JP2013062085A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system which, while restricting the degradation of a fuel cell, can improve the output efficiency of the fuel cell system as a whole.SOLUTION: In an FC system 12, when a request output Psys of loads 14 and 16 exceeds a lower limit output value lim1 and also falls below an upper limit output value lim2, fixation to a specific voltage value and tracking to the request output of loads are executed continuously. When the request output of the loads 14 and 16 falls below the lower limit output value or exceeds the upper limit output value, fixation to the specific voltage value is continued to be executed and also control is exerted on gas supply means so that an FC output Pfc fits within a maximum efficiency region Rhieff.

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 an oxidation-reduction potential has been proposed (Patent Document 1). In the fuel cell system of Patent Document 1, even when the system required power Wreq gradually increases, the output voltage Vfc of the fuel cell is limited once by the oxidation-reduction potential Voxpt, and the power corresponding to the limited voltage is supplied to the battery. Control to make up with. After that, even if the fuel cell power generation is no longer necessary due to the accelerator opening decreasing, etc., the fuel cell output voltage is maintained below the oxidation-reduction potential and power generation is continued until the remaining battery capacity exceeds a predetermined value. Continue power generation (summary).

  In addition, a fuel cell system aimed at improving the power generation efficiency of the entire system has been developed (Patent Document 2). In Patent Document 2, waste of power generation in the fuel cell is reduced, and the efficiency of the entire system including the fuel cell and the secondary battery is improved (summary). For this reason, the fuel cell system 10 in Patent Document 2 is a fuel cell device group including the fuel cell 20 and its peripheral devices, depending on the magnitude of the required driving power of the vehicle requested by the driver through the depression operation of the accelerator pedal. Determine operation / stop. When the required power for driving is obtained by the fuel cell power generation operation in the low load region where the threshold power is less than or equal to the threshold power Xps, the fuel cell device group is stopped and the motor 32 is operated by the remaining capacity Q by the secondary battery 30 alone. Rotate to drive the vehicle at the required drive power (summary).

JP 2007-005038 A JP 2001-307758 A

  As described above, in the control of Patent Document 1, the output voltage of the fuel cell is maintained below the oxidation-reduction potential, but in order to keep avoiding the oxidation-reduction potential, the electric power required by the load such as the travel motor is required. It is necessary to increase the output power of the fuel cell. In those cases, the surplus power of the fuel cell is charged into the battery. For this reason, in order to continue to avoid the oxidation-reduction potential, the frequency of charging and discharging of the battery increases. When the frequency of charging / discharging of the battery increases, the power loss accompanying charging / discharging increases, and the output efficiency of the entire fuel cell system decreases. Note that the present inventors have confirmed that there is a certain range of potential at which the oxidation-reduction reaction occurs. Hereinafter, the voltage range in which the oxidation-reduction reaction occurs is referred to as “oxidation reduction progress voltage range”.

  In the control of Patent Document 2, power generation is performed in a region where the power generation efficiency of the fuel cell is high. Usually, in the region where the power generation efficiency of the fuel cell is high, the output voltage of the fuel cell is within the oxidation-reduction progress voltage range. As a result, the deterioration of the fuel cell proceeds.

  The present invention has been made in consideration of such problems, and an object thereof is to provide a fuel cell system capable of improving the output efficiency of the entire fuel cell system while suppressing deterioration of the fuel cell. And

  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. A voltage adjusting means for adjusting the output voltage of the fuel cell; a load driven by the output power of the fuel cell; and a surplus of the output power supplied from the fuel cell to the load; And a power storage device that supplies the load to the load, and further includes a control unit that detects a required output of the load and controls the fuel cell, the gas supply unit, and the voltage adjustment unit. The control means controls the gas supply means in a state where the output voltage of the fuel cell is fixed to a specific voltage value outside the oxidation-reduction progress voltage range by controlling the voltage adjusting means. A voltage fixing / variable output control for varying the concentration of the oxygen or hydrogen supplied to the fuel cell so as to follow the required output of the load is performed, and the oxidation-reduction is performed in a normal power generation state of the fuel cell. When the output range of the fuel cell corresponding to the progress voltage range is defined as the redox progress output range, the voltage fixing / variable output control is executed when the required output of the load is within the redox progress output range. Further, in the voltage fixing / variable output control, the output efficiency of the fuel cell system is highest when the concentration of the oxygen or the hydrogen is varied while fixing the output voltage of the fuel cell to the specific voltage value. An upper limit output value and a lower limit output value of the fuel cell that are determined across a maximum efficiency region that is an output region of the fuel cell are set, and the required output of the load is set. When the value exceeds the lower limit output value and falls below the upper limit output value, the fixing to the specific voltage value and the follow-up to the required output of the load are continuously performed, and the required output of the load is lower than the lower limit output value. Alternatively, when the output value exceeds the upper limit output value, the gas supply means is controlled so that the output of the fuel cell becomes a value within the maximum efficiency region while continuously fixing to the specific voltage value. And

  According to the present invention, it is possible to improve the power generation efficiency of the entire fuel cell system during the voltage fixing / output variable control while suppressing the deterioration of the fuel cell by the voltage fixing / output variable control.

  In other words, in the fixed voltage / variable output control, the output voltage of the fuel cell is fixed to a specific voltage value outside the redox progressing voltage range, so that deterioration of the fuel cell due to the output voltage entering the redox progressing voltage range is avoided. be able to.

  Further, according to the present invention, when the required output of the load exceeds the lower limit output value and falls below the upper limit output value, the fixed output to the specific voltage value and the follow-up to the required output of the load are continuously performed. Is lower than the lower limit output value or higher than the upper limit output value, the gas supply means is controlled so that the output of the fuel cell becomes a value within the maximum efficiency region while continuing to be fixed to the specific voltage value. For this reason, if the output region where the output efficiency of the fuel cell deteriorates excessively is set by the lower limit output value and the upper limit output value, when there is a requested output of the load corresponding to the region where the output efficiency deteriorates excessively Rather, it is possible to generate power from the fuel cell with high output efficiency and store the surplus in the power storage device. As a result, the power generation efficiency of the entire fuel cell system can be increased.

  When the required output of the load falls below the lower limit output value or exceeds the upper limit output value, the output of the fuel cell is adjusted by the gas supply means so that the remaining capacity of the power storage device approaches a target value. Good. Thereby, the remaining capacity of the power storage device can be controlled favorably.

  The fuel cell system is a system mounted on a vehicle, and when the required output of the load is lower than the lower limit output value or higher than the upper limit output value, the output of the fuel cell is supplied to the gas supply means based on a regeneration history. You may adjust by. Thereby, the remaining capacity of the power storage device can be controlled favorably.

  According to the present invention, it is possible to improve the power generation efficiency of the entire fuel cell system during the voltage fixing / output variable control while suppressing the deterioration of the fuel cell by the voltage fixing / output variable control.

  In other words, in the fixed voltage / variable output control, the output voltage of the fuel cell is fixed to a specific voltage value outside the redox progressing voltage range, so that deterioration of the fuel cell due to the output voltage entering the redox progressing voltage range is avoided. be able to.

  Further, according to the present invention, when the required output of the load exceeds the lower limit output value and falls below the upper limit output value, the fixed output to the specific voltage value and the follow-up to the required output of the load are continuously performed. Is lower than the lower limit output value or higher than the upper limit output value, the gas supply means is controlled so that the output of the fuel cell becomes a value within the maximum efficiency region while continuing to be fixed to the specific voltage value. For this reason, if the output region where the output efficiency of the fuel cell deteriorates excessively is set by the lower limit output value and the upper limit output value, when there is a requested output of the load corresponding to the region where the output efficiency deteriorates excessively Rather, it is possible to generate power from the fuel cell with high output efficiency and store the surplus in the power storage device. As a result, the power generation efficiency of the entire fuel cell system can be increased.

1 is a schematic overall configuration diagram of a fuel cell vehicle equipped with a fuel cell system (FC 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 FC system. It is a figure which shows the relationship between a cathode stoichiometric ratio and a cell current. It is a flowchart in the second mode. It is a figure which shows the relationship between the target FC electric current 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 electric current, 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 electric current, and the target back pressure valve opening degree. It is a figure which shows the relationship between the target FC electric current in 2nd mode, and an air flow rate. 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. 10 is a flowchart for calculating a target FC current in a second mode. It is a figure which shows the relationship between FC output and the output efficiency of FC unit about each of 1st mode and 2nd mode. It is a figure which shows the relationship between FC output and the electric power generation efficiency of FC itself about each of 1st mode and 2nd mode. It is a figure explaining the setting method of the lower limit and upper limit used for FC output in the 2nd mode. It is a figure which shows the relationship between battery SOC and a regeneration average correction coefficient. It is a flowchart of torque control of a motor. It is an example of the time chart at the time of using the various control which concerns on the said embodiment and 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.

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 traveling 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” or “FC output Pfc”) includes the inverter 16 and the motor 14 (during power running), the DC / DC converter 22, and the high-voltage battery 20 ( In addition to 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. Is done.

  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 control and 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, three control methods (power supply modes) are used as power supply control methods (power supply modes) used in energy management. That is, in this embodiment, the first to third modes 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 output Pfc) are variable. The second mode is voltage fixed / current variable control (voltage fixed / output variable control) in which the target FC voltage Vfctgt is constant and the FC current Ifc (FC power Pfc) is variable. The third mode is voltage fixing / current fixing control (voltage fixing / output fixing control) in which the target FC voltage Vfctgt is constant and the FC current Ifc (FC output Pfc) is constant.

  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 fixed / current variable control) is mainly used when the system load Psys is relatively medium, and the target cell voltage Vcelltgt (= target FC voltage Vfctgt / number of cells) is oxidized. By fixing the reference potential {potential v2 (= 0.8 V) in this embodiment} set below a potential lower than the reduction region R3 and making the target oxygen concentration Cotgt basically variable, the FC current Ifc is variable (with some exceptions). 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.

  The third mode (voltage fixing / current fixing control) is mainly used when the system load Psys is relatively low, and the target cell voltage Vcelltgt (= target FC voltage Vfctgt / number of cells) is changed to the redox region. The potential outside R3 {in this embodiment, the potential v3 (= 0.9 V)} is fixed, and the FC current Ifc is constant. The shortage of the FC power Pfc is assisted from the battery 20, and the surplus of the FC power Pfc is charged to 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 determines whether or not the vehicle 10 is in a high load state. Specifically, the ECU 24 determines whether or not the system load Psys calculated in step S2 is greater than or equal to a threshold value P2 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. This means that the FC power Pfc obtained at this time is balanced with the system load Psys.

  When the system load Psys is greater than or equal to the threshold P2, the vehicle 10 is in a high load state, and when the system load Psys is not greater than or equal to the threshold P2, the vehicle 10 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 lower than a threshold value THVh 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 less than a threshold for determining a high load.

  When the vehicle 10 is in a high load state (S21: YES), in step S22, 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 (S21: NO), the process proceeds to step S23.

  In step S23, the ECU 24 determines whether or not the vehicle 10 is in a medium load state. Specifically, the ECU 24 determines whether or not the system load Psys calculated in step S2 is greater than or equal to a threshold value P1 for determining medium load. The medium load referred to here is, for example, a state in which oxygen is rich and the cell voltage Vcell is set to a value in the redox region R3 (the FC voltage Vfc is set to the value in the reduction region R3 × the number of cells) to generate FC40. This means a case where the FC power Pfc obtained at this time is balanced with the system load Psys.

  When the system load Psys is greater than or equal to the threshold value P1, the vehicle 10 is in an intermediate load state, and when the system load Psys is not greater than or equal to the threshold value P1, the vehicle 10 is not in an intermediate load state. The medium load state may be determined by other methods. For example, the medium load state can be determined based on whether or not the vehicle speed V is equal to or lower than a threshold value THVm for determining the medium load. Alternatively, the medium load state may be determined based on whether or not the acceleration of the vehicle 10 (change amount of the vehicle speed V) is equal to or less than a threshold value for determining the medium load.

  When the vehicle 10 is in a medium load state (S23: YES), in step S24, the ECU 24 performs the second mode (voltage fixing / current variable control) (details will be described later with reference to FIG. 13). When the vehicle 10 is not in the middle load state (S23: NO), in step S25, the ECU 24 performs the third mode (voltage fixing / current fixing control) (details will be described later).

(2-3-4. First mode)
As described above, the first mode is mainly used when the system load Psys is relatively high. In the state where the target oxygen concentration Cotgt is fixed (or oxygen is maintained in a rich state), The FC current Ifc is controlled by adjusting the 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 system load Psys, 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. 12, when the cathode stoichiometric ratio is increased, the cell current Icell becomes substantially constant and is substantially higher than the normal stoichiometric ratio in which the oxygen current is rich. 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 in the cathode channel 74. The cathode stoichiometric ratio is adjusted by controlling the oxygen concentration, for example.

  According to the first mode as described above, even if the system load Psys is high, basically all of the 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 system load Psys is a medium load, and the target cell voltage Vcelltgt (= target FC voltage Vfctgt / number of cells) is lower than that in the oxidation-reduction region R3. The FC current Ifc is made variable by fixing the reference potential {in this embodiment, the potential v2 (= 0.8 V)} set below the potential and making the target oxygen concentration Cotgt basically variable.

  That is, as shown in FIG. 10, in the second mode, the oxygen concentration Co is lowered by lowering the target oxygen concentration Cotgt while keeping the cell voltage Vcell constant. As shown in FIG. 12, when the cathode stoichiometric ratio (oxygen concentration Co) decreases, the cell current Icell (FC current Ifc) also decreases. For this reason, it is possible to control the cell current Icell (FC current Ifc) and the FC power Pfc by increasing or decreasing the target oxygen concentration Cotgt while keeping the cell voltage Vcell constant. Note that the shortage of the FC power Pfc is assisted from the battery 20.

  FIG. 13 shows a flowchart of the second mode. In step S31, the ECU 24 adjusts the step-up rate of the DC / DC converter 22 to thereby set a reference potential that is set to a potential lower than the oxidation-reduction region R3 (in this embodiment, the potential v2 (= 0.8 V)). }, The target FC voltage Vfctgt is fixed. In step S32, the ECU 24 calculates a target FC current Ifctgt corresponding to the system load Psys (details will be described later with reference to FIG. 19 and the like).

  In step S33, the ECU 24 calculates a target oxygen concentration Cotgt corresponding to the target FC current Ifctgt on the assumption that the target FC voltage Vfctgt is a reference potential (see FIGS. 10 and 14). FIG. 14 shows the relationship between the target FC current Ifctgt and the target oxygen concentration Cotgt when the FC voltage Vfc is the reference potential.

  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. 15 and 16, the target air pump speed Naptgt, the target water pump speed Nwptgt, and the target back pressure valve opening θbptgt are set according to the target oxygen concentration Cotgt. 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).

  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 level (see FIG. 17). Note that FIG. 17 illustrates a case where the flow rate Qc increases in the fourth stage and reaches the maximum flow rate 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 in the same manner, 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. 18, 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. If 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 equal to or lower than the target oxygen concentration (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 system load Psys is a medium load, the system is basically configured by adjusting the oxygen concentration Co (cathode stoichiometric ratio) while keeping the cell voltage Vcell constant. All of the load Psys can be covered by the FC power Pfc.

(2-3-6. Calculation of target FC current Ifctgt in the second mode)
FIG. 19 is a flowchart (details of S32 in FIG. 13) for calculating the target FC current Ifctgt in the second mode. In step S51, the ECU 24 determines whether or not relatively efficient power generation is possible in the second mode. Specifically, it is determined whether or not the system load Psys is not less than the lower limit value lim1 and not more than the upper limit value lim2. The lower limit value lim1 and the upper limit value lim2 will be described with reference to FIG.

  FIG. 20 is a diagram illustrating the relationship between the FC power Pfc and the output efficiencies E1 and E2 of the FC unit 18 for each of the first mode and the second mode.

The output efficiency E1 of the first mode is obtained by the following equation (1).
E1 = (Pfcm1-Pap-Ppg) / Eh (1)

  In the above formula (1), Pfcm1 is FC power Pfc (hereinafter referred to as “first mode FC power Pfcm1”) [kW] at a normal stoichiometric ratio when a predetermined amount (unit amount) of hydrogen is used. Pap is the power consumption of the air pump 60 when the predetermined amount of hydrogen is used (hereinafter referred to as “air pump consumption Pap”) [kW]. Ppg is the energy of hydrogen discharged from the purge valve 50 when the predetermined amount of hydrogen is used (hereinafter referred to as “purge consumption amount Ppg”) [kW]. Eh is the energy of the predetermined amount of hydrogen (hereinafter referred to as “hydrogen energy Eh”) [kW].

Similarly, the output efficiency E2 of the second mode is obtained by the following equation (2).
E2 = (Pfcm2-Pap-Ppg) / Eh (2)

  In the above equation (2), Pfcm2 is FC power Pfc (hereinafter referred to as “second mode FC power Pfcm2”) [kW] when the oxygen concentration Co is changed when the predetermined amount of hydrogen is used. . The air pump consumption Pap, the purge consumption Ppg, and the hydrogen energy EH are the same as in equation (1).

  As shown in FIG. 20, in the region where the FC power Pfc is close to zero, when the FC power Pfc increases, both the output efficiencies E1 and E2 increase, and then gradually decrease. This is influenced by the power generation efficiency of the FC 40 itself as described below.

  FIG. 21 is a diagram illustrating the relationship between the FC power Pfc and the power generation efficiencies Efc1 and Efc2 [%] of the FC 40 itself for each of the first mode and the second mode. The power generation efficiency Efc1 in the first mode is obtained by dividing the first mode FC power Pfcm1 by the hydrogen energy Eh (Efc1 = Pfcm1 / Eh). The power generation efficiency Efc2 in the second mode is obtained by dividing the second mode FC power Pfcm2 by the hydrogen energy Eh (Efc2 = Pfcm2 / Eh).

  As shown in FIG. 21, the power generation efficiency Efc1 of the FC 40 itself in the first mode decreases as the FC power Pfc increases. This is because the FC voltage Vfc is variable in the first mode, but when the cell voltage Vcell is low (that is, when the FC power Pfc is high), the heat radiation amount of each FC cell is high. On the other hand, the power generation efficiency Efc2 in the FC 40 itself in the second mode does not change depending on the FC power Pfc (it is constant in FIG. 21). This is because in the second mode, the FC voltage Vfc is constant, so that the heat radiation amount of each FC cell is constant.

  Since the power generation efficiencies Efc1 and Efc2 of the FC 40 itself have the above characteristics, the FC unit 18 as a whole has the output efficiencies E1 and E2 of FIG.

  As shown in FIG. 20, when the FC power Pfc is the same, the output efficiency E1 in the first mode is basically higher than the output efficiency E2 in the second mode. In FIG. 20, P1 is FC power Pfc corresponding to the case where the cell voltage Vcell is the potential v3 (= 0.9V), and P2 is the cell voltage Vcell being the potential v2 (= 0.8V). This is the FC power Pfc corresponding to the case.

  As described above, in the first mode, the FC current Ifc and the FC power Pfc are controlled by making the FC voltage Vfc (cell voltage Vcell) variable. Therefore, the first mode corresponds to the case where the cell voltage Vcell changes between the potential v2 and the potential v3 between the FC power P1 and the FC power P2. On the other hand, in the second mode, the FC current Ifc and the FC power Pfc are controlled by making the target oxygen concentration Cotgt variable while fixing the FC voltage Vfc (cell voltage Vcell). Therefore, in the second mode, the cell voltage Vcell remains constant at the potential v2 between the FC power P1 and the FC power P2 (the FC voltage Vfc remains constant at the potential v2 × the number of cells).

  Next, the lower limit value lim1 and the upper limit value lim2 will be described. As described above, the lower limit value lim1 and the upper limit value lim2 are used in the second mode, and are set across the maximum efficiency region Rhieff in the output efficiency E2, as shown in FIG. The maximum efficiency region Rhieff is a region including a maximum value (hereinafter referred to as “maximum efficiency realizing output Phieff” or “maximum value Phieff”) and a value in the vicinity thereof.

  The lower limit value lim1 and the upper limit value lim2 can be set by the following method, for example. That is, as shown in FIG. 22, the FC power Pfc that realizes a value that is a predetermined value ΔX% lower than the output efficiency E2 corresponding to the maximum value Phieff is set to the lower limit value lim1 and the upper limit value lim2. Here, the predetermined value ΔX can be selected, for example, by changing the predetermined value Δ while actually driving the vehicle 10 and by selecting the value with the best fuel consumption. Note that the lower limit value lim1 and the upper limit value lim2 can be set individually.

  Returning to FIG. 19, when the system load Psys is not less than the lower limit value lim1 and not more than the upper limit value lim2 (S51: YES), in step S52, the ECU 24 sets the system load Psys as the required load as the target FC output Pfctgt. (Pfctgt ← Psys).

  When the system load Psys is not lower than the lower limit value lim1 and lower than the upper limit value lim2 (S51: NO), relatively efficient power generation cannot be performed in the second mode (FIG. 20). Therefore, in step S53, the ECU 24 sets the maximum efficiency achievement output Phieff to the temporary target FC output Pfctgt_t (Pfctgt_t ← Phieff).

  In step S54, the ECU 24 sets a regenerative average correction coefficient α (hereinafter also referred to as “coefficient α”) according to the regenerative average power Pregave and the SOC of the battery 20. The regenerative average power Pregave is a moving average [kW / min] of the regenerative power Preg in a predetermined period (for example, a value set between 1 minute and 30 minutes), and indicates a regeneration history. The coefficient α is a coefficient for correcting the temporary target FC output Pfctgt_t according to the likelihood of regenerative power.

  FIG. 23 is a diagram illustrating the relationship between the SOC of the battery 20 and the coefficient α for each regenerative average power Pregave. In FIG. 23, the characteristic indicated by the solid line is a characteristic indicating the relationship between the SOC and the coefficient α when the regenerative average power Pregave is normal, and the characteristic indicated by the alternate long and short dash line is the SOC when the regenerative average power Pregave is less than normal. The two-dot chain line is a characteristic indicating the relationship between the SOC and the coefficient α when the regenerative average power Pregave is higher than usual. The reference value Sref is a target value for the SOC.

  As can be seen from FIG. 23, when the regenerative average power Pregave is small in a state where the battery SOC exceeds the reference value Sref, the coefficient α is set to a value close to 1 even if the SOC is away from the reference value Sref. On the other hand, when the regenerative average power Pregave is large in a state where the battery SOC exceeds the reference value Sref, the coefficient α is greatly increased from 1 when the SOC is away from the reference value Sref. By multiplying the temporary target FC output Pfctgt_t by such a coefficient α, it becomes easy to maintain the SOC at or near the reference value Sref.

  In addition, in the present embodiment, a region (dead zone) where the coefficient α remains unchanged at 1 is provided. For example, when the regenerative average power Pregave is normal, the battery SOC is a dead zone between S1 and S2.

  In selecting the coefficient α, the ECU 24 first selects the characteristics of the SOC and the coefficient α in accordance with the regenerative average power Pregave. Next, the coefficient α is selected according to the SOC. Note that the relationship between the regenerative average power Pregave, the SOC, and the coefficient α can be, for example, an experimental value or a simulation value, and is stored in advance in a storage unit (not shown) of the ECU 24.

  Returning to FIG. 19, in step S55, the ECU 24 multiplies the temporary target FC output Pfctgt_t by the coefficient α to obtain the target FC output Pfctgt.

  After step S52 or step S55, in step S56, the ECU 24 sets the target FC current Ifctgt according to the target FC output Pfctgt.

(2-3-7. Third mode)
As described above, the third mode is mainly used when the system load Psys is relatively low, and the target cell voltage Vcelltgt (= target FC voltage Vfctgt / number of cells) is set outside the redox region R3. The potential {in this embodiment, the potential v3 (= 0.9V)} is fixed, and the FC current Ifc is constant. The shortage of the FC power Pfc is assisted from the battery 20, and the surplus of the FC power Pfc is charged to the battery 20. The target oxygen concentration Cotgt is normally fixed to the oxygen concentration Conml (or oxygen is maintained in a rich state).

  That is, as shown in FIG. 10, in the third mode, the cell voltage Vcell is set to the potential while the current-voltage characteristic (IV characteristic) of the FC 40 is normal (represented by a solid line in FIG. 10). It is fixed at v3 (FC voltage Vfc is set to potential v3 × number of cells). Since the current-voltage characteristic (IV characteristic) of the FC 40 is assumed to be normal, the ECU 24 sets the normal oxygen concentration Conml as the target oxygen concentration Cogt, and the rotation speed Nap and water of the air pump 60 according to the target oxygen concentration Cogt. The rotational speed Nwp of the pump 80, the opening degree θbp of the back pressure valve 64, and the opening degree θc of the circulation valve 66 are set. Further, in order to fix the cell voltage Vcell to the potential v3, the ECU 24 boosts the secondary voltage V2 by the DC / DC converter 22 so that the FC voltage Vfc is equal to the potential v3 × the number of cells.

  According to the third mode as described above, when the system load Psys is a low load, the system load Psys can be covered by the FC power Pfc and the battery power Pbat.

[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 command values (for example, S34 in FIG. 13) of these devices calculated by energy management (S3 in FIG. 5).

[2-5. Torque control of motor 14]
FIG. 24 shows a flowchart of torque control of the motor 14. In step S61, the ECU 24 reads the motor rotational speed Nm from the rotational speed sensor 152. In step S <b> 62, the ECU 24 reads the opening degree θp of the accelerator pedal 154 from the opening degree sensor 150.

  In step S63, 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 S64, 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 S65, 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, when it is determined in step S64 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 S65. 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 S66, 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. Examples of Various Controls FIG. 25 shows an example of a time chart when various controls according to the present embodiment and various controls according to a comparative example are used. As for “FC current Ifc”, “cathode stoichiometric ratio”, and “output efficiency of FC unit” in FIG. 25, the solid line indicates the present embodiment, and the broken line indicates the comparative example. Is. The comparative example indicated by the broken line is the same control as the first to third modes (however, only the steps S52 and S56 of FIG. 19 are used in the second mode) (that is, the lower limit value lim1 and the upper limit in the second mode). Control without using the value lim2).

  From the time point t1 to the time point t2, the system load Psys is less than the threshold value P1 (S23: NO in FIG. 11), so the third mode is selected in both the present embodiment and the comparative example. From the time point t2 to the time point t4, the system load Psys is greater than or equal to the threshold value P1 and less than the threshold value P2 (S23 in FIG. 11: YES), so the second mode is selected in both the present embodiment and the comparative example.

  More specifically, since the system load Psys is not less than the lower limit value lim1 and not more than the upper limit value lim2 from the time point t2 to the time point t3 (S51: YES in FIG. 19), in both the present embodiment and the comparative example, The system load Psys is set as the target FC output Pfctgt as it is (S52), and the target FC current Ifctgt corresponding to the target FC output Pfctgt is set (S56).

  From the time point t3 to the time point t4, the system load Psys is less than the lower limit lim1 (S51: NO in FIG. 19). Therefore, in the present embodiment, relatively high-efficiency power generation is performed in the second mode (S53- S56). On the other hand, in the comparative example, relatively low-efficiency power generation is performed (S52, S56) (see FIG. 20).

  From the time point t4 to the time point t5, the system load Psys is less than the threshold value P1 (S23 in FIG. 11: NO), so the third mode is selected in both the present embodiment and the comparative example. Since the system load Psys is not less than the threshold value P1 and less than the threshold value P2 after the time point t5 (S23: YES in FIG. 11), the second mode is selected in both the present embodiment and the comparative example.

  More specifically, since the system load Psys is less than the lower limit value lim1 from time t5 to time t6 and from time t10 to time t11 (S51: NO in FIG. 19), in the present embodiment, in the second mode While relatively high-efficiency power generation is performed (S53 to S56), in the comparative example, relatively low-efficiency power generation is performed (S52, S56).

  Since the system load Psys is not less than the lower limit value lim1 and not more than the upper limit value lim2 from the time point t6 to the time point t7 and from the time point t8 to the time point t10 (S51 in FIG. 19: YES), both the present embodiment and the comparative example The system load Psys is set as the target FC output Pfctgt as it is (S52), and the target FC current Ifctgt according to the target FC output Pfctgt is set (S56).

  From the time point t7 to the time point t8, the system load Psys exceeds the upper limit value lim2 (S51: NO in FIG. 19). Therefore, in the present embodiment, relatively high-efficiency power generation is performed in the second mode (S53- (S56) In the comparative example, relatively low-efficiency power generation is performed (S52, S56).

  Note that the regenerative average correction coefficient α is set to 1 because the battery SOC is in the dead zone from time t1 to time t9. Since the battery SOC leaves the dead zone from time t9 to time t11, the coefficient α is set to a value different from 1 depending on the regenerative average power Pregave.

4). Effects of the Present Embodiment As described above, according to the present embodiment, the FC system 12 (during the voltage fixing / current variable control) while suppressing the deterioration of the FC 40 by the voltage fixing / current variable control (second mode). The overall output efficiency of the FC unit 18) can be improved.

  That is, in the voltage fixing / current variable control (second mode), the FC voltage Vfc enters the region R3 in order to fix the FC voltage Vfc to a specific voltage value (0.8 V × number of cells) outside the redox region R3. It is possible to avoid the deterioration of FC40 due to the above.

  Further, according to the present embodiment, when the system load Psys is not less than the lower limit value lim1 and not more than the upper limit value lim2, fixing to the specific voltage value and following the system load Psys are continuously performed, and the system load Psys is the lower limit value. When it is less than lim1 or exceeds the upper limit value lim2, the air pump 60 is controlled so that the FC output Pfc becomes a value within the maximum efficiency range Rhieff (maximum efficiency achievement output Phieff) while continuing to be fixed to a specific voltage value. To do. For this reason, if the output region where the output efficiency E2 of the FC unit 18 is excessively deteriorated is set by the lower limit value lim1 and the upper limit value lim2, there is a system load Psys corresponding to the region where the output efficiency E2 is excessively deteriorated. In this case, it is possible to generate the FC 40 with rather high output efficiency and charge the battery 20 with the surplus. As a result, the power generation efficiency of the FC system 12 as a whole can be increased.

  In the present embodiment, when the system load Psys is lower than the lower limit value lim1 or higher than the upper limit value lim2, the target SOC output Pfctgt corrected by the regenerative average correction coefficient α is used so that the battery SOC approaches the reference value Sref. The FC output Pfc is adjusted by the air pump 60. Thereby, battery SOC can be controlled satisfactorily.

  In the present embodiment, the FC system 12 is a system mounted on the vehicle 10, and when the system load Psys is below the lower limit lim1 or exceeds the upper limit lim2, the FC output is based on the average regenerative power Pregave as the regeneration history. Pfc is adjusted by the air pump 60. Thereby, battery SOC can be controlled satisfactorily.

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 embodiment, the FC system 12 is mounted on the FC vehicle 10, but is not limited thereto, and may be mounted on another target to which voltage fixing / current variable control (voltage fixing / output variable control) can be applied. For example, the FC system 12 can be used for a moving body such as a ship or an aircraft. Alternatively, it can be applied to a movable mechanism such as a robot arm, a crane, or a balancer. Alternatively, the FC system 12 may be applied to a household power system.

[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. 26, 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. 27, the FC 40 and the battery 20 are arranged in parallel. The structure to arrange | position may be sufficient. Alternatively, as shown in FIG. 28, 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.

[5-4. Power supply mode]
In the above embodiment, the first to third modes are used as the power supply mode, but the present invention can be applied as long as at least the second mode is used.

  In the above embodiment, the target FC voltage Vfctgt in the second mode is set to the potential v2 (= 0.8 V) × the number of cells, but this is not restrictive. For example, the target FC voltage Vfctgt in the second mode may be set to another potential in the reduction region R2 or the oxidation region R4.

  In the above embodiment, in order to control the oxygen concentration Co in the second mode, the circulation valve opening degree θc, the air pump rotation speed Nap, and the back pressure valve opening degree θbp are made variable. However, as long as the oxygen concentration Co can be controlled. Not limited to this. For example, the air pump rotation speed Nap may be constant, and the circulation valve opening degree θc may be variable. Thereby, since the output sound of the air pump 60 becomes constant, it becomes possible to prevent a sense of discomfort given to the occupant by making the output sound variable.

  In the above embodiment, both the lower limit value lim1 and the upper limit value lim2 are used, but only one of them can be used.

  In the above embodiment, when the system load Psys falls below the lower limit value lim1 or exceeds the upper limit value lim2, the maximum efficiency realized output Phieff is set as the temporary target FC output Pfctgt_t. It may be a value. Alternatively, at least the range between the lower limit value lim1 and the upper limit value lim2 can be set as the temporary target FC output Pfctgt_t. For example, when the system load Psys is less than the lower limit value lim1, the lower limit value lim1 can be set as the temporary target FC output Pfctgt_t. Similarly, when the system load Psys is less than the upper limit value lim2, the upper limit value lim2 can be set as the temporary target FC output Pfctgt_t.

  In the above embodiment, the regenerative average correction coefficient α is used. However, a configuration in which the coefficient α is not used is also possible.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell vehicle 12 ... Fuel cell system 14 ... Motor for driving | running | working (load) 16 ... Inverter (load)
20 ... High voltage battery (power storage device)
22 ... DC / DC converter (voltage adjusting means)
24 ... ECU (control means) 40 ... Fuel cell stack 60 ... Air pump (gas supply means, load) 66 ... Circulation valve (gas supply means)
80 ... Water pump (load) 90 ... Air conditioner (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 adjusting means for adjusting the output voltage of the fuel cell;
A load driven by the output power of the fuel cell;
A fuel cell system comprising: a power storage device that stores a surplus of the output power supplied from the fuel cell to the load and supplies a shortage to the load;
A control means for detecting the required output of the load and for controlling the fuel cell, the gas supply means and the voltage adjustment means;
The control means controls the gas supply means and supplies the fuel cell to the fuel cell in a state where the output voltage of the fuel cell is fixed to a specific voltage value outside the oxidation-reduction progress voltage range by controlling the voltage adjusting means. Performing a voltage fixing / output variable control for varying the oxygen or hydrogen concentration so as to follow the required output of the load,
When the output range of the fuel cell corresponding to the oxidation-reduction progress voltage range in the normal power generation state of the fuel cell is defined as the oxidation-reduction progress output range, the voltage fixing / output variable control is such that the required output of the load is It is executed when it is within the redox progress output range,
Furthermore, in the voltage fixing / output variable control,
The maximum efficiency region, which is the output region of the fuel cell, where the output efficiency of the fuel cell system is maximum when the concentration of the oxygen or the hydrogen is varied while fixing the output voltage of the fuel cell to the specific voltage value. An upper limit output value and a lower limit output value of the fuel cell determined by sandwiching
When the required output of the load exceeds the lower limit output value and falls below the upper limit output value, the fixed output to the specific voltage value and the follow-up to the required output of the load are continuously executed.
When the required output of the load is lower than the lower limit output value or higher than the upper limit output value, the output of the fuel cell becomes a value within the maximum efficiency range while continuously fixing to the specific voltage value. The fuel supply system is characterized by controlling the gas supply means as described above. The fuel cell system according to claim 1, wherein
When the required output of the load is less than the lower limit output value or exceeds the upper limit output value, the output of the fuel cell is adjusted by the gas supply means so that the remaining capacity of the power storage device approaches a target value. A fuel cell system. The fuel cell system according to claim 1 or 2,
The fuel cell system is a system mounted on a vehicle,
When the required output of the load falls below the lower limit output value or exceeds the upper limit output value, the output of the fuel cell is adjusted by the gas supply means based on the regeneration history.

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