JP4578890B2 - Starting method of fuel cell system - Google Patents

Description

  The present invention relates to a method for starting a fuel cell system.

  Conventionally, for example, a polymer electrolyte fuel cell is configured by stacking a plurality of cells on a cell formed by sandwiching a polymer electrolyte membrane between an anode (fuel electrode) and a cathode (air electrode) from both sides. Stack (hereinafter referred to as a fuel cell). When hydrogen is supplied to the anode as a fuel and air is supplied to the cathode as an oxidant, hydrogen ions generated by the catalytic reaction at the anode move through the solid polymer electrolyte membrane to the cathode and oxygen at the cathode. It is designed to generate electricity through an electrochemical reaction.

  Generally, the operating temperature of this type of fuel cell is about 70 ° C. to 80 ° C. However, since the power generation efficiency decreases at low temperatures, startability at low temperatures is a major issue. Therefore, when the fuel cell is used for a vehicle, there is a problem that it takes a long time to start when the outside air temperature is low, for example, when the fuel cell is started below freezing point.

In contrast, for example, Patent Document 1 includes a warm-up heater (in this case, a burner 94) in a flow path of a heat exchange medium circulating in the fuel cell stack, and the heat-exchange medium is supplied by the warm-up heater. There has been proposed a technique for heating a fuel cell stack by heating and flowing it into the fuel cell stack.
Japanese Patent Laid-Open No. 9-293526

  However, since the conventional technology is configured to heat the heat exchange medium to a constant temperature and supply a predetermined flow rate to the fuel cell stack, the heat quantity of the heat exchange medium may not be sufficiently transmitted to the fuel cell stack. is there. As a result, there is a problem that the temperature rise of the fuel cell stack becomes an obstacle, and heat energy is diffused wastefully.

  Accordingly, an object of the present invention is to provide a starting method of a fuel cell system that can efficiently transfer the heat energy of the heat exchange medium to the fuel cell stack and rapidly increase the temperature of the fuel cell stack.

The invention according to claim 1 is a method of starting a fuel cell system in which a heat exchange medium is circulated through the fuel cell stack to control the temperature of the fuel cell stack, and after the fuel cell stack is started, In the first mode in which the temperature change rate on the heat exchange medium outlet side is less than a predetermined change rate, the flow rate of the heat exchange medium is set to a predetermined first flow rate, and the temperature change rate on the heat exchange medium outlet side is In the second mode in which the rate of change is not less than the predetermined change rate and the difference between the temperature on the heat exchange medium inlet side of the fuel cell stack and the temperature on the heat exchange medium outlet side is not less than a predetermined value, the flow rate of the heat exchange medium is In the third mode in which the difference between the temperature on the heat exchange medium inlet side and the temperature on the heat exchange medium outlet side is less than a predetermined value, the flow rate of the heat exchange medium is set to a predetermined second flow rate. Specially set to 3 flow rates To.

  According to this invention, the flow rate of the heat exchange medium can be set to a flow rate suitable for each mode. That is, the temperature of the fuel cell stack can be increased more quickly by setting a larger flow rate of the heat exchange medium in the first mode and the second mode where the heating of the fuel cell stack is highly necessary. In the third mode in which the necessity for heating of the fuel cell stack is reduced, the power consumption of the means for circulating the heat exchange medium in the fuel cell stack is reduced by setting the flow rate of the heat exchange medium to be small. At the same time, since the diffusion of the thermal energy of the heat exchange medium can be suppressed, the power consumption can be reduced. In particular, when a fuel cell system is mounted on a hybrid vehicle, it can contribute to an improvement in fuel consumption.

The invention according to claim 2 is the invention according to claim 1 , wherein the second flow rate is equal to or higher than the first flow rate, and the first flow rate is larger than the third flow rate.
According to the present invention, in the first mode, the temperature of the fuel cell stack is increased while protecting the heat exchange medium having a high viscosity at a low temperature from a high load on the means for circulating the heat exchange medium in the fuel cell stack. Can do. Further, in the second mode, the temperature of the fuel cell stack can be quickly raised with the viscosity of the heat exchange medium lowered. Further, in the third mode, the diffusion of the heat energy of the heat exchange medium can be suppressed while increasing the temperature of the fuel cell stack, and the power consumption can be reduced.

The invention according to claim 3 is the one according to claim 1 or 2 , wherein the flow rate of the heat exchange medium is set by performing feedback control based on the pressure of the heat exchange medium. And
According to the present invention, the flow rate of the heat exchange medium can be quickly optimized, and finer control can be performed.

According to the invention which concerns on Claim 1 , the flow volume of the said heat exchange medium can be set to the flow volume suitable for each mode.
According to the invention which concerns on Claim 2 , the temperature of the said fuel cell stack can be raised rapidly. The diffusion of the heat energy of the heat exchange medium can be suppressed, and the power consumption can be reduced.
According to the third aspect of the invention, the flow rate of the heat exchange medium can be quickly optimized, and finer control can be performed.

  A method for starting a fuel cell system according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a fuel cell system 1 including a fuel cell stack 2 according to an embodiment of the present invention. The fuel cell stack 2 includes a predetermined number of unit cells (not shown) in which a solid polymer electrolyte membrane made of a sulfonic acid electrolyte material is sandwiched between a fuel electrode (anode) and an air electrode (cathode) from both sides. It has the structure which did.

  When hydrogen gas is supplied as a fuel gas to the fuel electrode of each cell configured as described above, and air containing oxygen as an oxidant is supplied to the air electrode, the hydrogen ions generated by the catalytic reaction at the fuel electrode become solid high. It passes through the molecular electrolyte membrane and moves to the air electrode, where it generates an electric power by causing an electrochemical reaction with oxygen at the air electrode to generate water.

  The fuel cell system 1 includes a fuel supply device such as a high-pressure fuel tank, supplies fuel gas to the fuel electrode of each cell via a fuel supply flow path, and includes a compressor (compressor) that is an air supply device, The air compressed by the compressor is supplied to the air electrode of each cell via the air supply flow path. Illustration of these members is omitted.

  The fuel cell system 1 includes a heat exchange medium circulation channel 3 connected to the fuel cell stack 2. A heat exchange medium (for example, oil) flows through the fuel cell stack 2 through the heat exchange medium circulation passage 3. The heat exchange medium acts as a heating medium when the fuel cell stack 2 is at a low temperature, and acts as a cooling medium that suppresses a temperature rise due to power generation when the fuel cell stack 2 generates power. The heat exchange medium circulation flow path 3 is provided with a pump 4. By operating the pump 4, the heat exchange medium is transferred from the outlet side heat exchange medium circulation flow path 3 b (3) to the inlet side heat exchange medium circulation flow. It pumps to the path 3a (3). Thereby, the heat exchange medium flows into the fuel cell stack 2 from the inlet side heat exchange medium circulation channel 3a, flows through the fuel cell stack 2, and then is discharged to the outlet side heat exchange medium circulation channel 3b. become. In the present embodiment, the flow rate of the heat exchange medium flowing through the fuel cell stack 2 is controlled by controlling the operating state of the pump 4.

  A heater 5 is disposed in the heat exchange medium circulation channel 3. By operating the heater 5, the heat exchange medium is heated. Thereby, when the temperature of the fuel cell stack 2 is low, the heat exchange medium is circulated in the fuel cell stack 2 as a heat medium. Note that a bypass passage (not shown) provided with a cooler is connected to the heat exchange medium circulation passage 3 so as to straddle the heater 5 (heating means). Then, at the time of power generation of the fuel cell stack 2, the heat exchange medium is cooled via a cooler and is circulated in the fuel cell stack 2 as a refrigerant.

  In addition, temperature sensors s1 and s2 and pressure sensors s1 'and s2' are provided in the inlet side heat exchange medium circulation channel 3a and the outlet side heat exchange medium circulation channel 3b, respectively. These sensors s1, s2 and pressure sensors s1 ', s2' detect the temperature T1 and pressure P1 on the inlet side of the fuel cell stack 2, and the temperature T2 and pressure P2 on the outlet side, respectively. In addition, a temperature sensor s3 and a pressure sensor s3 'are provided in a portion between the pump 4 and the heater 5 in the heat exchange medium circulation channel 3, and the temperature T3 and pressure P3 of the portion are detected.

A control method of the fuel cell stack 2 configured as described above will be described with reference to FIGS. FIG. 2 is a flowchart showing the contents of the heat exchange medium (heat medium) flow rate control process in the embodiment of the present invention. As shown in step S10 of the figure, when the flow control of the heat exchange medium is started, the rate of increase per unit time of the outlet side temperature T2 of the fuel cell stack 2 detected by the temperature sensor s2 is predetermined in step S12. It is determined whether or not the value is ΔT0 or more. If this determination result is NO , the process proceeds to step S14, and if this determination result is YES , the process proceeds to step S16.

  In step S14, it is determined that the first mode (mode 1) in which the rate of change in temperature on the heat exchange medium outlet side of the fuel cell stack is equal to or less than a predetermined rate of change. This mode will be described with reference to FIGS. FIG. 3 is a graph showing respective time changes of the inlet side temperature, the outlet side temperature, and the temperature difference between the inlet side and the outlet side of the heat exchange medium flow path of the fuel cell system. FIG. 4 is a state explanatory view showing the temperature state of the fuel cell stack shown in FIG. As shown in these figures, when the temperature on the outlet side of the fuel cell stack 2 is smaller than a predetermined value ΔT0, it is desired to quickly transfer the heat energy of the heat exchange medium to the fuel cell stack 2 to increase it. However, immediately after start-up, since the viscosity of the heat exchange medium is high, the flow rate of the heat exchange medium is set to 200 L / min, which is slightly higher, in order to prevent an excessive burden on the pump 4. Thus, in the first mode, the temperature of the fuel cell stack 2 can be increased while protecting the pump 4 for circulating the heat exchange medium into the fuel cell stack 2 from the high viscosity of the heat exchange medium. . After the process of step S14 is complete | finished, it returns to the first process of this flowchart.

  In step S16, it is determined whether or not the temperature difference between the temperature T1 on the inlet side and the temperature T2 on the outlet side of the fuel cell stack 2 is equal to or greater than a predetermined value ΔT0 ′. If the determination result is YES, the process proceeds to step S18, and if the determination result is NO, the process proceeds to step S20. Here, the temperatures T1 and T2 are detected by the temperature sensors s1 and s2.

In step S18, the second mode (mode 2) in which the difference between the temperature T1 on the inlet side of the fuel cell stack 2 and the temperature T2 on the outlet side is equal to or greater than a predetermined value ΔT0 ′ is determined. In this mode 2, although the heat energy of the heat exchange medium has begun to be transferred to the outlet side of the fuel cell stack 2, the difference from the temperature T1 on the inlet side is large. It is desired to increase the temperature of the fuel cell stack 2 by transferring the heat energy of the exchange medium.
On the other hand, since the rate of increase in the temperature T2 on the outlet side is equal to or greater than the predetermined value ΔT0, the viscosity of the heat exchange medium is reduced accordingly, and the burden on the pump 4 for circulating the heat exchange medium is also reduced. Therefore, in this mode 2, the flow rate of the heat exchange medium is set to a larger flow rate than that in the first mode, for example, 230 L / min. As a result, in the second mode, the temperature of the fuel cell stack can be quickly raised with the viscosity of the heat exchange medium lowered. After the process of step S18 is complete | finished, it returns to the first process of this flowchart.

In step S20, it is determined as the third mode (mode 3) in which the difference between the temperature T1 on the inlet side of the fuel cell stack 2 and the temperature T2 on the outlet side is less than a predetermined value ΔT0 ′. In this mode 3, the heat energy of the heat exchange medium is transmitted to the extent that it is also on the outlet side of the fuel cell stack 2, and if the flow rate of the heat exchange medium is increased, in addition to the heat energy transmitted to the fuel cell stack 2 The heat energy that is wasted to the outside becomes excessive. Therefore, in the third mode in which the necessity of heating the fuel cell stack 2 is reduced, the flow rate of the heat exchange medium is set to a flow rate smaller than the flow rate of the first mode, for example, 100 L / min. Accordingly, in the third mode, by setting the flow rate of the heat exchange medium to be small, the diffusion of the heat energy of the heat exchange medium can be suppressed, so that the power consumption can be reduced. In particular, when a fuel cell system is mounted on a hybrid vehicle, it can contribute to an improvement in fuel consumption. After the process of step S18 is complete | finished, it returns to the first process of this flowchart.
It should be noted that the flow rate values described above are merely examples, and can be appropriately changed according to various conditions such as the size of the fuel cell stack and the type of heat exchange medium.

  Furthermore, the process shown in FIG. 5 is performed in parallel with these processes. FIG. 5 is a flowchart showing the content of the feedback control of the flow rate control process in the embodiment of the present invention. As shown in the figure, in step S32, the difference between the inlet side pressure P1 and the outlet side pressure P2 of the fuel cell stack 2 detected by the pressure sensor s1 ′ and the pressure sensor s2 ′ is taken, and the actual flow rate is calculated from this difference. calculate. In step S34, the target flow rate is calculated from the map value based on the actual flow rate. Further, in step S36, feedback control by PID (proportional / integral / derivative) operation is executed from the difference between the actual flow rate and the target flow rate. Thereafter, the process returns to the first process of this flowchart. By controlling in this way, the flow rate of the heat exchange medium can be quickly optimized, and finer control can be performed.

  Of course, the contents of the present invention are not limited to the above-described embodiments. For example, in the embodiment, PID control is used as feedback control, but not limited to this, PI control may be used. In the embodiment, the temperature difference T1-T2 is used. However, the heat difference Q1-Q2 may be used for the determination. Furthermore, in the embodiment, the flow rate of the heat exchange medium is controlled by dividing into three modes, but the flow rate of the heat exchange medium is switched based on the temperature of the fuel cell stack and the rate of change thereof. What is necessary is just to have a structure.

1 is a schematic configuration diagram of a fuel cell system having a fuel cell stack in an embodiment of the present invention. It is a flowchart figure which shows the content of the heat exchange medium (heat medium) flow control process in embodiment of this invention. It is a graph which shows each time change of the inlet side temperature of a heat exchange medium flow path of a fuel cell system, outlet side temperature, and the temperature difference of an inlet side and an outlet side. It is a state explanatory view showing the temperature situation of the fuel cell stack shown in FIG. It is a flowchart figure which shows the content of the feedback control of the flow control process in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell system 2 ... Fuel cell stack 3 ... Heat exchange medium (refrigerant) circulation flow path 4 ... Pump 5 ... Heater (heating means)

Claims (3)

A method of starting a fuel cell system in which a heat exchange medium is circulated through the fuel cell stack to control the temperature of the fuel cell stack,
After starting the fuel cell stack,
In the first mode in which the rate of change in temperature on the heat exchange medium outlet side of the fuel cell stack is less than a predetermined rate of change, the flow rate of the heat exchange medium is set to a predetermined first flow rate,
The rate of change in temperature on the heat exchange medium outlet side is equal to or greater than the predetermined rate of change, and the difference between the temperature on the heat exchange medium inlet side of the fuel cell stack and the temperature on the heat exchange medium outlet side is equal to or greater than a predetermined value. In the second mode, the flow rate of the heat exchange medium is set to a predetermined second flow rate,
In the third mode in which the difference between the temperature on the heat exchange medium inlet side and the temperature on the heat exchange medium outlet side is less than a predetermined value, the flow rate of the heat exchange medium is set to a predetermined third flow rate. To start the fuel cell system. 2. The fuel cell system start method according to claim 1 , wherein the second flow rate is equal to or higher than the first flow rate, and the first flow rate is larger than the third flow rate. 3. The fuel cell system start method according to claim 1, wherein the flow rate of the heat exchange medium is set by performing feedback control based on the pressure of the heat exchange medium.

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