JP2013062097A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system which, while preventing the degradation of a fuel cell, can control the output of the fuel cell flexibly.SOLUTION: Power generation control means 24 of an FC vehicle 10 executes both modes of control: power generation amount increase control in which, when the requested power of a load 14 rises, the supply amount of at least one of oxygen and hydrogen to an FC unit 18 is increased while an FC current remains fixed, to raise an FC voltage out of an oxidoreduction progress voltage range, whereby the power generation amount of the FC unit 18 is increased; and power generation amount reduction control in which, when the requested power of the load 14 drops, the supply amount of at least one of oxygen and hydrogen to the FC unit 18 is reduced while the FC current remains fixed, to lower the FC voltage out of the oxidoreduction progress voltage range, whereby the power generation amount of the FC unit 18 is reduced.

Description

  The present invention relates to a fuel cell system that supplies power from a fuel cell to a load.

  Conventionally, in order to suppress deterioration of a fuel cell used in a fuel cell vehicle or the like, a fuel cell system that generates power by avoiding a specific voltage region has been proposed (Patent Document 1).

  Patent document 1 makes it a subject to implement | achieve deterioration suppression of a fuel cell, and maintenance of system efficiency in a fuel cell system with the output restriction request | requirement of a fuel cell (summary, [0006]). In order to solve the problem, the fuel cell system 1 of Patent Document 1 includes a fuel cell 2 that generates power upon receiving supply of a reaction gas, and a flow rate control unit 6 that controls a supply flow rate of the reaction gas to the fuel cell 2. The operation is switched between the first operation mode and the second operation mode having a lower efficiency than the first operation mode. The flow rate control means 6 controls the supply flow rate of the reaction gas so as to suppress the output voltage of the fuel cell 2 below the high potential avoidance voltage in the first operation mode when there is no output restriction request. Only when there is a restriction request, the supply flow rate of the reaction gas is controlled so as to switch the operation from the first operation mode to the second operation mode while maintaining the output voltage of the fuel cell 2 below the high potential avoidance voltage. (Summary)

JP 2010-157426 A

  As described above, in the first operation mode of Patent Document 1, the supply flow rate of the reaction gas is controlled so as to suppress the output voltage of the fuel cell 2 to be equal to or lower than the high potential avoidance voltage. In this control, when the low output state of the fuel cell 2 continues, it is necessary to maintain the output voltage of the fuel cell 2 at the high potential avoidance voltage (see FIGS. 2 and 3). When the state where the output voltage is the high potential avoidance voltage is maintained, the deterioration of the fuel cell 2 may proceed relatively depending on the setting of the high potential avoidance voltage.

  Further, for example, depending on the use situation of the motor, it may be necessary to make the output current of the fuel cell constant. However, in the control of Patent Document 1, it is necessary to reduce the output current in order to maintain the power generated by the fuel cell while maintaining the output voltage at the high potential avoidance voltage. I can not cope.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a fuel cell system capable of flexibly performing output control of a fuel cell while preventing deterioration of the fuel cell. .

  A fuel cell system according to the present invention includes a fuel cell that has a catalyst and generates power by reacting oxygen or hydrogen with the catalyst, and a gas supply unit that supplies at least one of the oxygen and the hydrogen to the fuel cell. And a voltage control means for controlling the output voltage of the fuel cell, a load driven by the power generated by the fuel cell, and a power generation control means for controlling the power generation amount of the fuel cell, The control means increases the supply amount of at least one of the oxygen and the hydrogen to the fuel cell in a state where the output current of the fuel cell is fixed when the required power of the load increases, and the output of the fuel cell A power generation amount increase control for increasing the power generation amount of the fuel cell by increasing the voltage outside the oxidation-reduction progress voltage range; In a state where the output current of the fuel cell is fixed, the supply amount of at least one of the oxygen and the hydrogen to the fuel cell is decreased, and the output voltage of the fuel cell is decreased outside the redox advance voltage range. Both the power generation amount reduction control for reducing the power generation amount of the fuel cell is executed.

  According to the present invention, it is possible to flexibly perform output control of a fuel cell while preventing deterioration of the fuel cell.

  That is, in both the power generation amount increase control and the power generation amount decrease control, the output voltage of the fuel cell is changed outside the oxidation-reduction progress voltage range. For this reason, it is possible to prevent deterioration due to the output voltage of the fuel cell being within the redox progressing voltage range. In both the power generation amount increase control and the power generation amount decrease control, the supply amount of at least one of oxygen and hydrogen and the output voltage of the fuel cell are changed while the output current of the fuel cell is fixed. Thereby, for example, even when the output of the fuel cell is low, the output voltage of the fuel cell can be changed. Therefore, compared with the case where the output voltage of the fuel cell is fixed near the oxidation-reduction progress voltage range, the fuel cell It is possible to increase the degree and frequency with which the output voltage of the battery moves away from the oxidation-reduction progress voltage range. Accordingly, it is possible to suitably suppress the deterioration of the fuel cell. Further, since the power generation amount of the fuel cell is changed in a state where the output current of the fuel cell is fixed, it can be suitably used when it is desired to change the size of the load while keeping the current supplied to the load constant.

  The fuel cell system is mounted on a vehicle, the fuel cell system further includes a power storage device that assists the output of the fuel cell, and the gas supply means supplies air to the fuel cell via an air supply pipe. An air pump to be supplied; an air return pipe branched from the air discharge pipe; communicated with the air supply pipe on the upstream side of the air pump; and returning the air off gas discharged from the fuel cell to the air supply pipe; And an adjustment device that adjusts the recirculation amount of the air-off gas in the piping, and the control means controls the adjustment device while keeping the drive amount of the air pump constant when the vehicle is in a predetermined low load state. The power generation amount increase control and the power generation amount decrease control may be performed by adjusting the recirculation amount of the air-off gas.

  According to this invention, when the vehicle is in a predetermined low load state, the driving amount of the air pump is made constant. For this reason, the output sound of the air pump does not change unexpectedly when the air pump stops when the amount of power stored in the power storage device reaches the set upper limit value in the low load state. Therefore, it is possible to appropriately maintain the amount of power stored in the power storage device without giving a sense of incongruity to the passenger about the output sound of the air pump in a low load state.

  Further, not only the driving amount of the air pump is made constant, but also the adjusting device is controlled to adjust the recirculation amount of the air off gas. Since the air-off gas has a low oxygen concentration, if the amount of air-off gas recirculation is increased, the amount of water generated inside the fuel cell is reduced, and the fuel cell is dried. When the inside of the fuel cell becomes dry, the deterioration of the fuel cell may be promoted. On the other hand, since the air off gas has passed through the inside of the fuel cell that generates moisture, it contains a relatively large amount of moisture. For this reason, by adjusting the recirculation amount of the air-off gas, the electrolyte membrane of the fuel cell can be favorably humidified, and deterioration of the fuel cell can be suppressed.

  Furthermore, the amount of power stored in the power storage device can be managed by reducing the generated current of the fuel cell in accordance with a predetermined low load state while obtaining the above effects (for example, exceeding the set upper limit value of the amount of stored power). Control and avoid unnecessary charging).

  The change rate of the output voltage of the fuel cell may be limited during execution of at least one of the power generation amount increase control and the power generation amount decrease control. When the output voltage of the fuel cell is suddenly changed, the fuel cell may be deteriorated. However, according to the above configuration, rapid fluctuations in the output voltage can be suppressed, so that deterioration of the fuel cell is suppressed. Is possible.

  According to the present invention, it is possible to flexibly perform output control of a fuel cell while preventing deterioration of the fuel cell.

1 is a schematic overall configuration diagram of a fuel cell vehicle equipped with a fuel cell system according to an embodiment of the present invention. It is a block diagram of the electric power system of the said fuel cell vehicle. It is a schematic block diagram of the fuel cell unit in the said embodiment. It is a figure which shows the detail of the DC / DC converter in the said embodiment. It is a flowchart of basic control in an electronic control unit (ECU). It is a flowchart which calculates a system load. It is a figure which shows the relationship between the present motor rotation speed and motor expected power consumption. It is a figure which shows an example of the relationship between the electric potential of the fuel cell which comprises a fuel cell, and the amount of degradation of a cell. It is a cyclic voltammetry figure which shows the example of the mode of progress of oxidation and the progress of reduction | restoration when the fluctuation speeds of the electric potential of a fuel cell differ. It is explanatory drawing of the several electric power supply mode in the said embodiment. 4 is a flowchart in which the ECU performs energy management of the fuel cell vehicle. It is a figure which shows the relationship of SOC of a battery, a charge / discharge coefficient, and average regenerative electric power. It is a figure which shows the relationship between a cathode stoichiometric ratio and a cell current. FIG. 14A is a diagram showing the relationship between the output current (FC current) and the output voltage (FC voltage) of the fuel cell in the second mode, and FIG. 14B shows the FC current and the generated power (FC) of the fuel cell in the second mode. It is a figure which shows the relationship of electric power. It is a flowchart in the second mode. It is a figure which shows the relationship between the target output voltage (target FC voltage) of a fuel cell in 2nd mode, and target oxygen concentration. It is a figure which shows the relationship between the target oxygen concentration in the 2nd mode, the target FC voltage, the target air pump rotational speed, and the target water pump rotational speed. It is a figure which shows the relationship between the target oxygen concentration in 2nd mode, the target FC voltage, and the target back pressure valve opening degree. It is a figure which shows the relationship between the target FC voltage and air flow rate in 2nd mode. It is a figure which shows the relationship between the opening degree of the circulation valve in 2nd mode, and the circulation gas flow rate. It is a flowchart of torque control of a motor. FIG. 22A is a diagram showing the relationship between FC current and FC voltage in the control according to the present embodiment (second mode) and the control according to the comparative example, and FIG. 22B is the control according to the present embodiment (second mode). It is a figure which shows the relationship between FC electric current and FC electric power in control which concerns on a comparative example. It is a block diagram which shows schematic structure of the 1st modification of the fuel cell vehicle which concerns on the said embodiment. It is a block diagram which shows schematic structure of the 2nd modification of the fuel cell vehicle which concerns on the said embodiment. It is a block diagram which shows schematic structure of the 3rd modification of the fuel cell vehicle which concerns on the said embodiment. It is an example of the time chart at the time of using the various control which concerns on the modification of the 2nd mode which makes a target air pump rotation speed constant and makes a target circulation valve opening variable.

1. Explanation of overall configuration [1-1. overall structure]
FIG. 1 schematically shows a fuel cell vehicle 10 (hereinafter referred to as “FC vehicle 10” or “vehicle 10”) equipped with a fuel cell system 12 (hereinafter referred to as “FC system 12”) according to an embodiment of the present invention. FIG. FIG. 2 is a block diagram of the power system of the FC vehicle 10. As shown in FIGS. 1 and 2, the FC vehicle 10 includes a travel motor 14 (hereinafter referred to as “motor 14”) and an inverter 16 in addition to the FC system 12.

  The FC system 12 includes a fuel cell unit 18 (hereinafter referred to as “FC unit 18”), a high voltage battery 20 (hereinafter also referred to as “battery 20”) (power storage device), a DC / DC converter 22, and electronic control. And a device 24 (hereinafter referred to as “ECU 24”).

[1-2. Drive system]
The motor 14 generates a driving force based on the electric power supplied from the FC unit 18 and the battery 20, and rotates the wheels 28 through the transmission 26 by the driving force. Further, the motor 14 outputs electric power (regenerative power Preg) [W] generated by performing regeneration to the battery 20 or the like (see FIG. 2).

  The inverter 16 is configured as a three-phase bridge type, performs DC / AC conversion, converts DC to three-phase AC and supplies it to the motor 14, and supplies the DC after AC / DC conversion accompanying the regenerative operation. It is supplied to the battery 20 or the like through the DC / DC converter 22.

  The motor 14 and the inverter 16 are collectively referred to as a load 30. The load 30 can also include components such as an air pump 60, a water pump 80, and an air conditioner 90 described later.

[1-3. FC system]
(1-3-1. Overall configuration)
FIG. 3 is a schematic configuration diagram of the FC unit 18. The FC unit 18 includes a fuel cell stack 40 (hereinafter referred to as “FC stack 40” or “FC40”), an anode system that supplies and discharges hydrogen (fuel gas) to and from the anode of the FC stack 40, A cathode system for supplying and discharging air containing oxygen (oxidant gas) to the cathode, a cooling system for cooling the FC stack 40, and a cell voltage monitor 42 are provided.

(1-3-2. FC stack 40)
The FC stack 40 has, for example, a structure in which fuel cell cells (hereinafter referred to as “FC cells”) formed by sandwiching a solid polymer electrolyte membrane from both sides between an anode electrode and a cathode electrode are stacked.

(1-3-3. Anode system)
The anode system includes a hydrogen tank 44, a regulator 46, an ejector 48, and a purge valve 50. The hydrogen tank 44 stores hydrogen as a fuel gas, and is connected to the inlet of the anode flow path 52 through a pipe 44a, a regulator 46, a pipe 46a, an ejector 48, and a pipe 48a. Thereby, the hydrogen in the hydrogen tank 44 can be supplied to the anode flow path 52 via the pipe 44a and the like. Note that a shutoff valve (not shown) is provided in the pipe 44a, and the shutoff valve is opened by the ECU 24 when the FC stack 40 generates power.

  The regulator 46 adjusts the pressure of the introduced hydrogen to a predetermined value and discharges it. That is, the regulator 46 controls the downstream pressure (anode hydrogen pressure) in accordance with the cathode pressure (pilot pressure) input via the pipe 46b. Accordingly, the hydrogen pressure on the anode side is linked to the air pressure on the cathode side. As will be described later, when the rotation speed of the air pump 60 is changed to change the oxygen concentration, the hydrogen pressure on the anode side also changes. To do.

  The ejector 48 generates a negative pressure by injecting hydrogen from the hydrogen tank 44 with a nozzle, and sucks the anode off gas of the pipe 48b by this negative pressure.

  The outlet of the anode flow path 52 is connected to the intake port of the ejector 48 through the pipe 48b. Then, the anode off gas discharged from the anode flow path 52 is introduced again into the ejector 48 through the pipe 48b, whereby the anode off gas (hydrogen) circulates.

  The anode off gas contains hydrogen and water vapor that were not consumed by the electrode reaction at the anode. The pipe 48b is provided with a gas-liquid separator (not shown) that separates and collects moisture {condensed water (liquid), water vapor (gas)} contained in the anode off gas.

  A part of the pipe 48b is connected to a dilution box 54 provided in a pipe 64b described later via a pipe 50a, a purge valve 50, and a pipe 50b. When it is determined that the power generation of the FC stack 40 is not stable, the purge valve 50 is opened for a predetermined time based on a command from the ECU 24. The dilution box 54 dilutes the hydrogen in the anode off gas from the purge valve 50 with the cathode off gas.

(1-3-4. Cathode system)
The cathode system includes an air pump 60, a humidifier 62, a back pressure valve 64, a circulation valve 66, flow rate sensors 68 and 70, and a temperature sensor 72.

  The air pump 60 compresses the outside air (air) and sends it to the cathode side, and the intake port thereof communicates with the outside of the vehicle (outside) via a pipe 60a. The discharge port of the air pump 60 is connected to the inlet of the cathode channel 74 through the pipe 60b, the humidifier 62, and the pipe 62a. When the air pump 60 operates in accordance with a command from the ECU 24, the air pump 60 sucks and compresses air outside the vehicle via the pipe 60a, and the compressed air is pumped to the cathode channel 74 through the pipe 60b and the like.

  The humidifier 62 includes a plurality of hollow fiber membranes 62e having moisture permeability. The humidifier 62 exchanges moisture between the air toward the cathode channel 74 and the humid cathode offgas discharged from the cathode channel 74 via the hollow fiber membrane 62e, and the air toward the cathode channel 74 Humidify.

  On the outlet side of the cathode channel 74, a pipe 62b, a humidifier 62, a pipe 64a, a back pressure valve 64, and a pipe 64b are arranged. The cathode off gas (oxidant off gas) discharged from the cathode channel 74 is discharged outside the vehicle through the pipe 62b and the like.

  The back pressure valve 64 is configured by, for example, a butterfly valve, and the air pressure in the cathode channel 74 is controlled by controlling the opening degree of the back pressure valve 64 by the ECU 24. More specifically, when the opening degree of the back pressure valve 64 is reduced, the air pressure in the cathode flow path 74 is increased, and the oxygen concentration (volume concentration) per volume flow rate is increased. On the contrary, when the opening degree of the back pressure valve 64 increases, the pressure of the air in the cathode flow path 74 decreases, and the oxygen concentration (volume concentration) per volume flow rate decreases.

  The pipe 64b is connected to the pipe 60a on the upstream side of the air pump 60 through the pipe 66a, the circulation valve 66, and the pipe 66b. As a result, a part of the exhaust gas (cathode off-gas) is supplied as circulation gas to the pipe 60a through the pipe 66a, the circulation valve 66, and the pipe 66b, merges with new air from the outside of the vehicle, and is taken into the air pump 60. Is done.

  The circulation valve 66 is constituted by, for example, a butterfly valve, and the flow rate of the circulation gas is controlled by the opening degree of the circulation valve 66 being controlled by the ECU 24.

  The flow rate sensor 68 is attached to the pipe 60b, detects the flow rate [g / s] of the air flowing toward the cathode flow path 74, and outputs it to the ECU 24. The flow rate sensor 70 is attached to the pipe 66b, detects the flow rate Qc [g / s] of the circulating gas toward the pipe 60a, and outputs it to the ECU 24.

  The temperature sensor 72 is attached to the pipe 64a, detects the temperature of the cathode off gas, and outputs it to the ECU 24. Here, since the temperature of the circulating gas is substantially equal to the temperature of the cathode off gas, the temperature of the circulating gas can be detected based on the temperature of the cathode off gas detected by the temperature sensor 72.

(1-3-5. Cooling system)
The cooling system includes a water pump 80, a radiator (not shown), a radiator fan, and the like. The water pump 80 cools the FC 40 by circulating cooling water (refrigerant) in the FC 40. The cooling water whose temperature has risen by cooling the FC 40 is radiated by the radiator that receives the air blown by the radiator fan.

(1-3-6. Cell voltage monitor 42)
The cell voltage monitor 42 is a device that detects a cell voltage Vcell for each of a plurality of single cells constituting the FC stack 40, and includes a monitor main body and a wire harness that connects the monitor main body and each single cell. The monitor main body scans all the single cells at a predetermined period, detects the cell voltage Vcell of each single cell, and calculates the average cell voltage and the lowest cell voltage. Then, the average cell voltage and the lowest cell voltage are output to the ECU 24.

(1-3-7. Power system)
As shown in FIG. 2, the power from the FC 40 (hereinafter referred to as “FC power Pfc”) is added to the inverter 16 and the motor 14 (during power running), the DC / DC converter 22 and the high voltage battery 20 (during charging). The air pump 60, the water pump 80, the air conditioner 90, the downverter 92 (step-down DC-DC converter), the low voltage battery 94, the accessory 96, and the ECU 24. As shown in FIG. 1, a backflow prevention diode 98 is disposed between the FC unit 18 (FC 40), the inverter 16, and the DC / DC converter 22. Further, the power generation voltage of FC 40 (hereinafter referred to as “FC voltage Vfc”) is detected by voltage sensor 100 (FIG. 4), and the power generation current of FC 40 (hereinafter referred to as “FC current Ifc”) is detected by current sensor 102. Both are output to the ECU 24.

[1-4. High voltage battery 20]
The battery 20 is a power storage device (energy storage) including a plurality of battery cells. For example, a lithium ion secondary battery, a nickel hydride secondary battery, or a capacitor can be used. In this embodiment, a lithium ion secondary battery is used. The output voltage of the battery 20 (hereinafter referred to as “battery voltage Vbat”) [V] is detected by the voltage sensor 104 (FIG. 2), and the output current of the battery 20 (hereinafter referred to as “battery current Ibat”) [A] is obtained. Are detected by the current sensor 106 and output to the ECU 24, respectively. The ECU 24 calculates the remaining capacity (hereinafter referred to as “SOC”) [%] of the battery 20 based on the battery voltage Vbat and the battery current Ibat.

[1-5. DC / DC converter 22]
The DC / DC converter 22 supplies FC power Pfc from the FC unit 18, power supplied from the battery 20 (hereinafter referred to as “battery power Pbat”) [W], and regenerative power Preg from the motor 14. To control.

  FIG. 4 shows details of the DC / DC converter 22 in the present embodiment. As shown in FIG. 4, one of the DC / DC converters 22 is connected to the primary side 1 </ b> S where the battery 20 is located, and the other is connected to the secondary side 2 </ b> S which is a connection point between the load 30 and the FC 40.

  The DC / DC converter 22 boosts the voltage on the primary side 1S (primary voltage V1) [V] to the voltage (secondary voltage V2) [V] (V1 ≦ V2) on the secondary side 2S and secondary voltage This is a step-up / step-down and chopper-type voltage converter that steps down the voltage V2 to the primary voltage V1.

  As shown in FIG. 4, the DC / DC converter 22 includes a phase arm UA disposed between the primary side 1S and the secondary side 2S, and a reactor 110.

  The phase arm UA includes an upper arm element (upper arm switching element 112 and antiparallel diode 114) and a lower arm element (lower arm switching element 116 and antiparallel diode 118). As the upper arm switching element 112 and the lower arm switching element 116, for example, a MOSFET or an IGBT is employed.

  Reactor 110 is inserted between the middle point (common connection point) of phase arm UA and the positive electrode of battery 20, and converts voltage between primary voltage V <b> 1 and secondary voltage V <b> 2 by DC / DC converter 22. In particular, it has the function of storing and releasing energy.

  The upper arm switching element 112 is turned on by the high level of the gate drive signal (drive voltage) UH output from the ECU 24, and the lower arm switching element 116 is turned on by the high level of the gate drive signal (drive voltage) UL. The

  The ECU 24 detects the primary voltage V1 with the voltage sensor 120 provided in parallel with the primary-side smoothing capacitor 122, and detects the primary-side current (primary current I1) [A] with the current sensor 124. To do. Further, the ECU 24 detects the secondary voltage V2 by the voltage sensor 126 provided in parallel with the secondary-side smoothing capacitor 128, and detects the secondary-side current (secondary current I2) [A] by the current sensor 130. To do.

[1-6. ECU 24]
The ECU 24 controls the motor 14, the inverter 16, the FC unit 18, the battery 20, and the DC / DC converter 22 via the communication line 140 (FIG. 1 and the like). In the control, a program stored in a memory (ROM) is executed, and the cell voltage monitor 42, the flow rate sensors 68 and 70, the temperature sensor 72, the voltage sensors 100, 104, 120, and 126, and the current sensors 102 and 106 are executed. , 124, 130 and the like are used.

  The various sensors here include an opening degree sensor 150 and a motor rotation speed sensor 152 (hereinafter referred to as “rotation speed sensor 152”) (FIG. 1) in addition to the above sensors. The opening sensor 150 detects the opening θp [degree] of the accelerator pedal 154. The rotational speed sensor 152 detects the rotational speed of the motor 14 (hereinafter referred to as “motor rotational speed Nm” or “rotational speed Nm”) [rpm]. The ECU 24 detects the vehicle speed V [km / h] of the FC vehicle 10 using the rotational speed Nm. Further, a main switch 156 (hereinafter referred to as “main SW 156”) is connected to the ECU 24. The main SW 156 switches whether or not power can be supplied from the FC unit 18 and the battery 20 to the motor 14, and can be operated by the user.

  The ECU 24 includes a microcomputer and has an input / output interface such as a timer, an A / D converter, and a D / A converter as necessary. Note that the ECU 24 is not limited to only one ECU, but can be composed of a plurality of ECUs for each of the motor 14, the FC unit 18, the battery 20, and the DC / DC converter 22.

  The ECU 24 determines the load required for the FC system 12 as a whole of the FC vehicle 10 determined based on the input (load request) from various switches and various sensors in addition to the state of the FC stack 40, the state of the battery 20, and the state of the motor 14. Thus, the load to be borne by the FC stack 40, the load to be borne by the battery 20, and the distribution (sharing) of the load to be borne by the regenerative power source (motor 14) are determined while arbitrating, and the motor 14, inverter 16, Commands are sent to the FC unit 18, the battery 20 and the DC / DC converter 22.

2. Control of this Embodiment Next, the control in ECU24 is demonstrated.

[2-1. Basic control]
FIG. 5 shows a flowchart of basic control in the ECU 24. In step S1, the ECU 24 determines whether the main SW 156 is on. If the main SW 156 is not on (S1: NO), step S1 is repeated. If the main SW 156 is on (S1: YES), the process proceeds to step S2. In step S2, the ECU 24 calculates a load (system load Psys) [W] required for the FC system 12.

  In step S3, the ECU 24 performs energy management of the FC system 12. The energy management here is mainly a process of calculating the power generation amount of the FC 40 (FC power Pfc) and the output of the battery 20 (battery power Pbat), while suppressing the deterioration of the FC stack 40 and the entire FC system 12. It is intended to make the output more efficient.

  In step S4, the ECU 24 controls peripheral devices of the FC stack 40, that is, the air pump 60, the back pressure valve 64, the circulation valve 66, and the water pump 80 (FC power generation control). In step S <b> 5, the ECU 24 performs torque control of the motor 14.

  In step S6, the ECU 24 determines whether the main SW 156 is off. If the main SW 156 is not off (S6: NO), the process returns to step S2. If the main SW 156 is off (S6: YES), the current process is terminated.

[2-2. Calculation of system load Psys]
FIG. 6 shows a flowchart for calculating the system load Psys. In step S <b> 11, the ECU 24 reads the opening degree θp of the accelerator pedal 154 from the opening degree sensor 150. In step S <b> 12, the ECU 24 reads the rotational speed Nm of the motor 14 from the rotational speed sensor 152.

  In step S13, the ECU 24 calculates the expected power consumption Pm [W] of the motor 14 based on the opening degree θp and the rotational speed Nm. Specifically, in the map shown in FIG. 7, the relationship between the rotational speed Nm and the predicted power consumption Pm is stored for each opening θp. For example, the characteristic 160 is used when the opening degree θp is θp1. Similarly, when the opening degree θp is θp2, θp3, θp4, θp5, and θp6, the characteristics 162, 164, 166, 168, and 170 are used, respectively. And after specifying the characteristic which shows the relationship between the rotation speed Nm and estimated power consumption Pm based on opening degree (theta) p, the expected power consumption Pm according to rotation speed Nm is specified.

  In step S14, the ECU 24 reads the current operation status from each auxiliary machine. The auxiliary machine here includes, for example, a high-voltage auxiliary machine including the air pump 60, the water pump 80 and the air conditioner 90, and a low-voltage auxiliary machine including the low-voltage battery 94, the accessory 96 and the ECU 24. It is. For example, in the case of the air pump 60 and the water pump 80, the rotation speed Nap and Nwp [rpm] are read. If it is the air conditioner 90, the output setting is read.

  In step S15, the ECU 24 calculates the power consumption Pa [W] of the auxiliary machine according to the current operation status of each auxiliary machine. In step S16, the ECU 24 calculates the sum of the predicted power consumption Pm of the motor 14 and the power consumption Pa of the auxiliary machine as the predicted power consumption of the FC vehicle 10 as a whole (that is, the system load Psys).

[2-3. Energy management]
As described above, the energy management in the present embodiment intends to improve the efficiency of the output of the entire FC system 12 while suppressing the deterioration of the FC stack 40.

(2-3-1. Assumptions)
FIG. 8 shows an example of the relationship between the potential (cell voltage Vcell) [V] of the FC cells constituting the FC stack 40 and the amount of cell degradation D. That is, the curve 180 in FIG. 8 shows the relationship between the cell voltage Vcell and the deterioration amount D.

  In FIG. 8, in a region below potential v1 (for example, 0.5 V) (hereinafter referred to as “platinum aggregation increasing region R1” or “aggregation increasing region R1”), a reduction reaction is performed on platinum (platinum oxide) contained in the FC cell. Proceeds violently and platinum aggregates excessively. The potential v1 to the potential v2 (for example, 0.8 V) is a region where the reduction reaction proceeds stably (hereinafter referred to as “platinum reduction region R2” or “reduction region R2”).

  The potential v2 to the potential v3 (for example, 0.9 V) is a region where the redox reaction proceeds with respect to platinum (hereinafter referred to as “platinum redox progress region R3” or “redox region R3”). The potential v3 to the potential v4 (for example, 0.95 V) is a region where the oxidation reaction of platinum proceeds stably (hereinafter referred to as “platinum oxidation stable region R4” or “oxidation region R4”). The potential v4 to OCV (open circuit voltage) is a region where the oxidation of carbon contained in the cell proceeds (hereinafter referred to as “carbon oxidation region R5”).

  As described above, in FIG. 8, if the cell voltage Vcell is in the platinum reduction region R2 or the platinum oxidation stable region R4, the progress of deterioration of the FC cell is small compared to the adjacent regions. On the other hand, when the cell voltage Vcell is in the platinum aggregation increasing region R1, the platinum oxidation-reduction progress region R3, or the carbon oxidation region R5, the progress of deterioration of the FC cell is larger than that of the adjacent region.

  In FIG. 8, the curve 180 is uniquely defined, but in actuality, the curve 180 changes according to the amount of fluctuation (fluctuation speed Acell) [V / sec] of the cell voltage Vcell per unit time. .

  FIG. 9 is a cyclic voltammetry diagram showing an example of the progress of oxidation and the progress of reduction when the fluctuation rates Acell are different. In FIG. 9, a curve 190 indicates a case where the fluctuation speed Acell is high, and a curve 192 indicates a case where the fluctuation speed Acell is low. As can be seen from FIG. 9, since the degree of progress of oxidation or reduction differs depending on the fluctuation speed Acell, the potentials v1 to v4 are not necessarily uniquely specified. In addition, the potentials v1 to v4 can change depending on individual differences of FC cells. For this reason, it is preferable to set the potentials v1 to v4 as those in which an error is reflected in the theoretical value, the simulation value, or the actual measurement value.

  Further, in the current-voltage (IV) characteristics of the FC cell, the cell current Icell [A] increases as the cell voltage Vcell decreases (see FIG. 10), as in a general fuel cell. In addition, the power generation voltage (FC voltage Vfc) of the FC stack 40 is obtained by multiplying the cell voltage Vcell by the number Nfc of serial connections in the FC stack 40. The serial connection number Nfc is the number of FC cells connected in series in the FC stack 40, and is also simply referred to as “cell number” hereinafter.

  Based on the above, in the present embodiment, when the DC / DC converter 22 is performing the voltage conversion operation, the target voltage (target FC voltage Vfctgt) [V] of the FC stack 40 is mainly set in the platinum reduction region R2. While setting, it is set in the platinum oxidation stable region R4 as necessary (a specific example will be described with reference to FIG. 10 and the like). By switching the target FC voltage Vfctgt in this way, the time during which the FC voltage Vfc is within the regions R1, R3, R5 (particularly, the platinum oxidation-reduction progress region R3) is shortened as much as possible, and the FC stack 40 is deteriorated. Can be prevented.

  In the above processing, there is a case where the power supplied to the FC stack 40 (FC power Pfc) and the system load Psys are not equal. In this regard, when the FC power Pfc is below the system load Psys, the shortage is supplied from the battery 20. Further, when the FC power Pfc exceeds the system load Psys, the excess is charged in the battery 20.

  In FIG. 8, the potentials v1 to v4 are specified as specific numerical values, but this is for performing the control described later, and the numerical values are determined taking into account the convenience of control. In other words, as can be seen from the curve 180, the deterioration amount D changes continuously, so that the potentials v1 to v4 can be appropriately set according to the control specifications.

  However, the platinum reduction region R2 includes the minimum value of the curve 180 (first minimum value Vlmi1). The platinum redox progression region R3 includes the maximum value (maximum value Vlmx) of the curve 180. The platinum oxidation stable region R4 includes another minimum value (second minimum value Vlmi2) of the curve 180.

(2-3-2. Power supply mode used in energy management)
FIG. 10 is an explanatory diagram of a plurality of power supply modes in the present embodiment. In the present embodiment, two control methods (power supply modes) are used as power supply control methods (power supply modes) used in energy management. That is, in the present embodiment, the first mode and the second mode are switched and used as the power supply mode (operation mode) used in energy management. The first mode is voltage variable / current variable control (voltage variable / output variable control) in which both the target FC voltage Vfctgt and the FC current Ifc (FC power Pfc) are variable. The second mode is voltage variable / current fixed control (current fixed / output variable control) in which the FC current Ifc (target FC current Ifctgt) is constant and the target FC voltage Vfctgt (FC power Pfc) is variable.

  The first mode (variable voltage / current variable control) is mainly used when the system load Psys is relatively high, and the target oxygen concentration Cotgt is fixed (or oxygen is maintained in a rich state). Thus, the FC current Ifc is controlled by adjusting the target FC voltage Vfctgt. Thus, basically, the system load Psys can be covered by the FC power Pfc.

  The second mode (voltage variable / current fixing control) is mainly used when the system load Psys is relatively low, and the target cell voltage Vcelltgt (= target FC voltage) with the target FC current Ifctgt fixed. Vfctgt / number of cells) is variable within the range of the reference potential {potential v2 (= 0.8 V)} in the present embodiment, which is set below the potential lower than the oxidation-reduction region R3, and the target oxygen concentration By making Cotgt variable, the FC power Pfc is made variable. Thus, basically, the system load Psys can be covered by the FC power Pfc (details will be described later). The shortage of the FC power Pfc is assisted from the battery 20.

(2-3-3. Overall flow of energy management)
FIG. 11 shows a flowchart in which the ECU 24 performs energy management of the FC system 12 (S3 in FIG. 5). In step S21, the ECU 24 calculates a system average load Psysave. The system average load Psysave is a moving average of the system load Psys calculated in step S2.

  In step S22, the ECU 24 calculates a charge / discharge coefficient α. The charge / discharge coefficient α is a coefficient for multiplying the system average load Psysave to calculate the target value of FC power Pfc (target FC power Pfctgt), and is the average value of the SOC of the battery 20 and the regenerative power Preg of the motor 14 ( (Hereinafter referred to as “average regenerative power Pregave”). The average regenerative power Pregave is an average value of the regenerative power Preg obtained within a predetermined period.

  FIG. 12 is a map showing the relationship among the SOC, the charge / discharge coefficient α, and the average regenerative power Pregave. In the example of FIG. 12, the target SOC is set to 50%, and when the SOC exceeds 50% (when in a sufficiently charged state), the charge / discharge coefficient α is set to less than 1. As a result, the target FC power Pfctgt can be reduced by multiplying the system average load Psysave by a multiplier of less than 1, and the excess SOC of the battery 20 can be consumed. Further, when the SOC is less than 50% (when charging is required), the charge / discharge coefficient α is made larger than 1. Accordingly, the target FC power Pfctgt can be increased by multiplying the system average load Psysave by a multiplier greater than 1, thereby making up for the shortage of the SOC.

  In the example of FIG. 12, the relationship between the SOC and the charge / discharge coefficient α is switched according to the average regenerative power Pregave. That is, as shown in FIG. 12, when the average regenerative power Pregave is low (in an environment where it is difficult to obtain the regenerative power Preg), the charge / discharge coefficient α is set in a range where the SOC exceeds 50% because the regenerative power Preg cannot be expected so much. The charge / discharge coefficient α is relatively far from 1 in a range where the SOC is relatively large and the SOC is less than 50%. On the other hand, when the average regenerative power Pregave is high (when it is in an environment where it is easy to obtain the regenerative power Preg), the charge / discharge coefficient α is relatively reduced in the range where the SOC exceeds 50%, as much as the regenerative power Preg can be expected. In the range where the SOC is less than 50%, the charge / discharge coefficient α is brought close to 1. The target SOC may be set to a value other than 50%. In addition, for example, measured values and simulation values can be used in the map of FIG.

  Returning to FIG. 11, in step S23, the ECU 24 calculates the target FC power Pfctgt by multiplying the system average load Psysave by the charge / discharge coefficient α.

  In step S24, the ECU 24 determines whether the vehicle 10 or the FC 40 is in a high load state (or whether it is not in a low load state). Specifically, the ECU 24 determines whether or not the target FC power Pfctgt calculated in step S23 is greater than or equal to a threshold value Pthp for determining a high load. The high load referred to here is, for example, a state in which oxygen is abundant and the cell voltage Vcell is set to a value in the reduction region R2 (the FC voltage Vfc is set to the value in the reduction region R2 × the number of cells) to generate FC40. FC power Pfc obtained at the time.

  When the target FC power Pfctgt is greater than or equal to the threshold Pthp, the vehicle 10 or FC40 is in a high load state, and when the target FC power Pfctgt is not greater than or equal to the threshold Pthp, the vehicle 10 or FC40 is not in a high load state. The determination of the high load state may be performed by other methods. For example, it is possible to determine the high load state based on whether or not the vehicle speed V is equal to or higher than a threshold value THV for determining a high load. Alternatively, the high load state may be determined based on whether or not the acceleration of the vehicle 10 (the amount of change in the vehicle speed V) is equal to or greater than a threshold for determining a high load. Or you may determine a high load state by whether the torque of the motor 14 is more than the threshold value for determining a high load.

  When the vehicle 10 or the FC 40 is in a high load state (S24: YES), in step S25, the ECU 24 performs the first mode (voltage variable / current variable control) (details will be described later). When the vehicle 10 is not in a high load state (S24: NO), in step S26, the ECU 24 performs the second mode (voltage variable / current fixing control) (details will be described later with reference to FIG. 14A and the like).

(2-3-4. First mode)
As described above, the first mode is mainly used when the target FC power Pfctgt (or system load Psys) is relatively high, and the target oxygen concentration Cotgt is fixed (or the oxygen is in a rich state). Maintained), the FC current Ifc is controlled by adjusting the target FC voltage Vfctgt.

  That is, as shown in FIG. 10, in the first mode, the current-voltage characteristic (IV characteristic) of the FC 40 is normal (represented by a solid line in FIG. 10). As in the case of a normal fuel cell, in the IV characteristics of FC40, the cell current Icell (FC current Ifc) increases as the cell voltage Vcell (FC voltage Vfc) decreases. Therefore, in the first mode, the target FC current Ifctgt is calculated according to the target FC power Pfctgt, and the target FC voltage Vfctgt corresponding to the target FC current Ifctgt is calculated. Then, the ECU 24 controls the DC / DC converter 22 so that the FC voltage Vfc becomes the target FC voltage Vfctgt. That is, the primary voltage V1 is boosted by the DC / DC converter 22 so that the secondary voltage V2 becomes the target FC voltage Vfctgt, thereby controlling the FC voltage Vfc and controlling the FC current Ifc.

  For example, as shown in FIG. 13, when the cathode stoichiometric ratio is increased, the cell current Icell becomes substantially constant and is substantially higher than the normal stoichiometric ratio where the cell is substantially saturated. Means oxygen in the region. The same applies when hydrogen is rich. The cathode stoichiometric ratio is the flow rate of air supplied to the cathode channel 74 / the flow rate of air consumed by the power generation of the FC 40, and approximates the oxygen concentration Co in the cathode channel 74. The cathode stoichiometric ratio is adjusted by controlling the oxygen concentration Co, for example.

  According to the first mode as described above, even if the vehicle 10 or the FC 40 has a high load, basically all of the target FC power Pfctgt (or system load Psys) can be covered by the FC power Pfc.

(2-3-5. Overall second mode)
As described above, the second mode is mainly used when the vehicle 10 or the FC 40 has a relatively low load, and the target cell voltage Vcelltgt (= target FC voltage) with the target FC current Ifctgt fixed. Vfctgt / number of cells) is variable within the range of the reference potential {potential v2 (= 0.8 V)} in the present embodiment, which is set below the potential lower than the oxidation-reduction region R3, and the target oxygen concentration By making Cotgt variable, the FC power Pfc is made variable.

  That is, as shown in FIG. 10, in the second mode, the cell voltage Vcell (FC voltage Vfc) is lowered and the target oxygen concentration Cotgt is lowered while the cell current Icell (FC current Ifc) is kept constant. To lower the oxygen concentration Co.

  FIG. 14A is a diagram illustrating a relationship between the FC current Ifc and the FC voltage Vfc in the second mode, and FIG. 14B is a diagram illustrating a relationship between the FC current Ifc and the FC power Pfc in the second mode.

  14A and 14B, the solid line is the current-voltage (IV) characteristic when the oxygen concentration Co is normal, and the broken line is the IV characteristic when the oxygen concentration Co is decreased by 50% from the normal value. The alternate long and short dash line is the IV characteristic when the oxygen concentration Co is decreased by 75% from the normal value, and the double dotted line is the IV characteristic when the oxygen concentration Co is decreased by 90% from the normal value.

  As shown in FIG. 14A, the FC current Ifc can be made constant by decreasing the FC voltage Vfc while decreasing the oxygen concentration Co. That is, as shown in FIG. 13, when the cathode stoichiometric ratio (oxygen concentration Co) decreases, the cell current Icell (FC current Ifc) also decreases. However, in this embodiment, when the oxygen concentration Co is decreased, the FC voltage Vfc is also decreased. Lower. As shown in FIG. 14A, if the oxygen concentration Co is constant, the FC current Ifc increases when the FC voltage Vfc is lowered. Therefore, the FC current Ifc can be kept constant by offsetting the decrease in the FC current Ifc due to the decrease in the oxygen concentration Co with the increase in the FC current Ifc due to the decrease in the FC voltage Vfc. Note that the shortage of the FC power Pfc is assisted from the battery 20.

  When the FC power Pfc is the product of the FC voltage Vfc and the FC current Ifc, the FC power Pfc can be made variable by making the FC voltage Vfc variable while keeping the FC current Ifc constant.

  FIG. 15 shows a flowchart of the second mode. In step S31, the ECU 24 fixes the target FC current Ifctgt. In the present embodiment, the FC current Ifc when the cell voltage Vcell is the potential v2 (= 0.8 V) (in other words, the FC voltage Vfc is the potential v2 × the number of cells) and the oxygen concentration Co is normal (FIG. 10) is set to the target FC current Ifctgt. The target FC current Ifctgt may be set to other values.

  In step S32, the ECU 24 calculates a target FC voltage Vfctgt corresponding to the target FC power Pfctgt. As described above, when the FC power Pfc is the product of the FC voltage Vfc and the FC current Ifc, if the FC current Ifc is determined, the FC voltage Vfc can also be determined. That is, the target FC voltage Vfctgt can be a quotient obtained by dividing the target FC power Pfctgt by the target FC current Ifctgt (Vfctgt ← Pfctgt / Ifctgt).

  However, when the change in the FC voltage Vfc is large, the deterioration amount of the FC 40 becomes large. Therefore, a limit (hereinafter referred to as “rate limit control”) can be provided for the amount of change per unit time of the target FC voltage Vfctgt (hereinafter referred to as “voltage change amount ΔVfctgt”). In the rate limit control, for example, an allowable value of the voltage change amount ΔVfctgt in one calculation cycle is set, and when the voltage change amount ΔVfctgt exceeds the allowable value, only a change up to the allowable value is recognized.

  In step S33, the ECU 24 calculates a target oxygen concentration Cotgt corresponding to the target FC voltage Vfctgt (see FIGS. 14A, 14B, and 16). FIG. 16 shows the relationship between the target FC voltage Vfctgt and the target oxygen concentration Cotgt.

  In step S34, the ECU 24 calculates and transmits a command value to each unit in accordance with the target oxygen concentration Cotgt. The command value calculated here includes the rotational speed of the air pump 60 (hereinafter referred to as “air pump rotational speed Nap” or “rotational speed Nap”), and the rotational speed of the water pump 80 (hereinafter referred to as “water pump rotational speed Nwp” or “ ), The opening of the back pressure valve 64 (hereinafter referred to as “back pressure valve opening θbp” or “opening θbp”), and the opening of the circulation valve 66 (hereinafter referred to as “circulation valve opening θc” or “ "Opening angle θc").

  That is, as shown in FIGS. 17 and 18, the target air pump rotation speed Naptgt, the target water pump rotation speed Nwptgt, and the target back pressure valve opening degree θbptgt are set according to the target oxygen concentration Cotgt (or the target FC voltage Vfctgt). Moreover, the target opening degree θctgt of the circulation valve 66 is set to an initial value (for example, an opening degree at which the circulating gas becomes zero). As will be described later, the target air pump speed Naptgt is constant regardless of the target oxygen concentration Cotgt (or the target FC voltage Vfctgt), and the oxygen concentration Co can be varied by adjusting the target opening degree θctgt of the circulation valve 66. You can also

  In step S35, the ECU 24 determines whether power generation by the FC 40 is stable. As the determination, when the lowest cell voltage input from the cell voltage monitor 42 is lower than the voltage obtained by subtracting the predetermined voltage from the average cell voltage {lowest cell voltage <(average cell voltage−predetermined voltage)}, the FC 40 Is determined to be unstable. As the predetermined voltage, for example, an experimental value, a simulation value, or the like can be used.

  When the power generation is stable (S35: YES), the current process is finished. When the power generation is not stable (S35: NO), in step S36, the ECU 24 increases the opening degree θc of the circulation valve 66 while monitoring the flow rate Qc [g / s] of the circulation gas via the flow rate sensor 70. Then, the flow rate Qc is increased by one step (see FIG. 19). FIG. 19 illustrates the case where the flow rate Qc is increased in the fourth stage and the maximum flow rate is obtained when the circulation valve 66 is fully opened.

  However, when the opening degree θc of the circulation valve 66 increases, the ratio of the circulation gas in the intake gas sucked into the air pump 60 increases. That is, the intake gas changes such that the ratio of the circulating gas increases in the ratio of new air (air taken from outside the vehicle) and the circulating gas. Therefore, the ability to distribute oxygen to all single cells is improved. Here, the oxygen concentration Co of the circulating gas (cathode off gas) is lower than the oxygen concentration Co of the new air. Therefore, before and after the control of the opening degree θc of the circulation valve 66, the oxygen concentration Co of the gas flowing through the cathode channel 74 decreases when the rotation speed Nap of the air pump 60 and the opening degree θbp of the back pressure valve 64 are the same. Will do.

  Therefore, in step S36, the increase in the rotational speed Nap of the air pump 60 and the opening degree θbp of the back pressure valve 64 are interlocked with the increase in the circulation gas flow rate Qc so that the target oxygen concentration Cotgt calculated in step S33 is maintained. Preferably, at least one of the reductions is performed.

  For example, when the flow rate Qc of the circulating gas is increased, it is preferable to increase the rotational speed Nap of the air pump 60 and increase the flow rate of new air. In this way, the flow rate of the entire gas (mixed gas of new air and circulating gas) toward the cathode flow path 74 increases, so that the ability to distribute oxygen to all single cells is further improved, and the FC 40 The power generation performance is easily recovered.

  Thus, since the circulating gas is merged with the new air while maintaining the target oxygen concentration Cotgt, the volume flow rate [L / s] of the gas flowing through the cathode channel 74 is increased. As a result, the gas whose volume flow rate has increased while the target oxygen concentration Cotgt is maintained can easily reach the entire cathode channel 74 formed in a complex manner in the FC 40. Accordingly, the gas is easily supplied to each single cell as well, and the unstable power generation of the FC 40 is easily resolved. In addition, water droplets (condensed water, etc.) adhering to the surface of the MEA (membrane electrode assembly) and the wall surface surrounding the cathode channel 74 are easily removed.

  In step S <b> 37, the ECU 24 determines whether or not the circulation gas flow rate Qc detected via the flow rate sensor 70 is equal to or higher than the upper limit value. The upper limit value serving as the determination criterion is set to a value at which the opening degree θc of the circulation valve 66 is fully opened.

  In this case, even if the circulation valve opening degree θc is the same, if the rotation speed Nap of the air pump 60 increases, the flow rate Qc of the circulating gas detected by the flow sensor 70 increases. In association with the number Nap, that is, when the rotation speed Nap of the air pump 60 is increased, the upper limit value is preferably set to be increased.

  When it is determined that the flow rate Qc of the circulating gas is not equal to or higher than the upper limit (S37: NO), the process returns to step S35. When it is determined that the flow rate Qc of the circulating gas is equal to or higher than the upper limit value (S37: YES), the process proceeds to step S38.

  Here, in steps S36 and S37, the process is executed based on the circulation gas flow rate Qc directly detected by the flow sensor 70, but the process may be executed based on the circulation valve opening θc. That is, in step S36, the circulation valve opening degree θc is increased in one step (for example, 30 °) in the opening direction. If the circulation valve 66 is fully open in step S37 (S37: YES), the process proceeds to step S38. It is good also as a structure to advance.

  In this case, the circulation gas flow rate Qc [g / s] can also be calculated based on the degree of opening θc of the circulation valve 66, the temperature of the circulation gas, and the map of FIG. As shown in FIG. 20, the density decreases as the temperature of the circulating gas increases, so that the flow rate Qc [g / s] decreases.

  In step S38, the ECU 24 determines whether or not power generation is stable, as in step S35. If the power generation is stable (S38: YES), the current process is terminated. When the power generation is not stable (S38: NO), in step S39, the ECU 24 increases the target oxygen concentration Cotgt by one step (approaches the normal concentration). Specifically, at least one of increasing the rotation speed Nap of the air pump 60 and decreasing the opening θbp of the back pressure valve 64 is performed in one step.

  In step S40, the ECU 24 determines whether or not the target oxygen concentration Cotgt is less than or equal to the target oxygen concentration Cogt (normal oxygen concentration Conml) in the normal IV characteristics. When the target oxygen concentration Cotgt is less than or equal to the normal oxygen concentration Conml (S40: YES), the process returns to step S38. When the target oxygen concentration Cotgt is not equal to or lower than the normal oxygen concentration Conml (S40: NO), the ECU 24 stops the FC unit 18 in step S41. That is, the ECU 24 stops the supply of hydrogen and air to the FC 40 and stops the power generation of the FC 40. Then, the ECU 24 turns on a warning lamp (not shown) to notify the driver that the FC 40 is abnormal. Note that the ECU 24 supplies electric power from the battery 20 to the motor 14 and continues running of the FC vehicle 10.

  According to the second mode as described above, when the vehicle 10 or the FC 40 has a low load, the FC voltage Ifc (target FC current Ifctgt) is kept constant, the FC voltage Vfc and the oxygen concentration Co (cathode stoichiometric ratio). ) Is basically able to cover all of the target FC power Pfctgt (or system load Psys) with the FC power Pfc.

[2-4. FC power generation control]
As described above, as the FC power generation control (S4 in FIG. 5), the ECU 24 controls peripheral devices of the FC stack 40, that is, the air pump 60, the back pressure valve 64, the circulation valve 66, and the water pump 80. Specifically, the ECU 24 controls these devices using a command value (for example, S34 in FIG. 15) of these devices calculated by energy management (S3 in FIG. 5).

[2-5. Torque control of motor 14]
FIG. 21 shows a flowchart of torque control of the motor 14 (S5 in FIG. 5). In step S51, the ECU 24 reads the motor rotational speed Nm from the rotational speed sensor 152. In step S52, the ECU 24 reads the opening degree θp of the accelerator pedal 154 from the opening degree sensor 150.

  In step S53, the ECU 24 calculates a temporary target torque Ttgt_p [N · m] of the motor 14 based on the motor rotational speed Nm and the opening degree θp. Specifically, a map that associates the rotational speed Nm, the opening degree θp, and the temporary target torque Ttgt_p is stored in a storage unit (not shown), and the temporary target torque is based on the map, the rotational speed Nm, and the opening degree θp. Ttgt_p is calculated.

  In step S54, the ECU 24 calculates a limit output (motor limit output Pm_lim) [W] of the motor 14 equal to a limit value (limit supply power Ps_lim) [W] of power that can be supplied from the FC system 12 to the motor 14. Specifically, the limit supply power Ps_lim and the motor limit output Pm_lim are calculated from the sum of the FC power Pfc from the FC stack 40 and the limit value of the power that can be supplied from the battery 20 (limit output Pbat_lim) [W]. The power consumption Pa is subtracted (Pm_lim = Ps_lim ← Pfc + Pbat_lim−Pa).

  In step S55, the ECU 24 calculates a torque limit value Tlim [N · m] of the motor 14. More specifically, the torque limit value Tlim is obtained by dividing the motor limit output Pm_lim by the vehicle speed V (Tlim ← Pm_lim / V).

  On the other hand, if it is determined in step S54 that the motor 14 is regenerating, the ECU 24 calculates the limit supply regenerative power Ps_reglim. The limit supply regenerative power Ps_reglim is obtained by subtracting the power consumption Pa of the auxiliary machine from the sum of the limit value of power that can be charged to the battery 20 (limit charge Pbat_chglim) and the FC power Pfc from the FC stack 40 (Ps_reglim = Pbat_chglim + Pfc−Pa). If regeneration is in progress, the ECU 24 calculates the regenerative torque limit value Treglim [N · m] of the motor 14 in step S55. Specifically, a value obtained by dividing the limit supply regenerative power Ps_reglim by the vehicle speed Vs is set as a torque limit value Tlim (Tlim ← Ps_reglim / Vs).

  In step S56, the ECU 24 calculates a target torque Ttgt [N · m]. Specifically, the ECU 24 sets the provisional target torque Ttgt_p, which is limited by the torque limit value Tlim, as the target torque Ttgt. For example, when the temporary target torque Ttgt_p is equal to or less than the torque limit value Tlim (Ttgt_p ≦ Tlim), the temporary target torque Ttgt_p is set as the target torque Ttgt as it is (Ttgt ← Ttgt_p). On the other hand, when the temporary target torque Ttgt_p exceeds the torque limit value Tlim (Ttgt_p> Tlim), the torque limit value Tlim is set as the target torque Ttgt (Ttgt ← Tlim).

  Then, the motor 14 is controlled using the calculated target torque Ttgt.

3. Comparison with Comparative Example FIG. 22A is a diagram illustrating a relationship between the FC current Ifc and the FC voltage Vfc in the control according to the present embodiment (second mode) and the control according to the comparative example, and FIG. It is a figure which shows the relationship between FC electric current Ifc and FC electric power Pfc in the control (2nd mode) which concerns, and the control which concerns on a comparative example. The comparative example here uses only the first mode without using the second mode. In FIG. 22A and FIG. 22B, the white arrow is related to the present embodiment, and the black arrow is related to the comparative example. In FIG. 22A, point A1 is a start point, point A2 is a point after movement in the comparative example, and point A3 is a point after movement in the present embodiment. Similarly, in FIG. 22B, a point B1 is a start point, a point B2 is a point after movement in the comparative example, and a point B3 is a point after movement in the present embodiment.

  As can be seen from FIGS. 22A and 22B, in the comparative example, the FC voltage Vfc and the FC current Ifc are determined using the IV characteristics of the normal oxygen concentration Co. For this reason, in the comparative example, both the FC voltage Vfc and the FC current Ifc are variable. And FC voltage Vfc will also take the value in oxidation reduction progress area | region R3. In contrast, in the present embodiment, the FC voltage Vfc and the oxygen concentration Co are determined while keeping the FC current Ifc constant. For this reason, in this embodiment, it is possible to avoid the FC voltage Vfc taking a value in the oxidation-reduction progress region R3.

4). Advantages of the present embodiment As described above, according to the present embodiment, the output control of the FC 40 can be flexibly performed while the deterioration of the FC 40 is prevented.

  That is, when the second mode is selected, the FC voltage Vfc is changed outside the redox region R3 when the target FC power Pfctgt is both increased and decreased. For this reason, it is possible to prevent deterioration due to the FC voltage Vfc being in the region R3. In addition, when the second mode is selected, the FC voltage Vfc and the oxygen concentration Co are set with the FC current Ifc (target FC current Ifctgt) being fixed, regardless of whether the target FC power Pfctgt is increasing or decreasing. Change. As a result, even when the vehicle 10 or the FC 40 has a low output, the FC voltage Vfc can be changed. Therefore, compared with the case where the FC voltage Vfc is fixed in the vicinity of the region R3, the FC voltage Vfc is changed from the region R3. It is possible to increase the degree and frequency of moving away. Therefore, it becomes possible to suppress deterioration of FC40 suitably. Further, since the FC power Pfc is changed in a state where the FC current Ifc (target FC current Ifctgt) is fixed, it is suitably used when it is desired to change the magnitude of the load while keeping the current supplied to the load such as the motor 14 constant. be able to.

  In this embodiment, rate limit control is performed when calculating the target FC voltage Vfc. When the FC voltage Vfc is suddenly changed, the FC 40 may be deteriorated. However, according to the above configuration, it is possible to suppress the rapid fluctuation of the FC voltage Vfc, and thus it is possible to suppress the deterioration of the FC 40. Become.

5. Modifications It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted based on the contents described in this specification. For example, the following configuration can be adopted.

[5-1. Installation target]
In the above-described embodiment, the FC system 12 is mounted on the FC vehicle 10. However, the present invention is not limited to this, and the FC system 12 may be mounted on another target as long as the FC system 12 can be mounted. For example, the FC system 12 can be used for a moving body such as a ship, a robot, a manufacturing apparatus, a home power system, a home appliance, and the like.

[5-2. Configuration of FC system 12]
In the above embodiment, the FC 40 and the high voltage battery 20 are arranged in parallel, and the DC / DC converter 22 is arranged in front of the battery 20, but this is not restrictive. For example, as shown in FIG. 23, the FC 40 and the battery 20 may be arranged in parallel, and the step-up, step-down or step-up / step-down DC / DC converter 22 may be arranged in front of the FC 40. Alternatively, as shown in FIG. 24, the FC 40 and the battery 20 are arranged in parallel, and the DC / DC converter 22a of the step-up, step-down or step-up / step-down type is placed in front of the FC 40, and the DC / DC converter 22 is placed in front of the battery 20. The structure to arrange | position may be sufficient. Alternatively, as shown in FIG. 25, the FC 40 and the battery 20 may be arranged in series, and the DC / DC converter 22 may be arranged between the battery 20 and the motor 14.

[5-3. Stoichi ratio]
In the above embodiment, the means or method for adjusting the stoichiometric ratio is one that adjusts the target oxygen concentration Cotgt. However, the present invention is not limited to this, and the target hydrogen concentration can also be adjusted. Further, instead of the target concentration, the target flow rate or both the target concentration and the target flow rate can be used.

  In the said embodiment, although the structure provided with the air pump 60 which supplies the air containing oxygen was illustrated, it is good also as a structure provided with the hydrogen pump which supplies hydrogen instead of or in addition to this.

  In the above-described embodiment, the configuration including the merging flow path (piping 66a, 66b) for merging the cathode off gas with the new air and the circulation valve 66 is illustrated, but instead of or in addition to this, the anode side is similarly configured. May be. For example, a circulation valve may be provided in the pipe 48b, and the flow rate of the anode off gas that joins the new hydrogen may be controlled by this circulation valve.

[5-4. Power supply mode]
In the said embodiment, although 1st mode and 2nd mode were used as electric power supply mode, you may use only 2nd mode. Alternatively, other power supply modes may be set in addition to the first mode and the second mode. For example, one or both of the first operation mode and the second operation mode described in Patent Document 1 can be combined.

  In the second mode, the target air pump rotational speed Naptgt and the circulation valve opening degree θc are made variable in order to change the oxygen concentration Co (FIGS. 17 and 20), but the FC voltage Vfc (FC If the electric power Pfc) can be made variable, it is not limited to this. For example, the target air pump rotation speed Naptgt may be constant and the target circulation valve opening degree θctgt may be variable.

  FIG. 26 shows an example of a time chart in the case of using various controls according to the modified example of the second mode (FIG. 15) in which the target air pump rotation speed Naptgt is constant and the target circulation valve opening degree θctgt is variable. ing. That is, in the present modification, the target air pump rotation speed Naptgt is made constant among the command values to each part in step S34 of FIG. 15 while using the flowchart of FIG. 11, and the target circulation valve opening θctgt is set to the target oxygen concentration Cotgt. Variable depending on Further, the target water pump rotational speed Nwptgt is variable depending on characteristics as shown in FIG. 17, for example. For example, the target back pressure valve opening degree θbptgt is made variable according to the characteristics shown in FIG. 18 or constant regardless of the target oxygen concentration Cotgt.

  In FIG. 26, the target FC power Pfctgt is always smaller than the threshold value Pthp (S24 in FIG. 11: NO). For this reason, in the present modification, the second mode is always selected.

  The target FC power Pfctgt is constant from time t1 to time t2. Accordingly, the vehicle speed V, the air pump rotation speed Nap, the circulation valve opening θc, the FC voltage Vfc, the FC current Ifc, and the FC power Pfc are all constant.

  The target FC power Pfctgt increases from time t2 to time t3. Accordingly, while keeping the FC current Ifc constant, the FC voltage Vfc is increased, and the circulation valve opening degree θc is lowered (the circulation valve 66 is closed) while the air pump rotational speed Nap is kept constant. increase. As a result, the FC power Pfc increases and the output of the motor 14 increases, so that the vehicle speed V increases.

  The target FC power Pfctgt is constant from time t3 to time t4. Accordingly, the vehicle speed V, the air pump rotation speed Nap, the circulation valve opening θc, the FC voltage Vfc, the FC current Ifc, and the FC power Pfc are all constant.

  The target FC power Pfctgt decreases from time t4 to time t5. Along with this, while keeping the FC current Ifc constant, the FC voltage Vfc is decreased and the air pump rotational speed Nap is kept constant and the circulation valve opening degree θc is increased (opening the circulation valve 66) to increase the oxygen concentration Co. Decrease. As a result, the FC power Pfc is reduced and the output of the motor 14 is reduced, whereby the vehicle speed V is reduced.

  Battery SOC is constant from time t1 to time t5. This means that the target FC power Pfctgt (or system load Psys) is all covered by the FC power Pfc.

  According to the control according to this modification, when the vehicle 10 is in a predetermined low load state (that is, when the second mode is selected), the air pump rotation speed Nap is made constant. For this reason, the output sound of the air pump 60 does not change unexpectedly by stopping the air pump 60 when the battery SOC reaches the set upper limit value in the low load state. Therefore, the battery SOC can be appropriately maintained without giving a sense of incongruity to the passenger about the output sound of the air pump 60 in the low load state.

  In addition, the air pump rotational speed Nap is not only made constant, but the circulation valve 66 is controlled to adjust the circulation gas flow rate Qc (the recirculation amount of the air-off gas). Since the air-off gas has a low oxygen concentration Co, increasing the amount of recirculation Qc of the air-off gas reduces the amount of moisture generated inside the FC 40 and makes the inside of the FC 40 dry. When the inside of the FC 40 becomes dry, the deterioration of the FC 40 may be promoted. On the other hand, since the air-off gas has passed through the inside of the FC 40 that generates moisture, it contains a relatively large amount of moisture. For this reason, by adjusting the recirculation amount Qc of the air-off gas, the electrolyte membrane of the FC 40 can be favorably humidified, and deterioration of the FC 40 can be suppressed.

  Further, the battery SOC is managed by reducing the FC current Ifc in accordance with a predetermined low load state while obtaining the above-described effect (for example, controlling so as not to exceed the set upper limit value of the SOC) And avoid unnecessary charging).

  In the above embodiment, the target FC voltage Vfctgt in the second mode is set to a value in the reduction region R2 (potential v2 (= 0.8 V) × number of cells or less), but the FC current Ifc (or target FC current Ifctgt) is set. The present invention is not limited to this as long as the FC power Pfc is adjusted by making the FC voltage Vfc and the oxygen concentration Co variable in a fixed state. For example, the target FC voltage Vfctgt in the second mode can be set to a value in the oxidation region R4.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell vehicle 12 ... Fuel cell system 14 ... Motor (load) 16 ... Inverter (load)
20 ... High voltage battery (power storage device)
22 ... DC / DC converter (voltage control means)
24 ... ECU (power generation control means) 30 ... Load 40 ... Fuel cell 60 ... Air pump (gas supply means, load)
60a, 60b, 62a ... piping (air supply piping)
62b, 64a, 64b ... piping (air discharge piping)
66 ... Circulation valve (regulator) 66a, 66b ... Piping (air recirculation piping)
80 ... Water pump (load) 90 ... Air conditioner (load)
92 ... Downverter (load) 94 ... Low voltage battery (load)
96 ... Accessories (load)

Claims (3)

A fuel cell having a catalyst and generating electricity by reacting oxygen or hydrogen with the catalyst;
Gas supply means for supplying at least one of the oxygen and the hydrogen to the fuel cell;
Voltage control means for controlling the output voltage of the fuel cell;
A load driven by power generated by the fuel cell;
A fuel cell system having power generation control means for controlling the power generation amount of the fuel cell,
The power generation control means includes
When the required power of the load increases, with the output current of the fuel cell being fixed, the supply amount of at least one of the oxygen and hydrogen to the fuel cell is increased, and the output voltage of the fuel cell is oxidized / reduced A power generation amount increase control for increasing the power generation amount of the fuel cell by increasing it outside the traveling voltage range;
When the required power of the load decreases, with the output current of the fuel cell fixed, the supply amount of at least one of the oxygen and hydrogen to the fuel cell is decreased, and the output voltage of the fuel cell is reduced to the oxidation Both the power generation amount reduction control for reducing the power generation amount of the fuel cell by decreasing outside the reduction progress voltage range is executed. The fuel cell system according to claim 1, wherein
The fuel cell system is mounted on a vehicle,
Further, the fuel cell system includes a power storage device that assists the output of the fuel cell,
The gas supply means includes
An air pump for supplying air to the fuel cell via an air supply pipe;
An air recirculation pipe branching from an air discharge pipe and communicating with the air supply pipe on the upstream side of the air pump to recirculate the air off gas discharged from the fuel cell to the air supply pipe;
An adjustment device that adjusts the amount of recirculation of the air-off gas in the air recirculation pipe;
When the vehicle is in a predetermined low load state, the control means controls the adjusting device to adjust the recirculation amount of the air-off gas while keeping the driving amount of the air pump constant, and the power generation amount increase control and The fuel cell system, wherein the power generation amount reduction control is performed. The fuel cell system according to claim 1 or 2,
During the execution of at least one of the power generation amount increase control and the power generation amount decrease control, the change rate of the output voltage of the fuel cell is limited.

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