Fuel cell system

Abstract

Fuel cell system (2) comprising: a fuel cell stack (10); Fuel cell auxiliary equipment used to operate the fuel cell stack (10); a battery (64) connected to an output terminal of the fuel cell stack (10); a load device connected to the output terminal of the fuel cell stack (10); and a controller (50) configured to control the fuel cell auxiliary equipment and the load device, wherein the controller (50) is configured to predicts the auxiliary equipment power consumption, wherein the auxiliary equipment power consumption is an amount of electrical power consumed by the fuel cell auxiliary equipment for operating the fuel cell stack (10), an estimated input and output power of the battery (64) is determined, determines a required output based on the predicted auxiliary equipment power consumption and the estimated input and output power, wherein the required output is a required output for the fuel cell stack (10), and determines an operating point of the fuel cell stack (10) based on the desired output, characterized in that the controller (50) has stored a desired output of the fuel cell stack (10) that includes an estimated power consumption of the fuel cell auxiliary equipment determined based on an outside air temperature and a predetermined estimated power consumption of the load device, and the load device is configured to control its operation in such a way that a difference between the demanded output and the desired output becomes zero.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The technique disclosed herein relates to fuel cell systems. A technique capable of responding to changes in the power consumption of fuel cell auxiliary equipment while mitigating sudden changes in the operating point of a fuel cell stack is presented. 2. Description of the state of the art

[0002] JP 4 458 126 B2 discloses a fuel cell system that determines the required output of a fuel cell stack (a required output) and the amount of heat that should be generated by the fuel cell stack (the required heat generation amount), and that determines an operating point to achieve the required output and the required heat generation amount. The required output includes the electrical power of electrical devices used to operate the fuel cell stack. In the specification, the electrical devices used to operate the fuel cell stack are referred to as fuel cell auxiliary equipment. Examples of fuel cell auxiliary equipment include an air compressor that supplies air to the fuel cell stack, a hydrogen pump that controls the circulation flow rate of hydrogen gas, and a cooling circulation pump that cools the fuel cell stack.

[0003] The fuel cell system of JP 4 458 126 B2 is installed in an automobile. The required heat generation amount is the amount of heat required to raise the temperature of the fuel cell stack itself, the amount of heat required to heat a passenger compartment, etc. A battery is connected to the fuel cell stack of JP 4 458 126 B2, and the output of the fuel cell stack and the output of the battery can be supplied to the fuel cell auxiliary equipment.

[0004] Furthermore, JP 2018 - 133 147 A and DE 10 2010 047 504 A1 each disclose a fuel cell system having the features of the preamble of patent claim 1. SUMMARY OF THE INVENTION

[0005] The above-mentioned fuel cell systems control the fuel cell stack to achieve the required output. The power consumption of the fuel cell auxiliary equipment changes moment by moment depending on the situation. The output of the fuel cell stack is not very responsive. The output of the fuel cell stack may not follow changes in power consumption. If the operating point of the fuel cell stack is forcibly and suddenly changed in response to changes in power consumption, the control of the fuel cell stack may become unstable. A technique is provided that can respond to changes in the power consumption of the fuel cell auxiliary equipment while reducing sudden changes in the operating point of a fuel cell stack.

[0006] According to the invention, the fuel cell system disclosed here contains the features of patent claim 1.

[0007] In the fuel cell system disclosed here, the operating point of the fuel cell stack is determined so as to achieve the predetermined desired output. The operating point means a combination of output current and output voltage of the fuel cell stack. If the desired output is set in advance to change slowly over time, the operating point will not change suddenly. The power consumption of the fuel cell auxiliary equipment (i.e., the required power) changes from moment to moment as described above. In the technique disclosed here, the difference between the required output and the desired output is absorbed by adjusting the operation (i.e., the power consumption) of the load device. Since the power consumption of the load device is adjusted according to changes in the required output, it is not necessary to adjust the desired output (i.e.,The fuel cell system disclosed herein can respond to a change in the power consumption of the fuel cell auxiliary equipment while reducing sudden changes in the operating point of the fuel cell stack. The desired output is determined in advance based on an estimated power consumption of the fuel cell auxiliary equipment, which is determined according to the outside air temperature, etc.

[0008] If the load device is turned off when the required output is greater than the desired output, the difference between the required output and the desired output cannot be eliminated. Accordingly, the desired output includes the estimated power consumption of the fuel cell auxiliary equipment, which is determined based on the outside air temperature, etc., and the estimated power consumption of the load device. Including the estimated power consumption of the load device in the desired output prevents the required output from becoming greater than the desired output.

[0009] In the fuel cell system disclosed here, the battery is connected to the fuel cell stack. The battery's output is more responsive than the fuel cell stack. The battery can therefore respond to sudden changes in power consumption. However, when the battery's state of charge (SOC) is low, there is a risk that sufficient power may not be supplied from the battery to the fuel cell auxiliary equipment if the power consumption suddenly increases. Accordingly, the estimated input and output power are determined in advance according to the battery's SOC, and the required output including the estimated input and output power is determined. When the SOC is low, for example, the predetermined power (charge power) from the fuel cell stack toward the battery is determined as the estimated input and output power.The battery is charged with part of the power of the fuel cell stack.

[0010] The battery has an allowable input and output range. The allowable input and output range is an allowable range for the input and output power. When the actual input and output power of the battery is greater than the allowable input and output range, the controller can correct the desired output to bring the actual input and output power back to a value within the allowable input and output range. While the input and output power of the battery is within the allowable range, it is not necessary to change the desired output, and sudden changes in the operating point are reduced. When the input and output power of the battery is outside the allowable range, the desired output is exceptionally corrected to protect the battery.

[0011] The controller determines the operating point (desired current and voltage) of the fuel cell stack to achieve the desired output. If it is desired to heat the fuel cell stack, the controller determines the desired heat generation amount of the fuel cell stack per unit time, as well as the operating point and stoichiometric ratio, to achieve the desired output and the desired heat generation amount. The stoichiometric ratio refers to the amount of oxygen supplied to the fuel cell stack relative to the amount of hydrogen. The smaller the stoichiometric ratio, the greater the power generation loss. The power generation loss is released as heat. The fuel cell stack can be heated by intentionally increasing the power generation loss.

[0012] Details of the technique disclosed herein and further improvements are described below in the "DETAILED DESCRIPTION EMBODIMENT" section. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] With reference to the accompanying drawings, in which like characters designate like elements, the features, advantages, and technical and industrial significance of an exemplary embodiment of the invention are described below. In the drawings: Fig. 1 is a block diagram of a fuel cell vehicle including a fuel cell system of an embodiment; and Fig. 2 a flowchart of a fuel cell stack control process. DETAILED DESCRIPTION EXAMPLE OF IMPLEMENTATION

[0014] With reference to the drawings, a fuel cell system 2 of an embodiment will now be described. The fuel cell system 2 is installed in a fuel cell vehicle 100. Fig. 1 is a block diagram of the fuel cell vehicle 100 including the fuel cell system 2. The fuel cell vehicle 100 receives electrical power from the fuel cell system 2 and runs on an electric motor 102. The output of a fuel cell stack 10 is boosted by a boost converter 62 and then converted by an inverter 101 into alternating current, which is supplied to the electric motor 102. In the description, the "output" of the fuel cell stack 10 means the output power. In the following description, the fuel cell stack 10 is sometimes referred to as the "FC stack 10" for simplicity. The state of charge of the battery is sometimes referred to as the "SOC."

[0015] A main battery 103 is also connected to an output terminal of the boost converter 62. From the output of the FC stack 10, the power not consumed by the electric motor 102 is stored in the main battery 103. The output of the FC stack 10 is not very responsive. The power of the main battery 103 can be used to improve the responsiveness to changes in the power supplied to the electric motor 102.

[0016] A buck converter 63 is also connected to the output terminal of the boost converter 62. A sub-battery 64 is connected to the output terminal of the buck converter 63. A portion of the output of the FC stack 10 is stepped down by the buck converter 63 and stored in the sub-battery 64.

[0017] The output voltage of the main battery 103 is higher than 100 volts. The output voltage of the auxiliary battery 64 is lower than 50 volts. The power of the main battery 103 is supplied to the electric motor 102. The power of the auxiliary battery 64 is supplied to devices that operate at voltages below 50 volts. The devices powered by the auxiliary battery 64 include low-power devices, such as various controllers (computers) and a radio 65. The power of the FC stack 10 is sometimes supplied to the low-power devices via the boost converter 62 and the buck converter 63.

[0018] The auxiliary battery 64 also supplies power to the auxiliary equipment of the fuel cell system 2 (the fuel cell auxiliary equipment). In other words, the fuel cell auxiliary equipment is powered by the auxiliary battery 64. The fuel cell auxiliary equipment is a general term for electrical devices used to start and operate the fuel cell stack. The fuel cell auxiliary equipment will be described later. The power of the FC stack 10 is sometimes supplied to the fuel cell auxiliary equipment via the boost converter 62 and the buck converter 63.

[0019] The fuel cell system 2 includes a voltage sensor 18b and a current sensor 19b. The voltage sensor 18b measures the voltage of the auxiliary battery 64, and the current sensor 19b measures the input and output current of the auxiliary battery 64. The measured values ​​of the voltage sensor 18b and the current sensor 19b are sent to a controller 50.

[0020] The fuel cell system 2 further includes the FC stack 10 and a fuel tank 20. The FC stack 10 is an assembly of a large number of fuel cells. As is widely known in the art, each fuel cell is divided into an anode side and a cathode side with an electrolyte membrane between them. Fuel gas is supplied to the anode side via an anode gas inlet 16a. Air is supplied to the cathode side via a cathode gas inlet 17a. Hydrogen contained in the fuel gas is ionized, and the hydrogen ions react with oxygen contained in the air on the cathode side to generate electricity. Since the chemical reaction in the fuel cell (the FC stack 10) is widely known in the art, a detailed description thereof will be omitted.

[0021] Excess fuel gas not consumed in the chemical reaction and impurities generated in the chemical reaction are discharged from an anode gas outlet 16b. The gas discharged from the anode gas outlet 16b is sometimes referred to as fuel off-gas. Produced water and excess air (oxygen) are discharged from a cathode gas outlet 17b.

[0022] The equipment on the fuel gas side of the fuel cell system 2 will now be described. The fuel cell system 2 includes a fuel supply pipe 21, an injector 22, an exhaust pipe 23, a gas-liquid separator 24, a recirculation pipe 25, a hydrogen pump 26, and an exhaust and discharge valve 27 as equipment for supplying fuel gas to the anode side of the FC stack 10.

[0023] The fuel supply pipe 21 connects the fuel tank 20 and the FC stack 10. Two valves 41a, 41b and the injector 22 are connected to the fuel supply pipe 21. The valve 41a is a main shutoff valve and prevents the release of fuel gas from the fuel tank 20 while the fuel cell system 2 is off. The valve 41b is a pressure regulating valve and regulates the fuel gas pressure to be supplied to the injector 22. The injector 22 increases the fuel gas pressure and supplies the resulting fuel gas to the FC stack 10.

[0024] The fuel supply pipe 21 is connected at one end to the anode gas inlet 16a of the FC stack 10 and supplies fuel gas to the anode side of the FC stack 10. The exhaust gas discharge pipe 23 is connected at one end to the anode gas outlet 16b and at the other end to the gas-liquid separator 24.

[0025] The gas-liquid separator 24 separates the fuel 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, etc. The nitrogen gas is the nitrogen contained in the air supplied to the cathode side, which has passed through the electrolyte membrane and reached the anode side. The residual fuel gas is discharged from a gas outlet, and the impurities are discharged from an impurity discharge port. Part of the impurity gas (nitrogen gas) flows out of the gas outlet along with the residual fuel gas.

[0026] The return pipe 25 is connected at one end to the gas outlet of the gas-liquid separator 24 and at the other end to the fuel supply pipe 21. The hydrogen pump 26 is attached to the return pipe 25. The hydrogen pump 26 returns the residual fuel gas separated by the gas-liquid separator 24 to the FC stack 10 via the return pipe 25 and the fuel supply pipe 21. The hydrogen pump 26 thus adjusts the circulation flow rate of the hydrogen gas.

[0027] The exhaust and drain valve 27 is connected to the impurity discharge port of the gas-liquid separator 24. An outlet pipe 32 is connected to an outlet of the exhaust and drain valve 27. When the exhaust and drain valve 27 is opened, the impurities separated from the fuel exhaust gas by the gas-liquid separator 24 are discharged into the outlet pipe 32.

[0028] The equipment on the air supply side of the fuel cell system 2 will now be described. The fuel cell system 2 includes an air supply pipe 31, an air compressor 34, and valves 41c, 41d as equipment for supplying air (oxygen) to the cathode side of the FC stack 10.

[0029] The air supply pipe 31 is connected at one end to the cathode gas inlet 17a of the FC stack 10 and is open to the outside air at the other end. The air compressor 34 and the valve 41c are attached to a central portion of the air supply pipe 31. The air compressor 34 compresses the outside air and supplies the compressed air to the cathode side of the FC stack 10 via the air supply pipe 31. The outlet pipe 32 is connected to the cathode gas outlet 17b of the FC stack 10. The valve 41d is attached to a central portion of the outlet pipe 32. The valves 41c, 41d are pressure regulating valves. The pressure regulating valves regulate the pressure of the air to be supplied to the FC stack 10.

[0030] The outlet pipe 32 is connected to the outlet of the exhaust and vent valve 27 and the cathode gas outlet 17b. The outlet pipe 32 mixes the air discharged from the cathode gas outlet 17b of the FC stack 10 and the impurity gas discharged from the outlet of the exhaust and vent valve 27, and discharges the resulting mixture to the outside air. The water generated by the FC stack 10 is also discharged to the outside of the fuel cell vehicle via the outlet pipe 32.

[0031] Although not shown in the figure, the fuel cell system 2 also includes a pressure sensor, a concentration sensor, or a flow sensor at various locations. A voltage sensor 18a and a current sensor 19a are attached to an output terminal of the FC stack 10. The current sensor 19a measures the output current of the FC stack 10, and the voltage sensor 18a measures the output voltage of the FC stack 10. The measured values ​​of these sensors are sent to the controller 50.

[0032] The fuel cell system 2 also includes a cooling system 70 that cools the FC stack 10. The cooling system 70 comprises a flow path pipe 71, a circulation pump 72, and a heat exchanger 73. Cooling water is enclosed in the flow path pipe 71. The circulation pump 72 circulates the cooling water in the flow path pipe 71. The flow path pipe 71 passes through the FC stack 10. The cooling water absorbs heat from the FC stack 10 as it flows through the FC stack 10. The heat absorbed in the FC stack 10 is transferred through the heat exchanger 73 to a passenger compartment heater 80. The passenger compartment heater 80 comprises a flow path pipe 81 and a pump 82. The pump 82 circulates a heating medium in the flow path pipe 81. The passenger compartment heater 80 heats the passenger compartment using the heat from the FC stack 10. The passenger compartment heater 80 also includes an electric heater 83.The electric heater 83 heats the heating medium when the heat of the FC stack 10 is not sufficient to heat the passenger compartment.

[0033] The controller 50 adjusts the output current and output voltage of the FC stack 10 by adjusting the output voltage of the boost converter 62.

[0034] The controller 50 controls the injector 22, the pumps 26, 72 and 82, the valves 41a to 41d (solenoid-operated valves), the exhaust and drain valve 27, the air compressor 34, the boost converter 62, the buck converter 63, the inverter 101 and the electric heater 83. Although these devices and the controller 50 are connected by signal lines, the signal lines are not in Fig. 1. The injector 22, the hydrogen pump 26, the circulation pump 72, the valves 41a to 41d, the exhaust and drain valve 27, the air compressor 34, the boost converter 62, the buck converter 63, and the controller 50 are included in the fuel cell auxiliary equipment. The electric heater 83, the pump 82, and the radio 65 are devices that are not involved in the start-up and operation of the FC stack 10. The power of the auxiliary battery 64 is supplied to the fuel cell auxiliary equipment and the electrical devices (the electric heater 83, the pump 82, and the radio 65) that are not involved in the operation of the FC stack 10. The power lines that connect the fuel cell auxiliary equipment and the other electrical devices to the auxiliary battery 64 are also not included. Fig. 1. The power of the FC stack 10 is sometimes supplied via the boost converter 62 and the buck converter 63 to the fuel cell auxiliary equipment and electrical devices not involved in the operation of the FC stack 10.

[0035] A non-volatile memory 51 is connected to the controller 50. The memory 51 stores programs executed by the controller 50 and variables used for the programs. The variables used for the programs include a desired output of the FC stack 10. A process executed by the controller 50 and the desired output will be described later.

[0036] The operation of the FC stack 10 in the fuel cell system 2 of the embodiment will now be described. As is widely known in the art, the FC stack 10 generates electricity through a reaction between fuel gas (hydrogen) and oxidizing gas (air). The amount of power generation by the FC stack 10 can be adjusted by the amounts of hydrogen and oxygen supplied to the FC stack 10. The controller 50 adjusts the amounts of hydrogen and oxygen supplied to the FC stack 10 by utilizing the fuel cell auxiliary equipment so that the required output of the FC stack 10 (the required output) is achieved.

[0037] An IV curve is determined for the FC stack 10 according to the amounts of hydrogen and oxygen supplied to the FC stack 10. The IV curve is a curve indicating the relationship between the output current (the desired current I) and the voltage of the FC stack 10 (the desired voltage V). The controller 50 determines an operating point (the combination of the desired current and the desired voltage of the FC stack 10) on the IV curve and controls the boost converter 62 to achieve the desired current. As described above, the controller 50 adjusts the output current of the FC stack 10 by adjusting the output voltage of the boost converter 62. When the desired current is reached, the desired voltage is also reached accordingly.

[0038] The output of the FC stack 10 is not very responsive. Therefore, the output of the FC stack 10 cannot follow sudden changes in the required output (which includes the power consumption of the fuel cell auxiliary equipment). If the operating point is forcibly and suddenly changed, the control may become unstable. The fuel cell system 2 of the embodiment can respond to changes in the power consumption of the fuel cell auxiliary equipment while reducing sudden changes in the operating point of the FC stack 10.

[0039] A process performed when the electric motor 102 is turned off and the FC stack 10 is rapidly warmed up will now be described. Rapid warm-up is a process in which the temperature of the FC stack 10 is increased by self-heating of the FC stack 10. Rapid warm-up occurs when a main switch of the fuel cell vehicle 100 is turned on in a low outside air temperature environment. Rapid warm-up also occurs when water is forcibly drained from the FC stack 10 or when the main switch of the fuel cell vehicle 100 is turned off in a low outside air temperature environment.

[0040] Fig. 2 is a flowchart of an FC stack control process (a rapid warm-up process) executed by the controller 50. When the rapid warm-up is necessary, the controller 50 repeats the process of Fig. 2 in a predetermined cycle (control cycle).

[0041] First, the controller 50 predicts a power consumption of the fuel cell auxiliary equipment (step S2). The predicted power consumption is referred to as the predicted auxiliary equipment power consumption. The controller 50 predicts the power consumption of the fuel cell auxiliary equipment based on the outside air temperature, the temperature of the FC stack 10, the internal pressure of the fuel tank 20, the state of the fuel cell auxiliary equipment, etc. For example, the controller 50 has stored therein a function to predict the predicted auxiliary equipment power consumption based on the outside air temperature, the temperature of the FC stack 10, the internal pressure of the fuel tank 20, etc. The detailed description of a specific example of the prediction process is omitted.

[0042] Next, the controller 50 determines an estimated input and output power of the sub-battery 64 (step S3). The estimated input and output power can be determined by a function that takes the SOC, etc., as inputs. The estimated input and output power is determined so that the current SOC is closer to a reference value (e.g., 60%). When the current SOC is lower than the reference value, the estimated input and output power is determined in such a direction that a current flows into the sub-battery 64. When the current SOC is higher than the reference value, the estimated input and output power is determined in such a direction that a current flows out of the sub-battery 64. When the current SOC is close to the reference value, the estimated input and output power is set to zero.The relationship between the SOC and the estimated input and output power is stored in advance in the controller 50 (the memory 51).

[0043] The controller 50 then determines a required output power (a required output) for the FC stack 10 (step S4). The required output is determined by the predicted auxiliary power consumption and the estimated input and output power. For example, the required output is determined as the sum of the predicted auxiliary power consumption and the estimated input and output power. In this case, the estimated input and output power is positive when a current flows toward the auxiliary battery 64.

[0044] Next, the controller 50 reads a desired output from the memory 51 (step S5). The desired output is a desired value of the output of the FC stack 10. The desired output is expressed in electric power (kilowatts). The desired power is stored in the memory 51 in the form of a map or function that takes as inputs the outside air temperature, the temperature of the FC stack 10, and the state of the fuel cell auxiliary equipment. The desired output includes the estimated power consumption of some electrical devices. For example, the estimated power consumption is defined as follows: When the outside air temperature is low, the electric heater 83 of the passenger compartment heater 80 is likely to be used. When the outside air temperature is high, passenger compartment cooling is likely to be used.The estimated power consumption is estimated in advance as the estimated power consumption of the electrical device(s) expected to operate according to the outside air temperature. The estimated power consumption may include the estimated power consumption of the fuel cell auxiliary equipment. The controller 50 determines the desired output based on the map or relational expression stored in the memory 51, according to the current outside air temperature, the temperature of the FC stack 10, etc.

[0045] In the battery protection process of step S6, the desired output is corrected when the power currently flowing into the sub-battery 64 is greater than a predetermined allowable range. The battery protection process will be described later. Here, it is assumed that correction of the desired output is not necessary.

[0046] The controller 50 controls specific load devices. The controller 50 controls the load devices so that the power consumption of the load devices equals the power difference between the requested power and the desired output (step S7). The load devices are predetermined electrical devices and are typically electrical devices that are not involved in the operation of the FC stack 10. For example, the load devices are the pump 82 and the electric heater 83 of the passenger compartment heater 80, the radio 65, etc.

[0047] Specifically, the controller 50 informs the load devices of the desired power consumption (i.e., the difference between the desired power and the required power). The load devices informed of the desired power consumption control their own operation so that their power consumption becomes equal to the desired power consumption. In other words, the load devices control their own operation so that the difference between the desired output and the required output becomes zero.

[0048] The fuel cell auxiliary equipment is sometimes included in the load devices. If the difference between the required power and the desired power is small, the fuel cell auxiliary equipment can be included in the load devices as long as it does not affect the power generation of the FC stack 10.

[0049] Next, the controller 50 determines a desired heat generation amount of the FC stack 10 per unit time (step S8). The desired heat generation amount is the amount of heat required for rapid warm-up. The desired heat generation amount per unit time is expressed in watts. The desired heat generation amount is determined depending on the outside air temperature, the temperature of the FC stack 10, and the state of the fuel cell vehicle 100. The desired heat generation amount is stored in the memory 51 in advance as a function (or map) that takes the outside air temperature, the temperature of the FC stack 10, and the state of the fuel cell vehicle 100 as inputs. The controller 50 determines the desired heat generation amount through the map or function stored in the memory 51 according to the current state of the fuel cell system 2.

[0050] As is widely known in the field of FC stacks, a suitable amount of oxygen has been determined for the amount of hydrogen. If the amount of oxygen is smaller than the amount of hydrogen, the power generation efficiency decreases. Power generation loss occurs as heat. If the amount of oxygen is intentionally reduced relative to the amount of hydrogen, the power generation loss increases. The FC stack 10 generates heat due to the energy loss, and the temperature of the FC stack 10 rises. The ratio of the amount of oxygen to the amount of hydrogen is called the stoichiometric ratio.

[0051] The controller 50 determines the stoichiometric ratio and operating point based on the desired output and the desired heat generation amount. The controller 50 then controls the FC stack 10 to achieve the determined stoichiometric ratio and operating point (step S9). In other words, the controller 50 controls the fuel cell auxiliary equipment to ensure that the FC stack 10 achieves the determined stoichiometric ratio and the desired output.

[0052] An example of calculating the operating point (the desired current and voltage of the FC stack 10) will now be described. As described above for the FC stack, a suitable amount of oxygen has been determined for the amount of hydrogen. The voltage when a suitable amount of oxygen is supplied for the amount of hydrogen is called the theoretical electromotive voltage. The required output is determined in step S4, and the desired heat generation amount (the desired heat generation amount per unit time) is determined in step S8. Here, the energy that should be output by the FC stack 10 is equal to (required output + desired heat generation amount). Assuming that a suitable amount of oxygen is supplied, the output current (the desired current) of the FC stack 10 is obtained by the following relational expression. Desired current = (required output + desired heat generation amount) / theoretical electromotive voltage

[0053] The stoichiometric ratio is determined so that the desired amount of heat generation is released as thermal energy. The power output of the FC stack 10 is therefore only the required output. Since required output = required current × desired voltage, the desired voltage is obtained by the following relational expression. Desired voltage = theoretical electronic voltage × required output / (required output + desired heat generation amount)

[0054] The controller repeats the above process until the temperature of the FC stack 10 reaches a predetermined temperature threshold (steps S10: NO, S2). When the temperature of the FC stack 10 reaches the temperature threshold, the controller 50 terminates the process (step S10: YES).

[0055] The advantages of the process of Fig. 2. The controller 50 determines the stoichiometric ratio and operating point of the FC stack 10 based on the predetermined desired output and the desired heat generation amount, which are determined by the outside air temperature and the temperature of the FC stack 10. The controller 50 then controls the fuel cell auxiliary equipment to achieve the determined stoichiometric ratio and operating point. The desired output is determined in advance to change slowly over time. The operating point will therefore change slowly, not suddenly.

[0056] The power consumption of the fuel cell auxiliary equipment used to operate the FC stack 10 changes from moment to moment. The controller 50 determines the operating point not in response to the power consumption (the required output of the FC stack 10), but according to the desired output. The FC stack 10 outputs a power corresponding to the desired output. There is a difference between the actual output (the desired output) of the FC stack 10 and the required output. The controller 50 controls the load devices to eliminate the difference.

[0057] Since the controller 50 of the fuel cell system 2 of the embodiment controls the output of the FC stack 10 so that the output of the FC stack 10 follows the desired output, the operating point will not change suddenly. Sudden changes in the operating point are thus reduced. The power consumption of the fuel cell auxiliary equipment (the required output) changes from moment to moment according to the state of the fuel cell auxiliary equipment and the temperature (the temperature of the FC stack or the outside air temperature). The difference between the actual output (the desired output) and the required output is adjusted by the power consumption of the load devices. The fuel cell system 2 of the embodiment can reduce sudden changes in the operating point while achieving the required output that changes from moment to moment.

[0058] The desired output includes the estimated power consumption of the load devices. If the requested power is greater than planned, the load devices are controlled so that the load device load consumption becomes less than the estimated power consumption. Since the actual power consumption of the load devices becomes less than the estimated load device load consumption included in the desired output, a larger amount of power is supplied to the fuel cell auxiliary equipment from the FC stack 10.

[0059] The battery protection process in step S6 of Fig. 2. The input and output power of the sub-battery 64 has an allowable range (an allowable input and output range). When the input and output power of the sub-battery 64 is outside the allowable input and output range, the controller 50 corrects the desired output of the FC stack 10 so that the actual input and output power of the sub-battery 64 returns to a value within the allowable input and output range. When the output of the sub-battery 64 is greater than the allowable input and output range, the controller 50 increases the desired output. By increasing the desired output, the actual output of the FC stack 10 increases and the output of the sub-battery 64 decreases.

[0060] Conversely, if the charging power supplied to the sub-battery 64 is greater than the allowable input and output range, the controller 50 reduces the desired output. By reducing the desired output, the actual output of the FC stack 10 and the charging power supplied to the sub-battery 64 decrease.

[0061] The controller 50 corrects the desired output when the input and output power of the auxiliary battery 64 has been greater than the upper limit of the allowable input and output range or less than the lower limit of the allowable input and output range by more than a predetermined amount for a predetermined period of time. After the main switch of the fuel cell vehicle 100 is turned on, the input and output power of the auxiliary battery 64 may fall outside the allowable input and output range several times. The predetermined period of time and the predetermined amount when the input and output power of the auxiliary battery 64 falls outside the allowable input and output range for the first time are referred to as the first predetermined period of time and the first predetermined amount.The predetermined time period and the predetermined amount when the input and output power of the sub-battery 64 falls outside the allowable input and output range for the second time and subsequent times are referred to as the second predetermined time period and the second predetermined amount. The second predetermined time period is set to a value shorter than the first predetermined time period, and the second predetermined amount is set to a value smaller than the first predetermined amount.

[0062] The points to be noted regarding the technique described in the embodiment will now be described. The auxiliary battery 64 is an example of the battery connected to the output terminal of the FC stack 10 and which supplies electrical power to the fuel cell auxiliary equipment. Typical examples of the load devices are electrical devices that do not participate in the operation of the FC stack 10, such as the radio 65. If the difference between the required power and the desired power is small, the fuel cell auxiliary equipment can be the load devices.

[0063] The process of Fig. 2 is executed when rapid warm-up (a rapid warm-up process of the FC stack 10) is required. The fuel cell vehicle 100 is stopped during the execution of this process. The inverter 101 and the electric motor 102 are therefore switched off. Therefore, the desired output is precisely determined in advance. When the process of Fig. 2 is executed while the fuel cell vehicle 100 is running, the desired output may be determined in advance as a function including the outside air temperature, the temperature of the FC stack, as well as the accelerator operation amount and the vehicle speed.

[0064] If rapid warm-up is not required, steps S8 and S10 of Fig. 2 is omitted. In this case, the stoichiometric ratio is determined in step S9 such that an optimal amount of oxygen is supplied for the amount of hydrogen to be supplied.

[0065] While specific examples of the invention have been described in detail above, these examples are merely illustrative and are not intended to limit the scope of the claims. The technique described in the claims encompasses various modifications and variations of the above examples.

Claims

[1] Fuel cell system (2) comprising: a fuel cell stack (10); Fuel cell auxiliary equipment used to operate the fuel cell stack (10); a battery (64) connected to an output terminal of the fuel cell stack (10); a load device connected to the output terminal of the fuel cell stack (10); and a controller (50) configured to control the fuel cell auxiliary equipment and the load device, wherein the controller (50) is configured to predicts the auxiliary equipment power consumption, wherein the auxiliary equipment power consumption is an amount of electrical power consumed by the fuel cell auxiliary equipment for operating the fuel cell stack (10), an estimated input and output power of the battery (64) is determined, determines a required output based on the predicted auxiliary equipment power consumption and the estimated input and output power, wherein the required output is a required output for the fuel cell stack (10), and determines an operating point of the fuel cell stack (10) based on the desired output, characterized by , that the controller (50) has stored a desired output of the fuel cell stack (10) that includes an estimated power consumption of the fuel cell auxiliary equipment determined based on an outside air temperature and a predetermined estimated power consumption of the load device, and the load device is configured to control its operation in such a way that a difference between the demanded output and the desired output becomes zero. [2] The fuel cell system (2) according to claim 1, wherein, when an actual input and output power of the battery (64) is greater than an allowable input and output range of the battery (64), the controller (50) corrects the desired output so as to cause the actual input and output power to return to a value within the allowable input and output range. [3] The fuel cell system (2) according to claim 1 or 2, wherein the estimated input and output power is determined based on a state of charge of the battery (64). [4] The fuel cell system (2) according to any one of claims 1 to 3, wherein the load device is an electrical device that does not affect the operation of the fuel cell stack (10). [5] The fuel cell system (2) according to any one of claims 1 to 4, wherein the controller (50) determines a desired heat generation amount of the fuel cell stack (10) per unit time based on the outside air temperature and a temperature of the fuel cell stack (10), and determines the operating point and a stoichiometric ratio of hydrogen and oxygen supplied to the fuel cell stack (10) based on the desired heat generation amount and the desired output.

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