JP2010129276A - Fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid freezing and closure of gas passages in a fuel cell at the time of starting below zero. <P>SOLUTION: The fuel cell system is provided with a fuel cell 5 which generates electric power by an electrochemical reaction of a hydrogen gas as a fuel gas and air as an oxidant gas. When the fuel cell system is started below zero in the condition of (the fuel cell temperature)<0°C<(an auxiliary equipment temperature), by estimating the moisture content at the time of starting below zero existing in the auxiliary equipment and the piping of the fuel cell which is necessary for operation of the fuel cell, the more the flow rate of the supply gas to be supplied to the fuel cell at the time of starting is restricted, the more the moisture content exists in the auxiliary equipment and the piping. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system having improved start-up performance at start-up below zero.

Conventionally, as this type of technology, for example, those described in the following documents are known (see Patent Document 1). In this document, when starting the fuel cell, if the temperature of the fuel cell is below the freezing point, the pump is operated at a higher rotational speed than the normal rotational speed, and the fuel cell is operated at a flow rate higher than the normal pressure, higher than the normal pressure. A technology is described in which air (low-temperature reaction gas) is supplied at a high pressure to generate high power in the fuel cell and prevent freezing of generated power in the fuel cell.
JP 2006-134673 A

  In the above conventional fuel cell system, if the auxiliary machine is not frozen or thawed, and the fuel cell is started with the temperature below the freezing point, the auxiliary machine and the condensed water in the pipe are In addition, there is a risk that the residual water flows into the fuel cell and the gas flow path is blocked due to freezing in the fuel cell.

  Accordingly, the present invention has been made in view of the above, and an object of the present invention is to provide a fuel cell system that avoids blockage of the gas flow path due to freezing in the fuel cell at the time of starting below zero. is there.

  In order to achieve the above object, the means for solving the problems of the present invention is to supply the supply gas by the reaction gas supply means in a state where the temperature of the fuel cell is below freezing and water is present in the reaction gas supply flow path. Is started, the flow rate of the supply gas supplied to the fuel cell is limited as the amount of water estimated by the water amount estimation means increases.

  According to the present invention, the amount of water supplied into the fuel cell is reduced as the amount of water flowing into the fuel cell is estimated to be less, so the amount of water flowing into the fuel cell is reduced, thereby reducing the possibility of blocking the gas flow path due to freezing. it can. On the other hand, power can be generated by supplying the supply gas, and thawing in the fuel cell can be promoted by self-heating or the like. Therefore, the fuel cell system can be activated while avoiding the blockage of the gas flow path.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best embodiment for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a fuel cell system according to Embodiment 1 of the present invention. In FIG. 1, the fuel cell system of the first embodiment includes a fuel cell 5 that is supplied with a fuel gas (supply gas) and an oxidant gas (supply gas) and generates electric power through an electrochemical reaction, and a voltage and an output of the fuel cell 5. A current measuring system 15 and a power control device 14 for controlling the voltage and the extraction current of the fuel cell 5 are provided.

  The fuel cell system is supplied from a hydrogen tank 13 (reactive gas supply means) for storing hydrogen as a fuel gas, a pressure reducing valve 1 for reducing the pressure of hydrogen supplied from the hydrogen tank 13, and a pressure reducing valve 1. The hydrogen pressure control valve 2 for adjusting the hydrogen pressure of the fuel cell 5 to control the anode inlet hydrogen pressure of the fuel cell 5, the anode inlet hydrogen temperature sensor 3 for detecting the hydrogen temperature at the anode inlet of the fuel cell 5, and the fuel cell 5 An anode inlet hydrogen pressure sensor 4 for detecting the hydrogen pressure at the anode inlet is provided. In addition, the hydrogen tank 13, the decompression valve 1 and the auxiliary devices and valves of the hydrogen pressure control valve 2 installed from the hydrogen tank 13 to the anode inlet are collectively referred to as a reaction gas supply channel.

  In addition, the fuel cell system is stored in the separator tank 6 that separates the power generation water and hydrogen discharged from the anode outlet of the fuel cell 5, the separator tank temperature sensor 7 that detects the temperature of the separator tank 6, and the separator tank 6. A drain valve 8 for draining the generated power generation water outside the fuel cell system is provided.

  The fuel cell system also includes a hydrogen circulation pump 9 that circulates hydrogen discharged from the anode outlet of the fuel cell 5 to the anode inlet, a hydrogen circulation pump temperature sensor 10 that detects the temperature of the hydrogen circulation pump 9, and the fuel cell 5. The hydrogen purge valve 11 for discharging the gas not used in the reaction in the anode catalyst layer of the hydrogen circulation system piping temperature for detecting the temperature of the piping for circulating unused hydrogen discharged from the anode outlet of the fuel cell 5 to the anode inlet A sensor 12 is provided.

  The fuel cell system also includes a compressor 16 (reactive gas supply means) that pressurizes air, which is an oxidant gas, and supplies it to the cathode catalyst layer of the fuel cell 5, and an air humidifier that humidifies the air supplied from the compressor 16. 17, an air humidifier temperature sensor 18 that detects the temperature of the air humidifier 17, a cathode inlet air temperature sensor 19 that detects the air temperature at the cathode inlet of the fuel cell 5, and the air pressure at the cathode inlet of the fuel cell 5. A cathode inlet air pressure sensor 20 to be detected and an air pressure control valve 21 for adjusting the pressure of air discharged from the cathode outlet of the fuel cell 5 and controlling the cathode inlet air pressure of the fuel cell 5 are provided. Note that the compressor 16, the air humidifier 17, and the auxiliary machines and valves of the air pressure control valve 21 and the flow path installed between the air intake portion of the compressor 16 and the cathode inlet are collectively referred to as a reaction gas supply flow path.

  The fuel cell system includes a cooling water circulation pump 22 that circulates cooling water for cooling the fuel cell 5, a fuel cell inlet cooling water temperature sensor 23 that detects a cooling water temperature at the inlet of the fuel cell 5, and a fuel cell. 5, a fuel cell outlet cooling water temperature sensor 24 that detects the cooling water temperature at the outlet 5, a heat exchanger 25 that radiates and cools the cooling water circulating from the outlet of the fuel cell 5 to the inlet, and a control unit (not shown). ).

  The control unit functions as a control center for controlling the operation of the system, and is provided with resources such as a CPU, a storage device, and an input / output device necessary for a computer that controls various operation processes based on a program, such as a microcomputer It is realized by. The control unit reads signals from the sensors (not shown) that collect information necessary for operation of the system, such as the above-mentioned sensors and other pressures, temperatures, concentrations, voltages, and currents that cannot be obtained by these sensors. Based on the various signals read and control logic (program) stored in advance, commands are sent to components that require control of the system, and this system is operated / stopped including subzero start-up control operations described below. It functions as an operation control means for controlling and controlling all necessary operations in a unified manner and a water amount estimation means (liquid water amount estimation means). In addition, the water content estimation means is only required to be able to estimate the liquid water amount, and may estimate the water content including ice.

  An operation when the fuel cell system having such a configuration requirement is in steady operation will be described.

First, hydrogen, which is a fuel gas, is supplied to the anode catalyst layer of the fuel cell 5 and air, which is an oxidizing gas, is supplied to the cathode catalyst layer, and electric power is generated by the electrochemical reaction shown below.
(Chemical formula 1)
Anode (hydrogen) electrode reaction: H ₂ → 2H ⁺ + 2e ⁻
Cathode (oxygen) electrode reaction: 2H ⁺ + 2e ⁻ + (1/2) O ₂ → H ₂ O

  In the hydrogen supply system that supplies hydrogen to the anode catalyst layer of the fuel cell 5, hydrogen is stored in the hydrogen tank 13, and the high-pressure hydrogen supplied from the hydrogen tank 13 is depressurized by the pressure reducing valve 1, and the hydrogen pressure control valve 2 To be supplied. Hydrogen supplied from the hydrogen pressure control valve 2 is mixed with hydrogen circulated from the hydrogen circulation pump 9 and supplied to the anode catalyst layer of the fuel cell 5.

  Here, the hydrogen temperature and pressure at the anode inlet of the fuel cell 5 are detected by the anode inlet hydrogen temperature sensor 3 and the anode inlet hydrogen pressure sensor 4, respectively.

  The hydrogen pressure control valve 2 controls the anode inlet hydrogen pressure based on the pressure detected by the anode inlet hydrogen pressure sensor 4. Hydrogen having a predetermined temperature and pressure is supplied to the anode inlet of the fuel cell 5 and used for power generation of the fuel cell 5. Unreacted hydrogen that has not been used for power generation is discharged from the anode outlet of the fuel cell 5 and then supplied again to the fuel cell 5 from the hydrogen circulation pump 9.

  The power generation water discharged from the anode outlet of the fuel cell 5 is collected by the separator tank 6. When the power generation generated water recovery amount in the separator tank 6 exceeds a predetermined amount, the power generation generated water is drained out of the fuel cell system by opening the drain valve 8.

  Nitrogen that has permeated from the cathode of the fuel cell 5 lowers the hydrogen concentration in the anode catalyst layer and causes deterioration of the catalyst layer due to starvation. Therefore, by periodically opening the hydrogen purge valve 11, nitrogen is discharged out of the fuel cell system. To do. Here, the temperatures of the separator tank 6, the hydrogen circulation pump 9, and the hydrogen circulation system pipe are detected by the separator tank temperature sensor 7, the hydrogen circulation pump temperature sensor 10, and the hydrogen circulation system pipe temperature sensor 12, respectively.

  On the other hand, in the air supply system that supplies air to the cathode catalyst layer of the fuel cell 5, the compressor 16 sucks air from outside air, pressurizes the sucked air, and sends it out. The sent air is humidified by the air humidifier 17 and supplied to the cathode catalyst layer of the fuel cell 5. Here, the air temperature and pressure at the cathode inlet of the fuel cell 5 are detected by a cathode inlet air temperature sensor 19 and a cathode inlet air pressure sensor 20, respectively. The temperature of the air humidifier 17 is detected by the air humidifier temperature sensor 18.

  Unreacted air and power generation product water that have not been used for power generation are discharged from the cathode outlet of the fuel cell 5 and then pass through the air humidifier 17 again. At this time, part of the power generation water (water vapor) that has passed through the air humidifier 17 is used to humidify the air sucked from the compressor 16. The cathode outlet exhaust air that has passed through the air humidifier 17 passes through the air pressure control valve 21. The air pressure control valve 21 controls the cathode inlet air pressure based on the pressure detected by the cathode inlet air pressure sensor 20. Here, the gas pressure of the fuel cell 5, that is, the anode inlet hydrogen pressure and the cathode inlet air pressure are variable pressures.

  The power control device 14 of the fuel cell 5 sets an appropriate gas pressure so that the fuel cell 5 can stably generate power depending on the output (current) taken out and the temperature of the fuel cell 5.

  If the temperature of the fuel cell 5 becomes too high, the anode catalyst layer may be dried, and the voltage may drop rapidly, or the polymer membrane used in the fuel cell 5 may suddenly soften and break. . For this reason, cooling water for cooling the fuel cell 5 is used. The cooling water that has absorbed the reaction heat of the fuel cell 5 dissipates heat in the heat exchanger 25 and is sent to the fuel cell 5 again by the cooling water circulation pump 22. Here, the coolant temperature at the inlet and outlet of the fuel cell 5 is detected by the fuel cell inlet coolant temperature sensor 23 and the fuel cell outlet coolant temperature sensor 24, respectively. The amount of heat release in the heat exchanger 25 is controlled based on the temperatures detected by the fuel cell inlet cooling water temperature sensor 23 and the fuel cell outlet cooling water temperature sensor 24.

  FIG. 2 shows the voltage behavior when the conventional fuel cell system which does not employ the technical idea of the present invention is started below zero after purging and stopping the operation. However, the cooling water temperature at the fuel cell outlet when starting below zero is 0 ° C or lower, the anode inlet hydrogen temperature, cathode inlet air temperature, separator tank temperature, hydrogen circulation pump temperature, hydrogen circulation system piping temperature, and air humidifier temperature are 0 ° C or higher. And

  In FIG. 2, in the conventional fuel cell system, when starting below zero under the above temperature condition, the voltage of the fuel cell 5 decreases with the start (after time T2 in FIG. 2), and is maintained in the state of being decreased. . The decrease in voltage is caused by the fact that condensed water in auxiliary equipment and piping such as the hydrogen circulation pump 9 and the air humidifier 17 flows into the fuel cell 5, freezes in the fuel cell 5, and the gas flow path is blocked, so that hydrogen and air Is due to the inhibition. When the voltage drops, the fuel cell output cannot be taken out until the voltage recovers, so the subzero startup time becomes longer.

  On the other hand, FIG. 3 shows the voltage behavior at the time of starting below zero when the present application is applied. In FIG. 3, when the present application is applied, by restricting the supply gas flow rate at the start-up so that the condensed water in the auxiliary machine and the piping does not flow into the fuel cell 5, the fuel cell is suppressed while suppressing the voltage drop at the start-up. Since the output can be taken out (after time T3 in FIG. 3), the start-up time below zero can be shortened.

  Next, the control procedure of the startup control for realizing the voltage behavior shown in FIG. 3 will be described with reference to the control flow shown in FIG.

  In FIG. 4, first, after purging and stopping the operation (step S401), the fuel cell 5, auxiliary equipment, piping, and fuel cell inlet gas temperature are detected (step S402). Here, fuel cell temperature is fuel cell outlet cooling water temperature, auxiliary equipment temperature is separator tank temperature and hydrogen circulation pump temperature, piping temperature is hydrogen circulation system piping temperature, fuel cell inlet temperature is anode inlet hydrogen temperature and cathode inlet air temperature. And

  As a result of the detection of each temperature, it is determined whether or not the requirements of fuel cell temperature <0 ° C. <auxiliary equipment, piping, and fuel cell inlet gas temperature are satisfied (step S403). As a result of the determination, if the above requirement is not satisfied, the supply gas flow rate at the start is not limited (step S404). When the temperature of the fuel cell 5 becomes 0 ° C. or higher after startup, the restriction is released (the same applies to the following Examples 2 to 4). In the present embodiment, the temperature of the fuel cell is set to a value lower than 0 ° C. as a condition for restricting the flow rate, but may be any temperature at which the liquid water is frozen (below freezing point). Moreover, although the temperature of auxiliary machines etc. was made into the value larger than 0 degreeC, what is necessary is just the temperature in which liquid water exists. Furthermore, as a condition for releasing the flow restriction, the temperature of the fuel cell is set to 0 ° C. or higher, but may be a temperature at which liquid water does not freeze (thawing temperature).

On the other hand, when the above requirement is satisfied, the supply gas flow rate is subsequently limited. However, since the supply gas flow rate at the time of starting below zero is set based on the amount of condensed water in the auxiliary device and piping, The amount of condensed water is estimated (step S405). The amount of condensed water is estimated by calculating from the following equations (1) and (2).
(Equation 1)
Saturated water vapor volume (l)
= System volume (l) x {saturated water vapor pressure (kPa_abs) /101.3 (kPa_abs)} (1)
Condensate volume (g)
= 18 (g / mol)
× {(standard state saturated water vapor volume during stop purge (l))
-(Standard saturated water vapor volume at start-up below zero (l))} / 22.4 (g / mol) (2)
Here, the volume of the system in formula (1) is the volume of the anode or cathode gas supply system. The saturated water vapor pressure is a function of only the reaction gas temperature, and the reaction gas temperature is the fuel cell inlet gas temperature.

  For example, if there are variations in auxiliary equipment temperature, piping temperature, and fuel cell inlet gas temperature, the reaction gas temperature representing the saturated water vapor pressure during stop purge uses the maximum value of those temperatures, and saturated water vapor during subzero start-up As the reaction gas temperature representing the pressure, the minimum value of these temperatures is used.

  Next, the limit value of the supply gas flow rate at startup is estimated with reference to the map (step S406), and the system is started according to the estimated limit value.

  FIGS. 5A and 5B show maps used for the above estimation showing the relationship between the starting supply gas flow rate limit value and the amount of condensed water. As shown in FIG. 5A, the limit value of the starting supply gas flow rate decreases as the amount of condensed water in the auxiliary machine and the pipe increases. Depending on the auxiliary equipment and the piping configuration, there may be a region where the supply gas flow rate at startup is constant regardless of the amount of condensed water in the auxiliary equipment and the piping, as shown in FIG. This is because, for example, when the condensed water is difficult to fly (difficult to be discharged) in a pipe in which the gas pipes meander and meander due to the configuration of the fuel cell, the condensed water remains even if some condensed water remains. This is because a gas flow rate region that does not require a gas flow rate restriction is assumed because it does not fly.

  The limit value of the supply gas flow rate at start-up, that is, the gas flow rate at which condensed water does not flow into the fuel cell is also affected by parameters other than the condensed water amount. For example, even if the amount of condensed water estimated by the above formulas (1) and (2) is small, if there is a structure where condensate tends to accumulate in the auxiliary equipment and piping, the amount of condensed water partially jumps. It is necessary to select the supply gas flow rate at start-up in consideration of the fact that there is a place where it becomes easy (easy to discharge). In addition, since the gas flow velocity is partially increased at locations where the cross-sectional area of the pipe or the like is small, the condensed water is likely to fly.

  Further, when left after the stop purge, air is mixed into the anode gas supply system with the passage of the standing time, and the gas density increases. When the gas density is increased, the gas flow rate is increased, so that the condensed water is likely to fly.

  Thus, since the limit value of the supply gas flow rate at the start is affected by the auxiliary equipment, the piping configuration, and the gas density, it is experimentally determined in advance through experiments and the result is created as a map or the like in advance. Prepare it, store it in the storage device of the control unit, and refer to it as needed.

  Thus, in this Example 1, when starting below zero in a temperature state where the fuel cell temperature <0 ° C. <auxiliary temperature, the larger the amount of condensed water in the auxiliary equipment and the piping, the more the supply gas flow rate at the time of starting. By limiting, the condensate in the auxiliary equipment and the piping is prevented from flowing into the fuel cell 5 to prevent water from being frozen in the fuel cell 5 and the gas flow path from being blocked by the frozen water. Can do.

  The amount of condensed water can be estimated easily and simply by estimating the amount of condensed water in the auxiliary equipment and the piping based on the difference between the supply gas temperature at the previous system stop and the supply gas temperature at the time of starting below zero.

  Even if there is a temperature distribution in the gas temperature in the auxiliary equipment and piping, the supply gas temperature at the time of the previous system shutdown is set to the maximum value of the auxiliary equipment and piping temperature, and the supply gas temperature at the time of starting below zero is set to the auxiliary equipment and piping temperature. By setting it as the minimum value, it becomes possible to estimate the maximum value of the amount of condensed water, and it is possible to appropriately limit the flow rate of the supply gas.

  By representing the temperature of the fuel cell as the cooling water temperature at the outlet of the fuel cell when the cooling water is circulated through the fuel cell 5 before starting, the average fuel cell temperature even when there is a temperature distribution in the fuel cell Can be estimated, and the flow rate of the supply gas can be appropriately limited.

  After the fuel cell temperature has surely reached 0 ° C. or higher, the restriction on the supply gas flow rate is released, so that it is possible to reliably avoid freezing in the fuel cell and blockage of the gas flow path, thereby performing stable operation. .

  Next, a second embodiment of the present invention will be described. In the first embodiment, the sub-zero start is performed after the stop purge. However, in the second embodiment, a control method in which the sub-start is performed after the operation is stopped without purging is adopted. The difference from 1 is that not only the amount of condensed water in the auxiliary equipment and piping but also the amount of residual water is taken into consideration. The configuration of the fuel cell system is the same as that of FIG. 1 described above, so that the description thereof will be omitted, and the control procedure will be described with reference to the flowchart shown in FIG.

  In FIG. 6, first, the fuel cell, auxiliary equipment, piping, and fuel cell inlet gas temperature are detected (step S601). Here, fuel cell temperature is fuel cell outlet cooling water temperature, auxiliary equipment temperature is separator tank temperature and hydrogen circulation pump temperature, piping temperature is hydrogen circulation system piping temperature, fuel cell inlet temperature is anode inlet hydrogen temperature and cathode inlet air temperature. And

  As a result of the detection of each temperature, it is determined whether or not the requirements of fuel cell temperature <0 ° C. <auxiliary equipment, piping, and fuel cell inlet gas temperature are satisfied (step S602). As a result of the determination, if the above requirement is not satisfied, the supply gas flow rate is not limited at the time of startup (step S603).

  On the other hand, when the above requirement is satisfied, the supply gas flow rate is subsequently limited. However, since the supply gas flow rate at the time of starting below zero is set based on the amount of condensed water in the auxiliary device and piping, The amount of condensed water is estimated (step S604). The amount of condensed water is estimated in the same manner as in the first embodiment. Subsequently, the amount of residual water in the auxiliary machine and the pipe is estimated with reference to a map as shown in FIG. 7 (step S605).

  When the output (current) of the fuel cell 5 increases and the amount of power generation generated water increases, and the amount of power generation generated water exceeds the amount recovered by the separator tank 6, power generation generated water that could not be recovered by the separator tank 6 remains. It remains in the anode gas supply system as water. The relationship between the amount of residual water in such auxiliary equipment and piping and the fuel cell output (current) when the operation is stopped is as shown in FIG. 7, for example.

  Next, returning to FIG. 6, a limit value of the supply gas flow rate at startup is estimated (step S606), and the system is started according to the estimated limit value.

  As shown in FIG. 8A, the limit value of the supply gas flow rate at startup decreases as (condensed water amount + residual water amount) increases. Depending on the configuration of the auxiliary equipment and piping, as shown in Fig. 8 (b), there is a region where the supply gas flow rate at startup is constant regardless of (condensed water amount + residual water amount) in the auxiliary equipment and piping. May be.

  The limit value of the supply gas flow rate at start-up, that is, the gas flow rate at which condensed water and residual water do not flow into the fuel cell are also affected by parameters other than the condensed water amount and residual water amount. For example, the amount of condensed water estimated in the equations (1) and (2) mentioned in the previous embodiment 1 and the amount of residual water having the relationship shown in FIG. In the case where there is, it is necessary to select the starting supply gas flow rate in consideration of the fact that there is a part where the amount of condensed water and residual water are likely to fly.

  In addition, since the gas flow velocity is partially increased at locations where the cross-sectional area of the pipe or the like is small, the condensed water and residual water are likely to fly. Furthermore, when left unattended after stopping, air is mixed into the anode gas supply system with the elapse of the standing time, and the gas density increases. When the gas density is increased, the gas flow rate is increased, so that condensed water and residual water are likely to fly. As described above, since the limit value of the supply gas flow rate at startup is affected by the auxiliary equipment, piping configuration, and gas density, it is experimentally obtained by conducting experiments in advance, and the result is prepared as a map etc. Then, it is stored in the storage device of the control unit and referred to when necessary.

  Thus, in the second embodiment, in addition to the effects obtained in the first embodiment, it is possible to estimate the residual water amount in the auxiliary equipment and the piping based on the fuel cell take-out current before the previous system stop. Become. This makes it possible to estimate the amount of water present in the auxiliary equipment and piping, which is the sum of the amount of condensed water and the amount of residual water, and appropriately restrict the supply gas flow rate even when the purge process is not performed when the system is stopped. It becomes possible.

  Next, a third embodiment of the present invention will be described. In the first and second embodiments described above, a control method for limiting the flow rate of the supply gas is employed in order to prevent condensed water and residual water from flowing into the fuel cell at the time of starting below zero. Therefore, in addition to the flow rate restriction employed in the second embodiment, a control method for restricting the pressure increase rate of the supply gas is employed.

  Since the configuration of the fuel cell system is the same as that of FIG. 1 shown in the first embodiment, a description thereof will be omitted, and the control procedure will be described with reference to the flowchart shown in FIG.

  9, first, the same control procedure (step S901 to step S906) as the control procedure (step S401 to step S406) of the first embodiment shown in FIG. 4 is executed.

  Thereafter, the startup gas pressure increase rate limit value is estimated based on the startup supply gas flow rate limit value obtained as a result of the above execution (step S907), and the system is started according to the estimated limit value.

  Since the hydrogen partial pressure is low at the initial stage of starting the system, it is necessary to prevent deterioration of the catalyst layer due to starvation by quickly increasing the anode inlet hydrogen pressure and increasing the hydrogen concentration in the anode catalyst layer. At this time, by opening the hydrogen purge valve 11, nitrogen that has permeated from the cathode side to the anode side is discharged out of the fuel cell system. When only the anode inlet hydrogen pressure is increased, the hydrogen permeated from the anode side to the cathode side reduces the oxygen concentration in the cathode catalyst layer and increases the differential pressure between the membrane and electrode assembly at the anode and cathode. The membrane / electrode assembly may be damaged. For this reason, it is necessary to increase the cathode inlet air pressure at a pressure increase rate similar to the anode inlet hydrogen pressure.

  On the other hand, in order to shorten the start-up time below zero, it is desired to quickly increase the anode inlet hydrogen pressure and the cathode inlet air pressure as described above. To increase the startup gas pressure increase rate, increase the startup supply gas flow rate. There is a need. However, as described in the first and second embodiments, since the start-up supply gas flow rate is limited, the start-up gas pressure increase rate is also limited.

  For this reason, the startup gas pressure increase rate is set based on a limit value map showing the relationship between the startup pressure below zero gas pressure and the supply gas flow rate at startup below zero, as shown in FIG. As shown in FIG. 10, the startup gas pressure increase rate increases as the startup supply gas flow rate limit value increases. The map shown in FIG. 10 is prepared in advance as a map of the results of experiments and the like, stored in the storage device of the control unit, and referenced as necessary.

  As described above, in the third embodiment, in addition to the effect obtained in the second embodiment, the gas pressure increase rate at the start-up is limited based on the supply gas flow rate at the start-up. Power generation can be started in a state where the nitrogen concentration in the inside is reduced, and thawing of the fuel cell 5 can be promoted.

  Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, in addition to the control method for limiting the flow rate and pressure increase rate of the supply gas employed in the first and second embodiments, a control method for limiting the power generation output (current) taken out from the fuel cell at the time of startup. Is adopted.

  Since the configuration of the fuel cell system is the same as that of FIG. 1 shown in the first embodiment, a description thereof will be omitted, and the control procedure will be described with reference to the flowchart shown in FIG.

  11, first, the same control procedure (step S1101 to step S1107) as the control procedure (step S901 to step S907) of the third embodiment shown in FIG. 4 is executed.

  Thereafter, the fuel cell take-out output limit value is estimated based on the start-up supply gas flow rate limit value, the gas pressure, and the fuel cell temperature obtained as a result of the above execution (step S1108).

  In the initial stage of starting the system, the output of the fuel cell cannot be increased because the temperature of the fuel cell is low and the membrane resistance of the electrolyte is high. For this reason, as shown in the maps of FIGS. 12 to 14, the fuel cell takeout output is limited with respect to the gas flow rate limit value, the gas pressure, and the fuel cell temperature, and the map is shown in FIGS. By selecting the maximum output value that satisfies all the relationships, the output limit value is estimated (step S1109), and the operation is performed with the output limited by the estimated output limit value.

  As shown in FIGS. 12 to 14, the fuel cell takeout output increases as the startup supply gas flow rate, gas pressure, and fuel cell temperature increase. The maps shown in FIGS. 12 to 14 are experimentally obtained and created in the same manner as the maps described above. Here, the fuel cell temperature refers to the fuel cell inlet cooling water temperature and the fuel cell outlet cooling water temperature.

  Next, it is determined whether or not the fuel cell temperature has become 0 ° C. or higher (step S1109). As a result of the determination, when the fuel cell temperature becomes 0 ° C. or higher, the restriction on the gas flow rate is released, and the normal power generation control preset according to the specifications of the fuel cell system is performed (step) S1110).

  Various amounts of supply gas flow rate, gas pressure, fuel cell temperature, auxiliary machine temperature, and fuel cell takeout output when starting below zero by executing such a control procedure and when starting below zero without executing FIG. 15 shows a case where the activation time is changed. FIGS. 15A to 15A show the case where they are executed, and FIGS. 15B-B4 show the case where they are not executed.

  When the control procedure employed in the fourth embodiment is executed, the supply gas flow rate at the time of startup is limited. Therefore, when the control procedure is normally started below zero (when the control procedure of the fourth embodiment is not executed), A large flow of gas cannot flow. When the start-up supply gas flow rate is limited, the gas pressure increase rate and the target gas pressure are also limited, so that the gas pressure increase rate and the target gas pressure are usually lower than when starting below zero. Further, when the supply gas flow rate and the gas pressure restriction are performed, the fuel cell takeout output is also restricted, so that the fuel cell takeout output is lower than that in the normal activation.

  As described above, when the supply gas flow rate, the gas pressure, and the fuel cell take-out output restriction are executed, the time required for the fuel cell temperature to become 0 ° C. or higher is longer than that in the case of starting under normal zero (FIG. 15). T15a shown in (a3)> T15b shown in FIG. However, the fuel cell temperature, auxiliary equipment, piping, and fuel cell inlet gas temperature for starting up below zero are all 0 ° C. or lower.

  On the other hand, when the present application is applied, fuel cell temperature <0 ° C. <auxiliary equipment, piping, and fuel cell inlet gas temperature. In such a temperature condition, when starting in the voltage drop state described in the first embodiment without executing the above control procedure, the anode catalyst layer deteriorates due to the starvation, so that the output is taken out from the fuel cell. Cannot be started. In addition, the time required for starting after the voltage drop is recovered is much longer than the time required for starting after executing the control procedure. Therefore, as a result, the sub-zero start-up time can be shortened by starting by executing the control procedure employed in the above-described fourth embodiment.

  As described above, in the fourth embodiment, in addition to the effects obtained in the third embodiment, the fuel cell take-out current at the start is calculated based on the supply gas flow rate at the start, the supply gas pressure, and the fuel cell temperature. By limiting, defrosting of the fuel cell can be promoted while preventing a decrease in power generation efficiency due to a reduction in starvation and the diffusion performance of the fuel cell catalyst layer.

1 is a diagram illustrating a configuration of a fuel cell system according to Example 1. FIG. It is a figure which shows the voltage behavior at the time of subzero starting when a fuel cell gas flow path is obstruct | occluded. It is a figure which shows the voltage behavior at the time of subzero starting in Example 1. FIG. 3 is a flowchart illustrating a control procedure according to the first embodiment. It is a figure which shows the map of the supply gas flow volume limiting value at the time of sub-zero starting in Example 1-amount of condensed water. 10 is a flowchart illustrating a control procedure according to the second embodiment. It is a figure which shows the relationship between the auxiliary machine in Example 2, the amount of residual water in piping, and a fuel cell taking-out output. It is a figure which shows the map of the supply gas flow volume limiting value at the time of the sub-zero starting in Example-condensate water amount + residual water amount. 10 is a flowchart illustrating a control procedure according to a third embodiment. It is a figure which shows the map of the gas pressure rise rate at the time of sub-zero start-up in Example 3-the supply gas flow rate restriction value at the time of sub-zero start-up. 10 is a flowchart illustrating a control procedure according to a fourth embodiment. It is a figure which shows the map of the fuel cell taking-out output at the time of sub-zero starting in Example 4-supply gas flow rate limiting value. It is a figure which shows the map of the fuel cell taking-out output-gas pressure at the time of the subzero starting in Example 4. It is a figure which shows the fuel cell takeout output at the time of sub-zero starting in Example 4-fuel cell temperature map. It is a figure which shows the change of the starting time of various parameters at the time of subzero starting.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pressure reducing valve 2 ... Hydrogen pressure control valve 3 ... Anode inlet hydrogen temperature sensor 4 ... Anode inlet hydrogen pressure sensor 5 ... Fuel cell 6 ... Separator tank 7 ... Separator tank temperature sensor 8 ... Drain valve 9 ... Hydrogen circulation pump 10 ... Hydrogen Circulation pump temperature sensor 11 ... Hydrogen purge valve 12 ... Hydrogen circulation system piping temperature sensor 13 ... Hydrogen tank 14 ... Power control device 15 ... Current measurement system 16 ... Compressor 17 ... Air humidifier 18 ... Air humidifier temperature sensor 19 ... Cathode inlet Air temperature sensor 20 ... Cathode inlet air pressure sensor 21 ... Air pressure control valve 22 ... Cooling water circulation pump 23 ... Fuel cell inlet cooling water temperature sensor 24 ... Fuel cell outlet cooling water temperature sensor 25 ... Heat exchanger

Claims (9)

In a fuel cell system including a fuel cell that generates electricity by an electrochemical reaction using a supply gas supplied by a reaction gas supply means,
Liquid water amount estimating means for estimating the amount of water at the time of startup existing in the reaction gas supply flow path to the fuel cell;
When the supply of the supply gas is started by the reaction gas supply means when the temperature of the fuel cell is below freezing and water is present in the reaction gas supply flow path, the water estimated by the liquid water amount estimation means The fuel cell system further comprises operation control means for restricting the flow rate of the supply gas supplied to the fuel cell as the amount increases. 2. The fuel cell system according to claim 1, wherein the liquid water amount estimation unit estimates that the amount of water increases as the difference between the supply gas temperature at the previous stop and the supply gas temperature at the current start-up increases. The supply gas temperature at the previous stop is the maximum temperature in the reaction gas supply flow path, and the supply gas temperature at the current start is the minimum temperature in the reaction gas supply flow path. The fuel cell system described. 2. The fuel cell system according to claim 1, wherein the liquid water amount estimation means estimates that the amount of water increases as the extraction current extracted from the fuel cell at the previous stop increases. The fuel cell system according to any one of claims 1 to 4, wherein the amount of water is a sum of an amount of condensed water and an amount of residual water. 6. The fuel cell system according to claim 1, wherein the operation control unit limits the pressure increase rate of the supply gas at the start-up as the start-up supply gas flow rate is limited. . 7. The fuel cell according to claim 6, wherein the operation control means limits the extraction current extracted from the fuel cell at startup based on the supply gas flow rate at startup, supply gas pressure, and fuel cell temperature. system. The fuel cell system according to any one of claims 1 to 7, wherein the fuel cell temperature is represented by an outlet cooling water temperature of the fuel cell. The fuel cell system according to any one of claims 1 to 8, wherein when the temperature of the fuel cell reaches a thawing temperature, the restriction on the supply gas flow rate is released.

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