JP5338489B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system provided with a hydrogen pump for feeding hydrogen gas in a hydrogen circulation passage.

  Fuel cells are high-efficiency and clean power generation devices that generate electricity by causing an electrochemical reaction between hydrogen and oxygen, and vehicles equipped with fuel cells have been actively developed. A fuel cell mounted on a vehicle is used as a fuel cell stack in which a plurality of membrane electrode assemblies and a plurality of separators that separate them are alternately stacked. In the fuel cell, water is generated by an electrochemical reaction, and since air is humidified and supplied to the stack, moisture is also present on the hydrogen electrode side.

  FIG. 4A shows a schematic plan view of the separator 50 on the hydrogen electrode side. FIG. 4B is an enlarged view of a circled part (hydrogen flow path outlet 52) in FIG. 4A. As shown in FIG. 4 (a), the separator 50 is formed by forming a hydrogen flow channel 51 through which hydrogen gas flows on one surface of a flat plate and a cooling water flow channel (not shown) on the other surface. In general, when the power generation operation of the fuel cell system is stopped, a scavenging operation is performed to remove water remaining in the hydrogen flow path 51. The hydrogen flow path outlet 52 is formed as shown in FIG. Since it has a comb-like shape that branches into a plurality of flow paths and has a total cross-sectional area larger than that of the upstream side, it is easy for water to collect (clogging easily). If the water temperature remains below freezing with water remaining at the hydrogen channel outlet 52, the hydrogen channel outlet 52 may freeze and close, causing a voltage drop during restart. Therefore, the scavenging time is long to sufficiently remove the water at the hydrogen flow path outlet 52.

  As a technique related to the present invention, a fuel cell system that changes the flow direction of hydrogen gas during a scavenging operation is disclosed. For example, Patent Document 1 includes a pump control unit that reversely rotates the rotation of a hydrogen gas circulation pump when the first water level detection unit detects that the water level of the stored water in the gas-liquid separator has decreased. A fuel cell system is disclosed. Patent Document 1 describes that the forward rotation and reverse rotation of the circulation pump are repeated.

  Further, Patent Document 2 discloses a fuel cell power generation stop control method including a flow direction reversal step for reversing a flow direction of a reaction gas in a reaction gas flow channel when a power generation stop signal is input. It is disclosed. In Patent Document 2, the dry gas is passed through the reaction gas channel in the reverse direction during the power generation stop process so that the electrolyte membrane is uniformly dried to a predetermined degree of drying, and moisture is also removed from the reaction gas channel. Therefore, it is described that at the time of stoppage, there is no moisture in the reaction gas flow path, and that an optimum moisture residual condition in which the electrolyte membrane is maintained in a desired uniform wet state is satisfied.

JP 2007-242381 A Japanese Patent Laid-Open No. 2005-209609

  As described above, since the system disclosed in Patent Document 1 repeats forward and reverse rotations of the circulation pump, it cannot be solved that water accumulates at the hydrogen channel outlet of the separator, and the scavenging operation time There is room for improvement from the viewpoint of shortening.

  The system disclosed in Patent Document 2 also has a long scavenging operation in order to establish an optimal moisture residual condition in which there is no moisture in the reaction gas channel and the electrolyte membrane is maintained in a desired uniform wet state. Therefore, there is room for improvement from the viewpoint of shortening the scavenging time, and the stored water in the gas-liquid separator is recirculated (backflow) due to the long-term backflow operation, and is discharged to the hydrogen channel outlet of the separator. It is difficult to eliminate the accumulation of water at the hydrogen channel outlet.

  An object of the present invention is to provide a fuel cell system capable of preventing water from remaining at the outlet of a hydrogen channel of a separator by a short scavenging operation.

The fuel cell system according to the present invention divides the hydrogen flow channel at the flow channel outlet into a plurality of fine flow channels, so that the hydrogen flow channel total cross-sectional area larger than the hydrogen flow channel total cross-sectional area at a portion other than the flow channel outlet is obtained. , A fuel cell body including a separator with reduced pressure loss at the flow path outlet, a supply channel connecting the hydrogen tank and the fuel cell body, and hydrogen gas discharged from the fuel cell body is resupplied to the fuel cell body A fuel that performs a scavenging operation when the power generation operation is stopped, including a circulation channel for performing the operation, a hydrogen pump that sends the hydrogen gas in the circulation channel, and a control unit that controls a driving state of the hydrogen pump In the battery system, when the power generation operation is stopped, the control unit sets the time obtained by dividing the circulation volume of the hydrogen gas by the scavenging flow rate of the hydrogen pump as the longest scavenging time. Drive in the opposite direction Rolling scavenge have rows, characterized in that scavenging micro-channel of the channel outlet of the separator.

  In addition, an exhaust valve that discharges hydrogen gas in the circulation channel to the outside is provided, and when the power generation operation is stopped, the control unit opens the exhaust valve while driving the hydrogen pump in the opposite direction to that during the power generation operation. It is preferable to discharge hydrogen gas.

  Further, an impedance measuring device for measuring the impedance of the fuel cell main body is provided, and the control unit sets the reverse scavenging time when the measured value by the impedance measuring device is equal to or greater than a predetermined threshold after the reverse scavenging is completed or during the reverse scavenging. It is preferable to extend.

  According to the fuel cell system of the present invention, when the power generation operation is stopped, the control unit uses the time obtained by dividing the circulation volume of the hydrogen gas by the scavenging flow rate of the hydrogen pump as the longest scavenging time. Since the reverse scavenging is performed by driving in the reverse direction to the power generation operation, it is possible to prevent water from remaining at the outlet of the hydrogen channel of the separator by the scavenging operation for a short time. That is, since it was difficult to remove residual water at the hydrogen channel outlet, a long scavenging operation was required. By rotating the hydrogen pump in reverse and sucking water from the hydrogen channel outlet, It became possible to remove water from the hydrogen channel outlet. Therefore, the hydrogen channel outlet of the separator is not frozen and clogged, and the occurrence of a voltage drop at the time of restart can be suppressed.

  Moreover, when the control unit is configured to discharge the hydrogen gas by opening the exhaust valve while driving the hydrogen pump in the opposite direction to that during the power generation operation when stopping the power generation operation, It is possible to prevent hydrogen gas from flowing in the flow direction (forward direction) during power generation operation, and to prevent clogging due to recirculation of water with respect to the hydrogen flow path outlet of the separator.

  In addition, when the measured value by the impedance measuring instrument is equal to or greater than a predetermined threshold after the end of the reverse scavenging or during the reverse scavenging, the control unit, for example, stops the power generation operation if the reverse scavenging time is extended. Even when a large amount of generated water is generated immediately before, a sufficient drainage level can be ensured from the viewpoint of preventing freezing and clogging at the hydrogen channel outlet or the like.

1 is a block diagram showing a schematic configuration of a fuel cell system in an embodiment according to the present invention. It is a flowchart which shows the control procedure of the reverse scavenging operation by the fuel cell system shown in FIG. 6 is a flowchart showing a modification of the control procedure of the reverse scavenging operation by the fuel cell system shown in FIG. 1. It is a schematic diagram which shows the separator by the side of the hydrogen electrode applied to the fuel cell system shown in FIG.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. In the following description, the fuel cell system 10 is a system mounted on a vehicle and has a drive system 15 for driving the vehicle. However, for example, various facilities (factories, office buildings, homes, etc.) It can also be applied to the installation power source.

  The configuration of the fuel cell system 10 will be described with reference to FIG. As shown in FIG. 1, the fuel cell system 10 includes a fuel cell stack 11 in which a plurality of fuel cells that generate electric power using an electrochemical reaction between hydrogen and oxygen are stacked. The fuel cell system 10 includes a hydrogen system 12 that supplies hydrogen gas to the fuel cell stack 11, an air system 13 that supplies air (oxygen gas), a cooling system 14 that cools the fuel cell stack 11, and a fuel cell. It has a drive system 15 that drives the vehicle with the electric power generated by the stack 11 and a control unit 35 that comprehensively controls the operation of the entire system.

  The fuel cell stack 11 is a fuel cell main body that generates electric power, and has a structure in which a plurality of membrane electrode assemblies (not shown) and a plurality of separators that separate them are alternately stacked. The form of the separator is not particularly limited, and a straight type or a serpentine type can be used.

  As described above (see FIG. 4A), the separator 50 on the hydrogen electrode side has a hydrogen channel 51 for flowing hydrogen gas on one surface of the flat plate, and a cooling water channel (not shown) on the other surface, respectively. It is formed. The hydrogen flow path outlet 52 has a total cross-sectional area of the flow path larger than that of the upstream portion, and has, for example, a comb shape as shown in FIG. Therefore, the hydrogen channel outlet 52 is easily clogged with water.

  The comb channel shape is adopted for the hydrogen flow path outlet 52 of the separator 50 in order to reduce pressure loss. That is, since the hydrogen flow path outlet 52 is a portion where water in the hydrogen gas concentrates, the total cross-sectional area of the flow path is increased to reduce pressure loss. Here, the comb shape is a shape in which the total cross-sectional area of the flow path is larger than the cross-sectional area of the upstream flow path and branches into a plurality of fine flow paths, and the cross-sectional area of each fine flow path is It is smaller than the cross-sectional area of the side channel. If such a tooth shape is adopted for the hydrogen flow path outlet 52, the total cross-sectional area of the flow path is increased, so that the pressure loss is reduced, but the flow velocity is also reduced, so that water does not flow easily and clogging is likely.

  The fuel cell stack 11 is formed by stacking fuel cells along a direction perpendicular to the paper surface of FIG. Peripheral devices such as a hydrogen system 12 and an air system 13 are connected to the fuel cell stack 11. For example, the hydrogen supply channel 17 of the hydrogen system 12 is connected to the hydrogen channel of the separator 50 via an end plate (not shown). 51. Hydrogen gas introduced from one end plate passes through an outlet manifold formed by communicating an inlet manifold (not shown), a hydrogen flow path 51, and an outlet manifold hole 53 shown in FIG. Discharged. A hydrogen circulation channel 18 is connected to the other end plate.

  The hydrogen system 12 includes a hydrogen tank 16 filled with a high-pressure hydrogen gas (which can also be a tank containing a hydrogen storage alloy), a hydrogen supply channel 17, a hydrogen circulation channel 18, and a hydrogen discharge flow. A passage 19 and a gas-liquid separator 20 are provided. Here, the hydrogen supply channel 17 is a channel that connects the hydrogen tank 16 and the inlet (inlet side end plate) of the hydrogen channel 51 of the separator 50, and the hydrogen circulation channel 18 is the hydrogen channel 51 of the separator 50. A hydrogen discharge channel 19, which is a channel connecting the outlet (end plate on the outlet side) and the hydrogen supply channel 17, is described as a channel connecting the gas-liquid separator 20 and the diluter 26.

  The hydrogen supply channel 17 is a channel for supplying the hydrogen gas from the hydrogen tank 16 to the fuel cell stack 11, and connects the hydrogen tank 16 and the inlet of the hydrogen channel 51 of the separator 50 as described above. To do. The hydrogen supply channel 17 includes a main stop valve 21 for opening and closing the channel, a pressure reducing valve 22 for reducing the upstream pressure of the channel to a predetermined secondary pressure, and an injector 23 for adjusting the flow rate and pressure of hydrogen gas. And are provided. In addition, the operation | movement of these valves is controlled by the control part 35 mentioned later.

  The hydrogen circulation channel 18 is a channel for returning the hydrogen gas (hydrogen offgas) discharged from the fuel cell stack 11 to the hydrogen supply channel 17 and recirculating it to the fuel cell stack 11 as described above. The outlet of the hydrogen channel 51 of the separator 50 is connected to the downstream side of the injector 23 of the hydrogen supply channel 17. Further, the hydrogen circulation channel 18 is provided with a hydrogen pump 24 for sending hydrogen gas in the channel.

  The hydrogen pump 24 is a device that compresses and pumps the hydrogen gas in the hydrogen circulation flow path 18, and widely includes what is called a blower (fan, blower) or a compressor. The hydrogen pump 24 is mainly composed of a compression unit having a centrifugal or axial flow type impeller, an electric motor for driving the impeller, an inverter for changing / adjusting the rotation direction and the number of rotations of the electric motor, and the like. It is configured. The applicable hydrogen pump 24 is not particularly limited, and is a turbo type (centrifugal, axial flow, diagonal flow, cross flow, etc.) or positive displacement type (rotation type (roots type, vane type, etc.)) Reciprocating type).

  Here, during the power generation operation of the fuel cell system 10, the hydrogen pump 24 is driven so that hydrogen gas is sent toward the hydrogen supply flow path 17 as indicated by a black arrow. In the present specification, the hydrogen gas flow direction during the power generation operation is referred to as a forward direction. The operation of the hydrogen pump 24 during the power generation operation and during the scavenging operation when stopping the power generation operation is controlled by the control unit 35. For example, the control unit 35 outputs a control command to the inverter of the hydrogen pump 24, The rotation direction and the number of rotations of the hydrogen pump 24 (electric motor) are changed.

  The hydrogen discharge channel 19 is a channel for discharging a part of the hydrogen gas (hydrogen offgas) whose hydrogen concentration has been reduced by circulation and used to the outside. As described above, the hydrogen discharge channel 19 and the gas-liquid separator 20 Connect to the diluter 26. The hydrogen discharge channel 19 also functions as a drainage channel for discharging water stored in the gas-liquid separator 20. An exhaust / drain valve 25 is provided in the hydrogen discharge channel 19, and hydrogen gas and water are discharged to the outside through the diluter 26 and the muffler 27 by opening this valve. Here, the diluter 26 is a portion that reduces the hydrogen gas concentration by mixing the discharged hydrogen gas and the air discharged from the air system 13. The hydrogen discharge channel 19 may be an exhaust-only channel that discharges only hydrogen gas, and an exhaust valve may be installed in the channel.

  The opening / closing operation (usually closed state) of the exhaust / drain valve 25 is controlled by the control unit 35 based on the pressure in the hydrogen system 12, the operating condition of the vehicle, and the like. For example, when the vehicle is running at a low speed and the amount of power generation is small, the amount of hydrogen gas consumed is small and the amount of water collected in the gas-liquid separator 20 is also small, so that the exhaust / drain valve 25 is difficult to open. On the other hand, when the vehicle is running at high speed and the amount of power generation is large, the amount of hydrogen gas consumed is large and the amount of water that accumulates in the gas-liquid separator 20 is large, so that the exhaust / drain valve 25 is easily opened. When the scavenging operation is finished, the exhaust drain valve 25 is opened, and the hydrogen gas and water in the hydrogen system 12 are discharged to the outside.

  The gas-liquid separator 20 is a container that separates and recovers moisture such as produced water contained in hydrogen gas and temporarily stores it, and is provided at a branch point between the hydrogen circulation channel 18 and the hydrogen discharge channel 19. It is done. As described above, when the power generation operation is terminated, the scavenging operation is performed, and the water present in the hydrogen channel 51 and the hydrogen circulation channel 18 is sent to the gas-liquid separator 20.

  The air system 13 has a function of supplying air sucked from the atmosphere to the fuel cell stack 11, and is an air supply flow connected to the inlet (inlet side end plate) of the oxidizing gas flow path of the separator of the fuel cell stack 11. A path 28 is provided. The air supply channel 28 is provided with an air cleaner 29, an air compressor 30 that pumps air, and a humidifier 31 that humidifies the air. In addition, an air pressure adjusting valve 33 for adjusting the air pressure is provided in the air discharge passage 32 connecting the outlet (manifold outlet) of the oxidizing gas passage of the separator in the fuel cell stack 11 and the diluter 26. Yes.

  The cooling system 14 includes a cooling water path for supplying and circulating cooling water to the fuel cell stack 11, a water pump for pumping the cooling water, a radiator including a fan, and ion exchange for adsorbing conductive ions in the cooling water. It consists of an ion exchange part filled with resin. The fuel cell needs to maintain a constant temperature (for example, 80 ° C.) in order to ensure power generation efficiency, and the cooling system 14 has a function of keeping the temperature of the fuel cell stack 11 constant.

  The drive system 15 includes an electric motor for driving a vehicle, a battery such as a lithium ion battery that stores electric power generated in the fuel cell stack 11, an electric motor for driving an auxiliary machine, a power control unit, and the like. The power control unit includes a DC-DC converter, an inverter, and a power control unit controller that controls the operation of the inverter under the control of the controller 35.

  The fuel cell system 10 also includes an impedance measuring device 34 that measures the impedance of the fuel cell stack 11. As the impedance measuring device 34, a known impedance measuring device can be used. For example, the impedance measuring device 34 is installed in several fuel cells such as the vicinity of both ends and the center of the fuel cell stack 11. The measured value of the impedance measuring device 34 is used to specify the amount of water in the corresponding fuel cell or fuel cell stack 11. As a specific method for calculating the amount of water, for example, a method of applying a measured value to a map showing the relationship between the impedance and the amount of water recorded in the control unit 35 or the like can be mentioned.

  As described above, the fuel cell system 10 includes the control unit (ECU) 35 that comprehensively controls the operation of the entire system. The control unit 35 is configured by a microcomputer including a CPU, a ROM, a RAM, an I / O, and the like, and executes processes such as various calculations according to a control program stored in the ROM. The control unit 35 includes an impedance measuring device 34, other sensors and measuring devices (not shown), information on gas pressure, current / voltage values, temperature, etc., system start / stop request signals, and loads such as the drive system 15 and the like. The required power signal is input. Based on these pieces of information, the control unit 35 controls the operation of devices and valves such as the hydrogen pump 24 and the exhaust / drain valve 25.

  The fuel cell system 10 has a function of preventing water from remaining at the hydrogen flow path outlet 52 of the separator 50 shown in FIG. As a component for realizing this function, the control unit 35 includes a reverse drive means 36, a reverse drive time extension means 37, and a discharge means 38.

  The reverse drive means 36 has a function of performing the reverse scavenging by driving the hydrogen pump 24 in the direction opposite to that during the power generation operation when the power generation operation is stopped. Here, the reverse scavenging means that the hydrogen pump 24 is driven in the reverse direction so that the hydrogen gas is sent in the direction opposite to that during the power generation operation as shown by the white arrow in FIG. This is a process for sending water present in the flow path 51 and the like to the gas-liquid separator 20. As will be described in detail later, in the fuel cell system 10, it is important to suck and remove the water clogged in the hydrogen flow path outlet 52 to the upstream side of the hydrogen flow path 51.

  Specifically, the reverse drive means 36 acquires a power generation operation end processing request signal from a vehicle (vehicle ECU) (not shown), and outputs a control signal to the inverter of the hydrogen pump 24 when the request signal is acquired. Then, the hydrogen pump 24 is driven in reverse. At this time, the rotation speed of the hydrogen pump 24 is set to, for example, a predetermined rotation speed applied during the reverse scavenging operation. For example, the rotation speed during the reverse scavenging operation can be set to the maximum rotation speed from the viewpoint of shortening the scavenging time.

  The reverse scavenging time executed by the reverse drive means 36 is determined based on the circulation volume of the hydrogen gas and the scavenging flow rate of the hydrogen pump 24. Specifically, the time obtained by dividing the circulation volume by the scavenging flow rate. Is the longest scavenging time. Also, the reverse scavenging time is changed according to the measured value of the impedance measuring device 34 before the start of the reverse scavenging. For example, when the impedance is low and the amount of water is small, the shortest scavenging time is the shortest possible operation of the hydrogen pump 24. It is also possible to shorten the time to. In addition, from the viewpoint of achieving both prevention of voltage drop at the time of restart and shortening of the scavenging time, a preferable reverse scavenging time is the above longest time from the time obtained by dividing the volume of the hydrogen channel 51 by the scavenging flow rate. Within the scavenging time range.

  Here, the circulation volume of hydrogen gas, which is one factor for determining the longest scavenging time, means the volume of the portion through which the hydrogen gas flows during the reverse scavenging operation. Specifically, the hydrogen circulation flow path 18, the separator 50 is a volume of a part of the 50 hydrogen flow paths 51, the gas-liquid separator 20, and the hydrogen supply flow path 17. In addition, as a circulation volume, although it changes a little with presence of water, the volume of the state in which water does not exist can be used, for example. The scavenging flow rate of the hydrogen pump 24, which is another factor for determining the longest scavenging time, can be expressed as the volume of hydrogen gas delivered per unit time. This scavenging flow rate changes depending on the rotation speed of the hydrogen pump 24. However, when the rotation speed of the hydrogen pump 24 during reverse rotation driving is set to the maximum rotation speed, the longest scavenging time can be set to a fixed value.

  As a specific reverse scavenging time, when the circulation volume of hydrogen gas is 20 L and the scavenging flow rate of the hydrogen pump 24 is 200 (L / min), the longest scavenging time is 20 (L) / 200 (L / Minutes) = 0.1 (minutes), that is, 6 (seconds). Moreover, if the volume of the hydrogen flow path 51 of the separator 50 is 10 L, a suitable reverse scavenging time is 3 seconds to 6 seconds.

  Thus, in the fuel cell system 10 that performs scavenging for a short time, an object is to remove at least water clogged in the hydrogen flow path outlet 52. This is because if water remains at the hydrogen flow path outlet 52 having a comb shape and freezes and closes, hydrogen gas does not flow into the hydrogen flow path 51 and a voltage drop at the time of restart is likely to occur. On the other hand, the portion other than the hydrogen channel outlet 52 has a large channel diameter, so even if some water remains, a voltage drop at the time of restart is unlikely to occur. That is, the fuel cell system 10 finds that the voltage drop at the time of restart can be sufficiently suppressed by sucking and removing the water clogged at the hydrogen passage outlet 52 to the upstream side of the hydrogen passage 51 by the reverse scavenging operation. As a result, the scavenging time can be significantly shortened compared to the conventional system. It should be noted that the water present in the hydrogen flow path 51 and the hydrogen circulation flow path 18 can generally be removed (sent to the gas-liquid separator 20) by the reverse scavenging time.

  The reverse scavenging time extending means 37 has a function of extending the reverse scavenging time of the hydrogen pump 24 based on the measurement value of the impedance measuring device 34. As described above, the amount of water in the fuel cell stack 11 can be calculated from the measurement value of the impedance measuring instrument 34, and the drainage level can be acquired. In the fuel cell system 10, the scavenging time is set to a short time, but there may be cases where short-time scavenging cannot be used, such as when the amount of power generation immediately before stopping the power generation operation is large. Therefore, even in such a case, a sufficient drainage level can be secured by the reverse scavenging time extending means 37 from the viewpoint of preventing freeze clogging of the hydrogen channel outlet 52 and the like.

  Specifically, the reverse scavenging time extending means 37 compares the measured value of the impedance measuring instrument 34 with a predetermined threshold after the completion of the reverse scavenging, and when the measured value is equal to or greater than the threshold, drainage is insufficient. Judge that there is, extend the reverse scavenging time. That is, after the reverse scavenging time set based on the hydrogen gas circulation volume and the scavenging flow rate of the hydrogen pump 24 is measured, the impedance of the fuel cell stack 11 is measured. Perform reverse scavenging for the set reverse scavenging time. This operation is repeated until the measured value becomes less than the threshold value. In addition, since the measurement / determination of the impedance is performed instantaneously, it is not necessary to temporarily stop the hydrogen pump 24 when extending the reverse scavenging time. On the other hand, during reverse scavenging, it is also possible to perform control for comparing the measured value of the impedance measuring instrument 34 with a predetermined threshold value. When the measured value is equal to or greater than the threshold value, the set reverse scavenging time is set according to the measured value. Can be corrected and extended.

  The discharge means 38 has a function of opening the exhaust drain valve 25 and discharging hydrogen gas to the outside after completion of the reverse scavenging operation. For example, the discharge means 38 is configured to open the exhaust / drain valve 25 after a predetermined waiting time has elapsed after stopping the reverse drive of the hydrogen pump 24 or to open the exhaust / drain valve 25 simultaneously with the stop of the reverse drive operation of the hydrogen pump 24. It can be set.

  Moreover, it is preferable that the discharge means 38 has a function of driving the hydrogen pump 24 in the reverse direction when the exhaust / drain valve 25 is opened. That is, the discharge means 38 opens the exhaust drain valve 25 and discharges hydrogen gas while driving the hydrogen pump 24 in the reverse direction. With such a configuration, it is possible to prevent hydrogen gas from flowing in the forward direction when the exhaust / drain valve 25 is opened, and to prevent clogging due to recirculation of water with respect to the hydrogen flow path outlet 52 of the separator 50. The exhaust means 38 can exhaust the hydrogen gas by opening the exhaust drain valve 25 while continuing the reverse drive state of the hydrogen pump 24 after the reverse scavenging time has elapsed.

  In addition, when the exhaust pump 25 is opened and the hydrogen gas is discharged while the hydrogen pump 24 is driven in the reverse direction, it is possible to control to reduce the rotation speed of the hydrogen pump 24 according to the residual pressure of the hydrogen gas.

  Control related to the reverse scavenging operation of the fuel cell system 10 having the above-described configuration will be described with reference to FIGS. Here, FIG. 2 and FIG. 3 are flowcharts showing the control procedure of the reverse scavenging operation. In the reverse scavenging operation shown in FIG. 2, impedance determination is performed, and in the reverse scavenging operation shown in FIG. The difference is that the hydrogen pump 24 is reversely driven during the hydrogen gas discharge operation after scavenging is completed without performing the determination.

  With reference to FIG. 2, the control procedure when the impedance determination is performed, in particular, the function of the control unit 35 will be described. First, it is determined whether or not a power generation operation end processing request signal has been acquired (S10). The termination process request signal is input from the ECU of the vehicle to the control unit 35 based on, for example, the operation of the vehicle user.

  When the end process request signal is acquired in S10, the reverse drive of the hydrogen pump 24 is started (S11). That is, reverse scavenging is quickly started at the same time as the power generation operation is stopped, for example, without performing forward rotation scavenging for sending hydrogen gas in the same forward direction as during power generation operation. Specifically, as described above, a control command for driving the electric motor in reverse rotation is output from the control unit 35 to the inverter of the hydrogen pump 24.

  Next, it is determined whether or not the set reverse scavenging time has passed (S12). The reverse scavenging time is determined based on the circulation volume of the hydrogen gas during scavenging and the scavenging flow rate of the hydrogen pump 24 as described above. For example, the time obtained by dividing the volume of the hydrogen flow path 51 by the scavenging flow rate. ~ Determined within the time range obtained by dividing the circulation volume by the scavenging flow rate. By setting such a scavenging time, it is possible to achieve both prevention of a voltage drop during restart and shortening of the scavenging time. The steps S10 to S12 are executed by the function of the reverse rotation driving means 36.

  When the set reverse scavenging time has elapsed, it is determined whether or not the impedance (measured value) of the fuel cell stack 11 measured by the impedance measuring device 34 has reached the target impedance (threshold value) (S13). In S13, the measured value is compared with the threshold value, and when it is determined that the measured value is equal to or greater than the threshold value, the reverse scavenging time is extended (S14). When it is determined that the measured value is less than the threshold value, the reverse drive of the hydrogen pump 24 is stopped and the reverse scavenging is finished (S15). The procedures of S13 to S15 are executed by the function of the reverse scavenging time extending means 37.

  When the reverse scavenging is completed, the exhaust / drain valve 25 is opened (S16). This procedure is executed by the function of the discharging means 38. By opening the exhaust / drain valve 25, water stored in the gas-liquid separator 20 together with hydrogen gas is discharged to the outside through the diluter 26 and the muffler 27. When exhaust drainage is completed, the exhaust drain valve 25 is closed, and the power generation operation stop process ends.

  Next, a control procedure in the case where reverse rotation driving of the hydrogen pump 24 is performed when the exhaust / drain valve 25 is opened will be described with reference to FIG. Here, the procedure from S10 to S11 is the same as the procedure shown in FIG.

  When the set reverse scavenging time has elapsed, the exhaust drain valve 25 is opened while continuing the reverse drive of the hydrogen pump 24 (S21). When the exhaust / drain valve 25 is opened, the hydrogen gas is exhausted to the outside. However, by continuing the reverse rotation of the hydrogen pump 24, the hydrogen gas is prevented from flowing in the forward direction. Alternatively, the driving of the hydrogen pump 24 may be stopped once the reverse scavenging time has elapsed, and the reverse driving of the hydrogen pump 24 may be started simultaneously with the opening of the exhaust / drain valve 25.

  Then, it is determined whether or not the discharge of hydrogen gas is completed (S22), and the drive of the hydrogen pump 24 is stopped by the determination of the completion of discharge (S23). The procedure of S21 to S23 is executed by the function of the discharging means 38. The completion of the hydrogen gas discharge can be determined using a pressure sensor (not shown).

  As described above, when the fuel cell system 10 stops the power generation operation, the fuel cell system 10 generates power using the time obtained by dividing the hydrogen gas circulation volume by the scavenging flow rate of the hydrogen pump 24 as the longest scavenging time. Since the control unit 35 including the reverse drive means 36 that performs reverse scavenging by driving in the opposite direction to that during operation is provided, water is sucked from the hydrogen flow path outlet 52 of the separator 50 to the upstream side of the flow path, so that a short time can be obtained. The residual water can be removed from the hydrogen flow path outlet 52 by the scavenging operation. Therefore, according to the fuel cell system 10, the hydrogen channel outlet 52 is not frozen and blocked, and the occurrence of a voltage drop at the time of restart can be suppressed.

  The control unit 35 also includes a reverse scavenging time extending means 37 for extending the reverse scavenging time, and a hydrogen pump when the measured value by the impedance measuring device 34 is equal to or greater than a predetermined threshold after the reverse scavenging is completed or during the reverse scavenging. 24, the exhaust drain valve 25 is opened and the hydrogen gas is discharged to open the exhaust drain valve 25, so that a sufficient drainage level can be ensured even when the amount of remaining water is large. Moreover, when the hydrogen gas is discharged, clogging due to recirculation of water with respect to the hydrogen passage outlet 52 can be prevented.

  DESCRIPTION OF SYMBOLS 10 Fuel cell system, 11 Fuel cell stack, 12 Hydrogen system, 13 Air system, 14 Cooling system, 15 Drive system, 16 Hydrogen tank, 17 Hydrogen supply flow path, 18 Hydrogen circulation flow path, 19 Hydrogen discharge flow path, 20 Air Liquid separator, 21 Main stop valve, 22 Pressure reducing valve, 23 Injector, 24 Hydrogen pump, 25 Exhaust drain valve, 26 Diluter, 27 Muffler, 28 Air supply channel, 29 Air cleaner, 30 Air compressor, 31 Humidifier, 32 Air discharge flow path, 33 Air pressure regulating valve, 34 Impedance measuring device, 35 Control unit, 36 Reverse rotation drive means, 37 Reverse rotation scavenging time extension means, 38 Discharge means, 50 Hydrogen electrode side separator, 51 Hydrogen flow path, 52 Hydrogen Channel outlet, 53 outlet manifold hole.

Claims (3)

Dividing the hydrogen channel at the channel outlet into a plurality of fine channels reduces the pressure loss at the channel outlet to a larger hydrogen channel total cross-sectional area than the hydrogen channel total cross-sectional area at the part other than the channel outlet A fuel cell body including a separator,
A supply flow path connecting the hydrogen tank and the fuel cell body;
A circulation passage for re-supplying the hydrogen gas discharged from the fuel cell body to the fuel cell body;
A hydrogen pump for sending hydrogen gas in the circulation channel;
A control unit for controlling the driving state of the hydrogen pump;
A fuel cell system that performs scavenging operation when power generation operation is stopped,
The control unit
When stopping the power generation operation, the time obtained by dividing the hydrogen gas circulation volume by the scavenging flow rate of the hydrogen pump is the longest scavenging time, and the hydrogen pump is driven in the opposite direction to that during power generation operation to perform reverse scavenging. A fuel cell system for scavenging a fine channel at the outlet of the separator . The fuel cell system according to claim 1, wherein
Equipped with an exhaust valve that discharges hydrogen gas in the circulation channel to the outside,
The control unit
A fuel cell system that, when stopping a power generation operation, opens an exhaust valve and discharges hydrogen gas while driving a hydrogen pump in a direction opposite to that during power generation operation. The fuel cell system according to claim 1 or 2,
It has an impedance measuring instrument that measures the impedance of the fuel cell body
The control unit
A fuel cell system, wherein the reverse scavenging time is extended when the measured value by the impedance measuring instrument is equal to or greater than a predetermined threshold after the reverse scavenging is completed or during the reverse scavenging.

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