JP2016048643A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of appropriately determining a dry state of electrolyte of a fuel cell on the basis of output current and output voltage of the fuel cell.SOLUTION: The fuel cell system comprises: a voltage detection unit 51 for detecting output voltage of a fuel cell 5; a DCDC converter 6 for controlling output power of the fuel cell 5; an ECU 7 for controlling input current to the DCDC converter 6 so that a current value of output current of the fuel cell 5 becomes equal to a preset target current value; and a dry state determination unit 71 for determining that an electrolyte of the fuel cell 5 is in a dry state, when a voltage value detected by the voltage detection unit 51 is smaller than a dry determination threshold in the case that the current value of output current of the fuel cell 5 has been the target current value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell system, and relates to a fuel cell system for determining a dry state of a fuel cell.

  A fuel cell that generates electric power by an electrochemical reaction is known, and this fuel cell usually constitutes a fuel cell stack by laminating a number of minimum structural units called cells. In the cell, a diffusion layer and a catalyst layer are sequentially laminated on one side of each of an anode electrode supplied with hydrogen and a cathode electrode supplied with oxygen in the air, and the diffusion layer and catalyst layer are laminated. The inner surface is the inside and the electrolyte is sandwiched in the center. An external circuit is connected between the power output terminals of the anode and cathode, and a load such as a motor is connected to the external circuit.

  In such a fuel cell, hydrogen molecules supplied to the anode electrode become active hydrogen atoms in the catalyst layer on the anode electrode side, and further become hydrogen ions to release electrons. The hydrogen ions move in the electrolyte from the anode electrode to the cathode electrode side along with moisture contained in the electrolyte, and the emitted electrons move to the cathode electrode through an external circuit connected to the anode electrode. This movement of electrons causes a current to flow through the load connected to the external circuit.

  On the other hand, oxygen molecules supplied to the cathode electrode receive electrons that have moved from the external circuit in the catalyst layer, become oxygen ions, and combine with hydrogen ions that have moved through the electrolyte to become water.

  Thus, when current flows from the fuel cell, the electrolyte needs moisture. It is generally known that the higher the relative humidity of the electrolyte, the higher the ionic conductivity of the electrolyte. However, when there is too much moisture, a phenomenon called flooding occurs, which hinders the movement of hydrogen gas, making it difficult for current to flow. Therefore, it is necessary for the electrolyte to generate power while maintaining a certain degree of humidification.

  In Patent Document 1, power generation is performed by a fuel cell, and the output voltage when the electrolyte corresponding to the output current is in a non-dry state is compared with the actual output voltage from the output current and output voltage of the fuel cell, and the electrolyte is dried. A fuel cell system for determining the state has been proposed.

JP 2010-114039 A

However, in such a fuel cell system described in Patent Document 1, depending on the current value of the output current, there may be no significant difference in the output voltage between the dry state and non-dry state of the electrolyte, In such a case, it is difficult to appropriately determine the dry state of the electrolyte.
Accordingly, an object of the present invention is to provide a fuel cell system that can appropriately determine the dry state of the electrolyte of the fuel cell based on the output current and output voltage of the fuel cell.

  An aspect of the invention of a fuel cell system that solves the above problems includes a fuel cell that generates electric power by electrochemically reacting fuel gas, a dry state determination unit that determines the dry state of the fuel cell, and the fuel cell that generates power. A control unit that controls electric power to be output and a voltage detection unit that detects an output voltage of the fuel cell, and the control unit sets the fuel current so that the current value of the output current of the fuel cell becomes a preset target current value. The power generated by the battery is controlled, and the dry state determination unit determines the dry state of the fuel cell based on the voltage value detected by the voltage detection unit when the current value of the output current of the fuel cell reaches the target current value. To do.

  Thus, according to one aspect of the present invention, the dry state of the electrolyte can be appropriately determined based on the output current and output voltage of the fuel cell.

FIG. 1 is a conceptual block diagram showing a fuel cell system according to an embodiment of the present invention. FIG. 2 is a diagram showing a fuel cell system according to an embodiment of the present invention, and is a graph showing the relationship between the output current and the output voltage of the fuel cell. FIG. 3 is a diagram showing a fuel cell system according to an embodiment of the present invention, and is a flowchart showing the dry state determination process. FIG. 4 is a diagram showing a fuel cell system according to an embodiment of the present invention, and is a time chart showing changes in output current and output voltage when the fuel cell electrolyte is in a normal state. FIG. 5 is a diagram showing a fuel cell system according to an embodiment of the present invention, and is a time chart showing changes in output current and output voltage when the electrolyte of the fuel cell is in a dry state.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In FIG. 1, a vehicle 1 equipped with a fuel cell system according to an embodiment of the present invention includes a motor 2, an inverter 3, a secondary battery 4, a fuel cell 5, and a direct current (DC) DC converter 6. And an ECU (Electronic Control Unit) 7 as a control unit.

  The motor 2 is configured by a synchronous motor including, for example, a rotor embedded with a plurality of permanent magnets and a stator around which a stator coil is wound. In the motor 2, a rotating magnetic field is formed in the stator by applying three-phase AC power to the stator coil, and the rotor rotates by the rotating magnetic field to generate power. The power generated by the motor 2 is shifted by a transmission (not shown) and transmitted to driving wheels (not shown) to cause the vehicle 1 to travel. Further, when power is transmitted from the drive wheel side to the motor 2 side when the vehicle 1 is decelerated, the motor 2 functions as a generator and generates regenerative power. The motor 2 is connected to the inverter 3.

  The inverter 3 supplies three-phase AC power to the motor 2 and controls the output torque of the motor 2. The inverter 3 controls the current amount of the three-phase AC power supplied to the motor 2 according to the torque command signal output from the ECU 7 so that the output torque of the motor 2 becomes the command torque of the torque command signal. The inverter 3 charges the secondary battery 4 by converting the three-phase AC power output from the motor 2 into DC power.

  The secondary battery 4 is made of, for example, a nickel storage battery or a lithium storage battery, and is configured by connecting a plurality of cells in series. The secondary battery 4 supplies power to the motor 2 via the inverter 3.

  The fuel cell 5 is an apparatus in which a fuel gas such as hydrogen gas and an oxygen-containing oxidant gas are electrochemically reacted through an electrolyte, and electric energy is directly taken out between electrodes provided on both surfaces of the electrolyte. The fuel cell 5 is provided with a voltage detector 51 that detects the output voltage of the fuel cell 5.

  The DCDC converter 6 converts the electric power generated by the fuel cell 5 so as to be compatible with the motor 2. The DCDC converter 6 controls input / output power under the control of the ECU 7. The DCDC converter 6 transmits a signal indicating an input current value, an input voltage value, and the like to the ECU 7. The output power of the fuel cell 5 is controlled by controlling the input power of the DCDC converter 6.

  The ECU 7 includes a computer unit including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an input port, an output port, and a network module. ing.

  The ROM of the ECU 7 stores a program for causing the computer unit to function as the ECU 7 along with various control constants, various maps, and the like. That is, in the ECU 7, the computer unit functions as the ECU 7 when the CPU executes a program stored in the ROM.

  Various sensors including the above-described voltage detection unit 51, a vehicle speed sensor (not shown), and an accelerator opening sensor are connected to the input port of the ECU 7. On the other hand, various control objects including the inverter 3, the secondary battery 4, the fuel cell 5, and the DCDC converter 6 are connected to the output port of the ECU 7. The vehicle speed sensor detects the vehicle speed of the vehicle 1. The accelerator opening sensor detects an operation amount of an accelerator pedal operated by a driver as an accelerator opening.

  The ECU 7 calculates the necessary output torque of the motor 2 based on the vehicle speed detected by the vehicle speed sensor and the accelerator opening detected by the accelerator opening sensor, and transmits a torque command signal to the inverter 3 to be necessary for the motor 2. Torque is output to control the traveling of the vehicle 1. At this time, the output power of the DCDC converter 6 is controlled to control the power supplied to the inverter 3.

  Here, the relationship between the output current of the power generation of the fuel cell 5 and the output voltage has a characteristic that, as shown in FIG. When the electrolyte of the fuel cell 5 is in a dry state, it becomes difficult to flow current, and as the output current value increases, the output voltage decreases as shown in the dashed line graph of FIG. Thus, the dry state of the electrolyte of the fuel cell 5 can be determined from the current value and voltage value of the output when the fuel cell 5 is started.

However, if the current value of the output when the fuel cell 5 is activated is near A1 in FIG. 2, there is no significant difference between the voltage value in the normal state and the voltage value in the dry state. It is difficult to determine whether it is in a dry state. For this reason, the ECU 7 increases the output current of the fuel cell 5 to a current value that can clearly determine the dry state of the electrolyte in the vicinity of A2 in FIG. 2, and determines the dry state of the electrolyte.
As shown in FIG. 1, the ECU 7 includes a dry state determination unit 71 that determines the dry state of the electrolyte of the fuel cell 5 and a humidity control unit 72 that controls the humidity of the electrolyte of the fuel cell 5.

  When an ignition switch (not shown) is turned on, the ECU 7 starts processing and activates the fuel cell 5. When the fuel cell 5 is activated, the ECU 7 controls the input power of the DCDC converter 6 to raise the output current of the fuel cell 5 to a preset target current value. Here, the target current value is a current value with which the dry state of the electrolyte can be clearly discriminated by the output voltage value of the fuel cell 5, obtained in advance through experiments or the like, and stored in the ROM of the ECU 7.

  When the dry state determination unit 71 determines that the output voltage value when the output current of the fuel cell 5 reaches the target current value is smaller than a preset dry determination threshold, the electrolyte of the fuel cell 5 is in a dry state. Is determined. Here, the drying determination threshold value is obtained in advance through experiments or the like and stored in the ROM of the ECU 7.

  When the dry state determination unit 71 determines that the electrolyte of the fuel cell 5 is in a dry state, the humidity control unit 72 controls to increase the humidity of the electrolyte of the fuel cell 5. Specifically, when it is determined that the electrolyte of the fuel cell 5 is in a dry state, the humidity control unit 72 uses the water generated by the power generation of the fuel cell 5 to increase the humidity of the electrolyte. The input power of the DCDC converter 6 is controlled so that the output current value of 5 becomes a current value during drying that is greater than that during normal power generation. Here, the current value during drying is obtained in advance by experiments or the like and stored in the ROM of the ECU 7.

  The dry state determination process by the fuel cell system according to the present embodiment configured as described above will be described with reference to FIG. The dry state determination process described below is executed when the fuel cell 5 is activated and power can be supplied from the inverter 3 to the motor 2.

  First, the ECU 7 controls the input power of the DCDC converter 6 so that the current value of the input current of the DCDC converter 6 becomes the aforementioned target current value (step S11). Next, the ECU 7 waits for the current value of the input current of the DCDC converter 6 to reach the target current value (step S12).

  When it is determined that the current value of the input current of the DCDC converter 6 has reached the target current value, the dry state determination unit 71 determines whether the output voltage value of the fuel cell 5 detected by the voltage detection unit 51 is equal to or greater than the above-described dry determination threshold value. Is determined (step S13). When the dry state determination unit 71 determines that the output voltage value of the fuel cell 5 is greater than or equal to the dry determination threshold value, the ECU 7 controls the fuel cell 5 to perform normal power generation (step S14) and ends the process. To do.

  When the dry state determination unit 71 determines that the output voltage value of the fuel cell 5 is not greater than or equal to the dry determination threshold value, the humidity control unit 72 determines that the output current value of the fuel cell 5 is the above-described current value during drying as the power generation for promoting moisture. The input power of the DCDC converter 6 is controlled so as to generate the power (step S15), and the process ends.

The operation | movement by such a dry condition determination process is demonstrated with reference to FIG.4 and FIG.5.
FIG. 4 is a time chart when the electrolyte of the fuel cell 5 is in a normal wet state. When the fuel cell 5 is started, not only the fuel cell 5 but also the DCDC converter 6, the secondary battery 4, and the inverter 3 can supply power to the motor 2, the input power of the DCDC converter 6 is controlled, and the fuel cell The output current of 5 is pulled up to the target current value. When the output current of the fuel cell 5 reaches the target current value at t2, the output voltage of the fuel cell 5 is compared with the dry determination threshold value, and when the output voltage of the fuel cell 5 is determined to be equal to or higher than the dry determination threshold value, the DCDC converter at t3. 6 is controlled, and the output current of the fuel cell 5 is lowered to the current value during normal power generation.

  FIG. 5 is a time chart when the electrolyte of the fuel cell 5 is in a dry state. As in the case of FIG. 4, at t <b> 11 when the fuel cell 5 is started and power can be supplied to the motor 2, the output current of the fuel cell 5 is raised until the target current value is reached. When the output current of the fuel cell 5 reaches the target current value at t12, the output voltage of the fuel cell 5 is compared with the drying determination threshold value. Here, if it is determined that the output voltage of the fuel cell 5 is smaller than the drying determination threshold value, the input power of the DCDC converter 6 is controlled at t13, and the output current of the fuel cell 5 is larger than the current value during normal power generation. The current value is controlled.

  The output voltage at this time is smaller than the voltage value during normal power generation because the current value of the output current is large and the electrolyte is in a dry state. Then, generation of water is promoted by power generation in which the output current value becomes the current value at the time of drying, and when the wet state of the electrolyte is recovered, the voltage value of the output voltage also increases. When the wet state of the electrolyte returns to the normal state, the output current of the fuel cell 5 is returned to the current value during normal power generation, and the output voltage also becomes the voltage value during normal power generation.

The effects of the fuel cell system of this embodiment will be described.
In the above-described embodiment, the ECU 7 that controls the input current of the DCDC converter 6 so that the current value of the output current of the fuel cell 5 becomes a preset target current value, and the current value of the output current of the fuel cell 5 is the target. A dry state determination unit 71 that determines that the electrolyte of the fuel cell 5 is in a dry state when the voltage value detected by the voltage detection unit 51 is smaller than the dry determination threshold when the current value is reached.

  Thereby, when the current value of the output current of the fuel cell 5 becomes the target current value that causes a significant difference in the voltage value of the output voltage of the fuel cell 5 between the normal state and the dry state of the electrolyte of the fuel cell 5, The dry state of the electrolyte of the fuel cell 5 is determined by the voltage value of the output voltage of the fuel cell 5. For this reason, the dry state of the electrolyte of the fuel cell 5 can be appropriately determined based on the output current and output voltage of the fuel cell 5.

  Moreover, the humidity control part 72 which controls the humidity of the electrolyte of the fuel cell 5 is provided, and the humidity control part 72 is the humidity of the fuel cell 5 when the dry state determination part 71 determines that the fuel cell 5 is in the dry state. Control to raise.

  Thereby, when it is determined that the electrolyte of the fuel cell 5 is in a dry state, the humidity of the electrolyte of the fuel cell 5 is controlled to increase. For this reason, the state of the electrolyte of the fuel cell 5 can be recovered quickly.

In addition, when the dry state determination unit 71 determines that the fuel cell 5 is in the dry state, the humidity control unit 72 increases the current value of the output current of the fuel cell 5 to the dry current value.
Thereby, when it is determined that the electrolyte of the fuel cell 5 is in a dry state, the output current of the fuel cell 5 is increased, and the amount of water generated in the fuel cell 5 is increased. For this reason, the humidity of the electrolyte of the fuel cell 5 can be raised.

  In this embodiment, when it is determined that the electrolyte of the fuel cell is in a dry state, the humidity control unit 72 sets the output current of the fuel cell 5 to the current value at the time of drying and sets the humidity of the electrolyte of the fuel cell 5. Although it has been increased, the apparatus includes a device for increasing the humidity of the electrolyte of the fuel cell, for example, a humidifier. When the humidity control unit 72 determines that the electrolyte of the fuel cell is in a dry state, the fuel cell 5 is The electrolyte humidity may be increased.

  While embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that changes may be made without departing from the scope of the invention. All such modifications and equivalents are intended to be included in the following claims.

DESCRIPTION OF SYMBOLS 1 Vehicle 5 Fuel cell 6 DCDC converter 51 Voltage detection part 71 Dry state determination part 72 Humidity control part

Claims (3)

A fuel cell that generates electric power by electrochemically reacting fuel gas; and
A dry state determination unit for determining a dry state of the fuel cell;
A control unit for controlling electric power generated by the fuel cell;
A voltage detector for detecting the output voltage of the fuel cell,
The control unit controls electric power generated by the fuel cell so that a current value of an output current of the fuel cell becomes a preset target current value, and the dry state determination unit is configured to output the output current of the fuel cell. A fuel cell system that determines the dry state of the fuel cell based on the voltage value detected by the voltage detector when the current value of the fuel cell becomes the target current value. A humidity control unit for controlling the humidity of the fuel cell;
2. The fuel cell system according to claim 1, wherein the humidity control unit performs control to increase the humidity of the fuel cell when the dry state determination unit determines that the fuel cell is in a dry state.   The humidity control unit increases the current value of the output current of the fuel cell to a preset dry current value when the dry state determination unit determines that the fuel cell is in a dry state. The fuel cell system described in 1.

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