JP5884687B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system.

  A fuel cell system using a fuel cell that generates power by an electrochemical reaction between an anode gas and a cathode gas as an energy source has attracted attention. Various techniques relating to means for recovering the output of the fuel cell system have been proposed (see, for example, Patent Document 1 below). For example, in the technique described in Patent Document 1, the activity of the catalyst is recovered when the output of the fuel cell is low and the operation request for the fuel cell is a high load.

JP 2010-118252 A JP 2009-4160 JP 2009-231225 A

  However, the technique described in Patent Document 1 limits the recovery means of the output of the fuel cell only to the recovery of the catalyst activity. In addition to recovering the activity of the catalyst, the output recovery means includes a method for increasing the cathode back pressure and a method for controlling the temperature of the fuel cell. On the other hand, these output recovery means have a problem that it is not known which method should be selected in any case. Therefore, a technique capable of optimizing the timing and method for recovering the output in the fuel cell system has been desired. In addition, in the conventional fuel cell system, it has been desired to reduce its size, save resources, facilitate manufacturing, improve manufacturing accuracy, improve workability, and the like.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms.
The first aspect of the present invention is:
A fuel cell system,
A fuel cell comprising an anode, a cathode and an electrolyte layer;
A measurement unit for measuring a parameter representing an operating state of the fuel cell;
A control unit;
A cooling unit for cooling the fuel cell by a cooling medium;
A temperature sensor for measuring the temperature of the cooling medium,
The controller is
When the increase in the required output to the fuel cell is a reference value or more, the back pressure control of the cathode is performed,
When the required output is larger than the output that can be generated by the fuel cell obtained based on the parameter, refresh control is performed to recover the activity of the catalyst supported on the electrolyte layer,
Control the temperature of the cooling unit so that the temperature of the cooling medium is an appropriate temperature,
The back pressure control is preferentially performed over the refresh control and the temperature control. The present invention can also be realized as the following forms.

(1) According to one aspect of the present invention, a fuel cell system is provided. The fuel cell system includes: a fuel cell including an anode, a cathode, and an electrolyte layer; a measurement unit that measures a parameter that represents an operating state of the fuel cell; and a control unit, and the control unit includes the fuel cell. The back pressure control of the cathode is performed when the increase width of the required output to the reference is greater than or equal to a reference value, and then the required output is greater than the output that can be generated by the fuel cell based on the parameters. Then, refresh control is performed to restore the activity of the catalyst supported on the electrolyte layer. According to the fuel cell system of this embodiment, the timing and method for recovering the output of the fuel cell can be optimized.

(2) The fuel cell system of the above aspect further includes a cooling unit that cools the fuel cell with a cooling medium; and a temperature sensor that measures the temperature of the cooling medium, and the control unit includes the cooling medium. The temperature of the cooling unit is controlled such that the temperature of the cooling unit becomes an appropriate temperature. According to the fuel cell system of this embodiment, the timing and method for recovering the output of the fuel cell including the temperature control of the fuel cell can be optimized.

  It should be noted that the present invention can be realized in various modes, for example, in the form of a vehicle or the like equipped with the fuel system of the present invention.

Schematic which shows the structure of the fuel cell system as one Embodiment of this invention. 3 is a flowchart showing processing when the control unit 10 controls the output of the fuel cell system 1;

A. Embodiment:
A1. Configuration of fuel cell system:
FIG. 1 is a schematic diagram showing the configuration of a fuel cell system as an embodiment of the present invention. In the present embodiment, the fuel cell system 1 is mounted on a vehicle.

  The fuel cell system 1 includes a fuel cell 60, a control unit 10, and a current control unit 30 that controls supply of current.

  The fuel cell system 1 includes a cathode gas supply circulation system 82 and an anode gas supply circulation system 84 in order to supply and circulate cathode gas and anode gas used for reaction in the fuel cell 60. The cathode gas supply circulation system 82 includes an air compressor 72 that compresses oxygen, which is a cathode gas, and a pressure gauge 76 that measures the pressure of the discharged cathode gas (cathode back pressure). The anode gas supply circulation system 84 includes an anode gas pump 74 that circulates hydrogen, which is an anode gas.

  The fuel cell 60 includes an anode part 62 and a cathode part 64. The fuel cell 60 is, for example, a solid polymer electrolyte fuel cell, and has a stack structure in which a large number of single cells (cells) are stacked. The unit cell of the fuel cell 60 has a cathode portion 64 on one surface of an electrolyte layer made of an ion exchange membrane, and an anode portion 62 on the other surface. For the electrode including the cathode portion 64 and the anode portion 62, for example, platinum Pt is used as a catalyst (electrode catalyst) based on a porous carbon material. Further, a pair of separators are provided so as to sandwich the cathode and the anode from both sides. Then, oxygen is supplied to the cathode gas supply circulation system 82 which is one separator, and hydrogen is supplied to the anode gas supply circulation system 84 which is the other separator. The fuel cell 60 generates electric power by supplying these gases. In addition to the solid molecular electrolyte type, various types such as a phosphoric acid type and a molten carbonate type can be adopted as the fuel cell 60.

  Since the fuel cell 60 generates heat by the above-described electrochemical reaction, the fuel cell 60 includes a cooling water circulation device 90 for cooling the fuel cell 60. The cooling water circulation device 90 includes a thermometer 92 that measures the temperature of the cooling water.

  The operation of the fuel cell system 1 is controlled by the control unit 10. The control unit 10 receives an output signal from the accelerator opening sensor 20. The control unit 10 is configured as a microcomputer including a CPU, RAM, ROM, timer, and the like. The control unit 10 controls the operation of the fuel cell system 1 by driving the anode gas pump 74 and controlling the current control unit 30 according to a program stored in the ROM.

A2. Control processing of the fuel cell system 1:
FIG. 2 is a flowchart showing processing when the control unit 10 controls the output of the fuel cell system 1. This is a process capable of optimizing the timing and method for recovering the output of the fuel cell 60 during operation of the fuel cell system 1. This process is repeatedly executed every predetermined time.

  When the operation of the fuel cell system 1 is started, first, the control unit 10 determines whether or not the increase amount of the required output is equal to or less than the reference value (step S50). The “required output” refers to an output required by the fuel cell 60 through an input to the accelerator opening sensor 20 calculated by the control unit 10. The “increase width of the required output” is determined by the control unit 10 based on an output signal from the accelerator opening sensor 20. Examples of the case where the required output increases while the vehicle is driving include when starting suddenly, overtaking another vehicle, or climbing a hill. The “reference value” is a value set in advance according to the output capacity of the fuel cell 60.

When it is determined in step S50 that the increase amount of the required output is equal to or greater than the reference value (step S50, NO), the control unit 10 calculates the following equation from the previous operation history (the previous operation state) in the fuel cell system 1. The required oxygen concentration is calculated according to (1) (step S52).
[Equation 1]
i = A _Pt i ^ref _{0, ORR} (1-θ) ^m (C _O2 / C ^ref _O2 ) ^γ exp (-α _c Fη _ORR / RT) (1)
“I” is the current density, “A _Pt ” is the cathode platinum surface area, “i ^ref _{0, ORR} ” is the cathode exchange current density, “θ” is the oxide film rate, “C _O2 ” is the required oxygen concentration, and “C “ ^ref _O2 ” is the reference oxygen concentration, “α _c ” is the charge transfer coefficient, “F” is the Faraday constant, “R” is the gas constant, “T” is the cooling water temperature, “η _ORR ” is the cathode overvoltage, “m, “γ” is an experimental constant.

Here, the value of the cathode platinum surface area “A _Pt ” and the value of the cathode exchange current density “i ^ref _{0, ORR} ” are constant values determined at the design stage of the fuel cell 60. The value of the oxide film ratio “θ” is a value determined by parameters determined at the design stage of the fuel cell 60 and the output current of the fuel cell 60 at that time. The value of the reference oxygen concentration “C ^ref _O2 ” is the oxygen concentration in the reference state, and 100 kpa-abs is conventionally used. “Kpa-abs” is a unit representing an absolute pressure. The value of the cooling water temperature “T” is obtained by the thermometer 92. The cathode overvoltage “η _ORR ” refers to the difference between the theoretical potential E thermodynamically determined at the cathode and the potential E _real when the reaction actually proceeds. The “theoretical potential E” is calculated according to the following equation (2), and “the potential E _real when the reaction actually proceeds _” is obtained from the cell voltage.
[Equation 2]
E = {− (ΔH ₀ −TΔS) −RT · ln (a _H2 · a _O2 ^1/2 / a _H20 )} / 2F (2)
“ΔH ₀ ” is the standard generation enthalpy, “ΔS” is the standard generation entropy, and “a” is the activity of each substance.

  After the calculation in step S52, the cathode back pressure is measured by the pressure gauge 76 so that the cathode back pressure becomes the required oxygen concentration, and the control unit 10 controls the cathode back pressure (step S54).

  According to the fuel cell system 1 of the present embodiment, when it is determined that the increase amount of the required output is greater than or equal to the reference value (step S50, NO), the controller 10 preferentially performs the cathode back pressure control. The back pressure control of the cathode is faster in response than temperature control (step S120) and refresh operation (step S160) described later. For this reason, the timing and method for recovering the output of the fuel cell 60 can be optimized.

  Next, after controlling the cathode back pressure in step S52, or after determining in step S50 that the increase in the required output is equal to or less than the reference value by the control unit 10 (step S50, YES), the fuel cell 60 is supplied to the fuel cell 60. It is determined whether the requested output is greater than the set output (step S100). Here, the “set output” refers to an output that can be generated by the fuel cell 60 calculated by the control unit 10 from the cell voltage and the cathode back pressure. If the requested output is smaller than the set output (S100, YES), the flow ends.

  In step S100, when the control unit 10 determines that the required output is larger than the set output (S100, NO), the control unit 10 calculates an appropriate temperature of cooling water for cooling the fuel cell 60 from the equation (1) ( Step S110). Here, “appropriate temperature” refers to the temperature of the cooling water at which the output efficiency of the fuel cell is high.

  After the calculation in step S110, the temperature of the cooling water is measured by the thermometer 92 so that the temperature of the cooling water becomes an appropriate temperature, and the control unit 10 controls the temperature of the cooling water (step S120). The time and method for recovering the output of the fuel cell 60 can be optimized by performing the process of controlling the temperature of the cooling water, which takes time until the effect appears, at an earlier stage than the other recovery processes.

  Subsequently, the control unit 10 recalculates the set output based on the changed cooling water temperature, and determines whether or not the requested output is larger than the set output (step S130). If the requested output is smaller than the set output in this determination (S130, YES), the flow is terminated.

On the other hand, when the control unit 10 determines that the requested output is larger than the set output (S130, NO), the control unit 10 calculates the activity term from the previous operation history in the fuel cell system 1 (step S140). The “active term” refers to the term “exp (−α _c Fη _ORR / RT)” in formula (1). The activity term calculated in step S140 is referred to as “current activity term”.

  As a result of the calculation in step S140, the value of the current activity term is compared with the value of the initial activity term (step S150). Here, the value of the “initial activity term” is a value that is stored and updated in the control unit 10 every predetermined time among the calculated values of the activity term.

  As a result of comparison between the current active term and the initial active term, if the initial active term is larger than the current active term (S150, YES), the control unit 10 performs a refresh operation (step S160). Here, the “refresh operation” refers to a reduction process in which the supply of oxygen to the fuel cell 60 is temporarily stopped and the generated voltage of the fuel cell 60 is lowered to the reduction region of the catalyst layer to activate the catalyst layer. . By this treatment, oxygen adsorbed on the catalyst is released, and a decrease in the output voltage of the fuel cell 60 can be suppressed.

  According to the fuel cell system 1 of the present embodiment, the refresh operation with less energy loss can be prioritized over the cathode back pressure control described later, so that the timing and method for recovering the output of the fuel cell can be optimized. .

  On the other hand, as a result of comparison between the current activity term and the initial activity term, if the initial activity term is smaller than the current activity term (S150, NO), the required oxygen concentration according to the formula (1) using the current activity term Is calculated (step S170). Each parameter other than the essential oxygen concentration in the formula (1) is obtained from the immediately preceding operation state as described above. After the calculation in step S170, the cathode back pressure is measured by the pressure gauge 76 so that the cathode back pressure becomes the required oxygen concentration, and the control unit 10 controls the cathode back pressure (step S180). After step S180, the flow returns to step S100.

  According to the fuel cell system 1 of the present embodiment, the temperature control (step S120), the refresh operation (step S160), and the back pressure control (step S180) can be performed at an optimal time.

  The “measurement unit” described in the means for solving the problem corresponds to the “accelerator opening sensor 20, pressure gauge 76” in the present embodiment. The “cooling unit” corresponds to the “cooling water circulation device 90”. The “temperature sensor” corresponds to the “thermometer 92”.

B. Variations:
Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and can be implemented in various modes without departing from the scope of the present invention. For example, the following modifications are possible.

B1. Modification 1:
In the above embodiment, the flow for performing the temperature control (step S120) is described, but the present invention is not limited to this. That is, the temperature control may be omitted, and the refresh operation (step S160) and the back pressure control (step S180) may be performed first. Thereby, refresh operation (step S160) and back pressure control (step S180) can be performed earlier.

B2. Modification 2:
In the above embodiment, the increase range of the required output is determined by the accelerator opening sensor 20, but the present invention is not limited to this. This is because the present invention is not limited to vehicles.

  In the above embodiment, parameters such as oxygen concentration and cooling water temperature are calculated using relational expressions, but the present invention is not limited to this. As a method other than the calculation from the relational expression, for example, a method using a map may be used.

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 10 ... Control part 20 ... Accelerator opening degree sensor 30 ... Current control part 60 ... Fuel cell 62 ... Anode part 64 ... Cathode part 72 ... Air compressor 74 ... Anode gas pump 76 ... Pressure gauge 82 ... Cathode gas supply circulation System 84 ... Anode gas supply circulation system 90 ... Cooling water circulation device 92 ... Thermometer

Claims (1)

A fuel cell system,
A fuel cell comprising an anode, a cathode and an electrolyte layer;
A measurement unit for measuring a parameter representing an operating state of the fuel cell;
A control unit;
A cooling unit for cooling the fuel cell by a cooling medium;
A temperature sensor for measuring the temperature of the cooling medium,
The controller is
When the increase in the required output to the fuel cell is a reference value or more, the back pressure control of the cathode is performed,
Before SL request output, when the fuel cell is greater than available power generation output obtained on the basis of the parameters, it performs a refresh control for recovering the supported catalyst activity in the electrolyte layer,
Control the temperature of the cooling unit so that the temperature of the cooling medium is an appropriate temperature ,
The fuel cell system , wherein the back pressure control is performed with priority over the refresh control and the temperature control .

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