Fuel cell system and method for controlling a fuel cell system

Abstract

Fuel cell system, comprising: a fuel cell (40) comprising an anode, a cathode and an electrolyte membrane; an oxidation gas channel (69) for supplying oxidation gas to the cathode and removing oxidation gas from the cathode; an oxidation gas supply and discharge system (60) with a compressor (604) provided on an upstream side of the fuel cell (40) in the oxidation gas channel (69) and a pressure control valve (614) provided on an downstream side of the fuel cell (40) in the oxidation gas channel (69); a coolant circulation system (80) designed to circulate a coolant that regulates the temperature of the fuel cell (40); an atmospheric pressure sensor (61) that measures atmospheric pressure; and a control unit (102) designed to control the operation of the fuel cell system using the atmospheric pressure measured by the atmospheric pressure sensor (61), wherein, when the measured atmospheric pressure falls below a predetermined atmospheric reference pressure, the control unit (102) is designed to perform temperature and pressure reduction control to actuate the coolant circulation system (80) to lower the temperature of the fuel cell (40) while simultaneously actuating the pressure control valve (614) to reduce back pressure of the compressor (604) on the cathode side, and wherein the control unit (102) is designed to Determine whether an operating point after reduction is located outside a pumping zone in which pumping occurs in the compressor (604), wherein the operating point after reduction is an operating point defined by a flow rate and pressure ratio of the compressor (604) after the measured atmospheric pressure has dropped to a value below the atmospheric reference pressure. Changing the operating point to the operating point after setback without executing the temperature and pressure reducing control, if the operating point after setback is located outside the pumping zone, and If the operating point after lowering is located within the pumping zone, implement the temperature and pressure reducing control in such a way that the operating point lies outside the pumping zone.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present disclosure relates to methods for fuel cell systems and, more particularly, to a fuel cell system and a method for controlling the fuel cell system. 2. Description of related technology

[0002] A method for reducing the energy consumption of a compressor pumping out oxidizing gas in a fuel cell vehicle is previously known. In this method, when the atmospheric pressure is lower than a reference pressure value, the inlet pressure of a cathode of a fuel cell is lowered (Japanese Patent Application Publication No. 2005-158647 (JP 2005-158647 A)). JP 2006-099988 A describes a fuel cell system comprising a fuel cell, an oxidizing gas channel for supplying oxidizing gas to the cathode and discharging oxidizing gas from the cathode, a compressor arranged in the oxidizing channel on an upstream side of the fuel cell, and a pressure regulating valve provided in the oxidizing channel on a downstream side of the fuel cell. A coolant circulation system circulates a coolant that regulates the temperature of the fuel cell, and a control unit is configured to regulate the operation of the fuel cell system.If the measured atmospheric pressure falls below a predetermined atmospheric reference pressure, the control unit implements pressure-reducing control by controlling the pressure control valve. DE 10 2016 213 108 A1 and DE 10 2014 107 096 A1 describe other relevant fuel cell systems. SUMMARY OF THE INVENTION

[0003] When the cathode inlet pressure is lowered, the amount of water vapor discharged from the fuel cell along with the cathode exhaust gas increases. As the amount of water vapor discharged from the fuel cell increases, a humidified fuel cell state may deviate significantly from the ideal humidified state where no drying occurs. In this case, if a humidifier is provided to humidify the interior of the fuel cell to maintain the ideal humidified state, the cost of the fuel cell system increases. The object of the present invention is to reduce the possibility of drying out of the electrolyte membrane and, at the same time, to reduce the possibility of increasing compressor energy consumption without installing a humidifier. (1) A first aspect of the present disclosure relates to a fuel cell system comprising a fuel cell, an oxidizing gas channel, an oxidizing gas supply and discharge system, a coolant circulation system, an atmospheric pressure sensor, and a control unit. The fuel cell has an anode, a cathode, and an electrolyte membrane. The oxidizing gas channel serves to supply oxidizing gas to the cathode and to discharge oxidizing gas from the cathode. The oxidizing gas supply and discharge system has a compressor arranged upstream of the fuel cell in the oxidizing gas channel and a pressure regulating valve arranged downstream of the fuel cell in the oxidizing gas channel. The coolant circulation system circulates a coolant that regulates the temperature of the fuel cell. The atmospheric pressure sensor measures an atmospheric pressure.The control unit regulates the operation of the fuel cell system using the atmospheric pressure measured by the atmospheric pressure sensor. When the measured atmospheric pressure falls below a predetermined atmospheric reference pressure, the control unit executes temperature and pressure-reducing control, in which the coolant circulation system is controlled to lower the temperature of the fuel cell, while the pressure control valve is controlled to reduce a backpressure of the compressor on the cathode side. According to this aspect, a potential increase in the compressor's energy consumption can be reduced by lowering the compressor's discharge pressure when the measured atmospheric pressure falls below the atmospheric reference pressure. According to this aspect, the temperature of the fuel cell is lowered when the measured atmospheric pressure falls below the atmospheric reference pressure.This reduces the possibility of the electrolyte membrane drying out when the discharge pressure is reduced. The above aspect can thus reduce the possibility of the electrolyte membrane drying out and simultaneously reduce the possibility of increased compressor energy consumption without the need to install a humidifier. (2) The control unit is designed to determine whether an operating point after reduction is located outside a surge zone in which surge occurs in the compressor, the operating point after reduction being an operating point defined by a discharge rate and a pressure ratio of the compressor after the measured atmospheric pressure has dropped to a value below the atmospheric reference pressure, to change the operating point to the operating point after reduction without performing the temperature and pressure reducing control if the operating point after reduction is located outside the surge zone in which surge occurs in the compressor, the operating point after reduction being an operating point defined by a discharge rate of the compressor and a pressure ratio after the measured atmospheric pressure has fallen below the atmospheric reference pressure,and for executing temperature and pressure reduction control such that the operating point lies outside the pumping zone when the operating point after reduction is within the pumping zone. If the operating point after reduction is within the pumping zone, the compressor can be operated with an operating point outside the pumping zone by executing temperature and pressure reduction control. According to this aspect, temperature and pressure reduction control is not executed when the operating point after reduction is outside the pumping zone. Thus, the fuel cell can generate electrical energy under the temperature condition that provides sufficient power generation efficiency of the fuel cell without executing temperature control in the temperature and pressure reduction control. (3) The fuel cell system may further comprise a storage unit configured to store a map relating a demand current value of the fuel cell, the measured atmospheric pressure, and a target temperature of the fuel cell. The target temperature of the fuel cell may be set to a temperature that does not cause the electrolyte membrane to dry out when the discharge pressure of the compressor is reduced as the measured atmospheric pressure decreases. In the temperature and pressure reducing control, the control unit may control the coolant circulation system to regulate the temperature of the fuel cell to the target temperature defined by the demand current value and the measured atmospheric pressure with the aid of the map.In this embodiment, the control unit can carry out the temperature and pressure reducing control with the help of the characteristic map, which can prevent drying out in the electrolyte membrane when the discharge pressure of the compressor is reduced. (4) A second aspect of the present invention relates to a method for controlling a fuel cell system. The fuel cell system comprises a fuel cell, an oxidizing gas channel, an oxidizing gas supply and discharge system, a coolant circulation system, and an atmospheric pressure sensor. The fuel cell system has an anode, a cathode, and an electrolyte membrane. The oxidizing gas channel serves to supply oxidizing gas to the cathode and to discharge oxidizing gas from the cathode. The oxidizing gas supply and discharge system has a compressor arranged upstream of the fuel cell in the oxidizing gas channel and a pressure control valve arranged downstream of the fuel cell in the oxidizing gas channel. The coolant circulation system circulates a coolant that regulates the temperature of the fuel cell. The atmospheric pressure sensor measures an atmospheric pressure. The control method comprises,When the atmospheric pressure measured by the atmospheric pressure sensor falls below a predetermined atmospheric reference pressure, executing temperature and pressure-reducing control, in which the coolant circulation system is controlled to reduce the temperature of the fuel cell while the pressure control valve is controlled to reduce a backpressure of the compressor on the cathode side; determining whether a post-reduction operating point is outside a surge zone in which surge occurs in the compressor, the post-reduction operating point being an operating point defined by a discharge rate and a pressure ratio of the compressor after the measured atmospheric pressure has dropped to a value below the atmospheric reference pressure; changing the operating point to the post-reduction operating point without executing temperature and pressure-reducing control;if the operating point after reduction is outside the pumping zone, and, if the operating point after reduction is within the pumping zone, the execution of the temperature and pressure reducing control in such a way that the operating point is outside the pumping zone.

[0004] The present disclosure may be implemented in various other aspects besides the aspects disclosed above. For example, the present disclosure may be implemented in aspects such as a vehicle with a built-in fuel cell system. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] In the following, features, advantages and technical and industrial significance of exemplary embodiments of the invention are described with reference to the accompanying drawings in which like reference numerals designate like elements, and in which: Fig. 1 is an explanatory view showing the configuration of a fuel cell system as a first embodiment of the present disclosure; Fig. 2 is a schematic diagram of an electrical configuration of the fuel cell system; Fig. 3 shows a relationship between the temperature of the fuel cell and the amount of water flowing out of the fuel cell; Fig. 4 is an explanatory view of a temperature map; Fig. 5 shows a drying map; Fig. Figure 6 shows a compressor map illustrating the performance characteristics of a compressor; Fig. 7 is a first flowchart of a control executed by a control unit; Fig. Fig. 8 is a second flowchart of a control executed by the control unit; and Fig. 9 is a first flowchart of a second embodiment executed by the control unit. DETAILED DESCRIPTION OF EMBODIMENTS A. First Embodiment

[0006] Fig. 1 is an explanatory view illustrating the configuration of a fuel cell system 20 as a first embodiment of the present disclosure. The fuel cell system 20 is mounted on a fuel cell vehicle 200 as one aspect of a moving object. The fuel cell system 20 outputs electric power in response to a driver's request, which power is mainly used as the driving force of the fuel cell vehicle 200. The fuel cell system 20 includes a fuel cell 40, a fuel gas supply and discharge system 50, an oxidizing gas supply and discharge system 60, a coolant circulation system 80, and a controller 100.

[0007] The control unit 100 includes a control unit 102 and a storage unit 104. The control unit 102 controls the operation of the fuel cell system 20 by executing various programs stored in the storage unit 104. For example, the control unit 102 controls the operation of the fuel cell system 20 using an atmospheric pressure measured by the atmospheric pressure sensor 61, which will be described later. The storage unit 104 stores, in addition to the various programs, a temperature map 106, a compressor map 108, and a dry-out map 109. The temperature map 106 is used to control the operation of the fuel cell system 20 according to the atmospheric pressure values ​​(measured atmospheric pressure). The compressor map 108 represents performance characteristics of the compressor 604.The dry-out map 109 shows a relationship between the temperature of the fuel cell 40 and the air pressure of the cathode, which can prevent the dry-out of an electrolyte membrane.

[0008] The fuel cell 40 is a polymer electrolyte fuel cell that generates electrical energy through an electrochemical reaction of oxygen and hydrogen when supplied with oxidizing gas and fuel gas as reactant gases. In the present embodiment, the oxidizing gas is air, and the fuel gas is hydrogen gas. The fuel cell 40 has a stacked structure in which a plurality of unit cells 41 are stacked. Each of the unit cells 41 is a power generation element that can individually generate electrical energy. The unit cells 41 each include a membrane-electrode assembly and two separators that hold the membrane-electrode assembly between them. The membrane-electrode assembly includes an electrolyte membrane, an anode disposed on one surface of the electrolyte membrane, and a cathode disposed on the other surface of the electrolyte membrane.The electrolyte membrane is a solid polymer thin film that exhibits high proton conductivity in a wet state, that is, the state in which the electrolyte membrane contains moisture. A manifold for reactant gas is provided in a peripheral end portion of each unit cell 41 (not shown). The manifold extends in the stacking direction in each of the unit cells 41 and is branched and connected to a power generation section in each of the unit cells 41. The unit cells 41 are fixed in the stacked state while being positioned between first and second end plates 43, 44.

[0009] The fuel gas supply and discharge system 50 has a fuel gas supply function, a fuel gas discharge function, and a fuel gas circulation function. The fuel gas supply function supplies fuel gas to the anode of the fuel cell 40. The fuel gas discharge function discharges the fuel gas discharged from the anode of the fuel cell 40 (also referred to as "fuel off-gas") to the outside. The fuel gas circulation function circulates fuel gas within the fuel cell system 20.

[0010] The fuel gas supply and discharge system 50 includes a fuel tank 502, a fuel gas supply channel 51 as a pipeline, a pressure reducing valve 52, an on-off valve 56, and a pressure sensor 55 on the upstream side of the fuel cell 40. The fuel gas supply channel 51 is a pipeline for supplying hydrogen as a fuel gas to the fuel cell 40 (to the anode, to be precise). The fuel tank 502 is filled with high-pressure hydrogen, which is to be supplied to the fuel cell 40. The fuel gas supply channel 51 is connected to the fuel tank 502 at the upstream end and to the fuel cell 40 at the downstream end. The on-off valve 56 is provided in the center of the fuel gas supply channel 51 and opens and closes the fuel gas supply channel 51 in response to a command from the control unit 102. The pressure reducing valve 52 is provided downstream of the on-off valve 56 in the fuel gas supply channel 51.The pressure reducing valve 52 regulates the pressure of the fuel gas in the fuel gas supply channel 51 when an opening degree of the pressure reducing valve 52 is controlled in response to a command from the control unit 102. The pressure sensor 55 measures the pressure of the fuel gas on the downstream side of a section in the fuel gas supply channel 51 connected to the fuel gas circulation channel 54 described later. The measured pressure is sent to the control unit 102.

[0011] The fuel gas supply and discharge system 50 further includes a fuel gas discharge passage 59 as a conduit, a fuel gas circulation passage 54 as a conduit, a circulation pump 53, and an exhaust valve 58 downstream of the fuel cell 40. The fuel gas discharge passage 59 is a conduit for discharging fuel gas from the fuel cell 40 (more precisely, the anode). The exhaust valve 58 is provided in the fuel gas discharge passage 59 and opens and closes the fuel gas discharge passage 59 in response to a command from the control unit 102. The control unit 102 normally maintains the exhaust valve 58 in a closed state. At a predetermined specific discharge timing or at a discharge timing of the inactive gas contained in the fuel off-gas, the control unit 102 switches the exhaust valve 58 to an open state.

[0012] The fuel gas circulation channel 54 is a conduit for returning the fuel gas discharged from the fuel cell 40 to the fuel gas supply channel 51. The fuel gas circulation channel 54 is connected at the upstream end to an upstream portion of the outlet valve 58 in the fuel gas discharge channel 59. The fuel gas circulation channel 54 is connected at the downstream end to a downstream portion of the pressure reducing valve 52 in the fuel gas supply channel 51. The operation of the circulation pump 53 is controlled in response to a command from the control unit 102. When the circulation pump 53 is operated, the fuel gas in the fuel gas circulation channel 54 is introduced into the fuel gas supply channel 51.

[0013] The oxidizing gas supply and discharge system 60 includes an oxidizing gas supply function that supplies oxidizing gas to the fuel cell 40, an oxidizing gas discharge function that discharges the oxidizing gas discharged from the fuel cell 40 (also referred to as "oxidizing off-gas") to the outside, and a bypass function that directs the supplied oxidizing gas past the fuel cell 40 without passing through the fuel cell 40. The oxidizing gas supply and discharge system 60 includes an oxidizing gas channel 69 for supplying oxidizing gas to the cathode and for discharging the oxidizing gas discharged from the cathode.

[0014] The oxidizing gas supply and discharge system 60 includes an oxidizing gas supply channel 66, an air filter 602, a compressor 604, a motor 605, an intercooler 606, an atmospheric pressure sensor 61, an ambient temperature sensor 62, an air mass meter 64, a gas inlet temperature sensor 63, a pressure-side pressure sensor 65, and an inlet valve 612.

[0015] The oxidizing gas supply channel 66 is a conduit upstream of the fuel cell 40. The air filter 602 is disposed upstream of the compressor 604 in the oxidizing gas supply channel 66 to remove impurities from the air supplied to the fuel cell 40. The compressor 604 is disposed upstream of the fuel cell 40 in the oxidizing gas supply channel 66 to supply compressed air to the cathode in response to a command from the control unit 102. The compressor 604 is a centrifugal turbocompressor driven by the motor 605 and operated in response to a command from the control unit 102. The compressor 604 draws in atmospheric air, pressurizes the air by rotating an impeller provided in the compressor 604, and discharges the pressurized air to the discharge side. The intercooler 606 is arranged downstream of the compressor 604 in the oxidation gas supply channel 66.The intercooler 606 cools the air compressed and thereby heated by the compressor 604. The inlet valve 612 is a motor valve for regulating a flow resistance of the oxidizing gas supply channel 66. In the present embodiment, when the compressor 604 is operated to cause electrical power generation of the fuel cell 40, the opening degree of the inlet valve 612 is set to 100%. When the compressor 604 is shut down to stop electrical power generation of the fuel cell 40, the opening degree of the inlet valve 612 is set to 0%.

[0016] The atmospheric pressure sensor 61 measures the atmospheric pressure. The atmospheric pressure sensor 61 is installed upstream of the air filter 602 in the oxidizing gas supply channel 66. The ambient temperature sensor 62 measures the temperature of the air sucked into the compressor 604 as oxidizing gas. The ambient temperature sensor 62 is installed upstream of the compressor 604 in the oxidizing gas supply channel 66. The installation locations of the atmospheric pressure sensor 61 and the ambient temperature sensor 62 are not limited to the disclosed positions. The sensors can be positioned arbitrarily as long as the atmospheric pressure and the ambient temperature can be measured. The air mass meter 64 measures the flow rate of the oxidizing gas sucked into the compressor 604. The air mass meter 64 is installed upstream of the compressor 604 in the oxidizing gas supply channel 66.The gas inlet temperature sensor 63 measures the temperature of the air supplied as oxidizing gas by the compressor 604. The pressure-side pressure sensor 65 measures the pressure of the air supplied as oxidizing gas by the compressor 604. The measured value of the pressure-side pressure sensor 65 is essentially identical to the pressure in the cathode of the fuel cell 40. The gas inlet temperature sensor 63 and the pressure-side pressure sensor 65 are located downstream of the compressor 604 in the oxidizing gas supply channel 66. The measured values ​​recorded by the various sensors 61, 62, 63, 64, and 65 are sent to the control unit 102.

[0017] The oxidizing gas supply and discharge system 60 further comprises a bypass channel 72, a flow divider valve 613 arranged on the bypass channel 72, an oxidizing gas discharge channel 68, and a pressure control valve 614 arranged in the oxidizing gas discharge channel 68 and positioned downstream of the fuel cell 40.

[0018] The bypass passage 72 is a conduit connected at one end to the oxidizing gas supply passage 66 and at the other end to the oxidizing gas discharge passage 68. The bypass passage 72 serves to discharge the air supplied by the compressor 604 past the fuel cell 40 to the outside. The flow divider valve 613 is a motor valve whose opening degree can be changed in response to a command from the control unit 102. By changing the opening degree of the flow divider valve 613, the flow resistance of the bypass passage 72 is changed, and the flow rate of air flowing from the oxidizing gas supply passage 66 into the bypass passage 72 is regulated.

[0019] The oxidizing gas discharge channel 68 is a conduit for discharging air as oxidizing exhaust gas from the cathode of the fuel cell 40. The pressure regulating valve 614 is a motor valve whose opening degree can be changed in response to a command from the control unit 102. By changing the opening degree of the pressure regulating valve 614, the flow resistance of the oxidizing gas discharge channel 68 is changed, and a back pressure of the cathode-side channel of the fuel cell 40 is regulated.

[0020] The coolant circulation system 80 includes a coolant circulation channel 81, a water pump 85, a radiator 82, a radiator fan 88, a three-way valve 87, and a temperature sensor 86. The coolant circulation system 80 regulates the temperature of the fuel cell 40 using water as the coolant. The coolant circulation channel 81 includes a coolant supply channel 81a, a coolant discharge channel 81b, a radiator channel 81c, and a coolant bypass channel 81d.

[0021] The coolant supply channel 81a is a pipe for supplying a coolant to the fuel cell 40. The water pump 85 pumps the coolant of the coolant supply channel 81a to the fuel cell 40 in response to a command from the control unit 102. The coolant discharge channel 81b is a pipe for discharging the coolant from the fuel cell 40. The temperature sensor 86 is provided in the coolant discharge channel 81b to measure the temperature of the coolant discharged from the fuel cell 40. The measured value detected by the temperature sensor 86 is sent to the control unit 102. Here, the temperature measured by the temperature sensor 86 is substantially equal to the temperature inside the fuel cell 40. Therefore, in the present embodiment, control is performed assuming that the temperature measured by the temperature sensor 86 is the temperature of the fuel cell 40.

[0022] The radiator duct 81c is a pipe connecting the coolant supply duct 81a and the coolant discharge duct 81b. The radiator 82 is arranged in the radiator duct 81c. The radiator 82 is provided with a radiator fan 88. The radiator fan 88 blows air to the radiator 82 in response to a command from the control unit 102 and regulates the level of heat radiation emitted by the radiator 82.

[0023] The coolant bypass passage 81d is a conduit for guiding the coolant from the coolant discharge passage 81b to the coolant supply passage 81a without passing through the radiator 82. The three-way valve 87 is arranged in a connecting portion between the coolant bypass passage 81d and the coolant discharge passage 81b. The three-way valve 87 regulates the flow rate of the coolant flowing from the coolant discharge passage 81b to the radiator passage 81c and the flow rate of the coolant flowing from the coolant discharge passage 81b to the coolant bypass passage 81d in response to a command from the control unit 102.

[0024] Fig. 2 is a schematic diagram of an electrical configuration of the fuel cell system 20. The fuel cell system 20 includes a secondary battery 96, an FDC 95, a DC / AC converter 98, a BDC 97, a cell voltage sensor 91, and a current sensor 92.

[0025] The cell voltage sensor 91 is connected to all unit cells 41 in the fuel cell 40 to measure the cell voltages of all unit cells 41, respectively. The cell voltage sensor 91 sends the measurement results to the control unit 102. The current sensor 92 measures the value of an output current of the fuel cell 40 and sends the value to the control unit 102.

[0026] The FDC 95 and the BDC 97 are circuits configured as DC / DC converters. The FDC 95 regulates the output current of the fuel cell 40 based on a current command value sent from the control unit 102. The current command value is a value used as a target value for the output current of the fuel cell 40 and is set by the control unit 102. The control unit 102 generates the current command value by calculating a demand current value using a demanded electric power amount of the fuel cell 40. The control unit 102 determines the demanded electric power amount in response to, for example, the degree of operation of the accelerator pedal of the fuel cell vehicle 200.

[0027] The FDC 95 functions as an input voltage meter and impedance meter. Specifically, the FDC 95 measures the value of an input voltage and sends the value to the control unit 102. The FDC 95 measures the impedance of the fuel cell 40 using an AC impedance method. The impedance frequency used in the present embodiment includes high frequencies, specifically 100 Hz to 1 kHz. The FDC 95 amplifies the input voltage and supplies the voltage to the DC / AC converter 98.

[0028] The BDC 97 controls the charging and discharging of the secondary battery 96 in response to a command from the control unit 102. The BDC 97 measures a state of charge (SOC) (remaining capacity) of the secondary battery 96 and sends the charge level to the control unit 102. The secondary battery 96 is composed of a lithium-ion battery and functions as an auxiliary power supply. The secondary battery 96 supplies electrical energy to the fuel cell 40 and charges the electrical energy generated by the fuel cell 40.

[0029] The DC / AC converter 98 is connected to the fuel cell 40 and a load 250. The DC / AC converter 98 converts the direct current electrical power output by the fuel cell 40 and the secondary battery 96 into alternating current electrical power and supplies the alternating current electrical power to the load 250.

[0030] Renewable electrical energy generated in the load 250 is converted into direct current by the DC / AC converter 98 and used by the BDC 97 to charge the secondary battery 96. The control unit 102 calculates the output command value taking into account the state of charge of the secondary battery 96 and the load 250.

[0031] Fig. Figure 3 shows a relationship between the temperature of the fuel cell 40 and the amount of water flowing out of the fuel cell 40. A dot-dash curve represents a relationship when the inlet pressure of the air supplied to the cathode is 100 kPa, while a solid line curve represents a relationship when the inlet pressure of the air supplied to the cathode is 200 kPa. As the temperature of the fuel cell 40 increases, as shown in Fig. As shown in Figure 3, the amount of water (vapor) discharged from the fuel cell 40 increases exponentially along with the oxidation gas discharged from the cathode, regardless of the magnitude of the inlet pressure (discharge pressure of the compressor 604). As the inlet pressure (discharge pressure of the compressor 604) of the air supplied to the cathode increases, the amount of water discharged decreases, even if the temperature of the fuel cell remains the same.

[0032] Fig. 4 is an explanatory view of the temperature map 106. The temperature map 106 is a map that relates a target temperature of the fuel cell to an atmospheric pressure measured by the atmospheric pressure sensor 61 for each demand current value. Fig. Figure 4 shows a relationship between the setpoint temperature and the measured atmospheric pressure at a given demand current value. The temperature map 106 defines the relationship for each demand current value at which the setpoint temperature of the fuel cell decreases when the measured atmospheric pressure falls below a predetermined atmospheric reference pressure. If the temperature map 106 according to Fig. 4. For a given demand current value, if the measured atmospheric pressure is equal to the reference atmospheric pressure, the target temperature is "TEa." Conversely, if the measured atmospheric pressure is lower than the reference atmospheric pressure, as "PEb," the target temperature is lower than "TEa." For example, the temperature TEa is 60°C and the temperature TEb is 40°C. The reference atmospheric pressure is set to a standard atmospheric pressure in the present embodiment. In the temperature map 106, the target temperature of the fuel cell 40 is set to a constant value when the measured atmospheric pressure is equal to or greater than the reference atmospheric pressure.In the temperature map 106, the target temperature of the fuel cell 40 can be set to a temperature that does not cause the electrolyte membrane to dry out when the discharge pressure of the compressor map 108 is reduced with a reduction in the measured atmospheric pressure.

[0033] A method for generating the temperature map 106 defined by the measured atmospheric pressure and the target temperature of the fuel cell 40 will now be described. Fig. 5 shows the dry-out map 109. The dry-out map 109 shows a relationship between the temperature of the fuel cell 40 and the air pressure of the cathode, which can prevent the electrolyte membrane from drying out. Fig. The dryout map 109 shown in Figure 5 is determined experimentally. Dryout is the condition in which the electrolyte membrane has a low moisture content, which significantly impairs the power generation efficiency of the fuel cell 40. The occurrence of dryout can be detected, for example, when the impedance of the fuel cell 40 exceeds a predetermined threshold. The measured value of the temperature sensor 86 ( Fig. 1) is used as the temperature of the fuel cell 40. The air pressure in the vertical axis of Fig. 5 represents the air pressure in the cathode of the fuel cell 40. The air pressure is a measured value of the pressure-side pressure sensor 65 ( Fig. 1) is used. In Fig. 5, no drying occurs in an area above a reference line SL (dry-out prevention zone), while drying occurs in an area below the reference line SL (dry-out zone). The control unit 102 determines the discharge pressure in the dry-out prevention zone as the target discharge pressure using the dry-out map 109.

[0034] Fig. 6 shows the compressor map 108, which represents the performance characteristics of the compressor 604. In Fig. 6, a vertical axis represents a pressure ratio of the compressor 604, while a horizontal axis represents a discharge of the compressor 604. An operating point of the compressor 604 is defined by a combination of the pressure ratio and the discharge. A surge zone is a zone of operating points where surge occurs in the compressor. A surge line is a line indicating a boundary of the range of operating points not included in the surge zone. The pressure ratio is a ratio of a suction-side air pressure (suction pressure) to a discharge-side air pressure (discharge pressure) of the compressor 604. The control unit 102 calculates a target air discharge using the following formula expression (1). The discharge in the following formula expression (1) is also referred to as a corrected mass flow rate. Discharge rate = flow rate ⋅ (standard air pressure / suction air pressure) √ (suction air temperature / standard air temperature)

[0035] A flow rate (NL / min) is a mass flow of the air sucked in by the compressor 604. The mass flow is determined by the control unit 102 using a target value of the demand flow (target demand flow value) of the fuel cell 40. The control unit 102 determines the flow rate for the demand flow value, for example, by using the characteristic map that represents a relationship between the flow rate and the demand flow value. The characteristic map is stored, for example, in the storage unit 104. The intake air temperature is a measured value of the ambient temperature sensor 62 ( Fig. 1). The standard air temperature is the suction air temperature used as a reference, and the temperature is a predetermined value (for example, 25 °C). The suction air pressure is the pressure of the air actually sucked in by the compressor 604, and the pressure is a measured value of the atmospheric pressure sensor 61 ( Fig. 1). The standard air pressure is a reference pressure for the air sucked by the compressor 604, and the pressure is a predetermined value (for example, standard atmospheric pressure).

[0036] Consider the case that, as in Fig. 6, the control unit 102 operates the compressor 604 at an operating point A in an environment with standard atmospheric pressure, and then the fuel cell vehicle 200 moves uphill to higher altitudes. As the fuel cell vehicle 200 climbs, the measured atmospheric pressure drops below a reference atmospheric pressure. In this case, the operating point shifts from the operating point A to an operating point B (hereinafter also referred to as the after-slump operating point). That is, when attempting to achieve the same discharge pressure in the compressor 604 as at the operating point A, the pressure ratio increases as the atmospheric pressure decreases. Depending on the degree of increase in the pressure ratio, the operating point A may shift toward the after-slump operating point (i.e., operating point B), which is located in the surge zone.Here, under the condition that the atmospheric pressure is lower than the standard atmospheric pressure, it may be considered to shift the operating point from operating point A to an operating point D outside the surge zone in order to achieve the same discharge pressure as at operating point A, while avoiding the operation of compressor 604 at the operating point after setback (operating point B). However, if compressor 604 is operated at operating point D, the discharge rate increases to a value that exceeds the value at operating point A. This makes it necessary to use flow divider valve 613 (. Fig. 1) to direct the air corresponding to the increased flow rate to the bypass channel 72. This means that when the operating point of the compressor 604 is shifted from operating point A to operating point D, the displacement of the compressor 604 must be greater than the flow rate of air required by the fuel cell 40. This results in the possibility of a deterioration in the fuel efficiency of the fuel cell system 20 due to the increase in energy consumption by the compressor 604.

[0037] In the case where the compressor 604 is operated at an operating point outside the surge zone under the condition that the atmospheric pressure falls below the standard atmospheric pressure while maintaining the discharge rate of the compressor 604, the following control can be considered. That is, when an operating point shifts from the operating point A to the operating point after the reduction (operating point B) due to the reduction in atmospheric pressure, the control unit 102 increases the opening degree of the pressure control valve 614 ( Fig. 1) to reduce the discharge pressure, and thereby the compressor 604 operates at the operating point C located outside the pumping zone. However, since the amount of water flowing out of the fuel cell 40 increases as a result of the reduced discharge pressure, as shown in Fig. 3, there is a possibility of drying out of the electrolyte membrane.

[0038] In the present embodiment, the control unit 102 therefore determines the temperature of the fuel cell 40 and the discharge pressure of the compressor 604, whereby the discharge of air to the outside via the bypass channel 72 can be suppressed and, at the same time, drying of the electrolyte membrane can be prevented, even when the atmospheric pressure falls below the standard atmospheric pressure. In particular, for each atmospheric pressure value below the standard atmospheric pressure, using the Fig. 6, an operating point of the compressor 604 at which the discharge pressure of the compressor 604 is lower than the discharge pressure under atmospheric standard pressure conditions is determined as the adjustment operating point. With the help of the Fig. 5, the control unit 102 next sets a target temperature of the fuel cell 40 with the discharge pressure at each of the adjustment operating points, which does not cause the electrolyte membrane to dry out. Fig. The adjustment operating point line shown in Figure 6 is a line connecting the adjustment operating points, which is created when the atmospheric pressure is the atmospheric pressure PEb ( Fig. 4). A normal operating point line is a line connecting the operating points when the atmospheric pressure is equal to or greater than the standard atmospheric pressure.

[0039] Fig. 7 is a first flowchart of a control executed by the control unit 102. The routine of the first flowchart is repeatedly executed at fixed time intervals while a start switch of the fuel cell vehicle is in the on state.

[0040] First, the control unit 102 calculates a demand current value from the demanded electric power amount of the fuel cell 40 (step S10). The control unit 102 detects a measured atmospheric pressure from the atmospheric pressure sensor 61 (step S20).

[0041] Next, the control unit 102 determines a target temperature of the fuel cell 40 using the temperature map 106 ( Fig. 4) (step S30). The control unit 102 then determines with the dry-out map 109 ( Fig. 5) a target discharge pressure of the compressor 604, which corresponds to the target temperature of the fuel cell 40 (step S40). If, for example, the measured atmospheric pressure in the previous routine is an atmospheric reference pressure and the measured atmospheric pressure in the current routine decreases from the atmospheric reference pressure (step S20), the control unit 102 executes the following control in steps S30 and S40. First, as the measured atmospheric pressure decreases, the target temperature of the fuel cell 40 is determined using the temperature map 106 ( Fig. 4) is lowered (step S30). By lowering the target temperature of the fuel cell 40, the control unit 102 also lowers the target discharge pressure of the compressor 604 using the dry-out map 109 (step S40).

[0042] Fig. 8 is a second flowchart of a control executed by the control unit 102. After determining the target temperature and the target discharge pressure in steps S30, S40, the control unit 102 executes the second flowchart. That is, the control unit 102 controls the coolant circulation system 80 to control the temperature of the fuel cell 40 to the target temperature (step S100). For example, if the target temperature falls below the target temperature of the previous routine, the control unit 102 lowers the temperature of the fuel cell 40 using at least one control method of the coolant circulation system 80 selected from a first method and a second method as described below. First procedure

[0043] The flow rate of a coolant supplied to the fuel cell 40 is increased by the water pump 85. Second procedure

[0044] The three-way valve 87 is controlled to increase the flow rate of the coolant flowing through the radiator channel 81c.

[0045] Next, the control unit 102 controls the opening degree of the pressure control valve 614 ( Fig. 1) to regulate the discharge pressure to the target discharge pressure (step S110). For example, if the target discharge pressure falls below the target discharge pressure of the previous routine, the control unit 102 increases the opening degree of the pressure regulating valve 614 to lower the discharge pressure. As the opening degree of the pressure regulating valve 614 increases, the channel resistance of the oxidizing gas supply channel 66 decreases, and the discharge rate of the compressor 604 increases. Therefore, to keep the discharge rate constant, the control unit 102 reduces the speed of the compressor 604.As described above, when the measured atmospheric pressure falls below the reference atmospheric pressure, the control unit 102 performs temperature and pressure reducing control to control the coolant circulation system 80 to reduce the temperature of the fuel cell 40 and to control the pressure regulating valve 614 to reduce the discharge pressure of the compressor 604 (steps S30, S40, S100, S110).

[0046] When the measured atmospheric pressure falls below the predetermined atmospheric reference pressure, the control unit 102 according to the first embodiment controls the coolant circulation system 80 so that the temperature of the fuel cell 40 is reduced (steps S20, S40 of Fig. 7, step S100 of Fig. 8). If the measured atmospheric pressure falls below the predetermined atmospheric reference pressure, the control unit 102 controls the pressure control valve 614 so that the discharge pressure of the compressor 604 is reduced (step S50 of Fig. 7, step S110 of Fig. 8). Thus, when the measured atmospheric pressure drops below the reference atmospheric pressure, the discharge pressure of the compressor 604 is reduced. This reduces the probability that the operating point of the compressor 604 is within the surge zone without increasing the discharge rate. This suppresses an increase in the energy consumption of the compressor 604 caused by the increase in the discharge rate. Since the increase in the energy consumption of the compressor 604 can be suppressed, the amount of electrical energy supplied to the compressor 604 by the fuel cell 40 can be reduced. As a result, the increase in the amount of power generated by the fuel cell 40 can be suppressed, and thus the increase in the temperature of the fuel cell 40 can be suppressed.Furthermore, an increase in the displacement of the compressor 604 is not necessary when the measured atmospheric pressure falls below the atmospheric reference pressure. This reduces the possibility of a deterioration in the efficiency of the fuel cell system 20. That is, according to the fuel cell system 20, it is not necessary to discharge the air corresponding to an increased displacement from the bypass channel 72 to the outside.

[0047] According to the first embodiment, the control unit 102 controls the coolant circulation system 80 using the temperature map 106 to regulate the temperature of the fuel cell 40 to the target temperature determined based on the demand current value and the measured atmospheric pressure (step S30 of Fig. 7, step S100 of Fig. 8). The target temperature of the fuel cell 40 is set to the temperature that does not cause the electrolyte membrane to dry out. This makes it possible to prevent the electrolyte membrane from drying out when the discharge pressure of the compressor 604 is lowered. Accordingly, since it is not necessary to provide the fuel cell system 20 with a humidifier for humidifying the electrolyte membrane, a cost increase in the fuel cell system 20 can be suppressed. B. Second embodiment

[0048] In the first embodiment, when the measured atmospheric pressure falls below the reference atmospheric pressure, the control unit 102 uniformly lowers the temperature of the fuel cell 40 and lowers the discharge pressure of the compressor 604. However, the present disclosure is not limited to this. A second embodiment of the first flowchart executed by the control unit 102 will be described below. Fig. Fig. 9 is a first flowchart of a second embodiment executed by the control unit 102. The flowchart differs from the first flowchart ( Fig. 7) of the first embodiment in that steps S25 and S50 are newly provided. Since other steps are similar to the steps in the first flowchart of the first embodiment, these similar steps are denoted by corresponding reference numerals, and the description will be omitted. The routine of the first flowchart in the second embodiment is repeatedly executed at fixed time intervals while a start switch of the fuel cell vehicle 200 is in the on state, just as in the routine of the first flowchart of the first embodiment.

[0049] After step S20, the control unit 102 determines whether the operating point of the compressor map 108 is outside the surge zone due to the change in the measured atmospheric pressure (step S25). That is, in step S25, the control unit 102 determines whether the operating point shifts from outside the surge zone to inside the surge zone due to the change in the pressure ratio of the compressor 604 caused by the change in the suction pressure of the compressor 604. If it is determined in step S25 that the operating point is outside the surge zone, the control unit 102 determines the target temperature of the fuel cell 40 without executing the temperature and pressure reducing control (step S50). That is, in step S50, the target temperature that provides sufficient power generation efficiency of the fuel cell 40 can be determined without executing temperature control in the temperature and pressure reducing control.For example, the control unit 102 may maintain a current target temperature without lowering the temperature in step S50.

[0050] If it is determined that the operating point is not outside the pumping zone, ie if the operating point is in the pumping zone in step S25, the control unit 102 determines the target temperature of the fuel cell 40 using the temperature map 106 ( Fig. 4) (step S30). Upon determining that the operating point is not outside the pumping zone, the control unit 102 determines the target discharge pressure of the compressor 604 according to the target temperature of the fuel cell 40 with the aid of the dry-out map 109 ( Fig. 5) (Step S40).

[0051] For example, if the measured atmospheric pressure in the previous routine is a reference atmospheric pressure and the measured atmospheric pressure decreases from the reference atmospheric pressure of the current routine (step S20), the control unit 102 executes the following control in steps S25 and S50. First, the control unit 102 executes a determination of step S25 as described above. If the determination in step S25 results in "Yes," the control unit 102 determines the target temperature of the fuel cell 40 without executing the temperature and pressure-reducing control (step S50). If the determination in step S25 results in "No," the control unit 102 lowers the target temperature of the fuel cell 40 with the decrease in the measured atmospheric pressure using the temperature map 106 ( Fig. 4) (Step S30). As the target temperature of the fuel cell 40 decreases, the control unit 102 also decreases the target discharge pressure of the compressor 604 with reference to the dry-out map 109 (Step S40). In Step S40, the target discharge pressure is determined such that the operating point is outside the surge zone.

[0052] After executing the first flowchart in the second embodiment, the same process as in the second flowchart ( Fig. 8) of the first embodiment. In step S110 of the second embodiment, the discharge pressure of the compressor 604 is reduced to shift the operating point from the operating point A, for example, to the operating point C located outside the surge zone, as shown in Fig. 6. By determining the target temperature in step S50 in Fig. 9, the coolant circulation system 80 is controlled to regulate the temperature of the fuel cell 40 to the specified target temperature. At the same time, the compressor 604 is operated at the operating point where the suction pressure is equal to the measured atmospheric pressure while maintaining the discharge pressure.

[0053] The second embodiment achieves the same effect as the first embodiment because the second embodiment has the same configuration as the first embodiment. When the operating point after depression is within the surge zone, the compressor 604 according to the second embodiment can be operated at the operating point outside the surge zone by executing the temperature and pressure reducing control. According to the second embodiment, the temperature and pressure reducing control is not executed when the operating point after depression is outside the surge zone. Thus, the fuel cell 40 can be caused to generate electric power under the temperature condition that provides sufficient power generation efficiency of the fuel cell 40 without executing temperature control in the temperature and pressure reducing control. C. Further embodiments

[0054] According to each of the aforementioned embodiments, a centrifugal turbocompressor is used as compressor 604. However, the present disclosure is not limited thereto. Compressor 604 may, for example, be an axial turbocompressor or may be a volumetric compressor. In each of the embodiments, the atmospheric reference pressure is the standard atmospheric pressure. However, the atmospheric reference pressure may, in particular but not exclusively, be lower or higher than the standard atmospheric pressure. The standard atmospheric pressure may be an atmospheric pressure at the altitude at which the fuel cell vehicle 200 normally travels, for example. According to each of the embodiments, the fuel cell system 20 includes the temperature map 106, the compressor map 108, and the dry-out map 109 ( Fig.1). However, these maps 106, 108, 109 may be stored on external servers, and the control unit 100 may use the maps 106, 108, 109 stored on the external servers.

[0055] The present disclosure is not limited to the disclosed embodiments and may encompass various modified examples. For example, the above-mentioned embodiments have been described in detail for the sake of easier understanding of the present invention. However, the present invention is not necessarily limited to these embodiments with all the components described therein. In one or more embodiments, some of the components may be replaced with the components of other modifications, and the components of one or more embodiments may be added to the components of other modifications. Furthermore, it is possible to omit or replace some of the components of the respective embodiments and add other components thereto. The embodiments, modifications, and modified examples may also be combined.

Claims

[1] Fuel cell system, comprising: a fuel cell (40) having an anode, a cathode and an electrolyte membrane; an oxidizing gas channel (69) for supplying oxidizing gas to the cathode and removing oxidizing gas from the cathode; an oxidizing gas supply and discharge system (60) having a compressor (604) provided on an upstream side of the fuel cell (40) in the oxidizing gas channel (69) and a pressure control valve (614) provided on a downstream side of the fuel cell (40) in the oxidizing gas channel (69); a coolant circulation system (80) configured to circulate a coolant that regulates the temperature of the fuel cell (40); an atmospheric pressure sensor (61) that measures an atmospheric pressure; and a control unit (102) configured to control the operation of the fuel cell system using the atmospheric pressure measured by the atmospheric pressure sensor (61), wherein, when the measured atmospheric pressure falls below a predetermined atmospheric reference pressure, the control unit (102) is designed to carry out a temperature and pressure reducing control for controlling the coolant circulation system (80) to lower the temperature of the fuel cell (40) while simultaneously controlling the pressure control valve (614) to reduce a back pressure of the compressor (604) on the cathode side, and wherein the control unit (102) is designed to Determining whether a post-sink operating point is outside a surge zone in which surge occurs in the compressor (604), the post-sink operating point being an operating point defined by a discharge rate and a pressure ratio of the compressor (604) after the measured atmospheric pressure has dropped to a value below the atmospheric reference pressure, Changing the operating point to the operating point after reduction without executing the temperature and pressure reducing control if the operating point after reduction is outside the pumping zone, and If the operating point after reduction is within the pumping zone, carry out the temperature and pressure reducing control in such a way that the operating point is outside the pumping zone. [2] The fuel cell system according to claim 1, further comprising: a storage unit (104) configured to store a map relating a demand current value of the fuel cell (40), the measured atmospheric pressure, and a target temperature of the fuel cell (40), wherein the setpoint temperature of the fuel cell (40) is set to a temperature which does not cause the electrolyte membrane to dry out when the discharge pressure of the compressor (604) is reduced with a decrease in the measured atmospheric pressure, and in the temperature and pressure reducing control, the control unit (102) controls the coolant circulation system (80) so as to regulate the temperature of the fuel cell (40) by reference to the characteristic map to the target temperature defined by the demand current value and the measured atmospheric pressure. [3] A control method of a fuel cell system, the fuel cell system comprising: a fuel cell (40) having an anode, a cathode, and an electrolyte membrane, an oxidizing gas channel (69) for supplying oxidizing gas to the cathode and discharging oxidizing gas from the cathode, an oxidizing gas supply and discharge system (60) having a compressor (604) provided on an upstream side of the fuel cell (40) in the oxidizing gas channel (69) and a pressure regulating valve (614) provided on a downstream side of the fuel cell (40) in the oxidizing gas channel (69), a coolant circulation system (80) circulating a coolant that regulates a temperature of the fuel cell (40), and an atmospheric pressure sensor (61) measuring an atmospheric pressure, the control method comprising, when the atmospheric pressure measured by the atmospheric pressure sensor (61) falls below a predetermined atmospheric reference pressure: Carrying out a temperature and pressure reducing control for controlling the coolant circulation system (80) to reduce the temperature of the fuel cell (40) while simultaneously controlling the pressure control valve (614) to reduce a back pressure of the compressor (604) on the cathode side, Determining whether a post-sink operating point is outside a surge zone in which surge occurs in the compressor (604), the post-sink operating point being an operating point defined by a discharge rate and a pressure ratio of the compressor (604) after the measured atmospheric pressure has dropped to a value below the atmospheric reference pressure, Changing the operating point to the operating point after reduction without executing the temperature and pressure reducing control if the operating point after reduction is outside the pumping zone, and If the operating point after reduction is within the pumping zone, carry out the temperature and pressure reducing control in such a way that the operating point is outside the pumping zone.

Images