Fuel cell system

Abstract

A control unit in a fuel cell system having a valve provided in an off-gas discharge passage controls the opening degree of the valve on the basis of a measured value of the temperature of a fuel cell measured by a temperature sensor and an output voltage difference defined as the difference between the optimum value of the output voltage of the fuel cell corresponding to a measured value of the output current of the fuel cell measured by a current sensor and a measured value of the output voltage of the fuel cell measured by a voltage sensor.

Description

fuel cell system

[0001] The present disclosure relates to a fuel cell system having a fuel cell that generates electricity when supplied with a fuel gas and an oxidant gas.

[0002] Patent Document 1 discloses a fuel cell system having an adjustment valve that adjusts the flow rate of air (oxidizing gas) flowing from the supply flow path to the discharge flow path to increase the flow rate of air supplied to the fuel cell when it is determined that the inside of the fuel cell is dry.

[0003] JP 2010-114039 A

[0004] The fuel cell system disclosed in Patent Document 1 uses an adjusting valve to reduce the amount of air supplied from the supply flow path to the fuel cell when it is determined that the inside of the fuel cell is dry, regardless of the temperature of the fuel cell. However, when the temperature of the fuel cell is low, there is a risk that a large amount of water will accumulate inside the fuel cell, and when the temperature of the fuel cell is high, there is a risk that the inside of the fuel cell will become dry.

[0005] If a large amount of water accumulates inside the fuel cell or if the inside of the fuel cell becomes dry, the chemical reaction during power generation in the fuel cell is suppressed, causing FC overvoltage, which may result in a decrease in the power generation efficiency of the fuel cell and deterioration of the fuel cell. Thus, if the inside of the fuel cell is not adjusted to an appropriate state according to the temperature of the fuel cell, a decrease in the power generation efficiency of the fuel cell and deterioration of the fuel cell may occur. Note that "FC overvoltage occurs" means that the output voltage of the fuel cell drops and there is a large difference between the output voltage and the optimal value (i.e., the value optimal for improving the power generation efficiency of the fuel cell).

[0006] Therefore, the present disclosure has been made to solve the above-mentioned problems, and aims to provide a fuel cell system that can adjust the state inside the fuel cell to an appropriate state depending on the temperature of the fuel cell, thereby preventing a decrease in the power generation efficiency of the fuel cell and deterioration of the fuel cell.

[0007] One aspect of the present disclosure made to solve the above problem is a fuel cell system having a fuel cell that generates electricity by receiving a supply of fuel gas and oxidant gas, an off-gas discharge passage through which oxidant off-gas, which is the oxidant gas not used for power generation, is discharged from the fuel cell, and a valve provided in the off-gas discharge passage, the system also having a temperature sensor that measures the temperature of the fuel cell, a current sensor that measures the output current of the fuel cell, a voltage sensor that measures the output voltage of the fuel cell, and a control unit that controls the valve, wherein when the difference between an optimal value of the output voltage of the fuel cell corresponding to the measured value of the output current of the fuel cell measured by the current sensor and the measured value of the output voltage of the fuel cell measured by the voltage sensor is defined as an output voltage difference, the control unit controls the opening degree of the valve based on the measured value of the temperature of the fuel cell measured by the temperature sensor and the output voltage difference.

[0008] According to this aspect, the valve opening can be controlled according to the state inside the fuel cell using the measured values ​​of the fuel cell temperature, output current, and output voltage, thereby adjusting the state inside the fuel cell to an appropriate state according to the fuel cell temperature, and preventing a decrease in the power generation efficiency of the fuel cell and deterioration of the fuel cell.

[0009] In the above aspect, it is preferable that the control unit controls the opening of the valve in the opening direction when the measured temperature of the fuel cell is less than a predetermined temperature and the output voltage difference is greater than or equal to a judgment value.

[0010] According to this aspect, if the temperature of the fuel cell is low and the measured output voltage of the fuel cell is far from the optimum value, it is determined that a large amount of water has accumulated in the fuel cell, and the valve is opened wider to facilitate the discharge of water from the fuel cell to the outside. This reduces the amount of water accumulated in the fuel cell, thereby preventing a decrease in the power generation efficiency of the fuel cell and preventing the fuel cell from deteriorating.

[0011] In the above aspect, it is preferable that the control unit controls the opening of the valve in the closing direction when the measured temperature of the fuel cell is less than a predetermined temperature and the output voltage difference is less than a judgment value.

[0012] According to this aspect, when the temperature of the fuel cell is low but the measured output voltage of the fuel cell is close to the optimum value, it is determined that not much water has accumulated in the fuel cell, and the valve opening is reduced to make it difficult for water to be discharged from the fuel cell to the outside. This makes it easier for water to be retained in the fuel cell, preventing the fuel cell from becoming dry, and therefore preventing a decrease in the power generation efficiency of the fuel cell and deterioration of the fuel cell.

[0013] In the above aspect, it is preferable that the control unit controls the opening of the valve in the closing direction when the measured temperature of the fuel cell is equal to or higher than a predetermined temperature and the output voltage difference is equal to or higher than a judgment value.

[0014] According to this aspect, if the temperature of the fuel cell is high and the measured output voltage of the fuel cell is far from the optimum value, it is determined that the inside of the fuel cell is in a dry state, and the valve opening is reduced to make it difficult for water to be discharged from the fuel cell to the outside. This makes it easier for water to be retained inside the fuel cell, alleviating the dry state inside the fuel cell, thereby preventing a decrease in the power generation efficiency of the fuel cell and the occurrence of fuel cell deterioration.

[0015] In the above aspect, it is preferable that the control unit controls the valve in the opening direction when the measured temperature of the fuel cell is equal to or higher than a predetermined temperature and the output voltage difference is less than a judgment value.

[0016] According to this aspect, if the temperature of the fuel cell is high but the measured output voltage of the fuel cell is close to the optimum value, it is determined that the inside of the fuel cell is not dry, and the valve is opened wider to facilitate the discharge of water from the fuel cell to the outside. This prevents a large amount of water from accumulating inside the fuel cell, thereby preventing a decrease in the power generation efficiency of the fuel cell and deterioration of the fuel cell.

[0017] According to the fuel cell system of the present disclosure, the state inside the fuel cell can be appropriately adjusted according to the temperature of the fuel cell, thereby preventing a decrease in the power generation efficiency of the fuel cell and deterioration of the fuel cell.

[0018] Fig. 1 is a diagram showing a schematic configuration of a fuel cell system of this embodiment. Fig. 2 is a flowchart showing the contents of the opening and closing control of an outlet air valve performed in this embodiment. Fig. 3 is a diagram showing the IV characteristics of an FC stack. Fig. 4 is a diagram showing an example of a map defining the relationship between a measured FC current value and an estimated FC voltage value. Fig. 5 is a diagram showing an example of a map defining the relationship between a measured FC current value and a judgment value.

[0019] An embodiment of a fuel cell system according to the present disclosure will now be described.

[0020] <Outline of Fuel Cell System> First, an outline of a fuel cell system 1 according to this embodiment will be described. The fuel cell system 1 is a system that is mounted on a fuel cell vehicle and supplies electric power to its drive motor (not shown).

[0021] 1, the fuel cell system 1 includes an FC stack 11, a hydrogen system 12, an air system 13, a cooling system 14, and a control unit 15. The FC stack 11 is an example of the "fuel cell" of the present disclosure.

[0022] The FC stack 11 generates electricity by receiving a supply of fuel gas and an oxidant gas. In this embodiment, the fuel gas is hydrogen gas, and the oxidant gas is air. That is, the FC stack 11 generates electricity by receiving a supply of hydrogen gas from the hydrogen system 12 and a supply of air from the air system 13. The electricity generated by the FC stack 11 is then supplied to a drive motor (not shown) via an inverter (not shown).

[0023] The FC stack 11 is also provided with a temperature sensor 16 that measures the temperature of the FC stack 11, a current sensor 17 that measures the output current of the FC stack 11, and a voltage sensor 18 that measures the output voltage of the FC stack 11. The "output current of the FC stack 11" is the current of the power generated by the FC stack 11. The "output voltage of the FC stack 11" is the voltage of the power generated by the FC stack 11.

[0024] The hydrogen system 12 is provided on the anode side of the FC stack 11. The hydrogen system 12 includes a hydrogen filling passage 20, a hydrogen gas supply passage 21, a hydrogen off-gas discharge passage 22, and a hydrogen circulation passage 23.

[0025] The hydrogen filling passage 20 is a passage for filling hydrogen gas into the hydrogen tank 31 from the filling port 30. The hydrogen gas supply passage 21 is a passage for supplying hydrogen gas from the hydrogen tank 31 to the FC stack 11.

[0026] The hydrogen off-gas discharge passage 22 is a passage through which hydrogen off-gas, which is hydrogen gas not used for power generation, is discharged from the FC stack 11. The hydrogen circulation passage 23 is a passage for circulating at least a portion of the hydrogen off-gas from the hydrogen off-gas discharge passage 22 to the hydrogen gas supply passage 21.

[0027] The hydrogen system 12 includes a valve 32, a pressure reducing valve 33, an injector 34, and an ejector 35 in this order from the hydrogen tank 31 side in the hydrogen gas supply passage 21.

[0028] The valve 32 switches between supplying and cutting off hydrogen gas from the hydrogen tank 31 to the hydrogen gas supply passage 21, and between supplying and cutting off hydrogen gas from the filling port 30 to the hydrogen tank 31. The pressure reducing valve 33 is a pressure regulating valve for reducing the pressure of hydrogen gas. The injector 34 is a valve that injects hydrogen gas toward the ejector 35. The ejector 35 is a device that combines the hydrogen gas introduced from the injector 34 with the hydrogen off-gas sucked from the hydrogen off-gas discharge passage 22, and circulates the combined hydrogen gas to the FC stack 11.

[0029] The hydrogen system 12 also includes a gas-liquid separator 41 and an exhaust drain valve 42 in the hydrogen off-gas discharge passage 22 .

[0030] The gas-liquid separator 41 is a device that separates moisture from the hydrogen off-gas and is connected to the ejector 35 via the hydrogen circulation passage 23. The exhaust drain valve 42 is a valve that controls the discharge of the hydrogen off-gas discharged from the FC stack 11 to the outside.

[0031] The air system 13 is provided on the cathode side of the FC stack 11. The air system 13 includes an air supply passage 51 and an air off-gas discharge passage 52. The air off-gas discharge passage 52 is an example of the "off-gas discharge passage" of the present disclosure.

[0032] The air supply passage 51 is a passage for supplying air to the FC stack 11 from outside the fuel cell system 1. The air off-gas discharge passage 52 is a passage for discharging air off-gas, which is air not used for power generation, from the FC stack 11.

[0033] The air system 13 includes an air compressor 61 in the air supply passage 51. The air compressor 61 is a device that supplies air to the FC stack 11.

[0034] The air system 13 is also provided with an outlet air valve 71 in the air off-gas discharge passage 52. The outlet air valve 71 is a valve that adjusts the flow rate of air off-gas discharged from the FC stack 11 to the air off-gas discharge passage 52. The outlet air valve 71 is an example of the "valve" in the present disclosure.

[0035] The cooling system 14 is a system that cools the FC stack 11, and includes a cooling water passage 81 and a cooling fan 82. The cooling water passage 81 is a passage through which cooling water flows. The cooling fan 82 is a device that cools the cooling water flowing through the cooling water passage 81.

[0036] The control unit 15 is a device having, for example, an arithmetic processing unit such as a CPU, a storage unit such as a ROM for storing control programs and control data processed by the CPU and a RAM used as various work areas for control processing, and an input / output interface unit. The control unit 15 performs various controls of the fuel cell system 1 in accordance with the control programs stored in the storage unit.

[0037] Specifically, the control unit 15 controls, for example, the rotation speed of the air compressor 61 and the opening degree of the outlet air valve 71. The control unit 15 also controls the valve 32, the pressure reducing valve 33, the injector 34, the exhaust drain valve 42, the cooling fan 82, and the like.

[0038] (Operation of Fuel Cell System) In the fuel cell system 1 configured as described above, in the hydrogen system 12, hydrogen gas supplied from the hydrogen gas supply passage 21 to the FC stack 11 is used for power generation in the FC stack 11 and then discharged as hydrogen off-gas from the FC stack 11 to the outside via the hydrogen off-gas discharge passage 22, or is sucked into the ejector 35 via the hydrogen off-gas discharge passage 22 and the hydrogen circulation passage 23. In addition, in the air system 13, air supplied from the air supply passage 51 to the FC stack 11 is used for power generation in the FC stack 11 and then discharged as air off-gas from the FC stack 11 to the outside via the air off-gas discharge passage 52.

[0039] <Regarding the opening and closing control of the outlet air valve> When the temperature of the FC stack 11 is low, there is a risk of a large amount of water accumulating inside the FC stack 11, whereas when the temperature of the FC stack 11 is high, there is a risk of the inside of the FC stack 11 becoming dry. If a large amount of water accumulates inside the FC stack 11 or the inside of the FC stack 11 becomes dry in this way, the chemical reaction during power generation in the FC stack 11 is suppressed, causing the output voltage of the FC stack 11 to deviate from the optimum value (i.e., the optimum value for improving the power generation efficiency of the FC stack 11), and FC overvoltage occurs, which could result in a decrease in the power generation efficiency of the FC stack 11 and deterioration of the FC stack 11. Note that "the occurrence of an FC overvoltage" means that the output voltage of the FC stack 11 drops and a large difference occurs between the optimum value and the output voltage.

[0040] Thus, if the inside of the FC stack 11 is not adjusted to an appropriate state according to the temperature of the FC stack 11, there is a risk of a decrease in the power generation efficiency of the FC stack 11 and deterioration of the FC stack 11. Therefore, it is desirable to adjust the inside of the FC stack 11 to an appropriate state according to the temperature of the FC stack 11 to prevent a decrease in the power generation efficiency of the FC stack 11 and deterioration of the FC stack 11.

[0041] Therefore, in this embodiment, the control unit 15 controls the opening degree of the outlet air valve 71 based on measurements of the temperature, output current, and output voltage of the FC stack 11, thereby adjusting the conditions inside the FC stack 11 to an appropriate state.

[0042] Specifically, the control unit 15 controls the opening degree of the outlet air valve 71 based on the measured FC temperature value and the FC voltage difference, which is the difference between the estimated FC voltage value and the measured FC voltage value.

[0043] The FC temperature measurement value is a measurement value of the temperature of the FC stack 11 measured by the temperature sensor 16. The FC voltage estimation value is an optimal value of the output voltage of the FC stack 11 corresponding to the FC current measurement value, and is an example of the "optimal value of the output voltage of the fuel cell" in the present disclosure. The FC voltage measurement value is a measurement value of the output voltage of the FC stack 11 measured by the voltage sensor 18. The FC voltage difference is an example of the "output voltage difference" in the present disclosure.

[0044] More specifically, the control unit 15 performs the control shown in the flowchart in Fig. 2. During operation of the fuel cell system 1, the control unit 15 performs the control shown in Fig. 2 every predetermined time (for example, every second).

[0045] As shown in FIG. 2, the control unit 15 determines whether the measured FC temperature value is less than a predetermined temperature (for example, 50° C.) (step S1).

[0046] If the measured FC temperature value is lower than the predetermined temperature (step S1: YES), the control unit 15 determines whether the condition of the following formula is satisfied (step S2): [Formula 1] (FC voltage estimate value - FC voltage measurement value) ≥ determination value In other words, the control unit 15 determines whether the value obtained by subtracting the FC voltage measurement value from the FC voltage estimate value, i.e., the FC voltage difference, is equal to or greater than the determination value.

[0047] Here, the estimated FC voltage value and the measured FC voltage value are each expressed as shown in Figure 3 in the IV characteristics of the FC stack 11. The estimated FC voltage value is estimated from the measured FC current value, for example, using the map in Figure 4. The judgment value is calculated from the measured FC current value, for example, using the map in Figure 5.

[0048] In the map of Figure 5, the judgment value changes in proportion to the measured FC current value; for example, when the measured FC current value is 10 A, the judgment value is 3 V, and when the measured FC current value is 30 A, the judgment value is 5 V.

[0049] Then, when the condition of the formula [Equation 1] is satisfied, that is, when the FC voltage difference is equal to or greater than the judgment value (step S2: YES), the control unit 15 sets (target outlet valve opening when FC temperature is low) to (old target outlet valve opening when FC temperature is low) + (Δ opening (e.g., 0.5°)), and controls the opening of the outlet air valve 71 in the opening direction by Δ opening.

[0050] In this way, when the measured FC temperature value is below the predetermined temperature and the FC voltage difference is equal to or greater than the determination value, the control unit 15 controls the opening of the outlet air valve 71 in the opening direction.

[0051] That is, in this embodiment, when the FC temperature is low and the FC voltage difference is large (i.e., when the measured FC voltage value is far from the estimated FC voltage value), the control unit 15 determines that a large amount of water has accumulated inside the FC stack 11. Then, the control unit 15 increases the opening of the outlet air valve 71 to make it easier for water to be discharged from inside the FC stack 11 to the outside.

[0052] This reduces the amount of water accumulated in the FC stack 11, promoting the chemical reaction between hydrogen and oxygen in the FC stack 11 and bringing the output voltage of the FC stack 11 closer to the optimum value, thereby preventing a decrease in the power generation efficiency of the FC stack 11 and preventing deterioration of the FC stack 11.

[0053] On the other hand, if the condition of the formula [Equation 1] is not satisfied in step S2, that is, if the FC voltage difference is less than the determination value (step S2: NO), the control unit 15 sets (target outlet valve opening when FC temperature is low) to (old target outlet valve opening when FC temperature is low) - (Δ opening (for example, 0.01°)), and controls the opening of the outlet air valve 71 in the valve closing direction by Δ opening (step S4). Note that the Δ opening in step S4 is set to a value much smaller than the Δ opening in step S3.

[0054] In this way, when the measured FC temperature value is below the predetermined temperature and the FC voltage difference is below the determination value, the control unit 15 controls the opening of the outlet air valve 71 in the valve closing direction.

[0055] That is, in this embodiment, when the FC temperature is low but the FC voltage difference is small (i.e., when the measured FC voltage value is close to the estimated FC voltage value), the control unit 15 determines that not much water has accumulated inside the FC stack 11. Then, the control unit 15 reduces the opening of the outlet air valve 71, making it difficult for water to be discharged from inside the FC stack 11 to the outside.

[0056] This makes it easier for water to be retained within the FC stack 11, preventing the inside of the FC stack 11 from becoming dry, thereby promoting the chemical reaction between hydrogen and oxygen in the FC stack 11 and bringing the output voltage of the FC stack 11 closer to the optimum value. As a result, it is possible to prevent a decrease in the power generation efficiency of the FC stack 11 and deterioration of the FC stack 11.

[0057] In particular, when it is determined that a large amount of water has accumulated inside the FC stack 11, the opening of the outlet air valve 71 is increased, making it easier for water to be discharged from inside the FC stack 11 to the outside.Therefore, when the inside of the FC stack 11 is about to become dry, the opening of the outlet air valve 71 is reduced, making it more difficult for water to be discharged from inside the FC stack 11 to the outside, thereby preventing the inside of the FC stack 11 from becoming dry.

[0058] Also, in step S1, if the FC temperature measurement value is equal to or higher than the predetermined temperature (step S1: NO), the control unit 15 determines whether the condition of the above-mentioned formula [Equation 1] is satisfied (step S5), similarly to step S2.

[0059] Then, when the condition of the formula [Equation 1] is satisfied (step S5: YES), the control unit 15 sets (target outlet valve opening when FC temperature is high) to (old target outlet valve opening when FC temperature is high) - (Δ opening (for example, 0.5°)), and controls the opening of the outlet air valve 71 in the valve closing direction by Δ opening.

[0060] In this way, when the measured FC temperature value is equal to or higher than the predetermined temperature and the FC voltage difference is equal to or higher than the determination value, the control unit 15 controls the opening of the outlet air valve 71 in the closing direction.

[0061] In other words, if the FC temperature is high and the measured FC voltage value is far from the estimated FC voltage value, it is determined that the inside of the FC stack 11 is dry, and the opening of the outlet air valve 71 is reduced, making it difficult for water to be discharged from the inside of the FC stack 11 to the outside.

[0062] This makes it easier for water to be retained within the FC stack 11, alleviating the dry state within the FC stack 11, and thus promoting the chemical reaction between hydrogen and oxygen in the FC stack 11, bringing the output voltage of the FC stack 11 closer to the optimum value. As a result, it is possible to prevent a decrease in the power generation efficiency of the FC stack 11 and prevent deterioration of the FC stack 11.

[0063] On the other hand, if the condition of the formula (1) is not satisfied in step S5 (step S5: NO), the control unit 15 sets (target outlet valve opening when FC temperature is high) to (old target outlet valve opening when FC temperature is high) + (Δ opening (for example, 0.01°)), and controls the opening of the outlet air valve 71 in the valve opening direction by Δ opening. Note that the Δ opening in step S7 is set to a value that is much smaller than the Δ opening in step S6.

[0064] In this way, when the measured FC temperature value is equal to or higher than the predetermined temperature and the FC voltage difference is less than the determination value, the control unit 15 controls the opening of the outlet air valve 71 in the opening direction.

[0065] That is, in this embodiment, if the FC temperature is high but the measured FC voltage value is close to the estimated FC voltage value, it is determined that the inside of the FC stack 11 is not dry, and the opening of the outlet air valve 71 is increased to make it easier for water to be discharged from the inside of the FC stack 11 to the outside.

[0066] This prevents a large amount of water from accumulating inside the FC stack 11, promoting the chemical reaction between hydrogen and oxygen in the FC stack 11 and bringing the output voltage of the FC stack 11 closer to the optimum value, thereby preventing a decrease in the power generation efficiency of the FC stack 11 and preventing deterioration of the FC stack 11.

[0067] In particular, since the opening of the outlet air valve 71 is reduced by determining that the inside of the FC stack 11 is dry, making it difficult for water to be discharged from inside the FC stack 11 to the outside, when a large amount of water is likely to accumulate inside the FC stack 11, the opening of the outlet air valve 71 can be increased, making it easier for water to be discharged from inside the FC stack 11 to the outside, thereby reducing the amount of water accumulated inside the FC stack 11.

[0068] It should be noted that the above-described embodiments are merely examples and do not limit the present disclosure in any way. It goes without saying that various improvements and modifications are possible within the scope of the gist of the present disclosure.

[0069] For example, the control unit 15 may perform control by switching the order of steps S1 and S2 or the order of steps S1 and S5 in FIG.

[0070] REFERENCE SIGNS LIST 1 fuel cell system 11 FC stack 12 hydrogen system 13 air system 14 cooling system 15 control unit 16 temperature sensor 17 current sensor 18 voltage sensor 51 air supply passage 52 air off-gas discharge passage 71 outlet air valve

Claims

1. A fuel cell system having a fuel cell which generates electricity by receiving a supply of fuel gas and oxidant gas, an off-gas exhaust passage through which oxidant off-gas, which is the oxidant gas not used for power generation, is exhausted from the fuel cell, and a valve provided in the off-gas exhaust passage, the fuel cell system further comprising: a temperature sensor which measures the temperature of the fuel cell, a current sensor which measures the output current of the fuel cell, a voltage sensor which measures the output voltage of the fuel cell, and a control unit which controls the valve, wherein when an output voltage difference is defined as the difference between an optimal value of the output voltage of the fuel cell corresponding to the measured value of the output current of the fuel cell measured by the current sensor and the measured value of the output voltage of the fuel cell measured by the voltage sensor, the control unit controls the opening of the valve based on the measured value of the temperature of the fuel cell measured by the temperature sensor and the output voltage difference.

2. A fuel cell system according to claim 1, characterized in that the control unit controls the valve opening in the opening direction when the measured temperature of the fuel cell is below a predetermined temperature and the output voltage difference is equal to or greater than a judgment value.

3. A fuel cell system according to claim 1 or 2, characterized in that, when the measured temperature of the fuel cell is below a predetermined temperature and the output voltage difference is less than a judgment value, the control unit controls the opening of the valve in the closing direction.

4. A fuel cell system according to claim 1, characterized in that the control unit controls the opening of the valve in the closing direction when the measured temperature of the fuel cell is equal to or higher than a predetermined temperature and the output voltage difference is equal to or higher than a judgment value.

5. A fuel cell system according to claim 1 or 4, characterized in that the control unit controls the valve in an opening direction when the measured temperature of the fuel cell is equal to or higher than a predetermined temperature and the output voltage difference is less than a judgment value.

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