WO2008099743A1

WO2008099743A1 - Fuel cell system

Info

Publication number: WO2008099743A1
Application number: PCT/JP2008/051988
Authority: WO
Inventors: Kenji Umayahara; Michio Yoshida; Tadaichi Matsumoto; Motohiko Taniyama
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2007-02-05
Filing date: 2008-01-31
Publication date: 2008-08-21

Abstract

A fuel cell system performs control as follows. When a request power for the fuel cell is lower than a predetermined value, supply of a reaction gas to a fuel cell is stopped and the output voltage of the fuel cell is maintained at a high potential-avoiding voltage (V1) lower than the open end voltage (OCV). When the request power for the fuel cell is higher than the predetermined value, the output voltage of the fuel cell is controlled to be the high potential-avoiding voltage (V1) at the highest. By setting the upper limit of the output voltage of the fuel cell to the high potential-avoiding voltage (V1) which is lower than the open end voltage (OCV), it is possible to suppress degradation of a catalyst caused by increase of the output voltage of the fuel cell to the open end voltage (OCV).

Description

Specification

Fuel cell system

Technical field

The present invention relates to a fuel cell system that performs operation control with an output voltage of a fuel cell being set to a high potential avoidance voltage that is lower than an open-circuit voltage. Background art

A fuel cell stack is a power generation system that directly converts energy released during an oxidation reaction into electrical energy by oxidizing fuel through an electrochemical process. The fuel cell stack has a membrane-one electrode assembly in which both side surfaces of a polymer electrolyte membrane for selectively transporting hydrogen ions are sandwiched by a pair of electrodes made of a porous material. Each of the pair of electrodes is mainly composed of carbon powder supporting a platinum-based metal catalyst, and is formed on the surface of the catalyst layer in contact with the polymer electrolyte membrane, and has both air permeability and electronic conductivity. Gas diffusion layer.

In a fuel cell vehicle equipped with a fuel cell system as a power source, in a high output region where the power generation efficiency is good, the fuel cell stack is generated and power is supplied to the traction motor from both the fuel cell stack and the secondary battery or only from the fuel cell stack. On the other hand, in the low output region where the power generation efficiency is low, the fuel cell stack is temporarily stopped to control the operation to supply power to the traction motor only from the secondary battery. In this way, temporarily stopping the operation of the fuel cell stack in a low load region where the power generation efficiency of the fuel cell system is low is called intermittent operation. In the low-load region where the power generation efficiency of the fuel cell system is reduced, intermittent operation can be performed to operate the fuel cell stack within a range where the energy conversion efficiency is high, increasing the efficiency of the entire fuel cell system. be able to. Japanese Laid-Open Patent Publication No. 2004-172028 refers to a fuel cell system that performs intermittent operation when the required load on the fuel cell stack is below a predetermined value. According to this publication, when the cell voltage of a fuel cell stack that has shifted to a power generation halt state due to intermittent operation falls below a predetermined value, an air conditioner is driven to supply oxygen gas to the fuel cell stack. It also mentions that the oxygen shortage at the cathode of the fuel cell stack can be resolved to restore the cell voltage and improve the response delay to power generation requirements.

[Patent Document 1] Japanese Patent Laid-Open No. 2004-172028 Disclosure of Invention

By the way, in the conventional intermittent operation, the supply of the reaction gas to the fuel cell stack is stopped, and the command voltage of the DC / DC converter connected in parallel to the output terminal of the fuel cell stack is set to the open-end voltage to The output terminal voltage of the battery stack was controlled to the open circuit voltage (OCV). By maintaining the output terminal voltage of the fuel cell stack at the open-circuit voltage, it is possible to control so that no current flows out of the fuel cell stack during intermittent operation.

However, if the output terminal voltage of the fuel cell stack is maintained at the open-circuit voltage during low-load operation, the platinum catalyst contained in the catalyst layer of the membrane-one electrode assembly may be ionized and eluted, so the performance of the fuel cell stack Suppressing the decline is an issue to be studied.

Therefore, an object of the present invention is to propose a fuel cell system capable of achieving both improvement in power generation efficiency of a fuel cell and maintenance of durability.

In order to solve the above-described problems, a fuel cell system according to the present invention includes a fuel cell that generates power upon receiving a reaction gas supply, and a reaction gas supply to the fuel cell when the required power for the fuel cell is less than a predetermined value. Control so that the output voltage of the fuel cell is maintained at a high potential avoidance voltage lower than the open-circuit voltage. And a control device for controlling the output voltage of the fuel cell with the high potential avoidance voltage as an upper limit when the required power for the fuel cell is a predetermined value or more.

By setting the upper limit of the output voltage of the fuel cell to a high potential avoidance voltage lower than the open end voltage, it is possible to suppress catalyst deterioration due to the output voltage of the fuel cell rising to the open end voltage.

The fuel cell system according to the present invention further includes a D C ZD C converter for controlling the output voltage of the fuel cell. When the required power for the fuel cell is less than a predetermined value, the control device stops driving the D C ZD C converter when the output voltage of the fuel cell is lower than the high potential avoidance voltage by a predetermined voltage.

By stopping the DC / DC converter drive when the output voltage of the fuel cell falls below the high potential avoidance voltage by a predetermined voltage, the switching loss of the DC / DC converter is suppressed and the reaction remaining inside the fuel cell An increase in the output voltage of the fuel cell due to gas can be avoided.

The fuel cell system according to the present invention further includes a power storage device. When the power generated by the fuel cell exceeds the sum of the power that can be charged by the power storage device and the power that can be consumed by the catcher, the control device can output the fuel cell up to the open-circuit voltage. Allow boosting.

When the generated power of the fuel cell exceeds the chargeable power of the power storage device, damage to the power storage device can be avoided by allowing the output voltage of the fuel cell to be boosted to the open-circuit voltage.

The fuel cell system according to the present invention further includes a traction motor. The control device allows the output voltage of the fuel cell to be boosted to the open-end voltage while regenerative braking is being performed by the traction motor.

While the regenerative braking by the traction motor is being implemented, by allowing the output voltage of the fuel cell to increase to the open end voltage, the power generation of the fuel cell during the regenerative braking is stopped and the regenerative power is reduced. More power storage devices can be charged. The fuel cell system according to the present invention further includes a plurality of shut-off valves arranged in a piping system for supplying a reaction gas to the fuel cell. The control device forms a closed space inside the piping system by closing a plurality of shut-off valves, and detects gas leaks by detecting gas pressure fluctuations inside the closed space. Allows the battery output voltage to be boosted to the open-circuit voltage.

During gas leak detection, by allowing the output voltage of the fuel cell to increase to the open-circuit voltage, the consumption of reactive gas due to power generation by the fuel cell during gas leak detection is suppressed, and gas leak detection is performed. Accuracy can be increased.

Here, the fuel cell is a cell stack formed by stacking a plurality of cells. The control device preferably corrects the high potential avoidance voltage so that the highest voltage among the output voltages of the plurality of cells is equal to or lower than a predetermined value. If the cell voltage varies, the highest output voltage of multiple cells may exceed the high potential avoidance voltage per cell. By correcting the high potential avoidance voltage so that the maximum voltage among the output voltages of multiple cells is below a predetermined value (for example, the voltage value obtained by dividing the target voltage of the cell stack by the total number of cells), the cell voltage It is possible to suppress a decrease in durability caused by variations in the thickness. Brief Description of Drawings

FIG. 1 is a system configuration diagram of a fuel cell system according to the present embodiment. FIG. 2 is an exploded perspective view of the cells constituting the fuel cell stack.

FIG. 3 is a timing chart showing operation control of the fuel cell system according to the present embodiment.

Figure 4 is a graph showing the stack voltage detection error.

Figure 5 is a graph showing cell voltage variation.

FIG. 6 is a timing chart showing intermittent stop of the DC / DC converter. FIG. 7 is an explanatory diagram showing conditions for executing the high potential avoidance control.

FIG. 8 is a timing chart showing operation control for switching on / off high potential avoidance control in accordance with the presence or absence of regenerative braking.

Figure 9 is a graph showing the relationship between the driving mode and the high potential avoidance voltage.

FIG. 10 is a timing chart showing operation control for switching high potential avoidance control on and off according to the presence or absence of gas leak detection. BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments according to the present invention will be described below with reference to the drawings. FIG. 1 shows a system configuration of a fuel cell system 10 that functions as an in-vehicle power supply system for a fuel cell vehicle.

The fuel cell system 10 functions as an in-vehicle power supply system mounted on a fuel cell vehicle. The fuel cell system 10 generates power by receiving a reaction gas (fuel gas, oxidation gas), and an oxidation system. An oxidizing gas supply system 30 for supplying air as gas to the fuel cell stack 20; a fuel gas supply system 40 for supplying hydrogen gas as fuel gas to the fuel cell stack 20; It includes a power system 50 for controlling the charging / discharging of the system and a controller 60 for controlling the entire system.

The fuel cell stack 20 is a solid polymer electrolyte cell stack in which a large number of cells are stacked in series. In the fuel cell stack 20, the oxidation reaction of the equation (1) occurs at the anode electrode, and the reduction reaction of the equation (2) occurs at the force sword electrode. The fuel cell stack 20 as a whole undergoes an electromotive reaction of the formula (3).

H ₂ → 2 H ++ 2 e ：… (1)

(1/2) 〇 2 + 2 H ++ 2 e · → H ₂ 0… (2)

H ₂ + (1/2) 0 ₂ → H ₂ 0… (3)

The fuel cell stack 20 has an output voltage (FC voltage) of the fuel cell stack 20 A voltage sensor 7 1 for detecting the current and a current sensor 7 2 for detecting the output current (FC current) are attached.

The oxidizing gas supply system 30 includes an oxidizing gas passage 3 3 through which oxidizing gas supplied to the cathode electrode of the fuel cell stack 20 flows, and an oxidizing off gas passage 3 4 through which oxidizing off gas discharged from the fuel cell stack 20 flows. have. The oxidant gas passage 3 3 includes an air conditioner 3 2 that takes in the oxidant gas from the atmosphere via the filter 3 1, and a humidifier 3 5 that humidifies the oxidant gas pressurized by the air compressor 3 2. A shutoff valve A 1 is provided for shutting off the oxidizing gas supply to the fuel cell stack 20. The oxidizing off gas passage 3 4 includes a shutoff valve A 2 for shutting off the oxidizing off gas discharge from the fuel cell stack 20, a back pressure adjusting valve A 3 for adjusting the oxidizing gas supply pressure, and an oxidizing gas. A humidifier 35 for exchanging moisture between the (dry gas) and the oxidizing off gas (wet gas) is provided.

The fuel gas supply system 40 includes a fuel gas supply source 41, a fuel gas passage 4 3 through which fuel gas supplied from the fuel gas supply source 41 to the anode of the fuel cell stack 20 flows, and a fuel cell stack 2 A circulation passage 4 4 for returning the fuel off-gas discharged from 0 to the fuel gas passage 4 3, a circulation pump 4 5 for pumping the fuel off-gas in the circulation passage 4 4 to the fuel gas passage 4 3, and a circulation passage 4 It has exhaust drainage passages 4 and 6 that are branched and connected to 4.

The fuel gas supply source 41 is composed of, for example, a high-pressure hydrogen tank or a hydrogen storage alloy, and stores high-pressure (for example, 35 MPa to 7 OMPa) hydrogen gas. When the shut-off valve HI is opened, the fuel gas flows out from the fuel gas supply source 4 1 to the fuel gas passage 4 3. The fuel gas is depressurized to, for example, about 200 kPa by the regulator H 2 and the injector 42 and supplied to the fuel cell stack 20.

The fuel gas supply source 41 is a hydrogen-rich reformed gas from hydrocarbon fuel. And a high-pressure gas tank that stores the reformed gas generated in the reformer in a high-pressure state.

In the fuel gas passage 4 3, there are a shutoff valve H 1 for shutting off or allowing the supply of fuel gas from the fuel gas supply source 4 1, a regulator H 2 for adjusting the pressure of the fuel gas, and a fuel cell stack 2 ◦ There are provided an indicator 42 for controlling the amount of fuel gas supplied to the fuel cell, a shutoff valve H3 for shutting off the fuel gas supply to the fuel cell stack 20, and a pressure sensor 74.

The regulator H 2 is a device that regulates the upstream pressure (primary pressure) to a preset secondary pressure, and is composed of, for example, a mechanical pressure reducing valve that reduces the primary pressure. The mechanical pressure reducing valve has a housing in which a back pressure chamber and a pressure adjusting chamber are formed with a diaphragm therebetween, and the primary pressure is reduced to a predetermined pressure in the pressure adjusting chamber by the back pressure in the back pressure chamber. To have a secondary pressure. By disposing the regulator H 2 on the upstream side of the injector 42, the upstream pressure of the injector 42 can be effectively reduced. For this reason, the degree of freedom in designing the mechanical structure of the injector 42 (valve body, casing, flow path, driving device, etc.) can be increased. Further, since the upstream pressure of the injector 42 can be reduced, the valve body of the injector 42 becomes difficult to move due to an increase in the differential pressure between the upstream pressure and the downstream pressure of the injector 42. This can be suppressed. Accordingly, it is possible to widen the adjustable pressure width of the downstream pressure of the injector 42, and to suppress a decrease in the response of the injector 42.

The injector 42 is an electromagnetically driven on / off valve that can adjust the gas flow rate and gas pressure by driving the valve body directly with a predetermined driving cycle with electromagnetic driving force and separating it from the valve seat. . The injector 42 has a valve seat having an injection hole for injecting gaseous fuel such as fuel gas, a nozzle body for supplying and guiding the gaseous fuel to the injection hole, and an axial direction (gas And a valve body that is accommodated and held so as to be movable in the flow direction) and opens and closes the injection hole. In the present embodiment, the valve body of the injector 42 is driven by a solenoid that is an electromagnetic drive device, and the opening area of the injection hole is switched in two stages by turning on and off the pulsed excitation current fed to the solenoid. be able to. By controlling the gas injection time and gas injection timing of the indicator 42 by the control signal output from the controller 60, the flow rate and pressure of the fuel gas are controlled with high accuracy. The injector 42 is a valve (valve body and valve seat) that opens and closes directly with an electromagnetic driving force, and has a high responsiveness because its driving cycle can be controlled to a highly responsive region. The injector 42 changes at least one of the opening area (opening) and the opening time of the valve body provided in the gas flow path of the injector 42 in order to supply the required gas flow rate downstream thereof. Adjust the gas flow rate (or hydrogen molar concentration) supplied downstream. The circulation passage 44 is connected to a shutoff valve H 4 for shutting off the fuel off-gas discharge from the fuel cell stack 20 and an exhaust / drain passage 46 branched from the circulation passage 44. An exhaust / drain valve H 5 is disposed in the exhaust / drain passage 46. The exhaust / drain valve H 5 is operated according to a command from the controller 60 to discharge the fuel off-gas and impurities including impurities in the circulation passage 44 to the outside. By opening the exhaust drain valve H 5, the concentration of impurities in the fuel off-gas in the circulation passage 44 can be lowered, and the hydrogen concentration in the fuel off-gas circulating in the circulation system can be increased.

The fuel off-gas discharged through the exhaust / drain valve H 5 is mixed with the oxidizing off-gas flowing through the oxidizing off-gas passage 34 and diluted by a diluter (not shown). The circulation pump 45 circulates and supplies the fuel off-gas in the circulation system to the fuel cell stack 20 by driving the motor.

The power system 50 includes a DC / DC converter 51, a battery 52, a traction inverter 5 3, a traction motor 5 4, and auxiliary equipment 5 5. Fuel cell system 10 DC / DC converter 5 1 and traction impeller Data parallel to the fuel cell stack 20 is connected to the fuel cell stack 20 in parallel. The DC / DC converter 51 boosts the DC voltage supplied from the battery 52 and outputs it to the traction inverter 53, and the DC power generated by the fuel cell stack 20 or traction by regenerative braking. It has a function to step down the regenerative power collected by the motor 54 and charge the battery 52. With these functions of the D CZD C converter 51, charging / discharging of the battery 52 is controlled. In addition, the operation point (output voltage, output current) of the fuel cell stack 20 is controlled by voltage conversion control by the D CZD C converter 51.

The battery 52 functions as a surplus power storage source, a regenerative energy storage source during regenerative braking, and an energy buffer during load fluctuations associated with acceleration or deceleration of the fuel cell vehicle. As the battery 52, for example, a secondary battery such as a nickel-powered lithium storage battery, a nickel-hydrogen storage battery, or a lithium secondary battery is preferable. The battery 52 is provided with a SOC sensor 73 for detecting SOC (State of charge).

The traction inverter 53 is, for example, a PWM inverter driven by a pulse width modulation method, and in accordance with a control command from the controller 60, the DC voltage output from the fuel cell stack 20 or the battery 52 is three-phased. It converts to AC voltage and controls the rotational torque of the Traction Motor 54. The traction motor 54 is, for example, a three-phase AC motor, and constitutes a power source for the fuel cell vehicle.

Auxiliary machinery 5 5 includes motors (for example, power sources such as pumps) disposed in each part of the fuel cell system 10, inverters for driving these motors, and various types of motors. In-vehicle accessories (for example, air compressors, injectors, cooling water circulation pumps, radiators, etc.) are generic names. Controller 60 is CPU, ROM, RAM, and I / O interface. This is a computer system equipped with a fuel cell and controls each part of the fuel cell system 10. For example, when the controller 60 receives the start signal IG output from the ignition switch, the controller 60 starts operation of the fuel cell system 10 and outputs the accelerator opening signal ACC output from the accelerator sensor or the vehicle speed sensor. The required power of the entire system is obtained based on the vehicle speed signal VC. The required power of the entire system is the sum of the vehicle travel power and auxiliary power.

Here, the auxiliary power includes the power consumed by in-vehicle auxiliary equipment (humidifier, air compressor, hydrogen pump, cooling water circulation pump, etc.), and equipment required for vehicle travel (transmission, wheel control device, Power consumed by steering devices, suspension devices, etc.) and power consumed by devices (air conditioners, lighting fixtures, audio, etc.) disposed in the passenger space.

Then, the controller 60 determines the output power distribution between the fuel cell stack 20 and the battery 52, and the oxidizing gas supply system 3 so that the power generation amount of the fuel cell stack 20 matches the target power. 0 and the fuel gas supply system 40, and also the DC / DC converter 51 to adjust the output voltage of the fuel cell stack 20 so that the operating point of the fuel cell stack 20 (output voltage, Output current). Further, the controller 60, for example, supplies each AC voltage command value of the U phase, V phase, and W phase to the traction inverter 53 as a switching command so as to obtain a target torque according to the accelerator opening. Output and control the output torque and rotation speed of the traction motor 54. FIG. 2 is an exploded perspective view of the cell 21 constituting the fuel cell stack 20. The cell 21 is composed of a polymer electrolyte membrane 2 2, an anode electrode 2 3, a force sword electrode 2 4, and separators 2 6 and 2 7. The anode electrode 2 3 and cathode electrode 2 4 are diffusion electrodes having a sandwich structure with the polymer electrolyte membrane 2 2 sandwiched from both sides. Separators 2 6, 2 7 made of a gas-impermeable conductive member are provided on the anode electrode 2 3 while sandwiching this sandwich structure from both sides. And a flow path for fuel gas and oxidizing gas between the cathode electrode 24 and the cathode electrode 24, respectively. The separator 26 is formed with a lip 26 a having a concave cross section. When the anode electrode 23 is in contact with the rib 26a, the opening of the rib 26a is closed and a fuel gas flow path is formed. The separator 27 is formed with a rib 27 a having a concave cross section. When the force sword pole 24 comes into contact with the rib 27a, the opening of the rib 27a is closed and an oxidizing gas flow path is formed.

The anode electrode 23 is mainly composed of carbon powder supporting a platinum-based metal catalyst (Pt, Pt—Fe, Pt_Cr, Pt—Ni, Pt_Ru, etc.) It has a catalyst layer 2 3a in contact with the polymer electrolyte membrane 22 and a gas diffusion layer 2 3b formed on the surface of the catalyst layer 2 3a and having both air permeability and electronic conductivity. Similarly, the force sword electrode 24 has a catalyst layer 24a and a gas diffusion layer 24b. More specifically, the catalyst layers 2 3 a and 2 4 a are formed by dispersing carbon powder carrying platinum or an alloy made of platinum and another metal in a suitable organic solvent, and adding an appropriate amount of an electrolyte solution. And screen printed on the polymer electrolyte membrane 22. The gas diffusion layers 2 3 b and 2 4 b are formed of carbon cloth, carbon paper, or carbon felt woven with carbon fiber yarns. The polymer electrolyte membrane 22 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 25 is formed by the polymer electrolyte membrane 2 2, the anode 2 3, and the cathode 2 4.

FIG. 3 is a timing chart showing operation control of the fuel cell system 10. The fuel cell system 10 improves power generation efficiency by switching the operation mode of the fuel cell stack 20 according to the operating load. For example, the fuel cell system 10 controls the operation by setting the power generation command value of the fuel cell stack 20 to zero in the low load region where the power generation efficiency is low (the operation region where the power generation request is less than a predetermined value). Battery power required for driving and system operation 5 2 (Hereinafter referred to as the first operation mode). On the other hand, in the high load region where power generation efficiency is high (the operation region where the power generation request exceeds a predetermined value), the power generation command value of the fuel cell stack 20 is calculated based on the accelerator opening and the vehicle speed, etc. However, the power required for vehicle travel and the power required for system operation are covered only by the power generated by the fuel cell stack 20 or by the power generated by the fuel cell stack 20 and the power from the battery 52 (hereinafter referred to as This is referred to as operation mode 2).

The fuel cell system 10 monitors the control flag indicating the operation mode at regular intervals, and controls the operation in the first operation mode when the control flag is turned on, and performs the second operation when the control flag is turned off. Control operation in mode. In any operation mode, the output voltage of the fuel cell stack 20 during normal operation is basically limited to the operation range between the upper limit voltage V I and the lower limit voltage V 2.

The upper limit voltage V 1 is preferably a voltage that satisfies the condition that the platinum catalyst contained in the catalyst layers 2 3 a and 2 4 a of the fuel cell stack 20 does not elute, Furthermore, in addition to the above conditions, when the output voltage of the fuel cell stack 20 is maintained at the upper limit voltage VI when the reaction gas supply to the fuel cell stack 20 is stopped, the fuel cell stack 20 It is preferable that the voltage satisfies the condition that it is in a voltage range that can be consumed by the auxiliary machinery 55. In the fuel cell stack 20, the platinum catalyst in the catalyst layer 24 a can be eluted, especially when the potential of the force sword electrode 24 is kept high, such as during low-density current operation or idle operation. There is sex. In this specification, controlling the output voltage of the fuel cell stack 20 to be equal to or lower than the upper limit voltage VI used and maintaining the durability of the fuel cell stack 20 is referred to as high potential avoidance control. The upper limit voltage V 1 may be referred to as a high potential avoidance voltage. In this embodiment, in principle, high potential avoidance control is executed in any operation mode. The The upper limit voltage VI is preferably set so that the voltage is about 0.9 V per cell, for example.

The lower limit voltage V 2 is preferably a voltage that satisfies the condition that the cell voltage is within a voltage range that does not decrease in the reduction region. If the fuel cell stack 20 is continuously operated in the oxidation region, an effective area of the platinum catalyst is reduced by forming an oxide film on the surface of the platinum catalyst contained in the catalyst layer 24 a. Then, since the activation voltage increases, the I-V characteristic of the fuel cell stack 20 decreases. By performing the catalyst activation treatment, the oxide film is reduced and the oxide film is removed from the platinum catalyst, so that the I-V characteristics can be recovered. However, the cell voltage is reduced between the oxidation region and the reduction region. If the transition is made frequently, the durability of the fuel cell stack 20 will decrease. In addition, if the cell voltage is raised to the oxidation region as the required load increases after the cell voltage is lowered to the reduction region, the carbon carrying the platinum catalyst may be oxidized. Taking these circumstances into consideration, it is possible to suppress a decrease in the durability of the fuel cell stack 20 by controlling the output voltage of the fuel cell stack 20 during normal operation to the lower limit voltage V 2 or more. . The lower limit voltage V 2 is preferably set so that the voltage is about 0.8 V per cell, for example.

In general, the output voltage of the fuel cell stack 20 during normal operation is controlled between the upper limit voltage VI and the lower limit voltage V 2 as a general rule. The output voltage may be controlled to the upper limit voltage V 1 or higher, or may be controlled to the lower limit voltage V 2 or lower. For example, when the SOC of the battery 52 is greater than or equal to the specified value, when gas leak detection is performed, or when regenerative power is recovered by regenerative braking, the output voltage of the fuel cell stack 20 is raised to the open-circuit voltage. . Further, when the catalyst activation process is performed, the output voltage of the fuel cell stack 20 is lowered to the use lower limit voltage V 2 or less. In the first operation mode, the controller 60 sets the power generation command value to zero, stops the supply of the reaction gas to the fuel cell stack 20, and sets the voltage command value to the DC / DC converter 51. Set to upper limit voltage VI (time t0 to t4). Even after the supply of the reaction gas is stopped, the unreacted reaction gas remains in the fuel cell stack 20, so that the fuel cell stack 20 generates a slight amount of power for a while.

The period from time t 0 to t 2 is a power generation period in which a minute amount of power generation is continued by converting the chemical energy of the residual reaction gas into electric energy. During this power generation period, the residual reaction gas has enough energy for the output voltage of the fuel cell stack 20 to maintain the upper limit voltage V 1, so the output voltage of the fuel cell stack 20 is equal to the upper limit voltage V 1 Continue to maintain. The power generated during this power generation period is consumed by the auxiliary machinery 55, but if it cannot be consumed by the auxiliary machinery 55, the battery 52 is charged.

During the period from time t 0 to t 1, the generated energy of the fuel cell stack 20 exceeds the consumption capacity of the accessories 55, so that a part of the generated energy is charged in the battery 52. However, the power generation energy released from the fuel cell stack 20 according to the consumption of the residual reactant gas gradually decreases, so the power generation energy released from the fuel cell stack 20 at the time t1. And the consumption capacity of the traps 55 is balanced, and the electric power charged to the battery 52 becomes a negative outlet. During the period from time t 1 to time t 2, the generated power released from the fuel cell stack 20 cannot cover the power consumption of the auxiliary machinery 5 5. Electric power is supplied from the battery 5 2 to the auxiliary machinery 5 5.

The period from time t 2 to t 4 is a power generation stop period in which the output voltage of the fuel cell stack 20 can no longer be maintained at the use upper limit voltage V 1 due to the consumption of residual reaction gas, and power generation stops. Use the output voltage of the fuel cell stack 20 When the residual reaction gas does not have the energy necessary to maintain the upper limit voltage V 1 for use, power generation is stopped, and the output voltage of the fuel cell stack 20 gradually decreases. During this power generation stop period, the power generated by the fuel cell stack 20 is zero, so the power supplied from the battery 52 to the auxiliary machinery 55 is substantially constant.

At the time t3 when the output voltage of the fuel cell stack 20 drops to the lower limit voltage V2, the oxidizing gas supply system 30 is driven, and the oxidizing gas is supplied to the fuel cell stack 20. Since the fuel cell stack 20 is supplied with the oxidizing gas and generates power, the output voltage of the fuel cell stack 20 starts to rise. When the output voltage of the fuel cell stack 20 is increased to a predetermined voltage (for example, 3600 V), the oxidizing gas supply is finished. In this way, during the power generation stop period, whenever the output voltage of the fuel cell stack 20 drops to the lower limit voltage V2, the oxidizing gas is appropriately replenished so that the output voltage does not fall below the lower limit voltage V2. Be controlled.

In the second operation mode, the controller 60 calculates the power generation command value according to the required load, controls the supply of the reaction gas to the fuel cell stack 20, and uses the fuel cell via the DC ZDC converter 51. Controls the operation point (output voltage, output current) of stack 20 (time t4 to time t5). At this time, the voltage command value to the D C ZD C converter 51 is limited to the operation range between the upper limit voltage V I and the lower limit voltage V 2.

As shown in FIG. 4, the measured voltage V _DC measured by the voltage sensor ₇₁ may be smaller than the actual voltage V _TC of the fuel cell stack 20 by ΔV _stack . The main causes of the error AV _stack are the voltage drop due to the diode 75 provided to prevent the backflow of the stack current and the measurement error due to the voltage sensor 71. When such an error occurs, the controller 60 controls the DC / DC converter 51 so that the measured voltage V _{DC that} is smaller by ΔV _stack than the actual voltage V _TC matches the target voltage. Therefore, the actual voltage V _TC The voltage is controlled to be higher by ΔV _stack than the pressure.

If the actual voltage V _TC is controlled to a voltage higher than the target voltage by Δ V _stack , the deterioration of the fuel cell stack 20 will be accelerated, so the measurement voltage VDC will be corrected taking into account the error Δ V _stack However, it is preferable to control the DC / DC converter 51 so that the actual voltage V _TC matches the target voltage. Specifically, if the voltage drop due to the diode 75 or the measurement error due to the voltage sensor 71 can be handled as a steady-state error, add ΔV _stack as the correction value to the measurement voltage _VDC. , which treated as actual voltage V _TC, actual voltage V _TC may be controlled urchin DC / DC converter 5 1 by matching the target voltage.

Actual voltage VTC is equal to the total value Vcelall of each cell 2 1 cell voltage measured by the cell monitor, calculated at a predetermined computation cycle error delta Vstack between V _ce _LL-aU and V _DC The DC / DC converter 51 may be controlled such that the measured voltage V _DC is corrected in real time in consideration of the error Δ V _stack and the actual voltage V _TC matches the target voltage.

However, even if the DCZDC converter 5 1 is controlled so that the actual voltage V _TC matches the target voltage, as shown in Fig. 5, the output voltage (cell voltage) of the cell 2 1 varies. (The target voltage per cell is the voltage obtained by dividing the target voltage of the fuel cell stack 20 by the total number of cells.) .) In such a case, the deterioration of some of the cells 21 is promoted, so that the controller 60 does not increase the target voltage so that the cell voltage of any cell 21 does not exceed the target voltage per cell. It is preferable to correct the voltage. Specifically, the controller 60 monitors the cell voltage of each cell 21 constituting the fuel cell stack 20 with a cell voltage detection device (not shown), and determines the maximum cell voltage V _ce i _Lmax and the average cell. It is preferable to correct the target voltage of the fuel cell stack 20 based on the difference AV _cel i from the voltage V _cel and _ave, and control so that the cell voltage of any cell 21 does not exceed the target voltage per cell. Good.

Figure 6 is a timing chart showing the intermittent stop of the DC / DC converter 51.

This timing chart shows a series of control processes in which the fuel cell vehicle gradually decelerates from low-speed traveling to stop the vehicle.

At time _t 10 when the load on the fuel cell vehicle running at low speed becomes light and the required load on the fuel cell stack 20 falls below a predetermined threshold, the control flag switches from off to on. As a result, the operation mode of the fuel cell system 10 is switched from the second operation mode to the first operation mode. Then, at time t 11 when the vehicle speed is equal to or less than a predetermined value (for example, about several km / h), the traveling flag is switched from on to off. The traveling flag is flag information indicating whether or not the vehicle is in a traveling state. When the fuel cell vehicle is traveling (the vehicle speed is a predetermined value or more), the traveling flag is turned on, When the vehicle is stopped (the vehicle speed is less than the predetermined value), the travel flag is turned off.

At time t 1 2 when the fuel cell vehicle is completely stopped, the motor drive permission flag is switched from on to off. The motor driving permission flag is flag information indicating whether or not the driving of the traction motor 54 is permitted. When the driving of the tractive motor 54 can be permitted, the motor driving permission flag is turned on. If the driving of the traction motor 54 cannot be permitted (the state where the traction motor 54 is shut down), the motor driving permission flag is turned off.

In the first operation mode, the controller 60 sets the power generation command value to zero, stops the supply of the reaction gas to the fuel cell stack 20, and sets the voltage command value to the DC ZD C converter 51. Use upper limit voltage V1. Immediately after the supply of the reaction gas is stopped, sufficient reaction gas is maintained in the fuel cell stack 20 to maintain the output voltage of the fuel cell stack 20 at the use upper limit voltage V1. Although it remains, the amount of residual reactive gas gradually decreases due to the small amount of power generated by the residual reactive gas. When the residual reaction gas no longer has the energy required to maintain the output voltage of the fuel cell stack 20 at the upper limit voltage V 1, power generation is stopped, and the output voltage of the fuel cell stack 20 gradually decreases. I will do it.

At time t 1 3 when the output voltage of the fuel cell stack 20 decreases from the upper limit voltage V 1 by Δ ν to reach the voltage V 3, the converter drive permission flag is switched from on to off. The converter drive permission flag is flag information indicating whether or not the drive of the DC / DC converter 51 is permitted. When the drive of the DC / DC converter 51 can be permitted, the converter drive permission flag is When it is turned on and the drive of the DC / DC converter 51 cannot be permitted, the converter drive permission flag is turned off.

At time t 1 4 when the output voltage of the fuel cell stack 20 falls below the lower limit voltage V 2, the controller 60 drives the oxidizing gas supply system 40 to replenish the fuel cell stack 20 with oxidizing gas. Since the fuel cell stack 20 generates electric power upon replenishment of the oxidizing gas, the output voltage of the fuel cell stack 20 starts to rise. Further, at time t 14 when oxidant gas supply to the fuel cell stack 20 is started, the converter drive permission flag is switched from OFF to ON, and the D CZD C converter 51 is restarted. At time t 1 4 when D CZD C converter 5 1 restarts, the control flag remains on, so the voltage command value to D CZD C comparator 51 is set to the upper limit voltage V 1 The As a result, the output voltage of the fuel cell stack 20 is controlled between the upper limit voltage V 1 and the lower limit voltage V 2.

In this way, driving the DC ZD C converter 5 1 on the condition that “the traction motor 54 is shut down” and “the output voltage of the fuel cell stack 20 has dropped only from the upper limit voltage VI” (Transistor switching operation) is stopped (hereinafter referred to as intermittent stop). The switching loss of the C / DC converter 51 can be reduced and energy efficiency can be increased.

Here, the reason why the above two conditions are used as conditions for intermittently stopping the DCZDC converter 51 will be described. If the driving of the DC / DC converter 51 is stopped when the traction motor 54 is not shut down, voltage control to the fuel cell stack 20 by the DC / DC converter 51 will not work. The output voltage is pulled down by the truncation inverter 53, resulting in not being out of control, and the output voltage of the fuel cell stack 20 may fall below the lower limit voltage V2. In addition, when the output voltage of the fuel cell stack 20 maintains the upper limit voltage V 1, there is a possibility that a sufficient amount of reaction gas remains in the fuel cell stack 20 and continues to generate electricity. . If the driving of the DC / DC converter 51 is stopped in such a state, the output of the fuel cell stack 20 is output by the amount of power generated by the fuel cell stack 20 that cannot be consumed by the traction impeller 53. There is a risk that the voltage will rise and exceed the upper limit of use voltage V1.

On the other hand, when the output voltage of the fuel cell stack 20 decreases by AV from the upper limit voltage V 1, the amount of residual reaction gas is very small and the power generation is stopped, so the DC / DC converter 51 is driven. Even when stopped, the output voltage of the fuel cell stack 20 does not rise. For these reasons, the above two conditions are the conditions for intermittently stopping the DC / DC converter 51. FIG. 7 is an explanatory diagram showing conditions for executing the high potential avoidance control.

As shown in the figure, in order to allow the execution of high potential avoidance control, (A1) 30 of battery 52 is 3001 or less, (B 1) the vehicle is not in regenerative braking, (C 1) It is necessary to satisfy all the conditions that gas leak detection is not being judged. On the other hand, the implementation of high potential avoidance control is prohibited. (A2) Notch 52 SOC is SOC 2 or higher, (B 2) Vehicle is in regenerative braking, (C 2) Gas leak detection is being judged. It is necessary that these conditions are satisfied.

(Battery)

The controller 60 periodically monitors the state of charge of the battery 52 by reading the signal output from the SOC sensor 73. When 30 of battery 52 reaches 3002 (for example, 75%) or more, controller 60 switches the high potential avoidance control function from on (permitted) to off (prohibited). When the high potential avoidance control function is turned off, the output voltage of the fuel cell stack 20 is maintained at the open end voltage. On the other hand, when the SOC of the battery 52 becomes SOC 1 (for example, 70%) or less, the controller 60 switches the high battery avoidance control function from OFF to ON. When the high potential avoidance control function is turned on, the output voltage of the fuel cell stack 20 is controlled below the upper limit voltage VI.

When the high battery avoidance control is performed in the first operation mode, the output voltage of the fuel cell stack 20 is set to the upper limit voltage VI of use even though the power generation command value to the fuel cell stack 20 is the outlet. As a result, the fuel cell stack 20 generates a small amount of electricity through an electrochemical reaction caused by residual reaction gas. The power generated by this power generation can be consumed by auxiliary equipment 55 as auxiliary equipment loss, but due to fluctuations in power generation by the fuel cell stack 20, fluctuations in power consumption by auxiliary equipment 55, etc. Auxiliary equipment 55 alone may not be fully consumed. In such a case, power that cannot be consumed by the auxiliary equipment 55 will be charged to the battery 52. However, if the SOC of the battery 52 is high, it will cause overcharge and damage the battery 52. There is a risk of doing. Therefore, as described above, on condition that the SOC of the battery 52 becomes SOC 2 or more, the high potential avoidance control function is switched from on to off, so that the battery 52 can be prevented from being damaged due to overcharging. In the above explanation, an example of setting the judgment condition for switching on / off the high potential avoidance control function based on the SOC of the battery 52 is shown. However, the charge capacity of the battery 52 is used as a reference. Judgment conditions for switching on / off the high potential avoidance control function may be set. For example, when the charging capacity of the battery 52 is equal to or lower than Win 1 (for example, 1 kW), the high potential avoidance control function is switched from OFF to ON, while the charging capacity of the battery 52 is decreased to Win 2 (for example, 1 At 2 kW) or more, the high potential avoidance control function is switched from on to off. However, the judgment condition for switching the high potential avoidance control function on and off does not necessarily have a hysteresis characteristic. .

(Regenerative braking)

The operation control for switching the high potential avoidance control on and off according to the presence or absence of regenerative braking will be described with reference to the timing chart shown in FIG. This timing chart shows a series of processes in which the fuel cell vehicle shifts from a running state to regenerative braking. When the driver depresses the brake pedal at time t 2 0, the traction motor 5 4 performs regenerative braking and converts the kinetic energy of the vehicle into electric energy. At time t 2 0, the regeneration flag switches from off to on. The regenerative flag is flag information indicating whether or not the vehicle is performing regenerative braking. When the vehicle is not regeneratively braked, the regenerative flag is off, and when the vehicle is regeneratively braking, regenerative braking is performed. The flag is turned on.

When the regeneration flag is turned on, the controller 60 changes the upper limit voltage of the fuel cell stack 2 0 from the upper limit voltage V 1 to the open circuit voltage, and the output voltage of the fuel cell stack 20 exceeds the upper limit voltage VI. Allow open circuit voltage. Since the required load on the fuel cell stack 20 during regenerative braking is light, the output voltage of the fuel cell stack 20 gradually increases and becomes equal to the open-circuit voltage at time t 21, and thereafter Continue to maintain the open circuit voltage. In addition, after time t2 1 when the output voltage of the fuel cell stack 20 becomes equal to the open-circuit voltage. The generated current becomes zero.

The fact that the power generation current of the fuel cell stack 20 becomes zero means that the fuel cell stack 20 does not generate power, so that it is not necessary to charge the generated power to the battery 52. As a result, the regenerative power can be sufficiently charged to the battery 52. Here, the regenerative power indicated by the solid line indicates the power that can be charged to the battery 52 by prohibiting the high potential avoidance control during regenerative braking, and the regenerative power indicated by the dotted line indicates that the high potential avoidance control is performed during regenerative braking. Indicates the power that can be charged to battery 52. The difference between the two is the regenerative power that can be recovered more by the battery 52 because the battery 52 does not need to be charged with the power generated by the fuel cell stack 20 during regenerative braking. Indicates.

As described above, when the vehicle is regeneratively braked, the high potential avoidance control function is turned off, so that the generated power of the fuel cell stack 20 can be reduced to zero and more regenerative power can be charged to the battery 52. Efficiency can be increased.

During regenerative braking, the high potential avoidance function may not be turned off, but the upper limit voltage V 1 may be controlled to be higher than the open circuit voltage. In addition, when the SOC of the battery 52 is low, not only the regenerative power collected by the traction motor 54 but also the power generated by the fuel cell stack 20 can be charged. High potential avoidance control may be turned off on condition that regenerative braking is performed when the value is equal to or greater than a predetermined value.

Further, the target value of the high potential avoidance voltage during regenerative braking may be changed according to the vehicle running mode ((/ Β range). Here, the D range is a driving mode used during normal driving, and the B range is used when a braking force greater than that during normal driving is required, such as when driving on a downhill or a road. This is the running mode used for. During regenerative braking by the Traction Motor 54, the motor regeneration The torque is converted into electric power and charged to the battery 52. Therefore, when high potential avoidance control is performed even during regenerative braking, the following electric power balance is established. Battery charge power + Auxiliary machine power consumption = Motor regenerative power + Fuel cell power generation-(4)

As shown in equation (4), if the fuel cell power generated during vehicle braking is large, the motor regenerative power will be reduced by that amount, and sufficient braking torque cannot be secured. For this reason, it is preferable to increase the high potential avoidance voltage during vehicle braking to reduce the fuel cell generated power and to ensure sufficient braking torque. Therefore, the controller 60 variably sets the high potential avoidance voltage so that the following equation (5) is satisfied during vehicle braking.

Battery charging power + Auxiliary machine power consumption Motor regenerative power + Fuel cell power generation…

( Five )

Here, the high potential avoidance voltage derived from the relational expression (5) may be held in the ROM in the controller 60 as map data as shown in FIG. In Fig. 9, the horizontal axis represents regenerative power, and the vertical axis represents high potential avoidance voltage. Since the braking torque is different between the B range and D / R range, different map data are used. The solid line shows the map data for the D range, and the broken line shows the map data for the B range. The controller 60 determines whether the driving mode of the vehicle is the D range or the B range based on the shift position. If the driving mode is the B range, the driving mode is the D range. The target value of the high potential avoidance voltage is increased to ensure a large braking force. As a result, the drivability of the vehicle can be improved.

(Gas leak detection)

The operation control for switching on / off the high potential avoidance control according to the presence or absence of gas leak detection will be described with reference to the timing chart shown in FIG. This timing chart shows that the stopped fuel cell vehicle is the first Gas leakage into the fuel gas piping system of the fuel cell system 10 during operation in the operation mode

A series of control processes for determining whether or not (hydrogen leakage) has occurred is shown.

At time t 3 0 when the required power for the fuel cell stack 20 becomes less than a predetermined value due to, for example, the vehicle stopping, the control flag switches from off to on. Then, the controller 60 controls the operation of the fuel cell stack 20 in the first operation mode.

The controller 60 is a gas leak for determining whether or not a hydrogen leak has occurred in the fuel gas piping system when the stopped fuel cell vehicle is operated and controlled in the first operation mode. Invoke the detection routine. When the gas leak detection routine is started, the shut-off valve H 3 arranged upstream of the fuel gas inlet of the fuel cell stack 20 and the shut-off valve H arranged downstream of the fuel gas outlet 4 and 4 are closed to form a sealed space inside the fuel gas piping system. The gas pressure inside the sealed space is detected by a pressure sensor 74. If the amount of gas pressure drop per unit time inside the enclosed space is greater than or equal to a predetermined threshold, it is determined that a gas leak has occurred.

At time t3 0 when the gas leak detection routine is started, the gas leak detection flag is switched from OFF to ON. The gas leak detection flag is flag information indicating whether or not the gas leak detection process is being performed. When the gas leak detection is being performed, the gas leak detection flag is turned on and the gas leak detection process is performed. If not, the gas leak detection flag is turned off.

At time t 30 when the gas leak detection flag is turned on, the high potential avoidance flag is switched from on to off. The high potential avoidance flag is flag information indicating whether or not high potential avoidance control is permitted. When high potential avoidance control is permitted, the high potential avoidance flag is turned on and the high potential avoidance control is enabled. When this is prohibited, the high potential avoidance flag is turned off. High potential avoidance during gas leak detection By prohibiting the control, the output voltage of the fuel cell stack 20 gradually increases from the use upper limit voltage VI at the time t 30 and eventually reaches the open-circuit voltage. When the output voltage of the fuel cell stack 20 matches the open-circuit voltage, power generation by the fuel cell stack 20 is stopped.

At time t 3 1, the gas leak detection completion flag switches from off to on at the time t 3 1 when the time required for gas leak detection has elapsed and the gas leak detection processing is complete. The gas leak detection completion flag is flag information indicating whether or not the gas leak detection is completed. When the gas leak detection is completed, the gas leak detection completion flag is turned on and the gas leak detection is not completed. Sometimes the gas leak detection completion flag is turned off.

At time t 31 when the gas leak detection process is completed, the gas leak detection flag is switched from on to off, and the high potential avoidance flag is switched from off to on. When the high potential avoidance flag is switched from OFF to ON, the output voltage of the fuel cell stack 20 gradually decreases from the open-circuit voltage at time t 3 1 and eventually reaches the use upper limit voltage V 1. When the gas leak detection process is completed, the shutoff valves 8 1 and 8 2 are opened.

If high-pressure avoidance control is permitted during gas leak detection by forming a sealed space inside the fuel gas piping system and measuring the amount of gas pressure drop inside the sealed space after a predetermined time has elapsed Since the fuel cell stack 20 generates power and consumes hydrogen gas in the sealed space, there is a possibility of erroneous determination. On the other hand, according to the present embodiment, high potential avoidance control is prohibited while gas leak detection is being performed, so that the hydrogen gas consumption inside the sealed space caused by power generation by the fuel cell stack 20 This makes it possible to carry out highly accurate gas leak determination.

In the above-described embodiment, the usage mode in which the fuel cell system 10 is used as an in-vehicle power supply system has been illustrated. However, the usage mode of the fuel cell system 10 is This is not limited to examples. For example, the fuel cell system 10 may be mounted as a power source for a mobile body (robot, ship, aircraft, etc.) other than the fuel cell vehicle. Further, the fuel cell system 10 according to this embodiment is installed in a power generation facility such as a house or a building.

It may be used as a stationary power generation system. Industrial applicability

According to the present invention, the upper limit of the output voltage of the fuel cell is set to a high potential avoidance voltage that is lower than the open-circuit voltage, so that the deterioration of the catalyst due to the increase of the output voltage of the fuel cell to the open-circuit voltage is prevented. Can be suppressed.

Claims

The scope of the claims

1. a fuel cell that generates power by receiving a supply of reaction gas;

Control is performed such that when the required power for the fuel cell is less than a predetermined value, supply of the reactive gas to the fuel cell is stopped and the output voltage of the fuel cell is maintained at a high potential avoidance voltage lower than the open-circuit voltage. A control device that controls the output voltage of the fuel cell with the high potential avoidance voltage as an upper limit when the required power for the fuel cell is equal to or greater than a predetermined value;

A fuel cell system comprising:

2. The fuel cell system according to claim 1, wherein

A DC / DC converter for controlling the output voltage of the fuel cell; and the control device is configured such that when the required power to the fuel cell is less than a predetermined value, the output voltage of the fuel cell is higher than the high potential avoidance voltage. A fuel cell system that stops driving the DC / DC converter when a predetermined voltage drops.

3. The fuel cell system according to claim 1, wherein

A power storage device,

When the generated power of the fuel cell exceeds the sum of the power that can be charged by the power storage device and the power that can be consumed by traps, the control device outputs an output voltage of the fuel cell. A fuel cell system that allows boosting to a voltage.

4. The fuel cell system according to claim 1, wherein

A traction motor,

The fuel cell system, wherein the control device permits the output voltage of the fuel cell to be boosted to an open-circuit voltage while regenerative braking by the traction motor is being performed.

5. The fuel cell system according to claim 1, wherein A plurality of shut-off valves disposed in a piping system for supplying the reaction gas to the fuel cell;

The control device forms a closed space inside the piping system by closing the plurality of shut-off valves, and detects a gas leak by detecting a gas pressure fluctuation inside the closed space. In the fuel cell system, the output voltage of the fuel cell is allowed to increase to the open-circuit voltage.

6. The fuel cell system according to claim 1, wherein

The fuel cell is a cell stack formed by stacking a plurality of cells, and the control device is configured to control the high potential avoidance voltage so that a maximum voltage among output voltages of the plurality of cells is a predetermined value or less. To correct the fuel cell system.