JP2018156747A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of recovering power generation performance while effectively reducing heating power of a fuel cell.SOLUTION: A fuel cell system 100 includes: a temperature sensor 50 for measuring a temperature of a fuel cell 40; a controller 80 for executing refresh control recovering power generation performance of the fuel cell 40 by lowering a voltage of the fuel cell 40 to a reduction potential. The controller 80, when a temperature detected by the temperature sensor 50 is not less than a predetermined value, executes refresh control regardless of a status of oxide film formed on a catalyst layer.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fuel cell system.

  The fuel cell generates power by chemically reacting hydrogen of fuel and oxygen in the air. The fuel cell is mounted on, for example, a fuel cell vehicle (FCV) and functions as an in-vehicle power supply system.

  In a fuel cell, a platinum catalyst that promotes a chemical reaction is oxidized with the passage of time, and the power generation performance is lowered by the accumulation of the oxide on the surface of the platinum catalyst (this state is also referred to as catalyst poisoning). For this reason, the fuel cell system temporarily reduces the cell voltage of the fuel cell by reducing the supply amount of one of oxygen and hydrogen. Thereby, since the oxide is reduced, the power generation performance of the fuel cell is restored. The operation for restoring the power generation performance in this way is referred to as “refresh control” in the following description. In Patent Document 1 below, refresh control for removing the oxide is performed according to the state of oxide accumulated on the surface of the catalyst, and the output of the fuel cell is recovered.

JP, 2014-078412, A

  By the way, the calorific value of the fuel cell increases particularly when a high load is required, for example. Since the above refresh control temporarily reduces the cell voltage of the fuel cell, there is a concept of reducing the amount of heat generated by the fuel cell by performing this refresh control, for example, when a high load is required. However, in Patent Document 1, refresh control is performed according to the state of oxides (in other words, the state of poisoning), so how to specifically perform refresh control in order to reduce the amount of heat generation. It was not considered at all.

  Therefore, an object of the present invention is to provide a fuel cell system that can restore power generation performance while effectively reducing the amount of heat generated by the fuel cell.

  A fuel cell system according to the present invention is a fuel cell system including a fuel cell that generates power by receiving supply of an oxidizing gas and a fuel gas, and a temperature sensor that measures the temperature of the fuel cell, and a voltage of the fuel cell is reduced. And a control unit that performs refresh control to restore the power generation performance of the fuel cell by lowering the potential to a potential, and the control unit is formed in the catalyst layer when the temperature detected by the temperature sensor is equal to or higher than a predetermined value. Refresh control is executed regardless of the state of the oxide film.

  According to this configuration, when the temperature of the fuel cell is equal to or higher than a predetermined value (for example, 90 ° C. or higher), refresh control is performed regardless of the state of the oxide film formed on the catalyst layer. Thus, the amount of heat generated by the fuel cell can be effectively reduced. As a result, the amount of heat generated by the fuel cell can be reduced by refresh control without adding and increasing the size of the device for radiating the heat generated in the fuel cell, and the power generation performance can be recovered.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell system which can recover electric power generation performance can be provided, reducing the emitted-heat amount of a fuel cell effectively.

It is a figure which shows the principal part structure of the fuel cell system which concerns on this embodiment. 2 is a flowchart showing an example of a control operation of the fuel cell system shown in FIG. It is explanatory drawing which shows that a voltage-current characteristic improves by refresh control. It is explanatory drawing which shows that the emitted-heat amount falls by refresh control.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that the following description of the preferred embodiment is merely an example, and is not intended to limit the present invention, its application, or its use.

  FIG. 1 is a schematic configuration of a vehicle equipped with a fuel cell system 100 according to the present embodiment. In the following description, a fuel cell vehicle (FCHV) is assumed as an example of the vehicle, but the present invention can also be applied to an electric vehicle and a hybrid vehicle. Further, the present invention can be applied not only to vehicles but also to various moving bodies (for example, ships, airplanes, robots, etc.), stationary power sources, and portable fuel cell systems.

The fuel cell 40 generates electric power by generating electric power by receiving a reaction gas (fuel gas and oxidizing gas) and performing a chemical reaction. The fuel cell 40 has a stack structure in which a plurality of single cells including MEAs and the like are stacked in series. The output voltage (hereinafter referred to as FC voltage) and output current (hereinafter referred to as FC current) at the actual operation point of the fuel cell 40 are detected by the voltage sensor 140 and the current sensor 150, respectively. A fuel gas such as hydrogen gas is supplied from the fuel gas supply source 10 to the fuel electrode (anode) of the fuel cell 40, while an oxidizing gas such as air is supplied from the oxidizing gas supply source 70 to the oxygen electrode (cathode). Supplied. In the fuel cell 40 in which a large number of single cells are stacked, the oxidation reaction of the formula (1) occurs at the anode electrode, and the reduction reaction of the equation (2) occurs at the cathode electrode. The fuel cell 40 as a whole undergoes an electromotive reaction of the formula (3).
H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  The anode electrode has a catalyst layer mainly composed of carbon powder supporting a platinum-based metal catalyst (Pt, Pt—Fe, Pt—Cr, Pt—Ni, Pt—Ru, etc.), and is in contact with the polymer electrolyte membrane; A gas diffusion layer formed on the surface of the catalyst layer and having both air permeability and electronic conductivity. Similarly, the cathode electrode has a catalyst layer and a gas diffusion layer. The polymer electrolyte membrane is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluororesin, and exhibits good electrical conductivity in a wet state. A membrane electrode assembly is formed by the polymer electrolyte membrane, the anode electrode, and the cathode electrode.

  The fuel gas supply source 10 includes, for example, a hydrogen tank, an injector, various valves, and the like, and controls the amount of fuel gas supplied to the fuel cell 40 by adjusting the valve opening, the ON / OFF time, and the like. .

  The oxidizing gas supply source 70 includes, for example, an air compressor, a motor that drives the air compressor, an inverter, and the like, and adjusts the amount of oxidizing gas supplied to the fuel cell 40 by adjusting the rotational speed of the motor.

  The battery 60 is a chargeable / dischargeable secondary battery, and is composed of, for example, a nickel metal hydride battery. Of course, instead of the battery 60, a chargeable / dischargeable capacitor (for example, a capacitor) other than the secondary battery may be provided. The battery 60 and the fuel cell 40 are connected in parallel to an inverter 110 for a traction motor, and a DC / DC converter 130 is provided between the battery 60 and the inverter 110.

  The inverter 110 is, for example, a pulse width modulation type PWM inverter, which converts DC power output from the fuel cell 40 or the battery 60 into three-phase AC power in accordance with a control command given from the control device 80, and a traction motor 115. To supply. The traction motor 115 is a motor for driving the wheels 116 </ b> L and 116 </ b> R, and the rotation speed of the motor is controlled by the inverter 110.

  The DC / DC converter 130 is a full-bridge converter configured by, for example, four power transistors and a dedicated drive circuit (all not shown). The DC / DC converter 130 functions to step up or step down the DC voltage input from the battery 60 and output it to the fuel cell 40 side, and step up or step down the DC voltage input from the fuel cell 40 or the like to the battery 60 side. It has a function to output. Further, charging / discharging of the battery 60 is realized by the function of the DC / DC converter 130.

  An auxiliary machine 120 such as a vehicle auxiliary machine or an FC auxiliary machine is connected between the battery 60 and the DC / DC converter 130. The battery 60 is a power source for these auxiliary machines 120. The vehicle auxiliary equipment refers to various electric power devices (lighting equipment, air conditioning equipment, hydraulic pump, etc.) used during vehicle operation, and the FC auxiliary equipment is used to operate the fuel cell 40. It refers to various power devices (pumps for supplying fuel gas and oxidizing gas, etc.).

  The control device 80 includes a CPU, a ROM, a RAM, and the like. The voltage sensor 140 that detects the FC voltage, the current sensor 150 that detects the FC current, the temperature sensor 50 that detects the temperature of the fuel cell 40, and the charging of the battery 60. Each part of the system is centrally controlled based on each sensor signal input from an SOC sensor that detects the state, an accelerator pedal sensor that detects the opening of the accelerator pedal, and the like. The temperature sensor 50 measures the temperature at the fuel cell outlet.

  By the way, a platinum catalyst that promotes a chemical reaction is applied to the surface of the electrolyte membrane of the fuel cell 40. The platinum catalyst is oxidized by power generation, and the oxide is accumulated on the surface of the platinum catalyst, so that the power generation performance of the fuel cell 40 is lowered. For this reason, the control device 80 executes refresh control for recovering the power generation performance. In the refresh control, the control device 80 temporarily reduces the cell voltage of the fuel cell 40 (for example, 0.6 (V) or less) by reducing the supply amount of one of the oxidizing gas and the hydrogen gas. Thereby, since the oxide is reduced, the power generation performance of the fuel cell is restored.

  There is an example in which such refresh control is performed, for example, when a high load is requested. That is, when the fuel cell 40 is mounted on a vehicle, for example, when the load is high, the amount of heat generated by the fuel cell increases. Therefore, the refresh control is executed to temporarily reduce the cell voltage of the fuel cell to reduce the amount of heat generated. It is conceivable to perform control so as to decrease. However, there are many transitional vehicles when a high load is required in the vehicle, and there is a risk of promoting deterioration of the fuel cell by performing refresh control more than necessary. As described above, since there is a possibility that the deterioration of the fuel cell is promoted by always executing the refresh control when a high load is requested, the refresh control is executed as follows in the present embodiment.

  FIG. 2 is a flowchart illustrating an example of refresh control executed in the fuel cell system according to the present embodiment.

  First, in step S10, oxidizing gas and hydrogen gas are supplied to the fuel cell 40, and power generation is started by an electrochemical reaction, that is, steady normal power generation is performed.

  Next, in step S20, it is determined whether or not the temperature detected by the temperature sensor 50 that detects the temperature of the fuel cell 40 is equal to or higher than a predetermined value (for example, 90 ° C.). If the temperature of the fuel cell 40 is equal to or higher than a predetermined value (step S20 (YES)), the process proceeds to step S30. On the other hand, if the temperature of the fuel cell 40 is less than the predetermined value (step S20 (NO)), the process proceeds to step S25.

  In step S25, the state of the oxide film formed on the catalyst layer (poisoning state) is determined, and it is determined whether or not refresh control needs to be executed in accordance with the state. As a situation of the oxide film, for example, it may be based on whether the amount (estimated amount) of the oxide film formed on the catalyst layer is a predetermined value or more. When it is determined that it is not necessary to execute the refresh control depending on the state of the oxide film formed on the catalyst layer (step S25 (NO)), the process returns to step S10 and the processes after step S10 are repeated. On the other hand, when it is determined that the refresh control needs to be executed depending on the state of the oxide film formed on the catalyst layer (step S25 (YES)), the process proceeds to step S40 and the later-described refresh control is executed.

  In step S30 following step S20 (YES), it is determined whether or not a specified time has elapsed since the previously executed refresh control (step S40 described later). The specified time can be set to any time, but for example, from the viewpoint of not promoting the deterioration of the fuel cell even when refresh control is executed, the reaction time for re-deposition of the oxide film on the catalyst is a guide. Set to. If this specified time has not elapsed, the process returns to step S10 and the processes in and after step S10 are repeated until it is determined that the specified time has elapsed. On the other hand, if it is determined that the specified time has elapsed since the last executed refresh control, the process proceeds to step S40.

  In step S40, refresh control is executed. As the refresh control, for example, the supply of the oxidizing gas to the fuel cell 40 is controlled, or the sweep current of the discharge device is controlled to lower the voltage of the fuel cell 40 to the reduction potential. For example, the reduction potential is lowered by intentionally reducing the supply of the oxidizing gas to be supplied or increasing the sweep current instantaneously. After execution of the refresh control, the process returns to step S10 and the processes after step S10 described above are repeated. Thus, in the present embodiment, when the temperature of the fuel cell 40 is equal to or higher than a predetermined value, the refresh control is executed regardless of the state of the oxide film formed on the catalyst layer.

  It will be described with reference to FIG. 3 and FIG. 4 that the current-voltage characteristics are improved and the heat generation amount of the fuel cell is reduced by executing the refresh control. FIG. 3 is a graph for explaining current-voltage characteristics before and after refresh, and FIG. 4 is a graph for explaining the relationship between current and heat generation before and after refresh. In FIG. 3, the horizontal axis represents current, and the vertical axis represents the cell voltage of the fuel cell 40. The cell voltage refers to the voltage of a single fuel cell constituting the fuel cell stack. In FIG. 4, the horizontal axis represents current, and the vertical axis represents the amount of heat generated by the fuel cell 40.

  The cell voltage decreases as the usage time elapses due to the accumulation of the oxide of the platinum catalyst, but increases when the refresh control is executed (A → A ′ shown in FIG. 3). That is, the voltage-current characteristic is improved, and the operating point of the output of the same fuel cell moves from A to A ′. Then, the operating point moves from B to B ′ on the heat generation amount-current characteristic shown in FIG. 4, and the heat generation amount of the fuel cell decreases. By reducing the amount of heat generation, a water temperature targeted for control can be realized even in a small heat radiating device (deviation becomes small), and the current (output) that can be swept increases.

  According to the embodiment described above, when the temperature of the fuel cell is equal to or higher than a predetermined value (for example, 90 ° C. or higher), refresh control is performed regardless of the state of the oxide film formed on the catalyst layer. The amount of heat generated by the fuel cell can be effectively reduced using the control. Thereby, the calorific value of a fuel cell system can be reduced, without adding the apparatus for radiating the heat which generate | occur | produced in the fuel cell, and enlarging. In addition, according to the present embodiment, the refresh control is executed on the condition that the specified time has passed since the refresh control executed last time. Therefore, it is limited to execute the refresh control more than necessary, and there is no such limitation. It is possible to suppress the deterioration of the fuel cell from being promoted as compared with the configuration in which the refresh control is executed.

  The embodiments described above are for facilitating the understanding of the present invention, and are not intended to limit the present invention. Each element included in the embodiment and its arrangement, material, condition, shape, size, and the like are not limited to those illustrated, and can be changed as appropriate. In addition, the structures shown in different embodiments can be partially replaced or combined.

DESCRIPTION OF SYMBOLS 10 ... Fuel gas supply source 40 ... Fuel cell 50 ... Temperature sensor 60 ... Battery 70 ... Oxidation gas supply source 80 ... Control apparatus 100 ... Fuel cell system 110 ... Inverter 115 ... Traction motor 120 ... Auxiliary machinery 130 ... Converter 140 ... Voltage Sensor 150 ... Current sensor

Claims (1)

A fuel cell system including a fuel cell including a membrane electrode assembly in which electrodes having a catalyst layer are arranged on both surfaces of a polymer electrolyte membrane,
A temperature sensor for measuring the temperature of the fuel cell;
A control unit that performs refresh control to recover the power generation performance of the fuel cell by lowering the voltage of the fuel cell to a reduction potential; and
The control unit performs the refresh control regardless of a state of an oxide film formed on the catalyst layer when the temperature detected by the temperature sensor is equal to or higher than a predetermined value. .

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