JP5262183B2 - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To promote the warmup of a fuel cell at the time of low-temperature startup by supplying an appropriate volume of oxidizing gas at the startup. <P>SOLUTION: In the case of carrying out the startup processing of a fuel cell equipped with one or two or more power-generating parts generating power by the use of fuel and oxidizing gas at starting from a standstill state, a startup target current as a target current at the startup is preset, and then, a startup oxidizing gas volume in accordance with the startup target current is set. Furthermore, after the startup processing is finished, it is determined whether or not a part of the power-generating parts is in a frozen state. If the state is determined, an oxidizing gas volume supplied to the fuel cell is set at a frozen-state oxidizing gas volume smaller than the startup oxidizing gas volume. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a fuel cell system. More specifically, it is suitable as a system for performing control at the time of starting a fuel cell that generates power using fuel and oxidizing gas.

  Conventionally, for example, Japanese Patent Application Laid-Open No. 2005-71626 discloses a fuel cell system having an electric circuit for adjusting a current or voltage taken out from the fuel cell. In this system, when the fuel cell is started below the freezing point, the extraction power is set so that the extraction current is maximized within a range in which the cell is not deteriorated regardless of the required load. According to this prior art, since the self-heating of the fuel cell is promoted by maximizing the extraction current, the warm-up time of the fuel cell can be shortened, and even when the fuel cell is started below freezing point The product water generated by the power generation can be prevented from freezing.

Japanese Patent Laying-Open No. 2005-71626

  However, even when the fuel cell is stopped by performing a predetermined drying process, some moisture may remain on the catalyst electrode. When the fuel cell is started in a low temperature environment after moisture remains on the catalyst electrode, the remaining moisture on the catalyst electrode of the fuel cell freezes and the flow path of the reactant (fuel or oxidizing gas) is blocked It may become a state. When the flow path of the reactant of the catalyst electrode is blocked, the area that functions as the reaction point of the catalyst electrode is reduced, so even if an amount of the reactant corresponding to the target output is supplied, the output corresponding to the reactant is output. It is possible that the situation will be impossible.

  In such a case, even if the extraction current is set to the maximum current as in the above-described prior art, the maximum current cannot be output, and the effect of promoting the warm-up at the start of the fuel cell by promoting self-heating is sufficiently obtained. It may be impossible to obtain. In such a case, since the area functioning as the reaction point of the catalyst electrode is reduced, a large amount of reactants that are not used for actual power generation are supplied to the fuel cell. The electric power necessary for driving such devices is wasted.

  The present invention has been made in order to solve the above-described problems. When the fuel cell is started, an appropriate amount of oxidizing gas is supplied even when the fuel cell is partially frozen. An object of the present invention is to provide an improved fuel cell system that can promote warm-up of the fuel cell.

In order to achieve the above object, a first invention is a fuel cell system,
A fuel cell having one or more power generation units that generate power using fuel and oxidizing gas;
A startup target current setting means for setting a startup target current, which is a target current at startup, when performing startup processing when starting the fuel cell from a stopped state;
A low temperature start detection means for detecting a low temperature start in which the fuel cell is started at a low temperature lower than a reference temperature; and
When performing the start-up process , if the low-temperature start-up is detected, the start- up target that is set when the fuel cell is started at a temperature higher than the reference temperature is set to the amount of oxidizing gas supplied to the fuel cell A starting oxidizing gas amount control means for controlling the starting oxidizing gas amount to be a gas amount smaller than the starting oxidizing gas amount according to the current;
The output current of the fuel cell detected after the start- up process is started and the amount of oxidizing gas supplied to the fuel cell is found to have reached the amount of oxidizing gas at start-up, and the start-up target A frozen state detecting means for detecting a frozen state in which a part of the power generation unit is frozen according to a difference with the current ,
If the previous SL freezing condition is detected, the amount of the oxidizing gas supplied to the fuel cell than said startup oxidizing gas amount, and freezing upon oxidation gas amount control means for controlling the fewer freezing the oxidation gas amount,
It is characterized by providing.

According to a second invention, in the first invention,
The starting oxidizing gas amount control means includes :
When the fuel cell is started at a temperature lower than the reference temperature, it is expressed as a ratio of an actually supplied oxidizing gas flow rate to an oxidizing gas flow rate necessary for obtaining a target current output in the starting process. The stoichiometric ratio of the oxidizing gas to be a starting stoichiometric ratio smaller than the stoichiometric ratio of the oxygen gas when starting at a temperature higher than the reference temperature ,
The freezing oxidizing gas amount control means includes :
If the frozen state is detected in the activation process, the stoichiometric ratio of the oxidizing gas, characterized by a small freezing stoichiometric ratio than the startup stoichiometric ratio.

According to a third invention, in the first or second invention,
The frozen state is detected when a difference between the output current and the target current at start-up is larger than a first reference difference.

In a fourth aspect based on the third aspect , the frozen state detecting means detects the frozen state when a difference between the output current and the startup target current is smaller than a second reference difference . The state is released .

According to a fifth invention, in any one of the first to fourth inventions,
An activation process end detection means for detecting the end of the activation process;
In a state where the frozen state is detected , when the end of the activation process is detected, a frozen state display means for displaying that the frozen state is present;
Is further provided.

  According to the first aspect of the present invention, when performing the start-up process of the fuel cell, the target current at start-up is set, the start-up oxidizing gas amount corresponding to this is set, and a part of the power generation unit of the fuel cell is frozen. While it is determined that the frozen state has been achieved, the amount of oxidizing gas supplied to the fuel cell is set to a freezing oxidizing gas amount that is smaller than the starting oxidizing gas amount. Thereby, when a part of the power generation unit is frozen at the time of startup and the area of the reaction point that functions as a catalyst is in a reduced state, the supply amount of the oxidizing gas can be reduced accordingly. . As a result, an appropriate amount of oxidizing gas can be supplied corresponding to the state of the catalyst in the power generation unit, and wasteful consumption of electric power can be suppressed, for example, when electric power is required for a supply system that supplies the oxidizing gas. it can.

  According to the second invention, the stoichiometric ratio of the oxidizing gas is set to the startup stoichiometric ratio corresponding to the startup target current, and the freezing is smaller than the startup stoichiometric ratio while the fuel cell is determined to be in the frozen state. Set to hour stoichiometric ratio. Then, the oxidizing gas amount is determined according to the set stoichiometric ratio. Thereby, even when the catalyst area of the power generation unit is in a reduced state due to the frozen state, an appropriate amount of oxidizing gas can be supplied in accordance with the state of the catalyst.

Further, according to the first invention, when the fuel cell is started at a low temperature lower than the reference temperature, the amount of the oxidizing gas is oxidized when the fuel cell is started at a temperature higher than the reference temperature. Set less than the amount of gas. As a result, the power loss of the fuel cell can be increased, the heat generation of the power generation unit at the start-up can be promoted, and the fuel cell can be warmed up in a shorter time even when starting at a low temperature. .

According to the second invention, when the fuel cell is started at a low temperature lower than the reference temperature, the oxidizing gas amount or the stoichiometric ratio at the start of the oxidizing gas is set at a temperature higher than the reference temperature. It is set to a value smaller than the stoichiometric ratio of the oxidizing gas when it is started. Thereby, the power loss of the fuel cell can be increased by reducing the amount of supplied oxidizing gas, and the heat generation of the power generation unit at the start-up can be promoted. As a result, even when starting at a low temperature, the fuel cell can be warmed up in a shorter time.

By the way, when it is in the said frozen state, it is possible that the supply channel of the reactant (fuel or oxidizing gas) to the power generation unit is blocked and the catalyst area of the power generation unit is in a reduced state. For this reason, even if the amount of oxidizing gas set in accordance with the target current is supplied, the actual current may not reach the vicinity of the target current. That is, it is considered that the difference between the actually detected current and the target current is large in the frozen state. Therefore, according to the first invention, the frozen state is determined by comparing the actual current with the target current at startup, and according to the third invention, the difference between the detected current value and the target current at startup is obtained. Thus, the frozen state is determined by determining whether or not the difference is larger than the first reference difference which is a determination criterion. By doing so, the frozen state can be reliably determined, and supply of excess oxidizing gas can be suppressed.

According to the fourth aspect of the present invention, the difference between the detected current value and the starting target current is obtained, and it is determined whether or not the difference is smaller than the second reference difference that is the determination reference, thereby determining the frozen state. Is released. In other words, by detecting that the actual current has approached the target current at start-up, the water that has been frozen by the warm-up of the fuel cell has been thawed and the catalyst area that functions as a reaction point has increased to a normal state. Can be reliably detected. Thereby, it is possible to return to an appropriate oxidizing gas supply amount according to the catalyst area that functions as a reaction point of the power generation unit, and it is possible to perform the startup process more reliably.

According to the fifth aspect of the present invention, it is possible to display that the fuel cell is in a frozen state when the startup process of the fuel cell is completed while the frozen state is determined. Thus, it is possible to reliably warn and immediately recognize that the fuel cell is currently in a frozen state and that the target output may not be generated even after the start-up process of the fuel cell is completed.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment.
FIG. 1 is a schematic diagram for illustrating a fuel cell system according to Embodiment 1 of the present invention. The fuel cell system can be used by being mounted on a moving body such as a vehicle. The fuel cell system in FIG. 1 includes a fuel cell 2. The fuel cell 2 includes a plurality of stacked cells 4. Each cell 4 has an electrolyte membrane and a membrane-electrode assembly (power generation unit) including an anode electrode and a cathode electrode which are a pair of catalyst electrodes arranged on both sides of the electrolyte membrane. Hydrogen as a fuel is supplied to the anode electrode of the fuel cell 2 and air as an oxidizing gas is supplied to the cathode electrode by a reaction gas supply / discharge system described later. The membrane-electrode assembly is supplied with hydrogen and air to cause an electrochemical reaction to generate electric power.

  A hydrogen supply path 12 is connected to a hydrogen inlet formed in the fuel cell 2. The upstream end of the hydrogen supply path 12 is connected to a high-pressure hydrogen tank 14 in which high-pressure hydrogen is stored. A valve 16 and a pressure regulating valve 18 are installed downstream of the high-pressure hydrogen tank 14 in the hydrogen supply path 12. A hydrogen circulation path 20 is connected to the hydrogen discharge port of the fuel cell 2. The hydrogen circulation path 20 joins the hydrogen supply path 12 at the other end. A gas-liquid separator 22 is installed in the hydrogen circulation path 20. A pump 24 is installed in the hydrogen circulation path 20 between the gas-liquid separator 22 and the junction of the hydrogen supply path 12. A discharge pipe 26 is connected to the gas-liquid separator 22, and a valve 28 is installed in the discharge pipe 26.

  On the other hand, the downstream end of the air supply path 30 is connected to the air inlet of the fuel cell 2. The upstream side of the air supply path 30 is connected to an air compressor 32. A humidifier 34 is installed in the air supply path 30 downstream of the air compressor 32. The air taken in from the outside by the air compressor 32 passes through the humidifier 34, passes through the air supply path 30, and is supplied from the air introduction port of the fuel cell 2 to the air flow path on the cathode electrode side of each cell 4. The

  An air discharge path 36 is connected to the air discharge port of the fuel cell 2. The air discharge path 36 is connected to the humidifier 34. The air off gas discharged from the air discharge port is guided to the humidifier 36. A discharge path 38 is connected to the humidifier 36. A discharge pipe 26 for discharging moisture and hydrogen off-gas from the gas-liquid separator 22 to the outside is joined to the discharge pipe 38. Moisture and hydrogen off-gas discharged through the discharge pipe 26 are diluted by dilution air (not shown) and discharged to the outside together with the air discharged together with the air off-gas.

  The fuel cell 2 is connected to a cooling water circulation path 40 for circulating cooling water into the fuel cell 2. In the middle of the cooling water circulation path 40, a water temperature sensor 42 for detecting the cooling water temperature, a radiator 44 for cooling the cooling water, and a pump 46 for supplying the cooled cooling water to each cell 4 of the fuel cell 2 again are installed. ing.

  This fuel cell system includes a control device 50. The control device 50 receives the output of various sensors such as the water temperature sensor 42 and the cell monitor 52 that detects the cell voltage and current, detects information related to the operating state of the fuel cell 2, and according to the operating state of the fuel cell 2. For example, the operation of the fuel cell 2 is controlled by issuing a control signal to the valves 16, 18, 28, the compressor 32, and the like.

  By the way, in order to improve the power generation performance of the fuel cell 2, it is necessary to warm up to a predetermined operating temperature at an earlier stage after the fuel cell 2 is started. In particular, when the fuel cell 2 is started in an environment below the freezing point and below a low temperature (hereinafter referred to as “low temperature start”), the temperature of the fuel cell 2 may be increased rapidly in order to start normal operation at an early stage. Required.

  In this fuel cell system, when the activation of the fuel cell 2 is a low temperature activation, an activation process is performed in which the air to be supplied to the fuel cell 2 is reduced to a state smaller than that during normal activation. In general, in the normal operation of the fuel cell 2, the ratio of the air flow rate supplied to the fuel cell to the theoretical air flow rate necessary for obtaining the target output (hereinafter referred to as “stoichiometric ratio”) is greater than 1.0. It is set to be large. That is, more air than theoretically required for power generation is supplied, thereby maintaining high power generation efficiency of the fuel cell.

  On the other hand, the stoichiometric ratio is set to a value smaller than the stoichiometric ratio during normal operation in order to perform quick warm-up by increasing heat loss when the fuel cell is started at a low temperature. That is, the flow rate of air supplied to the cathode electrode is reduced during low temperature startup. As a result, power loss (heat loss) can be increased, and the amount of generated heat can be increased positively (hereinafter referred to as “high heat generation operation”).

  The specific value of the start-up stoichiometric ratio ST1 when performing a high heat generation operation is obtained by experiment, and at the time of start-up that defines the relationship between the start-up target current Iref, the temperature T of the fuel cell 2, and the start-up stoichiometric ratio ST1 The map 1 is stored in the control device 50 in advance. At low temperature startup, the startup stoichiometric ratio ST1 is set according to the set startup target current Iref and the water temperature T.

  By the way, even when the drying process is performed so as to remove the moisture remaining on the anode electrode and the cathode electrode at the time of stoppage, some moisture may remain on the anode electrode and the cathode electrode of each cell 4. is there. In this state, when the fuel cell 2 is exposed to a low temperature below freezing and started at a low temperature, the residual moisture is frozen at the reaction point of the catalyst at the anode and cathode, and the gas flow to the reaction point by the frozen moisture. The road may be blocked. As a result, when the fuel cell 2 is activated in a low temperature environment (low temperature activation), the state of the catalyst functioning as a reaction point of the anode electrode or the cathode electrode is reduced (hereinafter referred to as “catalyst area reduced state”). Sometimes).

  Thus, when the catalyst area is reduced due to the blockage of the flow path due to freezing, the air stoichiometric ratio is set to a startup stoichiometric ratio smaller than the stoichiometric ratio during normal operation, and the flow rate of supplied air is reduced. As a result, even if warming up due to an increase in power loss is aimed at, power loss due to air shortage does not occur, and the current cannot be increased to the target current Iref. As a result, it is conceivable that the high heat generation operation cannot be executed efficiently and the warm-up of the fuel cell 2 cannot be promoted.

  Further, when the catalyst area is reduced as described above, air that is not actually used for power generation is wasted. Therefore, the unused air supply and the electric power required for driving the air compressor 32 are wasted. Therefore, it is desired to improve the power generation performance while suppressing such unnecessary power consumption.

  Therefore, in this embodiment, if the target current is not reached even when the air flow rate reaches the air amount corresponding to the set stoichiometric ratio, it is determined that the catalyst area reduction state is caused by the frozen state. In this case, the air stoichiometric ratio is reset to a freezing stoichiometric ratio ST2 that is smaller than the starting stoichiometric ratio ST1 at the time of low temperature starting, and the supplied air flow rate is further reduced.

  More specifically, when the detected current Imes has not risen to the target current Iref, it is determined that the frozen state (that is, the catalyst area is reduced). In this case, the air stoichiometric ratio is switched to a stoichiometric ratio ST2 at the time of freezing that is smaller than the stoichiometric ratio ST1 at the time of starting at a low temperature. This freezing stoichiometric ratio ST2 corresponds to the target current Iref and the water temperature T of the fuel cell 2 in the same manner as the starting stoichiometric ratio ST1, and the value of the freezing stoichiometric ratio ST2, the target current Iref and the temperature T This relationship is obtained in advance by experiments or the like and stored in the control device 50 as the freezing map 2. If it is determined that the vehicle is in a frozen state, the map is switched from the startup map 1 at low temperature startup to the freezing map 2, and the air flow rate is determined according to the stoichiometric ratio ST2 set based on the freezing map 2.

  Thus, it is possible to supply an air flow rate at which high heat generation operation can be performed according to the reduced catalyst area, that is, the catalyst area actually functioning as the reaction point of the catalyst. Therefore, even when the catalyst area is reduced due to the frozen state, it is possible to effectively increase the heat generation amount and promote the warm-up of the fuel cell 2.

  In this way, when the freezing stoichiometric ratio ST2 is set, when the air flow rate is limited and the warm-up of the fuel cell 2 proceeds and the actual current increases to a value close to the target current Iref, the frozen state is lost. It is presumed that the catalyst area functioning as a reaction point has returned to the normal area. Accordingly, the air stoichiometric ratio is reset to the startup stoichiometric ratio ST1, and the air flow rate is the air flow rate at the normal low temperature startup.

  Further, it may be determined that the start-up process has been completed before the resetting of the stoichiometric ratio. In this case, it is considered that a part of the catalyst area is reduced due to freezing even after the start-up process is completed. For this reason, a warning lighting process is performed to warn that the requested power generation amount cannot be output.

  In this case, the monitoring of the change in the output P of the fuel cell 2 and the change in the temperature T of the fuel cell 2 is continued, and it is confirmed that the output P has reached the reference power P0 or the temperature T is the reference. When it is confirmed that the temperature T0 has been reached, the warning is turned off.

  2 and 3 are flowcharts for explaining specific control routines executed by the system in the embodiment of the present invention. The routine of FIG. 2 is a routine that is repeated at regular intervals during the startup process of the fuel cell 2. In the routine of FIG. 2, first, when there is an instruction to start the fuel cell, it is first determined whether or not the start of the fuel cell 2 is a low temperature start (S100). Specifically, here, the reference temperature for determination is below freezing point, and whether or not it is cold start is determined based on whether or not the detected outside air temperature is below freezing point. If it is not recognized that the start-up is at a low temperature, the routine ends.

  Next, it is determined whether or not the flag F1 is OFF (S102). When the flag F1 is ON, it indicates that it is determined that the catalyst area has been reduced, and ON / OFF is controlled by a process described later.

  On the other hand, when it is recognized in step S100 that the engine is cold start and in step S102, it is recognized that the flag F1 is OFF, the target current Iref at the start is set to the current during the high heat generation operation ( S104). The target current Iref at the time of low-temperature startup is set to a high value so as to accelerate the warm-up of the fuel cell 2. The target current Iref that promotes warm-up at the time of start-up is a current that can be output at a minimum voltage in the IV performance of the fuel cell, and is determined according to the temperature of the fuel cell. The target current Iref is obtained in advance by experiments or the like and stored in the control device 50. Next, the temperature T of the cooling water for the fuel cell is detected (S106). The temperature T is obtained by taking the output of the water temperature sensor 42 into the control device 50.

  Next, an air stoichiometric ratio ST1 is set according to the target current Iref and the water temperature T (S108). The start-up stoichiometric ratio ST1 set here is the amount of air necessary to output the target current Iref at the current temperature T of the fuel cell 2, and is thus reduced to perform a high heat generation operation. The air flow rate is determined and is smaller than the air stoichiometric ratio during normal operation of the fuel cell 2. As described above, the relationship among the target current Iref, the water temperature T, and the startup stoichiometric ratio ST1 is obtained in advance by experiments or the like, and is stored in the control device 50 as the startup map 1. Here, the startup stoichiometric ratio ST1 corresponding to the target current Iref and the water temperature T is calculated according to the startup map 1. That is, the target current Iref set in step S104 is set to a start-up stoichiometric ratio ST1 smaller than that during normal operation, so that the flow rate of air supplied to each cell 4 decreases, and the cell resistance increases. It is a large current realized by By increasing the power loss of the fuel cell 2 in this way, heat generation is promoted, and warm-up of the fuel cell 2 is promoted.

Next, the supplied air flow rate Q is calculated according to the startup stoichiometric ratio ST1 and the target current Iref (S110). Specifically, the air flow rate Q is calculated by the following equation (1).
Air flow rate Q = a x target current Iref x stoichiometric ratio ST1 (1)

Here, a is a coefficient, which is the reciprocal of the Faraday constant divided by the O ₂ charge and the oxygen ratio in the air. That is, when the Faraday constant F = 96500, O ₂ charge = 4, and the oxygen ratio in the air = 0.21, the coefficient a is expressed by the following equation (2).
a = (1/96500) /4/0.21 (2)

  Next, the air flow rate is controlled to the set air flow rate Q (S112). Here, a control signal is transmitted from the control device 50 to the air compressor 32 to control the air flow rate. Next, the actual current Imes of the fuel cell 2 is detected (S114). The actual current Imes of the fuel cell 2 is detected based on the output of the cell monitor 52. Next, the current difference ΔI is calculated (S116). The current difference ΔI is a value obtained by subtracting the actual current Imes from the target current Iref.

  Next, it is determined whether or not the ratio between the air flow rate Q and the actual current Imes is greater than a reference value (S118). When the ratio between the air flow rate Q and the actual current Imes is larger than the reference value, it is determined that the air flow rate Q has increased to a flow rate corresponding to the set stoichiometric ratio. Therefore, when it is not recognized that the ratio of the air flow rate Q and the actual current Imes is larger than the reference value, the process returns to step S112, and the detection of the actual current Imes and the current difference ΔI is repeatedly performed, so that the air flow rate Q becomes the current difference ΔI. Based on the feedback control (S120), the air flow rate is increased to the set air flow rate Q.

  On the other hand, if it is determined in step S118 that the ratio between the air flow rate Q and the actual current Imes is greater than the reference value, it is next determined whether or not the current difference ΔI is equal to or less than the first reference difference I1 (S122). . When it is recognized that the current difference ΔI ≦ the first reference difference I1, the actual current Imes is close to the set target current Iref, and the actual current Imes corresponding to the air flow rate Q is output. Recognize.

  Accordingly, when it is recognized in step S122 that ΔI ≦ first reference difference I1, this routine is terminated. Thereafter, the above process is repeatedly executed at regular intervals until the completion of the activation process is recognized.

  On the other hand, if the establishment of the current difference ΔI ≦ the first reference difference is not recognized in step S122, the required target is obtained even though the air flow rate Q has increased to the flow rate corresponding to the set stoichiometric ratio ST1. It can be seen that the output of the current Iref is not obtained. That is, in this case, it is estimated that the catalyst area reduction state due to freezing occurs in the fuel cell 2. Therefore, if the establishment of the current difference ΔI ≦ the first reference difference is not recognized in step S122, or the flag F1 is not recognized to be OFF in step S102 (that is, it is determined that the catalyst area is reduced). In this case, the air flow rate is set by the freezing map 2 set to be smaller than the startup stoichiometric ratio ST1.

  Specifically, first, the temperature T of the fuel cell 2 is detected (S124). Next, the stoichiometric ratio is reset to the freezing stoichiometric ratio ST2 in accordance with the detected temperature T and target current Iref (S126). The freezing stoichiometric ratio ST2 is set as a value corresponding to the temperature T and the target current Iref according to the freezing time map 2 stored in the control device 50 in advance.

  Next, the air flow rate Q is recalculated according to the freezing stoichiometric ratio ST2 (S128). The calculation formula for air flow rate Q is the same as equation (1) except that the value of stoichiometric ratio ST2 at the time of freezing is used instead of the stoichiometric ratio ST1 at the start of equation (1) above, and a × target current Iref X Calculated from stoichiometric ratio ST2. Next, the reset air flow rate Q is controlled (S130).

  Next, the actual current Imes is detected (S132), and a current difference ΔI that is a value obtained by subtracting the actual current Imes from the target current Iref is obtained (S134). Next, it is determined whether or not the current difference ΔI is smaller than the second reference difference I2 (S136). The second reference difference I2 is larger than the first reference difference I1.

  If it is determined in step S136 that the current difference ΔI <the second reference difference I2 is established, it is determined that the actual current Imes has reached a value close to the target current Iref to some extent. That is, it can be considered that the frozen portion of the catalyst surface is reduced and the anode and cathode as a whole function as a catalyst. In this case, the flag F1 is turned off (S138), and the current process ends. Thereafter, this routine is periodically executed again until the startup process is completed. In the repetition of this routine, when returning from the state of air flow rate control with the stoichiometric ratio ST2 during freezing to the process with the start-time stoichiometric ratio ST1 in steps S106 to S122, the set air flow rate does not change abruptly. In addition, so-called annealing control may be executed.

  On the other hand, if it is not recognized that the actual current difference ΔI <the second reference difference I2 is established, the flag F1 is turned on (S140), and the current process ends. As a result, when this activation process routine is repeated while the flag F1 is ON, it is determined that the catalyst area is in a reduced state, and the air flow rate is set to the freezing stoichiometric ratio ST2.

  The routine of FIG. 3 is a routine that is repeatedly executed at regular intervals after the start-up process of the fuel cell 2 is started. In the routine of FIG. 3, when the completion of the activation process is detected (S150), it is next determined whether or not the flag F1 is ON (S152). If it is not recognized that the flag F1 is ON, the current process ends.

  On the other hand, if it is determined in step S152 that the flag F1 is ON, it is determined that the start-up process has been completed while the catalyst area is reduced. Therefore, next, a warning indicating that the catalyst area has been reduced due to freezing of the fuel cell 2 is turned on (S154). Thereafter, the temperature T and the output P of the fuel cell 2 are detected (S156, S158). Next, it is determined whether the temperature T is higher than the reference temperature T0 or the output P is higher than the reference output P0 (S160).

  In step S160, if none of the conditions of temperature T> reference temperature T0 and output P> reference output P0 is found, it is determined that the catalyst area is decreasing. In this case, the current process ends.

  On the other hand, if it is determined in step S160 that either temperature T> reference temperature T0 or output P> reference output P0 is satisfied, the warning is turned off (S162). Thereafter, the flag F1 indicating the catalyst area reduction state is turned OFF (S164), and the current process is terminated.

  As described above, according to this embodiment, when the catalyst area reduction state is determined by freezing, the supplied air flow rate Q can be further reduced by switching the stoichiometric ratio to the freezing map 2. it can. As a result, the supplied air flow rate can be reduced with respect to the catalyst area that can function as a reaction point, and high heat generation operation due to insufficient air flow rate can be realized. Therefore, even when the catalyst electrode is frozen and the catalyst area is reduced, warm-up can be promoted by self-heating of the fuel cell 2, and warm-up can be achieved in a short time. Further, by further reducing the air flow rate Q, the power consumption of an air compressor or the like can be reduced.

  In the embodiment, the case where the air flow rate is controlled according to the stoichiometric ratio maps 1 and 2 stored in advance has been described. However, the fuel cell system of the present invention is not limited to this. For example, a map that defines the relationship between the target current and the air amount or the air flow rate in each case of starting and freezing is prepared in advance. Based on this, the air amount or the air flow rate may be set directly. Further, as long as the air amount or the air flow rate is appropriately set as corresponding to each case of starting and freezing, it may be set by another method.

  Also, in the embodiment, when the air flow is set based on the start stoichiometric ratio ST1 at the time of start-up, high heat generation operation is performed, and the stoichiometric ratio is switched to a smaller freezing stoichiometric ratio ST2 when it is frozen. explained. However, the fuel cell system of the present invention is not limited to this, and can also be applied to the case where it is detected that the catalyst area is reduced when performing other start-up processes. Also in this case, the power consumption of the air compressor can be suppressed by switching from the normal air flow rate in the startup process to the air flow rate during freezing that is less than the flow rate. Further, the control of the air flow rate in this switching process may be executed by switching from a map of the stoichiometric ratio of the air flow rate at the normal time to a map of the stoichiometric ratio at the time of freezing. It may be one that uses a map to be set.

  In the embodiment, when the start-up process is completed with the catalyst area reduced, the warning light is turned on until the temperature of the fuel cell 2 rises to the reference temperature T0 or the output reaches the reference output P0. This has been explained (see FIG. 3). Accordingly, it is possible to call attention by notifying that the target output may not be obtained even after the start-up process of the fuel cell 2 is completed. However, the fuel cell system of the present invention is not necessarily limited to executing such a warning lighting process, and may perform another warning instead of the warning lighting. Further, the processing for notifying the reduction state of the catalyst area may not be performed.

  Further, in the above embodiment, when the number of each element, number, quantity, range, etc. is mentioned, it is mentioned unless otherwise specified or clearly specified in principle. The number is not limited. Further, the structures described in the embodiments, steps in the method, and the like are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

  In this embodiment, the “starting target current setting means” of the present invention is realized by executing step S104, and the “starting stoichiometric ratio setting means” is realized by executing step S108. By executing step S110, the “starting oxidizing gas amount setting means” is realized, and by executing step S114 or S132, “current detection means” is realized, and by executing step S122, “ "Frozen state determination means" is realized, "Stoichiometric ratio setting means during freezing" is realized by executing step S126, and "Oxidizing gas amount setting means during freezing" is realized by executing step S128, By executing step S150, the “start-up process end detection unit” is realized, and by executing step S154, the “freezing state display unit” is realized.

It is a schematic diagram for demonstrating the structure of the fuel cell system in Embodiment 1 of this invention. In Embodiment 1 of this invention, it is a flowchart for demonstrating the routine of control which a system performs. In Embodiment 1 of this invention, it is a flowchart for demonstrating the routine of control which a system performs.

Explanation of symbols

2 Fuel cell 4 cell 12 Hydrogen supply path 14 Hydrogen tank 16 Valve 18 Pressure regulating valve 20 Hydrogen circulation path 22 Gas-liquid separator 24 Pump 26 Discharge pipe 30 Air supply path 32 Air compressor 34 Humidifier 36 Air discharge path 38 Discharge pipe 40 Cooling water circulation path 42 Water temperature sensor 44 Radiator 46 Pump 50 Controller

Claims (5)

A fuel cell having one or more power generation units that generate power using fuel and oxidizing gas;
A startup target current setting means for setting a startup target current, which is a target current at startup, when performing startup processing when starting the fuel cell from a stopped state;
A low temperature start detection means for detecting a low temperature start in which the fuel cell is started at a low temperature lower than a reference temperature; and
When performing the start-up process , when the low-temperature start-up is detected, the start- up target that is set when the fuel cell is started at a temperature higher than the reference temperature is set to the amount of oxidizing gas supplied to the fuel cell. A starting oxidizing gas amount control means for controlling the starting oxidizing gas amount to be a gas amount smaller than the oxidizing gas amount according to the current;
The output current of the fuel cell detected after the start- up process is started and the amount of oxidizing gas supplied to the fuel cell is found to have reached the amount of oxidizing gas at start-up, and the start-up target A frozen state detecting means for detecting a frozen state in which a part of the power generation unit is frozen according to a difference with the current ,
If the frozen state has been detected, the amount of the oxidizing gas supplied to the fuel cell than said startup oxidizing gas amount, and freezing upon oxidation gas amount control means for controlling the fewer freezing the oxidation gas amount,
A fuel cell system comprising: The starting oxidizing gas amount control means includes :
When the fuel cell is started at a temperature lower than the reference temperature , the ratio of the actually supplied oxidizing gas flow rate to the theoretical value of the oxidizing gas flow rate necessary for obtaining the target current output in the starting process The stoichiometric ratio of the oxidant gas expressed as is a stoichiometric ratio at start-up that is smaller than the stoichiometric ratio of oxygen gas when starting at a temperature higher than the reference temperature ,
The freezing oxidizing gas amount control means includes:
2. The fuel cell system according to claim 1 , wherein when the frozen state is detected in the start-up process, the stoichiometric ratio of the oxidizing gas is set to a freeze-time stoichiometric ratio smaller than the start-up stoichiometric ratio. 3. The fuel cell system according to claim 1, wherein the frozen state is detected when a difference between the output current and the startup target current is larger than a first reference difference. 4. The frozen state detecting means releases the state in which the frozen state is detected when a difference between the output current and the target current at start-up is smaller than a second reference difference. The fuel cell system described in 1. An activation process end detection means for detecting the end of the activation process;
In a state where the frozen state is detected , when the end of the activation process is detected, a frozen state display means for displaying that the frozen state is present;
Further fuel cell system according to any one of claims 1 to 4, characterized in that it comprises a.

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