JP7646529B2 - Fuel Cell Systems - Google Patents

Description

The present invention relates to a fuel cell system.

There is a fuel cell system that calculates the amount of water remaining in the fuel cell based on the flow rate of oxidant gas (volume of oxidant gas per unit time) supplied to the fuel cell, and when the amount of water reaches or exceeds a threshold, the oxidant gas is used to blow air to expel the water remaining in the fuel cell. Related technology is disclosed in Patent Document 1.

However, when performing air blowing using oxidant gas, improvements were needed for cases where the flow rate of the oxidant gas is not as fast as desired. If the flow rate of the oxidant gas is not as fast as desired, it may be difficult to properly discharge the water remaining in the fuel cell. In particular, when the number of fuel cell cells that make up the fuel cell is relatively small, the flow rate of the oxidant gas is likely to be less than the desired rate.

On the other hand, simply increasing the supply of oxidant gas so that the flow rate meets the desired flow rate will increase the voltage of the fuel cell and cause the fuel cell to deteriorate.

JP 2019-145320 A

The object of one aspect of the present invention is to suppress deterioration due to potential fluctuations in a fuel cell system while suppressing water retention in the fuel cell.

A fuel cell system according to one embodiment of the present invention includes a fuel cell, an air compressor that supplies oxidant gas to the fuel cell, and a control unit that controls the operation of the air compressor.

The control unit controls the operation of the air compressor under normal conditions so that the power required by the load is supplied from the fuel cell system to the load, and controls the operation of the air compressor under specified conditions different from the normal conditions so that the power required by the load is supplied from the fuel cell system to the load and the flow rate of the oxidant gas supplied to the fuel cell is equal to or greater than a specified flow rate.

For example, by setting a predetermined condition for when water is likely to accumulate in the fuel cell and setting the flow rate of the oxidant gas capable of discharging water accumulated in the fuel cell to a predetermined flow rate, when water is likely to accumulate in the fuel cell, the water accumulated in the fuel cell can be discharged to the outside of the fuel cell by the oxidant gas, thereby reducing the amount of water accumulated in the fuel cell. Also, the power required by the load is supplied from the fuel cell system to the load, ensuring a destination for consumption of the power generated by the fuel cell. This prevents the potential rise of the fuel cell and suppresses deterioration of the fuel cell.

The control unit may also be configured to control the operation of the air compressor so that the power generated by the fuel cell changes stepwise under the normal conditions or the specified conditions.

This allows the flow rate of oxidant gas output from the air compressor to be changed in stages, preventing abrupt changes in the noise generated by the air compressor and mitigating the user's discomfort caused by the noise. In addition, the frequency with which the power generated by the fuel cell changes can be reduced, suppressing deterioration of the fuel cell.

The fuel cell system may also be configured to include a power storage device that is charged by receiving power from the fuel cell and discharged by supplying power to the load, and the control unit may be configured to control the operation of the air compressor under the normal conditions so that the target power generation of the fuel cell increases as the charge amount of the power storage device decreases within a range from a first charge amount to a second charge amount greater than the first charge amount, and the target power generation decreases as the charge amount of the power storage device increases, and to control the operation of the air compressor so that under the specified conditions, the target power generation of the fuel cell is maintained at zero until the charge amount of the power storage device decreases to the first charge amount, and then the target power generation of the fuel cell is increased until the charge amount of the power storage device increases to the second charge amount.

According to the present invention, in a fuel cell system, it is possible to suppress the accumulation of water in the fuel cell while suppressing deterioration due to fluctuations in the potential of the fuel cell.

1 is a diagram illustrating an example of a fuel cell system according to an embodiment. 10 is a flowchart showing an example of an operation of a control unit. 10 is a flowchart showing another example of the operation of the control unit. FIG. 4 is a diagram for explaining power generation control of a fuel cell under normal conditions. FIG. 4 is a diagram for explaining power generation control of a fuel cell under a low load operating condition. 1 is a diagram for explaining power generation control of a fuel cell when a power supply destination of the fuel cell system during normal power generation control is an on-vehicle load. FIG. 10 is a diagram for explaining power generation control of a fuel cell when a power supply destination of the fuel cell system during normal power generation control is an external load. FIG. 10 is a diagram for explaining power generation control of a fuel cell in a case where the power supply destination of the fuel cell system is an external load during power generation control for low-load operation. FIG. 13 is a diagram for explaining power generation control of a fuel cell in Modification 1. FIG. 13 is a diagram for explaining power generation control of a fuel cell in Modification 2. FIG. 13 is a diagram for explaining power generation control of a fuel cell in Modification 3. FIG.

The following describes the embodiment in detail with reference to the drawings.

Figure 1 shows an example of a fuel cell system FCS according to an embodiment.

The fuel cell system FCS shown in FIG. 1 is mounted on a vehicle Ve, and supplies power to an on-board load Lin mounted on the vehicle Ve and an external load Lout provided outside the vehicle Ve. The vehicle Ve may be an industrial vehicle such as a forklift, an automobile, or the like. The on-board load Lin may be an inverter that drives a drive motor or an inverter that drives a loading motor, and a relatively large amount of power is supplied from the fuel cell system FCS to the on-board load Lin when the vehicle Ve is traveling uphill or when loading and unloading relatively heavy loads. The external load Lout may be a home appliance such as a television or an electric fan, and a relatively small amount of power is supplied from the fuel cell system FCS to the external load Lout.

The fuel cell system FCS also includes a fuel cell FC, a hydrogen tank HT, an injector INJ, an air compressor ACP, an air pressure regulating valve ARV, a DCDC converter CNV, an energy storage device B, a current sensor Sif, a voltage sensor Svf, a current sensor Sib, a voltage sensor Svb, change-over switches SW1 and SW2, an inverter INV, and a control unit CNT.

A fuel cell FC is a fuel cell stack consisting of multiple fuel cell cells connected in series with each other, and generates electricity through an electrochemical reaction between the hydrogen contained in the fuel gas (such as hydrogen gas) and the oxygen contained in the oxidant gas (such as air).

The hydrogen tank HT is a storage container for fuel gas. The fuel gas stored in the hydrogen tank HT is supplied to the fuel cell FC via the injector INJ.

The injector INJ maintains the pressure of the fuel gas in the fuel cell FC at a predetermined pressure by adjusting the flow rate of the fuel gas supplied to the fuel cell FC.

The air compressor ACP compresses the oxidant gas present around the fuel cell system FCS and supplies it to the fuel cell FC.

The air pressure regulating valve ARV maintains the pressure of the oxidant gas in the fuel cell FC at a predetermined pressure by adjusting the flow rate of the oxidant gas supplied to the fuel cell FC.

The DCDC converter CNV is connected to the rear of the fuel cell FC and converts the voltage Vf output from the fuel cell FC to a predetermined voltage. The power output from the DCDC converter CNV is supplied to loads such as the vehicle load Lin and the external load Lout, auxiliary equipment such as the injector INJ, the air compressor ACP, and the air pressure regulating valve ARV, and the power storage device B. For example, the DCDC converter CNV converts the voltage of the fuel cell FC to 48 [V]. A part of the power output from the DCDC converter CNV is supplied to the air compressor ACP, which is an auxiliary equipment of the 48 [V] system. In addition, the voltage converted to 48 [V] by the DCDC converter CNV is converted to a voltage of 12 [V] by another DCDC converter (not shown). The power output from the other DCDC converter is supplied to the auxiliary equipment of the 12 [V] system, the injector INJ and the air pressure regulating valve ARV.

The storage device B is composed of a capacitor etc. and is connected between the DCDC converter CNV and the change-over switches SW1, SW2. When the supply power equivalent to the difference between the power output from the DCDC converter CNV and the total value of the power supplied to the 48V system auxiliary equipment and the 12V system auxiliary equipment is greater than the required power requested by the vehicle load Lin or the external load Lout, the required power of the supply power is supplied to the vehicle load Lin or the external load Lout, and the remaining power is supplied to the storage device B. When power is supplied from the DCDC converter CNV to the storage device B, the storage device B is charged and the charge amount of the storage device B increases. In addition, when the supply power corresponding to the difference between the power output from the DCDC converter CNV and the total value of the power supplied to the 48 [V] system auxiliary equipment and the 12 [V] system auxiliary equipment is smaller than the required power required by the in-vehicle load Lin or the external load Lout, the supply power is supplied to the in-vehicle load Lin or the external load Lout, and the shortage power is supplied from the power storage device B to the in-vehicle load Lin or the external load Lout. When power is supplied from the power storage device B to the in-vehicle load Lin or the external load Lout, the power storage device B is discharged and the charge amount of the power storage device B decreases. Note that the charge amount is the charge rate [%] of the power storage device B (the ratio of the remaining capacity to the full charge capacity of the power storage device B), or the open circuit voltage [V] of the power storage device B when no current flows through the power storage device B, or the closed circuit voltage [V] of the power storage device B when a current flows through the power storage device B, or the integrated value [Ah] of the current flowing through the power storage device B, or the like.

The current sensor Sif is composed of a shunt resistor, a Hall element, etc., and detects the current If flowing from the fuel cell FC to the DCDC converter CNV and sends the detected current If to the control unit CNT.

The voltage sensor Svf is composed of a voltage dividing resistor and the like, detects the voltage Vf output from the fuel cell FC, and sends the detected voltage Vf to the control unit CNT. The control unit CNT obtains the multiplication result of the current If and the voltage Vf as the generated power (output power) of the fuel cell FC.

The current sensor Sib is composed of a shunt resistor, a Hall element, etc., and detects the current Ib flowing from the DCDC converter CNV to the storage device B or the current Ib flowing from the storage device B to the vehicle load Lin or the external load Lout, and sends the detected current Ib to the control unit CNT.

The voltage sensor Svb is composed of a voltage dividing resistor, etc., detects the voltage Vb of the storage device B, and sends the detected voltage Vb to the control unit CNT.

The changeover switches SW1 and SW2 are composed of electromagnetic relays or the like, and are controlled by the control unit CNT to switch the output destination of the fuel cell system FCS to either the vehicle load Lin or the external load Lout. Note that, as a configuration other than this embodiment, the control unit CNT may be controlled to switch the output destination of the fuel cell system FCS between both the vehicle load Lin and the external load Lout, or only the vehicle load Lin.

The inverter INV converts the DC power output from the DCDC converter CNV or the power storage device B into AC power and supplies it to the external load Lout.

The control unit CNT is composed of a microcomputer and other components, and controls the operation of auxiliary equipment such as the air compressor ACP, the air pressure regulating valve ARV, and the injector INJ to control the power generated by the fuel cell FC.

In addition, during normal power generation control or low-load operation-compatible power generation control, the control unit CNT gradually changes the target power generation power Pt according to the charge amount of the storage device B.

In addition, during normal power generation control or low-load operation compatible power generation control, the control unit CNT controls the operation of the 48[V] system auxiliary equipment and the 12[V] system auxiliary equipment so that the power generated by the fuel cell FC follows the target power generation power Pt, thereby controlling the power generated by the fuel cell FC. For example, the control unit CNT controls the operation of the 48[V] system auxiliary equipment and the 12[V] system auxiliary equipment by PI (Proportional-Integral) control so that the difference between the power generated by the fuel cell FC and the target power generation power Pt becomes zero.

Figure 2 is a flowchart showing an example of the operation of the control unit CNT.

First, in step S1, the control unit CNT determines whether or not the user has pressed an external power supply button (not shown) provided on the fuel cell system FCS side or on the vehicle Ve side.

Next, when the control unit CNT determines that the external power supply button has not been pressed by the user (step S1: No), it determines that the normal conditions are met (step S2). The normal conditions are conditions under which the fuel cell system FCS is operated under normal power generation control, which will be described later, and a relatively large amount of power is supplied from the fuel cell system FCS to the vehicle load Lin. Note that under normal conditions, the power required by the vehicle load Lin becomes greater than the target power generation power of the fuel cell FC, and the output power of the power storage device B becomes relatively large, and the charge amount of the power storage device B may decrease sufficiently. Also, under normal conditions, the target power generation power Pt of the fuel cell FC and the flow rate of the oxidant gas supplied to the fuel cell FC increase as the charge amount of the power storage device B decreases due to the normal power generation control, which will be described later, so that it is not necessary to intentionally increase the flow rate of the oxidant gas.

Next, if the control unit CNT determines that the conditions are normal, it controls the operation of the changeover switches SW1 and SW2 so that the fuel cell system FCS supplies power to the vehicle load Lin (step S3), and controls the power generated by the fuel cell FC using normal power generation control (step S4).

On the other hand, when the control unit CNT determines that the external power supply button has been pressed by the user (step S1: Yes), it determines that the operation is under low-load operating conditions (predetermined conditions) (step S5). The low-load operating conditions are conditions under which the fuel cell system FCS is operated in low-load operation-compatible power generation control, which will be described later, and in which a relatively small amount of power is supplied from the fuel cell system FCS to the external load Lout compared to normal power generation control. Note that under low-load operating conditions, the power required from the external load Lout is relatively small, so the output power of the power storage device B is relatively small and the charge amount of the power storage device B is unlikely to decrease. Therefore, when normal power generation control, which will be described later, is performed under low-load operating conditions, the output power of the fuel cell FC is unlikely to increase, and the flow rate of the oxidant gas supplied to the fuel cell FC is unlikely to increase, so water is likely to remain in the fuel cell FC. Therefore, under low-load operating conditions, in order to discharge the water remaining in the fuel cell FC to the outside of the fuel cell FC using the oxidant gas, the target power generation power Pt of the fuel cell FC is forcibly increased by the low-load operation-compatible power generation control described below, thereby intentionally increasing the flow rate of the oxidant gas supplied to the fuel cell FC. Also, under low-load operating conditions, in order to prevent the power storage device B from becoming overcharged, the charge amount of the power storage device B is reduced before the target power generation power Pt of the fuel cell FC is increased.

Next, if the control unit CNT determines that the low-load operating conditions exist, it controls the operation of the change-over switches SW1 and SW2 so that the power supply destination of the fuel cell system FCS is the external load Lout (step S6), controls the power generation of the fuel cell FC using low-load operation-compatible power generation control (step S7), and then determines again whether the external power supply button has been pressed by the user (step S8).

If the control unit CNT determines that the external power supply button has not been pressed by the user (step S8: No), it continues the low-load operation-compatible power generation control in step S7. If the control unit CNT determines that the external power supply button has been pressed by the user (step S8: Yes), it determines that the low-load operation conditions have been switched to normal conditions (step S2), and executes the processing from step S3 onward.

That is, while the external power supply button is not pressed by the user, normal conditions are in effect, and while the external power supply button is pressed by the user and then pressed again, low-load operating conditions are in effect. The control unit CNT controls the power generated by the fuel cell FC using normal power generation control under normal conditions, and controls the power generated by the fuel cell FC using low-load operation-compatible power generation control under low-load operating conditions. In this way, by determining whether the external power supply button has been pressed, it is possible to easily switch between normal power generation control and low-load operation-compatible power generation control.

Figure 3 is a flowchart showing another example of the operation of the control unit CNT. Note that in the flowchart shown in Figure 3, steps that are the same as those shown in Figure 2 are given the same reference numerals, and their explanations are omitted.

The flowchart shown in FIG. 3 differs from the flowchart shown in FIG. 2 in that if the output power of the fuel cell system FCS is greater than a predetermined power (step S1': No), it is determined that normal conditions exist in step S2, and if the state in which the output power of the fuel cell system FCS is equal to or less than the predetermined power continues for a certain period of time or more (step S1': Yes), it is determined that low-load operation conditions exist in step S5. Note that when the output power of the fuel cell system FCS continues to be equal to or less than the predetermined power (step S8': No), low-load operation-compatible power generation control continues, and when the output power of the fuel cell system FCS becomes greater than the predetermined power (step S8': Yes), it is determined that the low-load operation conditions have been switched to normal conditions (step S2), and the processing from step S3 onwards is executed.

In other words, if the output power of the fuel cell system FCS is greater than the predetermined power or if the state in which the output power of the fuel cell system FCS is equal to or less than the predetermined power does not continue for a certain period of time or more, the normal conditions are established, and from the time when the state in which the output power of the fuel cell system FCS is equal to or less than the predetermined power continues for a certain period of time or more until the output power of the fuel cell system FCS becomes greater than the predetermined power, the low-load operating conditions are established. Then, under normal conditions, the control unit CNT controls the power generated by the fuel cell FC using normal power generation control, and under low-load operating conditions, it controls the power generated by the fuel cell FC using low-load operation-compatible power generation control. In this way, by determining whether the state in which the output power of the fuel cell system FCS is equal to or less than the predetermined power continues for a certain period of time or more, it is possible to easily switch between normal power generation control and low-load operation-compatible power generation control.

When the flowchart shown in FIG. 3 is used for power generation control of the fuel cell FC, the fuel cell system FCS may supply power only to the vehicle load Lin. When configured in this manner, the changeover switches SW1 and SW2 may be omitted, and the vehicle load Lin may be directly connected to the DCDC converter CNV.

Figure 4 is a diagram for explaining normal power generation control. The charge amount of the storage device B is assumed to vary in the range from charge amount V1 (first charge amount) to charge amount V2 (second charge amount) greater than charge amount V1. Also, threshold Vth11 (charge amount V1) < threshold Vth12 < threshold Vth13 < threshold Vth14 < threshold Vth15 < threshold Vth16 (charge amount V2). Also, the target power generation Pt0 is set to zero, and the target power generation Pt0 < target power generation Pt1 < target power generation Pt2 < target power generation Pt3. Also, when the output power of the fuel cell FC is following the target power generation Pt3, the water remaining in the fuel cell FC is discharged outside the fuel cell FC by a predetermined flow rate of oxidant gas. Furthermore, the difference between the target power generation Pt3 and the target power generation Pt2, the difference between the target power generation Pt2 and the target power generation Pt1, and the difference between the target power generation Pt1 and the target power generation Pt0 may each be a constant value or may be a different value. Furthermore, the larger the target power generation Pt, the greater the power output from the fuel cell FC, and the smaller the target power generation Pt, the smaller the power output from the fuel cell FC. Furthermore, when the target power generation Pt becomes the target power generation Pt0, power generation by the fuel cell FC stops and the power output from the fuel cell FC becomes zero.

When the charge amount of the storage device B becomes equal to or less than the threshold value Vth15 while the target power generation Pt is equal to the target power generation Pt0, the control unit CNT changes the target power generation Pt from the target power generation Pt0 to the target power generation Pt1.

In addition, when the charge amount of the storage device B becomes equal to or less than the threshold value Vth13 while the target power generation Pt is the target power generation Pt1, the control unit CNT changes the target power generation Pt from the target power generation Pt1 to the target power generation Pt2.

In addition, when the charge amount of the storage device B becomes equal to or less than the threshold value Vth11 while the target power generation Pt is equal to the target power generation Pt2, the control unit CNT changes the target power generation Pt from the target power generation Pt2 to the target power generation Pt3.

In addition, when the charge amount of the storage device B becomes equal to or greater than the threshold value Vth12 while the target power generation Pt is equal to the target power generation Pt3, the control unit CNT changes the target power generation Pt from the target power generation Pt3 to the target power generation Pt2.

In addition, when the charge amount of the storage device B becomes equal to or greater than the threshold value Vth14 while the target power generation Pt is set to the target power generation Pt2, the control unit CNT changes the target power generation Pt from the target power generation Pt2 to the target power generation Pt1.

In addition, when the charge amount of the storage device B becomes equal to or greater than the threshold value Vth16 while the target power generation Pt is equal to the target power generation Pt1, the control unit CNT changes the target power generation Pt from the target power generation Pt1 to the target power generation Pt0.

In other words, as normal power generation control, the control unit CNT controls the power generated by the fuel cell FC so that the power output from the fuel cell FC increases stepwise as the charge level of the power storage device B decreases, or so that the power output from the fuel cell FC decreases stepwise as the charge level of the power storage device B increases.

As a result, under normal conditions, when the power required from the vehicle load Lin becomes relatively large and the charge amount of the power storage device B becomes relatively small, the flow rate of the oxidant gas supplied to the fuel cell FC increases in order to increase the output power of the fuel cell FC, thereby reducing the amount of water remaining in the fuel cell FC.

Figure 5 is a diagram for explaining the power generation control for low-load operation. The charge amount of the storage device B is assumed to change in the range from the charge amount V1 (first charge amount) to the charge amount V2 (second charge amount) greater than the charge amount V1. Also, the threshold Vth21 (charge amount V1) < threshold Vth22 < threshold Vth23 < threshold Vth24 < threshold Vth25 < threshold Vth26 (charge amount V2). Also, the threshold Vth21 may be the same value as the threshold Vt11 or a different value. Also, the threshold Vth22 may be the same value as the threshold Vt12 or a different value. Also, the threshold Vth23 may be the same value as the threshold Vt13 or a different value. Also, the threshold Vth24 may be the same value as the threshold Vt14 or a different value. Also, the threshold Vth25 may be the same value as the threshold Vt15 or a different value. Additionally, threshold value Vth26 may be the same as threshold value Vt16 or may be a different value.

When the charge amount of the storage device B becomes equal to or less than the threshold value Vth21 while the target power generation Pt is equal to the target power generation Pt0, the control unit CNT changes the target power generation Pt from the target power generation Pt0 to the target power generation Pt1.

In addition, when the charge amount of the storage device B becomes equal to or greater than the threshold value Vth22 while the target power generation Pt is set to the target power generation Pt1, the control unit CNT changes the target power generation Pt from the target power generation Pt1 to the target power generation Pt2.

In addition, when the charge amount of the storage device B becomes equal to or greater than the threshold value Vth23 while the target power generation Pt is equal to the target power generation Pt2, the control unit CNT changes the target power generation Pt from the target power generation Pt2 to the target power generation Pt3.

In addition, when the charge amount of the storage device B becomes equal to or greater than the threshold value Vth24 while the target power generation Pt is equal to the target power generation Pt3, the control unit CNT changes the target power generation Pt from the target power generation Pt3 to the target power generation Pt2.

In addition, when the charge amount of the storage device B becomes equal to or greater than the threshold value Vth25 while the target power generation Pt is set to the target power generation Pt2, the control unit CNT changes the target power generation Pt from the target power generation Pt2 to the target power generation Pt1.

In addition, when the charge amount of the storage device B becomes equal to or greater than the threshold value Vth26 while the target power generation Pt is equal to the target power generation Pt1, the control unit CNT changes the target power generation Pt from the target power generation Pt1 to the target power generation Pt0.

In addition, when the target power generation Pt changes from the target power generation Pt1 to the target power generation Pt0, the control unit CNT maintains the target power generation Pt at the target power generation Pt0 until the charge amount of the storage device B becomes equal to or less than the threshold value Vth21.

In other words, as a power generation control for low-load operation, the control unit CNT maintains the target power generation Pt at the target power generation Pt0 until the charge amount of the storage device B becomes equal to or less than the threshold Vth21, regardless of the magnitude of the power required from the vehicle load Lin or the external load Lout, and then forcibly changes the target power generation Pt from the target power generation Pt0 to the target power generation Pt3 and forcibly changes the target power generation Pt from the target power generation Pt3 to the target power generation Pt0, and repeats this process.

As a result, even when a relatively small amount of power is continuously supplied from the fuel cell system FCS to the external load Lout, such as under low-load operating conditions, the power output from the fuel cell FC can be forcibly increased to the target power generation power Pt3 by the low-load operation-compatible power generation control, so that the flow rate of the oxidant gas supplied to the fuel cell FC can be increased and the amount of water remaining in the fuel cell FC can be reduced.

In addition, in normal power generation control or low-load operation power generation control, the flow rate of the oxidant gas output from the air compressor ACP can be changed in stages, preventing abrupt changes in the noise generated by the air compressor ACP and reducing the user's discomfort regarding the noise.

In addition, in normal power generation control or low-load operation power generation control, the power output from the fuel cell FC can be changed in stages according to the charge level of the power storage device B, reducing the frequency with which the power generated by the fuel cell FC changes and suppressing deterioration of the fuel cell.

In addition, because the power required by the vehicle load Lin and the external load Lout is supplied from the fuel cell system FCS to the vehicle load Lin and the external load Lout, a destination for consumption of the power generated by the fuel cell FC is secured. This makes it possible to suppress the rise in the potential of the fuel cell FC and to suppress deterioration of the fuel cell FC.

When the flowchart shown in FIG. 3 is used for power generation control of the fuel cell FC, and the fuel cell system FCS supplies power only to the vehicle load Lin, taking into consideration that regenerative power is supplied from the vehicle load Lin to the fuel cell system FCS, when the target power generation Pt is the target power generation Pt0 and the charge amount of the storage device B becomes equal to or greater than the threshold value Vth21, the target power generation Pt may be changed from the target power generation Pt0 to the target power generation Pt1.

Here we explain a specific example of normal power generation control.

Figure 6 is a diagram for explaining the power generation control of the fuel cell FC when the power supply destination of the fuel cell system FCS is the vehicle load Lin during normal power generation control. The horizontal axis of the two-dimensional coordinate system in Figure 6(a) indicates time, and the vertical axis indicates the output power [kW] of the fuel cell system FCS, and the solid line in Figure 6(a) shows an example of the change in the output power of the fuel cell system FCS over time when the normal power generation control shown in Figure 4 is performed. The horizontal axis of the two-dimensional coordinate system in Figure 6(b) indicates time, and the vertical axis indicates the charge amount of the storage device B, and the solid line in Figure 6(b) shows an example of the change in the charge amount of the storage device B over time when the normal power generation control shown in Figure 4 is performed. The horizontal axis of the two-dimensional coordinate system in Figure 6(c) indicates time, and the vertical axis indicates the output power [kW] of the fuel cell FC, and the solid line in Figure 6(c) shows an example of the change in the output power of the fuel cell FC over time when the normal power generation control shown in Figure 4 is performed. The horizontal axis of the two-dimensional coordinate system in FIG. 6(d) indicates time, and the vertical axis indicates the flow rate [NL/min] of the oxidant gas supplied to the fuel cell FC. The solid line in FIG. 6(d) shows an example of the change in the flow rate of the oxidant gas over time when the normal power generation control shown in FIG. 4 is performed. The horizontal axis (time axis) in FIG. 6(a) to FIG. 6(d) is the same as each other. In addition, between time t11 and time t13, the output power (power required from the vehicle load Lin) of the fuel cell system FCS is greater than the target power generation power Pt1 to Pt3, and the insufficient power is supplied from the power storage device B to the vehicle load Lin, thereby discharging the power storage device B and reducing the charge amount of the power storage device B. In addition, the power P1<power P2<power P3. In addition, the flow rate F1<flow rate F2<flow rate F3. In addition, the flow rate F3 (predetermined flow rate) is the flow rate of the oxidant gas supplied to the fuel cell FC when the water remaining in the fuel cell FC is discharged to the outside of the fuel cell FC.

First, when the charge amount of the power storage device B is gradually decreasing due to the supply of power from the power storage device B to the vehicle load Lin, if the charge amount of the power storage device B becomes equal to or less than the threshold value Vth15 at time t11, the target power generation Pt changes from the target power generation Pt0 to the target power generation Pt1. Then, in order to increase the output power of the fuel cell FC from zero to power P1 equivalent to the target power generation Pt1, the flow rate of the oxidant gas supplied to the fuel cell FC increases from zero to flow rate F1.

Next, when the charge amount of the power storage device B continues to decrease due to the supply of power from the power storage device B to the vehicle load Lin, if the charge amount of the power storage device B falls below the threshold value Vth13 at time t12, the target power generation Pt changes from the target power generation Pt1 to the target power generation Pt2. Then, in order to increase the output power of the fuel cell FC from power P1 equivalent to the target power generation Pt1 to power P2 equivalent to the target power generation Pt2, the flow rate of the oxidant gas supplied to the fuel cell FC increases from flow rate F1 to flow rate F2.

When the charge amount of the power storage device B continues to decrease due to the supply of power from the power storage device B to the vehicle load Lin, if the charge amount of the power storage device B falls below the threshold value Vth11 at time t13, the target power generation Pt changes from the target power generation Pt2 to the target power generation Pt3. Then, in order to increase the output power of the fuel cell FC from power P2 equivalent to the target power generation Pt2 to power P3 equivalent to the target power generation Pt3, the flow rate of the oxidant gas supplied to the fuel cell FC increases from flow rate F2 to flow rate F3.

In this way, in normal power generation control, the output power of the fuel cell FC may rise to a voltage V3 corresponding to the target power generation power Pt3 due to a power request from the vehicle load Lin, and the flow rate of the oxidant gas can be increased to a flow rate F3, thereby reducing the amount of water remaining in the fuel cell FC.

Next, we will explain the case where the power generated by the fuel cell FC is controlled using normal power generation control even after the power supply destination of the fuel cell system FCS is switched from the vehicle load Lin to the external load Lout.

Figure 7 is a diagram for explaining the power generation control of the fuel cell FC when the power supply destination of the fuel cell system FCS during normal power generation control is the external load Lout. The horizontal axis of the two-dimensional coordinate system in Figure 7(a) indicates time, and the vertical axis indicates the output power [kW] of the fuel cell system FCS, and the solid line in Figure 7(a) shows an example of the change in the output power of the fuel cell system FCS over time when the normal power generation control shown in Figure 4 is performed. The horizontal axis of the two-dimensional coordinate system in Figure 7(b) indicates time, and the vertical axis indicates the charge amount of the storage device B, and the solid line in Figure 7(b) shows an example of the change in the charge amount of the storage device B over time when the normal power generation control shown in Figure 4 is performed. The horizontal axis of the two-dimensional coordinate system in Figure 7(c) indicates time, and the vertical axis indicates the output power [kW] of the fuel cell FC, and the solid line in Figure 7(c) shows an example of the change in the output power of the fuel cell FC over time when the normal power generation control shown in Figure 4 is performed. The horizontal axis of the two-dimensional coordinate system in FIG. 7(d) indicates time, and the vertical axis indicates the flow rate [NL/min] of the oxidant gas supplied to the fuel cell FC. The solid line in FIG. 7(d) shows an example of the change in the flow rate of the oxidant gas over time when the normal power generation control shown in FIG. 4 is performed. The horizontal axis (time axis) in FIG. 7(a) to FIG. 7(d) is the same as each other. In addition, between time t21 and time t23, the output power (power required from the external load Lout) of the fuel cell system FCS is smaller than the target power generation power Pt1, and when the target power generation power Pt changes to the target power generation power Pt1, the power storage device B is charged and the charge amount of the power storage device B increases. In addition, the power P1<power P2<power P3. In addition, the flow rate F1<flow rate F2<flow rate F3. In addition, the flow rate F1 is the flow rate of the oxidant gas supplied to the fuel cell FC when the fuel cell FC is in a state where water is likely to remain in the fuel cell FC. In FIG. 6(b), the charge amount of the storage device B varies depending on the difference between the supplied power and the required power, so strictly speaking it will have a complex waveform, but for the sake of explanation it has been simplified to change linearly. The same applies to the following FIGs. 7(b), 8(b), 9(b), 10(b), and 11(b).

First, when the charge amount of the power storage device B is decreasing due to the supply of power from the power storage device B to the external load Lout, if the charge amount of the power storage device B falls below the threshold value Vth15 at time t21, the target power generation Pt changes from the target power generation Pt0 to the target power generation Pt1. Then, in order to increase the output power of the fuel cell FC from zero to power P1 equivalent to the target power generation Pt1, the flow rate of the oxidant gas supplied to the fuel cell FC increases from zero to flow rate F1. Also, the power storage device B is charged with a portion of the power output from the fuel cell FC, and the charge amount of the power storage device B increases.

Next, when the charge amount of the storage device B becomes equal to or greater than the threshold value Vth16 at time t22, the target power generation Pt changes from the target power generation Pt1 to the target power generation Pt0. Then, the output power of the fuel cell FC decreases from the power P1 equivalent to the target power generation Pt1 to zero, and the flow rate of the oxidant gas supplied to the fuel cell FC decreases from the flow rate F1 to zero. Furthermore, when the output power of the fuel cell FC becomes zero, power begins to be supplied from the storage device B to the external load Lout, and the charge amount of the storage device B decreases again.

Next, when the charge amount of the storage battery B becomes equal to or less than the threshold value Vth15 at time t23, the target power generation Pt changes from the target power generation Pt0 to the target power generation Pt1. Then, in order to increase the output power of the fuel cell FC from zero to power P1 equivalent to the target power generation Pt1, the flow rate of the oxidant gas supplied to the fuel cell FC increases from zero to flow rate F1. Also, the storage battery B is charged with a portion of the power output from the fuel cell FC, and the charge amount of the storage battery B increases again.

After this, the flow rate of the oxidizer gas repeatedly increases and decreases between zero and flow rate F1.

In this way, when the power generation power of the fuel cell FC is controlled by normal power generation control even after the power supply destination of the fuel cell system FCS is switched from the vehicle load Lin to the external load Lout, the charge amount of the power storage device B can only be changed between thresholds Vth16 and Vth15, so the output power of the fuel cell FC can only be increased to power P1 equivalent to the target power generation power Pt1. Therefore, the flow rate of the oxidant gas supplied to the fuel cell FC can only be increased to flow rate F1, and water is likely to remain in the fuel cell FC.

Therefore, in the fuel cell system FCS of the embodiment, the power supply destination of the fuel cell system FCS is switched from the vehicle load Lin to the external load Lout, and then the power generation of the fuel cell FC is controlled by low-load operation-compatible power generation control.

Figure 8 is a diagram for explaining the power generation control of the fuel cell FC when the power supply destination of the fuel cell system FCS during low-load operation-compatible power generation control is set to the external load Lout. The horizontal axis of the two-dimensional coordinates in Figure 8(a) indicates time, and the vertical axis indicates the output power [kW] of the fuel cell system FCS, and the solid line in Figure 8(a) shows an example of the change in the output power of the fuel cell system FCS over time when the low-load operation-compatible power generation control shown in Figure 5 is performed. The horizontal axis of the two-dimensional coordinates in Figure 8(b) indicates time, and the vertical axis indicates the charge amount of the storage device B, and the solid line in Figure 8(b) shows an example of the change in the charge amount of the storage device B over time when the low-load operation-compatible power generation control shown in Figure 5 is performed. The horizontal axis of the two-dimensional coordinates in Figure 8(c) indicates time, and the vertical axis indicates the output power [kW] of the fuel cell FC, and the solid line in Figure 8(c) shows an example of the change in the output power of the fuel cell FC over time when the low-load operation-compatible power generation control shown in Figure 5 is performed. The horizontal axis of the two-dimensional coordinate system in FIG. 8(d) indicates time, and the vertical axis indicates the flow rate [NL/min] of the oxidant gas supplied to the fuel cell FC. The solid line in FIG. 8(d) shows an example of the change in the flow rate of the oxidant gas over time when the low-load operation power generation control shown in FIG. 5 is performed. The horizontal axis (time axis) in FIG. 8(a) to FIG. 8(d) is the same as each other. In addition, between time t30 and time t36, the output power of the fuel cell system FCS is smaller than the target power generation power Pt1, and when the target power generation power Pt changes to any of the target power generation powers Pt1 to Pt3, the power storage device B is charged and the charge amount of the power storage device B increases. In addition, power P1<power P2<power P3. In addition, flow rate F1<flow rate F2<flow rate F3. In addition, flow rate F3 is the flow rate of the oxidant gas supplied to the fuel cell FC when the water remaining in the fuel cell FC is being discharged outside the fuel cell FC.

First, between time t30 and time t31, when the target power generation Pt is maintained at the target power generation Pt0, the charge amount of the storage device B gradually decreases.

Next, when the charge amount of the power storage device B falls below the threshold value V21 at time t31, the target power generation Pt changes from the target power generation Pt0 to the target power generation Pt1. Then, in order to increase the output power of the fuel cell FC from zero to power P1 equivalent to the target power generation Pt1, the flow rate of the oxidant gas supplied to the fuel cell FC is increased from zero to flow rate F1. In addition, the power storage device B is charged with a portion of the power output from the fuel cell FC, and the charge amount of the power storage device B increases.

Next, when the charge amount of the storage device B becomes equal to or greater than the threshold value V22 at time t32, the target power generation Pt changes from the target power generation Pt1 to the target power generation Pt2. Then, in order to increase the output power of the fuel cell FC from power P1 equivalent to the target power generation Pt1 to power P2 equivalent to the target power generation Pt2, the flow rate of the oxidant gas supplied to the fuel cell FC is increased from flow rate F1 to flow rate F2. In addition, the storage device B is charged with a portion of the power output from the fuel cell FC, and the charge amount of the storage device B is further increased.

Next, when the charge amount of the storage device B becomes equal to or greater than the threshold value V23 at time t33, the target power generation Pt changes from the target power generation Pt2 to the target power generation Pt3. Then, in order to increase the output power of the fuel cell FC from power P2 equivalent to the target power generation Pt2 to power P3 equivalent to the target power generation Pt3, the flow rate of the oxidant gas supplied to the fuel cell FC is increased from flow rate F2 to flow rate F3. In addition, the storage device B is charged with a portion of the power output from the fuel cell FC, and the charge amount of the storage device B is further increased.

Next, when the charge amount of the storage device B becomes equal to or greater than the threshold value V24 at time t34, the target power generation Pt changes from the target power generation Pt3 to the target power generation Pt2. Then, in order to reduce the output power of the fuel cell FC from power P3 equivalent to the target power generation Pt3 to power P2 equivalent to the target power generation Pt2, the flow rate of the oxidant gas supplied to the fuel cell FC is reduced from flow rate F3 to flow rate F2. In addition, the storage device B is charged with a portion of the power output from the fuel cell FC, and the charge amount of the storage device B is further increased.

Next, when the charge amount of the storage battery B becomes equal to or greater than the threshold value V25 at time t35, the target power generation Pt changes from the target power generation Pt2 to the target power generation Pt1. Then, in order to reduce the output power of the fuel cell FC from power P2 equivalent to the target power generation Pt2 to power P1 equivalent to the target power generation Pt1, the flow rate of the oxidant gas supplied to the fuel cell FC is reduced from flow rate F2 to flow rate F1. In addition, the storage battery B is charged with a portion of the power output from the fuel cell FC, and the charge amount of the storage battery B is further increased.

Then, at time t36, when the charge amount of the storage device B becomes equal to or greater than the threshold value V26, the target power generation Pt changes from the target power generation Pt1 to the target power generation Pt0. Then, in order to reduce the output power of the fuel cell FC from the power P1 corresponding to the target power generation Pt1 to zero, the flow rate of the oxidant gas supplied to the fuel cell FC is reduced from the flow rate F1 to zero. Also, because the power output from the fuel cell FC becomes zero, the charge amount of the storage device B gradually decreases again.

After this, the flow rate of the oxidizer gas repeatedly increases and decreases between zero and flow rate F3.

In this way, when the power supply destination of the fuel cell system FCS is switched from the vehicle load Lin to the external load Lout, and then the power generation of the fuel cell FC is controlled using low-load operation power generation control, the output power of the fuel cell FC can be forcibly increased to a voltage V3 corresponding to the target power generation power Pt3, so that the flow rate of the oxidant gas can be increased to a flow rate F3, thereby reducing the amount of water remaining in the fuel cell FC.

The present invention is not limited to the above-described embodiment, and various improvements and modifications are possible without departing from the spirit of the present invention.

<Modification 1>
The control unit CNT may be configured to change the target power generation Pt from the target power generation Pt3 to the target power generation Pt0 when the charge amount of the power storage device B becomes equal to or greater than a threshold value Vth24 in a state in which the target power generation Pt is the target power generation Pt3 during the low load operation corresponding power generation control shown in Fig. 5. Even with this configuration, for example, as shown in Fig. 9, the output power of the fuel cell FC can be increased to a power P3 equivalent to the target power generation Pt3, and therefore the flow rate of the oxidant gas supplied to the fuel cell FC can be increased to a flow rate F3. Note that when configured in this way, it is not necessary to determine the threshold values Vth25 and Vth26 in advance.

<Modification 2>
The control unit CNT may be configured to change the target power generation Pt from the target power generation Pt0 to the target power generation Pt3 when the charge amount of the power storage device B becomes equal to or less than a threshold value Vth21 in a state where the target power generation Pt is the target power generation Pt0 during the low load operation corresponding power generation control shown in Fig. 5. Even with this configuration, for example, as shown in Fig. 10, the output power of the fuel cell FC can be increased to a power P3 equivalent to the target power generation Pt3, and therefore the flow rate of the oxidant gas supplied to the fuel cell FC can be increased to a flow rate F3. Note that when configured in this way, it is not necessary to determine the threshold values Vth22 and Vth23 in advance.

<Modification 3>
The control unit CNT may be configured to change the target power generation Pt from the target power generation Pt0 to the target power generation Pt3 when the charge amount of the storage device B becomes equal to or less than the threshold Vth21 in a state where the target power generation Pt is the target power generation Pt0 during the low load operation-compatible power generation control shown in Fig. 5, and to change the target power generation Pt from the target power generation Pt3 to the target power generation Pt0 when the charge amount of the storage device B becomes equal to or more than the threshold Vth24 in a state where the target power generation Pt is the target power generation Pt3. Even with this configuration, for example, as shown in Fig. 11, the output power of the fuel cell FC can be increased to the power P3 equivalent to the target power generation Pt3, and the flow rate of the oxidant gas supplied to the fuel cell FC can be increased to the flow rate F3. Note that, when configured in this manner, it is not necessary to previously determine the thresholds Vth22, Vth23, Vth25, and Vth26.

<Modification 4>
In the fuel cell system FCS of the above embodiment, the target power generation Pt of the fuel cell FC is changed (increased or decreased) in stages according to the charge amount of the storage device B, but the target power generation Pt of the fuel cell FC may also be changed (increased or decreased) linearly according to the charge amount of the storage device B.

<Modification 5>
In the above embodiment, the fuel cell system FCS is configured as a generator that supplies power to the vehicle load Lin or the external load Lout, but the fuel cell system FCS may be configured as a stationary generator or an emergency power source that cooperates with a commercial power source to supply power to an external load. In this case, it is preferable that the control unit CNT monitors the power required by the external load, and when the required power falls below a predetermined power and this state continues for a predetermined time or more, it determines that the external load is a target for low-load operation power generation control.

FCS Fuel cell system CNT Control unit Ve Vehicle Lin Vehicle load Kout External load FC Fuel cell HT Hydrogen tank INJ Injector ACP Air compressor CNV DCDC converter ARV Air pressure regulating valve INV Inverter B Electric storage device SW1, SW2 Change-over switches Svf, Svb Voltage sensors Sif, Sib Current sensor

Claims (5)

A fuel cell;
a power storage device that is charged by receiving power from the fuel cell and discharged by supplying the power to a load;
an air compressor for supplying an oxidant gas to the fuel cell;
a control unit that changes a target power generation amount in accordance with a charge amount of the power storage device and controls an operation of the air compressor so that the power generation amount of the fuel cell follows the target power generation amount;
Equipped with
The control unit is
changing the target power generation from zero to a first target power generation that is greater than zero when the charge amount of the power storage device becomes equal to or less than a first charge amount under normal conditions;
When the charge amount of the power storage device becomes equal to or less than a second charge amount smaller than the first charge amount under a predetermined condition different from the normal condition, the target power generation is changed from zero to the first target power generation or to a second target power generation larger than the first target power generation.
A fuel cell system comprising: 2. The fuel cell system according to claim 1,
The control unit changes the target power generation in a stepwise manner according to a charge amount of the power storage device under the normal condition or the predetermined condition.
A fuel cell system comprising: 2. The fuel cell system according to claim 1,
The control unit is
under the normal condition, the target power generation of the fuel cell is increased as the charge amount of the power storage device decreases within a range from the first charge amount to a third charge amount that is smaller than the first charge amount, and the target power generation of the fuel cell is decreased as the charge amount of the power storage device increases,
Under the specified condition, the target power generation of the fuel cell is maintained at zero until the charge amount of the power storage device falls to the second charge amount, and thereafter, the target power generation of the fuel cell is maintained at the second target power generation until the charge amount of the power storage device rises to a fourth charge amount that is greater than the second charge amount.
A fuel cell system comprising: 2. The fuel cell system according to claim 1,
The control unit, when the charge amount of the power storage device becomes equal to or less than the second charge amount under the specified conditions, changes the target power generation of the fuel cell from zero to a third target power generation power smaller than the second target power generation power, then to a fourth target power generation power smaller than the second target power generation power and larger than the third target power generation power, and then to the second target power generation power. A fuel cell;
a power storage device that is charged by receiving power from the fuel cell and discharged by supplying the power to a load;
an air compressor for supplying an oxidant gas to the fuel cell;
a control unit that changes a target power generation amount in accordance with a charge amount of the power storage device and controls an operation of the air compressor so that the power generation amount of the fuel cell follows the target power generation amount;
Equipped with
The control unit is
Under normal conditions, when the charge amount of the power storage device becomes equal to or less than a first charge amount, the target power generation is changed from zero to a first target power generation power greater than zero, when the charge amount of the power storage device becomes equal to or less than a second charge amount smaller than the first charge amount, the target power generation is changed from the first target power generation to a second target power generation power greater than the first target power, when the charge amount of the power storage device becomes equal to or less than a third charge amount smaller than the second charge amount, the target power generation is changed from the second target power generation to a third target power generation power greater than the second target power,
When the charge amount of the power storage device becomes equal to or less than the third charge amount under a predetermined condition different from the normal condition, the target power generation is changed from zero to the third target power generation.
A fuel cell system comprising:

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