JP4984392B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system having a compressor for supplying an oxidant gas.

Conventionally, it is applied to a fuel cell device that includes a fuel cell that is supplied with fuel and an oxidant to generate electric power, and an air supply system that has a compressor that supplies air as an oxidant to the fuel cell. A technique is known in which when the absolute value of the difference from the value is equal to or greater than a predetermined value and a predetermined time has elapsed, it is determined that the air supply system has failed (for example, see Patent Document 1).
JP 2004-179072 A

  By the way, when the required output value for the fuel cell increases, the work (efficiency) of the compressor increases, and the temperature of the gas discharged from the compressor tends to increase. When the temperature of the discharge gas of the compressor exceeds the allowable limit value, each component (for example, the fuel cell itself or the humidification module) on the downstream side of the compressor, that is, the fuel cell (stack) side is damaged.

  Therefore, an object of the present invention is to realize, at a low cost, a configuration capable of monitoring the temperature of a discharge gas from a compressor in a fuel cell system having a compressor for supplying an oxidant gas.

In order to achieve the above object, according to the present invention, in a fuel cell system having a compressor for supplying an oxidant gas to a fuel cell, a measured value of the pressure of the oxidant gas on the discharge side of the compressor is obtained. The compression ratio γ of the compressor, which is a value divided by the measured value of the pressure of the oxidant gas on the intake side, the measured value Tin of the temperature of the oxidant gas on the intake side of the compressor, and the oxidant gas A discharge temperature calculation means for calculating the temperature of the oxidant gas on the discharge side of the compressor based on a formula of Tin * γ ^ (κ−1 / κ) using a known specific heat ratio κ. A fuel cell system is provided.

In the above-described configuration, the discharge temperature calculation means multiplies the equation of Tin * γ ^ (κ−1 / κ) by a correction coefficient expressed as a function of the rotation speed of the compressor, thereby calculating the calculated discharge of the compressor. The temperature of the oxidant gas on the side may be corrected.

The above configuration may further include an abnormality determination unit that determines that the system is abnormal when the calculated temperature of the oxidant gas on the discharge side of the compressor exceeds a predetermined reference value. The above configuration may further include an abnormality determination unit that determines that the system is abnormal when the corrected temperature of the oxidant gas on the discharge side of the compressor exceeds a predetermined reference value.

As described above, according to the present invention, since the discharge temperature can be calculated without providing a means for measuring the temperature on the compressor discharge side, the system can be simplified. Thereby, the structure which can monitor the temperature of the discharge gas of a compressor is realizable at low cost.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a main part configuration diagram showing an embodiment of a fuel cell system according to the present invention. The fuel cell system includes a fuel cell 10. The fuel cell 10 is, for example, a polymer electrolyte fuel cell, and has a stack structure in which a plurality of single cells 20 are stacked. The single cell 20 has an anode and a cathode on both sides of the electrolyte membrane, and a separator is provided outside the anode and the cathode. Each single cell 20 is laminated so that one anode side faces the other cathode side, and the single cells 20 are separated from each other via a separator. Hereinafter, the configuration on the cathode side according to the present invention will be mainly described.

  An oxidant gas supply system 40 that supplies air or a gas containing an oxidant (hereinafter referred to as “oxidant gas”) is disposed upstream of the fuel cell 10. The oxidant gas is supplied to the air compressor 42 after impurities in the gas are removed by the air cleaner 44. A flow sensor 45 is provided in front of the air compressor 42. The air compressor 42 is controlled by an electronic control unit 41 (hereinafter referred to as a compressor ECU 41), compresses the oxidant gas sucked from the inlet side (air cleaner 44 side) and discharges it to the outlet side using the motor 42a as a power source. The oxidant gas compressed and discharged by the air compressor 42 is cooled by the intercooler 46 and supplied to the fuel cell 10.

  The heat generated by the operation of the air compressor 42 is released to the outside through the radiator 50. That is, cooling water for heat exchange in the air compressor 42 and the intercooler 46 is circulated in the cooling circuit including the radiator 50 by the pump 54 driven by the motor 52. For example, when the fuel cell system is mounted on a vehicle, the radiator 50 is provided at the front portion of the vehicle in the same manner as a normal radiator.

  From the inlet side of the fuel cell 10, the oxidant gas is distributed and supplied to each single cell 20 and is subjected to an electrochemical reaction that proceeds on the anode side of each single cell 20. On the anode side, similarly, the fuel gas is distributed and supplied to the fuel gas flow path of each unit cell 20 via the fuel gas supply manifold, and is supplied to the electrochemical reaction that proceeds on the cathode side of each unit cell 20. Is done. Thus, the electromotive force generated in each single cell 20 is taken out via an output terminal (not shown) provided near the end of the laminate.

  An exhaust pipe 60 is connected to the downstream side of the fuel cell 10 via a pressure regulating valve 62. A pressure sensor 64 is provided between the pressure regulating valve 62 and the fuel cell 10. The pressure regulating valve 62 is controlled to open and close by an appropriate controller (ECU) so as to adjust the inside of the fuel cell 10 (stack) to a predetermined pressure (control pressure) based on the detection value of the pressure sensor 64. In the example shown in FIG. 1, the exhaust pipe 60 is branched and connected to the front stage of the air compressor 42 via the valve 66, and a part of the oxidant gas discharged from the fuel cell 10 is in the front stage of the air compressor 42. A mixed cathode circulation system is configured. In this case, since moisture is imparted to the oxidant gas introduced into the fuel cell 10 by the exhaust gas having a relatively high moisture content, it is not necessary to provide a humidification module between the intercooler 46 and the fuel cell 10. However, the present invention is also applicable to a configuration in which a humidification module is provided between the intercooler 46 and the fuel cell 10.

  During operation of the fuel cell system, the compressor ECU 41 controls the work amount of the air compressor 42 according to, for example, a required output value (target power generation amount) for the fuel cell 10. When the work amount of the air compressor 42 is large, the temperature of the oxidant gas discharged from the air compressor 42 (hereinafter referred to as “discharge temperature Tout [K]”) increases. When the discharge temperature Tout rises above a certain limit, the temperature cannot be lowered sufficiently by the intercooler 46, and various components (the fuel cell 10 and the humidification module) on the downstream side of the air compressor 42 are damaged. Such an excessive increase in the discharge temperature Tout can also occur when any abnormality occurs in the air compressor 42 or the like.

  Each embodiment described below pays new attention to such a problem, and without using a temperature sensor downstream of the air compressor 42, it is possible to estimate and calculate the discharge temperature Tout by effectively using the measured value of an existing sensor or the like. This effectively prevents damage to the fuel cell 10 and the like due to an increase in the discharge temperature Tout at a low cost.

  FIG. 2 is a flowchart illustrating main processing that may be executed by the calculation unit (CPU) of the compressor ECU 41 according to the first embodiment.

  First, in step 100, the compressor ECU 41 sets the rotational speed REV of the air compressor 42 (hereinafter referred to as “air compressor rotational speed REV”, the air flow rate V [L / min]) of the air compressor 42, and the air compressor 42. Air compressor based on the intake side oxidant gas temperature (hereinafter referred to as “intake air temperature Tin [K]”) and the compressor intake side oxidant gas pressure (hereinafter referred to as “intake pressure Pin”) The volume flow rate Fair [NL / min] of the oxidant gas supplied to 42 is obtained.

  Here, the air flow rate V of the air compressor 42 can be obtained from a predetermined relational expression (which may be a typical proportional expression) with the air compressor rotational speed REV. The air compressor rotation speed REV may be a value measured by a tachometer that is provided in the air compressor 42 and measures the rotation speed of the air compressor 42. Or the value based on the rotation speed instruction | indication value (target rotation speed) with respect to the motor 42a of the air compressor 42 by compressor ECU41 which controls the air compressor 42 may be used.

  As the intake air temperature Tin, a value measured by a temperature sensor 70 provided on the upstream side of the air compressor 42 is used. The temperature sensor 70 shown in FIG. 1 is provided near the inlet (atmosphere side) of the supply pipe for oxidant gas, but may be set at any appropriate location as long as it is upstream from the air compressor 42. For example, it may be provided immediately before the air compressor 42. Similarly, the measured value by the pressure sensor 72 provided on the upstream side of the air compressor 42 is used as the intake pressure Pin. The pressure sensor 72 shown in FIG. 1 is provided near the inlet (atmosphere side) of the oxidant gas supply pipe, but may be set at any appropriate location as long as it is upstream of the air compressor 42. For example, it may be provided immediately before the air compressor 42. The volume flow rate Fair is obtained by converting the air supply flow rate V of the air compressor 42 into the standard state by the gas state equation using the intake air temperature Tin and the intake air pressure Pin.

  Next, in step 110, the compressor ECU 41 obtains the pressure of the oxidant gas on the discharge side of the air compressor 42 (hereinafter referred to as “discharge pressure Pout”) from the control pressure of the oxidant gas. The discharge pressure Pout can be obtained from a predetermined relational expression between a measured value by the pressure sensor 64 provided between the pressure regulating valve 62 and the fuel cell 10 described above. This relational expression may be specific to the system, may be prepared in advance as a map format, and is stored in the memory of the compressor ECU 41.

  In the following step 120, the compressor ECU 41 determines the discharge temperature Tout from the values measured or calculated in the steps 100 and 110, that is, the volume flow rate Fair, the discharge pressure Pout, the intake pressure Pin, the intake air temperature Tin, and the compressor efficiency η. Is calculated.

Here, the discharge temperature Tout is obtained by the following equation using the intake air temperature Tin and the compressor efficiency η.
Tout = Tin / η
However, η = Wad / W0
Here, W0 [kW] is the total adiabatic compression work, and Wad is the theoretical adiabatic compression work.
The theoretical adiabatic compression work Wad is expressed by the following equation.
Wad = Gc * hc / 1000
= Fair * ρair * Cp * ΔTc / 60/1000/1000
= Fair * ρair * Cp * Tin * {γ ^ (κ-1 / κ) -1} / 60/1000/1000
However,
Gc [kg / sec]: Mass flow rate
hc [J / kg]: Thermal insulation head ρair [kg / m ³ ]: Oxidant gas density
Cp [J / kg · K]: Specific heat of oxidant gas ΔTc [K]: Increase in theoretical temperature κ: Specific heat ratio of oxidant gas, the above are known values. As the physical property values ρair, κ, etc. of the oxidant gas, those calculated using the same physical property value of the carrier gas (air or water vapor) of the oxidant may be used. A specific heat ratio of about 1.4 may be used.

  Further, γ is a compression ratio of the air compressor 42 (compression ratio = discharge pressure Pout / intake pressure Pin), and is obtained by using measured values of the discharge pressure Pout and the intake pressure Pin.

  In subsequent step 130, the compressor ECU 41 determines whether or not the discharge temperature Tout obtained in step 120 has exceeded a predetermined reference value (upper limit allowable value). If the determination is negative, the system is operating normally. This routine is terminated. On the other hand, if the determination is affirmative, that is, if the discharge temperature Tout exceeds a predetermined reference value, it is determined that an abnormality has occurred in the system, and the process proceeds to a discharge temperature abnormality processing routine (step 140). In step 140, the compressor ECU 41 may realize, for example, output restriction of the air compressor 42 (output restriction of the fuel cell 10) or operation stop.

As described above, according to this embodiment, a temperature sensor is not provided directly on the downstream side of the air compressor 42 (between the outlet side of the air compressor 42 and the intercooler 46), and the discharge temperature Tout is not directly measured. Since the discharge temperature Tout can be estimated with high accuracy by effectively using various measured values or calculated values necessary for controlling the fuel cell system, an excellent fail-safe function can be realized at low cost.

In the present embodiment, the air flow rate V of the air compressor 42 uses the measured values of the compressor rotational speed REV and the intake air temperature Tin as variables so as to compensate for the difference in altitude (the corresponding difference in external atmospheric pressure). Alternatively, it may be obtained by linear approximation using the following approximate expression.
V = a * REV + b
Here, as shown in FIG. 3, a and b are determined by linear approximation so as to match experimental values measured at different points of altitude. In FIG. 3, the experimental value under the flat ground condition (101.3 kPa-abs) and the high ground condition (70 kPa-abs) are plotted. Thus, at least two types of relational expressions for obtaining the air supply flow rate V may be prepared depending on the difference between the flat ground condition and the highland condition. In this case, for example, even when the fuel cell 10 is mounted on a mobile body having high mobility such as a vehicle, the difference in altitude is compensated, so that high accuracy of the discharge temperature Tout can be maintained.

  As described above, the first embodiment is a fuel cell system having a compressor for supplying an oxidant gas, and includes a volume flow rate calculation means (compressor ECU 41) for calculating the volume flow rate of the oxidant gas and the compressor discharge of the oxidant gas. Discharge pressure calculating means (compressor ECU 41) for calculating the pressure, intake air temperature measuring means (70) for measuring the compressor intake temperature of the oxidant gas, and intake pressure measuring means (72) for measuring the compressor intake pressure of the oxidant gas The fuel cell system calculates the compressor discharge temperature of the oxidant gas from the volume flow rate, the discharge pressure, the intake air temperature, and the intake air pressure.

  FIG. 4 is a flowchart illustrating main processing that may be executed by the calculation unit (CPU) of the compressor ECU 41 according to the second embodiment.

  First, in step 200, the compressor ECU 41 obtains measured values of the intake air temperature Tin of the air compressor 42 and the intake air pressure Pin of the air compressor 42.

  As the intake air temperature Tin, a value measured by a temperature sensor 70 provided on the upstream side of the air compressor 42 is used. Similarly, the measured value by the pressure sensor 72 provided on the upstream side of the air compressor 42 is used as the intake pressure Pin.

  In the next step 210, the compressor ECU 41 obtains the discharge pressure Pout of the air compressor 42 from the control pressure of the oxidant gas. The discharge pressure Pout can be obtained from a predetermined relational expression between a measured value by the pressure sensor 64 provided between the pressure regulating valve 62 and the fuel cell 10 described above. This relational expression may be specific to the system, may be prepared in advance as a map format, and is stored in a memory accessible by the compressor ECU 41.

  In the following step 220, the compressor ECU 41 calculates the compression ratio γ (= discharge) of the air compressor 42 from the measured values of the intake air temperature Tin of the air compressor 42 and the intake air pressure Pin acquired in steps 200 and 210. Calculate pressure Pout / intake pressure Pin).

In the subsequent step 230, the compressor ECU 41 uses the intake air temperature Tin acquired in step 200 and the compression ratio γ of the air compressor 42 obtained in step 220 to calculate the discharge temperature Tout of the air compressor 42 from the following relational expression. Ask for.
Tout = Tin * γ ^ (κ-1 / κ)
In the following step 240, the compressor ECU 41 determines whether or not the discharge temperature Tout obtained in the above step 230 exceeds a predetermined reference value. If the determination is negative, the routine of this time is determined that the system is operating normally. Is terminated. On the other hand, if the determination is affirmative, that is, if the discharge temperature Tout exceeds a predetermined reference value, it is determined that an abnormality has occurred in the system, and the process proceeds to a discharge temperature abnormality processing routine (step 250). In step 250, the compressor ECU 41 may realize, for example, output restriction of the air compressor 42 (output restriction of the fuel cell 10) or operation stop.

As described above, according to the present embodiment, as in the first embodiment, the temperature sensor is not provided directly on the downstream side of the air compressor 42, and the discharge temperature Tout is not directly measured. The discharge temperature Tout can be estimated with high accuracy by effectively using the various measured values or calculated values required for the above, so that an excellent fail-safe function can be realized at low cost.

  FIG. 5 is a flowchart illustrating main processing that may be executed by the calculation unit (CPU) of the compressor ECU 41 according to the third embodiment.

  First, in step 300, the compressor ECU 41 acquires measured values of the air compressor rotational speed REV, the intake air temperature Tin of the air compressor 42, and the intake air pressure Pin of the air compressor 42.

  As the air compressor rotation speed REV, a measurement value of a tachometer that measures the rotation speed of the air compressor 42 may be used. Or the value based on the rotation speed instruction | indication value (target rotation speed) with respect to the motor 42a of the air compressor 42 by compressor ECU41 which controls the air compressor 42 may be used. As in the above embodiments, the intake air temperature Tin is measured by a temperature sensor 70 provided on the upstream side of the air compressor 42. Similarly, the measured value by the pressure sensor 72 provided on the upstream side of the air compressor 42 is used as the intake pressure Pin.

  In the next step 310, the compressor ECU 41 obtains the discharge pressure Pout of the air compressor 42 from the control pressure of the oxidant gas. The discharge pressure Pout can be obtained from a predetermined relational expression between a measured value by the pressure sensor 64 provided between the pressure regulating valve 62 and the fuel cell 10 described above. This relational expression may be specific to the system, may be prepared in advance as a map format, and is stored in a memory accessible by the compressor ECU 41. In the next step 320, the compressor ECU 41 obtains the compression ratio γ of the air compressor 42 from the measured values of the intake air temperature Tin of the air compressor 42 and the intake pressure Pin of the air compressor 42 acquired in steps 300 and 310. .

In the following step 330, the compressor ECU 41 uses the air compressor rotational speed REV, the intake air temperature Tin acquired in step 300, and the compression ratio γ of the air compressor 42 obtained in step 320 to calculate the air The discharge temperature Tout of the compressor 42 is obtained.
Tout = Tin * γ ^ (κ-1 / κ) * α
Here, α is a correction coefficient introduced in order to take into account the temperature rise of the discharge temperature Tout caused by the heat generated from the air compressor 42 (changes depending on the efficiency of the air compressor 42), and is expressed as follows. The
α = A * REV + B
As shown in FIG. 6, A and B are determined by linear approximation so as to conform to the relationship between the air compressor rotational speed REV obtained by experiment and the ratio of the measured value to the theoretical value of the discharge temperature Tout. .

  In the following step 340, the compressor ECU 41 determines whether or not the discharge temperature Tout obtained in step 330 has exceeded a predetermined reference value. If the determination is negative, the routine of this time is determined as the system is operating normally. Is terminated. On the other hand, if the determination is affirmative, that is, if the discharge temperature Tout exceeds a predetermined reference value, it is determined that an abnormality has occurred in the system, and the process proceeds to a discharge temperature abnormality processing routine (step 350). In step 350, the compressor ECU 41 may realize, for example, output restriction of the air compressor 42 (output restriction of the fuel cell 10) or operation stop.

As described above, according to this embodiment, a temperature sensor is not provided directly on the downstream side of the air compressor 42 and the discharge temperature Tout is directly measured, as in the above embodiments. The discharge temperature Tout can be estimated with high accuracy by effectively using the various measured values or calculated values required for the above, so that an excellent fail-safe function can be realized at low cost. Further, since the influence of the heat generated by the air compressor 42 itself on the actual discharge temperature Tout is taken into account by the correction coefficient α adapted by experiment, the estimation accuracy of the discharge temperature Tout is improved.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  For example, in the above-described embodiment, the discharge pressure Pout of the air compressor 42 is obtained from the control pressure of the oxidant gas (measured value by the pressure sensor 64), but the fuel cell system maintains the control pressure at a predetermined constant value. In this case, the discharge pressure Pout of the air compressor 42 may be a fixed value determined in advance from the constant control pressure. In this case, it is not necessary to use the measurement value of the pressure sensor 64. The discharge pressure Pout may be acquired as a measured value by setting a pressure sensor on the outlet side of the air compressor 42 (between the outlet side of the air compressor 42 and the intercooler 46), for example.

It is a principal part block diagram which shows one Example of the fuel cell system by this invention. 4 is a flowchart illustrating main processing that may be executed by a calculation unit (CPU) of the compressor ECU 41 according to the first embodiment. It is explanatory drawing of the approximation which compensates for the difference in altitude. 7 is a flowchart illustrating main processing that may be executed by a calculation unit (CPU) of a compressor ECU 41 according to a second embodiment. 12 is a flowchart illustrating main processing that may be executed by a calculation unit (CPU) of a compressor ECU 41 according to a third embodiment. FIG. 5 is an approximate explanatory diagram for compensating for a temperature rise of a discharge temperature Tout due to heat generation of the air compressor 42;

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fuel cell 20 Single cell 40 Oxidant gas supply system 41 Compressor ECU
42 Air compressor 42a Motor 44 Air cleaner 45 Flow rate sensor 46 Intercooler 50 Radiator 52 Motor 54 Pump 60 Exhaust pipe 62 Pressure regulating valve 64 Pressure sensor 66 Valve 70 Temperature sensor 72 Pressure sensor

Claims (4)

In a fuel cell system having a compressor for supplying oxidant gas to a fuel cell ,
A compression ratio γ of the compressor, which is a value obtained by dividing a measured value of the pressure of the oxidant gas on the discharge side of the compressor by a measured value of the pressure of the oxidant gas on the intake side of the compressor;
A measured value Tin of the temperature of the oxidant gas on the intake side of the compressor;
Using the known specific heat ratio κ of the oxidant gas, discharge temperature calculation for calculating the temperature of the oxidant gas on the discharge side of the compressor based on the equation of Tin * γ ^ (κ−1 / κ) A fuel cell system comprising means . The discharge temperature calculating means multiplies the equation of Tin * γ ^ (κ−1 / κ) by a correction coefficient expressed as a function of the rotation speed of the compressor, thereby calculating the calculated discharge side of the compressor. The fuel cell system according to claim 1, wherein the temperature of the oxidant gas is corrected . 2. The fuel cell system according to claim 1, further comprising an abnormality determination unit that determines that the system is abnormal when the calculated temperature of the oxidant gas on the discharge side of the compressor exceeds a predetermined reference value . 3. The fuel cell system according to claim 2, further comprising an abnormality determination unit that determines that the system is abnormal when the corrected temperature of the oxidant gas on the discharge side of the compressor exceeds a predetermined reference value .

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