JP2007122911A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell system capable of completing warm-up power generation at timing without any partial freezing inside a fuel cell stack, based on a change in the temperature rise speed of the fuel cell stack, by executing the warm-up power generation of the fuel cell stack in activation. <P>SOLUTION: The fuel cell system 1 continues warm-up power generation, when the temperature of the fuel cell stack 2 is equal to or higher than first prescribed temperature T1 and the temperature rise speed of the fuel cell stack 2 is less than a prescribed threshold. Then warm-up power generation is stopped when it detects that the temperature rise speed of the fuel cell stack 2 becomes larger than a prescribed threshold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell system that performs warm-up power generation of a fuel cell stack at startup, and more particularly to a fuel cell system that determines the end of warm-up power generation based on a change in the temperature rise rate of the fuel cell stack.

  As a method for warming up the fuel cell stack at the time of low temperature startup of the fuel cell system, there is a method of increasing the heat generation amount by deteriorating the power generation efficiency. As a conventional example of such a fuel cell system, for example, Japanese Patent Application Laid-Open No. 2004-30979 (Patent Document 1) is disclosed. In this conventional example, when the temperature of the fuel cell is low, the fuel cell is warmed up by increasing the heat generation amount due to insufficient oxygen supply.

  As another conventional example, Japanese Patent Application Laid-Open No. 2002-313388 (Patent Document 2) reduces the power generation efficiency by lowering the supply pressure of the reaction gas supplied to the fuel cell at the time of low temperature startup than in the steady operation. The fuel cell stack is warmed up.

Further, when warm-up power generation is performed at low temperature startup, it is necessary to determine the end of warm-up, and as a method for this, there is a method of determining by the temperature of the fluid at the fuel cell stack outlet. As a conventional example of such a fuel cell system, Japanese Unexamined Patent Application Publication No. 2003-151597 (Patent Document 3) is disclosed. In this conventional example, when the fluid temperature at the outlet of the fuel cell stack rises to a predetermined temperature, or when the temperature difference between the fluid at the inlet and outlet of the fuel cell stack increases to the predetermined temperature difference, it is determined that the warm-up is completed. Like to do.
JP 2004-30979 A JP 2002-313388 A JP 2003-151597 A

  However, in the conventional examples disclosed in Patent Documents 1 and 2, the method for ending warm-up power generation at low temperature startup is not clear. Therefore, when warm-up is finished at a lower temperature in order to shorten the startup time, the fuel cell stack In some cases, the warm-up may end while the interior is partially at a low temperature or in a frozen state. If the load is increased in this state, the generated current cannot be taken out and the voltage will be abnormally reduced.

  Further, in the conventional example disclosed in Patent Document 3, there is a case where the inside of the fuel cell stack is cooled partially due to the supply of the low-temperature reaction gas or the circulation of the low-temperature cooling liquid after the start of the warm-up power generation and partially becomes a low temperature or a frozen state. is there. Even in such a state, since the generated voltage is equal to or higher than the threshold value, the voltage does not drop abnormally. However, if the end timing of warm air power generation is determined based on the outlet fluid temperature of the fuel cell stack, the outlet fluid temperature of the fuel cell stack reflects the averaged temperature inside the stack. Cannot be partially reflected in the cold or frozen state. Therefore, even if the inside of the fuel cell stack is partially in a low temperature or frozen state, it may be determined that the warm-up is finished.If the load is increased in this state, the generated current cannot be taken out and the voltage drops abnormally. There was a problem that it was.

  In order to solve the above-described problems, a fuel cell system of the present invention includes a fuel cell stack that generates power by reacting a fuel gas and an oxidant gas by an electrochemical reaction, and warms up the power generation of the fuel cell stack at startup. The end of the warm-up power generation is determined based on a change in the temperature rise rate of the fuel cell stack.

  In the fuel cell system according to the present invention, the end of warm-up power generation is determined based on the change in the temperature rise rate of the fuel cell stack, so that there is a part of the fuel cell stack that is partially cold or frozen. Thus, it is possible to accurately detect the end timing of warm-up power generation.

  Embodiments of a fuel cell system according to the present invention will be described below with reference to the drawings.

  Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating the configuration of the fuel cell system according to the first embodiment.

  As shown in FIG. 1, the fuel cell system 1 of the present embodiment includes a fuel cell stack 2 that is supplied with a fuel gas and an oxidant gas and generates power by an electrochemical reaction, and a fuel cell unit that constitutes the fuel cell stack 2. A cell voltage sensor V1 for detecting a voltage generated by the cell, a temperature sensor S1 for detecting the temperature of the fuel cell stack 2, a hydrogen supply tank 3 for storing and supplying hydrogen gas, and a hydrogen supply tank 3 A hydrogen pressure regulator 4 for depressurizing the high-pressure hydrogen, a pressure sensor P1 for detecting the pressure of hydrogen gas at the inlet of the fuel cell stack 2, a temperature sensor S2 for detecting the temperature of hydrogen gas at the inlet of the fuel cell stack 2, A temperature sensor S3 for detecting the temperature of the hydrogen gas at the outlet of the fuel cell stack 2 and the hydrogen gas not consumed in the fuel cell stack 2 are recirculated. A fuel circulation path 5 that circulates, a hydrogen circulation pump 6 that circulates the hydrogen gas in the fuel circulation path 5, a purge valve 7 that discharges impurities not used in the reaction in the fuel cell stack 2, and an oxidant gas An air supply device (oxidant gas supply means) 8 that pressurizes and supplies the air to the cathode of the fuel cell stack 2, a temperature sensor S4 that detects the temperature of the air sucked into the air supply device 8 from the outside air, A temperature sensor S5 that detects the temperature of air sent from the air supply device 8, a pressure sensor P2 that detects the pressure of air at the inlet of the fuel cell stack 2, and a temperature of air at the inlet of the fuel cell stack 2 are detected. The temperature sensor S6, the temperature sensor S7 for detecting the temperature of the air at the outlet of the fuel cell stack 2, and the pressure of the air in the fuel cell stack 2 are adjusted. An air pressure regulating valve 9 that circulates, a coolant pump 10 that circulates a coolant that cools the fuel cell stack 2, a temperature sensor S8 that detects the temperature of the coolant at the inlet of the fuel cell stack 2, and an outlet of the fuel cell stack 2 A temperature sensor S9 for detecting the temperature of the coolant in the air, a coolant pump 11 for circulating the coolant for cooling the air supply device 8, and a temperature sensor S10 for detecting the temperature of the coolant that has cooled the air supply device 8. A heat exchanger 12 that radiates and cools the heat of the coolant, a current sensor I1 that detects a current output from the fuel cell stack 2, and a voltage sensor V2 that detects a voltage output from the fuel cell stack 2 A power converter 14 that takes out an output such as electric power or current from the fuel cell stack 2 and supplies the output to the load device 13, and electric power generated by the fuel cell stack 2 Secondary battery 15 that stores the voltage, voltage sensor V3 that detects the voltage of secondary battery 15, current sensor I2 that detects the current of secondary battery 15, and temperature sensor that detects the temperature in the vicinity of secondary battery 15 S11 and a heater (heating means) 16 for heating the fuel cell stack 2 are provided.

  Here, in the fuel cell system 1 described above, in the fuel cell stack 2, hydrogen gas as fuel gas is supplied to the anode, and air as oxidant gas is supplied to the cathode, and power generation is performed by the following electrochemical reaction. It has been broken.

Anode (fuel electrode): H2 → 2H ++ 2e- (1)
Cathode (oxidizer electrode): 2H ++ 2e-+ (1/2) O2 → H2O (2)
In the hydrogen supply system, hydrogen gas is supplied from the hydrogen supply tank 3 to the anode of the fuel cell stack 2 through the hydrogen pressure regulator 4. The high-pressure hydrogen supplied from the hydrogen supply tank 3 is controlled by the hydrogen pressure regulator 4 so as to have a desired pressure. Further, the hydrogen gas that has not been consumed at the anode of the fuel cell stack 2 is recirculated to the anode of the fuel cell stack 2 through the fuel circulation path 5 by the hydrogen circulation pump 6 (hereinafter referred to as circulating hydrogen). Therefore, a mixed hydrogen of hydrogen supplied from the hydrogen supply tank 3 and circulating hydrogen is supplied to the anode. Among them, the circulating hydrogen contains a lot of water vapor, and is mixed with the dry hydrogen in the hydrogen supply tank 3 to humidify the hydrogen supplied to the anode, thereby sufficiently humidifying the polymer electrolyte membrane. Further, in order to discharge nitrogen accumulated in the hydrogen supply system, a purge line is branched from the fuel circulation path 5 and nitrogen, which is an impurity, is discharged by a purge valve 7 installed in the purge line, and fuel In order to recover the cell voltage of the battery stack 2, the function of blowing water clogged in the gas flow path is also achieved.

  On the other hand, in an air supply system for supplying air as an oxidant gas, air sucked from the outside is pressurized and sent out by the air supply device 8 and supplied to the cathode of the fuel cell stack 2. Here, the air supply apparatus 8 can be comprised by a compressor, for example. The air pressure at the cathode is detected by the pressure sensor P2, and the air pressure at the cathode is controlled by adjusting the rotation speed of the air supply device 8 and the opening area of the air pressure regulating valve 9 based on the detected value.

  Further, in the cooling system for cooling the fuel cell stack 2, the coolant is circulated by the coolant pump 10 to cool the fuel cell stack 2. In addition, a cooling system for cooling the air supply device 8 is also provided, and a cooling liquid is circulated by the cooling liquid pump 11 to cool a motor for rotating a compressor that is the air supply device 8. The coolant whose temperature has been increased by cooling the air supply device 8 is circulated by reducing the temperature by releasing heat from the heat exchanger 12. Here, the heat exchanger 12 is a radiator or a radiator fan in a vehicle or the like.

  The fuel cell stack 2 is connected to a load device 13 that consumes the generated power. Here, an inverter is connected as the power converter 14, and the power generated by the fuel cell stack 2 is converted into energy and supplied to the drive motor as the load device 13. Then, the power generation amount in the load device 13 is set so that the load current is taken out from the fuel cell stack 2. Further, electric power is stored in the secondary battery 15 and supplied to the load device 13.

  Next, the warm-up power generation control process at the start-up by the fuel cell system 1 of the present embodiment will be described based on the flowchart of FIG.

  As shown in FIG. 2, first, the fuel cell system 1 is started to start supplying air and supplying hydrogen (S201). In this embodiment, the hydrogen circulation pump 6 is provided in the hydrogen system so as to keep the hydrogen stoichiometry high, so the hydrogen circulation pump 6 also starts rotating here. Further, a purge valve 7 for periodically discharging accumulated nitrogen is provided at the anode outlet of the fuel cell stack 2, but the purge valve 7 is started while being closed. However, after starting, purge control for periodically opening and closing the purge valve 7 is started. The driving of the coolant pump 11 for cooling the compressor motor of the air supply device 8 is also started here, and the coolant temperature at the outlet of the air supply device 8 detected by the temperature sensor S10 by circulating the coolant is the target temperature. Control to become. On the other hand, the driving of the coolant pump 10 for cooling the fuel cell stack 2 is not performed at the time of low temperature startup, and the coolant is not circulated.

  Next, warm-up power generation of the fuel cell stack 2 is started (S202). At this time, driving of the coolant pump 10 is started simultaneously with the start of warm-up power generation, and the coolant is circulated through the fuel cell stack 2. Then, the fuel cell stack 2 itself is warmed by the power generation of the fuel cell stack 2, and the coolant is also warmed.

  When the warm-up power generation is started in this way, the end condition for determining the warm-up power generation is set (S203). In the present invention, in order to determine whether or not the warm-up power generation can be terminated, the stack temperature rising speed during the warm-up power generation is used. Therefore, a temperature range is set for determining whether or not warm-up power generation can be terminated. When the warm-up power generation is started and the stack temperature is equal to or higher than the first predetermined temperature T1, the end determination of the warm-up power generation is started. In the present embodiment, the first predetermined temperature T1 is a fixed value set in advance.

  Further, the temperature used for the end determination of the warm-up power generation includes the stack temperature of the fuel cell stack 2, the coolant temperature at the outlet of the fuel cell stack 2 detected by the temperature sensor S9, and the fuel cell stack detected by the temperature sensor S7. The end of warm-up power generation is determined using either the air temperature at the outlet 2 and the hydrogen temperature at the outlet of the fuel cell stack 2 detected by the temperature sensor S3. Any temperature may be used, but in this embodiment, the coolant temperature detected by the temperature sensor S9 is used.

  Thus, since the end of warm-up power generation is determined using the value detected by any one of the temperature sensors, the timing for ending the warm-up power generation of the fuel cell stack 2 is determined without using many temperature sensors. be able to.

  Further, although the heater 16 for warming the fuel cell stack 2 is installed, a temperature sensor installed in the vicinity of the heater 16 is not used. In the present embodiment, the coolant temperature by the temperature sensor S9 installed at a predetermined distance from the fuel cell stack 2 is set so that the influence of the radiant heat of the heater 16 installed in the fuel cell stack 2 is not directly transmitted to the temperature sensor. Use it. Therefore, in the following description, the expression “stack temperature” refers to the coolant temperature at the outlet of the fuel cell stack 2.

  Next, the timing for ending warm-up power generation is determined (S204). Specifically, it will be described based on the flowchart of FIG.

  When the determination of the timing to end the warm-up power generation is started in this way, the temperature increase acceleration process for accelerating the stack temperature increase is executed until the condition for setting the warm-up power generation end flag is satisfied (S205). . Specific processing will be described based on a flowchart of FIG. 5 described later.

  When the warm-up power generation end flag is set, the start-up of the fuel cell system 1 is terminated (S206), the operation is shifted to the normal operation state (S207), and the warm-up at the time of start-up by the fuel cell system 1 of the present embodiment. The machine power generation control process is terminated.

  Next, the warm-up power generation end determination process in step S204 of the flowchart of FIG. 2 will be described with reference to FIGS. FIG. 3 is a flowchart showing a warm-up power generation end determination process, and FIG. 4 is a diagram for explaining a temporal change in the coolant temperature and the generated current.

  First, warm-up power generation is started at time t1 in FIG. 4 and the generated current is taken out from the fuel cell stack 2, and it is determined whether or not the coolant temperature at the outlet of the fuel cell stack 2 is equal to or higher than the first predetermined temperature T1. (S301). Here, when the coolant temperature is equal to or lower than the first predetermined temperature T1, the warm-up power generation end flag is cleared (S302), and then jumps to return and waits for the temperature rise.

  On the other hand, if the coolant temperature is equal to or higher than the first predetermined temperature T1 (after time t2 in FIG. 4), whether or not the temperature rise rate of the coolant at the outlet of the fuel cell stack 2 has become a predetermined threshold value or less. Is determined (S303). As this predetermined threshold value, the temperature increase rate when the cooling water temperature rises to the first predetermined temperature T1 or higher can be used. However, in order to avoid misjudgment, it may be added on condition that the temperature increase rate is equal to or lower than a predetermined threshold for a predetermined time or more, or when the cooling water temperature rises to the first predetermined temperature T1 or higher. An increase rate obtained by subtracting a predetermined margin from the temperature increase rate may be used as the predetermined threshold value.

  The state in which the temperature increase rate of the coolant temperature becomes slow in this way is a state in which freezing and thawing are repeatedly occurring inside the fuel cell stack 2, and the generated current is increased in such a state. This may cause an abnormal drop in voltage. Therefore, in this step, when the temperature rise rate of the coolant is equal to or lower than the predetermined threshold, the current state is maintained by controlling so as not to increase the generated current of the fuel cell stack 2 (S304, time t3 in FIG. 4). t4).

  And if the state which is maintaining the electric power generation current of warm-up power generation is continued, the internal temperature of the fuel cell stack 2 will rise, and there will be no part which is frozen inside the stack. As a result, a point at which the temperature rise rate of the coolant increases again appears. By determining whether or not the temperature rise rate of the coolant has exceeded a predetermined threshold (S305), the fuel cell stack 2 is frozen. It is determined whether or not there are no more parts. The predetermined threshold is a temperature increase rate when the temperature rises to the first predetermined temperature T1. However, in order to make a more accurate determination, it may be determined whether or not the current temperature rise rate is equal to or higher than a predetermined threshold and the state continues for a predetermined time or more.

  If the temperature rise rate of the coolant is smaller than the predetermined threshold, the warm-up power generation end flag is cleared (S302), and the process jumps to return. On the other hand, when the temperature rise rate of the coolant becomes equal to or higher than the predetermined threshold (after time t4 in FIG. 4), in order to determine whether or not the fuel cell stack 2 can withstand a transient load rise, It is determined whether or not the coolant temperature at the outlet is equal to or higher than a second predetermined temperature T2 (S306).

  When the coolant temperature is lower than the second predetermined temperature T2, the warm-up power generation end flag is cleared (S302), and the process jumps to return. On the other hand, when the coolant temperature is equal to or higher than the second predetermined temperature T2, the generated current of the fuel cell stack 2 is increased with a predetermined inclination (S307, after time t5 in FIG. 4).

  Thereafter, it is determined whether or not the coolant temperature at the outlet of the fuel cell stack 2 rises following an increase in the generated current within a predetermined determination time (fixed value) (S308). If the temperature does not rise, the warm-up power generation end flag is cleared (S302), the process jumps to return, waits for the coolant temperature to rise, and is determined again in the next control cycle. On the other hand, if the coolant temperature rises following this, it is determined that the warm-up power generation can be terminated, a warm-up power generation end flag is set (S309), and the warm-up power generation end determination process is terminated.

  Next, the temperature increase acceleration process in step S205 of the flowchart of FIG. 2 will be described based on FIG. FIG. 5 is a flowchart showing the temperature rise acceleration process.

  As shown in FIG. 5, first, it is determined whether or not the warm-up power generation end flag is in the clear state (S501). If the warm-up power generation end flag is not in the clear state, jump to return and end the temperature increase acceleration process.

  On the other hand, when the warm-up power generation end flag is in the clear state, the flow rate of the coolant is first reduced to a predetermined flow rate in order to accelerate the temperature rise of the fuel cell stack 2 (S502). At this time, as shown in FIG. 6, the coolant may be stopped when the coolant temperature is low, and the coolant flow rate may be increased as the coolant temperature increases. Further, the coolant may be supplied so as to be repeatedly supplied and stopped intermittently.

  Next, the power consumption of the air supply device 8 is reduced, and the power is controlled to be consumed by the heater 16 (S503). Here, in order to reduce the power consumption of the air supply device 8, the air flow rate is reduced to reduce the rotational speed by N1. Further, the operating pressure of the air supply device 8, that is, the operating pressure at the cathode of the fuel cell stack 2 may be decreased by p1.

  Then, the pressure increase and decrease of the cathode and anode of the fuel cell stack 2 are repeated (S504). Here, FIG. 7 shows a process of repeatedly increasing and decreasing the pressure. As shown in FIG. 7, the pressure to the fuel cell stack 2 is increased so that the fuel gas is distributed throughout, and the generated water is discharged with a change in flow rate when the pressure is rapidly decreased. If only the product water is discharged, only the cathode pressure needs to be increased or decreased. However, if the differential pressure is applied to air and hydrogen, the fuel cell may be damaged, so the anode pressure is also synchronized. To increase or decrease.

  When the pressure is increased or decreased in step S504, the process jumps to return and ends the temperature increase acceleration process.

  As described above, in the fuel cell system 1 of this embodiment, the end of warm-up power generation is determined based on the change in the temperature rise rate of the fuel cell stack 2, so that the temperature inside the fuel cell stack 2 is partially lowered or frozen. It is possible to detect that there is a state portion, and thereby it is possible to accurately determine the end timing of warm-up power generation.

  Further, in the fuel cell system 1 of the present embodiment, warm-up power generation is continued when the temperature of the fuel cell stack 2 is equal to or higher than the first predetermined temperature T1 and the temperature increase rate of the fuel cell stack 2 is smaller than a predetermined threshold. Therefore, it is possible to detect a state in which the inside of the fuel cell stack 2 is partially at a low temperature or is frozen by detecting that the change in the rate of temperature rise is moderate. Warm power generation can be continued by more accurately determining the state where freezing remains in the stack 2.

  Furthermore, in the fuel cell system 1 of the present embodiment, when the temperature of the fuel cell stack 2 is equal to or higher than the first predetermined temperature T1 and the temperature rise rate of the fuel cell stack 2 is smaller than a predetermined threshold value, power generation by warm-up power generation is performed. Since the current is not increased, the generated water can be prevented from being excessively extracted when the generated water is partially low in temperature or frozen in the fuel cell stack 2, resulting in an abnormal voltage drop. The thawing of the frozen portion inside the fuel cell stack 2 can be continued.

  Further, in the fuel cell system 1 of the present embodiment, after detecting that the temperature of the fuel cell stack 2 is equal to or higher than the first predetermined temperature T1 and the temperature increase rate of the fuel cell stack 2 is smaller than a predetermined threshold value, Since the warm-up power generation is terminated when the temperature rise rate of the fuel cell stack 2 becomes larger than the predetermined threshold value, the ice is completely melted after the change in the temperature rise rate becomes gradual, and the slope of the temperature rise rate starts again. By detecting that the fuel cell stack 2 is suddenly detected, it is possible to detect that the inside of the fuel cell stack 2 has been completely thawed, and it is possible to more accurately determine the end timing of warm-up power generation.

  Furthermore, in the fuel cell system 1 of the present embodiment, the predetermined threshold value of the temperature increase rate is set to the temperature increase rate when the temperature of the fuel cell stack 2 rises to the first predetermined temperature T1, so that the fuel cell stack 2 It can be detected that the inside has completely thawed and the temperature has started to rise, and the end timing of warm-up power generation can be determined more accurately.

  Further, in the fuel cell system 1 of the present embodiment, when the temperature of the fuel cell stack 2 rises to a second predetermined temperature T2 higher than the first predetermined temperature T1, the power generation current for warm-up power generation is increased, Accordingly, the warm-up power generation is terminated when the temperature of the fuel cell stack 2 rises following the temperature rise. Therefore, when the ice inside the fuel cell stack 2 is completely melted, the temperature rise follows the increase in the generated current. Thus, it is possible to detect that the inside of the fuel cell stack 2 has been completely thawed and accurately determine the end timing of warm-up power generation that can withstand the increase in load.

  Furthermore, in the fuel cell system 1 of the present embodiment, as the temperature of the fuel cell stack 2, the cell temperature of the fuel cell stack 2, the coolant outlet temperature of the fuel cell stack 2, the oxidant gas outlet temperature of the fuel cell stack 2, the fuel Since determination is made using any one of the fuel gas outlet temperatures of the battery stack 2, the end of warm-up power generation is determined using the value detected by any one of the temperature sensors without using many temperature sensors. be able to.

  Further, in the fuel cell system 1 of the present embodiment, the flow rate of the coolant in the fuel cell stack 2 is reduced or intermittent when the warm-up power generation is continued, so that the coolant flow rate is reduced. By doing so, the temperature rise of the fuel cell stack 2 can be accelerated, and the warm-up power generation can be promptly terminated.

  Further, in the fuel cell system 1 of this embodiment, the flow rate of the coolant is increased as the temperature of the fuel cell stack 2 rises, so that the temperature distribution inside the fuel cell stack 2 is relaxed (partial overtemperature). Mitigation) The temperature of the entire fuel cell stack 2 can be increased faster.

  Further, in the fuel cell system 1 of the present embodiment, the electric power of the air supply device 8 is reduced and the energization amount of the heater 16 is increased when the warm-up power generation is continued, so that the temperature of the fuel cell stack 2 can be increased more quickly. Can be raised.

  Furthermore, in the fuel cell system 1 of the present embodiment, the pressure of the air and hydrogen gas supplied to the fuel cell stack 2 when the warm-up power generation is continued is increased or decreased at predetermined intervals. It is possible to generate power by spreading the raw fuel over the entire interior, whereby the temperature of the raw material gas is also increased, and the temperature of the entire fuel cell stack 2 can be raised rapidly. Further, the generated water remaining in the fuel cell stack 2 can be discharged by increasing or decreasing the pressure.

  Next, a second embodiment of the present invention will be described with reference to the drawings. The fuel cell system of the present embodiment is different from that of the first embodiment in that the predetermined threshold value to be compared with the temperature rise rate of the coolant is corrected in step S305 of FIG. Since the configuration of the fuel cell system of this embodiment and the processes other than step S305 are the same as those of the first embodiment, detailed description thereof is omitted.

  In the first embodiment, the temperature increase rate when the temperature rises to the first predetermined temperature T1 is used as the predetermined threshold value to be compared with the temperature increase rate of the coolant in step S305. Correction is performed on the threshold value.

  Here, the threshold value correction processing by the fuel cell system of the present embodiment will be described with reference to FIG. First, as shown in step S801, a correction coefficient R1 is set such that the predetermined threshold value increases as the temperature increase rate when the temperature of the fuel cell stack 2 rises to the first predetermined temperature T1 decreases. The correction coefficient R1 is obtained based on this relationship. At this time, when the temperature increase acceleration process performed in step S205 in FIG. 2 is executed, the predetermined threshold value is changed to a correction coefficient R2 that is larger than the correction coefficient R1.

  On the other hand, in step S802, a correction coefficient R3 is set such that the predetermined threshold value increases as the time when the temperature of the fuel cell stack 2 rises to the first predetermined temperature T1 or more becomes longer. Based on this, a correction coefficient R3 is obtained.

  Thus, the correction coefficient R1 or R2 obtained in step S801 is compared with the correction coefficient R3 obtained in step S802, and the larger one is determined as the correction coefficient (S803). Then, the correction coefficient is multiplied by a predetermined threshold value (temperature increase rate when the temperature rises to the first predetermined temperature T1) (S804), and the corrected predetermined threshold value is calculated to implement this embodiment. The threshold correction process by the example fuel cell system is terminated.

  The corrected predetermined threshold value calculated in this way and the temperature rise rate of the coolant are compared in step S305 in FIG. 3, and it is determined whether or not the temperature rise rate of the coolant is equal to or higher than the predetermined threshold value. It is detected that there is no part that is frozen inside the stack 2.

  Thus, in the fuel cell system of the present embodiment, the predetermined threshold value of the temperature increase rate is corrected to a larger value as the temperature increase rate when the temperature of the fuel cell stack 2 rises to the first predetermined temperature T1 becomes smaller. Even in a situation where the temperature of the fuel cell stack 2 rises to the first predetermined temperature T1 is slow, and there are many low temperature portions in the fuel cell stack 2 and partial low temperatures and freezing are likely to remain. In addition, it is possible to more accurately determine the end timing of warm-up power generation without a frozen portion.

  In the fuel cell system of the present embodiment, the predetermined threshold value of the temperature increase rate is corrected to a larger value as the time during which the temperature of the fuel cell stack 2 rises to the first predetermined temperature becomes longer. Even in a situation where there are many low-temperature portions and partial low-temperature or freezing tends to remain, the end timing of warm-up power generation without low-temperature or freezing portions can be determined more accurately.

  Furthermore, in the fuel cell system of the present embodiment, when the temperature increase acceleration process is performed, the predetermined threshold value of the temperature increase rate is corrected to a larger value. Therefore, when the temperature increase acceleration process is performed, the fuel cell stack 2 is warmed up. It is possible to prevent erroneous determination of the end timing of the mechanical power generation.

  Next, Embodiment 3 of the present invention will be described with reference to the drawings. In the fuel cell system of the present embodiment, the determination time in the tracking determination of the coolant temperature performed in step S308 of FIG. 3 in the first embodiment can be set according to the temperature rise of the fuel cell stack 2. This is different from the first embodiment. Since the configuration of the fuel cell system of this embodiment and the processes other than step S308 are the same as those of the first embodiment, detailed description thereof is omitted.

  In the first embodiment, in step S308, it is determined whether or not the coolant temperature increases following the increase in the generated current within a predetermined determination time (fixed value). The determination time can be set according to the rising speed when the coolant temperature of the fuel cell stack 2 rises to the first predetermined temperature T1 and the time until it rises.

  Here, the determination time setting process by the fuel cell system of the present embodiment will be described with reference to FIG. First, as shown in step S901, a determination time X1 is set such that the temperature rise rate when the cooling water temperature of the fuel cell stack 2 rises to the first predetermined temperature T1 increases as the temperature rises. The determination time X1 is obtained based on this relationship.

  On the other hand, in step S902, a determination time X2 is set such that the time when the cooling water temperature of the fuel cell stack 2 rises to the first predetermined temperature T1 or higher becomes longer, and based on this relationship. Determination time X2 is obtained.

  Then, the determination time X1 obtained in step S901 and the determination time X2 obtained in step S902 are compared to determine the larger one as the determination time (S903), and the determination time is set by the fuel cell system of this embodiment. The process ends.

  The follow-up determination of the coolant temperature in step S308 of FIG. 3 is performed using the corrected determination time thus calculated.

  Further, when the follow-up determination is performed, the current taken out from the fuel cell stack 2 is increased. In the fuel cell system of this embodiment, the current value of the current taken out from the fuel cell stack 2 is as shown in FIG. In addition, the fuel cell stack 2 is set to become smaller as the cooling water temperature becomes lower.

  Thus, in the fuel cell system of the present embodiment, the determination time for determining whether or not the temperature of the fuel cell stack 2 has increased following the power generation current is used, and the temperature of the fuel cell stack 2 is the first. Since the temperature rise rate is set to be longer as the temperature rises when the temperature rises to the predetermined temperature T1, it can be reliably detected that the temperature of the fuel cell stack 2 has increased following the generated current. Even when the temperature of No. 2 rises to the first predetermined temperature T1 and the fuel cell stack 2 has a lot of low temperature parts and the temperature is partially low and freezing tends to remain, the temperature is surely low or frozen. The end timing of the warm-up power generation without a part can be determined.

  In the fuel cell system of the present embodiment, the determination time for determining whether or not the temperature of the fuel cell stack 2 has increased following the generated current is used, and the temperature of the fuel cell stack 2 is the first predetermined temperature. Since the setting is made such that the longer it takes to rise to T1, the temperature of the fuel cell stack 2 can be reliably detected to follow the generated current, and the temperature of the fuel cell stack 2 can be detected. Even in a situation where the time to rise to the first predetermined temperature T1 is long and there are many low temperature parts in the fuel cell stack 2 and the temperature tends to remain partially freezing, it is ensured that there is no low temperature or no freezing part. The end timing of the mechanical power generation can be determined.

  Further, in the fuel cell system of the present embodiment, when the generated current for warm-up power generation is increased, the increase in generated current is reduced as the temperature of the fuel cell stack 2 is lower. The occurrence of a drop can be prevented.

  Although the fuel cell system of the present invention has been described based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each part is replaced with an arbitrary configuration having the same function. Can do.

1 is a block diagram showing a configuration of a fuel cell system according to Example 1. FIG. 3 is a flowchart showing a control process for warm-up power generation at the time of startup by the fuel cell system according to Embodiment 1; 3 is a flowchart showing a warm-up power generation end determination process by the fuel cell system according to Embodiment 1; It is a figure for demonstrating the time change of the coolant temperature and power generation current of the fuel cell system which concerns on Example 1. FIG. 3 is a flowchart showing temperature increase acceleration processing by the fuel cell system according to Embodiment 1; It is a figure which shows the relationship between the cooling fluid temperature of a fuel cell stack and the cooling water flow volume in the temperature rise acceleration process of the fuel cell system which concerns on Example 1. FIG. It is a figure for demonstrating the change of the pressure in the temperature rise acceleration process of the fuel cell system which concerns on Example 1. FIG. 6 is a flowchart showing a threshold correction process in a warm-up power generation end determination process of a fuel cell system according to Example 2; 12 is a flowchart illustrating a determination time setting process in a warm-up power generation end determination process of a fuel cell system according to Example 3; It is a figure which shows the relationship between the cooling water temperature of the fuel cell stack in the fuel cell system which concerns on Example 3, and the electric power generation electric current used for a follow-up determination.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell system 2 Fuel cell stack 3 Hydrogen supply tank 4 Hydrogen pressure regulator 5 Fuel circulation path 6 Hydrogen circulation pump 7 Purge valve 8 Air supply device 9 Air pressure regulating valve 10 Coolant pump 11 Coolant pump 12 Heat exchanger 13 Load device 14 Power converter 15 Secondary battery 16 Heater (heating means)
V1 to V3 Voltage sensors P1 and P2 Pressure sensors S1 to S11 Temperature sensors I1 and I2 Current sensors

Claims (17)

A fuel cell system comprising a fuel cell stack for generating electric power by reacting a fuel gas and an oxidant gas by an electrochemical reaction, and performing warm-up power generation of the fuel cell stack at startup,
An end of the warm-up power generation is determined based on a change in the temperature rise rate of the fuel cell stack.   2. The fuel according to claim 1, wherein the warm-up power generation is continued when the temperature of the fuel cell stack is equal to or higher than a first predetermined temperature and the temperature increase rate of the fuel cell stack is smaller than a predetermined threshold. Battery system.   2. The generated current by the warm-up power generation is not increased when the temperature of the fuel cell stack is equal to or higher than a first predetermined temperature and the temperature increase rate of the fuel cell stack is smaller than a predetermined threshold value. Or the fuel cell system in any one of Claim 2.   After detecting that the temperature of the fuel cell stack is equal to or higher than a first predetermined temperature and the temperature increase rate of the fuel cell stack is smaller than a predetermined threshold, the temperature increase rate of the fuel cell stack is higher than the predetermined threshold. The fuel cell system according to any one of claims 1 to 3, wherein the warm-up power generation is terminated when the value becomes larger.   The predetermined threshold value of the temperature increase rate is set to a temperature increase rate when the temperature of the fuel cell stack rises to the first predetermined temperature. 5. 2. The fuel cell system according to item 1.   6. The predetermined threshold value of the temperature increase rate is corrected to a larger value as the temperature increase rate when the temperature of the fuel cell stack increases to the first predetermined temperature becomes smaller. Fuel cell system.   6. The fuel cell system according to claim 5, wherein the predetermined threshold value of the temperature increase rate is corrected to a larger value as the time during which the temperature of the fuel cell stack rises to the first predetermined temperature becomes longer.   6. The fuel cell system according to claim 5, wherein when the temperature increase acceleration process for accelerating the temperature increase of the fuel cell stack is performed, the predetermined threshold value of the temperature increase rate is corrected to a larger value.   When the temperature of the fuel cell stack rises above a second predetermined temperature that is higher than the first predetermined temperature, the generated current of the warm-up power generation is increased, and the temperature of the fuel cell stack follows accordingly. The fuel cell system according to any one of claims 1 to 8, wherein the warm-up power generation is terminated when the temperature rises.   The determination time for determining whether or not the temperature of the fuel cell stack has increased following the generated current is such that the temperature increase rate when the temperature of the fuel cell stack increases to the first predetermined temperature is small. The fuel cell system according to claim 9, wherein the fuel cell system is set to be longer.   The determination time for determining whether or not the temperature of the fuel cell stack has increased following the generated current is longer as the time when the temperature of the fuel cell stack is increased to the first predetermined temperature is longer. The fuel cell system according to claim 9, wherein the fuel cell system is set to be   The fuel according to any one of claims 9 to 11, wherein when the generated current of the warm-up power generation is increased, the increase in the generated current is reduced as the temperature of the fuel cell stack is lower. Battery system.   The temperature of the fuel cell stack is one of a cell temperature of the fuel cell stack, a coolant outlet temperature of the fuel cell stack, an oxidant gas outlet temperature of the fuel cell stack, and a fuel gas outlet temperature of the fuel cell stack. The fuel cell system according to any one of claims 1 to 12, wherein the determination is made using temperature.   14. The fuel cell stack according to claim 1, wherein when the warm-up power generation is continued, the flow rate of the coolant of the fuel cell stack is reduced or intermittently. Fuel cell system.   The fuel cell system according to claim 14, wherein the flow rate of the coolant is increased as the temperature of the fuel cell stack rises.   When the warm-up power generation is continued, the power of the oxidant gas supply means for supplying the oxidant gas to the fuel cell stack is reduced, and the energization amount of the heating means for heating the fuel cell system is increased. The fuel cell system according to any one of claims 1 to 15, wherein   The oxidant gas supplied to the fuel cell stack and the pressure of the fuel gas are increased or decreased at a predetermined interval when the warm-up power generation is continued. The fuel cell system according to item.

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