JP5074669B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system that can be suitably operated at a low temperature such as at the time of startup.

Since the fuel cell has low operating characteristics at a low temperature before warm-up, a device for improving the low-temperature starting performance is desired. As a system for improving the cold start performance and the restart performance, for example, Japanese Patent Application Laid-Open No. 2004-39524 proposes a system in which a large capacity fuel cell and a small capacity fuel cell are arranged in series. In this device, only a small-capacity fuel cell is generated at startup, air from the large-capacity fuel cell and surplus hydrogen from the small-capacity fuel cell are supplied to the combustor and burned, and the combustion gas is discharged into the small-capacity fuel cell. There has been proposed a fuel cell power generator configured to lead to the air electrode (Patent Document 1). In this conventional apparatus, combustion gas containing moisture is supplied to the small-capacity fuel cell by burning hydrogen at the low-temperature start, so that the small-capacity fuel cell is efficiently warmed up. Was supposed to be shortened.
JP 2004-39524 A (0008, 0009) JP 2003-288911 A

  However, in the conventional fuel cell power generator, temperature vs. output characteristics of the small capacity fuel cell are not particularly considered. In this fuel cell power generator, it is presumed that the large-capacity fuel cell and the small-capacity fuel cell are treated as having the same temperature versus output characteristics. This is because, for example, a heat treatment is required in which a combustor is further provided, hydrogen is burned and the combustion gas is supplied to heat the small-capacity fuel cell. In this conventional fuel cell power generation apparatus, since the small capacity fuel cell is not operating with sufficient efficiency immediately after the start before the small capacity fuel cell is warmed up, only a low power generation amount is obtained. There wasn't. For this reason, there is still room for improvement in the low-temperature starting characteristics of the conventional fuel cell power generator.

  Therefore, an object of the present invention is to provide a fuel cell system capable of generating power with a relatively high output at low temperatures.

  In order to solve the above problems, a fuel cell system according to the present invention efficiently generates power at a lower temperature side among a plurality of fuel cells having different temperature-to-output characteristics and a plurality of fuel cells at the time of starting. And a control device that generates power by selecting a fuel cell having temperature vs. output characteristics.

The fuel cell system of the present invention includes a plurality of fuel cells having different temperature-to-output characteristics, a plurality of cooling paths through which a refrigerant for cooling each of the plurality of fuel cells circulates, and a forced circulation of the refrigerant. a circulation device, a temperature detection device for detecting the temperature of the refrigerant, when the temperature of the refrigerant detected by the temperature detector is lower than a predetermined temperature, among the plurality of fuel cells, efficient power generation at a lower temperature side a control device for power generation by selecting a fuel cell having a temperature versus output characteristic which includes a respective cooling path is common cooling path part is formed, the forced circulation device, the common cooling path Is provided.

According to the configuration of the present invention, the plurality of fuel cells are adjusted to have different temperature-output characteristics. When the temperature is lower than a predetermined temperature, for example, even in a state before warming up at the time of starting or restarting, a fuel cell having a temperature-output characteristic that efficiently generates power at a low temperature is selected and started. Therefore, efficient operation in the fuel cell selected before warm-up is performed. For this reason, a relatively high output can be obtained even when the engine is not warmed up at all.
Further, according to the above configuration, since the forced circulation device is provided in the common cooling path, the refrigerant that has risen due to the operation of the fuel cell that is started at a relatively low temperature becomes a fuel cell that exhibits high efficiency at a relatively high temperature. Supplied. For this reason, the warm-up time of the fuel cell operated at a relatively high temperature can be shortened. In addition, since the common forced circulation device is provided, the number of parts can be reduced.

  Here, it is preferable to further include a heating device for heating the refrigerant in the common cooling path. If the proper operating temperature of a fuel cell that is efficient at a relatively high temperature is higher than a certain level, the temperature of the fuel cell that is properly operated at a temperature higher than a certain level can be increased by sufficiently raising the temperature of the refrigerant with a heating device. Even machine time can be reduced.

  That is, when the fuel cell that efficiently generates power at a lower temperature is operating, it is preferable to heat the refrigerant by the heating device. This is because it is possible to sufficiently raise the refrigerant temperature while only an efficient fuel cell is operated at a relatively low temperature.

  In the present invention, when the temperature of the refrigerant becomes higher than a predetermined temperature, a fuel cell that efficiently generates power on a higher temperature side is selected from the plurality of fuel cells to generate power. According to this configuration, if the temperature of the refrigerant is sufficiently increased, an appropriate fuel cell operating temperature range that is efficient at a relatively high temperature is obtained. It is because it is appropriate to switch.

  Here, when the temperature of the refrigerant is within a predetermined temperature range, a plurality of fuel cells may generate power simultaneously. For example, if a fuel cell that efficiently generates electricity at a relatively low temperature can be operated and the fuel cell that efficiently generates electricity at a relatively high temperature falls within the operable temperature range, both This is because the total output can be increased by operating the engine, and the refrigerant temperature can be increased more quickly.

  That is, in such a fuel cell system, when the temperature of the refrigerant is lower than the first temperature, the fuel cell that efficiently generates power on the lower temperature side is operated, and the temperature of the refrigerant is higher than the first temperature. A fuel cell that efficiently generates power on a higher temperature side when the temperature is equal to or higher than 2, and a plurality of fuel cells when the temperature of the refrigerant is equal to or higher than the first temperature and lower than the second temperature. Will be driven together.

  The fuel cell system of the present invention has a maximum output value on the lower temperature side as compared with the first fuel cell having a predetermined temperature-to-output characteristic and the predetermined temperature-to-output characteristic in the first fuel cell. A second fuel cell, a temperature detection device that measures the temperature of a refrigerant that cools the first fuel cell or the second fuel cell, and a temperature of the refrigerant detected by the temperature detection device is lower than a predetermined temperature. A control device that preferentially generates power by the second fuel cell and preferentially generates power by the first fuel cell when the temperature is higher than a predetermined temperature, and a first cooling path that supplies refrigerant to the first fuel cell And a second cooling path for supplying the second fuel cell with a refrigerant common to the first cooling path, and a switching means for switching between the first cooling path and the second cooling path. If the second fuel cell is generating electricity It is to supply the refrigerant to both the first fuel cell and a second fuel cell, when the first fuel cell is generating is to supply the refrigerant to the first fuel cell.

  It is a specific embodiment of the present invention. When the temperature is relatively low, power generation is started by the second fuel cell that can operate at a relatively low temperature, the fuel cell is operated while the refrigerant is heated, and the first fuel cell can output due to the temperature rise of the refrigerant. When the temperature reaches, the operation is switched to the first fuel cell. For this reason, it is possible to start the system quickly and then to extract a large output according to the temperature.

  According to the present invention, a fuel cell having an efficient temperature-to-output characteristic is selected at a relatively low temperature at a low temperature such as at the time of start-up, so that an efficient operation with a high output can be performed before warm-up. Is called. A relatively high output can be obtained even in the initial state where no warm-up is performed.

  A preferred embodiment of the present invention will be described with reference to the drawings. The following embodiment relates to an example in which the fuel cell system of the present invention is mounted on an electric vehicle that is a moving body. These embodiments are exemplifications of the present invention, and the present invention is not limited to the following embodiments and can be variously modified and implemented.

(Embodiment 1)
Embodiment 1 of the present invention relates to an invention for switching the operation of two fuel cells based on a predetermined temperature.
FIG. 1 shows a schematic block diagram of a fuel cell system of the present invention mounted on an electric vehicle.
As shown in FIG. 1, this fuel cell system has a cooling path 1 for cooling a fuel cell 10 as a main power source and a cooling path 2 for cooling a fuel cell 26 as a sub power source. , Partly configured as a common path.

  That is, the cooling path 1 and the cooling path 2 are formed by joining two cooling paths in a common path that is a partial section. A circulation pump 12, a cooling device 14, and a refrigerant tank 16 are provided on the common path. The cooling path 1 and the cooling path 2 merge upstream of the circulation pump 12, and are divided into a cooling path 1 and a cooling path 2 at a branch point downstream of the refrigerant tank 16. In addition, a refrigerant | coolant means what added the well-known additive, for example, ethylene glycol etc., for improving a rust prevention effect and freezing prevention capability to pure water, and there is no limitation in the kind.

  A shut-off valve 28 according to the switching means of the present invention is provided before the junction of the cooling path 2 and the cooling path 1. The control unit 3 controls the shut-off valve 28 to control whether the refrigerant is circulated in both the cooling path 2 and the cooling path 1 or only in the cooling path 1. Specifically, when the shutoff valve 28 is closed, the refrigerant circulates only in the cooling path 1, and when the shutoff valve 28 is opened, the refrigerant flows through both the cooling path 1 and the cooling path 2. It has become.

  In addition, you may comprise so that a three-way valve and a rotary valve may be provided in the branch point of the cooling path | route 1 and the cooling path | route 2, and / or a confluence | merging point. If comprised in this way, it will become controllable so that a refrigerant | coolant may be selectively sent through either the cooling path 1 or the cooling path 2, or both. In addition, the amount of refrigerant flowing through the cooling path 1 and the cooling path 2 can be adjusted.

  The circulation pump 12 provided on the common path is related to the forced circulation device of the present invention, and can forcibly circulate the refrigerant (coolant) in the common path based on the control of the control unit 3. . It is also possible to apply a device that forcibly generates a flow, such as an ejector, instead of the circulation pump.

  The cooling device 14 has a configuration capable of depriving the heat of the refrigerant flowing through the common path. The cooling device 14 is an optional component. The structure of the cooling device 14 is not limited, but as a typical configuration, for example, a forced air cooling device composed of a combination of a radiator and a fan is conceivable. The radiator is configured such that the refrigerant is divided into a plurality of pipes and flows, and the pipes are provided with a large number of fins for increasing the contact area with the air. When the air flows between the fins, the refrigerant is cooled by heat exchange. The fan forcibly generates an air flow by the control unit 3 and enables desired cooling even in an environment where a natural air flow cannot be obtained such as when the vehicle is stopped. In addition, as a cooling device, you may give the cooling performance which exceeds air cooling by providing structures, such as a capacitor | condenser.

  The refrigerant tank 16 is a storage tank that stores excess refrigerant. In particular, the heater 20 is accommodated in the refrigerant tank 16 so as to be able to exchange heat with the refrigerant. The heater 20 is electrically connected to the battery 22 via a switch 24 that is electrically disconnected and connected under the control of the control unit 3. When the switch 24 is turned on, the heater 20 generates heat and can heat the refrigerant. The heater 20 is also an optional component, and may be omitted when the amount of heat generated by the fuel cell 26 is large or when it is limited to use in a warm region.

  A temperature sensor Tin capable of measuring the refrigerant inlet temperature is provided at the inlet of the fuel cell 10, and a temperature sensor Tout capable of measuring the refrigerant outlet temperature is provided at the outlet. Any one of these temperature sensors may be provided. Further, it may be provided in the cooling path 2. In this embodiment, since the refrigerant is shared by the common path, the refrigerant temperature can be appropriately measured at any piping position. In particular, when the fuel cell 26 is in operation, the internal temperature of the fuel cell 26 can be measured by the temperature sensor Tin, and the internal temperature of the fuel cell 10 can be measured by the temperature sensor Tout.

  The fuel cell 10 and the fuel cell 26 each have a stack structure in which a plurality of power generation structures called single cells are stacked. Basically, a single cell sandwiches a power generation body called MEA (Membrane Electrode Assembly) between a pair of separators each provided with hydrogen gas as a fuel gas, air as an oxidizing gas, and a flow path of a refrigerant according to the present invention. It has a structure. The MEA is configured by sandwiching a polymer electrolyte membrane between two electrodes, an anode and a cathode. The anode has an anode catalyst layer provided on the porous support layer, and the cathode has a cathode catalyst layer provided on the porous support layer. The fuel cell 10 is a fuel cell for normal operation, and a large number of single cells are stacked so that high output is possible. The fuel cell 26 is a fuel cell for starting at a low temperature, and has a structure capable of generating electric power with a relatively small output sufficient to drive the system at the time of starting.

  Hydrogen gas is supplied to the fuel cell 10 by opening the shutoff valve 30 and the shutoff valve 32, and air is supplied by opening the shutoff valve 34 and the shutoff valve 36. Further, hydrogen gas is supplied to the fuel cell 26 by opening the shutoff valve 40 and the shutoff valve 42, and air is supplied by opening the shutoff valve 44 and the shutoff valve 46. All of these shut-off valves can be controlled to be opened and closed by the control unit 3.

  The hydrogen gas supply system that supplies hydrogen gas to the fuel cell 10 and the fuel cell 26 includes a hydrogen tank that is charged and stored with hydrogen gas, various shut-off valves that control the supply of hydrogen gas from the hydrogen tank, and a pressure regulator that adjusts the pressure of the hydrogen gas. It includes a pressure valve, a gas-liquid separator that removes moisture from the hydrogen off-gas, a purge valve that removes impurities, a pump that causes hydrogen gas to flow, and the like. Such a hydrogen gas supply system may be a shared system or an independent system. It is more economical to provide a common configuration and to control the supply of hydrogen gas to both fuel cells by controlling the shutoff valve.

  The air supply system that supplies air to the fuel cell 10 and the fuel cell 26 includes an air cleaner that takes in air from a radiator, a compressor that supplies air, a humidifier that exchanges humidity with the air off gas, and an air off gas. A gas-liquid separator that removes excess water, a diluter for diluting hydrogen off-gas with air off-gas, and a silencer that silences noise in the piping. Such an air supply system, like hydrogen gas, may have a common configuration or an independent system. It is more economical to provide a common configuration and to control the supply of air to both fuel cells by controlling the shutoff valve.

  In the fuel cell 10 and the fuel cell 26, single cells are connected in series so that a high voltage is generated at both ends. The output voltage between the anode and cathode of the fuel cell 26 is input to the primary side of the converter 52 via the switch 50 that can be controlled by the control unit 3, and is converted into a voltage that matches the output voltage of the fuel cell 10. It is output to the next side. The secondary side of the converter 52 is connected between the anode and cathode of the fuel cell 10. The output voltage of the fuel cell 10 is further input to the primary side of the converter 54, converted to a voltage that matches the voltage of a battery (not shown), and output to the secondary side. The secondary side of the converter 54 is connected to a battery (not shown), a traction motor (not shown) that is a power consumption source, and the like. The battery 22 that supplies power to the heater 20 is charged by any one of the converter outputs.

  The control unit 3 has a configuration as a general-purpose computer having a CPU, a RAM, a ROM, an interface circuit, and the like. The control unit 3 can execute the fuel cell control method of the present invention by sequentially executing software programs stored in a built-in ROM or the like.

  Here, the present embodiment is characterized in that the fuel cell 10 and the fuel cell 26 have different temperature-to-output characteristics. Specifically, the fuel cell 10 exhibits a temperature-output characteristic in which the output increases at a relatively high temperature, while the fuel cell 26 exhibits a temperature-output characteristic in which the output increases at a relatively low temperature. In other words, the fuel cell 10 has a maximum output value in a relatively high temperature zone, and the fuel cell 26 has a maximum output value in a relatively low temperature zone.

FIG. 4 shows the temperature-output characteristics of the fuel cell 10 and the fuel cell 26, respectively.
As shown in FIG. 4, the fuel cell 10 generates power at a relatively high output, and a maximum output is obtained in the vicinity of an environmental temperature (refrigerant temperature) of 60 to 70 ° C. That is, the fuel cell 10 for normal operation can generate power from, for example, an environmental temperature of 10 ° C., but is inefficient at that temperature, and generates power at an output close to the maximum output after the environmental temperature exceeds 50 ° C. It is possible to do. On the other hand, the fuel cell 26 for starting at low temperature can generate power from around the ambient temperature of −20 ° C., and the maximum output comes out at around the ambient temperature of 20 to 30 ° C. Instead, the fuel cell 26 has a relatively low power generation output sufficient for initial operation, such as at the time of startup. Thus, since the fuel cell 26 can output the maximum output at a relatively low temperature compared to the fuel cell 10, it can generate power in a short time without warming up even at the start or at a low temperature. . From the characteristics of FIG. 4, the operable region of the low temperature startup fuel cell 26 in this embodiment is −20 to 40 ° C., and the operable region of the fuel cell 10 for normal operation is 10 to 90 ° C. and 40 to 80 ° C. It can be said that ° C is more preferable.

  Such temperature-output characteristics for each fuel cell can be varied depending on various factors. For example, it depends on the flow path structure of each single cell, the MEA specifications and the material. In general, when a fuel cell is configured such that the water retention of MEA is low, the output tends to decrease when the operating temperature exceeds 50 ° C.

  In the present invention, when the temperature of the refrigerant is lower than the predetermined threshold temperature TL, the fuel cell 26 preferentially generates power, and when the refrigerant temperature is higher than the temperature TL, the fuel cell 10 preferentially generates power. To do. The difference in temperature-output characteristics does not necessarily correlate with the output amount of the fuel cell.

The operation of the present embodiment will be described with reference to the flowchart of FIG.
The process shown in FIG. 2 is usually applied at the time of startup or restart. However, if it is carried out periodically during normal operation, the fuel cell can be switched when the environmental temperature is extremely low.
First, the circulation pump 12 is driven (S1). If already driven, the operation is continued. When the circulation of the refrigerant is started by driving the circulation pump 12, the temperature becomes uniform and appropriate temperature measurement can be performed.

  Next, the detection signal from the temperature sensor Tin is taken in, and the refrigerant temperature t is measured (S2). When the temperature t of the refrigerant is lower than the threshold temperature TL (S3: YES), it is determined that the temperature of the fuel cell 26 for low temperature startup is started. For this reason, the shutoff valve 28 is opened in order to extend the circulation of the refrigerant to the cooling path 2 (S4). That is, in order to circulate the refrigerant through both the cooling path 2 and the cooling path 1, the circulation pump 12 is driven at a predetermined rotational speed.

  Further, as an option, the switch 24 is turned on, and current is supplied from the battery 22 to the heater 20 for raising the refrigerant temperature (S5). Thereby, the refrigerant in the refrigerant tank 16 is heated with energy corresponding to the electric power supplied to the heater 20. The forced heating by the heater is, for example, when the refrigerant temperature is lower than a predetermined temperature, and it takes time for the refrigerant temperature to rise to a temperature at which the fuel cell 10 can be efficiently operated only by heat generated by the operation of the fuel cell 26. A case where the refrigerant temperature is lower than the temperature that the fuel cell 26 can efficiently perform is considered. For example, when the refrigerant temperature is extremely low (−20 ° C.) to below the freezing point (≦ 0 ° C.), the heater 20 is used.

  Subsequently, each auxiliary machine of a hydrogen gas supply system and an air supply system is started. Further, the shutoff valves 40, 42, 44, 46 are opened, and hydrogen gas and air are supplied to the fuel cell 26 for cold start (S6). At this time, since the shut-off valves 30, 32, 34, and 36 are still closed, the fuel cell 10 for normal operation still stops power generation. By the above processing, an electrochemical reaction occurs only in the fuel cell 26, and a voltage is generated between the anode and the cathode. Then, as the fuel cell 26 is operated, the refrigerant temperature rises due to heat generated in response to the electrochemical reaction, and in some cases, heat generated by the heater 20. Since this refrigerant circulates through the cooling path 2 and the cooling path 1, it is supplied from the cooling path 1 to the separator inside the fuel cell 10, and gradually warms the fuel cell 10.

  In FIG. 3A, a path through which the refrigerant circulates by the switching is indicated by a solid line. As shown in FIG. 3A, the refrigerant flowing by driving the circulation pump 12 through the common path is heated by the heat generated when the heater 20 is turned on, heated by the heat generated by the power generation of the fuel cell 26, and is not operated. It is warmed from the inside and returned to the common path again.

  On the other hand, when the refrigerant temperature t is equal to or higher than the threshold temperature TL (S3: NO), the refrigerant temperature is already suitable for the fuel cell 10 for normal operation. The operation of the battery 10 is started. First, in order to circulate the refrigerant only in the cooling path 1, the shutoff valve 28 is closed (S10). Further, the circulation pump 12 is driven at a rotation speed suitable for circulating the refrigerant in the cooling path 1.

  If the heater 20 has been turned on, it is assumed that the refrigerant temperature has already risen sufficiently, and the switch 24 is disconnected, and heating by the heater 20 is stopped (S11).

  Then, the shut-off valves 40, 42, 44, 46 of the cold start fuel cell 26 are closed so that hydrogen gas and air are supplied only to the fuel cell 10, while the fuel cell 10 for normal operation is closed. The shut-off valves 30, 32, 34, and 36 are opened (S12). By these processes, the refrigerant circulates only in the cooling path 1 and only the fuel cell 10 generates power.

  In FIG. 3B, a path through which the refrigerant circulates by the switching is indicated by a solid line. As shown in FIG. 3B, the refrigerant flows only in the cooling path 1 without flowing into the fuel cell 26. Since the power source of the heater 20 is cut off, the heater 20 is eventually heated by the heat generated by the operation of the fuel cell 10. If the temperature of the refrigerant seems to be too high, the cooling device 14 is optionally driven to adjust the refrigerant temperature.

  The threshold value TL may be set to an intermediate temperature that is higher than the temperature at which the low temperature startup fuel cell 26 exhibits the maximum value and lower than the temperature at which the normal operation fuel cell 10 exhibits the maximum value. preferable. In the present embodiment, as shown in FIG. 4, the output peak of the fuel cell 26 for low temperature startup is in the vicinity of 20 to 30 ° C., and the fuel cell 10 for normal operation has an output peak at 60 to 70 ° C. For example, the threshold value TL may be set around 40 ° C.

  In the above embodiment, the fuel cell is selected based on whether or not the temperature of the refrigerant is lower than the threshold value. However, when the system is started or restarted after a predetermined time has elapsed, the temperature of the entire fuel cell is determined. The fuel cell may be switched depending on the assumption that the battery is lowered or not (when restarting). That is, when the system is activated or restarted after a predetermined time has elapsed, only the fuel cell 26 is selected and activated, or both the fuel cell 26 and the fuel cell 10 are activated. Can be. And you may comprise so that the driving | operation by only the fuel cell 10 may be carried out after fixed time progress, or when a refrigerant | coolant temperature is more than fixed like the said embodiment.

  Moreover, in the said embodiment, although the output of each fuel cell was connected in parallel via the converter, it is good also as a series connection. Moreover, you may comprise an electric power grid | system separately, respectively.

  As described above, according to the configuration of the first embodiment, the two fuel cells 10 and 26 are adjusted to have different temperature-output characteristics. At a temperature lower than the threshold value TL, the fuel cell 26 having a temperature-output characteristic that efficiently generates power at a low temperature is selected and started. Therefore, the efficiency of the fuel cell selected before warm-up is improved. Good driving is done. For this reason, a relatively high output can be obtained even when the engine is not warmed up at all.

  Further, according to the configuration of the first embodiment, the cooling path 1 and the cooling path 2 are partially configured as a cooling path. And since the circulation pump 12 which circulates a refrigerant | coolant to a common cooling path | route is provided, the fuel cell 10 provided with the temperature-output characteristic which generates electric power efficiently at a higher temperature with the reaction heat of the fuel cell 26 driven previously is provided. It can warm up effectively. For this reason, the warm-up time of the fuel cell 10 operated at a relatively high temperature can be shortened. In addition, since the auxiliary machines can be shared on a common cooling path, the number of parts can be reduced as compared with the case where an independent cooling path is provided.

  Further, according to the configuration of the first embodiment, since the heater 20 for heating the refrigerant is provided, when the temperature of the refrigerant is extremely low, or the appropriate operating temperature of the fuel cell that is efficient at a relatively high temperature is considerably high. Even in this case, it is possible to shorten the warm-up time of the fuel cell.

  Further, according to the configuration of the first embodiment, when the fuel cell 26 that efficiently generates power at a lower temperature side is operating, the heater 20 heats the fuel cell 26, so that only the fuel cell 26 with a short startup time is operated. During this time, it is possible to sufficiently raise the refrigerant temperature and to warm up the fuel cell 10 with high output.

  Further, according to the configuration of the first embodiment, the fuel cell 10 that efficiently generates power on the higher temperature side is selected from the plurality of fuel cells when the temperature of the refrigerant becomes equal to or higher than the threshold value TL. Therefore, it is possible to select a fuel cell with good power generation efficiency at the temperature according to the refrigerant temperature.

(Embodiment 2)
Embodiment 2 of the present invention relates to an invention for operating two fuel cells together in a predetermined temperature range.
FIG. 5 shows a schematic block diagram of the fuel cell system according to the second embodiment.
As shown in FIG. 5, the fuel cell system basically has the same system configuration as that of the first embodiment. However, the fuel cell system according to the second embodiment is different in that the cooling path 1 includes a shutoff valve 29 that can be controlled to be opened / closed by the control unit 3. The shutoff valve 29 provided in the cooling path 1 and the shutoff valve 28 provided in the cooling path 2 can be controlled to be opened / closed independently by the control unit 3. That is, by closing the shut-off valve 28 and opening the shut-off valve 29, the refrigerant can be circulated only in the cooling path 1. Further, the coolant can be circulated only in the cooling path 2 by opening the shut-off valve 28 and closing the shut-off valve 29. Furthermore, the refrigerant can be circulated through both the cooling path 1 and the cooling path 2 by opening both the shut-off valves 28 and 29.

Next, the operation of the second embodiment will be described with reference to the flowchart of FIG.
The process shown in FIG. 6 is usually applied at the time of startup or restart. However, if it is carried out periodically during normal operation, the fuel cell can be switched when the environmental temperature is extremely low.
First, the circulation pump 12 is driven (S20). If already driven, the operation is continued. When the circulation of the refrigerant is started by driving the circulation pump 12, the temperature becomes uniform and appropriate temperature measurement can be performed.

  Next, a detection signal from the temperature sensor Tin is taken in, and the refrigerant temperature t is measured (S21). When the temperature t of the refrigerant is lower than the first threshold temperature T1 (S22: YES), it is determined that the fuel cell 26 for starting at least the low temperature should be operated. As shown in FIG. 4, the first threshold temperature T1 is preferably set to an upper limit temperature at which the low temperature startup fuel cell 26 can generate power and the output does not decrease. At this temperature, it is determined that the temperature of the refrigerant is relatively low. Therefore, as an option, the switch 24 is turned on to supply current from the battery 22 to the heater 20 for increasing the refrigerant temperature ( S23). Thereby, the refrigerant in the refrigerant tank 16 is heated with energy corresponding to the electric power supplied to the heater 20.

  Further, it is determined whether or not the refrigerant temperature t is lower than a second threshold temperature T2 that is lower than the first threshold temperature T1 (S24). As shown in FIG. 4, it is preferable that the second threshold temperature T2 is a lower limit temperature at which the fuel cell 10 for normal operation can generate power while having low efficiency. If the refrigerant temperature t is lower than the second threshold temperature T2 (S24: YES), it means that the refrigerant temperature is too low to be suitable for the operation of the fuel cell 10 for normal operation. For this reason, it is necessary to operate only the fuel cell 26 for cold start. In order to allow the circulation of the refrigerant only to the cooling path 2, the shutoff valve 28 is opened and the shutoff valve 29 is closed (S25). By this control, the refrigerant can be circulated only in the cooling path 2 and circulates at the rotational speed of the circulation pump 12.

  Subsequently, each auxiliary machine of a hydrogen gas supply system and an air supply system is started. Further, the shut-off valves 40, 42, 44, and 46 are opened, and hydrogen gas and air are supplied to the fuel cell 26 for cold start (S26). At this time, since the shut-off valves 30, 32, 34, and 36 are still closed, the fuel cell 10 for normal operation still stops power generation. By the above processing, an electrochemical reaction occurs only in the fuel cell 26, and a voltage is generated between the anode and the cathode. Then, as the fuel cell 26 is operated, the refrigerant temperature rises due to heat generated in response to the electrochemical reaction, and in some cases, heat generated by the heater 20. Since this refrigerant circulates through the cooling path 2 and the cooling path 1, it is supplied from the cooling path 1 to the separator inside the fuel cell 10, and gradually warms the fuel cell 10.

  On the other hand, when the refrigerant temperature t is equal to or higher than the second threshold temperature T2 (S24: NO), the refrigerant temperature t is equal to the first threshold temperature T1 and the second threshold temperature T2. Is in the temperature range between. In this temperature range, it means that both the fuel cell 10 for normal operation and the fuel cell 26 for cold start can generate power. For this reason, in order to operate both the fuel cells 10 and the fuel cell 26, both the shutoff valve 28 and the shutoff valve 29 are opened (S28). By this control, the refrigerant can be circulated in both the cooling path 1 and the cooling path 2.

  Then, all the shut-off valves 30, 32, 34, 36, 40, 42, 44, 46 are opened so that hydrogen gas and air are supplied to both the fuel cell 10 and the fuel cell 26 ( S29). Through these processes, the refrigerant circulates through both the cooling path 1 and the cooling path 2, and both the fuel cell 10 and the fuel cell 26 generate power.

  In step S22, when the refrigerant temperature t is equal to or higher than the first threshold temperature T1 (S22: NO), at least the temperature of the low-temperature startup fuel cell 26 is not suitable for operation. Means that Therefore, if the heater 20 is turned on, it is assumed that the refrigerant temperature has already risen sufficiently, and the switch 24 is disconnected, and heating by the heater 20 is stopped (S30).

  Then, the shutoff valve 28 is closed and the shutoff valve 29 is opened so that the refrigerant circulates only through the cooling path 1 (S31). Then, the shut-off valves 40, 42, 44, 46 of the cold start fuel cell 26 are closed so that hydrogen gas and air are supplied only to the fuel cell 10, while the fuel cell 10 for normal operation is closed. The shut-off valves 30, 32, 34, and 36 are opened (S32). By these processes, the refrigerant circulates only in the cooling path 1 and only the fuel cell 10 generates power.

As mentioned above, according to the structure of this Embodiment 2, there exists an effect similar to Embodiment 1. FIG.
In particular, according to the second embodiment, when the temperature of the refrigerant is in the temperature range between the first threshold temperature T1 and the second threshold temperature T2, the two fuel cells 10 and 26 generate power simultaneously. Therefore, the total output can be increased when the temperature is within such a temperature range, and the refrigerant temperature can be increased more quickly.

(Embodiment 3)
Embodiment 3 of the present invention relates to an example in which a plurality of fuel cell stacks are housed in the same casing.
FIG. 7 is a schematic block diagram of the fuel cell system according to the third embodiment.
As shown in FIG. 7, the present fuel cell system is characterized in that one fuel cell 10 is divided into two stack blocks 101 and 102 in which the same fastening load is managed. The portion corresponding to the stack block 101 corresponds to the fuel cell for normal operation of the above embodiment, and the portion corresponding to the stack block 102 corresponds to the fuel cell for low temperature startup of the above embodiment. The output characteristics are adjusted. The peripheral structure for each fuel cell can be considered in the same manner as in the first or second embodiment.

  The operation according to the third embodiment can be considered in the same manner as in the above embodiment. That is, when the cooling path 2 is enabled or disabled by the shutoff valve 28, it can be controlled by opening or closing the shutoff valve 28 as in the first embodiment. Further, when the shut-off valve 29 is further provided in the cooling path 1, it can be operated in the same manner as in the second embodiment.

  According to the third embodiment, the structure of the fuel cell is configured to be equivalent to the case where a plurality of fuel cells are provided by managing the same fastening load in one housing, so that the effects of the present invention can be achieved without wasting space. Obtainable. Moreover, since the fuel cell has a single casing, it is economical.

  In addition, the cooling path can be a common cooling path that flows in common to the plurality of stack blocks, similarly to a normal fuel cell system. With this configuration, heat generation in the stack block for low-temperature startup is directly exerted on the stack block for normal operation, so that the warm-up time can be shortened.

(Modification)
The present invention is not limited to the above-described embodiment, and can be variously modified and applied.
For example, as shown in FIG. 8, the power system in the plurality of fuel cells 10 and 26 may be configured to be connected in series so as to extract the output. If comprised in this way, it is possible to reduce the number of converters and it is economical. At this time, it is preferable to provide a configuration that electrically bypasses the fuel cell that is not generating power.

  Further, for example, as shown in FIG. 9, main power generation by a main fuel cell for normal operation (corresponding to the fuel cell 10 of the above embodiment) and a sub fuel cell for low temperature start-up (the fuel cell 26 of the above embodiment) Hysteresis specification may be given to the switching between subordinate power generation by the equivalent). That is, when the temperature rises from the low temperature side to the high temperature side, power is generated by the secondary fuel cell until the temperature reaches a predetermined temperature TH, and the main fuel cell is switched to only after the temperature TH is exceeded. Further, when the temperature drops from the high temperature side to the low temperature side, the main fuel cell is switched to the sub fuel cell only after the temperature falls below the temperature TL (<TH). By providing the hysteresis in this way, it can occur when the fuel cell is switched based on the temperature, such as vibration that is repeatedly switched without stabilizing between the two fuel cells when the fuel cell is switched. It is possible to prevent the phenomenon.

  Furthermore, in the above-described embodiment, only switching between two fuel cells has been described, but switching between fuel cells may be performed. That is, in such a fuel cell system, a plurality of fuel cells having different temperature-to-output characteristics, a temperature sensor for detecting the refrigerant temperature, and a temperature-to-output that can generate power most efficiently at the temperature detected by the temperature sensor. A control device for selecting and generating a fuel cell having characteristics is provided. According to this configuration, the fuel cell having the highest power generation efficiency at the current refrigerant temperature is selected.

  Note that the present invention can be applied not only to a moving body such as a vehicle, a ship, and an aircraft equipped with a fuel cell system, but also to a fuel cell system placed in a closed space such as a building or a house.

1 is a block diagram of a fuel cell system according to a first embodiment. Flowchart for explaining the operation of the first embodiment Circulation of refrigerant at low temperatures Circulation of refrigerant at high temperatures Temperature-output characteristics diagram between multiple fuel cells Block configuration diagram of the fuel cell system of Embodiment 2 Flowchart for explaining the operation of the second embodiment Block configuration diagram of the fuel cell system of Embodiment 3 Block configuration diagram of fuel cell system according to modification Switching explanatory diagram between fuel cells with hysteresis characteristics of a modified example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Cooling path, 3 ... Control part, 10 ... Fuel cell, 12 ... Circulation pump, 14 ... Cooling device, 16 ... Refrigerant tank, 20 ... Heater, 22 ... Battery, 24 ... Switch, 26 ... Fuel cell, 28 29, 30, 32, 34, 36, 40, 42, 44, 46 ... shut-off valve, 50 ... switch, 52, 54 ... converter, 101, 102 ... stack block, Tin, Tout ... temperature sensor

Claims (6)

A plurality of fuel cells having different temperature vs. output characteristics;
A plurality of cooling paths through which a refrigerant for cooling each of the plurality of fuel cells circulates;
A forced circulation device for circulating the refrigerant;
A temperature detection device for detecting the temperature of the refrigerant ;
When the temperature of the refrigerant detected by the temperature detection device is lower than a predetermined temperature, a fuel cell having a temperature-to-output characteristic that efficiently generates power on a lower temperature side is selected from the plurality of fuel cells. and a control unit for generating Te,
Each of the cooling paths has a common cooling path formed in part,
The forced circulation device is provided in the common cooling path,
Fuel cell system.   The fuel cell system according to claim 1, further comprising a heating device that heats the refrigerant in the common cooling path.   The fuel cell system according to claim 2, wherein when the fuel cell that efficiently generates electric power at a lower temperature side is operating, the refrigerant is heated by the heating device.   3. The fuel cell according to claim 1, wherein when the temperature of the refrigerant is higher than a predetermined temperature, a fuel cell that efficiently generates power on a higher temperature side is selected from the plurality of fuel cells to generate power. Fuel cell system.   3. The fuel cell system according to claim 1, wherein when the temperature of the refrigerant is in a predetermined temperature range, the plurality of fuel cells are caused to generate power simultaneously. A first fuel cell having predetermined temperature vs. output characteristics;
A second fuel cell having a maximum output value on a lower temperature side compared to the predetermined temperature-to-output characteristic in the first fuel cell;
A temperature detecting device for measuring a temperature of a refrigerant for cooling the first fuel cell or the second fuel cell;
When the temperature of the refrigerant detected by the temperature detection device is lower than a predetermined temperature, the second fuel cell preferentially generates power, and when the temperature is higher than the predetermined temperature, the first fuel cell has priority. A control device for generating electricity,
A first cooling path for supplying a refrigerant to the first fuel cell;
A second cooling path for supplying the second fuel cell with a refrigerant common to the first cooling path;
Switching means for switching between the first cooling path and the second cooling path,
The switching means supplies the refrigerant to both the first fuel cell and the second fuel cell when the second fuel cell is generating power, and the first fuel cell generates power. A fuel cell system, wherein a refrigerant is supplied to the first fuel cell.

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