JP5675509B2 - Fuel cell system and vehicle equipped with the system - Google Patents

Description

  The present invention relates to a fuel cell system that prevents deterioration of a fuel cell that generates power by an electrochemical reaction of both oxidant gas and fuel gas and improves system efficiency, and a vehicle equipped with the system.

  The fuel cell includes, for example, an electrolyte membrane / electrode structure (MEA) in which a solid polymer electrolyte membrane in which a thin film of perfluorosulfonic acid is impregnated with water is sandwiched between a cathode electrode and an anode electrode. The cathode electrode and the anode electrode include a gas diffusion layer made of carbon paper or the like, and carbon particles carrying catalyst (hereinafter also referred to as Pt catalyst) particles such as platinum alloy on the surface of the gas diffusion layer. And an electrode catalyst layer formed by coating. The electrode catalyst layers are formed on both sides of the solid polymer electrolyte membrane.

  A technique for suppressing the deterioration of the fuel cell is proposed in Patent Document 1. In the technique proposed in Patent Document 1, when the fuel cell is generated, the Pt catalyst avoids a redox advance voltage that causes a sintering phenomenon (aggregation of the Pt catalyst).

JP 2007-5038 ([0041], FIG. 11 etc.)

  By the way, in Patent Document 1, in order to keep avoiding the oxidation-reduction progress voltage related to the Pt catalyst, the generated power of the fuel cell is increased or decreased relative to the required power of the load such as the travel motor.

  The surplus power when the generated power of the fuel cell increases relative to the required power is charged to the battery, while the insufficient power when the generated power of the fuel cell decreases is discharged from the battery. It is funded.

  However, the battery has a problem that a loss occurs every time charging and discharging are repeated, resulting in a deterioration in system efficiency.

  Further, in the control of Patent Document 1, traveling on a highway (running at a relatively medium load), where starting at a constant speed often continues for a relatively long time, and starting and stopping are repeated relatively frequently. No consideration has been given to the output efficiency of the entire fuel cell system for driving in urban areas (traveling at a relatively low load).

  The present invention has been made in view of such problems, and a fuel cell system capable of suppressing deterioration of system efficiency and improving system efficiency while preventing deterioration of the fuel cell, and the system An object is to provide an onboard vehicle.

The 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 adjusts the supply amount of at least one of the oxygen and the hydrogen, and the fuel cell. A fuel cell system comprising: a gas supply unit that supplies gas; a voltage adjustment unit that adjusts an output voltage of the fuel cell; and a load that is driven by the output power of the fuel cell. And a control means for controlling the fuel cell, the gas supply means, and the voltage adjusting means, and the control means controls the voltage adjusting means so that the output voltage of the fuel cell is out of the redox advance voltage range. In a state where the predetermined voltage value is fixed, the gas supply means is controlled so that the concentration of oxygen or hydrogen supplied to the fuel cell follows the required power of the load. In a first control mode to be changed, and in a state where the voltage adjusting means is controlled and the output voltage of the fuel cell is fixed to the predetermined voltage value, the gas supply means is controlled to supply the oxygen or the oxygen a second control mode to maintain the concentration of hydrogen in a predetermined concentration range, which is executed, the output voltage of the fuel cell corresponding to the required power of the load, be in the redox progression voltage range, The first control mode is executed when the loss in the first control mode is equal to or higher than the switching voltage lower than the loss in the second control mode, and the second control mode is executed when the loss is lower than the switching voltage. It is characterized by performing.

  According to the present invention, when the voltage of the fuel cell corresponding to the required power of the load is equal to or higher than a predetermined value (switching voltage) within the oxidation-reduction progress voltage range of the fuel cell, the control means A first control mode in which the concentration of the oxygen or hydrogen supplied to the fuel cell is varied so as to follow the required power of the load in a state where the output voltage is fixed to a predetermined voltage value outside the range of the redox progressing voltage. And the output voltage of the fuel cell is oxidized when the voltage of the fuel cell corresponding to the required power of the load is less than a predetermined value (switching voltage) within the oxidation-reduction progress voltage range of the fuel cell. Since the control is performed in the second control mode in which the concentration of oxygen or hydrogen is maintained within the predetermined concentration range while being fixed at a predetermined voltage value outside the reduction progress voltage range, the output voltage of the fuel cell is the redox progress voltage. While preventing deterioration of the fuel cell to avoid the 囲内, thereby improving the system efficiency.

  And a power storage device that is charged by the output power of the fuel cell and supplies power to the fuel cell system, wherein the control means detects the SOC value of the power storage device during execution of the first control mode. When the detected SOC value is less than a predetermined value, the SOC value of the power storage device can be prevented from excessively decreasing by executing the second control mode.

  A vehicle equipped with the above fuel cell system is also included in the present invention.

  According to the present invention, by preventing the output voltage of the fuel cell from being within the oxidation-reduction progress voltage range, the deterioration of the fuel cell is prevented and the deterioration of the system efficiency is suppressed, thereby improving the system efficiency. The effect of being able to be achieved is achieved.

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 circuit diagram which shows the detail of the DC / DC converter in the said embodiment. 3 is a flowchart of basic control (main routine) in an electronic control unit (ECU). It is a flowchart which calculates a system load and an average 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 voltage 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 advancing of oxidation, and the progress of reduction | restoration in case the fluctuation speed of the voltage of a fuel cell differs. It is explanatory drawing of the normal current-voltage characteristic of a fuel cell. It is a figure which shows the relationship between a cathode stoichiometric ratio and a cell current. It is a flowchart with which description of embodiment which concerns on the electric power generation control of a fuel cell is provided. It is explanatory drawing of the several electric power supply mode in a fuel cell. It is a figure which shows the relationship between the SOC value of a battery, and a charging / discharging coefficient. It is a figure which shows the relationship between target FC electric current and target oxygen concentration. It is a figure which shows the relationship between target FC current, target air pump rotation speed, and target water pump rotation speed. It is a figure which shows the relationship between target FC electric current and target back pressure valve opening. It is a flowchart of torque control of a motor. It is a figure which shows the relationship between the electric power generated of a fuel cell, and electric power generation efficiency. 20A shows a loss in low oxygen stoichiometric ratio variable fixed voltage power generation, FIG. 20B shows a loss in normal stoichiometric ratio fixed voltage power generation, and FIG. 20C superimposes the loss characteristics of FIGS. 20A and 20B. FIG. It is a time chart which compares and demonstrates embodiment and the technique which concerns on a comparative example. It is a block diagram which shows schematic structure of the 1st modification of a fuel cell system. It is a block diagram which shows schematic structure of the 2nd modification of a fuel cell system. It is a block diagram which shows schematic structure of the 3rd modification of a fuel cell system.

  FIG. 1 is a schematic overall configuration diagram of a fuel cell vehicle 10 (hereinafter referred to as “FC 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. 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 (drive motor) and an inverter (bidirectional DC / AC converter) 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), and a DC / DC converter 22 (voltage adjusting means). ) And an electronic control unit 24 (hereinafter referred to as “ECU 24”).

  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).

  Inverter 16 {also referred to as PDU (Power Drive Unit). } Has a three-phase full-bridge configuration, performs DC / AC conversion, converts DC to three-phase AC and supplies it to the motor 14, while AC / DC conversion accompanying the regenerative operation of the motor 14. 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 (also referred to as a main load 30 when distinguished from an auxiliary load 31 described later). The main load 30 and the auxiliary load 31 are collectively referred to as a load 33 (also referred to as a total load 33).

  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 54 that supplies and discharges hydrogen (fuel gas) to and from the anode of the FC stack 40, and the FC stack 40. A cathode system 56 that supplies and discharges oxygen-containing air (oxidant gas) to and from the cathode, a cooling system 58 that circulates cooling water (refrigerant) that cools the FC stack 40, and a cell voltage monitor 42.

  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.

  The anode system 54 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 via a pipe 44a, a regulator 46, a pipe 46a, an ejector 48, and a pipe 48a. Thereby, 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 the negative off-pressure of the pipe 48b can be sucked 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 that has not been consumed by the electrode reaction at the anode and water vapor. 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 diluter (not shown) provided in the pipe 64c via the pipe 50a, the purge valve 50, and the 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 diluter dilutes the hydrogen in the anode off gas from the purge valve 50 with the cathode off gas and discharges it to the atmosphere.

  The cathode system 56 includes an air pump 60, a humidifier 62, and a back pressure valve 64.

  The air pump 60 compresses the outside air (air) and sends it to the cathode side, and its intake port communicates with the outside of the vehicle (outside, outside air) via the 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. Then, 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 humidifies the air toward the cathode channel 74. To do.

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

  The back pressure valve 64 is constituted 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 temperature sensor 72 is attached to the pipe 64a, detects the temperature of the cathode off gas, and outputs it to the ECU 24.

  The cooling system 58 includes a water pump 80 and a radiator 82 (heat radiator). The water pump 80 circulates cooling water (refrigerant), and its discharge port is connected to the suction port of the water pump 80 through the pipe 80a, the refrigerant flow path 84, the pipe 82a, the radiator 82, and the pipe 82b in this order. It is connected. When the water pump 80 is operated in accordance with a command from the ECU 24, the cooling water circulates between the refrigerant flow path 84 and the radiator 82 to cool the FC stack 40.

  The cell voltage monitor 42 is a measuring 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 cycle, detects the cell voltage Vcell of each single cell, and calculates the average cell voltage and the lowest voltage. Then, the average cell voltage and the lowest cell voltage are output to the ECU 24.

  As shown in FIG. 2, electric power from the FC stack 40 (hereinafter referred to as “FC electric power Pfc”) is supplied to the inverter 16 and the motor 14 (during power running), and also through the DC / DC converter 22, the high voltage battery 20. (During charging) and further supplied to the air pump 60, the water pump 80, the air conditioner 90, the downverter 92, the low voltage battery 94, the accessory 96, and the ECU 24. A backflow prevention diode 98 is disposed between the FC stack 40 and the inverter 16 and the DC / DC converter 22. In addition, the power generation voltage of the FC stack 40 (hereinafter referred to as “FC voltage Vfc”) is detected by the voltage sensor 100 (FIG. 4), and the power generation current Ifc of the FC stack 40 (hereinafter referred to as “FC current Ifc”). Both are detected by the current sensor 102 and output to the ECU 24.

  The battery 20 is a power storage device (energy storage) including a plurality of battery cells, and for example, a lithium ion secondary battery or the like can be used. A capacitor may be used. In this embodiment, a lithium ion secondary battery is used. The output voltage (hereinafter referred to as “battery voltage Vbat or primary voltage V1”) [V] of the battery 20 is detected by the voltage sensor 120, and the output current of the battery 20 (hereinafter referred to as “battery current Ibat or primary current I1”). .) [A] is detected by the current sensor 124 and output to the ECU 24, respectively. Further, the remaining capacity (hereinafter referred to as “SOC”) [%] of the battery 20 is detected by the SOC sensor 104 (FIG. 2) and output to the ECU 24.

  The DC / DC converter 22 determines the supply destination of the FC power Pfc from the FC unit 18, the power supplied from the battery 20 (hereinafter referred to as “battery power Pbat”) [W], and the regenerative power from the motor 14 to the ECU 24. Control under the control of.

  FIG. 4 shows an example of the DC / DC converter 22 in this embodiment. As shown in FIG. 4, one of the DC / DC converters 22 is connected to the primary side 1S where the battery 20 is located, and the other is connected to the secondary side 2S which is a connection point between the load 33 and the FC stack 40. Yes.

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

  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 diode 114) as a high side arm and a lower arm element (lower arm switching element 116 and diode 118) as a low side arm. 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 releasing and storing 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 a voltage sensor 120 provided in parallel with the smoothing capacitor 122 on the primary side 1S, and the current on the primary side 1S (primary current I1) [A] with the current sensor 124. Is detected. Further, the ECU 24 detects the secondary voltage V2 by a voltage sensor 126 provided in parallel with the smoothing capacitor 128 on the secondary side 2S, and the current 2 on the secondary side 2S (secondary current I2) [A] by the current sensor 130. Is detected.

  At the time of boosting of the DC / DC converter 22, at the first timing, the gate drive signal UL is set to the high level and the gate drive signal UH is set to the low level, and energy is accumulated from the battery 20 in the reactor 110 (the positive side of the battery 20). Current path from the reactor 110 to the reactor 110, the lower arm switching element 116, and the negative side of the battery 20). At the second timing, the gate drive signal UL is set to the low level and the gate drive signal UH is set to the low level, and the energy stored in the reactor 110 is supplied to the secondary side 2S through the diode 114 (from the positive side of the battery 20). Reactor 110, diode 114, secondary side 2S positive side, load 33, etc., secondary side 2S negative side, battery 20 negative side current path). Thereafter, the first timing and the second timing at the time of boosting are repeated.

  At the time of step-down of the DC / DC converter 22, at the first timing, the gate drive signal UH is set to the high level and the gate drive signal UL is set to the low level, and the secondary side 2S (the FC stack 40 or the motor 14 is being regenerated) in the reactor 110. The energy is accumulated from the load 33) and the battery 20 is charged. At the second timing, the gate drive signal UH is set to the low level and the gate drive signal UL is set to the low level, the energy accumulated in the reactor 110 is supplied to the battery 20 through the diode 118 and the reactor 110, and the battery 20 is charged. . As can be seen from FIG. 2, the regenerative power can be supplied to the auxiliary load 31 such as the air pump 60. Thereafter, the first timing and the second timing at the time of step-down are repeated.

  The DC / DC converter 22 can operate not only as the above-described chopper type but also as a direct connection type. When operating as a direct connection type, when the gate drive signal UH is set to high level and the gate drive signal UL is set to low level, and the battery 20 is discharged, the primary side 1S is changed to the secondary side 2S through the diode 114. When current is supplied (for example, power is supplied from the battery 20 to the load 33) and the battery 20 is charged, current is supplied from the secondary side 2S to the battery 20 through the upper arm switching element 112 (for example, The regenerative power is supplied from the motor 14 to the battery 20).

  The ECU 24 controls the motor 14, the inverter 16, the FC unit 18, the auxiliary load 31, the battery 20, the DC / DC converter 22, and the like 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 sensor 68, the temperature sensor 72, the voltage sensors 100, 120, 126, the current sensors 102, 124, 130, the SOC Detection values of various sensors such as the sensor 104 are used.

  The various sensors here include an opening sensor 150, a motor rotation number sensor 152, and a vehicle speed sensor 154 (FIG. 1) in addition to the above sensors. The opening sensor 150 detects an opening (accelerator opening) θp [degree] that is a stepping angle of the accelerator pedal 156. The rotation speed sensor 152 detects the rotation speed Nm [rpm] of the motor 14. The vehicle speed sensor 154 detects the vehicle speed Vs [km / h] of the FC vehicle 10. Further, a main switch 158 (hereinafter referred to as “main SW 158”) is connected to the ECU 24. The main SW 158 switches whether or not power can be supplied from the FC unit 18 and the battery 20 to the motor 14, and is a switch that can be operated by the user (a switch corresponding to an ignition switch of the engine vehicle).

  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 is 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. From the load, 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. , Sends a command to the FC unit 18, the battery 20 and the DC / DC converter 22.

  Next, the control operation of the ECU 24 will be described.

  FIG. 5 shows a flowchart of basic control (main routine) in the ECU 24. In step S1, the ECU 24 determines whether or not the main SW 158 is on. If the main SW 158 is not on (S1: NO), step S1 is repeated. If the main SW 158 is on (S1: YES), the process proceeds to step S2. In step S2, the ECU 24 calculates a load (referred to as system load Psys or system required load Psys) [W] required for the FC system 12.

  In step S3, the ECU 24 performs energy management of the FC system 12 based on the calculated system load Psys. The energy management here is intended to improve the output efficiency (system efficiency) of the entire FC system 12 while suppressing the deterioration of the FC stack 40.

  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, and the water pump 80 (FC power generation control) based on the energy management processing result. Further, in step S <b> 5, the ECU 24 performs torque control of the motor 14.

  In step S6, the ECU 24 determines whether or not the main SW 158 is off. If the main SW 158 is not off (S6: NO), the process returns to step S2. If the main SW 158 is off (S6: YES), the current process is terminated.

  FIG. 6 shows a flowchart for calculating the system load Psys in step S2. In step S <b> 11, the ECU 24 reads the opening degree θp of the accelerator pedal 156 from the opening degree sensor 150. In step S <b> 12, the ECU 24 reads the rotational speed Nm [rpm] 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 (characteristics) between the current motor rotation speed Nm [rpm] and the expected motor power consumption Pm [W] shown in FIG. 7, the relationship between the rotation speed Nm and the predicted power consumption Pm for each opening θp. Remember. For example, when the opening degree θp is θp1, the characteristic 180 is used. Similarly, when the opening degree θp is θp2, θp3, θp4, θp5, and θp6, the characteristics 182, 184, 186, 188, and 190 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 addition, during acceleration on the power running side, a positive value is assumed, and during deceleration on the regeneration side, the expected power consumption Pm is a negative value, that is, expected regenerative power.

  In step S <b> 14, the ECU 24 reads the current operation status from each auxiliary machine load 31. For example, as shown in FIG. 2, the auxiliary load 31 includes a high voltage auxiliary machine including an air pump 60, a water pump 80 and an air conditioner 90, a low voltage battery 94, an accessory 96 and an ECU 24. Including low voltage auxiliary equipment. 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 expected power consumption Pm of the motor 14 and the power consumption Pa of the auxiliary machine (temporary system load Pm + Pa), and the expected power consumption of the FC vehicle 10 as a whole, that is, the system load Psys (Psys = Pm + Pa and Psys ← Pm + Pa.) Are calculated.

  In step S17, the ECU 24 calculates the average system load Psysave each time the system load Psys is calculated in step S16. The average system load Psysave is calculated as a moving average of the system load Psys for a predetermined time, for example, 10 seconds.

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

  FIG. 8 shows an example of the relationship between the voltage (cell voltage Vcell) [V] of the FC cells constituting the FC stack 40 and the amount of cell degradation D. That is, the curve (characteristic) 140 in FIG. 8 shows the relationship between the cell voltage Vcell and the deterioration amount D.

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

  The voltage v2 to the voltage 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 progress region R3”). A voltage v3 to a voltage 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 stable region R4”). The voltage v4 to OCV (open circuit voltage) is a region where the oxidation of carbon contained in the FC cell proceeds (hereinafter referred to as “carbon oxidation progress region R5”).

  As described above, in FIG. 8, if the cell voltage Vcell is in the platinum reduction stable region R2 or the platinum oxidation stable region R4, the progress degree of the deterioration of the FC cell is small. On the other hand, if the cell voltage Vcell is in the platinum aggregation increasing region R1, the platinum oxidation-reduction progress region R3, or the carbon oxidation progress region R5, the progress of the deterioration of the FC cell is large.

  In FIG. 8, the curve (characteristic) 140 is uniquely defined, but in actuality, the curve (variation speed Acell) per unit time (fluctuation speed Acell) [V / sec] (Characteristic) 140 changes.

  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 solid curve (characteristic) 170 indicates a case where the fluctuation speed Acell is high, and a broken curve (characteristic) 172 indicates a case where the fluctuation speed Acell is low. As can be seen from FIG. 9, the degree of progress of oxidation or reduction differs depending on the fluctuation speed Acell, and thus the voltages v1 to v4 are not necessarily uniquely specified. Moreover, each voltage v1-v4 may change also with the individual difference of FC cell. For this reason, it is preferable to set the voltages v1 to v4 as those in which an error is reflected in a theoretical value, a simulation value, or an actual measurement value.

  Further, the current / voltage characteristics (IV characteristics) of the FC cell are similar to those of a general fuel battery cell, as shown by an IV characteristic (usually referred to as a normal IV characteristic) 162 shown in FIG. The cell current Icell [A] increases as Vcell decreases. 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.

  The normal IV characteristic 162 in FIG. 10 is a characteristic obtained when the cathode stoichiometric ratio (≈oxygen concentration) is in a state in which oxygen is higher than the normal stoichiometric ratio (normal stoichiometric ratio). In other words, the oxygen concentration is higher than the normal oxygen concentration. Note that the cathode stoichiometric ratio = the air flow rate supplied to the cathode electrode / the air flow rate consumed by power generation. In this embodiment, the cathode stoichiometric ratio is also simply referred to as the stoichiometric ratio.

  As shown in FIG. 11, the oxygen-rich state means that even if the cathode stoichiometric ratio (≈oxygen concentration) is increased, the cell current (current output from a single cell) Icell becomes substantially constant and becomes saturated. Usually means oxygen in the region of the stoichiometric ratio or higher.

  The same applies to hydrogen. That is, the anode stoichiometric ratio (≈hydrogen concentration) = the flow rate of hydrogen supplied to the anode electrode / the flow rate of hydrogen consumed by power generation.

  Next, the FC power generation control in step S4 will be described with reference to the flowchart of FIG.

  In step S21, the ECU 24 calculates the charge / discharge coefficient α of the battery 20, and calculates the target FC power Pfctgt by multiplying the calculated charge / discharge coefficient α by the average system load Psysave calculated in step S17 (Pfctgt ← Psysave). × α).

  Here, the charge / discharge coefficient α is calculated based on the current SOC value input from the SOC sensor 104 and the characteristic (map) 163 in FIG. As the characteristic 163 in FIG. 14, for example, an actual measurement value or a simulation value can be used, and is stored in the ECU 24 in advance. In addition, here, a case where the target SOC (target power storage amount) of the battery 20 is set to 50 [%] is illustrated, but the present invention is not limited to this. As shown in FIG. 14, in a region where the SOC value needs to be smaller than 50 [%], the power generation of the FC stack 40 is made surplus, and the charge / discharge coefficient α is charged so that the surplus power is charged in the battery 20. Tends to be larger than “1”. On the other hand, in a region where the state of charge where the SOC value is larger than 50 [%] is sufficient, the charge / discharge coefficient α is set so that the power generation of the FC stack 40 is insufficient and the battery 20 is discharged so as to compensate for the insufficient power. It tends to be smaller than “1”.

  For the convenience of understanding the following description, it is assumed here that the charge / discharge coefficient α is α = 1 (Pfctgt = Psysave).

  Next, in step S22, the ECU 24 determines whether or not the target FC power Pfctgt calculated in step S21 is equal to or greater than the threshold power Pthp (Pfctgt ≧ Pthp).

Here, the threshold power Pthp is “a cell voltage Vcell determined that the catalyst is not deteriorated (Vcell = v2 = 0.8 V, switching voltage, predetermined voltage)” and “the number of single cells Nfc constituting the FC stack 40”. And “the current value Icellp when the cell voltage is set to 0.8 V in the normal IV characteristic 162 of the FC stack 40 (see FIG. 10)”, and a fixed value shown in the following equation (1) It is. Note that in FIG. 10, the axis of the target FC power Pfctgt is not linear.
Pthp = 0.8 [V] × Nfc × Icellp (1)

  When the target FC power Pfctgt is greater than or equal to the threshold power Pthp (step S22: YES), variable voltage / current variable control (mode A control) is executed in step S23 to obtain the target FC power Pfctgt.

  This mode A control is mainly used when the target FC power Pfctgt is relatively high, and the target FC voltage is maintained in a state where the target oxygen concentration Cotgt is kept normal (including a state where oxygen is rich). The FC current Ifc is controlled by adjusting Vfctgt.

  That is, as shown in FIG. 13, in the mode A control executed when the target FC power Pfctgt is equal to or higher than the threshold power Pthp, the normal IV characteristic 162 of the FC stack 40 (the same as that shown in FIG. 10) is used. In the mode A control, 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.

  According to the mode A control as described above, even when the target FC power Pfctgt is a high load equal to or higher than the threshold power Pthp, the secondary voltage V2 (FC voltage Vfc) is set to the normal IV characteristic 162 according to the target FC power Pfctgt. As a result, the system load Psys can basically be covered by the FC power Pfc.

  On the other hand, if it is determined in step S22 that the target FC power Pfctgt is less than the threshold power Pthp (step S22: NO), in step S24, the target FC power Pfctgt calculated in step S24 is less than the threshold power Pthq (Pfctgt < Pthq) is determined. Here, the threshold power Pthq is determined in accordance with, for example, the cell voltage Vcell corresponding to Vcell = v3 = 0.9 [V]. The threshold power Pthq is set to a value lower than the threshold power Pthp (Pthq <Pthp, see FIG. 13).

  If the determination in step S24 is negative, that is, if the target FC power Pfctgt is less than the threshold power Pthp and greater than or equal to the threshold power Pthq (step S24: NO, Pthq ≦ Pfctgt <Pthp), step In S25, it is determined whether or not the target FC power Pfctgt [W] is not less than the first predetermined load value PL1 [W] and less than the second predetermined load value PL2 [W].

  Here, as shown in FIG. 13, the first predetermined load value PL1 is within a redox region (R3) between the voltage v2 and the voltage v3 realized on the normal stoichiometric ratio (on the normal IV characteristic 162). The threshold power Pthr at the voltage ve [V] (= the first predetermined load value PL1) is set, and the second predetermined load value PL2 is a voltage v2 (here, a normal stoichiometric ratio (on the normal IV characteristic 162)). The threshold power Pthp (= second predetermined load value PL2) at v2 = 0.8 V) is set.

  When the target FC power Pfctgt [W] calculated this time is equal to or larger than the first predetermined load value PL1 [W] and less than the second predetermined load value PL2 [W] (step S25: YES). In step S26, the mode D control (second control mode: voltage fixation / stoichiometric ratio normal / current fixation control) is executed. This mode D control is mainly used when the average system load Psysave is relatively low, and the target cell voltage Vcelltgt (= target FC voltage Vfctgt / number of cells Nfc) is lower than the oxidation-reduction progress region R3. The reference voltage {voltage v2 (= 0.8V) in this embodiment} set below the voltage is fixed, that is, the FC voltage Vfc is oxidized / reduced voltage range (redox progress region R3 by the DC / DC converter 22). ) The external voltage v2 (= 0.8V) × Nfc is fixed (Vfc = v2 × Nfc is fixed), and power is generated at a normal stoichiometric ratio. The surplus of the generated power in the mode D control is charged in the battery 20.

  On the other hand, if the determination in step S25 is negative, that is, if the target FC power Pfctgt [W] calculated this time is less than the first predetermined load value PL1 [W] and greater than or equal to the threshold power Pthq, In step S27, it is determined whether or not the SOC value of the battery 20 is less than a predetermined value, for example, 50 [%] (target SOC value).

  When the SOC value of the battery 20 is less than the predetermined value and the determination in step S27 is affirmative, the mode D control in step S26 described above is executed.

  On the other hand, if the SOC value of the battery 20 exceeds the predetermined value and the determination in step S27 is negative, the mode B control in step S28 (first control mode: voltage fixed / stoichiometric ratio variable current variable) Control) is executed.

  This mode B control is mainly used when the average system load Psysave is relatively medium, and the target cell voltage Vcelltgt (= target FC voltage Vfctgt / number of cells Nfc) is calculated from the redox progress region R3. Is fixed to a reference voltage {voltage v2 (= 0.8V) in this embodiment} that is set to a lower voltage or lower, that is, the FC voltage Vfc is fixed to v2 × Nfc by the DC / DC converter 22, and the target oxygen By making the concentration Cotgt variable, the FC current Ifc is made variable.

  That is, as shown in FIG. 13, in the mode B control, the oxygen concentration is decreased by lowering the target oxygen concentration Cotgt in a state where the cell voltage Vcell is kept constant (Vcell = v2) in the range of the threshold powers Pthq to Pthr. Lower Co.

  As shown in FIG. 11, when the cathode stoichiometric ratio (≈oxygen concentration Co) decreases, the cell current Icell (FC current Ifc) also decreases. For this reason, the cell current Icell (FC current Ifc) and the FC power Pfc can be controlled by increasing / decreasing the target oxygen concentration Cotgt while keeping the cell voltage Vcell constant (Vcell = v2 = 0.8V). It becomes. Note that the shortage of the FC power Pfc is assisted from the battery 20.

  In this case, the ECU 24 adjusts the step-up rate of the DC / DC converter 22, thereby setting a reference voltage that is set to a voltage lower than the oxidation-reduction progress region R <b> 3 {voltage v <b> 2 (= 0.8 V in this embodiment). }, The target FC voltage Vfctgt is fixed, and the target FC current Ifctgt corresponding to the target FC power Pfctgt is calculated.

  Further, on the assumption that the target FC voltage Vfctgt is a reference voltage, a target oxygen concentration Cotgt corresponding to the target FC current Ifctgt is calculated (see FIGS. 11 and 15). FIG. 15 shows the relationship between the target FC current Ifctgt and the target oxygen concentration Cotgt when the FC voltage Vfc is the reference voltage.

  Here, the ECU 24 calculates and transmits a command value to each unit according to 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 “ And the opening of the back pressure valve 64 (hereinafter referred to as “back pressure valve opening θbp” or “opening θbp”).

  That is, as shown in FIGS. 16 and 17, the target air pump rotation speed Naptgt, the target water pump rotation speed Nwptgt, and the target back pressure valve opening θbptgt are set according to the target oxygen concentration Cotgt.

  As described above, the mode B control in step S28 is executed.

  Returning to the flowchart of FIG. 12 again, when the determination in step S24 is affirmative, that is, when the target FC power Pfctgt is less than the threshold power Pthq, in step S29, the SOC value of the battery 20 is It is determined whether it is less than a predetermined value, for example, 50 [%] (target SOC value).

  When the SOC value of the battery 20 is less than the predetermined value and the determination in step S27 is affirmative, the mode D control in step S26 described above is executed.

  On the other hand, if the SOC value of the battery 20 is greater than the predetermined value and the determination in step S29 is negative, the mode C control in step S30 is executed.

  As shown in FIG. 13, the mode C control is mainly used when the FC target power Pfctgt is relatively lowest, and the target cell voltage Vcelltgt (= target FC voltage Vfctgt / number of cells) is reduced by oxidation / reduction. The voltage outside the advancing region R3 is fixed at {voltage v3 (= 0.9V)} in this embodiment, and the FC current Ifc is variable. 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.

  In the mode C control, as shown in FIG. 13, the oxygen concentration Co is lowered by lowering the target oxygen concentration Cotgt while keeping the cell voltage Vcell constant (Vcell = v3).

  As shown in FIG. 11, when the cathode stoichiometric ratio (≈oxygen concentration Co) decreases, the cell current Icell (FC current Ifc) also decreases. For this reason, the cell current Icell (FC current Ifc) and the FC power Pfc can be controlled by increasing or decreasing the target oxygen concentration Cotgt while keeping the cell voltage Vcell constant (Vcell = v3 = 0.9V). It becomes. Note that the shortage of the FC power Pfc is assisted from the battery 20.

  During the execution of the stoichiometric ratio variable process in the mode B in step S28 and the mode C in step S30, in step S31, the ECU 24 determines whether or not the power generation by the FC stack 40 is stable. As the determination, if 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)}, FC It is determined that the power generation of the stack 40 is unstable. As the predetermined voltage, for example, an experimental value, a simulation value, or the like can be used.

  If power generation is stable (S31: YES), the current process is terminated. When the power generation is not stable (S31: NO), in step S32, 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.

  Next, in step S33, the ECU 24 determines whether or not the target oxygen concentration Cotgt is less than the target oxygen concentration (normal oxygen concentration Conml) in the normal IV characteristics. When the target oxygen concentration Cotgt is less than the normal oxygen concentration Conml (S33: YES), the process returns to step S31. When the target oxygen concentration Cotgt is not less than the normal oxygen concentration Conml (S33: NO), the ECU 24 stops the FC unit 18 in step S34. That is, the ECU 24 stops the supply of hydrogen and air to the FC stack 40 and stops the power generation of the FC stack 40. Then, the ECU 24 turns on a warning lamp (not shown) to notify the driver that the FC stack 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.

  As described above, the FC power generation control in step S4 is executed.

  Next, FIG. 18 shows a flowchart of torque control of the motor 14 according to the process of step S5. In step S41, the ECU 24 reads the vehicle speed Vs from the vehicle speed sensor 154. In step S <b> 42, the ECU 24 reads the opening degree θp of the accelerator pedal 156 from the opening degree sensor 150.

  In step S43, the ECU 24 calculates a temporary target torque Ttgt_p [N · m] of the motor 14 based on the vehicle speed Vs and the opening degree θp. Specifically, a map that associates the vehicle speed Vs, the opening θp, and the temporary target torque Ttgt_p is stored in a storage unit (not shown), and the temporary target torque Ttgt_p is determined based on the map, the vehicle speed Vs, and the opening θp. calculate.

  In step S44, 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 S45, the ECU 24 calculates a torque limit value Tlim [N · m] of the motor 14. Specifically, the torque limit value Tlim is obtained by dividing the motor limit output Pm_lim by the vehicle speed Vs (Tlim ← Pm_lim / Vs).

  In step S46, 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.

  FIG. 19 shows the relationship between the mode A control, the mode B control, the mode C control, the mode D control, the FC power Pfc [W], and the power generation efficiency [%] of the FC stack 40 related to the power supply mode described above. It is shown. As can be seen from FIG. 19, in the mode A control, basically, the power generation efficiency of the FC stack 40 can be kept high while the average system load Psysave is covered by the FC power Pfc. In the mode D control of the v2 voltage fixed stoichiometric ratio normal control, basically, the average system load Psysave is covered by the FC power Pfc, so that the frequency of charging / discharging of the battery 20 is suppressed and the output efficiency of the FC system 12 as a whole is increased. It is possible to maintain. In the mode B control of the v2 voltage fixed low oxygen stoichiometric ratio variable control, basically, the average system load Psysave is covered by the FC power Pfc, so that the frequency of charging / discharging of the battery 20 is suppressed, and the output efficiency of the entire FC system 12 is controlled. Can be increased according to the mode D control. In the mode C control, the average system load Psysave is covered by the FC power Pfc and the battery power Pbat.

  Note that the form of FC power generation control (S4) described with reference to FIG. 12 is also applied to a fuel cell system in which the FC power Pfc is made to follow the average system load Psysave and a fixed percentage is output from the battery 20. Applicable.

  Next, with respect to how to determine the threshold power Pthr that defines the above-described mode B control (fixed v2 and low oxygen stoichiometric ratio variable control) and mode D control (fixed v2 and stoichiometric ratio normal control), FIG. 20A, FIG. 20B, This will be described with reference to FIG. 20C.

  FIG. 20A shows the characteristics of the loss Lb with respect to the power generation amount [W] during the low oxygen stoichiometric ratio variable v2 fixed power generation, and FIG. 20B shows the loss with respect to the power generation amount [W] during the normal stoichiometric ratio v2 fixed power generation. The characteristics of La are shown, and FIG. 20C shows the characteristics of the loss [W] in which the loss Lb and the loss La are superimposed on the power generation amount [W].

  The loss Lb shown in FIG. 20A is a loss obtained by subtracting the loss generated in the v2 fixed power generation with a variable low oxygen stoichiometric ratio from the FC loss normally generated on the IV characteristic 162, and the loss Lb increases as the oxygen concentration Co decreases. Become.

  The loss La shown in FIG. 20B is a loss obtained by adding a loss caused by charging the battery 20 with a surplus that is a loss generated in the normal stoichiometric ratio v2 fixed power generation and a loss of the DC / DC converter 22 at that time. It becomes smaller as the power generation amount [W] becomes larger.

  As illustrated in FIG. 20C, the loss Lb and the loss La having different maximum values intersect with each other at the threshold power Pthr corresponding to the first predetermined load value PL1 described above. Therefore, the power generation amount (average system load Psysave [W]) is a value that is greater than or equal to the first predetermined load value PL1 (Pthr) [W] and less than the second predetermined load value PL2 (Pthp) [W]. In this case, the mode B control executed by the low oxygen stoichiometric ratio variable v2 fixed power generation is stopped, the FC voltage Vfc is fixed to v2 × Nfc by the DC / DC converter 22 (Vfc = v2 × Nfc), and the normal stoichiometry is performed. The efficiency of the FC stack 40 can be improved by executing the mode D control with the ratio v2 fixed power generation. That is, loss [W] can be reduced.

  FIG. 21 shows a time chart when the mode D control is established in a state where a constant load continues such as a cruise traveling state. In FIG. 21, in the time chart drawn below the SOC value (in the figure, the predetermined value is a target SOC value of 50 [%]), the one indicated by a thick broken line indicates the change characteristic according to the comparative example and is thick. What is indicated by a solid line indicates the change characteristic according to the embodiment.

  Mode A control is executed until time t1, and mode B control (low oxygen stoichiometric variable control at v2 = 0.8 V) is executed from time t1 to time t2. At time t2, the determination condition in step S25 is satisfied (affirmed) Therefore, the fixed voltage low oxygen stoichiometric variable flag Fs is turned from on to off, and the fixed voltage stoichiometric ratio normal control (mode D control) is executed between time t2 and time t3. Since the determination condition in step S25 is not satisfied (negative) at time t3, mode B control is executed after time t3.

[Summary of Embodiment]
As described above, the fuel cell system 12 according to the embodiment includes the catalyst, and the FC stack 40 that generates power by reacting oxygen or hydrogen with the catalyst, and at least one of the oxygen and hydrogen is converted into FC. Gas supply means {fuel gas supply means (hydrogen tank 44), oxidant gas supply means (air pump 60)} supplied to the stack 40, and a DC / DC converter 22 (adjustable) the FC voltage Vfc of the FC stack 40 ( Voltage adjusting means) and a load 33 driven by the output power of the FC stack 40.

  The fuel cell system 12 includes an ECU 24 (control means) that detects the average system load Psysave (load required power) of the load 33 and controls the FC stack 40, the gas supply means, and the DC / DC converter 22. .

  The ECU 24 uses the FC voltage Vfc of the FC stack 40 when the voltage of the FC stack 40 corresponding to the average system load Psysave of the load 33 corresponds to the oxidation reduction progress voltage range (oxidation reduction progress region R3) of the FC stack 40. When it is set outside the redox progress voltage range (redox progress region R3) and the generated power of the FC stack 40 is within a predetermined power range (PL1 ≦ Psys ≦ PL2), the second control mode {FC stack 40 The cell voltage Vcell is fixed at a voltage v2 outside the oxidation-reduction progress voltage range, and the mode D control for maintaining the oxygen or hydrogen concentration in a predetermined concentration range (normal control of stoichiometric ratio)} is executed, and the generated power of the FC stack 40 Is outside the predetermined power range and small (Pthq ≦ Psys <PL1), the first control mode { The cell voltage Vcell of the C stack 40 is fixed to a voltage v2 outside the redox progress voltage range (redox progress region R3), and the oxygen or hydrogen concentration is changed to follow the required power (low oxygen stoichiometric ratio variable control). ) Mode B control} is executed, so that deterioration of the FC stack 40 is prevented by avoiding that the cell voltage Vcell of the FC stack 40 falls within the oxidation-reduction progression voltage range (oxidation-reduction progression region R3). However, it is possible to improve the system efficiency by suppressing the deterioration of the system efficiency.

  More specifically, the voltage (average required voltage) corresponding to the average system load Psysave of the load 33 is a predetermined voltage value {first control mode (mode B control) in the redox progress voltage range (redox progress region R3). ) And the switching voltage of the FC stack 40 whose efficiency is reversed in the second control mode (mode D control)} ve (see FIG. 13) or less, and when the voltage is the lower limit voltage v2 or more, The power generation voltage Vfc is fixed to the voltage v2, and control is performed such that the FC power Pfc exceeds the average system load Psysave by the stoichiometric ratio normal control (mode D control), and surplus power is charged in the battery 20. Further, the voltage (average required voltage) corresponding to the average system load Psysave is a value that exceeds the predetermined voltage value ve in the redox progress voltage range (redox progress region R3) and is in the redox progress voltage range (redox progress). When the value is lower than the upper limit voltage v3 in the region R3), the FC power Pfc is average system load Psysave by the stoichiometric ratio variable control (mode B control) with the power generation voltage Vfc of the FC stack 40 fixed to the voltage v2. Control to follow.

  When the ECU 24 includes the high voltage battery 20 (power storage device) that is charged by the FC power Pfc of the FC stack 40 and supplies power to the fuel cell system 12, the ECU 24 is executing the first control mode (mode B control), for example. In addition, when the SOC value of the high-voltage battery 20 is detected and the detected SOC value becomes a predetermined value, for example, a value less than 50 [%], the second control mode (mode D control) is executed. Thus, it is possible to prevent the SOC value of the high voltage battery 20 from excessively decreasing.

[Modification]
Note 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 description in this specification. For example, the following configuration can be adopted.

  In the said embodiment, although FC system 12 was mounted in FC vehicle 10, you may mount not only in this but in another object. For example, the FC system 12 can be used for a moving body such as a ship or an aircraft. Alternatively, the FC system 12 may be applied to a household power system.

  In the above embodiment, the FC stack 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 the present invention is not limited to this. For example, as shown in FIG. 22, the FC stack 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 stack 40. . Alternatively, as shown in FIG. 23, the FC stack 40 and the battery 20 are arranged in parallel, the DC / DC converter 160 is arranged in front of the FC stack 40, and the DC / DC converter 22 is arranged in front of the battery 20. May be. Alternatively, as illustrated in FIG. 24, the FC stack 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.

  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.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell vehicle 12 ... Fuel cell system 14 ... Drive motor (load) 16 ... Inverter (load)
18 ... Fuel cell unit 20 ... High voltage battery (power storage device)
22 ... DC / DC converter (voltage adjusting means)
24 ... ECU (control device) 33 ... Load 40 ... FC stack 44 ... Hydrogen tank 60 ... Air pump (load) 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 adjusting the supply amount of at least one of the oxygen and the hydrogen and supplying 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;
In a fuel cell system comprising:
A controller that detects the required power of the load and controls the fuel cell, the gas supply unit, and the voltage adjustment unit;
The control means includes
The concentration of oxygen or hydrogen supplied to the fuel cell by controlling the gas supply means in a state where the voltage adjusting means is controlled and the output voltage of the fuel cell is fixed at a predetermined voltage value outside the redox progress voltage range. A first control mode that varies the power to follow the required power of the load;
In a state where the voltage adjusting means is controlled and the output voltage of the fuel cell is fixed at the predetermined voltage value, the concentration of the oxygen or the hydrogen supplied to the fuel cell by controlling the gas supply means is set within a predetermined concentration range. A second control mode to maintain;
Is to execute
The output voltage of the fuel cell corresponding to the required power of the load, be in the redox progression voltage range, the loss in the first control mode is switched voltage or below the loss in the second control mode In this case, the first control mode is executed, and when the voltage is lower than the switching voltage, the second control mode is executed. The fuel cell system according to claim 1, wherein
And a power storage device that is charged by the output power of the fuel cell and supplies power to the fuel cell system,
The control means includes
The SOC value of the power storage device is detected during execution of the first control mode, and the second control mode is executed when the detected SOC value is less than a predetermined value. Fuel cell system.   A vehicle equipped with the fuel cell system according to claim 1.

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