WO2011036766A1 - Fuel cell system - Google Patents

Abstract

Disclosed is a fuel cell system (FCS) which comprises: a voltage measuring means (EC2) for measuring the open circuit voltage of an fuel cell (FC); a film thickness calculating means (EC3) for calculating the film thickness of a unit cell constituting the fuel cell (FC) on the basis of the difference between the theoretical electromotive voltage of the fuel cell (FC) and the open circuit voltage measured by the voltage measuring means (EC2); and an informing means (EC4) for informing of the case when the film thickness calculated by the film thickness calculating means (EC3) is equal to or less than a predetermined limit film thickness.

Description

Fuel cell system

The present invention relates to a fuel cell system that generates power by supplying a fuel gas containing hydrogen and an oxidizing gas to the fuel cell.

Examples of fuel cells that generate electricity using an electrochemical reaction between hydrogen and oxygen include solid polymer fuel cells. The polymer electrolyte fuel cell includes a stack configured by stacking a plurality of cells. A cell constituting the stack includes an anode (fuel electrode) and a cathode (air electrode), and a solid polymer electrolyte membrane having a sulfone sun group as an ion exchange group is interposed between the anode and the cathode. Intervene.

The fuel gas (reformed hydrogen obtained by reforming hydrogen gas or hydrocarbon to be hydrogen rich) is supplied to the anode, and the oxidizing gas containing oxygen as an oxidant (air as an example) is supplied to the cathode. By supplying the fuel gas to the anode, hydrogen contained in the fuel gas reacts with the catalyst of the catalyst layer constituting the anode, thereby generating hydrogen ions. The generated hydrogen ions pass through the solid polymer electrolyte membrane and cause an electrical reaction with oxygen at the cathode. Power generation is performed by this electrochemical reaction (see, for example, Patent Document 1 below).

JP 2008-269813 A

By the way, although the single cell constituting the fuel cell is composed of a solid polymer electrolyte membrane, this film thickness becomes thinner as it deteriorates, and it is stable to accurately grasp the decrease in the film thickness. This is necessary for the operation of the fuel cell system. However, the above-described conventional technique cannot grasp such a film thickness.

The present invention has been made in view of such problems, and an object thereof is to provide a fuel cell system capable of estimating the film thickness of a single cell constituting the fuel cell.

In order to solve the above-described problems, a fuel cell system according to the present invention is a fuel cell system in which a fuel gas containing hydrogen and an oxidizing gas are supplied to a fuel cell to generate electric power, and the open circuit voltage of the fuel cell is Voltage measuring means for measuring, and film thickness calculating means for calculating the film thickness of the single cell constituting the fuel cell based on the difference between the theoretical electromotive voltage of the fuel cell and the open circuit voltage measured by the voltage measuring device And a notifying means for notifying when the film thickness calculated by the film thickness calculating means is equal to or less than a predetermined limit film thickness.

According to the present invention, based on the difference between the theoretical electromotive voltage calculated by the voltage calculating means and the open circuit voltage measured by the voltage measuring means, the film thickness of the single cell constituting the fuel cell can be calculated. Further, when the calculated film thickness is equal to or less than a predetermined limit film thickness, it is possible to notify the user so that the user can recognize it, and to prompt the user to take measures such as replacement of the fuel cell.

According to the present invention, it is possible to provide a fuel cell system capable of estimating the thickness of a single cell constituting a fuel cell.

It is a figure which shows the structure of the fuel cell system mounted in the fuel cell vehicle which is embodiment of this invention. It is a flowchart which estimates the single cell film thickness of the fuel cell used for the fuel cell system shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same constituent elements in the drawings will be denoted by the same reference numerals as much as possible, and redundant description will be omitted.

First, a fuel cell system FCS mounted on a fuel cell vehicle according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a system configuration of a fuel cell system FCS that functions as an in-vehicle power supply system for a fuel cell vehicle. The fuel cell system FCS can be mounted on a vehicle such as a fuel cell vehicle (FCHV), an electric vehicle, or a hybrid vehicle.

The fuel cell system FCS includes a fuel cell FC, an oxidizing gas supply system ASS, a fuel gas supply system FSS, a power system ES, a cooling system CS, and a controller EC. The fuel cell FC is configured to generate electric power upon receiving a supply of reaction gas (fuel gas, oxidizing gas). The oxidizing gas supply system ASS is a system for supplying air as an oxidizing gas to the fuel cell FC. The fuel gas supply system FSS is a system for supplying hydrogen gas as fuel gas to the fuel cell FC. The power system ES is a system for controlling charge / discharge of power. The cooling system CS is a system for cooling the fuel cell FC. The controller EC is a controller that performs overall control of the entire fuel cell system FCS.

The fuel cell FC is configured as a solid polymer electrolyte type cell stack in which a large number of cells (a single battery (a power generator) including an anode, a cathode, and an electrolyte) are stacked in series. The fuel cell FC is provided with a temperature sensor and a gas flow rate sensor not shown in the figure. In a normal operation, the fuel cell FC undergoes an oxidation reaction of formula (1) at the anode and a reduction reaction of formula (2) at the cathode. The fuel cell FC 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 oxidizing gas supply system ASS has an oxidizing gas passage AS3 and an oxidizing off gas passage AS4. The oxidizing gas flow path AS3 is a flow path through which oxidizing gas supplied to the cathode of the fuel cell FC flows. The oxidation off gas flow path AS4 is a flow path through which the oxidation off gas discharged from the fuel cell FC flows.

In the oxidizing gas flow path AS3, an air compressor AS2 and a humidifier AS5 are provided. The air compressor AS2 is a compressor for taking in the oxidizing gas from the atmosphere via the filter AS1. The humidifier AS5 is a humidifier for humidifying the oxidizing gas pressurized by the air compressor AS2.

In the oxidation off gas flow path AS4, a pressure sensor S6, a back pressure adjustment valve A3, and a humidifier AS5 are provided. The back pressure adjustment valve A3 is a valve for adjusting the oxidizing gas supply pressure. The humidifier AS5 is provided for exchanging moisture between the oxidizing gas (dry gas) and the oxidizing off gas (wet gas).

The fuel gas supply system FSS has a fuel gas supply source FS1, a fuel gas flow path FS3, a circulation flow path FS4, a circulation pump FS5, and an exhaust drainage flow path FS6. The fuel gas channel FS3 is a channel through which the fuel gas supplied from the fuel gas supply source FS1 to the anode of the fuel cell FC flows. The circulation flow path FS4 is a flow path for returning the fuel off-gas discharged from the fuel cell FC to the fuel gas flow path FS3. The circulation pump FS5 is a pump that pressure-feeds the fuel off-gas in the circulation flow path FS4 to the fuel gas flow path FS3. The exhaust drainage channel FS6 is a channel that is branched and connected to the circulation channel FS4.

The fuel gas supply source FS1 is composed of, for example, a high-pressure hydrogen tank or a hydrogen storage alloy, and stores high-pressure (for example, 35 MPa to 70 MPa) hydrogen gas. When the shutoff valve H1 is opened, the fuel gas flows out from the fuel gas supply source FS1 to the fuel gas flow path FS3. The fuel gas is decompressed to, for example, about 200 kPa by the regulator H2 and the injector FS2, and supplied to the fuel cell FC.

The fuel gas flow path FS3 is provided with a shutoff valve H1, a regulator H2, an injector FS2, a shutoff valve H3, and a pressure sensor S4. The shutoff valve H1 is a valve for shutting off or allowing the supply of the fuel gas from the fuel gas supply source FS1. The regulator H2 adjusts the pressure of the fuel gas. The injector FS2 controls the amount of fuel gas supplied to the fuel cell FC. The shutoff valve H3 is a valve for shutting off the fuel gas supply to the fuel cell FC.

The regulator H2 is a device that regulates the upstream side pressure (primary pressure) to a preset secondary pressure, and includes, 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. It has a configuration for the next pressure. By arranging the regulator H2 on the upstream side of the injector FS2, the upstream pressure of the injector FS2 can be effectively reduced.

The injector FS2 is an electromagnetically driven on-off valve capable of adjusting a gas flow rate and a gas pressure by driving a valve body directly with a predetermined driving cycle with an electromagnetic driving force and separating it from a valve seat. The injector FS2 moves in an axial direction (gas flow direction) with respect to 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 the nozzle body. And a valve body that is stored and held so as to open and close the injection hole.

The valve body of the injector FS2 is driven by a solenoid that is an electromagnetic drive device, and is configured such that the gas injection time and gas injection timing of the injector FS2 can be controlled by a control signal output from the controller EC. Injector FS2 changes downstream by changing at least one of the opening area (opening) and the opening time of the valve provided in the gas flow path of injector FS2 in order to supply the required gas flow rate downstream. The gas flow rate (or hydrogen molar concentration) supplied to the side is adjusted.

In the circulation channel FS4, a shutoff valve H4 is provided, and an exhaust / drain channel FS6 is connected. An exhaust / drain valve H5 is provided in the exhaust / drain flow path FS6. The exhaust / drain valve H5 is a valve for discharging the fuel off-gas containing impurities in the circulation flow path FS4 and moisture to the outside by operating according to a command from the controller EC. By opening the exhaust / drain valve H5, the concentration of impurities in the fuel off-gas in the circulation flow path FS4 is reduced, 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 H5 is mixed with the oxidizing off-gas flowing through the oxidizing off-gas passage AS4 and diluted by a diluter (not shown). The circulation pump FS5 circulates and supplies the fuel off gas in the circulation system to the fuel cell FC by driving the motor.

The power system ES includes a DC / DC converter ES1, a battery ES2, a traction inverter ES3, a traction motor ES4, and auxiliary machinery ES5. The fuel cell system FCS is configured as a parallel hybrid system in which a DC / DC converter ES1 and a traction inverter ES3 are connected to the fuel cell FC in parallel.

The DC / DC converter ES1 boosts the DC voltage supplied from the battery ES2 and outputs it to the traction inverter ES3, and the DC power generated by the fuel cell FC or the regenerative power recovered by the traction motor ES4 by regenerative braking. It has a function of stepping down and charging the battery ES2. The charging / discharging of the battery ES2 is controlled by these functions of the DC / DC converter ES1. Further, the operating point (output terminal voltage, output current) of the fuel cell FC is controlled by voltage conversion control by the DC / DC converter ES1. A voltage sensor S1 and a current sensor S2 are attached to the fuel cell FC. The voltage sensor S1 is a sensor for detecting the output terminal voltage of the fuel cell FC. The current sensor S2 is a sensor for detecting the output current of the fuel cell FC.

The battery ES2 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 ES2, for example, a secondary battery such as a nickel / cadmium storage battery, a nickel / hydrogen storage battery, or a lithium secondary battery is preferable. An SOC sensor S3 for detecting SOC (State of charge) is attached to the battery ES2.

The traction inverter ES3 is, for example, a PWM inverter driven by a pulse width modulation method. The traction inverter ES3 converts the DC voltage output from the fuel cell FC or the battery ES2 into a three-phase AC voltage according to a control command from the controller EC, and controls the rotational torque of the traction motor ES4. The traction motor ES4 is a three-phase AC motor, for example, and constitutes a power source of the fuel cell vehicle.

Auxiliary machinery ES5 includes motors (for example, power sources such as pumps) arranged in each part in the fuel cell system FCS, inverters for driving these motors, and various in-vehicle auxiliary machinery ( For example, an air compressor, an injector, a cooling water circulation pump, a radiator, etc.) are collectively referred to.

The cooling system CS includes a radiator CS1, a coolant pump CS2, a coolant forward path CS3, and a coolant return path CS4. The radiator CS1 radiates and cools the coolant for cooling the fuel cell FC. The coolant pump CS2 is a pump for circulating the coolant between the fuel cell FC and the radiator CS1. The coolant forward path CS3 is a channel connecting the radiator CS1 and the fuel cell FC, and is provided with a coolant pump CS2. When the coolant pump CS2 is driven, the coolant flows from the radiator CS1 to the fuel cell FC through the coolant forward path CS3. The coolant return path CS4 is a flow path connecting the fuel cell FC and the radiator CS1, and is provided with a water temperature sensor S5. When the coolant pump CS2 is driven, the coolant that has cooled the fuel cell FC returns to the radiator CS1.

The controller EC (control unit) is a computer system including a CPU, a ROM, a RAM, and an input / output interface, and controls each unit of the fuel cell system FCS. For example, the controller EC starts the operation of the fuel cell system FCS when receiving the start signal IG output from the ignition switch. Thereafter, the controller EC obtains the required power of the entire fuel cell system FCS based on the accelerator opening signal ACC output from the accelerator sensor, the vehicle speed signal VC output from the vehicle speed sensor, and the like. The required power of the entire fuel cell system FCS is the total value of the vehicle travel power and the auxiliary power.

Here, auxiliary electric power includes electric 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, steering) Power consumed by devices, suspension devices, etc.), power consumed by devices (air conditioners, lighting equipment, audio, etc.) disposed in the passenger space, and the like.

Then, the controller EC determines the distribution of the respective output powers of the fuel cell FC and the battery ES2. The controller EC controls the oxidizing gas supply system ASS and the fuel gas supply system FSS so that the power generation amount of the fuel cell FC matches the target power, and also controls the DC / DC converter ES1 to operate the fuel cell FC. Control points (output terminal voltage, output current). Further, the controller EC outputs, for example, each U-phase, V-phase, and W-phase AC voltage command value to the traction inverter ES3 as a switching command so as to obtain a target torque corresponding to the accelerator opening, Controls the output torque and rotation speed of the motor ES4. Further, the controller EC controls the cooling system CS so that the fuel cell FC has an appropriate temperature.

The fuel cell system FCS of the present embodiment has the above-described configuration, voltage calculation means EC1 for calculating the theoretical electromotive voltage of the fuel cell FC, voltage measurement means EC2 for measuring the open circuit voltage of the fuel cell FC, and voltage calculation means. Based on the difference between the theoretical electromotive voltage calculated by EC1 and the open circuit voltage measured by the voltage measuring means EC2, the film thickness calculating means EC3 for calculating the film thickness of the single cell constituting the fuel cell FC, and the membrane pressure calculating means It functions as a fuel cell system provided with notifying means EC4 for notifying when the film thickness calculated by EC3 is not more than a predetermined limit film thickness. Therefore, the controller EC functions as voltage calculation means EC1, voltage measurement means EC2, membrane pressure calculation means EC3, and notification means EC4.

FIG. 2 is a flowchart showing a flow for calculating the film thickness of the single cells constituting the fuel cell FC in the fuel cell system FCS of the present embodiment. In step S01, the voltage measuring means EC2 measures the open circuit voltage (OCV: Open Circuit Voltage) of the fuel cell FC. In order to prevent the oxidation of Pt in the catalyst, when the operation is limited with a voltage lower than the open circuit voltage (OC avoidance voltage), the OC state is temporarily set to detect the film thickness. Transition. When the OC avoidance state continues for a certain time or more, the same condition is easily formed, and the film thickness detection accuracy is further improved by shifting to the OC state from there.

In step S02 following step S01, the film thickness calculation means EC3 calculates the film thickness of the single cells constituting the fuel cell FC. Specifically, first, the voltage calculation means EC1 calculates the theoretical electromotive voltage of the fuel cell FC. The theoretical electromotive voltage E of a single cell is obtained by equation (4).
E = -Δg _f / 2F (4)
In equation (4), Δg _f is Gibbs free energy and F is a Faraday constant. For a single cell operating below 100 ° C., this value is about 1.2V. Accordingly, the theoretical electromotive voltage of the fuel cell FC is obtained from this value and the number of cells. For this reason, the theoretical electromotive voltage may be calculated each time by the voltage calculation means EC1, or may be determined in advance based on the specifications of the fuel cell FC.

Subsequently, ΔV, which is the difference between the theoretical electromotive voltage and the open circuit voltage, is expressed by Equation (5).
ΔV = RT / 2αF × ln (i _cross / i) (5)
In equation (5), R is a gas constant, F is a Faraday constant, and α is a charge transfer coefficient. The charge transfer coefficient α is a coefficient determined by the catalyst used in the fuel cell FC. Further, i is an output current, and i _cross is an internal current due to a fuel gas _cross leak. When conditions such as temperature are constant, the right side of Equation (5) is a constant other than the internal current i _cross due to fuel gas _cross leak. Therefore, the internal current i _cross can be obtained from ΔV. here,
i _cross = Q _cross × 2F (6)
Q _cross = a × P _H2 × S / L (7)
There is a relationship. Q _cross is a gas _cross leak amount, a is a film physical property value, P _H2 is a hydrogen partial pressure, S is a film area of a single cell, and L is a film thickness of the single cell. The film thickness calculation means EC3 calculates the film thickness L based on the equations (5), (6), and (7).

In step S03 subsequent to step S02, it is determined whether the film thickness L obtained in step S02 is less than a predetermined limit film thickness L '. This limit film thickness L ′ is determined in advance from the strength of the film. If the calculated film thickness L is less than the limit film thickness L ′, the process proceeds to step S <b> 04. If the calculated film thickness L is not less than the limit film thickness L ′, the process ends.

In step S04, the notification means EC4 notifies that the fuel cell FC has deteriorated so that it can be recognized by the user via an alert lamp or a speaker.

FCS: Fuel cell system FC: Fuel cell ASS: Oxidizing gas supply system AS1: Filter AS2: Air compressor AS3: Oxidizing gas channel AS4: Oxidizing off gas channel AS5: Humidifier A3: Back pressure regulating valve CS: Cooling system CS1: Radiator CS2: Coolant pump CS3: Coolant forward path CS4: Coolant return path FSS: Fuel gas supply system FS1: Fuel gas supply source FS2: Injector FS3: Fuel gas channel FS4: Circulation channel FS5: Circulation pump FS6: Exhaust drainage Flow path H1: Shut-off valve H2: Regulator H3: Shut-off valve H4: Shut-off valve H5: Exhaust drain valve ES: Power system ES1: DC / DC converter ES2: Battery ES3: Traction inverter ES4: Traction motor ES5: Auxiliary equipment EC: Controller S1: Voltage sensor S2: Current sensor S3: SOC sensor S4 S6: a pressure sensor S5: the water temperature sensor ACC: accelerator opening signal IG: activation signal VC: vehicle speed signal

Claims (1)

A fuel cell system for generating power by supplying a fuel gas containing hydrogen and an oxidizing gas to a fuel cell,
Voltage measuring means for measuring an open circuit voltage of the fuel cell;
Based on the difference between the theoretical electromotive voltage of the fuel cell and the open circuit voltage measured by the voltage measuring means, the film thickness calculating means for calculating the film thickness of the single cells constituting the fuel cell;
A fuel cell system comprising: an informing means for informing when the film thickness calculated by the film thickness calculating means is equal to or less than a predetermined limit film thickness.

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