JP7276249B2 - Fuel cell system and fuel cell control method - Google Patents

Description

The present disclosure relates to a fuel cell system and a fuel cell control method.

It is known that in warm-up operation due to low-efficiency operation, hydrogen ions generated at the anode and transferred to the cathode receive electrons to generate pumping hydrogen. If the amount of pumping hydrogen generated increases, the concentration of hydrogen in the cathode offgas (hereinafter referred to as exhaust hydrogen concentration) may increase. Patent Document 1 discloses a method of estimating the amount of pumping hydrogen generated by correcting the theoretical amount of pumping hydrogen generated, which is derived from the operating current of the fuel cell and the number of cells, using a correction coefficient according to the voltage of the fuel cell. is disclosed.

WO2011/013226

However, there is room for improving the accuracy of estimation of the exhaust hydrogen concentration.

The present disclosure can be implemented as the following forms.

(1) According to one aspect of the present disclosure, a fuel cell system is provided. A fuel cell system includes a fuel cell in which cells are stacked, a voltage sensor that detects voltage in units of one or more cells, and a control unit that determines an operating point of the fuel cell and operates the fuel cell. a control unit that operates the fuel cell at a low-efficiency operating point that is lower in efficiency than a reference operating point during warm-up operation of the fuel cell, wherein the control unit controls, during the warm-up operation, the voltage A total number of the cells whose detection voltage of the sensor is equal to or lower than a predetermined first reference voltage is calculated, and the exhaust hydrogen concentration is calculated using the total number of cells. According to this aspect, the exhaust hydrogen concentration can be accurately estimated by using the total number of cells in which the cell voltage has decreased.
(2) The fuel system of the above aspect further includes a temperature sensor for detecting the temperature of the fuel cell, and a map in which a correction coefficient for the current temperature of the fuel cell is associated with each starting temperature of the fuel cell. and a storage device that stores a map in which the value of the correction coefficient increases as the temperature at startup is lower, wherein the control unit stores the temperature at startup acquired from the temperature sensor at startup, and uses the map. Then, the correction coefficient corresponding to the starting temperature and the current temperature obtained from the temperature sensor is acquired, and the exhaust hydrogen concentration is calculated using the value obtained by multiplying the total number of sheets by the correction coefficient. good. According to this aspect, the exhaust hydrogen concentration can be accurately estimated by using the correction coefficient corresponding to the starting temperature.
(3) In the fuel system of the above aspect, the control unit may execute hydrogen concentration reduction processing when the exhaust hydrogen concentration is higher than a predetermined reference concentration. According to this aspect, when the accurately estimated exhaust hydrogen concentration is higher than the reference concentration, the exhaust hydrogen concentration can be reduced.
(4) In the fuel system of the above aspect, the voltage sensor includes a first voltage sensor that detects the voltage of one of the cells and a second voltage sensor that detects the voltage of two of the cells, When the voltage detected by the first voltage sensor is equal to or less than the first reference voltage, the control unit counts the cell whose voltage is equal to or less than the first reference voltage as one, and the voltage detected by the second voltage sensor is counted as one. If the voltage is equal to or less than the first reference voltage, the number of cells equal to or less than the first reference voltage is counted as two, and the voltage detected by the second voltage sensor is greater than the first reference voltage and the first reference. When the voltage is equal to or less than a predetermined second reference voltage which is higher than the voltage, the cell having the voltage equal to or less than the first reference voltage may be counted as one cell, and the total number of cells may be calculated. According to this aspect, even when one voltage sensor is provided for two cells, the total number of cells can be calculated.
(5) According to one aspect of the present disclosure, a fuel cell system is provided. A fuel cell system includes a fuel cell in which cells are stacked, a voltage sensor that detects a voltage in units of one or more of the cells, and a predetermined voltage detected by the voltage sensor among the plurality of cells. A control unit that calculates the number of specific cells whose voltage is equal to or lower than one reference voltage and operates the fuel cell using the calculated number of cells; a storage device storing a reference map associated with a heat generation amount, wherein the larger the number of sheets, the smaller the required heat generation amount is stored; and the control unit uses the detection voltage The number of fuel cells is calculated, the required calorific value corresponding to the calculated number of fuel cells is acquired using the reference map, and the fuel cell is operated using the acquired required calorific value as a target value. According to this aspect, the required heat generation amount corresponding to the calculated total number of sheets is set as a target value using a reference map that is predetermined so that the exhaust hydrogen concentration becomes the reference concentration, so that the exhaust hydrogen concentration is the reference concentration. It is possible to control the concentration of the fuel cell.
(6) According to one aspect of the present disclosure, a fuel cell system is provided. A fuel cell system includes a fuel cell in which cells are stacked, a voltage sensor that detects voltage in units of one or more cells, and a voltage detected by the voltage sensor among the stacked cells is predetermined. a control unit that calculates the number of specific cells whose voltage is equal to or lower than a first reference voltage and operates the fuel cell using the calculated number of cells; a storage device storing a reference map associated with a required current amount, wherein the larger the number of sheets, the smaller the required current amount is stored; and the control unit uses the detected voltage The number of fuel cells is calculated using the reference map, and the required current amount corresponding to the calculated number of fuel cells is acquired using the reference map, and the fuel cell is operated using the acquired required current amount as a target value. According to this aspect, the exhaust hydrogen concentration is set to the reference concentration by setting the required current amount corresponding to the calculated total number of sheets to the target value using the reference map that is defined in advance so that the exhaust hydrogen concentration becomes the reference concentration. It is possible to control the concentration of the fuel cell.
The present disclosure can be realized in various forms, and in addition to the fuel cell system, for example, a control method of the fuel cell system, a computer program for causing a computer to execute the control method, and a computer program are recorded. It can be realized in the form of a non-transitory recording medium or the like.

1 is an explanatory diagram showing a schematic configuration of a fuel cell system mounted on a vehicle; FIG. 4 is a flowchart of exhaust hydrogen determination processing according to the first embodiment; 7 is a flowchart of cell count calculation processing according to the first embodiment; FIG. 5 is a diagram showing the relationship between the current temperature and the first voltage threshold for each sweep current; It is a figure which shows the relationship between present temperature and a correction coefficient. It is a figure which shows the relationship between a sweep current and a 1st voltage threshold. 10 is a flowchart of cell number calculation processing according to the second embodiment. It is a figure which shows the relationship between the target current and 2nd voltage threshold which concern on 2nd Embodiment. It is a figure explaining the operating point map for determining the target operating point which concerns on 3rd Embodiment. FIG. 11 is a diagram showing the correlation between the number of pumping hydrogen cells for each sweep current and the exhaust hydrogen concentration according to the third embodiment; FIG. 11 is a diagram showing the correlation between the amount of heat generated for each exhaust hydrogen concentration and the number of pumping hydrogen cells according to the third embodiment; 10 is a flowchart of exhaust hydrogen concentration control processing according to the third embodiment; FIG. 10 is a diagram showing a reference map that defines the correlation between the number of pumping hydrogen cells and the required heat generation amount according to the third embodiment;

A. First embodiment:
FIG. 1 is a diagram showing a schematic configuration of a fuel cell system 100 mounted on a vehicle. The fuel cell system 100 includes a fuel cell 10, an oxidizing gas system circuit 20, a fuel gas system circuit 40, a cooling system circuit 60, a load 71, a controller 80, a current sensor 11, a voltage sensor 12, A temperature sensor 14 and a muffler 52 are provided. The fuel cell 10 uses a fuel gas and an oxidizing gas to generate electricity through an electrochemical reaction. The fuel cell 10 has a stack structure in which a plurality of cells 90 are stacked. The cell 90 has a structure in which a MEGA (Membrane Electrode and Gas Diffusion Layer Assembly) (not shown) is sandwiched between separators (not shown). MEGA is a MEA (Membrane Electrolyte) having an electrode catalyst layer (not shown) functioning as an anode on one side of an electrolyte membrane (not shown) and an electrode catalyst layer (not shown) functioning as a cathode on the other side. Gas diffusion layers (not shown) are provided on both sides of the Electrode Assembly (not shown). In this embodiment, hydrogen is used as the fuel gas, and oxygen in the air is used as the oxidizing gas. Electric power generated by the fuel cell 10 is boosted by the DC/DC converter 72, supplied to the load 71, and consumed. A current sensor 11 that detects the output current of the fuel cell 10 is provided between the fuel cell 10 and the load 71 . In this embodiment, a voltage sensor 12 is provided to detect the voltage of each cell 90 as a unit. The control unit 80 includes a CPU (central processing unit) (not shown) and a storage device 81 , and controls the oxidizing gas system circuit 20 , the fuel gas system circuit 40 and the cooling system circuit 60 . The storage device 81 stores a program for an exhaust hydrogen determination process, which will be described later, each map such as a map defining a first voltage threshold Vs1 used in the exhaust hydrogen determination process, and values such as the total number of sensors N. . Voltage sensor 12 , current sensor 11 , and temperature sensor 14 are each connected to control unit 80 . Detected values detected by current sensor 11 , voltage sensor 12 , and temperature sensor 14 are transmitted to control unit 80 . Each of the voltage sensors 12 is assigned a number, with the voltage sensor 12 provided in one of the cells 90 at either end of the fuel cell 10 being number one. The control unit 80 identifies from what order the detected voltage received from the voltage sensor 12 is the detected voltage transmitted from the voltage sensor 12 . The control unit 80 controls the output voltage of the fuel cell 10 by controlling the output current of the fuel cell 10 using the DC/DC converter 72 .

The oxidizing gas system circuit 20 is a circuit for supplying air to the cathode of the fuel cell 10 . The oxidant gas system circuit 20 includes an oxidant gas supply pipe 21, an air cleaner 22, an air compressor 23, a bypass pipe 24, an oxidant offgas discharge pipe 25, an oxidant gas supply valve 26, a bypass valve 27, and a cathode offgas exhaust. a valve 28; The oxidizing gas supply pipe 21 connects the air cleaner 22 and the cathode of the fuel cell 10, that is, an oxidizing gas inlet (not shown). The oxidant off-gas discharge pipe 25 communicates an oxidant off-gas discharge port (not shown) of the fuel cell 10 with the atmosphere. A muffler 52 is arranged in the oxidation off-gas discharge pipe 25 . The air compressor 23 compresses the air from which dust has been removed by the air cleaner 22 and supplies the compressed air to the fuel cell 10 via the oxidizing gas supply pipe 21 . The oxidant gas supply valve 26 is arranged in the oxidant gas supply pipe 21 and cuts off or permits the supply of air to the fuel cell 10 by opening and closing the flow path of the oxidant gas supply pipe 21 . The cathode offgas exhaust valve 28 is arranged in the oxidation offgas exhaust pipe 25 and controls the amount of cathode offgas exhausted from the oxidation offgas exhaust port of the fuel cell 10 to adjust the back pressure of the fuel cell 10 . The bypass pipe 24 connects the oxidizing gas supply pipe 21 and the oxidizing off-gas discharge pipe 25 . A bypass valve 27 is arranged in the bypass pipe 24 and cooperates with the air compressor 23 and the cathode offgas exhaust valve 28 to regulate the flow rate of air flowing through the fuel cell 10 .

The fuel gas system circuit 40 is a circuit for supplying fuel gas to the anode of the fuel cell 10 . The fuel gas system circuit 40 includes a fuel gas supply pipe 41, a fuel gas tank 42 as a fuel gas source, a main stop valve 43, a pressure regulating valve 44, an injector 45, a fuel exhaust gas pipe 46, and a gas-liquid separator 47. , an exhaust/drain valve 48 , a reflux pipe 49 , and a reflux pump 50 . The fuel gas supply pipe 41 connects the fuel gas tank 42 and the anode of the fuel cell 10, that is, a fuel gas inlet (not shown). A fuel gas tank 42 stores high-pressure hydrogen gas. A main stop valve 43 , a pressure regulating valve 44 and an injector 45 are arranged in this order from the fuel gas tank 42 toward the fuel cell 10 in the fuel gas supply pipe 41 . The main stop valve 43 blocks or permits the supply of hydrogen gas from the fuel gas tank 42 by opening and closing the flow path of the fuel gas supply pipe 41 . The pressure regulating valve 44 reduces the pressure of the high pressure hydrogen gas to a predetermined hydrogen pressure. The injector 45 is provided to adjust the amount of hydrogen gas supplied to the fuel cell 10 . The injector 45 adjusts the fuel gas supply amount (fuel gas amount) by controlling the injection interval, that is, the opening interval. The fuel exhaust gas pipe 46 connects a fuel offgas discharge port (not shown) of the fuel cell 10 and the oxidation offgas discharge pipe 25 . A gas-liquid separator 47 and an exhaust drain valve 48 are arranged in this order from the fuel cell 10 toward the muffler 52 in the fuel exhaust gas pipe 46 . The reflux pipe 49 connects the gas-liquid separator 47 and the fuel gas supply pipe 41 on the downstream side of the injector 45 . The fuel off-gas discharged from the fuel off-gas outlet of the fuel cell 10 is separated into a gas component and a liquid component by the gas-liquid separator 47 . The exhaust drain valve 48 switches the fuel exhaust gas pipe 46 between communication and non-communication. The gas component of the fuel exhaust gas separated by the gas-liquid separator 47 is returned to the fuel gas supply pipe 41 by the reflux pump 50 . Thereby, unreacted hydrogen contained in the fuel off-gas is reused. When the concentration of gas components other than hydrogen gas in the fuel off-gas increases, the exhaust drain valve 48 is opened to discharge the liquid components and the fuel off-gas. The fuel off-gas flowing through the fuel exhaust gas pipe 46 and the cathode off-gas flowing through the oxidation off-gas discharge pipe 25 are mixed and exhausted via the muffler 52 .

A cooling system circuit 60 is a circuit for cooling the fuel cell 10 . The cooling system circuit 60 includes a coolant supply pipe 61 , a radiator 64 and a coolant pump 65 . The coolant flowing through the coolant supply pipe 61 is cooled by the radiator 64 and circulated in the fuel cell 10 by the coolant pump 65 . A temperature sensor 14 is provided in the coolant supply pipe 61 . Since the temperature of the coolant discharged from the fuel cell 10 and the temperature of the fuel cell 10 are substantially equal, the temperature of the coolant can be the temperature of the fuel cell 10 . Note that a temperature sensor may be provided in the fuel cell 10 .

Normal operation and warm-up operation in the fuel cell 10 will be described. In normal operation, power is generated by supplying a theoretical amount of air or more required to generate the target output power. On the other hand, during warm-up operation, power generation is performed with an air amount less than the amount of air supplied during normal operation in order to reduce operating efficiency. Here, the operating point of the fuel cell 10 controlled during warm-up operation, which is the operating point when power is generated with an amount of air less than the amount of air supplied during normal operation, is referred to as the low-efficiency operating point. During warm-up operation, the air stoichiometric ratio, which is the ratio of the amount of air actually supplied to the theoretical amount of air required to generate the target output power, is set to, for example, about 1.0. By operating the fuel cell 10 at a low efficiency operating point, the concentration overvoltage increases and the fuel cell 10 is warmed up by self-heating. In normal operation, the control unit 80 determines the operating point of the fuel cell 10 and operates the fuel cell 10 so that the operating efficiency is appropriate from the viewpoint of fuel consumption. The operating efficiency is the efficiency obtained from the amount of fuel gas supplied to the fuel cell 10 and the electric power output from the fuel cell 10 . During warm-up operation, the fuel cell 10 is operated at a low-efficiency operating point, which is lower in efficiency than the reference operating point, among the operating points of the fuel cell 10 . Here, the reference operating point is an operating point for operating the fuel cell 10 by supplying a theoretical amount of air equal to or greater than the amount of air required to generate the target output power. In warm-up operation, for example, a target heat generation amount is set according to the starting temperature of the fuel cell 10, and a target value for the low efficiency operating point is determined based on the set target heat generation amount.

Warm-up operation is mainly performed when the outside air temperature is below freezing. When the temperature is below freezing, moisture remaining in the fuel cell 10 may freeze, blocking the flow path of the oxidizing gas in the fuel cell 10 . Therefore, the pressure loss of the oxidizing gas increases, the actual fuel gas supply amount becomes smaller than the target fuel gas supply amount, and the actual cell voltage drops relative to the target cell voltage. In addition, pumping hydrogen is generated when the amount of fuel gas supplied decreases. Pumping hydrogen is hydrogen that is generated when hydrogen ions that have moved to the cathode receive electrons. Since the amount of hydrogen ions that move to the cathode is proportional to the amount of current that is swept from the fuel cell 10, the amount of pumping hydrogen that is generated is proportional to the amount of current that is swept.

The exhaust hydrogen determination process executed by the control unit 80 will be described with reference to FIG. After being activated, the control unit 80 repeatedly executes the exhaust hydrogen determination process. At startup, the control unit 80 stores the temperature detected by the temperature sensor 14 in the storage device 81 as the temperature at startup when the fuel cell 10 is started. The control unit 80 determines whether or not warm-up operation is necessary based on the detection value of a temperature sensor (not shown) that detects the outside air temperature provided in the oxidizing gas supply pipe 21 (FIG. 1), for example. When it is determined that operation is necessary, the warm-up operation flag is turned on, and warm-up operation is started. Specifically, the control unit 80 causes the oxidizing gas system circuit 20 to start supplying air to the fuel cell 10, causes the fuel gas system circuit 40 to start supplying fuel gas to the fuel cell 10, and causes the fuel cell 10 to start generating power. Let Further, when ending the warm-up operation, the control unit 80 switches the warm-up operation flag to off. The control unit 80 operates the fuel cell 10 at the low efficiency operating point during warm-up operation.

When starting the exhaust hydrogen determination process, the control unit 80 determines whether or not the fuel cell 10 is warming up (step S10). The fuel cell 10 refers to the warm-up operation flag, and when the warm-up operation flag is off, determines that the fuel cell 10 is not in the warm-up operation (step S10: NO), and terminates this processing routine. If the warm-up flag is ON (step S10: YES), the control unit 80 executes the cell count calculation process (step S20).

The number-of-cells calculation process will be described with reference to FIG. The inventors paid attention to the fact that the more cells 90 in which the cell voltage is lowered, the greater the amount of pumping hydrogen generated. In order to calculate the amount of pumping hydrogen generated, the number of cells 90 in which pumping hydrogen is estimated to be generated (hereinafter referred to as "the number of pumping hydrogen cells") Nh is counted. In the cell count calculation process, it is determined that pumping hydrogen is generated in the cells 90 whose cell voltage is equal to or less than the first voltage threshold Vs1, and the cells 90 in which pumping hydrogen is estimated to be generated (hereinafter referred to as "pumping hydrogen (referred to as a "generation cell").

FIG. 4 is a map defining the first voltage threshold Vs1 for current temperature and sweep current. Here, the sweep current is the current taken out from the fuel cell 10 by the DC/DC converter 72 . The horizontal axis of FIG. 4 is the current temperature [° C.] of the fuel cell 10, and the vertical axis is the first voltage threshold Vs1 [V]. The first voltage threshold Vs1 is defined for each sweep current. Since the output voltage of the fuel cell 10 decreases as the output current increases, the first voltage threshold Vs1 is set smaller as the sweep current of the fuel cell 10 increases. A characteristic line Lb1 is a characteristic line in which the first voltage threshold Vs1 is set constant regardless of the current temperature of the fuel cell 10 . The lower the temperature of the fuel cell 10, the higher the resistance of the electrolyte membrane and the lower the cell voltage output from the cell 90. Therefore, characteristic lines such as characteristic lines La1 and Lc1 may be used that reflect the characteristics of the fuel cell 10 in which the lower the current temperature is, the lower the cell voltage is. In this embodiment, the characteristic line La1 is used.

When starting the number-of-cells calculation process (FIG. 3), the control unit 80 sets the sensor number n indicating the number of the voltage sensor 12 used in this subroutine to the initial value of 1. The generated cell number m indicating the total number of 90 is set to the initial value of zero. The control unit 80 refers to the map shown in FIG. 4, sets the target current as the sweep current, and sets the current temperature detected by the temperature sensor 14 and the first voltage threshold Vs1 (an example of the first reference voltage) corresponding to the sweep current. Acquire (step S100). The control unit 80 determines whether or not the voltage detected by the n-th voltage sensor 12 is equal to or lower than the first voltage threshold Vs1 (step S110). When the control unit 80 determines that the detected voltage is equal to or lower than the first voltage threshold Vs1 (step S110: YES), the control unit 80 estimates that pumping hydrogen is generated in the target cell, and adds 1 to the generated cell number m ( Step S120), and the process proceeds to step S130. When the control unit 80 determines that the detected voltage is not equal to or less than the first voltage threshold Vs1, that is, is greater than the first voltage threshold Vs1 (step S110: NO), the control unit 80 estimates that pumping hydrogen is not generated in the target cell, and proceeds to step S120. is skipped, and the process proceeds to step S130. In order to determine the next voltage sensor 12, the control unit 80 adds 1 to the sensor number n (step S130), and determines whether or not the sensor number n is equal to or greater than the total number of sensors N of the voltage sensors 12. (Step S140). When the control unit 80 determines that the sensor number n is not equal to or greater than the sensor total number N, that is, is less than the sensor total number N (step S140: NO), the control unit 80 returns to step S110 to determine the next voltage sensor 12. FIG. When the control unit 80 determines that the sensor number n is greater than or equal to the total number of sensors N (step S140: YES), the control unit 80 terminates this subroutine because the determination of all the voltage sensors 12 has been completed.

Returning to FIG. 2, after executing step S20, the control unit 80 determines whether or not the exhaust hydrogen concentration can be estimated (step S30). Specifically, the control unit 80 determines whether each value such as the total air flow rate Va used in formulas (1) to (3), which are formulas for calculating the exhaust hydrogen concentration, is appropriate. to judge. Examples of conditions are shown in (a) to (j). At least one of items (a) to (j) is used as a criterion. If even one of the one or more criteria used is met, it is determined that the exhaust hydrogen concentration cannot be estimated.
(a) When the absolute value of the cell voltage is equal to or less than the reference value.
(b) When the cell voltage is below the command voltage value.
(c) When the cell voltage does not change within a predetermined range with respect to the command voltage value.
(d) When the current temperature is below the reference value.
(e) When the absolute value of the air flow rate is below the reference value.
(f) When the air flow rate is equal to or less than the command flow rate value.
(g) When the air flow rate does not change within a predetermined range with respect to the command flow rate value.
(h) When the absolute value of the output current is below the reference value.
(i) When the output current is equal to or less than the command current value.
(j) When the output current does not change within a predetermined range with respect to the command current value.
The air flow rate is, for example, a value estimated from the rotational speed of the air compressor 23 and the opening degree of the bypass valve 27 . When the control unit 80 determines that the exhaust hydrogen concentration cannot be estimated (step S30: NO), the processing routine ends. When the control unit 80 determines that it is possible to determine the exhaust hydrogen concentration (step S30: YES), the process proceeds to step S40.

Here, the formula for calculating the exhaust hydrogen concentration Ch, which is used in steps S50 and S60 later, will be described. The inventors paid attention to the fact that the pumping hydrogen generation amount is proportional to the number of pumping hydrogen cells and the current swept from the fuel cell 10 . Assuming that the same current value flows through each cell 90, the exhaust hydrogen concentration Ch is calculated using the following equations (1) to (3).
Vh=CF×I/(2×F)×22.4×60×Nh Expression (1)
Vo=I/(4×F)×22.4×60×(Na−Nh) Formula (2)
Ch=Vh/(Va−Vo+Vh)×100 Expression (3)
Formula (1) is a formula for calculating the estimated amount of pumping hydrogen generated (hereinafter referred to as "pumping hydrogen amount"), and formula (2) is a formula for calculating the amount of oxygen consumed. Formula (3) is a formula for calculating the exhaust hydrogen concentration Ch, and is substituted with the pumping hydrogen amount Vh and the oxygen consumption amount Vo calculated by formulas (1) and (2).
Definitions of parameters in equations (1) to (3) are as follows.
Vh: Pumping hydrogen amount [NL/min]
Vo: Oxygen consumption [NL/min]
Ch: Exhaust hydrogen concentration [%]
Va: total air flow rate [NL/min]
CF: correction factor I: sweep current [A]
Nh: Number of pumping hydrogen cells Na: Total number of cells F: Faraday constant “Total number of cells” indicates the total number of cells 90 . The number "2" in equation (1) is the number of electrons received from the cathode when two hydrogen ions become one hydrogen molecule at the cathode. The number "4" in equation (2) is the number of electrons received from the cathode when one oxygen molecule becomes water at the cathode. Based on the sweep current I, the amount of charge delivered per second to the cathode is estimated. For example, in the calculation of the pumping hydrogen amount Vh in Equation (1), the number of pumping hydrogen molecules to be generated is calculated from the estimated charge amount using the Faraday constant. The calculated number of molecules is the pumping hydrogen amount Vh [NL/min], which is the volume of pumping hydrogen generated per minute using the volume per 1 mol of gas (22.4 [L/mol]) in the standard state. converted to

The correction coefficient CF in the formula (1) is a coefficient for correcting the theoretical value of the pumping hydrogen generation amount derived from the sweep current I and the number of pumping hydrogen cells Nh to the measured value, and is a value obtained by experiments or the like. .

As described above, in the cell number calculation process (FIG. 3), the cells 90 having the cell voltages equal to or lower than the first voltage threshold Vs1 are determined to be pumping hydrogen generating cells. In the determination, the cell voltage is clearly divided into two between the pumping hydrogen-producing cell and the cell 90 that is assumed to be not producing pumping hydrogen (hereinafter referred to as "pumping hydrogen non-producing cell"). Ideal. However, actually, the measured cell voltage is distributed from near 0V to near the target cell voltage. Therefore, depending on the value of the first voltage threshold Vs1, the cells 90 in which no pumping hydrogen is actually generated are erroneously counted as pumping hydrogen generating cells, and the cells 90 in which pumping hydrogen is actually generated are counted as pumping hydrogen cells. A cell may be erroneously counted as a non-generating cell. A correction factor CF is used to correct for such erroneous counting.

FIG. 5 is a map that defines the correction coefficient CF for the current temperature for each starting temperature. The horizontal axis of FIG. 5 is the current temperature [° C.] of the fuel cell 10, and the vertical axis is the correction coefficient CF. Characteristic lines Ld1 to Ld3 correspond to different starting temperatures, and the starting temperature is lower in the order of characteristic line Ld1, characteristic line Ld2, and characteristic line Ld3. The starting temperature will be described later.

In fact, the erroneous counting in which the cells 90 generating pumping hydrogen are counted as the cells not generating pumping hydrogen tends to occur when the temperature of the fuel cell 10, which has been below the freezing point, rises above the freezing point. During warm-up operation, the fuel cell 10 is operated in an operating range in which the amount of change in output voltage with respect to the amount of change in air stoichiometric ratio is large. During warm-up operation, when the amount of fuel gas supplied increases due to, for example, the melting of frozen water in the fuel cell 10, the cell voltage rises significantly. Therefore, even though pumping hydrogen is being generated, the measured value is greater than the first voltage threshold Vs1, and the cells 90 generating pumping hydrogen are erroneously counted as cells not generating pumping hydrogen.

On the contrary, the erroneous counting that the cell 90 which actually does not generate pumping hydrogen is counted as the pumping hydrogen generating cell occurs when the amount of change in the output voltage with respect to the amount of change in the temperature of the fuel cell 10 is small, near the sweep current of 0 A. easily occur. FIG. 6 is a diagram showing the relationship between the sweep current I for each current temperature and the first voltage threshold Vs1. The horizontal axis of FIG. 6 is the sweep current I [A], and the vertical axis is the first voltage threshold Vs1 [V]. Characteristic lines La1 to La3 correspond to current temperatures of -10°C, -20°C and -30°C, respectively. Near the sweep current of 0 A, the amount of change in the output voltage with respect to the amount of change in the temperature of the fuel cell 10 is small. For this reason, even a slight detection error is likely to cause erroneous counting. For example, when the temperature of the target cell 90 is lower than the temperature detected by the temperature sensor 14, the determination is made using the first voltage threshold Vs1 corresponding to the current temperature higher than the actual current temperature. In this case, cells 90 in which pumping hydrogen is not generated are erroneously counted as pumping hydrogen generating cells.

If the cells 90 generating pumping hydrogen are erroneously counted as cells not generating pumping hydrogen, it is necessary to correct the counted number of cells to a larger value. Conversely, if cells 90 that do not generate pumping hydrogen are erroneously counted as pumping hydrogen generating cells, it is necessary to correct the counted number of cells to a smaller value. The correction coefficient CF is set in consideration of the above events.

Next, the reason why the correction coefficient CF map is defined for each starting temperature will be described. The inventors have found that even if the current operating point is the same, the lower the starting temperature, the more likely pumping hydrogen is generated. This is because the lower the starting temperature, the greater the amount of heat required for warming up, and the lower the command voltage, that is, the less air is supplied. Therefore, by using a map in which the correction coefficient CF is increased as the starting temperature is lower, the pumping hydrogen amount can be calculated with high accuracy.

Returning to FIG. 2, when the control unit 80 determines that the exhaust hydrogen concentration can be estimated (step S30: YES), it refers to the map shown in FIG. A correction coefficient CF corresponding to the temperature is obtained (step S40). The control unit 80 substitutes the current current detected by the current sensor 11 for the sweep current I, and substitutes the number m of generated cells for the number Nh of pumping hydrogen cells to obtain the above equations (1) to (3). , the exhaust hydrogen concentration Ch is calculated (step S50). The exhaust hydrogen concentration Ch calculated by substituting the current current is referred to as a first estimated hydrogen concentration Ca. The control unit 80 substitutes the target current for the sweep current I and calculates the exhaust hydrogen concentration Ch based on the above equations (1) to (3) (step S60). The exhaust hydrogen concentration Ch calculated by substituting the target current is referred to as a second estimated hydrogen concentration Cb. The control unit 80 controls the sweep current so as to match the target current, but the sweep current may not match the target current if, for example, the moisture remaining in the fuel cell 10 is not completely melted. . The first estimated hydrogen concentration Ca and the second estimated hydrogen concentration Cb may deviate. Therefore, both the first estimated hydrogen concentration Ca and the second estimated hydrogen concentration Cb are calculated, and concentration determination (steps S70 and S80) is performed based on each of them, thereby performing hydrogen concentration reduction processing when the exhaust hydrogen concentration is high. (Step S90) can be reliably executed.

The control unit 80 determines whether or not the first estimated hydrogen concentration Ca is equal to or higher than a concentration threshold value (an example of reference concentration) based on, for example, environmental standards (step S70). When the control unit 80 determines that the first estimated hydrogen concentration Ca is equal to or higher than the concentration threshold (step S70: YES), the process proceeds to step S90 to decrease the exhaust hydrogen concentration. When the control unit 80 determines that the first estimated hydrogen concentration Ca is not equal to or higher than the concentration threshold, that is, is less than the concentration threshold (step S70: NO), it determines whether the second estimated hydrogen concentration Cb is equal to or higher than the concentration threshold. (step S80). When the control unit 80 determines that the second estimated hydrogen concentration Cb is equal to or higher than the concentration threshold (step S80: YES), the process proceeds to step S90 to decrease the exhaust hydrogen concentration. When the control unit 80 determines that the second estimated hydrogen concentration Cb is not equal to or higher than the concentration threshold, that is, is less than the concentration threshold (step S80: NO), the processing routine ends. In order to reduce the generation of pumping hydrogen, the control unit 80 executes hydrogen concentration reduction processing to change the operating point of the fuel cell 10 to a high efficiency operating point that is more efficient than the current operating point (step S90), Terminate this processing routine. The hydrogen concentration reduction process may be any process as long as it can reduce the hydrogen concentration, for example, a process of making the target current value smaller than the current set value. This reduces the exhaust hydrogen concentration.

According to the exhaust hydrogen determination process described above, the pumping hydrogen generating cells are specified based on the voltage detected by the voltage sensor 12, and the exhaust hydrogen concentration Ch is calculated based on the number of pumping hydrogen cells Nh. can be calculated with high accuracy. The hydrogen concentration reduction process is executed when the exhaust hydrogen concentration Ch is equal to or higher than the concentration threshold. Since the accurately calculated exhaust hydrogen concentration Ch can be used to determine whether to execute the hydrogen concentration reduction process, the hydrogen concentration reduction process can be executed when the actual exhaust hydrogen concentration is not equal to or higher than the concentration threshold. Suppressed. When the exhaust hydrogen concentration Ch is equal to or higher than the concentration threshold, the operating point is moved to the high efficiency side. Therefore, if the calculation accuracy of the exhaust hydrogen concentration Ch is poor, the operating point excessively shifts (hunting). Excessive movement (hunting) of the operating point can be suppressed by accurately calculating the exhaust hydrogen concentration Ch. In addition, since the hydrogen concentration reduction process is executed during warm-up operation, it is possible to suppress an increase in the amount of pumping hydrogen that accompanies an increase in the sweep current after shifting to normal operation. The inventors have found that once pumping hydrogen is generated, the catalyst surface of the electrode catalyst layer that functions as the cathode becomes hydrogen-rich, inhibiting the supply of oxygen to the catalyst surface and inhibiting the power generation reaction. When the catalyst surface is in a hydrogen-rich state and the operation is shifted to normal operation, the sweep current of the fuel cell 10 is increased, and the amount of pumping hydrogen is also increased in accordance with the increase in the sweep current. Therefore, by executing the hydrogen concentration reduction process during the warm-up operation before shifting to the normal operation, it is possible to suppress the increase in the pumping hydrogen amount.

B: Second Embodiment In the first embodiment, the fuel cell system 100 is provided with the voltage sensor 12 that detects the voltage of each cell 90 as a unit. In contrast, the fuel cell system of the second embodiment includes a voltage sensor 12 (hereinafter referred to as a , referred to as a "first voltage sensor"). A voltage sensor 12 (hereinafter referred to as a "second voltage sensor") that detects the voltage in units of two cells 90 is provided for the intermediate cells 90 excluding the plurality of cells 90 at both ends. The voltage detected by the voltage sensor 12 that detects the voltages of the two cells 90 is the sum of the voltages of the cells 90 . The process of calculating the number of generated cells according to the second embodiment is a process that enables specification of the pumping hydrogen generating cells even in a configuration in which the voltage sensor 12 detects voltages of two cells 90 . The exhaust hydrogen determination process according to the second embodiment is the same as the exhaust hydrogen determination process according to the first embodiment except for the cell number calculation process, and thus the description thereof is omitted.

When the cell voltage of only one of the two cells 90 to be detected by the second voltage sensor is low, the detected voltage of the second voltage sensor is that the cell voltage of both of the two cells 90 is low. The value is between the detected voltage when there is no cell and the detected voltage when both of the two cells 90 have decreased cell voltages. Therefore, a second voltage sensor in which only one of the two cells 90 has a decreased cell voltage is identified using a second voltage threshold Vs2 larger than the first voltage threshold Vs1. FIG. 8 is a map that defines the second voltage threshold Vs2 with respect to the target current for each current temperature. The horizontal axis of FIG. 8 is the target current [A], and the vertical axis is the second voltage threshold Vs2. The characteristic lines Le1 to Le3 correspond to different current temperatures, and the current temperature is lower in the order of characteristic line Le1, characteristic line Le2, and characteristic line Le3. The cell voltage of the cell 90 in which pumping hydrogen is not generated becomes a value corresponding to the target voltage of the fuel cell 10. FIG. Therefore, the second voltage threshold Vs2 is set to a value corresponding to the target voltage. In the cell count calculation process according to the second embodiment, when the voltage detected by the second voltage sensor is greater than the first voltage threshold and equal to or less than the second voltage threshold Vs2, the number of pumping hydrogen generating cells is counted as one. be.

When the control unit 80 starts the cell number calculation process (FIG. 7), the sensor number n, which is a variable used in this subroutine, is set to the initial value of 1, and the generated cell number m is set to the initial value, as in the first embodiment. set to zero. The control unit 80 refers to the map shown in FIG. 2 to acquire the first voltage threshold Vs1 corresponding to the current temperature and the current detected by the current sensor 11 (step S210). Control unit 80 refers to the map shown in FIG. 8 to acquire second voltage threshold Vs2 (an example of a second reference voltage) corresponding to the current temperature and target current (step S220).

The control unit 80 sets the number of cells 90 detected by the target n-th voltage sensor 12 as the cell number Nc (step S230). The number of cells Nc is set to 1 for the first voltage sensor, and the number of cells Nc is set to 2 for the second voltage sensor. The control unit 80 determines whether or not the voltage detected by the target n-th voltage sensor 12 is equal to or lower than the first voltage threshold Vs1 (step S240). When the control unit 80 determines that the detected voltage is equal to or lower than the first voltage threshold Vs1 (step S240: YES), it is estimated that pumping hydrogen is generated in the target cell. is added (step S250), and the process proceeds to step S260. If it is the first voltage sensor, 1 is added to the generated cell number m, and if it is the second voltage sensor, 2 is added to the generated cell number m.

When the control unit 80 determines that the detected voltage is not equal to or lower than the first voltage threshold Vs1, that is, is greater than the first voltage threshold Vs1 (step S240: NO), the number of cells 90 detected by the target voltage sensor 12 is two. (step S280). If the control unit 80 determines that the target voltage sensor 12 is the first voltage sensor and the number of detected sheets is not two (step S280: NO), the process proceeds to step S260. When the control unit 80 determines that the detected number of sheets is two (step S280: YES), it determines whether or not the target n-th detected voltage is equal to or lower than the second voltage threshold Vs2 (step S290). . When the control unit 80 determines that the detected voltage is not equal to or less than the second voltage threshold Vs2, that is, is greater than the second voltage threshold Vs2 (step S290: NO), the process proceeds to step S260. When the control unit 80 determines that the detected voltage is equal to or lower than the second voltage threshold Vs2 (step S290: YES), it adds 1 to the generated cell number m (step S300).

In order to determine the next voltage sensor 12, the control unit 80 adds 1 to the sensor number n (step S260), and determines whether the sensor number n is equal to or greater than the total number of sensors N of the voltage sensors 12. (Step S270). When the control unit 80 determines that the sensor number n is not equal to or greater than the sensor total number N, that is, is less than the sensor total number N (step S270: NO), the control unit 80 returns to step S230 to determine the next voltage sensor 12. FIG. When the control unit 80 determines that the sensor number n is greater than or equal to the total number of sensors N (step S270: YES), the control unit 80 terminates this subroutine because the determination of all the voltage sensors 12 has been completed.

According to the number-of-cells calculation process according to the second embodiment described above, the voltage sensor 12 includes a voltage sensor in units of one cell 90 and a voltage sensor in units of two cells 90. Even in this case, the pumping hydrogen cell number Nh can be calculated with high accuracy.

C. Third Embodiment In the third embodiment, the fuel cell 10 is set to the operating point at which the exhaust hydrogen concentration Ch is equal to or less than the reference concentration by using a reference map that is predetermined so that the exhaust hydrogen concentration Ch is equal to or less than the reference concentration. controlled by As a result, the exhaust hydrogen concentration Ch of the fuel cell 10 can be maintained below the reference concentration.

FIG. 9 is a diagram illustrating an operating point map for determining a target operating point during warm-up operation of the fuel cell 10. FIG. Note that the operating point determined using FIG. 9 is the operating point during warm-up operation, and is the low-efficiency operating point whose efficiency is lower than that of the reference operating point, as described above. The horizontal axis of FIG. 9 is the current of the fuel cell 10 and the vertical axis is the voltage of the fuel cell 10 . FIG. 9 shows a constant power line PL that indicates the operating point at which the amount of generated power is the same, and constant Q lines QL1 and QL2 that indicate the operating point at which the amount of heat generated is the same. Here, the calorific value is the amount of heat generated per unit time as the fuel cell 10 generates power. The equal Q lines QL1 and QL2 have different calorific values. The equal Q line QL1 generates a calorific value qmax, and the equal Q line QL2 generates a calorific value qa. The calorific value qmax is the maximum value of the target calorific value set in the warm-up operation, and is larger than the calorific value qa. In normal operation, the target operating point is set according to the required power generation amount. On the other hand, in the warm-up operation, the target heat generation amount is determined, and the target operating point is determined according to the determined target heat generation amount. Specifically, the intersection of the equal Q line of the target heat generation amount and the equal power line of the target power generation amount is set as the target operating point. During warm-up operation, the fuel cell 10 is operated in an operating range in which the amount of change in output voltage with respect to the amount of change in the air stoichiometric ratio is large, so the target power generation amount is fixed at a predetermined value. . That is, the operating point in warm-up operation is set to the operating point on the equal power line PL in FIG. Further, the rotational speed of the air compressor 23 is fixed at a predetermined value, and the total air flow rate Va supplied to the fuel cell system 100 is fixed at a predetermined value. In the warm-up operation, it is preferable to set the target calorific value as large as possible in order to shorten the warm-up operation time. Therefore, warm-up operation is started at a target operating point corresponding to the amount of heat generated qmax. Specifically, the operation is started at the target operating point OP1, which is the intersection of the constant Q line QL1, which is the amount of heat generated qmax, and the constant power line PL. The target power generation amount per hour in warm-up operation is, for example, 10.3 kW. Also, the calorific value qmax is, for example, 56 kW per hour.

As described in the first embodiment, the exhaust hydrogen concentration Ch can be calculated using equation (3) using the pumping hydrogen cell number Nh, the sweep current I, and the like. Here, the sweep current I is the current drawn from the fuel cell 10 by the DC/DC converter 72 . Note that the exhaust hydrogen concentration Ch is, in detail, the concentration in the oxidation off-gas discharge pipe 25 on the downstream side of the connection point between the oxidation off-gas discharge pipe 25 and the bypass pipe 24 . Also, the total air flow rate Va is a fixed value. The total air flow rate Va is the flow rate of air supplied from the air compressor 23 to the fuel cell system 100, and more specifically, the total amount of the air flow rate supplied to the fuel cell 10 and the air flow rate circulating through the bypass pipe 24. is. Here, in the third embodiment, the pumping hydrogen amount Vh to be substituted into equation (3) is calculated using the following equation (4). Equation (4) differs from Equation (1) in that there is no correction factor CF included in Equation (1).
Vh=I/(2×F)×22.4×60×Nh Expression (4)
As described above, the cell voltage drops in the cell 90 where pumping hydrogen is being generated. Therefore, in the first embodiment, the cells 90 in which the cell voltage is equal to or lower than the first voltage threshold Vs1, which is a value greater than 0 V, are counted, and the correction coefficient CF is used to determine, for example, the cells in which pumping hydrogen is not actually generated. An erroneous count such as 90 being counted as a pumping hydrogen generating cell, which is a specific cell, is corrected. Here, the cell voltage of the pumping hydrogen generating cell is typically a negative voltage. Therefore, in the present embodiment, the first voltage threshold Vs1 is set to 0 V, for example, and cells 90 with a cell voltage of 0 V or less are counted as pumping hydrogen generating cells. Then, the pumping hydrogen amount Vh is calculated without correction using the correction coefficient CF. Substituting equations (4) and (2) into equation (3) and arranging them yields the following equation (5).
Ch=2Nh/(4F/I×Va/(22.4×60)−Na+3Nh) Equation (5)

Here, the inventors found that when the total air flow rate Va is a fixed value, the exhaust hydrogen concentration Ch can be calculated based on the number of pumping hydrogen cells Nh and the sweep current I. , the correlation between the pumping hydrogen cell number Nh and the sweep current I can be defined in advance. Based on the correlation between the number of pumping hydrogen cells Nh and the sweep current I at which the exhaust hydrogen concentration Ch is equal to or lower than the reference concentration, the fuel cell 10 is operated at the operating point at which the sweep current I is obtained. It is possible to realize the control of the fuel cell 10 in which the concentration is equal to or less than the reference concentration. Details are given below.

FIG. 10 is a diagram showing the correlation between the pumping hydrogen cell number Nh and the exhaust hydrogen concentration Ch for each sweep current I, calculated using Equation (5). The characteristic lines L1 to L5 have the sweep currents I1 to i5, respectively, and the current value of the sweep current I increases in the order of the characteristic lines L1, L2, L3, L4, and L5. As shown in FIG. 10, when the pumping hydrogen cell number Nh is the same, the larger the sweep current I, the higher the exhaust hydrogen concentration Ch. Further, when the sweep current I is the same, the greater the pumping hydrogen cell number Nh, the higher the exhaust hydrogen concentration Ch.

FIG. 11 is a map that defines the correlation between the calorific value and the pumping hydrogen cell number Nh for each exhaust hydrogen concentration. The map shown in FIG. 11 is a map including a reference map used in exhaust hydrogen concentration control processing, as will be described later. The reference map is a map when the fuel cell 10 is generated at an operating point on an equal power line, and the total air flow rate Va, which is the amount of air supplied to the fuel cell system 100 by the air compressor 23, is a fixed value. . As shown in equation (5), when the total air flow rate Va and the total cell number Na are fixed values, the exhaust hydrogen concentration Ch is calculated using the sweep current I and the pumping hydrogen cell number Nh. As described above, in the present embodiment, the target heat generation amount is determined, the target operating point is determined according to the target heat generation amount, and the fuel cell 10 is controlled to the determined target operating point. Therefore, the map shown in FIG. 11 defines the correlation between the amount of heat generation and the number of pumping hydrogen cells Nh, not the sweep current I. In this embodiment, during warm-up operation, the control unit 80 operates the fuel cell 10 at an operating point on the constant power line PL, so that the sweep current I and the required heat generation amount can be associated one-to-one. . Therefore, the correlation between the amount of heat generated and the number of pumping hydrogen cells Nh can be defined in advance. Specifically, the sweep current I can be converted into the amount of heat generated by using the operating point map shown in FIG. 9, for example. As shown in FIG. 10, once the pumping hydrogen cell number Nh and the exhaust hydrogen concentration Ch are determined, the sweep current I is uniquely determined. Then, as shown in FIG. 9, when the sweep current I is determined, the amount of heat generated is uniquely determined. The exhaust hydrogen concentrations Ch of the characteristic lines CL1 to CL6 are concentrations c1 to c6, respectively, and the exhaust hydrogen concentrations Ch gradually increase in the order of the characteristic lines CL1, CL2, CL3, CL4, CL5 and CL6. As shown in FIG. 11, in order to reduce the exhaust hydrogen concentration Ch to, for example, the concentration c3 or lower, the operating point of the fuel cell 10 should be set to an operating point at which the larger the number Nh of pumping hydrogen cells, the smaller the amount of heat generated.

Exhaust hydrogen concentration control processing according to the third embodiment will be described with reference to FIG. Steps similar to those of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate. After being activated, the control unit 80 repeatedly executes the exhaust hydrogen concentration control process. The control unit 80 executes steps S10 and S20. As described above, in step S20 in this embodiment, the first voltage threshold Vs1 is set to 0V, for example. Using the reference map shown in FIG. 13, the control unit 80 acquires the required calorific value corresponding to the pumping hydrogen cell number Nh calculated in step S20 at a predetermined reference concentration (step S400).

The reference map shown in FIG. 13 shows a calorific value qmax and, among the characteristic lines CL1 to CL6 shown in FIG. 11, a characteristic line CL3 where the exhaust hydrogen concentration Ch is the concentration c3. 11 and 13 have different axes. In FIG. 13, the horizontal axis indicates the number of pumping hydrogen cells Nh, and the vertical axis indicates the required heat generation amount [kW]. In this embodiment, a fixed density is set in advance as the reference density, and the standard density is the density c3. The storage device 81 stores in advance a reference map in which the exhaust hydrogen concentration is the concentration c3. By using the reference map in which the exhaust hydrogen concentration is c3, the control unit 80 can obtain the required heat generation amount corresponding to the pumping hydrogen cell number Nh, which is the reference concentration.

After executing step S400 (FIG. 12), the control unit 80 executes rate processing with the required heat generation amount as a target value (step S410). Rate processing is the process of changing the operating point corresponding to the current target heat generation amount to the operating point corresponding to the new target heat generation amount, and the change rate, which is the amount of change in the heat generation amount per unit time, is determined in advance. This is a process for setting a reference rate. Here, the reference rate is, for example, 12 [kw/sec] for both the ascending rate and descending rate. By executing rate processing, it is possible to suppress rapid changes in the amount of heat generated. Specifically, the control unit 80 adjusts the air flow rate to the fuel cell 10 by adjusting the degree of opening of the bypass valve 27 and, for example, using the DC/DC converter 72 to change the sweep current of the fuel cell 10 to By changing the rate according to the reference rate, the operating point of the fuel cell 10 is switched. For example, as shown in FIG. 13, when the pumping hydrogen cell number Nh is the number na, the required heat generation amount acquired in step S400 is the heat generation amount qa. In this case, as shown in FIG. 9, the operating point corresponding to the new target heat generation amount is the target operating point OP2. Therefore, when the current operating point is the target operating point OP1, the operating point is switched along the equal power line PL toward the new target operating point OP2. If there is a cell 90 generating pumping hydrogen, the operating point is switched to a more efficient operating point, so that the sweep current I is reduced and the exhaust hydrogen concentration Ch is reduced. Further, for example, when the temperature of the fuel cell 10 rises and the pumping hydrogen cell number Nh decreases, the operating point is switched from the target operating point OP2 to the target operating point OP1, for example. In this case, the exhaust hydrogen concentration is maintained at or below the reference concentration, and control is performed to increase the amount of heat generated. In this way, by executing steps S20, S400, and S410 during the warm-up operation, control is performed such that the exhaust hydrogen concentration is maintained at or below the reference concentration and the calorific value is increased as much as possible. Warm-up time can be shortened.

As described above, according to the third embodiment, the number of specific cells is set so that the exhaust hydrogen concentration Ch, which is accurately calculated using the pumping hydrogen cell number Nh as the number of specific cells, is equal to or lower than the reference concentration. By setting the calorific value corresponding to the calculated pumping hydrogen cell number Nh as the required calorific value using a reference map in which the required calorific value for the pumping hydrogen cell number Nh is associated, the exhaust hydrogen concentration Ch becomes the reference concentration. It is possible to control the fuel cell 10 as follows.

D. Other embodiments:
(D1) In the exhaust hydrogen determination process according to the first embodiment, a first estimated hydrogen concentration Ca and a second estimated hydrogen concentration Cb are calculated and compared with concentration thresholds. On the other hand, a process of calculating either the first estimated hydrogen concentration Ca or the second estimated hydrogen concentration Cb, and executing the hydrogen concentration reduction process if either of the calculated concentrations is equal to or higher than the concentration threshold. Good content. As a result, the number of processing steps can be reduced, and the load associated with the exhaust hydrogen determination processing can be reduced.

(D2) The number-of-cells calculation process according to the second embodiment is a process of counting the number of pumping hydrogen cells in a fuel cell system provided with a voltage sensor 12 for detecting voltage in units of two cells 90. be. Also in the fuel cell system provided with the voltage sensor 12 for detecting the voltage in units of three or more cells 90, the reference voltage used to determine whether or not pumping hydrogen is generated is increased, and the second embodiment The number of pumping hydrogen cells can be counted in a similar manner. For example, in the case of a configuration including voltage sensors 12 that detect voltage in units of three cells 90, a first voltage sensor 12 for detecting pumping hydrogen is generated in the three cells 90 to be detected. In addition to one reference voltage, the reference voltage for characterizing the voltage sensor 12 in which pumping hydrogen is generated in two of the three cells 90 to be detected, and the pumping hydrogen in one cell 90 By using a reference voltage to characterize the voltage sensor 12 in which is occurring, the number of pumped hydrogen cells can be counted.

(D3) In the first embodiment described above, different correction coefficients CF are applied according to the starting temperature (see FIG. 5). Alternatively, the same correction coefficient may be applied regardless of the starting temperature. Thereby, the processing load can be reduced.

(D4) In the second embodiment, different second voltage thresholds Vs2 are applied according to the current temperature (see FIG. 8). Alternatively, the same second voltage threshold Vs2 may be applied regardless of the current temperature. Thereby, the processing load can be reduced.

(D5) In the first embodiment, in the hydrogen concentration reduction process, the operating point of the fuel cell 10 is changed to a high-efficiency operating point that is more efficient than the current operating point, and the amount of pumping hydrogen generated is reduced. Exhaust hydrogen concentration is reduced. On the other hand, in the hydrogen concentration reduction process, the hydrogen concentration may be reduced without changing the operating point of the fuel cell 10 by increasing the flow rate of the air flowing through the bypass pipe 24 .

(D6) The hydrogen concentration reduction process in the first embodiment is, for example, a process of making the target current value smaller than the current set value. Alternatively, as the hydrogen concentration reduction process, the exhaust hydrogen concentration Ch may be reduced by increasing the total air flow rate Va and diluting the cathode off-gas discharged from the cathode of the fuel cell 10 with air.

(D7) In the above-described third embodiment, the reference map defining the correlation between the required calorific value and the pumping hydrogen cell number Nh, where the exhaust hydrogen concentration is the reference concentration, is used to correspond to the pumping hydrogen cell number Nh. A heat generation amount to be generated is determined, and an operating point is determined according to the determined heat generation amount. On the other hand, the sweep current as the required current amount is determined using a map that defines the correlation between the sweep current and the number of pumping hydrogen cells Nh, with the exhaust hydrogen concentration as the reference concentration. A configuration may be adopted in which the operating point is determined according to the current. By setting the sweep current amount corresponding to the calculated number of cells using a reference map in which the sweep current is associated with the number of specific cells so that the exhaust hydrogen concentration is equal to or less than the reference concentration, It is possible to control the fuel cell 10 so that the exhaust hydrogen concentration becomes the reference concentration.

(D8) In the third embodiment, the reference density is predetermined. On the other hand, for example, a configuration may be adopted in which the reference density is variably set according to the temperature. When the reference concentration is set variably, the reference map of the reference concentration after change is used to define the correlation between the required calorific value and the number of pumping hydrogen cells Nh for each reference concentration. is used to determine the amount of heat generated corresponding to the number of pumping hydrogen cells Nh, and the operating point is determined according to the determined amount of heat generated.

(D9) In the third embodiment, the total air flow rate Va is fixed during warm-up operation. Alternatively, the total air flow rate Va may be set variably. When this total air flow rate Va is set variably, the total air flow rate after change is determined by using a predetermined correlation between the number of pumping hydrogen cells Nh and the required calorific value for each total air flow rate Va. By acquiring the required heat generation amount corresponding to Va and operating the fuel cell 10 with the acquired required heat generation amount as the target value, the exhaust hydrogen concentration Ch can be made equal to or lower than the reference concentration.

(D10) In the third embodiment, the control unit 80 controls the fuel cell 10 at one operating point on the equal power line PL during warm-up operation. Alternatively, the target power generation amount may be variably set. In the case of a configuration in which the target power generation amount is variably set, a new target power generation amount is determined, a reference map including a plurality of equal power lines PL is used, and the reference map is used to determine the new target heat generation amount and , the operating point corresponding to the new required heat generation amount is set to the operating point after the change.

(D11) In the third embodiment, the exhaust hydrogen concentration control process is performed during warm-up operation, but the exhaust hydrogen concentration control process may be performed during normal operation. For example, when the fuel cell system 100 includes a secondary battery that functions as a power source for the fuel cell system 100, and when it is desired to limit the charge/discharge amount of the secondary battery, the fuel cell 10 is set to a low efficiency operating point. The exhaust hydrogen concentration control process may be performed when the engine is operated by As a result, the exhaust hydrogen concentration Ch can be made equal to or lower than the reference concentration while limiting the output current and suppressing the generation of surplus electric power.

(D12) In the above third embodiment, the pumping hydrogen amount Vh is calculated using equation (4). The pumping hydrogen amount Vh may be calculated by the formula (1), as in the first embodiment, instead of the formula (4).

(D13) In the third embodiment, the reference rate for changing the operating point is, for example, 12 [kw/sec] for both the rising rate and the falling rate. The reference rate is not limited to this value, and the rising rate and falling rate may be different values.

(D14) In the third embodiment, the rotation speed of the air compressor 23 is fixed at a predetermined value, and the total air flow rate Va supplied to the fuel cell system 100 is fixed at a predetermined value. In contrast, during warm-up operation, the rotation speed of the air compressor 23 may be changed. When the rotation speed of the air compressor 23 is changed, the total air flow rate Va is also changed. When the rotation speed of the air compressor 23 is changed and the total air flow rate Va is changed, for example, the following configuration may be applied. A map defining the correlation between the amount of heat generated and the number of pumping hydrogen cells Nh is stored in advance in the storage device 81 for each total air flow rate Va so that the exhaust hydrogen concentration Ch becomes the reference concentration. In the map corresponding to the total air flow rate Va corresponding to the rotation speed of the air compressor 23 after the change, the calorific value corresponding to the pumping hydrogen cell number Nh is set as the required calorific value. As a result, the fuel cell 10 can be controlled so that the exhaust hydrogen concentration Ch becomes the reference concentration.

The present disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from the scope of the present disclosure. For example, the technical features of the embodiments corresponding to the technical features in each form described in the outline of the invention are used to solve some or all of the above problems, or Alternatively, replacements and combinations can be made as appropriate to achieve all. Also, if the technical features are not described as essential in this specification, they can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10... Fuel cell 11... Current sensor 12... Voltage sensor 14... Temperature sensor 20... Oxidant gas system circuit 21... Oxidant gas supply pipe 22... Air cleaner 23... Air compressor 24... Bypass pipe 25... Oxidation off-gas discharge pipe 26 Oxidation gas supply valve 27 Bypass valve 28 Cathode off-gas exhaust valve 40 Fuel gas system circuit 41 Fuel gas supply pipe 42 Fuel gas tank 43 Main stop valve 44 Pressure regulating valve 45 Injector 46 Fuel exhaust gas pipe 47 Gas-liquid separator 48 Exhaust drain valve 49 Circulation pipe 50 Reflux pump 52 Muffler 60 Cooling system circuit 61 Refrigerant Supply pipe 64 Radiator 65 Refrigerant pump 71 Load 72 DC/DC converter 80 Control unit 81 Storage device 90 Cell 100 Fuel cell system

Claims (9)

a fuel cell in which cells are stacked;
a voltage sensor that detects voltage in units of one or more of the cells;
A control unit that determines an operating point of the fuel cell and operates the fuel cell, the control unit operating the fuel cell at a low-efficiency operating point that is lower in efficiency than a reference operating point during warm-up operation of the fuel cell. and
The control unit
A fuel cell system for calculating, during the warm-up operation, the total number of cells in which the voltage detected by the voltage sensor is equal to or lower than a predetermined first reference voltage, and calculating the concentration of exhaust hydrogen using the total number of cells. The fuel cell system of claim 1, further comprising:
a temperature sensor that detects the temperature of the fuel cell;
a storage device that stores a map in which a correction coefficient for the current temperature of the fuel cell is associated with each start-up temperature of the fuel cell, the map having a larger correction coefficient value as the start-up temperature is lower; prepared,
The control unit
storing the starting temperature obtained from the temperature sensor at the time of starting, using the map to obtain the correction coefficient corresponding to the starting temperature and the current temperature obtained from the temperature sensor;
A fuel cell system for calculating the exhaust hydrogen concentration using a value obtained by multiplying the total number of sheets by the correction coefficient. 3. The fuel cell system according to claim 1 or 2,
The control unit
A fuel cell system for executing hydrogen concentration reduction processing when the exhaust hydrogen concentration is higher than a predetermined reference concentration. The fuel cell system according to any one of claims 1 to 3,
The voltage sensor is
a first voltage sensor that detects the voltage of one of the cells;
a second voltage sensor that detects voltages of the two cells;
The control unit
when the voltage detected by the first voltage sensor is equal to or lower than the first reference voltage, counting the cell having the voltage equal to or lower than the first reference voltage as one;
when the voltage detected by the second voltage sensor is equal to or lower than the first reference voltage, counting the number of cells equal to or lower than the first reference voltage as two;
When the voltage detected by the second voltage sensor is greater than the first reference voltage and is less than or equal to a predetermined second reference voltage that is greater than the first reference voltage, the cell that is less than or equal to the first reference voltage is counted as one,
A fuel cell system for calculating the total number of sheets. a fuel cell in which cells are stacked;
a voltage sensor that detects voltage in units of one or more of the cells;
a control unit that calculates the number of specific cells, among the stacked cells, for which the voltage detected by the voltage sensor is equal to or lower than a predetermined first reference voltage, and operates the fuel cell using the calculated number of cells; ,
A reference map is stored in which the requested heat generation amount is associated with the number of the specific cells so that the exhaust hydrogen concentration is equal to or lower than the reference concentration, and the required heat generation amount decreases as the number of the specific cells increases. a storage device containing
The control unit
The number of fuel cells is calculated using the detected voltage, the required heat generation amount corresponding to the calculated number of fuel cells is acquired using the reference map, and the fuel cell is operated with the acquired required heat generation amount as a target value. fuel cell system. a fuel cell in which cells are stacked;
a voltage sensor that detects voltage in units of one or more of the cells;
a control unit that calculates the number of specific cells, among the stacked cells, for which the voltage detected by the voltage sensor is equal to or lower than a predetermined first reference voltage, and operates the fuel cell using the calculated number of cells; ,
A reference map is stored in which the required current amount is associated with the number of the specific cells so that the exhaust hydrogen concentration is equal to or lower than the reference concentration, and the required current amount decreases as the number of cells increases. a storage device containing
The control unit
The number of sheets is calculated using the detected voltage, the requested current amount corresponding to the calculated number of sheets is obtained using the reference map, and the fuel cell is operated with the obtained requested current amount as a target value. fuel cell system. A control method for a fuel cell system comprising a voltage sensor that detects voltage in units of one or more cells, comprising:
a step of operating the fuel cell at a low-efficiency operating point that is lower in efficiency than a reference operating point during warm-up of the fuel cell;
calculating the total number of cells whose voltage detected by the voltage sensor is equal to or lower than a predetermined first reference voltage during the warm-up operation, and calculating the exhaust hydrogen concentration using the total number of cells. control method. A control method for a fuel cell system comprising a fuel cell in which cells are stacked and a voltage sensor that detects a voltage in units of one or more of the cells, the method comprising:
calculating the number of specific cells, among the stacked cells, for which the voltage detected by the voltage sensor is equal to or lower than a predetermined first reference voltage;
The required heat generation amount corresponding to the calculated number of cells is calculated using a reference map in which the required heat generation amount is associated with the number of the specific cells, wherein the greater the number of cells, the smaller the required heat generation amount. and operating the fuel cell using the acquired required heat generation amount as a target value. A control method for a fuel cell system comprising a fuel cell in which cells are stacked and a voltage sensor that detects a voltage in units of one or more of the cells, the method comprising:
calculating the number of specific cells, among the stacked cells, for which the voltage detected by the voltage sensor is equal to or lower than a predetermined first reference voltage;
The required current amount corresponding to the calculated number of cells is calculated using a reference map in which the required current amount corresponding to the number of the specific cells is associated, wherein the larger the number of cells, the smaller the required current amount. and operating the fuel cell using the acquired required current amount as a target value.

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