell system1begins operation.

The fuel-gas supply valve12and the oxidant gas supply valve16are opened first, and the oxidant-gas supply unit5and the circulation blower19are driven. Thus, the fuel gas is supplied form the fuel tank3to the fuel electrode of the fuel cell2, and the oxidant gas is supplied from the oxidant-gas supply unit5to the oxidant electrode of the fuel cell2. A supply flow rate of the oxidant gas is regulated by the oxidant-gas supply unit5based on a command of the controller30. The fuel gas having been supplied to the fuel electrode and the oxidant gas having been supplied to the oxidant electrode react electrochemically through the electrolyte membrane. This converts the chemical energy into the electric energy, so that the fuel cell2generates electric power. The generated electric power is outputted from the fuel cell2and an electric voltage and an electric current are converted in the power converter11. The generated electric power is supplied to the load from the power converter11.

The fuel gas having passed through the fuel electrode is drawn into the fuel-gas circulation channel9. Since the oxidant-gas discharge valve18is open, the oxidant gas having passed through the oxidant electrode is discharged outside from the oxidant-gas discharge channel8.

The fuel gas having flown into the fuel-gas circulation channel9is fed to the fuel-gas supply channel4by the circulation blower19and is again supplied to the fuel electrode. In this manner, the fuel gas is circulated to be recycled during the operation of the fuel cell system1.

During the operation of the fuel cell system1, the determination unit31of the controller30determines a mixing ratio of inert gas in the fuel gas, and a power control unit24changes an operation condition of the fuel cell system1based on the determined mixing ratio.

More specifically, the first pressure gauge14and the second pressure gauge15measure pressure values P1 and P2 of the fuel gas in the fuel-gas supply channel4, and the measured pressure values are transmitted to the controller30. The ammeter22measures an electric current value of the generated electric power outputted from the fuel cell2, and the measured electric current value is transmitted to the controller30. The determination unit31of the controller30calculates a fuel gas supply amount based on the pressure value P1 measured by the first pressure gauge14, the pressure value P2 measured by the second pressure gauge15, and a stored opening degree of the flow-rate regulation valve13. In addition, the determination unit31calculates a fuel gas consumption amount based on the electric current value measured by the ammeter22. When a difference between the fuel gas supply amount and the fuel gas consumption amount is greater than a predetermined threshold value, it is determined that a mixing ratio of inert gas in the fuel gas is large.

When the determination unit31determines that the mixing ratio of inert gas is large, the operation control unit32decreases an upper limit value of the generated electric current of the fuel cell2, and decreases the fuel gas supply amount. For example, the operation control unit32controls the power converter11to decrease the upper limit value of the generated electric current, and controls the flow-rate regulation valve13to decrease the fuel gas supply amount. This decreases a supply flow rate of the fuel gas to be supplied to the fuel electrode of the fuel cell system1, to thereby decrease an accumulation rate of inert gas to be accumulated in the fuel electrode and to prevent performance degradation of the fuel cell.

Thereafter, when the mixing ratio of inert gas in the fuel gas decreases, the determination unit31may determine that the mixing ratio of inert gas is not large. More specifically, when the aforementioned difference between the fuel gas supply amount and the fuel gas consumption amount is equal to or less than a predetermined threshold value, it may be determined that the mixing ratio of inert gas in the fuel gas is not large. In this case, the operation control unit may restore the upper limit value of the generated electric current of the fuel cell2and the fuel gas supply amount.

Namely, according to this embodiment, the operation condition of the fuel cell system1is changed based on the mixing ratio of inert gas in the fuel gas to be supplied to the fuel cell2. Thus, even when the mixing ratio of inert gas in the fuel gas is large, the fuel cell system can be suitably operated based thereon. This allows the operation to be continued even when the fuel gas contains the inert gas.

In addition, according to this embodiment, the determination unit31determines the mixing ratio of inert gas based on the fuel gas supply amount to the fuel cell2and the fuel gas consumption amount in the fuel cell2. This allows the determination unit31to exactly determine the mixing ratio of inert gas in the fuel gas.

In addition, according to this embodiment, the determination unit31can calculate the fuel gas supply amount based on the pressure value P1 measured by the first pressure gauge14, the pressure value P2 measured by the second pressure gauge15, and the opening degree of the flow-rate regulation valve13. The determination unit31can calculate the fuel gas consumption amount based on the generated electric current value measured by the ammeter22. The mixing ratio of inert gas can be determined based on the calculated fuel gas supply amount and the calculated fuel gas consumption amount. This can improve determination accuracy of the mixing ratio of inert gas.

In addition, according to this embodiment, the operation control unit32regulates the upper limit value of the generated electric current of the fuel cell2and regulates the fuel gas supply amount, based on the mixing ratio of inert gas determined by the determination unit31. Thus, when the mixing ratio of inert gas increases, the upper limit value of the generated electric current of the fuel cell2can be decreased, and the fuel gas supply amount can be decreased. This decreases an accumulation rate of inert gas to be accumulated in the fuel electrode, to thereby prevent performance degradation of the fuel cell. This allows the operation to be continued even when the fuel gas contains the inert gas.

When the fuel gas contains the inert gas, the specific gravity of the fuel gas increases, which may increase pressure loss of the fuel gas. In this case, a regulatable range of the fuel gas by the fuel rate regulation valve13may be decreased, and a regulatable maximum flow rate value may be decreased. In contrast, according to this embodiment, the operation control unit32decreases the upper limit value of the generated electric current of the fuel cell2and decreases the fuel gas supply amount, based on the mixing ratio of inert gas determined by the determination unit31. This can decrease the supply flow rate of the fuel gas so that the regulatable range of the fuel gas by the flow-rate regulation valve13can be increased.

When the fuel gas containing the inert gas is supplied, an accumulation rate of inert gas in an anode system including the fuel-gas supply channel4and the fuel-gas circulation channel9may increase. In this case, even when the degassing valve20is opened to discharge outside the fuel gas, it may be difficult to decrease the mixing ratio of inert gas to maintain a hydrogen concentration in the fuel gas at a predetermined concentration. In contrast, according to this embodiment, the upper limit value of the generated electric current of the fuel cell2is decreased and the fuel gas supply amount is decreased, based on the mixing ratio of inert gas determined by the determination unit31. The decrease in the fuel gas supply amount can decrease the accumulation rate of inert gas to be accumulated in the anode system, and degassing through the degassing channel10can maintain the hydrogen concentration in the fuel gas at a predetermined concentration.

In the aforementioned embodiment, an example in which the operation control unit32decreases the upper limit value of the generated electric current of the fuel cell2and decreases the fuel supply amount, based on the mixing ratio of inert gas, was described. However, this embodiment is not limited to this example. For example, the operation control unit32may regulate a time interval t1 (seeFIG.2) in which the degassing valve20is closed, based on the mixing ratio of inert gas determined by the determination unit31.

For example, when the determination unit31determines that the mixing ratio of inert gas is large, the operation control unit32may decrease the time interval t1 in which the degassing valve20is closed. This can increase a time ratio in which the degassing valve20is open, so that the fuel gas can be efficiently released outside from the degassing channel10. This can decrease the mixing ratio of inert gas in the fuel gas. Thereafter, when the mixing ratio of inert gas in the fuel gas decreases, the time interval t1 in which the degassing valve20is closed may be restored.

In addition, for example, the operation control unit32may regulate a time interval t2 in which the degassing valve20is open, for example, may increase the time interval t2 in which the degassing valve20is open, based on the mixing ratio of inert gas determined by the determination unit31. This can increase a time ratio in which the degassing valve20is open, so that the fuel gas can be efficiently released outside from the degassing channel10. This can decrease the mixing ratio of inert gas in the fuel gas. Thereafter, when the mixing ratio of inert gas in the fuel gas decreases, the time interval t2 in which the degassing valve20is open may be restored.

Second Embodiment

Next, a fuel cell system according to a second embodiment is described with reference toFIGS.3and4.

The second embodiment shown inFIGS.3and4differs from the first embodiment shown inFIGS.1and2mainly in that a time interval in which the degassing valve is closed, or a time interval in which the degassing valve is open is regulated, based on a pressure value measured by a third pressure gauge, and is substantially the same as the first embodiment in other configurations. InFIGS.3and4, the same parts as in the first embodiment shown inFIGS.1and2are indicated by the same symbols and detailed description thereof is omitted.

As shown inFIG.3, a fuel cell system1in this embodiment comprises a third pressure gauge50. The fuel cell system1according to this embodiment may not comprise the aforementioned determination unit31.

The third pressure gauge50is configured to measure a pressure value of a fuel gas in a fuel-gas circulation channel9. The third pressure gauge50is provided downstream of a circulation blower19in the fuel-gas circulation channel9. The third pressure gauge50may be provided between the circulation blower19and a branch point to a degassing channel10. A pressure value measured by the third pressure gauge50is transmitted to a controller30. The third pressure gauge50may be provided upstream of the circulation blower19.

An operation control unit32in this embodiment regulates a time interval t1 (seeFIG.2) in which a degassing valve20is closed, based on a pressure value P3 measured by the third pressure gage50. In addition, the operation control unit32may regulate a time interval t2 (seeFIG.2) in which the degassing valve20is open, based on the pressure value P3 measured by the third pressure gauge50.

For example, the operation control unit32may regulate the time interval t1 in which the degassing valve20is closed, based on an increase rate of the pressure value P3 measured by the third pressure gauge50. When the increase rate of the pressure value P3 is greater than a predetermined threshold value, the time interval t1 in which the degassing valve20is closed may be decreased.

In addition, the operation control unit32may regulate the time interval t2 in which the degassing valve20is open, when the increase rate of the pressure value P3 measured by the third pressure gauge50is greater than the predetermined threshold value. When the increase rate of the pressure value P3 is greater than the predetermined threshold value, the time interval t2 in which the degassing valve20is open may be increased.

When the fuel gas contains no inert gas, a nitrogen gas in the oxidant gas moves from a cathode system including an oxidant-gas supply channel6to an anode system. This may increase a mixing ratio of inert gas in the fuel gas. An increase rate of the mixing ratio of inert gas in this case is relatively slow. On the other hand, when the fuel gas contains the inert gas, the fuel gas containing the inert gas is supplied, in addition to the movement of the nitrogen gas from the cathode system to the anode system. Thus, the increase rate of the mixing ratio of inert gas in the fuel gas is relatively quick in the anode system. In this case, since the increase rate of the pressure value P3 measured by the third pressure gauge50increases, the mixing ratio of inert gas contained in the fuel gas increases. Monitoring of the increase rate of the pressure value P3 measured by the third pressure gauge50is effective in determining the mixing ratio of inert gas.

Namely, according to this embodiment, an operation condition of the fuel cell system1is changed based on the pressure value P3 measured by the third pressure gauge50provided on the fuel-gas circulation channel9. Thus, even when the mixing ratio of inert gas in the fuel gas is large, the fuel cell system can be suitably operated based thereon. This allows the operation to be continued even when the fuel gas contains the inert gas.

In addition, according to this embodiment, the time interval t1 in which the degassing valve20is closed is regulated based on the increase rate of the pressure value P3 measured by the third pressure gauge50. The use of increase rate of the pressure value P3 allows the mixing ratio of inert gas contained in the oxidant gas to be determined, separately from the nitrogen gas which has been moved from the cathode system to the anode system. Thus, degassing by the degassing valve20can effectively decrease the mixing ratio of inert gas contained in the fuel gas. This allows the operation to be continued even when the fuel gas contains the inert gas.

In addition, according to this embodiment, the time interval t2 in which the degassing valve20is open is regulated based on the increase rate of the pressure value P3 measured by the third pressure gauge50. The use of increase rate of the pressure value P3 allows the mixing ratio of inert gas contained in the oxidant gas to be determined, separately from the nitrogen gas which has been moved from the cathode system to the anode system. Thus, degassing by the degassing valve20can effectively decrease the mixing ratio of inert gas contained in the fuel gas. This allows the operation to be continued even when the fuel gas contains the inert gas.

In the aforementioned embodiment, an example in which the time interval t1 in which the degassing valve20is closed, and the time interval t2 in which the degassing valve20is open are regulated, based on the increase rate of the pressure value P3 of the fuel gas in the fuel-gas circulation channel9, was described. However, this embodiment is not limited to this example. The operation control unit32may open/close the degassing valve20, based on the pressure value P3 of the fuel gas in the fuel-gas circulation channel9. For example, as shown inFIG.4, when the pressure value P3 measured by the third pressure gauge50reaches a desired upper limit value Pa, the degassing valve20is opened. This allows the fuel gas with a high mixing ratio of inert gas to be discharged outside from the degassing channel10. The fuel-gas circulation channel9is supplied with a fuel gas supplied from the fuel tank3, so that the mixing ratio of inert gas in the fuel gas present in the fuel-gas circulation channel9can be decreased. The decrease in mixing ratio of inert gas results in decrease in pressure loss of the fuel gas and decrease in pressure value P3. When the pressure value P3 reaches a desired lower limit value Pb, the operation control unit32may close the degassing valve20. This can prevent the fuel gas with low mixing ratio of inert gas from being discharged outside from the degassing channel10. Since the pressure value P3 can be regulated between the upper limit value Pa and the lower limit value Pb, the fuel cell system1can be suitably operated continuously.

Third Embodiment

Next, a fuel cell system in a third embodiment is described with reference toFIG.5.

The third embodiment shown inFIG.5differs from the first embodiment shown inFIGS.1and2mainly in that an operation condition of the fuel cell system is changed based on information stored in a superordinate control system of the fuel cell system, and is substantially the same as the first embodiment in other configurations. InFIG.5, the same parts as in the first embodiment shown inFIGS.1and2are indicated by the same symbols and detailed description thereof is omitted.

As shown inFIG.5a superordinate control system60is connected to a controller30. The control system60issues various commands, such as operation commands, to the controller30. The controller30controls operation of a fuel cell2based on these commands. The control system60stores various information, and the controller30acquires from the control system60information necessary to control the operation of the fuel cell2. The fuel cell system1according to this embodiment may not comprise the aforementioned determination unit31.

An operation control unit32according to this embodiment changes an operation condition of the fuel cell system1, based on the information stored in the control system60. The information stored in the control system60includes a purge end timing of the aforementioned purge process which was performed when the fuel tank3is replenished with the fuel. The controller30may acquire the purge end timing, and the operation control unit32may change the operation condition of the fuel cell system1based on the purge end timing. For example, until a predetermined elapsed period of time has passed from the purge end timing, operation control unit32may determine that a mixing ratio of inert gas is large, and may change the operation condition of the fuel cell system1. The elapsed period of time may be optionally regulated. For example, the elapsed period of time may be either a period of time in which electric power generation of the fuel cell2continues, or a period of time until an amount of generated electric power of the fuel cell2reaches a predetermined amount of electric power. For example, the elapsed period of time may be optionally regulated based on a type of gas used in the purge process, or may be optionally regulated based on the number of substitutions by the purge gas.

In this case, until the aforementioned predetermined elapsed period of time has passed from the purge end timing, the operation control unit32may decrease an upper limit value of the generated electric current of the fuel cell2, and may decrease a fuel gas supply amount. This decreases an accumulation rate of inert gas to be accumulated in the fuel electrode of the fuel cell2, to thereby prevent performance degradation of the fuel cell. A decrease rate of the upper limit value of the generated electric current and a decrease rate of the fuel gas supply amount may be optionally regulated. For example, the decrease rate of the upper limit value of the generated electric current and a decrease rate of the fuel gas supply amount may be optionally regulated based on a type of gas used in the purge process or the number of substitutions by the purge gas. After the aforementioned elapsed period of time has passed from the purge end timing, the operation control unit31may restore the upper limit value of the generated electric current and the fuel gas supply amount.

Alternatively, until the aforementioned elapsed period of time has passed from the purge end timing, the operation control unit32may decrease a time interval t1 (seeFIG.2) in which a degassing valve20is closed. This can increase a time ratio in which the degassing valve20is open, so that fuel gas can be efficiently released outside from a degassing channel10. Thus, a mixing ratio of inert gas in the fuel gas can be decreased. Further, until the aforementioned elapsed period of time has passed from the purge end timing, the operation control unit32may increase a time interval t2 (seeFIG.2) in which the degassing valve20is open. After the aforementioned elapsed period of time has passed from the purge end timing, the operation control unit32may restore the time interval t1 in which the degassing valve20is closed, and the time interval t2 in which the degassing valve20is open.

Namely, according to this embodiment, the operation of the fuel cell system1is controlled based on the information stored in the superordinate control system60of the fuel cell system1. Thus, even when the mixing ratio of inert gas in the fuel gas is large, the fuel cell system can be suitably operated based thereon. This allows the operation to be continued even when the fuel gas contains the inert gas.

In the aforementioned embodiment, an example in which the fuel cell system1does not comprise the determination unit31was described. However, this embodiment is not limited to this example. For example, the fuel cell system1may comprise the determination unit31.

The fuel cell system1generally monitors a difference between a fuel gas supply amount to the fuel electrode and a fuel gas consumption amount calculated from the generated electric current of the fuel cell2, in order to detect leakage of the fuel gas. Since a molecular weight of the inert gas is greater than a molecular weight of the fuel gas, the fuel gas supply amount to the fuel electrode is excessively detected because of the presence of inert gas. In this case, the difference between the fuel gas supply amount and the fuel gas consumption ratio is likely to be overestimated, whereby leakage of the fuel gas is likely to be falsely detected.

In order to address this false detection, until the aforementioned period of time has passed from the purge end timing, the determination unit31may determine that a mixing ratio of inert gas has increased when the difference between the fuel gas supply amount and the fuel gas consumption amount is greater than a first threshold value. The operation control unit32may change the operation condition of the fuel cell system1similarly to the above, based on the mixing ratio of inert gas determined by the determination unit31. When determining that the mixing ratio of inert gas in the fuel gas is not large, the operation control unit32may restore the operation condition of the fuel cell system1. After the predetermined period of time has passed, the determination unit31may determine that the mixing ratio of inert gas has increased when the difference between the fuel gas supply amount and the fuel gas consumption amount is greater than a second threshold value. In this case, the operation control unit32may change the operation condition of the fuel cell system1similarly. The second threshold value may be smaller than the first threshold value. When determining that the mixing ratio of inert gas in the fuel gas is not large after the aforementioned period of time has passed, the operation control unit32may restore the operation condition of the fuel cell system1. In this manner, the operation can be continued by increasing the first threshold value used by the determination unit31until the aforementioned period of time has passed from the purge end timing.

Another example in which the fuel cell system1comprises the determination unit31is described. In this case, the information stored in the control system60includes a concentration of the inert gas in the fuel gas. The controller30may acquire the concentration of the inert gas, and the determination unit31may determine whether the mixing ratio of inert gas in the fuel gas to be supplied to the fuel cell2is large, based on the concentration of the inert gas. For example, when the concentration of the inert gas stored in the control system60is greater than a predetermined threshold value, the determination unit31may determine that the mixing ratio of inert gas has increased. The operation control unit32may change the operation condition of the fuel cell system1, based on the mixing ratio of inert gas determined by the determination unit31. When the determination unit31determines that the concentration of the inert gas stored in the control system60is not greater than the predetermined threshold value, the operation control unit32may restore the operation condition of the fuel cell system1.

According to the aforementioned embodiment, the operation can be continued even when the fuel gas contains the inert gas.