JP2021114457A - Fuel cell system and fuel cell control method - Google Patents

Abstract

To improve the estimation accuracy of estimating exhaust hydrogen concentration.SOLUTION: A fuel cell system includes: a fuel cell with a stack of cells; a voltage sensor that detects a voltage using one or more cells as a unit; and a control unit that determines an operating point of the fuel cell to operate the fuel cell and operates the fuel cell at a low-efficiency operating point that is less efficient than a reference operating point during warm-up operation of the fuel cell. During the warm-up operation, the control unit calculates the total number of cells for which the detection voltage of the voltage sensor is less than or equal to a predetermined first reference voltage and calculates the exhaust hydrogen concentration using the total number of cells.SELECTED DRAWING: Figure 1

Description

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

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

International Publication No. 2011/013226

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

The present disclosure can be realized in the following forms.

(1) According to one form of the present disclosure, a fuel cell system is provided. The fuel cell system is a fuel cell in which cells are stacked, a voltage sensor that detects a voltage in units of one or a plurality of the cells, and a control unit that determines an operating point of the fuel cell and operates the fuel cell. The control unit includes a control unit that operates the fuel cell at a low-efficiency operating point that is less efficient than the reference operating point during the warm-up operation of the fuel cell, and the control unit has the voltage during the warm-up operation. The total number of the cells whose detection voltage of the sensor is equal to or lower than the predetermined first reference voltage is calculated, and the exhaust hydrogen concentration is calculated using the total number of cells. According to this form, the exhaust hydrogen concentration can be estimated accurately by using the total number of cells in which the cell voltage has decreased.
(2) In the fuel system of the above-described embodiment, 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. A storage device that stores a map in which the value of the correction coefficient increases as the starting temperature is lower is provided, and the control unit stores the starting temperature acquired from the temperature sensor at the time of starting and uses the map. Further, the exhaust hydrogen concentration may be calculated by acquiring the correction coefficient corresponding to the starting temperature and the current temperature acquired from the temperature sensor, and using the value obtained by multiplying the total number of sheets by the correction coefficient. good. According to this form, the exhaust hydrogen concentration can be estimated accurately by using the correction coefficient corresponding to the starting temperature.
(3) In the fuel system of the above embodiment, the control unit may execute the hydrogen concentration reduction process when the exhaust hydrogen concentration is higher than a predetermined reference concentration. According to this form, when the exhaust hydrogen concentration estimated with high accuracy is higher than the reference concentration, the exhaust hydrogen concentration can be reduced.
(4) In the fuel system of the above embodiment, the voltage sensor includes a first voltage sensor that detects the voltage of one cell and a second voltage sensor that detects the voltage of the two cells. When the detection voltage of the first voltage sensor is equal to or less than the first reference voltage, the control unit counts the cells having the detection voltage of the first reference voltage or less as one, and the detection voltage of the second voltage sensor becomes one. When the voltage is equal to or less than the first reference voltage, the cells having the first reference voltage or less are counted as two cells, the detection voltage of the second voltage sensor is larger than the first reference voltage, and the first reference voltage is present. When it is equal to or less than a predetermined second reference voltage larger than the voltage, the cells having the first reference voltage or less may be counted as one and the total number of cells may be calculated. According to this form, the total number of cells can be calculated even when one voltage sensor is provided for two cells.
(5) According to one form of the present disclosure, a fuel cell system is provided. The fuel cell system includes a fuel cell in which cells are stacked, a voltage sensor that detects a voltage in units of one or a plurality of the cells, and a voltage sensor in which the detection voltage of the voltage sensor is predetermined among the plurality of cells. A control unit that calculates the number of specific cells that are 1 reference voltage or less and operates the fuel cell using the calculated number, and a request for the number of specific cells so that the exhaust hydrogen concentration is equal to or less than the reference concentration. A reference map to which the calorific value is associated, and a storage device for storing the reference map in which the required calorific value is smaller as the number of sheets is larger, is provided, and the control unit uses the detection voltage. The number of sheets is calculated, the required heat generation amount corresponding to the calculated number of sheets is acquired by using the reference map, and the fuel cell is operated with the acquired required heat generation amount as a target value. According to this form, the exhaust hydrogen concentration is used as a reference by setting the required calorific value corresponding to the calculated total number of sheets as the target value using a reference map defined in advance so that the exhaust hydrogen concentration becomes the reference concentration. It is possible to control the fuel cell that becomes the concentration.
(6) According to one form of the present disclosure, a fuel cell system is provided. In the fuel cell system, a fuel cell in which cells are stacked, a voltage sensor that detects a voltage in units of one or a plurality of the cells, and a voltage sensor in the stacked cells, the detection voltage of the voltage sensor is predetermined. The number of specific cells that is equal to or less than the first reference voltage is calculated, and the calculated number of cells is used to operate the fuel cell. A reference map to which a required current amount is associated, and a storage device for storing a reference map in which the required current amount is smaller as the number of sheets is larger, and the control unit uses the detection voltage. The number of sheets is calculated, the required current amount corresponding to the calculated number of sheets is acquired using the reference map, and the fuel cell is operated with the acquired required current amount as a target value. According to this form, the exhaust hydrogen concentration is used as a reference by setting the required current amount corresponding to the calculated total number of sheets as the target value using a reference map defined in advance so that the exhaust hydrogen concentration becomes the reference concentration. It is possible to control the fuel cell that becomes the concentration.
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-transient recording medium or the like.

It is explanatory drawing which shows the schematic structure of the fuel cell system mounted on a vehicle. It is a flowchart of the exhaust hydrogen determination process which concerns on 1st Embodiment. It is a flowchart of the cell number calculation process which concerns on 1st Embodiment. It is a figure which shows the relationship between the present temperature and the 1st voltage threshold value for every sweep current. It is a figure which shows the relationship between the present temperature and a correction coefficient. It is a figure which shows the relationship between a sweep current and a 1st voltage threshold value. It is a flowchart of the cell number calculation process which concerns on 2nd Embodiment. It is a figure which shows the relationship between the target current and the 2nd voltage threshold value which concerns on 2nd Embodiment. It is a figure explaining the operating point map for determining the target operating point which concerns on 3rd Embodiment. It is a figure which shows the correlation between the number of pumping hydrogen cells for every sweep current and exhaust hydrogen concentration which concerns on 3rd Embodiment. It is a figure which shows the correlation between the calorific value for every exhaust hydrogen concentration and the number of pumping hydrogen cells which concerns on 3rd Embodiment. It is a flowchart of the exhaust hydrogen concentration control processing which concerns on 3rd Embodiment. It is a figure which shows the reference map which defines the correlation between the number of pumping hydrogen cells and the required calorific value which concerns on 3rd 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 oxide gas system circuit 20, a fuel gas system circuit 40, a cooling system circuit 60, a load 71, a control unit 80, a current sensor 11, a voltage sensor 12, and the like. A temperature sensor 14 and a muffler 52 are provided. The fuel cell 10 uses fuel gas and oxidation gas to generate electricity by 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 by a separator (not shown). MEGA is a MEA (Membrane) having an electrode catalyst layer (not shown) that functions as an anode on one surface of an electrolyte membrane (not shown) and an electrode catalyst layer (not shown) that functions as a cathode on the other surface. A gas diffusion layer (not shown) is 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 oxidation gas. The 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 for detecting 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 that detects a voltage in units of one cell 90 is provided. The control unit 80 includes a CPU (central processing unit) and a storage device 81 (not shown), and controls the oxidation gas system circuit 20, the fuel gas system circuit 40, and the cooling system circuit 60. The storage device 81 stores each value such as a program for exhaust gas determination processing described later, each map such as a map defining the first voltage threshold Vs1 used in the exhaust hydrogen determination processing, and the total number of sensors N. .. The voltage sensor 12, the current sensor 11, and the temperature sensor 14 are each connected to the control unit 80. The detected values detected by the current sensor 11, the voltage sensor 12, and the temperature sensor 14 are transmitted to the control unit 80. Each of the voltage sensors 12 is numbered so that the voltage sensor 12 provided in the cell 90 at either end of the fuel cell 10 is number 1. The control unit 80 identifies the detection voltage transmitted from the voltage sensor 12 as the detection voltage received 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 oxidation gas system circuit 20 is a circuit for supplying air to the cathode of the fuel cell 10. The oxidation gas system circuit 20 includes an oxidation gas supply pipe 21, an air cleaner 22, an air compressor 23, a bypass pipe 24, an oxidation off gas discharge pipe 25, an oxidation gas supply valve 26, a bypass valve 27, and a cathode off gas exhaust. It has a valve 28 and. The oxidation gas supply pipe 21 connects the air cleaner 22 and the cathode of the fuel cell 10, that is, the oxidation gas introduction port (not shown). The oxidation-off gas discharge pipe 25 communicates the oxidation-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 oxidation gas supply pipe 21. The oxidation gas supply valve 26 is arranged in the oxidation gas supply pipe 21 and shuts off or allows the supply of air to the fuel cell 10 by opening and closing the flow path of the oxidation gas supply pipe 21. The cathode off-gas exhaust valve 28 is arranged in the oxidation-off gas discharge pipe 25, controls the amount of cathode-off gas discharged from the oxidation-off gas discharge port of the fuel cell 10, and adjusts the back pressure of the fuel cell 10. The bypass pipe 24 connects the oxidation gas supply pipe 21 and the oxidation off gas discharge pipe 25. The bypass valve 27 is arranged in the bypass pipe 24, and cooperates with the air compressor 23 and the cathode off-gas exhaust valve 28 to adjust 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. The exhaust / drain valve 48, the recirculation pipe 49, and the recirculation pump 50 are provided. The fuel gas supply pipe 41 connects the fuel gas tank 42 and the anode of the fuel cell 10, that is, the fuel gas introduction port (not shown). The fuel gas tank 42 stores high-pressure hydrogen gas. In the fuel gas supply pipe 41, 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. The main check valve 43 shuts off or allows 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 for adjusting the supply amount of hydrogen gas 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 the fuel off-gas discharge port (not shown) of the fuel cell 10 and the oxidation-off gas discharge pipe 25. In the fuel exhaust gas pipe 46, a gas-liquid separator 47 and an exhaust drain valve 48 are arranged in order from the fuel cell 10 toward the muffler 52. 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 discharge port 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 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 recirculation pump 50. As a result, unreacted hydrogen contained in the fuel off gas is reused. When the concentration of the gas component other than the hydrogen gas in the fuel off gas becomes high, the exhaust drain valve 48 is opened and the liquid component and the fuel off gas are discharged. 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 through the muffler 52.

The cooling system circuit 60 is a circuit for cooling the fuel cell 10. The cooling system circuit 60 includes a refrigerant supply pipe 61, a radiator 64, and a refrigerant pump 65. The refrigerant flowing through the refrigerant supply pipe 61 is cooled by the radiator 64 and circulates in the fuel cell 10 by the refrigerant pump 65. The refrigerant supply pipe 61 is provided with a temperature sensor 14. Since the temperature of the refrigerant discharged from the fuel cell 10 and the temperature of the fuel cell 10 are substantially equal to each other, the temperature of the refrigerant can be set to the temperature of the fuel cell 10. The temperature sensor may be provided in the fuel cell 10.

The normal operation and the warm-up operation of the fuel cell 10 will be described. In normal operation, power is generated by supplying more air than the theoretical amount required to generate the target output power. On the other hand, in the warm-up operation, in order to reduce the operation efficiency, power generation is performed with an amount of air less than the amount of air supplied in the normal operation. Here, the operating point of the fuel cell 10 controlled in the warm-up operation, which is the operating point when power is generated with an amount of air less than the amount of air supplied in the normal operation, is referred to as a low-efficiency operating point. In the 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 the 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 as to obtain appropriate operating efficiency from the viewpoint of fuel consumption. The operating efficiency is the efficiency required by the amount of fuel gas supplied to the fuel cell 10 and the electric power output from the fuel cell 10. In the warm-up operation, the fuel cell 10 is operated at a low-efficiency operating point whose efficiency is lower than the reference reference operating point among the operating points. Here, the reference operating point is an operating point for operating the fuel cell 10 by supplying more than the theoretical amount of air required to generate the target output power. In the warm-up operation, for example, a target calorific value is set according to the starting temperature of the fuel cell 10, and a target value of a low-efficiency operating point is determined based on the set target calorific value.

Warm-up operation is mainly performed when the outside air temperature is below freezing. Below the freezing point, the water remaining in the fuel cell 10 may freeze, and the flow path of the oxidizing gas of the fuel cell 10 may be blocked. Therefore, the pressure loss of the oxide gas increases, the actual fuel gas supply amount decreases with respect to the target fuel gas supply amount, and the actual cell voltage decreases with respect to the target cell voltage. In addition, pumping hydrogen is generated when the fuel gas supply amount is reduced. Pumping hydrogen is hydrogen generated by hydrogen ions that have moved to the cathode and receive electrons. Since the amount of hydrogen ions transferred to the cathode is proportional to the amount of current swept from the fuel cell 10, the amount of pumped hydrogen generated is proportional to the amount of current swept.

The exhaust hydrogen determination process executed by the control unit 80 will be described with reference to FIG. After the start-up, the control unit 80 repeatedly executes the exhaust hydrogen determination process. The control unit 80 stores the detected temperature of the temperature sensor 14 at the time of starting as the starting temperature at the time of starting the fuel cell 10 in the storage device 81. The control unit 80 determines whether or not warm-up operation is necessary based on the detection value of a temperature sensor (not shown) for detecting the outside air temperature provided in the oxide gas supply pipe 21 (FIG. 1), for example, and warms up. When it is determined that the operation is necessary, the warm-up operation flag is switched on and the warm-up operation is started. Specifically, the control unit 80 starts the oxidation 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 starts power generation to the fuel cell 10. Let me. Further, when the warm-up operation is terminated, the control unit 80 switches the warm-up operation flag to off. The control unit 80 operates the fuel cell 10 at a low-efficiency operating point during warm-up operation.

When the exhaust hydrogen determination process is started, the control unit 80 determines whether or not the fuel cell 10 is in warm-up operation (step S10). The fuel cell 10 refers to the warm-up operation flag, and when the warm-up operation flag is off, it is determined that the fuel cell 10 is not in the warm-up operation (step S10: NO), and this processing routine is terminated. When the warm-up operation flag is on (step S10: YES), the control unit 80 executes the cell number calculation process (step S20).

The cell number calculation process will be described with reference to FIG. The inventors have noted that the amount of pumping hydrogen generated increases as the number of cells 90 in which the cell voltage decreases increases. 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 number calculation process. In the cell number calculation process, it is determined that pumping hydrogen is generated in the cell 90 whose cell voltage is equal to or less than the first voltage threshold value Vs1, and it is estimated that pumping hydrogen is generated in the cell 90 (hereinafter, “pumping hydrogen”). It is specified as "generated cell").

FIG. 4 is a map that defines the first voltage threshold value Vs1 with respect to the current temperature and the sweep current. Here, the sweep current is a 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 value Vs1 [V]. The first voltage threshold value Vs1 is defined for each sweep current. Since the output voltage of the fuel cell 10 becomes smaller as the output current is larger, the first voltage threshold Vs1 is set smaller as the sweep current of the fuel cell 10 is larger. The characteristic line Lb1 is a characteristic line in which the first voltage threshold value Vs1 is set to be 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, a characteristic line such as the characteristic line La1 and the characteristic line Lc1 that reflects the characteristics of the fuel cell 10 in which the cell voltage becomes lower as the current temperature is lower may be used. In this embodiment, the characteristic line La1 is used.

When the control unit 80 starts the cell number calculation process (FIG. 3), the sensor number n indicating the number of the voltage sensor 12 used in this subroutine is set to the initial value of 1, and the cell in which pumping hydrogen is generated is set. The number m of generated cells 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, and sets the first voltage threshold Vs1 (an example of the first reference voltage) corresponding to the current temperature and the sweep current detected by the temperature sensor 14 as the sweep current with the target current as the sweep current. Acquire (step S100). The control unit 80 determines whether or not the detection voltage of the nth voltage sensor 12 is equal to or less than the first voltage threshold value Vs1 (step S110). When the control unit 80 determines that the detected voltage is equal to or less than the first voltage threshold value Vs1 (step S110: YES), it estimates that pumping hydrogen is generated in the target cell, and adds 1 to the number of generated cells m (step S110: YES). Step S120), 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 value Vs1, that is, is larger than the first voltage threshold value Vs1 (step S110: NO), it estimates that pumping hydrogen is not generated in the target cell, and steps 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 sensor 12. (Step S140). When the control unit 80 determines that the sensor number n is not equal to or greater than the total number of sensors N, that is, less than the total number of sensors N (step S140: NO), the control unit 80 returns to step S110 to determine the next voltage sensor 12. When the control unit 80 determines that the sensor number n is equal to or greater than the total number of sensors N (step S140: YES), the control unit 80 has completed the determination of all the voltage sensors 12, and thus terminates this subroutine.

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 or not each value such as the total air flow rate Va used in the formulas (1) to (3) for calculating the exhaust hydrogen concentration, which will be described later, is appropriate. To judge. Examples of the conditions are as shown in (a) to (j). At least one of the items (a) to (j) is used as a criterion. If any one or more of the criteria used is applicable, it is judged that the exhaust hydrogen concentration cannot be estimated.
(A) When the absolute value of the cell voltage is less than or equal to the reference value.
(B) When the cell voltage is less than or equal to the command voltage value.
(C) When the cell voltage does not change within the specified range with respect to the command voltage value.
(D) When the current temperature is below the standard value.
(E) When the absolute value of the air flow rate is less than or equal to the reference value.
(F) When the air flow rate is less than or equal to the command flow rate value.
(G) When the air flow rate does not change within the specified range with respect to the command flow rate value.
(H) When the absolute value of the output current is less than or equal to the reference value.
(I) When the output current is less than or equal to the command current value.
(J) When the output current does not change within the specified range with respect to the command current value.
The air flow rate is, for example, a value estimated from the rotation 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 control unit 80 ends this processing routine. When the control unit 80 determines that the exhaust hydrogen concentration can be determined (step S30: YES), the control unit 80 proceeds to step S40.

Here, the formula for calculating the exhaust hydrogen concentration Ch, which is used in the later steps S50 and S60, will be described. The inventors have noted that the amount of pumping hydrogen generated is proportional to the number of pumping hydrogen cells and the current swept from the fuel cell 10. It is assumed that a current having the same current value flows through each cell 90, and the exhaust hydrogen concentration Ch is calculated using the following equations (1) to (3).
Vh = CF x I / (2 x F) x 22.4 x 60 x Nh ... Equation (1)
Vo = I / (4 × F) × 22.4 × 60 × (Na—Nh) ・ ・ ・ Equation (2)
Ch = Vh / (Va-Vo + Vh) × 100 ... Equation (3)
The formula (1) is a formula for calculating the estimated amount of pumping hydrogen generated (hereinafter, referred to as "pumping hydrogen amount"), and the formula (2) is a formula for calculating the amount of oxygen consumed. The formula (3) is a formula for calculating the exhaust hydrogen concentration Ch, and the pumping hydrogen amount Vh and the oxygen consumption amount Vo calculated by the formulas (1) and (2) are substituted.
The definitions of the parameters in the equations (1) to (3) are as shown below.
Vh: Pumping hydrogen amount [NL / min]
Vo: Oxygen consumption [NL / min]
Ch: Exhaust hydrogen concentration [%]
Va: Total air flow rate [NL / min]
CF: Correction coefficient 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 numerical value "2" in the formula (1) is the number of electrons received from the cathode when two hydrogen ions become one molecule of hydrogen at the cathode. The numerical value "4" in the formula (2) is the number of electrons received from the cathode when one molecule of oxygen becomes water at the cathode. Based on the sweep current I, the amount of charge supplied to the cathode per second is estimated. For example, in the calculation of the pumping hydrogen amount Vh in the formula (1), the number of molecules of the generated pumping hydrogen is calculated from the estimated amount of electric charge by using the Faraday constant. The calculated number of molecules 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, and the amount of pumping hydrogen Vh [NL / min]. Is converted to.

The correction coefficient CF in the equation (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 actually measured value, and is a value obtained by an experiment or the like. ..

As described above, in the cell number calculation process (FIG. 3), the cell 90 whose cell voltage is equal to or less than the first voltage threshold value Vs1 is determined to be the pumping hydrogen generating cell. At the time of judgment, the cell voltage may be clearly divided into two by the pumping hydrogen generating cell and the cell 90 in which pumping hydrogen is presumed not generated (hereinafter, referred to as "pumping hydrogen non-generating cell"). It is ideal. However, in reality, the measured value of the cell voltage is distributed from the vicinity of 0V to the vicinity of the target cell voltage. Therefore, depending on the value of the first voltage threshold value Vs1, the cell 90 in which pumping hydrogen is not actually generated is erroneously counted as the pumping hydrogen generating cell, and the cell 90 in which pumping hydrogen is actually generated is pumped hydrogen. In some cases, the cells may be erroneously counted as non-generated cells. The correction coefficient CF is used to correct such an erroneous count.

FIG. 5 is a map that defines a correction coefficient CF with respect to 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. The characteristic lines Ld1 to Ld3 correspond to different starting temperatures, and the starting temperature is lower in the order of the characteristic line Ld1, the characteristic line Ld2, and the characteristic line Ld3. The starting temperature will be described later.

An erroneous count in which the cell 90 in which pumping hydrogen is actually generated is counted as a cell in which pumping hydrogen is not generated is likely to occur when the temperature of the fuel cell 10 which was below the freezing point shifts to the freezing point or higher. In the warm-up operation, the fuel cell 10 is operated in an operating range in which the amount of change in the output voltage with respect to the amount of change in the air stoichiometric ratio is large. In the warm-up operation, for example, when the supply amount of fuel gas increases in response to the melting of the frozen water in the fuel cell 10, the cell voltage rises significantly. Therefore, although the pumping hydrogen is generated, the actually measured value becomes larger than the first voltage threshold value Vs1, and the cell 90 in which the pumping hydrogen is generated is erroneously counted as the pumping hydrogen non-generating cell.

On the contrary, the erroneous counting in which the cell 90 in which the pumping hydrogen is not actually generated is counted as the pumping hydrogen generating cell is in the vicinity of the sweep current 0A where 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. It is easy to occur. FIG. 6 is a diagram showing the relationship between the sweep current I for each current temperature and the first voltage threshold value Vs1. The horizontal axis of FIG. 6 is the sweep current I [A], and the vertical axis is the first voltage threshold value Vs1 [V]. The characteristic lines La1 to La3 correspond to the current temperatures of −10 ° C., −20 ° C., and −30 ° C., respectively. In the vicinity of 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. Therefore, even a slight detection error tends to cause an erroneous count. For example, when the temperature of the target cell 90 is lower than the detected temperature of the temperature sensor 14, the determination is made using the first voltage threshold value Vs1 corresponding to the current temperature higher than the actual current temperature. In this case, the cell 90 in which pumping hydrogen is not generated is erroneously counted as the pumping hydrogen generating cell.

When the cell 90 in which pumping hydrogen is generated is erroneously counted as a cell in which pumping hydrogen is not generated, it is necessary to correct the counted number of cells to a large value. On the contrary, when the cell 90 in which the pumping hydrogen is not generated is erroneously counted as the pumping hydrogen generating cell, it is necessary to correct the counted number of cells to a small value. The correction coefficient CF is set in consideration of the above-mentioned events.

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

Returning to FIG. 2, when the control unit 80 determines that the exhaust hydrogen concentration can be estimated (step S30: YES), the control unit 80 refers to the map shown in FIG. 5 and refers to the current temperature which is the detection temperature of the temperature sensor 14 and the start time. The correction coefficient CF corresponding to the temperature is acquired (step S40). The control unit 80 substitutes the current current, which is the detection current of the current sensor 11, into the sweep current I, substitutes the value of the number of generated cells m into the number of pumping hydrogen cells Nh, and substitutes the above equations (1) to (3). The exhaust hydrogen concentration Ch is calculated based on (step S50). The exhaust hydrogen concentration Ch calculated by substituting the current current is referred to as the 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 so that the sweep current becomes the target current, but for example, when the water remaining in the fuel cell 10 is not completely melted, a state in which the sweep current does not match the target current may occur. .. The first estimated hydrogen concentration Ca and the second estimated hydrogen concentration Cb may deviate from each other. Therefore, by calculating both the first estimated hydrogen concentration Ca and the second estimated hydrogen concentration Cb and performing concentration determination (steps S70 and S80) based on each, 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, for example, equal to or higher than the concentration threshold value (an example of the reference concentration) based on the environmental standard (step S70). When the control unit 80 determines that the first estimated hydrogen concentration Ca is equal to or higher than the concentration threshold value (step S70: YES), the control unit 80 proceeds to step S90 in order to lower 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 value, that is, is lower than the concentration threshold value (step S70: NO), the control unit 80 determines whether or not the second estimated hydrogen concentration Cb is equal to or higher than the concentration threshold value. (Step S80). When the control unit 80 determines that the second estimated hydrogen concentration Cb is equal to or higher than the concentration threshold value (step S80: YES), the control unit 80 proceeds to step S90 in order to lower 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 value, that is, is lower than the concentration threshold value (step S80: NO), the control unit 80 ends this processing routine. The control unit 80 executes a hydrogen concentration reduction process of changing the operating point of the fuel cell 10 to a highly efficient operating point that is more efficient than the current operating point in order to reduce the generation of pumping hydrogen (step S90). Terminate this processing routine. The hydrogen concentration reduction treatment may be any treatment as long as the hydrogen concentration can be reduced. For example, the hydrogen concentration reduction treatment is a treatment in which the target current value is made smaller than the current set value. As a result, the exhaust hydrogen concentration is reduced.

According to the exhaust hydrogen determination process described above, the pumping hydrogen generating cell is specified based on the detection voltage of the voltage sensor 12, and the exhaust hydrogen concentration Ch is calculated based on the number of pumping hydrogen cells Nh. Therefore, the exhaust hydrogen concentration Ch Can be calculated accurately. The hydrogen concentration reduction process is executed when the exhaust hydrogen concentration Ch is equal to or higher than the concentration threshold value. Since the exhaust hydrogen concentration Ch calculated accurately can be used to determine whether or not to execute the hydrogen concentration reduction treatment, the hydrogen concentration reduction treatment can be executed when the actual exhaust hydrogen concentration is not equal to or higher than the concentration threshold value. It is suppressed. When the exhaust hydrogen concentration Ch is equal to or higher than the concentration threshold value, the operating point is moved to the high efficiency side. Therefore, if the calculation accuracy of the exhaust hydrogen concentration Ch is poor, excessive movement (hunting) of the operating point will occur. By accurately calculating the exhaust hydrogen concentration Ch, excessive movement (hunting) of the operating point can be suppressed. Further, since the hydrogen concentration reduction process is executed during the warm-up operation, it is possible to suppress an increase in the pumping hydrogen amount due to an increase in the sweep current after shifting to the normal operation. The inventors have found that once pumping hydrogen is generated, the catalyst surface of the electrode catalyst layer that functions as a cathode becomes hydrogen-rich, oxygen supply to the catalyst surface is inhibited, and the power generation reaction is inhibited. 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 also increases as the sweep current increases. Therefore, it is possible to suppress an increase in the amount of pumping hydrogen by executing the hydrogen concentration reduction process during the warm-up operation before shifting to the normal operation.

B: Second Embodiment In the first embodiment, the fuel cell system 100 is provided with a voltage sensor 12 that detects a voltage in units of one cell 90. On the other hand, in the fuel cell system according to the second embodiment, among the stacked cells 90, the voltage sensors 12 (hereinafter referred to as the voltage sensors 12) that detect the voltage of the plurality of cells 90 at both ends in units of one cell 90. , "First voltage sensor") is provided. A voltage sensor 12 (hereinafter, referred to as a “second voltage sensor”) for detecting a voltage in units of the two cells 90 is provided for the intermediate cell 90 excluding the plurality of cells 90 at both ends. The detection voltage of the voltage sensor 12 that detects the voltages of the two cells 90 is the sum of the voltages of the respective cells 90. The process of calculating the number of generated cells according to the second embodiment is a process that enables the identification of pumping hydrogen generating cells even in a configuration in which the voltage sensor 12 detects the voltages of the two cells 90. The exhaust gas 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 will be omitted.

When the cell voltage of only one of the two cells 90 detected by the second voltage sensor is low, the detection 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 detection voltage when there is no cell voltage and the detection voltage when the cell voltage of both of the two cells 90 is low. Therefore, using a second voltage threshold value Vs2 larger than the first voltage threshold value Vs1, a second voltage sensor in which only one of the two cells 90 has a lower cell voltage is specified. FIG. 8 is a map that defines the second voltage threshold value 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 value Vs2. The characteristic lines Le1 to Le3 correspond to different current temperatures, and the current temperature is lower in the order of the characteristic line Le1, the characteristic line Le2, and the 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. Therefore, the second voltage threshold value Vs2 is set to a value corresponding to the target voltage. In the cell number calculation process according to the second embodiment, when the detection voltage of the second voltage sensor is larger than the first voltage threshold value and is equal to or less than the second voltage threshold value Vs2, the pumping hydrogen generating cells are counted as one cell. NS.

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 1 as the initial value, and the number of generated cells m is set as the initial value, as in the first embodiment. Set to zero. The control unit 80 acquires the first voltage threshold value Vs1 corresponding to the current temperature and the detected current of the current sensor 11 with reference to the map shown in FIG. 2 (step S210). The control unit 80 acquires the second voltage threshold value Vs2 (an example of the second reference voltage) corresponding to the current temperature and the target current with reference to the map shown in FIG. 8 (step S220).

The control unit 80 sets the number of cells 90 detected by the target nth voltage sensor 12 to the number of cells Nc (step S230). In the case of the first voltage sensor, the number of cells Nc is set to 1, and in the case of the second voltage sensor, the number of cells Nc is set to 2. The control unit 80 determines whether or not the detection voltage of the target nth voltage sensor 12 is equal to or less than the first voltage threshold value Vs1 (step S240). When the control unit 80 determines that the detected voltage is equal to or less than the first voltage threshold value 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. In the case of the first voltage sensor, 1 is added to the number of generated cells m, and in the case of the second voltage sensor, 2 is added to the number of generated cells m.

When the control unit 80 determines that the detection voltage is not equal to or less than the first voltage threshold value Vs1, that is, is larger than the first voltage threshold value Vs1 (step S240: NO), the number of detected cells 90 detected by the target voltage sensor 12 is two. (Step S280). When the control unit 80 determines that the target voltage sensor 12 is the first voltage sensor and the number of detected voltage sensors is not two (step S280: NO), the process proceeds to step S260. When the control unit 80 determines that the number of detected elements is two (step S280: YES), the control unit 80 determines whether or not the target nth detected voltage is equal to or less than the second voltage threshold value Vs2 (step S290). .. When the control unit 80 determines that the detected voltage is not equal to or less than the second voltage threshold value Vs2, that is, is larger than the second voltage threshold value Vs2 (step S290: NO), the control unit 80 proceeds to step S260. When the control unit 80 determines that the detected voltage is equal to or less than the second voltage threshold value Vs2 (step S290: YES), the control unit 80 adds 1 to the number of generated cells 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 or not the sensor number n is equal to or greater than the total number of sensors N of the voltage sensor 12. (Step S270). When the control unit 80 determines that the sensor number n is not equal to or greater than the total number of sensors N, that is, less than the total number of sensors N (step S270: NO), the control unit 80 returns to step S230 to determine the next voltage sensor 12. When the control unit 80 determines that the sensor number n is equal to or greater than the total number of sensors N (step S270: YES), the control unit 80 has completed the determination of all the voltage sensors 12, and thus terminates this subroutine.

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

C. Third Embodiment In the third embodiment, the fuel cell 10 is set to an operating point where the exhaust hydrogen concentration Ch is equal to or lower than the reference concentration by using a reference map defined in advance so that the exhaust hydrogen concentration Ch is equal to or lower than the reference concentration. Is controlled. 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 in the warm-up operation of the fuel cell 10. The operating point determined using FIG. 9 is an operating point in warm-up operation, and as described above, is a low-efficiency operating point whose efficiency is lower than the reference operating point. 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 an equal power line PL showing an operating point having the same amount of power generation and an equal Q line QL1 and QL2 showing an operating point having the same amount of heat generation. Here, the calorific value is the calorific value per hour generated by the power generation of the fuel cell 10. The equivalence Q lines QL1 and QL2 have different calorific values, the equivalence Q line QL1 has a calorific value qmax, and the equivalence Q line QL2 has 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 calorific value is determined, and the target operating point is determined according to the determined target calorific value. Specifically, the intersection of the equal Q line of the target calorific value and the equal power line of the target power generation is set as the target operating point. In the warm-up operation, since the fuel cell 10 is operated in the operating range in which the amount of change in the output voltage with respect to the amount of change in the air stoichiometric ratio is large, the target power generation amount is fixed to a predetermined value. .. That is, the operating point in the warm-up operation is set to the operating point on the equal power line PL shown in FIG. Further, the rotation speed of the air compressor 23 is fixed to a predetermined value, and the total air flow rate Va supplied to the fuel cell system 100 is fixed to 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, the warm-up operation is started at the target operating point according to the calorific value qmax. Specifically, the operation is started at the target operating point OP1 which is the intersection of the equal Q line QL1 and the equal power line PL, which is the calorific value qmax. The target amount of power generation per hour in warm-up operation is, for example, 10.3 kW. 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 by using the formula (3) using the number of pumping hydrogen cells Nh, the sweep current I, and the like. Here, the sweep current I is a current taken out from the fuel cell 10 by the DC / DC converter 72. 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. Further, 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. Specifically, the total amount of the air flow rate supplied to the fuel cell 10 and the air flow rate flowing through the bypass pipe 24. Is. Here, in the third embodiment, the pumping hydrogen amount Vh substituted into the formula (3) is calculated using the following formula (4). Equation (4) is different from equation (1) in that there is no correction coefficient CF included in equation (1).
Vh = I / (2 x F) x 22.4 x 60 x Nh ... Equation (4)
As described above, in the cell 90 in which pumping hydrogen is generated, the cell voltage drops. Therefore, in the first embodiment, cells 90 having a cell voltage greater than 0V and equal to or less than the first voltage threshold Vs1 are counted, and a correction coefficient CF is used to, for example, a cell 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 value Vs1 is set to, for example, 0V, and the cell 90 having a cell voltage of 0V or less is counted as a pumping hydrogen generating cell. Then, the pumping hydrogen amount Vh is calculated without performing the correction using the correction coefficient CF. Substituting equations (4) and (2) into equation (3) and rearranging them gives the following equation (5).
Ch = 2Nh / (4F / I × Va / (22.4 × 60) -Na + 3Nh) ... Equation (5)

Here, when the total air flow rate Va is set to a fixed value, the inventors can calculate the exhaust hydrogen concentration Ch based on the number of pumping hydrogen cells Nh and the sweep current I, so that each exhaust hydrogen concentration Ch It was noted that the correlation between the number of pumping hydrogen cells 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, where the exhaust hydrogen concentration Ch is equal to or less than the reference concentration, the fuel cell 10 is operated at the operating point where the sweep current I is obtained to obtain the exhaust hydrogen concentration Ch. 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. It will be described in detail below.

FIG. 10 is a diagram showing the correlation between the number of pumping hydrogen cells Nh and the exhaust hydrogen concentration Ch for each sweep current I calculated using the equation (5). The characteristic lines L1 to L5 have a sweep current I of i1 to i5, respectively, and the current value of the sweep current I gradually increases in the order of the characteristic lines L1, L2, L3, L4, and L5. As shown in FIG. 10, when the number of pumping hydrogen cells 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 larger the number of pumping hydrogen cells Nh, the higher the exhaust hydrogen concentration Ch.

FIG. 11 is a map that defines the correlation between the calorific value and the number of pumping hydrogen cells Nh for each exhaust hydrogen concentration. The map shown in FIG. 11 is a map including a reference map used in the exhaust hydrogen concentration control process, as will be described later. The reference map is a map when the fuel cell 10 is generated at an operating point on the 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 the formula (5), when the total air flow rate Va and the total number of cells Na are fixed values, the exhaust hydrogen concentration Ch is calculated by using the sweep current I and the number of pumping hydrogen cells Nh. As described above, in the present embodiment, the target calorific value is determined, the target operating point is determined according to the target calorific value, and the fuel cell 10 is controlled to the determined target operating point. Therefore, in the map shown in FIG. 11, the correlation between the calorific value and the number of pumping hydrogen cells Nh is defined instead of the sweep current I. In the present embodiment, in the warm-up operation, the control unit 80 operates the fuel cell 10 at the operating point on the equal power line PL, so that the sweep current I and the required heat generation amount can be associated one-to-one with each other. .. Therefore, the correlation between the calorific value and the number of pumping hydrogen cells Nh can be defined in advance. Specifically, the conversion from the sweep current I to the calorific value can be performed using, for example, the operating point map shown in FIG. As shown in FIG. 10, if the number of pumping hydrogen cells Nh and the exhaust hydrogen concentration Ch are determined, the sweep current I is uniquely determined. Then, as shown in FIG. 9, if the sweep current I is determined, the calorific value 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 concentration Ch gradually increases 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 less, the operating point of the fuel cell 10 may be set to an operating point where the larger the number of pumping hydrogen cells Nh, the smaller the calorific value.

The exhaust hydrogen concentration control process according to the third embodiment will be described with reference to FIG. The same steps as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate. After the start-up, 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 the present embodiment, the first voltage threshold value Vs1 is set to, for example, 0V. Using the reference map shown in FIG. 13, the control unit 80 acquires the required calorific value corresponding to the number of pumping hydrogen cells Nh calculated in step S20 at a predetermined reference concentration (step S400).

In the reference map shown in FIG. 13, the calorific value qmax and the characteristic line CL3 in which the exhaust hydrogen concentration Ch is the concentration c3 among the characteristic lines CL1 to CL6 shown in FIG. 11 are shown. The axes of FIGS. 11 and 13 are different, the horizontal axis of FIG. 13 is the number of pumping hydrogen cells Nh, and the vertical axis is the required calorific value [kW]. In the present embodiment, a fixed concentration is set in advance as the reference concentration, and the reference concentration is the concentration c3. The storage device 81 stores in advance a reference map having an exhaust hydrogen concentration of c3. By using the reference map in which the exhaust hydrogen concentration is the concentration c3, the control unit 80 can acquire the required calorific value corresponding to the number of pumping hydrogen cells Nh, which is the reference concentration.

After executing step S400 (FIG. 12), the control unit 80 executes rate processing with the required calorific value as a target value (step S410). In the rate processing, in the process of changing from the operating point corresponding to the current target calorific value to the operating point corresponding to the new target calorific value, the change rate, which is the amount of change in the calorific value per unit time, is predetermined. This is a process that uses the reference rate. Here, the reference rate is, for example, 12 [kW / sec] for both the ascending rate and the descending rate. By executing the rate processing, it is possible to suppress a sudden change in the calorific value. Specifically, the control unit 80 adjusts the air flow rate to the fuel cell 10 by adjusting the opening degree of the bypass valve 27, and uses, for example, a DC / DC converter 72 to reduce the sweep current of the fuel cell 10. The operating point of the fuel cell 10 is switched by changing the rate according to the reference rate. For example, as shown in FIG. 13, when the number of pumping hydrogen cells Nh is na, the required calorific value acquired in step S400 is the calorific value qa. In this case, as shown in FIG. 9, the operating point corresponding to the new target calorific value is the target operating point OP2. Therefore, when the current operating point is the target operating point OP1, the operating point is switched toward the new target operating point OP2 along the isopower line PL. When there is a cell 90 in which pumping hydrogen is generated, the sweep current I is reduced by switching to a more efficient operating point, so that the exhaust hydrogen concentration Ch is reduced. Further, for example, when the temperature of the fuel cell 10 rises and the number of pumping hydrogen cells Nh decreases, the operating point is switched from, for example, the target operating point OP2 to the target operating point OP1. In this case, the exhaust hydrogen concentration is maintained below the reference concentration, and the amount of heat generated is controlled to be larger. As described above, by executing steps S20, S400, and S410 during the warm-up operation, the exhaust hydrogen concentration is maintained below the reference concentration, and the calorific value is controlled to be as large as possible. The warm-up time can be shortened.

According to the third embodiment described above, the number of specific cells is set so that the exhaust hydrogen concentration Ch calculated accurately using the number of pumping hydrogen cells Nh as the number of specific cells is equal to or less than the reference concentration. By setting the calorific value corresponding to the calculated pumping hydrogen cell number Nh as the required calorific value using the reference map associated with the required calorific value for the pumping hydrogen cell number Nh, the exhaust hydrogen concentration Ch becomes the reference concentration. The fuel cell 10 can be controlled.

D. Other embodiments:
(D1) In the exhaust gas determination process according to the first embodiment, the first estimated hydrogen concentration Ca and the second estimated hydrogen concentration Cb are calculated and compared with the concentration threshold value. 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 when any of the calculated concentrations is equal to or higher than the concentration threshold value. It may be the content. As a result, the processing steps can be reduced and the load related to the exhaust hydrogen determination processing can be reduced.

(D2) The cell number 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 that detects a voltage in units of two cells 90. be. Also in the fuel cell system provided with the voltage sensor 12 that detects the voltage in units of three or more cells 90, the reference voltage used for determining whether or not pumping hydrogen is generated is increased, and the second embodiment The number of pumping hydrogen cells can be counted by the same method as in. For example, in the case of a configuration including a voltage sensor 12 that detects a voltage in units of three cells 90, a first for identifying a voltage sensor 12 in which 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 cells 90 out of the three cells 90 to be detected, and pumping hydrogen in one cell 90. The number of pumping hydrogen cells can be counted by using the reference voltage for characterizing the voltage sensor 12 in which the above is generated.

(D3) In the first embodiment, a different correction coefficient CF is applied depending on the starting temperature (see FIG. 5). On the other hand, the same correction coefficient may be applied regardless of the starting temperature. As a result, the processing load can be reduced.

(D4) In the second embodiment, different second voltage thresholds Vs2 are applied depending on the current temperature (see FIG. 8). On the other hand, the configuration may be such that the same second voltage threshold value Vs2 is applied regardless of the current temperature. As a result, 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, a process of increasing the air flow rate flowing through the bypass pipe 24 and lowering the hydrogen concentration may be executed without changing the operating point of the fuel cell 10.

(D6) The hydrogen concentration reduction treatment in the first embodiment is, for example, a treatment in which the target current value is made smaller than the current set value. In addition, as the hydrogen concentration reduction treatment, 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 third embodiment, the pumping hydrogen cell number Nh is supported by using a reference map in which the correlation between the required calorific value and the pumping hydrogen cell number Nh is defined, where the exhaust hydrogen concentration is the reference concentration. The calorific value to be generated is determined, and the operating point according to the determined calorific value is determined. On the other hand, the sweep current as the required current amount is determined by using a map that defines the correlation between the sweep current and the number of pumping hydrogen cells Nh, where the exhaust hydrogen concentration is the reference concentration, and the determined sweep. The configuration may be such that the operating point is determined according to the current. By setting the sweep current amount corresponding to the calculated number of sheets to the required current amount using the reference map associated with the sweep current for 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 having the exhaust hydrogen concentration as a reference concentration.

(D8) In the third embodiment, the reference concentration is predetermined. On the other hand, for example, the reference concentration may be variably set according to the temperature or the like. When this reference concentration is set variably, the reference map of the changed reference concentration is used for each reference concentration, using a reference map that defines the correlation between the required calorific value and the number of pumping hydrogen cells Nh. It is preferable that the processing content is such that the calorific value corresponding to the number of pumping hydrogen cells Nh is determined by using the above, and the operating point is determined according to the determined calorific value.

(D9) In the third embodiment, the total air flow rate Va is fixed in the warm-up operation. On the other hand, 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 the change is changed 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 calorific value corresponding to Va and operating the fuel cell 10 with the acquired required calorific value as the target value, the exhaust hydrogen concentration Ch can be set to the reference concentration or less.

(D10) In the third embodiment, the control unit 80 controls the fuel cell 10 at an operating point on one equal power line PL in the warm-up operation. On the other hand, the target power generation amount may be set variably. In the case of a configuration in which this target power generation amount is set variably, 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 set a new target heat generation amount. , It is advisable to set the operating point corresponding to the new required heat generation amount as the changed operating point.

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

(D12) In the third embodiment, the pumping hydrogen amount Vh is calculated using the formula (4). The pumping hydrogen amount Vh may be calculated not by the formula (4) but by the formula (1) as in the first embodiment.

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

(D14) In the third embodiment, the rotation speed of the air compressor 23 is fixed to a predetermined value, and the total air flow rate Va supplied to the fuel cell system 100 is fixed to a predetermined value. On the other hand, in the 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 also changes. 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. For each total air flow rate Va, a map defining the correlation between the calorific value and the number of pumping hydrogen cells Nh, in which the exhaust hydrogen concentration Ch becomes the reference concentration, is stored in the storage device 81 in advance. In the map corresponding to the total air flow rate Va according to the changed rotation speed of the air compressor 23, the calorific value corresponding to the number of pumping hydrogen cells Nh is set as the required calorific value. As a result, it is possible to control the fuel cell 10 in which the exhaust hydrogen concentration Ch becomes the reference concentration.

The present disclosure is not limited to the above-described embodiment, and can be realized by various configurations within a range not deviating from the gist thereof. For example, the technical features of the embodiments corresponding to the technical features in each embodiment described in the column of the outline of the invention are for solving a part or all of the above-mentioned problems, or a part of the above-mentioned effects. Alternatively, they can be replaced or combined as appropriate to achieve all of them. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

10 ... Fuel cell, 11 ... Current sensor, 12 ... Voltage sensor, 14 ... Temperature sensor, 20 ... Oxidation gas circuit, 21 ... Oxidation 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 pipe, 47 ... Gas-liquid separator, 48 ... Exhaust drain valve, 49 ... Reflux pipe, 50 ... Recirculation pump, 52 ... Muffler, 60 ... Cooling system circuit, 61 ... Refrigerator 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 with stacked cells and
A voltage sensor that detects voltage in units of one or more of the cells, and
A control unit that determines the operating point of the fuel cell and operates the fuel cell, and controls the operation of the fuel cell at a low-efficiency operating point that is less efficient than the reference operating point during warm-up operation of the fuel cell. With a department,
The control unit
A fuel cell system that calculates the total number of cells whose detection voltage of the voltage sensor is equal to or lower than a predetermined first reference voltage during the warm-up operation, and calculates the exhaust hydrogen concentration using the total number of cells. The fuel cell system according to claim 1, further
A temperature sensor that detects the temperature of the fuel cell and
A storage device that stores a map in which a correction coefficient with respect to the current temperature of the fuel cell is associated with each starting temperature of the fuel cell, and the value of the correction coefficient increases as the starting temperature decreases. Prepare,
The control unit
The starting temperature acquired from the temperature sensor at the time of starting is stored, and the correction coefficient corresponding to the starting temperature and the current temperature acquired from the temperature sensor is acquired using the map.
A fuel cell system that calculates the exhaust hydrogen concentration using a value obtained by multiplying the total number of sheets by the correction coefficient. The fuel cell system according to claim 1 or 2.
The control unit
A fuel cell system that executes a hydrogen concentration reduction process 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,
Includes a second voltage sensor that detects the voltage of the two cells.
The control unit
When the detection voltage of the first voltage sensor is equal to or less than the first reference voltage, the cells having the first reference voltage or less are counted as one cell.
When the detection voltage of the second voltage sensor is equal to or less than the first reference voltage, the cells having the first reference voltage or less are counted as two cells.
When the detection voltage of the second voltage sensor is larger than the first reference voltage and is greater than or equal to the first reference voltage and is equal to or less than a predetermined second reference voltage, the cell is equal to or less than the first reference voltage. Is counted as one sheet,
A fuel cell system that calculates the total number of sheets. A fuel cell with stacked cells and
A voltage sensor that detects voltage in units of one or more of the cells, and
A control unit that calculates the number of specific cells in which the detection voltage of the voltage sensor is equal to or lower than a predetermined first reference voltage among the stacked cells, and operates the fuel cell using the calculated number of cells. ,
A reference map in which the required calorific value for the number of sheets of the specific cell is associated so that the exhaust hydrogen concentration is equal to or less than the reference concentration, and the reference map in which the required calorific value is smaller as the number of sheets is larger is stored. With a storage device,
The control unit
The number of sheets is calculated using the detected voltage, the required heat generation amount corresponding to the calculated number of sheets 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 with stacked cells and
A voltage sensor that detects voltage in units of one or more of the cells, and
A control unit that calculates the number of specific cells in which the detection voltage of the voltage sensor is equal to or lower than a predetermined first reference voltage among the stacked cells, and operates the fuel cell using the calculated number of cells. ,
A reference map in which the required current amount for the number of sheets of the specific cell is associated so that the exhaust hydrogen concentration is equal to or less than the reference concentration, and the reference map in which the required current amount is smaller as the number of sheets is larger is stored. With a storage device,
The control unit
The number of sheets is calculated using the detected voltage, the required current amount corresponding to the calculated number of sheets is acquired using the reference map, and the fuel cell is operated with the acquired required current amount as a target value. Fuel cell system. A control method for a fuel cell system including a voltage sensor that detects a voltage in units of one or more cells.
The process of operating the fuel cell at a low-efficiency operating point, which is less efficient than the reference operating point during warm-up operation of the fuel cell, and
The step includes a step of calculating the total number of cells in which the detection voltage of 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 method for controlling a fuel cell system including a fuel cell in which cells are stacked and a voltage sensor that detects a voltage in units of one or a plurality of the cells.
A step of calculating the number of specific cells in which the detection voltage of the voltage sensor is equal to or less than a predetermined first reference voltage among the stacked cells.
It is a reference map in which the required heat generation amount is associated with the number of the specific cells, and the required heat generation amount corresponding to the calculated number of sheets is calculated by using the reference map in which the required heat generation amount is smaller as the number of the number is larger. A control method comprising a step of acquiring and operating the fuel cell with the acquired required calorific value as a target value. A method for controlling a fuel cell system including a fuel cell in which cells are stacked and a voltage sensor that detects a voltage in units of one or a plurality of the cells.
A step of calculating the number of specific cells in which the detection voltage of the voltage sensor is equal to or less than a predetermined first reference voltage among the stacked cells.
It is a reference map in which the required current amount is associated with the number of the specific cells, and the required current amount corresponding to the calculated number of sheets is calculated by using the reference map in which the required current amount is smaller as the number of the number is larger. A control method comprising a step of acquiring and operating the fuel cell with the acquired required current amount as a target value.

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