JP2022006714A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of continuously outputting a constant output power for a long period of time. SOLUTION: The fuel cell system keeps the output power of the FC stack and the FC stack constant, adjusts the oxidant stoichiometric ratio to the first oxidant stoichiometric ratio, and adjusts the supply pressure of the oxidant gas to the FC stack. The FC stack is operated by adjusting to the first pressure and adjusting the fuel stoichiometric ratio to the first fuel stoichiometric ratio. When the output current of the FC stack exceeds the humidification start current value, the controller changes the oxidant stoichiometric ratio from the first oxidant stoichiometric ratio to the second oxidant stoichiometric ratio, and changes the supply pressure from the first pressure to the second pressure. The fuel stoichiometric ratio is changed from the first fuel stoichiometric ratio to the second fuel stoichiometric ratio. The second oxidant stoichiometric ratio is smaller than the first oxidant stoichiometric ratio, and the second fuel stoichiometric ratio is larger than the first fuel stoichiometric ratio. The second pressure is higher than the first pressure. [Selection diagram] Fig. 2

Description

The techniques disclosed herein relate to fuel cell systems. The present specification provides a fuel cell system capable of maintaining the humidity of the fuel cell stack in an appropriate range and keeping the output power constant for a long period of time.

Patent Document 1 discloses a fuel cell system that keeps the output power constant. It is known that if the output power of the fuel cell stack is kept constant under the same conditions, the inside of the fuel cell becomes dry or excessive in water, and the power generation efficiency decreases. That is, if the humidity in the fuel cell stack is out of the appropriate range, the power generation efficiency will decrease. Inside the fuel cell stack by changing the stoichiometric ratio of the oxidant gas (typically air) supplied to the cathode of the fuel cell stack and the stoichiometric ratio of the fuel gas (typically hydrogen gas) supplied to the anode. It is known that the fuel cell can be dried or humidified (for example, Patent Document 2). Specifically, when the stoichiometric ratio of the oxidant gas is small and the stoichiometric ratio of the fuel gas is increased, the inside of the fuel cell stack is humidified. At the same time, increasing the supply pressure of the oxidant gas to the fuel cell stack promotes humidification. The fuel gas stoichiometric ratio means the ratio of the fuel gas flow rate to the theoretical fuel gas flow rate at a current density of 0.6 [A / cm ² ]. The oxidant gas stoichiometric ratio means the ratio of the oxidant gas flow rate to the theoretical oxidant gas flow rate at a current density of 0.6 [A / cm ² ]. In the following, for convenience of explanation, the oxidant gas stoichiometric ratio may be referred to as an oxidant stoichiometric ratio, and the fuel gas stoichiometric ratio may be referred to as a fuel stoichiometric ratio.

JP-A-2017-091922 Japanese Unexamined Patent Publication No. 2019-139966

As mentioned earlier, if the humidity inside the fuel cell stack is out of the proper range, the power generation efficiency will drop. If the power generation efficiency drops excessively, it may not be possible to maintain a constant output power. In the present specification, the oxidant stoichiometric ratio, the fuel stoichiometric ratio, and the supply pressure are appropriately adjusted so as to prevent the fuel cell stack from drying and excessive water content, and a constant output power can be continuously output for a long period of time. Providing technology.

The fuel cell system disclosed herein comprises a fuel cell stack and a controller. The controller keeps the output power of the fuel cell stack constant, and adjusts the oxidant stoichiometric ratio and the fuel stoichiometric ratio supplied to the fuel cell stack, and the supply pressure of the oxidant gas to the fuel cell stack. The controller adjusts the oxidant stoichiometric ratio to the first oxidant stoichiometric ratio, adjusts the supply pressure of the oxidant gas to the fuel cell stack to the first pressure, and adjusts the fuel stoichiometric ratio to the first fuel stoichiometric ratio. Drive the fuel cell stack. When the output current of the fuel cell stack exceeds the predetermined humidification start current value, the controller changes the oxidant stoichiometric ratio from the first oxidant stoichiometric ratio to the second oxidant stoichiometric ratio, and changes the supply pressure from the first pressure to the first pressure. The pressure is changed to 2 and the fuel stoichiometric ratio is changed from the first fuel stoichiometric ratio to the second fuel stoichiometric ratio. The second oxidant stoichiometric ratio is smaller than the first oxidant stoichiometric ratio, and the second fuel stoichiometric ratio is larger than the first fuel stoichiometric ratio. The second pressure is higher than the first pressure. By lowering the oxidant stoichiometric ratio, increasing the fuel stoichiometric ratio, and increasing the supply pressure, the inside of the fuel cell stack is humidified.

The fuel cell system controller disclosed herein monitors the output current of the fuel cell stack. When the inside of the fuel cell stack dries, the power generation efficiency decreases, and as a result, the output voltage decreases. Since the controller keeps the output power constant, the output current is increased to compensate for the decrease in the output voltage. That is, under the condition that the output power is constant, the increase in the output current is an index of the dryness of the fuel cell stack. When the output current exceeds a predetermined threshold (humidification start current value), the controller determines that the humidity inside the fuel cell stack is lower than the appropriate allowable range, lowers the oxidant stoichiometric ratio, and fuel stoichiometric. Increase the ratio and increase the supply pressure. By changing the stochastic ratio and supply pressure, the amount of water transferred from the anode to the cathode inside the fuel cell stack increases, and the humidity rises. The output voltage is restored by alleviating the drying inside the fuel cell stack. As the output voltage recovers, the controller reduces the output current so that the output power remains constant.

The technique disclosed herein utilizes the relationship between drying and a drop in output voltage under conditions that keep the output power constant. To keep the output power constant, the controller of the fuel cell system increases the output current as the output voltage drops. When the output current exceeds a predetermined humidification start current value, the controller changes the stoichiometric ratio and the supply pressure to promote humidification in the fuel cell stack and restore power generation efficiency. As a result, the fuel cell system disclosed in the present specification can continue to output a constant output power for a long period of time. Further, by adopting the technique disclosed in the present specification, it is possible to omit the humidifier that humidifies the oxidant gas, or to keep the output power of the fuel cell stack constant even if the humidifier fails. Can be done.

Details and further improvements to the techniques disclosed herein will be described in the "Modes for Carrying Out the Invention" section below.

It is a block diagram of the fuel cell vehicle including the fuel cell system of an Example. It is a time chart which shows the operation of a fuel cell system. It is a time chart which shows the operation of a fuel cell system (the first modification). It is a time chart which shows the operation of a fuel cell system (second modification). It is a time chart which shows the operation of a fuel cell system (third modification).

The fuel cell system 2 of the embodiment will be described with reference to the drawings. The fuel cell system 2 is mounted on the electric vehicle 100. FIG. 1 shows a block diagram of an electric vehicle 100 including a fuel cell system 2. The electric vehicle 100 receives electric power from the fuel cell system 2 and runs on the electric motor 103. The output power of the fuel cell system 2 is converted into alternating current by the inverter 102 and supplied to the electric motor 103.

The fuel cell system 2 includes a fuel cell stack 10, a battery 3, and a boost converter 4. In the following, for the sake of simplicity, the fuel cell stack 10 may be referred to as the FC stack 10.

The output power of the FC stack 10 is boosted by the boost converter 4 and then supplied to the inverter 102. The battery 3 is connected to the output end of the boost converter 4. The boosted output power of the FC stack 10 and the output power of the battery 3 are supplied to the inverter 102.

The boost converter 4 is controlled by a controller 5 described later. When the output voltage of the boost converter 4 is increased, the ratio of the current of the FC stack 10 to the current supplied to the inverter 102 increases, and the ratio of the current of the battery 3 decreases. On the contrary, when the output voltage of the boost converter 4 is lowered, the ratio of the current of the FC stack 10 to the current supplied to the inverter 102 decreases, and the ratio of the current of the battery 3 increases. That is, the controller 5 can control the current output from the FC stack 10 by adjusting the boost ratio of the boost converter 4.

At the output end of the FC stack 10, a voltage sensor 6 for measuring the output voltage of the FC stack 10 and a current sensor 7 for measuring the output current of the FC stack 10 are provided. The controller 5 boosts the voltage based on the measured values of the voltage sensor 6 and the current sensor 7 so that the output power of the FC stack 10 (that is, the product of the measured value of the voltage sensor 6 and the measured value of the current sensor 7) becomes constant. Controls the converter 4. When the output voltage of the FC stack 10 drops, the controller 5 raises the output voltage of the boost converter 4 to increase the output current of the FC stack 10. When the output voltage of the FC stack 10 increases, the controller 5 lowers the output voltage of the boost converter 4 and lowers the output current of the FC stack 10. In this way, the output power of the FC stack 10 is kept constant.

Of the electric power generated by the FC stack 10, the remaining electric power not consumed by the electric motor 103 is charged to the battery 3.

The FC stack 10 will be described. The FC stack 10 is a laminated body in which a large number of fuel cells are laminated. In FIG. 1, for the sake of understanding, the structure of one fuel cell is schematically shown in a rectangle showing the FC stack 10. In the FC stack 10 (fuel cell), the anode catalyst layer 12 and the cathode catalyst layer 14 face each other with the electrolyte membrane 13 interposed therebetween. The anode diffusion layer 11 is located on the outside of the anode catalyst layer 12 (on the side opposite to the electrolyte membrane 13). The cathode diffusion layer 15 is located on the outside of the cathode catalyst layer 14 (on the side opposite to the electrolyte membrane 13).

Fuel gas is supplied to the anode diffusion layer 11 through the anode gas inlet 16a. Oxidizing agent gas (air) is supplied to the cathode diffusion layer 15 through the cathode gas inlet 17a. Hydrogen contained in the fuel gas is ionized and reaches the cathode catalyst layer 14 through the anode catalyst layer 12 and the electrolyte membrane 13. In the cathode catalyst layer 14, hydrogen ions combine with oxygen in the oxidant gas to become water. Hydrogen is ionized on the anode side, and hydrogen ions combine with oxygen on the cathode side to generate an electron flow, that is, an electric current. Since the chemical reaction in the FC stack 10 (FC cell) is well known, detailed description thereof will be omitted.

The fuel gas surplus in the chemical reaction and the impurities generated in the chemical reaction are discharged from the anode gas outlet 16b. The gas discharged from the anode gas outlet 16b may be referred to as off gas.

The generated water and the surplus oxidant gas (air) are discharged from the cathode gas outlet 17b. The gas discharged from the cathode gas outlet 17b (exhausted air) may also contain hydrogen and water.

The equipment on the fuel gas side in the fuel cell system 2 will be described. The fuel cell system 2 is equipped with a fuel supply pipe 21, an injector 22, an off-gas discharge pipe 23, a gas-liquid separator 24, a return pipe 25, a pump 26, and exhaust drainage as equipment for sending fuel gas to the anode side of the FC stack 10. It is equipped with a valve 27.

The fuel supply pipe 21 connects the fuel tank 20 and the FC stack 10. Two valves 41a and 41b, an injector 22, and a pressure sensor 42a are connected to the fuel supply pipe 21. The valve 41a is a main check valve and stops the release of fuel gas from the fuel tank 20 while the fuel cell system 2 is stopped. The valve 41b is a pressure regulating valve and regulates the pressure of the fuel gas supplied to the injector 22. The injector 22 increases the pressure of the fuel gas and supplies it to the FC stack 10. The pressure sensor 42a is provided on the downstream side of the injector 22 and measures the pressure of the fuel gas supplied to the FC stack 10.

One end of the fuel supply pipe 21 is connected to the anode gas inlet 16a of the FC stack 10 and supplies the fuel gas to the anode diffusion layer 11 of the FC stack 10. One end of the off-gas discharge pipe 23 is connected to the anode gas outlet 16b, and the other end of the off-gas discharge pipe 23 is connected to the gas inlet 24a of the gas-liquid separator 24.

The gas-liquid separator 24 separates the off gas discharged from the anode gas outlet 16b into hydrogen gas (residual fuel gas) and impurities. Typical impurities separated by the gas-liquid separator 24 are nitrogen gas, water, and the like. The nitrogen gas is the nitrogen contained in the oxidant gas (air) supplied to the cathode side, which has passed through the electrolyte membrane 13 and reached the anode side. The residual fuel gas is discharged from the gas outlet 24b, and impurities are discharged from the impurity discharge port 24c.

One end of the return pipe 25 is connected to the gas outlet 24b of the gas-liquid separator 24, and the other end of the return pipe 25 is connected to the fuel supply pipe 21. A pump 26 is attached to the return pipe 25. The pump 26 pushes the residual fuel gas separated by the gas-liquid separator 24 into the fuel supply pipe 21. An exhaust drain valve 27 is connected to the impurity discharge port 24c of the gas-liquid separator 24. An exhaust pipe 32 is connected to the outlet of the exhaust drain valve 27. When the controller 5 opens the exhaust drain valve 27, impurities separated from the off-gas by the gas-liquid separator 24 are discharged to the exhaust pipe 32.

The equipment on the oxidant gas supply side of the fuel cell system 2 will be described. The fuel cell system 2 includes an air supply pipe 31, an air compressor 34, a flow rate adjusting valve 41c, and a pressure regulating valve 41d as equipment for sending an oxidant gas (air) to the cathode side of the FC stack 10.

One end of the air supply pipe 31 is connected to the cathode gas inlet 17a of the FC stack 10, and the other end is open to the outside air. An air compressor 34, a flow rate adjusting valve 41c, and a pressure sensor 42b are attached in the middle of the air supply pipe 31. The air compressor 34 compresses the outside air and supplies the air to the FC stack 10 (cathode diffusion layer 15) through the air supply pipe 31. An exhaust pipe 32 is connected to the cathode gas outlet 17b of the FC stack 10. A pressure regulating valve 41d is attached to the exhaust pipe 32.

The flow rate adjusting valve 41c is a three-way valve, and connects the air supply pipe 31 to the bypass pipe 33. The bypass pipe 33 bypasses the FC stack 10 and guides a part of the air sucked by the air compressor 34 to the exhaust pipe 32. By adjusting the opening degree of the flow rate adjusting valve 41c, the flow rate of the oxidant gas (air) supplied to the FC stack 10 can be adjusted. When the opening degree of the flow rate adjusting valve 41c is reduced, the flow rate of the air supplied to the FC stack 10 decreases.

Further, by adjusting the opening degree of the pressure regulating valve 41d, the pressure (supply pressure) of the oxidant gas (air) supplied to the FC stack 10 (cathode diffusion layer 15) is adjusted. When the opening degree of the pressure regulating valve 41d is reduced, the supply pressure increases. A pressure sensor 42b is connected to the downstream side of the flow control valve 41c, and measures the pressure (supply pressure) of the oxidant gas (air) supplied to the FC stack 10. The controller 5 controls the opening degree of the pressure regulating valve 41d while monitoring the measured value of the pressure sensor 42b, and adjusts the supply pressure.

The exhaust pipe 32 is connected to the outlet of the exhaust drain valve 27 and the cathode gas outlet 17b. The exhaust pipe 32 mixes the exhaust air discharged from the cathode gas outlet 17b of the FC stack 10 and the impurity gas discharged from the outlet of the exhaust drain valve 27 and discharges them to the outside air. A muffler 35 is connected to the downstream side of the exhaust pipe 32. The exhaust gas (mixed gas of exhaust air and impurity gas) is released to the outside air through the muffler 35.

The controller 5 controls the injector 22, the pump 26, the valves 41a-41d, the exhaust drain valve 27, the air compressor 34, and the boost converter 101. The measured values of the pressure sensors 42a and 42b are sent to the controller 5.

As described above, the controller 5 controls the boost converter 4 so that the output power of the FC stack 10 becomes constant based on the measured values of the voltage sensor 6 and the current sensor 7. Further, the controller 5 adjusts the stoichiometric ratio of the fuel gas supplied to the FC stack 10 (fuel stoichiometric ratio) and the stoichiometric ratio of the oxidant gas (oxidant stoichiometric ratio). The controller 5 can adjust the flow rate of the oxidant gas supplied to the FC stack 10, that is, the oxidant stoichiometric ratio by adjusting the opening degree of the flow rate adjusting valve 41c. Further, the controller 5 can adjust the flow rate of the fuel gas supplied to the FC stack 10, that is, the fuel stochastic ratio by adjusting the output of the injector 22. As described above, the controller 5 can adjust the supply pressure of the oxidant gas to the FC stack 10 by adjusting the opening degree of the pressure regulating valve 41d.

As is well known, if the oxidant stoichiometric ratio is set relatively high and the fuel stoichiometric ratio is set relatively low, drying proceeds (humidity decreases) inside the FC stack 10. On the contrary, when the oxidant stoichiometric ratio is set relatively low and the fuel stoichiometric ratio is set relatively high, the inside of the FC stack 10 is humidified (humidity rises). The power generation efficiency of the FC stack 10 decreases when the internal humidity exceeds a predetermined allowable range. The fuel cell system 2 periodically adjusts the fuel stoichiometric ratio, the oxidant stoichiometric ratio, and the supply pressure (the supply pressure of the oxidant gas to the FC stack 10) to bring the humidity of the FC stack 10 into an appropriate allowable range. While maintaining it, the output power can be kept constant for a long period of time. Hereinafter, the control executed by the controller 5 will be described.

The controller 5 stores the following two types of set value groups. The first set value group includes a first oxidant stoichiometric ratio, a first fuel stoichiometric ratio, and a first pressure. The second set value group includes a second oxidant stoichiometric ratio, a second fuel stoichiometric ratio, and a second pressure. The first pressure and the second pressure are set values of the supply pressure of the oxidant gas. Both the first set value group and the second set value group are conditions for operating the FC stack 10.

The controller 5 controls the opening degree of the flow control valve 41c to adjust the oxidant stoichiometric ratio to the first stoichiometric ratio, and controls the opening degree of the pressure regulating valve 41d to adjust the supply pressure of the oxidant gas to the first pressure. Then, the output of the injector 22 is controlled to adjust the fuel stoichiometric ratio to the first fuel stoichiometric ratio. When a predetermined condition is satisfied, the controller 5 changes the oxidant stoichiometric ratio from the first oxidant stoichiometric ratio to the second oxidant stoichiometric ratio, changes the supply pressure from the first pressure to the second pressure, and changes the fuel stoichiometric ratio. The ratio is changed from the first fuel stoichiometric ratio to the second fuel stoichiometric ratio.

The first set value group, that is, the first oxidant stoichiometric ratio, the first fuel stoichiometric ratio, and the first pressure are set to values that can obtain ideal power generation efficiency. On the other hand, when the FC stack 10 is operated using the first set value group that can obtain the ideal power generation efficiency, the inside of the FC stack 10 is gradually dried. In the second set value group, that is, the second oxidant stoichiometric ratio, the second fuel stoichiometric ratio, and the second pressure, the power generation efficiency is lower than that in the case of using the first set value group, but the anode in the FC stack 10 is used. It is set so that water is sufficiently transferred from the cathode to the cathode. The second oxidant stoichiometric ratio is smaller than the first oxidant stoichiometric ratio, the second pressure is higher than the first pressure, and the second fuel stoichiometric ratio is greater than the first fuel stoichiometric ratio.

The controller 5 normally operates the FC stack 10 using the first set value group. When the operation of the FC stack 10 using the first set value group is continued, the inside of the FC stack 10 gradually dries. As described above, the controller 5 keeps the output power of the FC stack 10 constant. As the FC stack 10 dries, the power generation efficiency of the FC stack 10 drops, and the output voltage drops. When the output voltage of the FC stack 10 drops, the controller 5 increases the output current to keep the output power constant. That is, when the FC stack 10 is controlled so as to keep the output power constant, an increase in the output current is an index of the progress of drying of the FC stack 10. When the output current exceeds a predetermined threshold value (humidification start current value), the controller 5 changes the set value group for operating the FC stack 10 from the first set value group to the second set value group. That is, when the output current of the FC stack 10 exceeds the humidification start current value, the controller 5 changes the oxidant stoichiometric ratio from the first oxidant stoichiometric ratio to the second oxidant stoichiometric ratio, and changes the supply pressure from the first pressure. The pressure is changed to the second pressure, and the fuel stoichiometric ratio is changed from the first fuel stoichiometric ratio to the second fuel stoichiometric ratio. When the operation of the FC stack 10 is continued using the second set value group, the inside of the FC stack 10 is humidified and the dry state is alleviated.

When the dry state inside the FC stack 10 is relaxed, the power generation efficiency of the FC stack 10 is restored and the output voltage rises. The controller 5 lowers the output current as the output voltage rises in order to keep the output power constant. When the output current of the FC stack 10 falls below another predetermined threshold value (humidification stop current value), the controller 5 returns the set value group to be used from the second set value group to the first set value group. That is, when the output current of the FC stack 10 exceeds the humidification start current value and then falls below the humidification stop current value lower than the humidification start current value, the controller 5 sets the oxidant stoichiometric ratio from the second oxidant stoichiometric ratio to the second. The 1 oxidant stoichiometric ratio is returned, the supply pressure is returned from the second pressure to the first pressure, and the fuel stoichiometric ratio is returned from the second fuel stoichiometric ratio to the first fuel stoichiometric ratio. Humidification of the FC stack 10 is stopped by returning the set value group used for operating the FC stack 10 to the first set value group. After that, the drying gradually progresses again inside the FC stack 10. By alternately using the first set value group and the second set value group, the controller 5 can keep the humidity inside the FC stack 10 within an appropriate allowable range and keep the output power constant for a long period of time. ..

The operation of the fuel cell system 2 will be described with reference to FIG. In the time chart of FIG. 2, graph G1 shows the output power of the FC stack 10. Graph G2 shows an output voltage, and graph G3 shows an output current. Graph G4 shows the opening degree of the flow rate adjusting valve 41c, graph G5 shows the oxidant stoichiometric ratio, and graph G6 shows the opening degree of the pressure regulating valve 41d. Graph G7 shows the supply pressure of the oxidant gas, graph G8 shows the output of the injector 22, and graph G9 shows the fuel stochastic ratio. The meanings of the graphs of G1-G9 are the same in the figures after FIG.

Until the output current of the FC stack 10 exceeds the humidification start current value Is1, the controller 5 sets the opening degree of the flow rate adjusting valve 41c to the first opening degree Fv1 so that the oxidant stoichiometric ratio becomes the first oxidant stoichiometric ratio Cst1. To control. Further, the controller 5 controls the opening degree of the pressure regulating valve 41d to the first opening degree Pv1 so that the supply pressure becomes the first pressure Psp1. The controller 5 controls the output of the injector 22 to the first injector output In1 so that the fuel stoichiometric ratio becomes the first fuel stoichiometric ratio Fst1. The controller 5 operates the FC stack 10 using the first set value group (first oxidant stoichiometric ratio Cst1, first pressure Psp1, first fuel stoichiometric ratio Fst1).

The first set value group is set so that ideal power generation efficiency can be obtained. On the other hand, when the first set value group is used, the inside of the FC stack 10 is gradually dried. As the inside of the FC stack 10 becomes dry, the power generation efficiency of the FC stack 10 decreases. When the power generation efficiency of the FC stack 10 decreases, the output voltage of the FC stack 10 decreases. The controller 5 increases the output voltage of the boost converter 4 so that the output power of the FC stack 10 becomes constant, and as a result, the output current of the FC stack 10 increases.

At time T1, the output current of the FC stack 10 exceeds the humidification start current value Is1. At time T1, the controller 5 adjusts the opening degree of the flow rate adjusting valve 41c from the first opening degree Fv1 to the second so that the oxidant stoichiometric ratio decreases from the first oxidant stoichiometric ratio Cst1 to the second oxidant stoichiometric ratio Cst2. Reduce the opening to Fv2. The controller 5 narrows the opening degree of the pressure regulating valve 41d from the first opening degree Pv1 to the second opening degree Pv2 so that the supply pressure rises from the first pressure Psp1 to the second pressure Psp2. Since the pressure regulating valve 41d is a pressure regulating valve on the oxidizing agent gas discharge side of the FC stack 10, the supply pressure of the FC stack 10 rises when the opening degree of the pressure regulating valve 41d is narrowed.

Further, the controller 5 increases the output of the injector 22 from the first injector output In1 to the second injector output In2 so that the fuel stoichiometric ratio increases from the first fuel stoichiometric ratio Fst1 to the second fuel stoichiometric ratio Fst2. As described above, the second oxidant stoichiometric ratio Cst2 is smaller than the first oxidant stoichiometric ratio Cst1, the second pressure Psp2 is higher than the first pressure Psp1, and the second fuel stoichiometric ratio Fst2 is the first fuel stoichiometric. It is larger than the ratio Fst1.

When the second fuel stoichiometric ratio Fst2 is large, a large amount of hydrogen is supplied and the transfer of water from the anode to the cathode is promoted. Further, when the second pressure Psp2 is large, a large amount of water in the air is supplied to the FC stack 10, and when the second oxidant stoichiometric ratio Cst2 is small, the water (liquid) inside the cathode side of the FC stack 10 is discharged. The amount goes down. That is, increasing the supply pressure and lowering the oxidant stoichiometric ratio promotes humidification of the FC stack 10.

When the FC stack 10 is operated using the second set value group, the drying inside the FC stack 10 is relieved, the power generation efficiency is restored, and the output voltage of the FC stack 10 becomes high. Since the controller 5 controls the boost converter 4 so that the output power becomes constant, the output current decreases as the output voltage increases. At time T2, the output current of the FC stack 10 falls below the humidification stop current value Is2. At this time, the controller 5 returns the set value group such as the oxidant stoichiometric ratio from the second set value group to the first set value group. Humidification inside the FC stack 10 stops, and it gradually dries again. When the output current exceeds the humidification start current value Is1 again at time T3 (and time T5), the controller 5 switches the set value group from the first set value group to the second set value group. When the output current of the FC stack 10 gradually decreases and the output current falls below the humidification stop current value at time T4 (time T6), the controller 5 returns the set value group to the first set value group again. The controller 5 can keep the output power of the FC stack 10 constant for a long period of time by alternately switching between the first set value group and the second set value group according to the output current of the FC stack 10.

Changes in the opening degree of the flow rate adjusting valve 41c are actually accompanied by a response delay. However, it should be noted that graphs G4-G9 in FIG. 2 show ideal changes ignoring response delays. Note that the time charts of FIGS. 3-5 also show ideal changes, ignoring response delays.

(First Modification Example) A first modification example of control of the FC stack 10 by the controller 5 will be described with reference to FIG. In the first modification, the controller 5 executes a wastewater treatment for draining water from the FC stack 10 when the output current of the FC stack 10 exceeds the humidification start current value Is1 and then falls below the humidification stop current value Is2. In the flowchart of FIG. 3, the output current of the FC stack 10 exceeds the humidification start current value Is1 at time T1 as in the flowchart of FIG. Therefore, the controller 5 switches the set value group from the first set value group to the second set value group. The output current of the FC stack 10 falls below the humidification stop current value Is2 at time T2. From time T2 to time T2a, the controller 5 executes wastewater treatment. In the wastewater treatment, the controller 5 increases the opening degree of the flow rate adjusting valve 41c to the third opening degree Fv3 and returns the opening degree of the pressure regulating valve 41d to the first opening degree Pv1. When the flow rate adjusting valve 41c is opened to the third opening degree Fv3, the oxidant stoichiometric ratio rises to the third oxidant stoichiometric ratio Cst3. When the pressure regulating valve 41d is returned to the first opening Pv1, the supply pressure returns to the first pressure Psp1.

The third opening degree Fv3 of the flow rate adjusting valve 41c is larger than the first opening degree Fv1, and a large amount of oxidant gas is supplied to the FC stack 10. The discharge of the residual oxidant gas pushes out the water accumulated inside the FC stack 10. The controller 5 returns the set value group to the first set value group at time T2a, and continues the operation of the FC stack 10.

By changing the set value group for operating the FC stack 10 from the first set value group to the second set value group, the humidification of the FC stack 10 progresses, and the dry state in the FC stack 10 is alleviated. At the same time, water may collect inside the FC stack 10. Even if excessive water remains inside the FC stack 10, the power generation efficiency is lowered. The controller 5 humidifies the inside of the FC stack 10 using the second set value group, and then executes a wastewater treatment to discharge excess water from the FC stack 10. By discharging excess water, the subsequent power generation efficiency is improved.

(Second Modification Example) A second modification of the control of the FC stack 10 by the controller 5 will be described with reference to FIG. FIG. 4 is a time chart of the processing of the second modification. In the second modification, when the output current of the FC stack 10 exceeds the humidification start current value Is1, the controller 5 switches the first set value group to the second set value group and operates the FC stack 10. After the predetermined humidification time dT has elapsed, the controller 5 returns the set value group to the first set value group. The predetermined humidification time dT is set so that the drying inside the FC stack 10 is sufficiently eliminated. The controller 5 may execute the wastewater treatment for draining water from the FC stack 10 after the humidification time dT has elapsed. The wastewater treatment is as described in the first modification.

(Third Modification Example) A third modification example of control of the FC stack 10 by the controller 5 will be described with reference to FIG. FIG. 5 is a time chart of the processing of the third modification. In FIG. 5, the time chart of the opening degree of the flow rate adjusting valve 41c (graph G4), the opening degree of the pressure regulating valve 41d (graph G6), and the output of the injector 22 (graph G8) is omitted.

In the third modification, the controller 5 operates the FC stack 10 using the first set value group. The controller 5 operates the FC stack 10 by switching the set value from the first set value group to the second set value group for a certain humidification time dT in a certain cycle Cy. After the humidification time dT has elapsed, the set value is returned from the second set value group to the first set value group again, and the operation of the FC stack 10 is continued.

The controller 5 periodically switches between the first set value group and the second set value group. However, when the output current of the FC stack 10 exceeds the humidification start current value Is1, the controller 5 adjusts the oxidant stoichiometric ratio to the second oxidant stoichiometric ratio Cst2 regardless of the cycle, and adjusts the supply pressure to the second pressure Psp2. The fuel stoichiometric ratio is adjusted to the second fuel stoichiometric ratio Fst2, and the time counting of the cycle is restarted. That is, the cycle using the second set value group is recounted from zero. After restarting the timekeeping of the cycle, the controller 5 again switches the set value from the first set value group to the second set value group for a constant humidification time dT in the cycle Cy, and operates the FC stack 10. That is, the controller 5 operates the FC stack 10 using the second set value group during the humidification time dT. After the humidification time dT has elapsed, the set value is returned to the first set value group, and the operation of the FC stack 10 is continued.

In the example of FIG. 5, the set value group is switched from the first set value group to the second set value group at time T1, and the FC stack 10 is operated. When the humidification time dT has elapsed from the time T1, the set value group is returned to the first set value group. The controller 5 plans to switch the set value group to the second set value group at the time T2 (time T1 + cycle Cy) after the time T1.

For example, the output current of the FC stack 10 exceeds the humidification start current value Is1 at the time T3 before the time T2. When the controller 5 detects that the output current exceeds the humidification start current value Is1, the controller 5 switches the set value group from the first set value group to the second set value group and operates the FC stack 10 regardless of the cycle. .. After the humidification time dT has elapsed, the controller 5 returns the set value group to the first set value group.

The controller 5 restarts the time cycle at time T3. That is, the controller 5 switches the set value group from the first set value group to the second set value group at the time T4 (time T3 + cycle Cy) after the time T3.

In the third modification, the controller 5 operates the FC stack 10 while periodically switching between the first set value group and the second set value group. By operating the FC stack 10 in this way, it is possible to stably output a constant output power while maintaining the humidity inside the FC stack 10 within an appropriate allowable range. However, when the output current of the FC stack 10 exceeds the humidification start current value Is1, the FC stack 10 is operated using the second set value group regardless of the cycle to eliminate the drying inside the FC stack 10.

The fuel cell system 2 (including the modified example) of the embodiment can stably output a constant electric power for a long period of time even if it does not have a humidifier for humidifying the oxidant gas. Alternatively, the fuel system 2 can stably output a certain amount of electric power even if the humidifier is out of order.

The points to be noted regarding the technique described in the examples will be described. In the embodiment, the oxidant stoichiometric ratio is adjusted by controlling the flow rate adjusting valve 41c. An air compressor 34 may be used to change the oxidant stoichiometric ratio. The means for changing the fuel stoichiometric ratio and the means for changing the supply pressure of the oxidant gas may also be different from the means of the embodiment. Similarly, for draining the FC stack 10, a means different from the means of the embodiment may be used.

Further, a device different from the boost converter 4 may be used to keep the output power of the FC stack 10 constant.

The first set value group, that is, the first oxidant stoichiometric ratio, the first fuel stoichiometric ratio, and the first pressure may change according to the output power required for the fuel cell system 2. Alternatively, the first set value group may change according to the flow rate of the fuel gas supplied to the FC stack 10. However, the second oxidant stoichiometric ratio is smaller than the first oxidant stoichiometric ratio immediately before switching the set value group to the second set value group. The second fuel stoichiometric ratio is larger than the first fuel stoichiometric ratio immediately before switching the set value group to the second set value group. The second pressure is larger than the first pressure immediately before switching the set value group to the second set value group.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of claims. The techniques described in the claims include various modifications and modifications of the specific examples exemplified above. The technical elements described herein or in the drawings exhibit their technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the techniques exemplified in the present specification or the drawings can achieve a plurality of purposes at the same time, and achieving one of the purposes itself has technical usefulness.

2: Fuel cell system 3: Battery 4: Boost converter 5: Controller 6: Voltage sensor 7: Current sensor 10: Fuel cell stack (FC stack) 20: Fuel tank 21: Fuel supply pipe 22: Injector 23: Off gas discharge pipe 24 : Fuel separator 25: Return pipe 26: Pump 27: Exhaust drain valve 31: Air supply pipe 32: Exhaust pipe 33: Bypass pipe 34: Air compressor 35: Muffler 41a-41d: Valve 42a, 42b: Pressure sensor 100: Electric vehicle 101: Boost converter 102: Injector 103: Electric motor

Claims (6)

With the fuel cell stack,
While keeping the output power of the fuel cell stack constant, the stoichiometric ratio of the oxidant gas supplied to the fuel cell stack (oxidant stoichiometric ratio) is adjusted to the first oxidant stoichiometric ratio, and the fuel of the oxidant gas is adjusted. A controller that adjusts the supply pressure to the battery stack to the first pressure and adjusts the fuel gas stoichiometric ratio (fuel stoichiometric ratio) to the first fuel stoichiometric ratio.
Equipped with
When the output current of the fuel cell stack exceeds a predetermined humidification start current value, the controller changes the oxidant stoichiometric ratio from the first oxidant stoichiometric ratio to the second oxidant stoichiometric ratio, and changes the supply pressure. The first pressure was changed to the second pressure, and the fuel stoichiometric ratio was changed from the first fuel stoichiometric ratio to the second fuel stoichiometric ratio.
The second oxidant stoichiometric ratio is smaller than the first oxidant stoichiometric ratio.
The second pressure is higher than the first pressure,
The second fuel stoichiometric ratio is larger than the first fuel stoichiometric ratio.
Fuel cell system. When the output current exceeds the humidification start current value and then falls below the humidification stop current value lower than the humidification start current value, the controller returns the oxidant stoichiometric ratio to the first oxidant stoichiometric ratio. The fuel cell system according to claim 1, wherein the supply pressure is returned to the first pressure, and the fuel stoichiometric ratio is returned to the first fuel stoichiometric ratio. The fuel cell system according to claim 2, wherein the controller executes a wastewater treatment for draining water from the fuel cell stack when the output current exceeds the humidification start current value and then falls below the humidification stop current value. .. When a predetermined humidification time elapses after the output current exceeds the humidification start current value, the controller returns the oxidant stoichiometric ratio to the first oxidant stoichiometric ratio and sets the supply pressure to the first pressure. The fuel cell system according to claim 1, wherein the fuel cell ratio is returned to the first fuel stoichiometric ratio. The fuel cell system according to claim 4, wherein the controller executes a wastewater treatment for draining water from the fuel cell stack after the humidification time elapses after the output current exceeds the humidification start current value. The controller
The oxidant stoichiometric ratio is changed from the first oxidant stoichiometric ratio to the second oxidant stoichiometric ratio during a predetermined humidification time in a predetermined cycle, and the supply pressure is changed from the first pressure to the second pressure. The fuel cell stack is operated by changing the fuel stoichiometric ratio from the first fuel stoichiometric ratio to the second fuel stoichiometric ratio.
When the output current exceeds the humidification start current value, the oxidant stoichiometric ratio is adjusted to the second oxidant stoichiometric ratio, the supply pressure is adjusted to the second pressure, and the second pressure is adjusted regardless of the cycle. The fuel cell system according to claim 1, wherein the fuel stoichiometric ratio is adjusted to the second fuel stoichiometric ratio and the time counting of the cycle is restarted.

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