JP4881027B2 - Fuel cell system and method for starting fuel cell at low temperature - Google Patents

Description

  The present invention relates to a fuel cell system for normally starting a fuel cell at a temperature below the freezing point of water and a method for starting the fuel cell at a low temperature.

  For example, in a polymer electrolyte fuel cell, an electrolyte membrane / electrode structure in which an anode electrode (fuel electrode) and a cathode electrode (oxidant electrode) are provided on both sides of an electrolyte membrane made of a polymer ion exchange membrane is used as a separator. Is held between. This fuel cell is normally used as a fuel cell stack by alternately laminating a predetermined number of electrolyte membrane / electrode structures and separators.

  In this fuel cell, a fuel gas, for example, a hydrogen-containing gas, supplied to the anode electrode is ionized on the electrode catalyst and moves to the cathode side electrode side through the electrolyte membrane. Electrons generated during that time are taken out to an external circuit and used as direct current electric energy. Since the cathode electrode is supplied with an oxidant gas, for example, an oxygen-containing gas such as air, water reacts with the hydrogen ions, electrons, and oxygen at the cathode electrode.

  By the way, in this type of fuel cell, it is necessary to appropriately humidify the electrolyte membrane in order to maintain ionic conductivity. Furthermore, water produced by the reaction is present at the cathode electrode as described above. For this reason, when starting the fuel cell below freezing point (below the freezing temperature of water), the water in the fuel cell is likely to freeze, and it is pointed out that the electrochemical reaction is difficult to occur in the fuel cell. Yes.

  Therefore, for example, Patent Document 1 discloses that electrolyte membranes such as NAFION (registered trademark) manufactured by Dupont and experimental membranes manufactured by Dow (product number XUX 13204.10) have a temperature of −20 ° C. It is disclosed that it is sufficiently ionically conductive to allow an electrochemical reaction in the fuel cell.

  However, in the above-mentioned Patent Document 1, there is a problem that the hydrogen flow is not properly performed because the passage through which hydrogen flows is blocked by water or ice for about 4 minutes after the start of operation. Further, when connected to a load of 50 amperes after 4 minutes, an output of about 45 amperes is obtained, but the output current drops to about 15 amperes in about 8 seconds. This is because the produced water has been frozen.

  As described above, in Patent Document 1, although the fuel cell can be activated even when the temperature is below the freezing point, it is difficult to quickly shift to a desired power generation state by freezing ice or generated water. is there.

  A technique for solving this problem is proposed in Patent Document 2.

  In the technique proposed in Patent Document 2, the output current fluctuates depending on the gas pressures of both reaction gases under a specific voltage in an environment below the water point, as shown in FIG. 7, without inducing a voltage drop. Utilizing a causal relationship that can stably extract the maximum current.

  That is, the output current to be taken out increases in proportion to the increase in the gas pressure of both reaction gases.

  Furthermore, the technique proposed in Patent Document 2 has the relationship shown in FIG. 8 between the high and low gas pressures of both reaction gases and the limit load under a specific voltage in an environment below the freezing temperature of water. When the gas pressure is set higher than the gas pressure of the normal operation condition, a causal relationship is obtained that a characteristic that the limit load (maximum output current) that can be stably taken out is increased is obtained.

  That is, when the residual water is present in a frozen state in the electrode catalyst or the gas diffusion layer at the time of starting below freezing point, the electrode reaction area is reduced and the diffusibility of the reaction gas is significantly reduced. Therefore, at the time of starting below the freezing point, the conventional low temperature starting technology according to Patent Document 2 can reliably supply the reaction gas to the reaction site where the electrode reaction occurs by increasing the gas pressure of the reaction gas to be supplied. This is considered to improve the output current that can be taken out. Moreover, in the environment where the temperature is below freezing, increasing the gas pressure of the reaction gas has a greater effect of improving the power generation characteristics than increasing the gas pressure of the reaction gas in a normal operation state.

JP 2000-512068A (FIG. 6) Japanese Patent Laying-Open No. 2005-44795 (FIG. 4)

  By the way, when the fuel cell system is stopped below the freezing point, when the fuel cell system is started below the freezing point with the ignition switch turned on, the ignition of the fuel cell system is insufficient due to the convenience of the operator such as the driver. The switch may be turned off.

  Such an operation of a stop request after power generation for a short time below freezing (operation to stop the fuel cell system in a short time after power generation after starting below freezing, in other words, an operation to stop the fuel cell system immediately after starting slightly below freezing, When the system is stopped after a so-called “choking operation” is performed, the system is again restarted below freezing point (after power generation is stopped for a short time after freezing and then restarted, in other words, restarting after choking) Even when activated by the below-freezing point control technology according to the prior art described in the above-mentioned Patent Document 2, as shown in FIG. It has been found that the current / voltage characteristics at the time of starting below freezing at the time (when restarting after stopping after power generation for a short time below freezing = when restarting after peeling off) deteriorate.

  The present invention solves this type of problem, and makes it possible to improve the current / voltage characteristics at the time of restart after power generation after a short period of freezing and at the time of restart (after restart). And it aims at providing the starting method under low temperature of a fuel cell.

  The fuel cell system according to the present invention is a fuel cell system including a fuel cell that generates electric power using supplied reaction gas, and has the following features (1) to (3).

(1) Internal temperature detection means for detecting the internal temperature of the fuel cell, sub-freezing experience storage means for storing that the internal temperature has become below the freezing point during the stop period of the fuel cell, and the fuel cell When the temperature below sub-freezing temperature is stored in the sub-freezing experience storage means at the start-up time of the start-up, the pressure of the reaction gas is increased compared with the normal start-up, and the fuel cell First freezing point starting means for starting the fuel cell, warming state determining means for determining whether or not the warming of the fuel cell has been stopped in a sufficient state at the time of stopping after the starting by the first below freezing point means, When the fuel cell was restarted after it was determined that the temperature was not sufficient, it was stored in the sub-freezing experience storage means that the temperature was below the freezing point during the stop period before the restarting. When Serial below freezing by applying further increasing the pressure of the reaction gas by the first start means, characterized in that it comprises a sub-zero second activation means for activating the fuel cell.

  According to the invention having the feature (1), when the fuel cell is in a sub-freezing state or in a sub-freezing state at the time of starting the fuel cell, the reaction gas is compared with the normal starting by the sub-freezing first starting means. The fuel cell is started up by increasing the pressure of the fuel cell, and after the startup by the first below-freezing means, the fuel cell is restarted after the power generation is stopped in a state where the fuel cell is not sufficiently warmed up (choi When the fuel cell is in a sub-freezing state or when it is in a sub-freezing state at the time of restarting after ashing, the reaction gas pressure by the sub-freezing first starting unit is further increased by the sub-freezing second starting unit. Since the fuel cell is started up, the current / voltage characteristics at the time of restarting after stopping after power generation for a short time below freezing point (at the time of restarting after choking) can be improved.

(2) In the invention having the feature (1), in the fuel cell system according to claim 1, the flow rate of the reaction gas at the time of start-up by the first freezing means below freezing is the flow rate of the reaction gas at the time of normal start-up. The flow rate of the reaction gas when compared with the second starting means below the freezing point is increased in comparison with the flow rate increased by the first starting means below freezing point.

  According to the invention having the feature (2), the generated water on the cathode electrode side can be more reliably discharged to the outside of the fuel cell by the increased flow rate of the reaction gas. A decrease in performance can be suppressed.

(3) In the invention having the feature (1) or (2), the warm-up state determination means includes the internal temperature of the fuel cell at the start of power generation by the first below-freezing start means and the first below-freezing start means. And determining whether or not the fuel cell is sufficiently warmed up based on the internal temperature at the end of power generation after startup by the above.

  According to the invention having the feature (3), it is possible to automatically determine whether or not the activation by the below-freezing second activation means is necessary.

  In this case, basically, if the internal temperature at the start of power generation is close to the freezing point temperature, it is determined that the warm-up is sufficient even if the internal temperature at the end of power generation is relatively low. When the temperature is lower than the freezing point temperature, it can be determined that the warm-up is insufficient unless the internal temperature at the end of power generation is higher as the temperature is lower.

(4) A low temperature start-up method for a fuel cell according to the present invention is a low-temperature start-up method for a fuel cell that generates power using a supplied reaction gas, and an internal temperature detection step for detecting an internal temperature of the fuel cell; The below-freezing experience storage step for storing that the internal temperature has become below the freezing point during the stop period of the fuel cell, and at the start-up period of the fuel cell, the temperature has been below the freezing point during the stop period before the start-up. Is stored in the below-freezing experience storing step, the first starting step below the freezing point for starting the fuel cell by increasing the pressure of the reaction gas compared to the normal starting time, and after the starting by the first starting step below the freezing point A warm-up state determination step for determining whether or not the fuel cell has been warmed up in a sufficient state at the time of stopping, and a stop when it is determined that the warm-up is not in a sufficient state. When the fuel cell is restarted after being operated, when the temperature below the freezing point is stored in the subzero freezing experience storing step during the stop period before the restarting, the reaction by the first starting step below the freezing point is performed. And a second sub-freezing start step for starting the fuel cell by further increasing the pressure of the gas.

  According to the invention having the feature (4), when the fuel cell is in a sub-freezing state or when the fuel cell is in a sub-freezing state, the pressure of the reaction gas is reduced by the first sub-freezing start step as compared with the normal starting time. The fuel cell is started up by increasing the pressure, and after the start-up by the first freezing step below the freezing point, when the fuel cell is restarted after power generation is stopped due to insufficient warm-up of the fuel cell (after choking) When the fuel cell is in a sub-freezing state or at a sub-freezing state at the time of restart), the fuel cell is further increased in the first sub-freezing step by increasing the pressure of the reaction gas in the sub-freezing second starting step. Therefore, it is possible to improve the current / voltage characteristics at the time of power generation after a short period of freezing and restarting after stopping (when restarting after choking).

  According to the present invention, at the time of restart after being stopped after power generation for a short time below freezing point, the pressure of the reaction gas is increased compared to the pressure of the reaction gas at the time of the previous freezing point start. It is possible to improve the current / voltage characteristics at the time of restart after stop after time power generation (at the time of restart after choking).

  In addition, when the fuel cell system is restarted after power generation for a short time after freezing (after restarting after choking), the anode electrode side operating pressure is increased and the cathode electrode side operating pressure is increased compared to the conventional below-freezing start control. Since the flow rate of the cathode electrode side reaction gas is increased, the reaction gas necessary for power generation can be more distributed to the fuel cell.

  According to this invention, the starting performance at the time of starting below freezing improves.

  In this embodiment, the “stop after a short period of freezing power generation” described above is called “choking” as a general rule in consideration of easy understanding.

  FIG. 1 is a schematic configuration explanatory view of a fuel cell system 10 for carrying out a low temperature start-up method of a fuel cell according to an embodiment of the present invention.

  The fuel cell system 10 is mounted on a vehicle such as an automobile, for example, and includes a fuel cell (FC) 12.

  The fuel cell 12 is a fuel configured by holding an electrolyte membrane / electrode structure in which an anode electrode and a cathode electrode are arranged on both sides of a solid polymer electrolyte membrane, sandwiched between a pair of separators in which a reaction gas flow path is formed. It has a stack structure in which a plurality of battery cells are stacked and integrated.

  The fuel cell 12 includes a hydrogen supply port 20 for supplying a fuel gas, which is one of the reaction gases, here hydrogen gas, and exhaust gas containing unused hydrogen gas discharged from the fuel cell 12. In order to discharge the hydrogen discharge port 22, the oxidant gas, which is the other reaction gas to the fuel cell 12, here the air supply port 24 for supplying air, and air containing unused oxygen from the fuel cell 12. The air discharge port 26 is provided.

  The fuel cell system 10 includes a fuel gas supply system 28, an oxidant gas supply system 30, and a cooling medium supply system (not shown). The fuel gas supply system 28 includes a hydrogen supply flow path 32 that supplies hydrogen gas to the fuel cell 12, a hydrogen discharge flow path 33 that discharges exhaust gas containing unused hydrogen gas from the fuel cell 12, and a hydrogen supply flow for exhaust gas. And a hydrogen circulation passage 34 for returning to the middle of the passage 32 and supplying the fuel cell 12.

  The hydrogen supply flow path 32 includes a hydrogen tank 36 that stores high-pressure hydrogen, a shut-off valve 37 that shuts off or opens high-pressure hydrogen, and a pressure of hydrogen gas supplied from the hydrogen tank 36 through the shut-off valve 37 to reduce the pressure. A pressure regulating valve 38 to be adjusted, a decompressed hydrogen gas is supplied to the fuel cell 12, an ejector 40 for sucking exhaust gas from the hydrogen circulation passage 34 and returning it to the fuel cell 12, and a fuel cell 12 And a pressure gauge 42 for detecting the pressure of the hydrogen gas.

  The hydrogen discharge flow path 33 is provided with a hydrogen discharge valve 44 for discarding exhaust gas discharged from the fuel cell 12, while the hydrogen circulation flow path 34 has a flow rate of hydrogen gas supplied to the fuel cell 12. A hydrogen pump 46 is provided for control.

  The oxidant gas supply system 30 includes an air supply passage 48 for supplying air to the fuel cell 12, an air discharge passage 50 for discarding exhaust gas containing unused air discharged from the fuel cell 12, and the like. Is provided.

  The air supply channel 48 is provided with an air compressor 52 for compressing and supplying air, and a pressure gauge 54 for detecting the pressure of the air supplied to the fuel cell 12. In the air discharge channel 50, a thermometer (internal temperature detection means) 56 that detects the air outlet temperature of the fuel cell 12 as an internal temperature (also referred to as a power plant temperature) Ti [° C.] of the fuel cell 12, a fuel A back pressure adjustment valve 58 for controlling the pressure of the air supplied to the battery 12 is provided.

  The internal temperature Ti of the fuel cell 12 is not limited to the air outlet temperature, and any one of the hydrogen gas inlet temperature, the hydrogen gas outlet temperature, the housing temperature of the fuel cell 12, and the temperature of the cooling medium can be used. Two or more may be used. Further, the internal temperature Ti of the fuel cell 12 is measured at predetermined time intervals in both periods of power generation and stoppage of the fuel cell system 10 and is continuously stored in the memory 61 with the time as an address.

  Further, the fuel cell system 10 is provided with a CPU (control device) 60. The CPU 60 controls the opening / closing of the shutoff valve 37 and the hydrogen discharge valve 44 (command), adjusts the discharge air amount (flow rate) based on the rotation speed control (command) of the air compressor 52, and controls the rotation speed of the hydrogen pump 46. Adjustment of hydrogen gas flow based on (command), adjustment of hydrogen gas pressure by control (command) of valve opening of pressure regulating valve 38, oxidant gas by control (command) of valve opening of back pressure adjustment valve 58 All operations of the fuel cell system 10 are controlled including pressure adjustment and the like.

  In this embodiment, the CPU 60 executes a program stored in the memory 61 based on various inputs such as pressures from the pressure gauges 42 and 54, an internal temperature from the thermometer 56, and an on / off operation of an ignition switch (not shown). Thus, the above-described various valves 37, 38, 44, 58, the air compressor 52, and the hydrogen pump 46 are controlled to operate as functional means for realizing various functions.

  The memory 61 includes ROM, RAM, and EEPROM, and the EEPROM of the memory 61 functions as a below-freezing experience storage unit.

  In this embodiment, the CPU 60 functions as a part of or all of the first freezing point starting means, the warm-up state determining means (the power generation determining means for a short time after starting at low temperature), and the second starting means below the freezing point. It functions as a counter / timer).

  The operation of the fuel cell system 10 configured as described above will be described below with reference to the flowcharts shown in FIGS. 2 and 3 and the time chart for determining whether or not to experience experience shown in FIGS. 4A to 4E. 4A, FIG. 4B, and FIG. 4F show time charts when there is experience with choking, and FIGS. 4C, 4D, and 4E show time charts when there is no choking experience.

  In the time charts of FIGS. 4A to 4E, the fuel cell system 10 generates power at room temperature (ambient temperature is 0 [° C.] or higher) until time t0, and after the ignition switch is turned off from the on state at time t0. During the stop of the fuel cell system 10, so-called soak (during the stop period of the fuel cell 12), as shown at time t 1, it is detected in step S 1 that the ignition switch has changed from the off state to the on state. In step S2, it is determined whether the fuel cell 12 needs to be controlled below the freezing point.

  The determination in step S2 is performed whether or not the internal temperature Ti of the fuel cell 12 measured by the thermometer 56 is below the freezing point during the soak at the time t0 to the time t1 (Ti <0 ° C.). ), Or the internal temperature Ti at time t1 {referred to as the internal temperature Ts at the start of power generation (Ti = Ts). } Is a temperature below the freezing point (Ti = Ts <0 ° C.).

  When the determination in step S2 is not established, the below-freezing start control is not required, and normal start control is performed in step S3. The normal start-up control means that the operating pressure of the anode electrode in the fuel cell 12 is normally controlled by the pressure control of the hydrogen gas of the pressure regulating valve 38, and the flow rate of the hydrogen gas in the fuel cell 12 is normally controlled by the rotation speed control of the hydrogen pump 46. The air pressure of the cathode electrode in the fuel cell 12 by the back pressure control of the back pressure regulating valve 58 is normally, and the air flow rate of the cathode electrode in the fuel cell 12 by the rotation speed control of the air compressor 52 is normal. Controlled in a normal state.

  If it is determined in step S2 that the below-freezing start control is necessary, it is determined in step S4 whether or not the choice flag F is set (F = 1). The setting process of the choice flag F will be described later.

  When the chopping flag F is not set (F = 0), the first freezing point first-starting means performs the below-freezing point control at step S5, and on the other hand, when the chopping flag F is set. (F = 1) In step S6, the below freezing point freezing point control by the below freezing point second starting means is performed.

  When the initial start-up freezing point control or the restarting freezing-point control is performed and power generation is performed, in step S7, it is detected whether the ignition switch has been changed from the on state to the off state.

  When it is detected that the ignition switch has been turned off, a setting process for setting the flag F is performed in step S8.

  The setting process of the choice flag F in step S8 will be described with reference to the flowchart of FIG.

  The setting of the squeeze flag F indicates that the fuel cell 12 is sufficiently warmed up after the fuel cell system 10 (fuel cell 12) starts below freezing (starting by the first freezing point starting means or the second freezing point starting means). The determination is made based on whether or not the ignition switch is turned off later and the fuel cell system 10 (fuel cell 12) is stopped.

  This warm-up state determination is based on the preset choi based on the internal temperature Ti (the internal temperature Ts at the start of power generation and the internal temperature Te at the end of power generation) at the start of power generation and at the end of power generation in the below-freezing start control shown in FIG. This is done automatically with reference to the cliff experience determination map 100.

  The joying experience presence / absence determination map 100 is divided into a warm-up insufficient range (range in which it is determined that there is chopping experience) 102 and a warm-up sufficient range (range in which it is determined that there is no chopping experience) 104. The minimum temperature at which the fuel cell 12 can be activated (minimum temperature that can be activated) Tcold (approximately −20 ° C. to −10 ° C.) and the maximum internal temperature that performs the below-freezing activation control, that is, 0 ° C. The range of a triangle surrounded by three points of the minimum internal temperature Temin at the end of power generation (in this embodiment, Temin = 30 ° C.) for determining whether the warm-up is sufficient at the end of power generation at the temperature Tcold is the insufficient warm-up range 102 It is said.

  Therefore, the coordinate point (Ts,) between the internal temperature Ts at the start of power generation measured by the thermometer 56 (for example, time t1) and the internal temperature Te at the end of power generation (for example, time t2) at the end of power generation. It can be easily determined from Te) whether the warm-up has been sufficient.

  The threshold temperature Tth that separates the warm-up insufficient range 102 and the warm-up sufficient range 104 is determined by the following equation (1), which is a linear equation.

Tth = {(Temin−Tcold) / Tcold} × Ts + Tcold (1)

Tth: threshold temperature and function,
Temin: the minimum internal temperature at the end of power generation at which the warm-up is sufficient at the lowest startable temperature Tcold, a constant,
Ts: Internal temperature at the start of power generation and a variable (measured value).

  As the internal temperature Ts at the start of power generation is lower than the freezing point from the negative slope of the threshold temperature Tth of the determination experience presence / absence determination map 100, warm-up is sufficient if the internal temperature Te at the end of power generation is not high. It turns out that it is not judged.

  4A to 4E, the internal temperature Ti = Ts at the start of power generation at the time of starting below the freezing point (first time) at time t1 in FIGS. 4A to 4E is lower than 0 ° C. (Ti = Ts <0 ° C.), and is shown in FIGS. 4C and 4E. Thus, if the internal temperature Ti = Te at the end of power generation at the time of turning off the ignition switch at time t2 is a temperature that exceeds the threshold temperature Tth (Ti = Te> Tth), it is determined that the temperature is within the warm-up sufficient range 104. In step S8b, it is determined that the player has no experience of sticking, and in step S8d, the sticking flag F is reset (F ← 0).

  On the other hand, the internal temperature Ti = Ts at the start of power generation at the time of starting below the freezing point (initial time) at time t1 in FIGS. 4A to 4E is a temperature lower than 0 ° C. (Ti = Ts <0 ° C.), and FIG. 4A and FIG. As shown, when the internal temperature Ti = Te at the end of power generation when the ignition switch is turned off at the time t2 is a temperature lower than the threshold temperature Tth (Ti = Te <Tth), the warm-up insufficient range 102 Judgment is made and it is determined that there is experience in the selection in step S8b, and the selection flag F is set in step S8c (F ← 1).

  In this way, the choice flag F is set.

  Therefore, if the below-freezing start determination at step S2 is established and the squeeze flag F is not set at step S4 (F = 0), at the time of the first starting by the below-freezing first starting means at step S5. Below freezing point control is performed.

  In the sub-freezing start control (first freezing control) by the first sub-freezing starting means, the anode electrode pressure is controlled by the pressure control of the hydrogen gas by the pressure regulating valve 38 so that the output current can be larger than the normal starting control described above. And the flow rate of hydrogen gas in the fuel cell 12 by the control of the rotational speed of the hydrogen pump 46 is the same as or increased, and the air pressure of the cathode electrode is increased by the back pressure control of the back pressure adjusting valve 58, and the air compressor In addition to the normal flow rate of the cathode electrode air by the rotation speed control 52, control such as changing the use map of the hydrogen discharge valve 44 or changing the power generation cell voltage protection threshold to a value smaller than normal is performed.

  As described above, the two sub-freezing start control at time t1 in FIGS. 4A and 4C and the one sub-freezing control at time t3 in FIG. 4C are performed by the first sub-freezing start means.

  On the other hand, if the below-freezing start determination at step S2 is established and the squeeze flag F is set at step S4 (F = 1), at the time of restart by the below-freezing second starting means at step S6. Below freezing point control is performed.

  In this sub-freezing start control by the sub-freezing second starting means (hereinafter referred to as “freezing freezing point control”), the pressure regulating valve 38 is controlled so that the output current can be larger than that of the above-described starting control by the first sub-freezing starting means. The pressure of the hydrogen gas is further increased by the pressure control, the flow rate of the hydrogen gas by the rotation speed control of the hydrogen pump 46 is the same as or more than usual, and the air pressure is further increased by the back pressure control of the back pressure adjustment valve 58. Further, the air flow rate is further increased by controlling the rotation speed of the air compressor 52, and the use map of the hydrogen discharge valve 44 is made the same as the below-freezing start control by the below-freezing first starting means, and the power generation cell voltage protection threshold is the below-freezing first starting means. The same control as the below-freezing start control by the

  As described above, in FIG. 4C, the below-freezing start control at the time point t3 is performed at the time of restart by the second below-freezing start means.

  As a result, as shown in FIG. 6, in the fuel cell system 10, when the temperature is below freezing at the time of restart after choking, by using the freezing freezing point control (below freezing point control by the second freezing point starting means) It can be seen that the start-up performance is improved compared to the conventional freezing point control, the current / voltage characteristics are improved, and the power generation stability is improved.

  As described above, according to the above-described embodiment, in the fuel cell system 10 including the fuel cell 12 that generates power using the supplied reaction gas (hydrogen gas and air), the fuel is obtained by the thermometer 56 as the internal temperature detecting means. The internal temperature Ti of the battery 12 is detected. The memory 61 as sub-freezing experience storage means stores that the internal temperature Ti has become a temperature below the freezing point during the soak that is the stop period of the fuel cell 12. When the fuel cell 12 is activated, the CPU 60 as the first below-freezing start means stores the reaction at the sub-freezing temperature in the memory 61 when the fuel cell 12 is activated. The fuel cell 12 is started by increasing the gas pressure. The CPU 60 as the warm-up state determination means (short-time power generation determination means after starting at low temperature) determines whether or not the warm-up of the fuel cell 12 has been stopped in a sufficient state at the stop after the start-up by the first freezing point sub-freezing point. Then, the CPU 60 as the second freezing point starting means determines that the warm-up is not sufficient, and when the fuel cell 12 is restarted after being stopped, the CPU 60 reaches a temperature below the freezing point during the stop period before the restarting. When this is stored in the memory 61, the fuel cell 12 is started by further increasing the pressure of the reaction gas by the first below-freezing point starting means.

  As described above, when the fuel cell 12 is in a freezing state or when it is in a freezing state, the reaction gas pressure is increased by the first freezing means below freezing compared to the normal starting time. After the fuel cell 12 is activated and activated by the first below-freezing first activation means, when the fuel cell 12 is restarted after power generation is stopped in a state where the fuel cell 12 is not warmed up sufficiently When the fuel cell 12 is in a sub-freezing state or in a sub-freezing state, the fuel cell 12 further increases the pressure of the reaction gas by the sub-freezing second starting means by the sub-freezing second starting means. Therefore, it is possible to improve the current / voltage characteristics at the time of power generation after a short period of freezing and restarting after stopping (when restarting after choking).

  Note that the above-mentioned “CPU 60 as the warm-up state determination means determines whether or not the warm-up of the fuel cell 12 has been stopped in a sufficient state at the time of stop after the start-up by the first sub-freezing start means. When the fuel cell 12 is restarted after determining that the warm-up is not in a sufficient state, the CPU 60 as the means indicates that “the CPU 60 as the power generation determination means for a short time after starting at low temperature is below freezing. After the activation by the first activation means, it is determined that the fuel cell 12 has been stopped after short-time power generation. When this determination is made, the CPU 60 as the second freezing point second activation means restarts the fuel cell 12 after being stopped. Sometimes it may be.

  In this case, the flow rate of the reaction gas at the time of startup by the first below-freezing means is also increased compared to the flow rate of the reaction gas at the time of normal startup, and the reaction gas at the time of restarting by the second below-freezing point startup means. Is further increased from the flow rate increased by the first freezing means below the freezing point, the generated water on the cathode electrode side can be more reliably discharged to the outside of the fuel cell 12 by the increased flow rate of the reaction gas. Since it can do, the fall of the gas diffusion performance by freezing of produced water is suppressed, and mobility is improved.

  It should be noted that whether the warm-up state after the chopping is sufficient is determined based on the internal temperature Ts of the fuel cell 12 at the start of power generation by the first below-freezing start means and the power generation after startup by the first below-freezing start means. It can be automatically determined based on the internal temperature Te at the end.

  In this case, as can be seen from the selection experience determination map 100 in FIG. 5, basically, when the internal temperature Ts at the start of power generation is close to the freezing point temperature 0 ° C., the internal temperature Te at the end of power generation is relatively low. If the internal temperature Ts at the start of power generation is lower than the freezing point temperature of 0 ° C., the lower the temperature is, the lower the internal temperature at the end of power generation. If the temperature Te is not a higher temperature, it can be determined that the temperature is in the insufficient warm-up range 102.

  In addition, the low temperature start method for the fuel cell 12 according to this embodiment is a low temperature start method for the fuel cell 12 that generates power using the supplied reaction gas, and an internal temperature detection step for detecting the internal temperature Ti of the fuel cell 12. And a sub-freezing experience storing step for storing that the internal temperature Ti has become a temperature below the freezing point during the stop period of the fuel cell 12, and at the start of the fuel cell 12, the sub-freezing temperature is set to a temperature below the freezing point. When it is stored in the below-freezing experience storing step (S2: YES), a first below-freezing-starting step (S5) for starting the fuel cell 12 by increasing the pressure of the reaction gas compared to the normal starting time. The warm-up state determination step (S8b) for determining whether or not the warm-up of the fuel cell 12 has been stopped in a sufficient state at the stop after the start-up in the first freezing point step When the fuel cell 12 is restarted after it is determined that the warm-up is not sufficient, and the fuel cell 12 is restarted, the temperature below the freezing point is stored in the sub-freezing experience storing step. If so, a second below-freezing-starting step (S6) of starting the fuel cell 12 by further increasing the pressure of the reaction gas in the first below-freezing-starting step is provided.

  According to the method for starting the fuel cell 12 at a low temperature according to this embodiment, when the fuel cell 12 is in a sub-freezing state or when the fuel cell 12 is in a sub-freezing state, the sub-freezing first starting step (S5) After the fuel cell 12 is started by increasing the pressure of the reaction gas compared to the time of startup, and after the startup by the first below-freezing step, the power generation is stopped after the fuel cell 12 is not warmed up sufficiently. When the fuel cell 12 is in a sub-freezing state or when the fuel cell 12 is in a sub-freezing state at the time of restarting the fuel cell 12 (at the time of restarting after choking), the sub-freezing second starting step (S6) Since the fuel cell is started by further increasing the pressure of the reaction gas in the start-up step, the power at the time of stop after restart after power generation for a short time below freezing point (at the time of restart after choking) - voltage characteristics can be improved to. As a result, at the time of sub-freezing start after chopping (after the start of sub-freezing, the ignition switch is turned off while the inside of the fuel cell 12 is not warmed up, and after that, under the condition of sub-freezing or sub-freezing experience again Start-up) and power generation stability are improved.

BRIEF DESCRIPTION OF THE DRAWINGS It is schematic structure explanatory drawing of the fuel cell system for implementing the low temperature starting method of the fuel cell which concerns on embodiment of this invention. It is a flowchart of the said low temperature starting method. FIG. 3 is a detailed flowchart of a selection flag setting process in FIG. 2. FIG. 4A is a time chart for explaining the first freezing start and the freezing start after chopping. FIG. 4A is a description of the second freezing start after the chopping and FIG. 4B is a description of the flag state in that case. FIG. 4C is a time chart for explaining the second sub-freezing activation and the first sub-freezing activation, FIG. 4D explaining the flag state in that case, and FIG. 4E explaining the ignition switch ON / OFF state. It is explanatory drawing of a presence experience presence map. It is a comparison figure of the current / voltage characteristic after the conventional freezing point control and the current / voltage characteristic after the freezing point freezing control at the time of restart after the peeling. It is a relationship figure of output current and gas pressure in the environment below the freezing temperature of water. FIG. 4 is a relationship diagram between the level of gas pressure and the limit load in an environment below the freezing temperature of water. It is a comparison figure of the electric current and voltage characteristic at the time of starting by the conventional sub-freezing control, and the electric current and voltage characteristic at the time of restart after the choking in the conventional sub-freezing control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell system 12 ... Fuel cell stack 56 ... Thermometer 60 ... CPU
61 ... Memory 100 ... Choking experience presence / absence determination map 102 ... Warm-up insufficient range 104 ... Warm-up sufficient range

Claims (4)

In a fuel cell system including a fuel cell that generates power using a supplied reactive gas,
Internal temperature detection means for detecting the internal temperature of the fuel cell;
Sub-freezing experience storage means for storing that the internal temperature has become below the freezing point during the stop period of the fuel cell;
When the fuel cell is started, when the temperature below the freezing point is stored in the below freezing point experience storage means during the stop period before the starting time, the pressure of the reaction gas is increased compared to the normal starting point. First below-freezing starting means for starting the fuel cell;
A warm-up state determination unit that determines whether the warm-up of the fuel cell has been stopped in a sufficient state at the time of stop after startup by the first below-freezing means;
When the fuel cell is restarted after it is determined that the warm-up is not sufficient, it is stored in the sub-freezing experience storage means that the temperature has fallen below freezing during the stop period before the restart. And a second below-freezing point starting means for starting the fuel cell by further increasing the pressure of the reaction gas by the below-freezing first starting part. The fuel cell system according to claim 1, wherein
The flow rate of the reaction gas at the time of start-up by the first below-freezing means is increased compared to the flow rate of the reaction gas at the time of normal start-up, and the flow rate of the reaction gas at the time of restart by the second below-freezing-point start means is The fuel cell system is further increased from the flow rate increased by the first starting means below freezing point. The fuel cell system according to claim 1 or 2,
The warm-up state determination means is configured to determine whether the fuel cell has an internal temperature at the start of power generation by the first below-freezing start means and an internal temperature at the end of power generation after the start-up by the first below-freezing start means. A fuel cell system characterized by determining whether or not the warm-up is sufficient. In a low temperature start-up method of a fuel cell that generates power with the supplied reaction gas,
An internal temperature detecting step for detecting the internal temperature of the fuel cell;
A sub-freezing experience storage step for storing that the internal temperature has become a temperature below the freezing point during the stop period of the fuel cell;
When the fuel cell is started, when the temperature below the freezing point is stored in the sub-freezing experience storing step during the stop period before the starting time, the pressure of the reaction gas is increased as compared with the normal starting time. A first sub-freezing start step for starting the fuel cell;
A warm-up state determination step for determining whether the warm-up of the fuel cell is stopped in a sufficient state at the time of stop after the start-up by the first below-freezing step;
When the fuel cell is restarted after it is determined that the warm-up is not sufficient, it is stored in the sub-freezing experience storage step that the temperature has reached a sub-freezing temperature during the stop period before the restart. And a second sub-freezing start step for starting the fuel cell by further increasing the pressure of the reaction gas in the first sub-freezing start step.

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