Fuel cell module

Abstract

To avoid the inside of a fuel cell stack becoming partially dry.SOLUTION: A fuel cell module FCM is configured to comprise a fuel cell stack FCS for supplying power to a load Lo and a control section Cf for controlling power generation of the fuel cell stack FCS on the basis of a power command value from a host system STM. When charge transfer resistance Ic of the fuel cell stack FCS becomes equal to or higher than a threshold Icth at the time of normal power generation control, the control section Cf transmits an abnormality notification showing that a state of the fuel cell stack FCS is abnormal to the host system STM.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell module. [Background technology]

[0002] There is a fuel cell module that, when a relatively high frequency AC current is passed through a fuel cell stack and the internal resistance of the fuel cell stack calculated from the AC voltage superimposed on the output voltage of the fuel cell stack is equal to or greater than a threshold value, determines that the inside of the fuel cell stack is dry overall and increases the pressure of the air supplied to the fuel cell stack to prevent the inside of the fuel cell stack from drying out.Related technology is disclosed in Patent Document 1.

[0003] However, if a fuel cell stack continues to generate electricity for a relatively long period of time, the amount of moisture carried away by the air exceeds the amount of moisture produced by the electrochemical reaction only in the area near the air inlet of the fuel cell stack, causing the area to become dry, while other areas may become wet. In other words, if a fuel cell stack continues to generate electricity for a relatively long period of time, the inside of the fuel cell stack may become partially dry.

[0004] Furthermore, as described above, when determining the dry state within a fuel cell stack using internal resistance measured at a relatively high frequency, it is possible to determine whether the fuel cell stack is dry overall, but it is not possible to determine whether the fuel cell stack is partially dry.

[0005] Therefore, the fuel cell module cannot determine whether the fuel cell stack is partially dry, and there is a risk that the fuel cell stack may become partially dry. Furthermore, if the fuel cell stack becomes partially dry, there is a risk that the output voltage of the fuel cell stack may decrease. In particular, if the fuel cell module is controlled by a higher-level system to generate power, continuing to generate power while the fuel cell stack is dry could cause the fuel cell stack to deteriorate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-146971 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of one aspect of the present invention is to prevent the inside of a fuel cell stack from becoming partially dry. [Means for solving the problem]

[0008] One form of the fuel cell module according to the present invention is a fuel cell module provided in a host system that supplies power to a load, and comprises a fuel cell stack that supplies power to the load, and a control unit that controls the power generation of the fuel cell stack based on a power command value from the host system, and during normal power generation control, when the charge transfer resistance of the fuel cell stack exceeds a threshold value, the control unit sends an abnormality notification to the host system indicating that the state of the fuel cell stack is abnormal.

[0009] This allows the user to be prompted to restore the state of the fuel cell stack even if the inside of the fuel cell stack becomes partially dry by running the fuel cell stack continuously for a relatively long period of time, and allows the control to transition from normal power generation control to state restoration control upon receiving a state restoration instruction from the user. Therefore, running the fuel cell stack continuously for a relatively long period of time can prevent the inside of the fuel cell stack from becoming partially dry.

[0010] The control unit may be configured to continue the normal power generation control after sending the abnormality notification to the host system.

[0011] This makes it possible to notify the user that the fuel cell stack is in an abnormal state without reducing the power supplied to the load.

[0012] In addition, the upper system may be configured to, upon receiving a state recovery instruction from a user to recover the state of the fuel cell stack, send a state recovery command to the control unit, and the control unit, upon receiving the state recovery command from the upper system, transition from the normal power generation control to state recovery control.

[0013] This allows the state of the fuel cell stack to be restored at any time depending on the user's convenience, the load situation, and the like. [Effects of the Invention]

[0014] According to the present invention, it is possible to prevent the inside of the fuel cell stack from becoming partially dry. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram illustrating an example of a fuel cell module according to an embodiment; [Figure 2] FIG. 2 is a diagram showing the state inside the fuel cell stack. [Figure 3] 10A and 10B are diagrams illustrating an example of charge transfer resistance, output voltage of a fuel cell stack, and electrolyte membrane resistance. [Figure 4] 10A to 10C are diagrams illustrating examples of information indicating the correspondence relationship between the target current and the air stoichiometric ratio, information indicating the correspondence relationship between the target current and the air pressure, and information indicating the correspondence relationship between the target current and the refrigerant temperature. [Figure 5] 5 is a diagram showing an example of required power, output power of a fuel cell stack, output power of a power storage device, and output power of a higher-level system. FIG. [Figure 6] 4 is a flowchart showing the operation of a control unit on the fuel cell module side. [Figure 7] 10 is a flowchart showing the operation of a control unit on the host system side. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0017] FIG. 1 is a diagram illustrating an example of a fuel cell module according to an embodiment.

[0018] The fuel cell module FCM shown in FIG. 1 is provided in a host system STM, and cooperates with a power storage device B to supply power to a load Lo.

[0019] For example, if the host system STM is a stationary generator such as an industrial stationary generator, a home stationary generator, or an emergency stationary generator, the load Lo is assumed to be industrial machinery, home appliances, etc. In this case, the load Lo is assumed to be provided outside the host system STM.

[0020] Furthermore, for example, if the host system STM is a vehicle such as a forklift, a towing tractor, or an automatic guided vehicle (AGV), the load Lo is assumed to be an inverter circuit that drives a cargo handling device or a travel motor, etc. In this case, the load Lo is assumed to be provided inside the host system STM.

[0021] Furthermore, the host system STM includes a control unit Cs, a fuel tank HT, a radiator R, and the like, in addition to the fuel cell module FCM and the power storage device B. The devices and components included in the fuel cell module FCM may vary depending on the type of host system STM. For example, if the host system STM is a stationary generator, the power storage device B, fuel tank HT, and radiator R may be provided outside the fuel cell module FCM, as shown in FIG. 1. If the host system STM is a vehicle, the power storage device B, fuel tank HT, and radiator R may be provided inside the fuel cell module FCM.

[0022] The control unit Cs is configured with a microcomputer or the like, and sends to the fuel cell module FCM a power command value calculated from the power requested by the load Lo, the charging rate of the power storage device B (the proportion [%] of the remaining capacity relative to the fully charged capacity of the power storage device B), and the maximum value of the output power of the fuel cell module FCM. For example, if the power requested by the load Lo is greater than the maximum value of the output power of the fuel cell module FCM and the charging rate of the power storage device B is a predetermined charging rate (for example, the charging rate of the power storage device B when the power storage device B is in a fully charged state), the control unit Cs sends the maximum value of the output power of the fuel cell module FCM as a power command value to the fuel cell module FCM. In this case, power equivalent to the maximum value of the output power of the fuel cell module FCM is supplied from the fuel cell module FCM to the load Lo, and the power storage device B supplies the shortfall in power to the load Lo (power equivalent to the difference between the power requested by the load Lo and the maximum value of the output power of the fuel cell module FCM). Furthermore, when the power requested from the load Lo is smaller than the maximum value of the output power of the fuel cell module FCM and the charging rate of the power storage device B is smaller than a predetermined charging rate, the control unit Cs sends the sum of the power requested from the load Lo and the power required to charge the power storage device B as a power command value to the fuel cell module FCM. In this case, power equivalent to the requested power is supplied from the fuel cell module FCM to the load Lo, and the power required to charge the power storage device B is supplied from the fuel cell module FCM.

[0023] The power storage device B is configured, for example, by a lithium ion capacitor, and is connected between the fuel cell module FCM and the load Lo, and as described above, cooperates with the fuel cell module FCM to supply power to the load Lo. When power is supplied from the power storage device B to the load Lo, the power storage device B is discharged and the charging rate of the power storage device B decreases. Furthermore, when power is supplied from the fuel cell module FCM to the power storage device B, the power storage device B is charged and the charging rate of the power storage device B increases.

[0024] The fuel tank HT is a storage container for hydrogen gas as fuel gas (anode gas). The hydrogen gas stored in the fuel tank HT is supplied to the fuel cell module FCM.

[0025] The radiator R exchanges heat between the cold soot (for example, water) discharged from the fuel cell module FCM and the outside air, and then sends the cooled soot to the fuel cell module FCM.

[0026] The fuel cell module FCM includes a fuel cell stack FCS, which is the main unit, and a number of types of auxiliary units for causing the fuel cell stack FCS to generate electricity.

[0027] That is, the fuel cell module FCM includes hydrogen gas auxiliary equipment such as an injector INJ, a gas-liquid separator GLS, a hydrogen circulation pump HP, and an exhaust drain valve EDV.

[0028] The fuel cell module FCM also includes air system accessories such as a flow sensor Sf, an air compressor ACP, a pressure sensor Sp, an air pressure regulating valve ARV, and a diluter DIL.

[0029] The fuel cell module FCM also includes cooling system accessories such as a water pump WP and a temperature sensor St.

[0030] The fuel cell module FCM also includes a DC-DC converter CNV as an electrical auxiliary device.

[0031] The fuel cell module FCM further includes a memory unit Str and a control unit Cf.

[0032] The fuel cell stack (FCS) is made up of multiple fuel cell cells connected in series, and generates electricity through an electrochemical reaction between the hydrogen contained in hydrogen gas and the oxygen contained in the air. The fuel cell cells are polymer electrolyte fuel cells (PEFC).

[0033] The injector INJ adjusts the flow rate of hydrogen gas supplied from the fuel tank HT to the fuel cell stack FCS.

[0034] The gas-liquid separator GLS separates hydrogen gas, which contains unreacted hydrogen and is discharged from the fuel cell stack FCS, from liquid water.

[0035] The hydrogen circulation pump HP supplies the hydrogen gas separated by the gas-liquid separator GLS back to the fuel cell stack FCS. That is, the hydrogen circulation pump HP is equipped with a pump P that compresses the hydrogen gas separated by the gas-liquid separator GLS and supplies it to the fuel cell stack FCS, a motor M that drives the pump P, and an inverter circuit INV that drives the motor M. Note that as the rotation speed of the motor M increases, the flow rate of hydrogen gas supplied to the fuel cell stack FCS increases.

[0036] The exhaust drain valve EDV sends the liquid water separated by the gas-liquid separator GLS to the diluter DIL. The liquid water sent to the diluter DIL accumulates in a tank inside the diluter DIL. In addition, the hydrogen gas and air discharged from the fuel cell stack FCS join together in the diluter DIL and are discharged to the outside or inside of the fuel cell module FCM.

[0037] The flow rate sensor Sf detects the flow rate of air as an oxidant gas (cathode gas) supplied to the air compressor ACP from outside the fuel cell module FCM, and sends the detected flow rate to the control unit Cf.

[0038] The air compressor ACP compresses air supplied from outside the fuel cell module FCM and supplies it to the fuel cell stack FCS via a supply path FP.

[0039] The air pressure regulating valve ARV adjusts the pressure and flow rate of the air supplied to the fuel cell stack FCS.

[0040] The pressure sensor Sp detects the pressure in the flow path from the air compressor ACP to the air pressure regulating valve ARV, including the supply path FP, and sends the detected pressure to the control unit Cf.

[0041] The water pump WP supplies the fuel cell stack FCS with cold soot that has been cooled by the radiator R. The temperature of the air supplied to the fuel cell stack FCS is adjusted by the cold soot supplied to the fuel cell stack FCS.

[0042] The temperature sensor St detects the temperature of the cooled soot and sends the detected temperature to the control unit Cf.

[0043] The DC-DC converter CNV converts the voltage output from the fuel cell stack FCS into a predetermined voltage. The power output from the DC-DC converter CNV is supplied to the auxiliary devices, the load Lo, and the power storage device B.

[0044] The storage unit Str is configured by a non-volatile memory such as a ROM (Read Only Memory), a flash memory, etc. The storage unit Str stores information Ds1, Ds2, Dp1, Dp2, Dt1, Dt2, etc., which will be described later.

[0045] The control unit Cf is configured with a microcomputer or the like and controls the power generation of the fuel cell stack FCS. For example, during normal power generation control of the fuel cell stack FCS, the control unit Cf controls the operation of each auxiliary device so that the output power of the fuel cell stack FCS follows the power command value sent from the control unit Cs.

[0046] When the host system STM is a stationary generator, the control unit Cf may repeatedly cause the fuel cell stack FCS to continuously generate power for a predetermined time T1 and then stop the fuel cell stack FCS from generating power for a predetermined time T2 during normal power generation control and during state recovery control (described later). That is, the control unit Cf causes the fuel cell stack FCS to intermittently generate power. For example, the predetermined times T1 and T2 may each be several hours, with the predetermined time T1 being greater than the predetermined time T2. Alternatively, the predetermined time T1 may be a period from Monday to Friday in a week, and the predetermined time T2 may be a period from Saturday to Sunday in a week. Alternatively, the predetermined time T1 may be a period from several hours in a day, and the predetermined time T2 may be a period from Saturday to Sunday in a week.

[0047] <Conditions inside the fuel cell stack FCS when generating electricity for a relatively long period of time> FIG. 2 is a diagram showing the state inside any one of the fuel cell cells SEL when the fuel cell stack FCS is continuously generating power for a relatively long period of time. The "relatively long period" is, for example, the predetermined period T1. During normal power generation control of the fuel cell stack FCS, air supplied to the fuel cell stack FCS is supplied into the fuel cell cell SEL through the air-side inlet INa and then discharged to the outside of the fuel cell SEL through the air-side outlet OUTa. Also, hydrogen gas supplied to the fuel cell stack FCS is supplied into the fuel cell cell SEL through the hydrogen gas-side inlet INh and then discharged to the outside of the fuel cell SEL through the hydrogen gas-side outlet OUTh. The solid arrows in FIG. 2 indicate the flow of air inside the fuel cell SEL, and the dashed arrows in FIG. 2 indicate the flow of hydrogen gas inside the fuel cell SEL. The wet region WET in FIG. 2 indicates a region with a relatively high moisture content inside the fuel cell SEL, and the dry region DRY in FIG. 2 indicates a region with a relatively low moisture content inside the fuel cell SEL.

[0048] When a fuel cell stack FCS including fuel cell cells SEL configured in this way generates power continuously for a relatively long period of time, air continues to flow from the air-side inlet INa to the air-side outlet OUTa, and the amount of moisture carried away by the air near the air-side inlet INa exceeds the amount of moisture generated by the electrochemical reaction, which may cause the dry region DRY near the air-side inlet INa to expand, as shown in Figure 2. Furthermore, generally, when the dry region DRY within a fuel cell SEL becomes larger, the internal resistance of the fuel cell SEL increases, and the output voltage of the fuel cell stack FCS decreases. In other words, if the fuel cell stack FCS continues to generate power, the fuel cell stack FCS may become partially dry, which may cause the output voltage of the fuel cell stack FCS to decrease, raising concerns about a decrease in performance of the fuel cell module FCM.

[0049] Therefore, if the fuel cell stack FCS is partially dry, it is possible to control the power generation of the fuel cell stack FCS so that the dry state changes to a wet state. This power generation control is hereinafter referred to as state recovery control. Even if the fuel cell stack FCS becomes partially dry when the fuel cell stack FCS is continuously generating power for a relatively long period of time, the dry state of the fuel cell stack FCS can be changed to a wet state by performing state recovery control. This makes it possible to prevent the fuel cell stack FCS from becoming partially dry even when the fuel cell stack FCS is continuously generating power for a relatively long period of time, thereby suppressing an increase in the internal resistance of the fuel cell stack FCS and suppressing a decrease in the output voltage of the fuel cell stack FCS.

[0050] <How to determine if the fuel cell stack (FCS) is dry or not> One method for determining whether the inside of the fuel cell stack FCS is dry is the AC impedance method, which measures the internal resistance of the fuel cell stack FCS and determines that the fuel cell SEL is dry if the measured internal resistance is equal to or greater than a threshold value.

[0051] For example, if the electrolyte membrane resistance Ie, among the multiple types of internal resistances of the fuel cell stack FCS, measured by applying an AC input (AC voltage or AC current) of a relatively high frequency (e.g., several hundred Hz to several kHz) to the fuel cell stack FCS, is equal to or greater than a threshold value Ieth, it can be determined that the inside of the fuel cell stack FCS is generally dry. Also, if the charge transfer resistance Ic, among the multiple types of internal resistances of the fuel cell stack FCS, measured by applying an AC input (AC voltage or AC current) of a relatively low frequency (e.g., several Hz to several tens of Hz) to the fuel cell stack FCS, is equal to or greater than a threshold value Icth, it can be determined that the inside of the fuel cell stack FCS is partially dry. In other words, the frequency of the AC input applied to the fuel cell stack FCS to measure the charge transfer resistance Ic is lower than the frequency of the AC input applied to the fuel cell stack FCS to measure the electrolyte membrane resistance Ie.

[0052] For example, the control unit Cf measures the AC voltage superimposed on the output voltage of the fuel cell stack FCS when a relatively low-frequency AC current (AC input) is flowing through the fuel cell stack FCS, or measures the AC current superimposed on the output current of the fuel cell stack FCS when a relatively low-frequency AC voltage (AC input) is applied to the fuel cell stack FCS, and determines the internal resistance calculated from the ratio of the AC current and the AC voltage as the charge transfer resistance Ic. If the charge transfer resistance Ic is equal to or greater than the threshold Icth, the control unit Cf sends an abnormality notification to the control unit Cs of the host system STM, indicating that the fuel cell stack FCS is in an abnormal state. After sending the abnormality notification to the host system STM, the control unit Cf continues to perform normal power generation control. When the control unit Cs receives the abnormality notification from the control unit Cf, it notifies the user that the fuel cell stack FCS is in an abnormal state. When the control unit Cs receives a state recovery command from the user, it sends a state recovery command to the control unit Cf. When the state recovery command is received, the control unit Cf transitions from normal power generation control to state recovery control.

[0053] When the fuel cell stack FCS is partially dry, the fluctuation range of the electrolyte membrane resistance Ie per unit time is small, so the characteristics of this electrolyte membrane resistance Ie may be used to determine whether the fuel cell stack FCS is partially dry. That is, by using not only the charge transfer resistance Ic but also the electrolyte membrane resistance Ie as a parameter for determining whether the fuel cell stack FCS is partially dry, the accuracy of determining whether the fuel cell stack FCS is partially dry can be improved. For example, when the charge transfer resistance Ic is equal to or greater than the threshold value Icth and the fluctuation range of the electrolyte membrane resistance Ie per unit time is equal to or less than the threshold value Ieth, it can be considered to determine that the fuel cell stack FCS is partially dry.

[0054] Specifically, the control unit Cf measures the AC voltage superimposed on the output voltage of the fuel cell stack FCS when a relatively high-frequency AC current is passed through the fuel cell stack FCS, or measures the AC current superimposed on the output current of the fuel cell stack FCS when a relatively high-frequency AC voltage is applied to the fuel cell stack FCS, and determines the internal resistance Ie as the electrolyte membrane resistance. If the charge transfer resistance Ic is equal to or greater than the threshold Icth and the fluctuation range per unit time of the electrolyte membrane resistance Ie is equal to or less than the threshold Ieth, the control unit Cf sends an abnormality notification to the control unit Cs of the host system STM indicating that the fuel cell stack FCS is in an abnormal state. After sending the abnormality notification to the host system STM, the control unit Cf continues to perform normal power generation control. Upon receiving the abnormality notification from the control unit Cf, the control unit Cs notifies the user that the fuel cell stack FCS is in an abnormal state, and upon receiving a state recovery instruction from the user, sends a state recovery command to the control unit Cf. When the control unit Cf receives the state recovery command, it transitions from normal power generation control to state recovery control.

[0055] <Charge transfer resistance Ic, fuel cell stack FCS output voltage, and electrolyte membrane resistance Ie when the fuel cell stack FCS is generating electricity continuously for a relatively long period of time> Figure 3(a) shows an example of charge transfer resistance Ic when the fuel cell stack FCS is generating electricity continuously for a relatively long period of time, Figure 3(b) shows an example of the output voltage of the fuel cell stack FCS when the fuel cell stack FCS is generating electricity continuously for a relatively long period of time, and Figure 3(c) shows an example of the electrolyte membrane resistance Ie when the fuel cell stack FCS is generating electricity continuously for a relatively long period of time.

[0056] The horizontal axis of the two-dimensional coordinate system shown in Figure 3(a) represents time, and the vertical axis represents resistance. The solid line in Figure 3(a) represents the charge transfer resistance Ic when the fuel cell stack FCS is caused to generate electricity using normal power generation control during the period from time t0 to time t1. The dashed line in Figure 3(a) represents the charge transfer resistance Ic when the fuel cell stack FCS is caused to generate electricity using state recovery control during the period from time t1 to time t2. The dashed line in Figure 3(a) represents the charge transfer resistance Ic when the fuel cell stack FCS is caused to generate electricity using normal power generation control after time t2.

[0057] In addition, the horizontal axis of the two-dimensional coordinate system shown in Figure 3(b) represents time, and the vertical axis represents voltage. The solid line in Figure 3(b) represents the output voltage of the fuel cell stack FCS when the fuel cell stack FCS is caused to generate power using normal power generation control during the period from time t0 to time t1. The dashed line in Figure 3(b) represents the output voltage of the fuel cell stack FCS when the fuel cell stack FCS is caused to generate power using state recovery control during the period from time t1 to time t2. The dashed line in Figure 3(b) represents the output voltage of the fuel cell stack FCS when the fuel cell stack FCS is caused to generate power using normal power generation control after time t2.

[0058] In addition, the horizontal axis of the two-dimensional coordinate system shown in Figure 3(c) represents time, and the vertical axis represents resistance. The solid line in Figure 3(c) represents the electrolyte membrane resistance Ie when the fuel cell stack FCS is caused to generate electricity using normal power generation control during the period from time t0 to time t1. The dashed line in Figure 3(c) represents the electrolyte membrane resistance Ie when the fuel cell stack FCS is caused to generate electricity using state recovery control during the period from time t1 to time t2. The dashed line in Figure 3(c) represents the electrolyte membrane resistance Ie when the fuel cell stack FCS is caused to generate electricity using normal power generation control after time t2.

[0059] 3(a) and 3(b), the output voltage of the fuel cell stack FCS decreases as the charge transfer resistance Ic increases from time t0 to time t1. In the example shown in FIG. 3(c), the electrolyte membrane resistance Ie is substantially constant from time t0 to time t1.

[0060] Next, at time t1, when the charge transfer resistance Ic becomes equal to or greater than the threshold value Icth, the power generation control of the fuel cell stack FCS switches from normal power generation control to state recovery control. When the power generation control of the fuel cell stack FCS switches from normal power generation control to state recovery control, the charge transfer resistance Ic and the output voltage of the fuel cell stack FCS become values ​​corresponding to various control parameters for controlling the power generation of the fuel cell stack FCS. That is, the charge transfer resistance Ic and the output voltage of the fuel cell stack FCS during the period from time t1 to time t2 shown in FIGS. 3(a) and 3(b) become values ​​corresponding to the control parameters. Examples of the control parameters include the air stoichiometric ratio of the fuel cell stack FCS (the ratio of the air flow rate actually supplied to the fuel cell stack FCS to the theoretical air flow rate required to make the current output from the fuel cell stack FCS follow the target current), the pressure of the air supplied to the fuel cell stack FCS (hereinafter referred to as air pressure), and the temperature of the refrigerant. For example, a decrease in the air stoichiometric ratio results in a decrease in the output voltage of the fuel cell stack FCS. Furthermore, an increase in the air pressure results in an increase in the output voltage of the fuel cell stack FCS. Furthermore, when the temperature of the coolant drops, the output voltage of the fuel cell stack FCS drops. Note that even if the temperature of the coolant drops, the output voltage of the fuel cell stack FCS may rise. In the example shown in FIG. 3(a), the charge transfer resistance Ic during the period from time t1 to time t2 is greater than the threshold value Ict, and in the example shown in FIG. 3(b), the output voltage of the fuel cell stack FCS during the period from time t1 to time t2 is less than the threshold value Vmin. Note that, as shown in FIG. 3(c), even when the power generation control of the fuel cell stack FCS switches from normal power generation control to state recovery control, the electrolyte membrane resistance Ie remains substantially constant. Furthermore, the threshold value Icth is set to the charge transfer resistance Ic corresponding to the minimum allowable voltage (threshold value Vmin) of the output voltage of the fuel cell stack FCS.

[0061] Then, at time t2, when the state recovery control is switched to the normal power generation control, the output voltage of the fuel cell stack FCS decreases again as the charge transfer resistance Ic increases. Note that even after time t2, the electrolyte membrane resistance Ie remains at a substantially constant value.

[0062] In this way, when the fuel cell stack FCS is generating electricity continuously for a relatively long period of time, it is possible to transition from normal power generation control to state recovery control at the timing when the charge transfer resistance Ic becomes equal to or greater than the threshold value Icth.

[0063] Furthermore, the timing at which the output voltage of the fuel cell stack FCS becomes equal to or lower than the minimum voltage (threshold Vmin) can be delayed from time t1 to time t2, so the operating time of the load Lo can be extended.

[0064] <An example of state recovery control> As a state recovery control, for example, there is a method of reducing the air stoichiometric ratio of the fuel cell stack FCS.

[0065] Here, Fig. 4(a) is a diagram showing an example of information in which target currents and air stoichiometric ratios are associated with each other. Note that the horizontal axis of the two-dimensional coordinate system shown in Fig. 4(a) represents current, and the vertical axis represents air stoichiometric ratio. Furthermore, the dashed line shown in Fig. 4(a) represents information Ds1 indicating the correspondence relationship between target currents and air stoichiometric ratios during normal power generation control, and the solid line shown in Fig. 4(a) represents information Ds2 indicating the correspondence relationship between target currents and air stoichiometric ratios during state recovery control. Furthermore, the air stoichiometric ratios corresponding to all target currents shown in information Ds2 are assumed to be smaller than the air stoichiometric ratios shown in information Ds1.

[0066] During normal power generation control, the control unit Cf references information Ds1 shown in Fig. 4(a) and sets the air stoichiometric ratio corresponding to the current target current as the target air stoichiometric ratio, and controls the operation of the air compressor ACP and the operation of the air pressure regulating valve ARV so that the air stoichiometric ratio obtained from the flow rate detected by the flow sensor Sf becomes the target air stoichiometric ratio. Furthermore, during state recovery control, the control unit Cf references information Ds2 shown in Fig. 4(a) and sets the air stoichiometric ratio corresponding to the current target current as the target air stoichiometric ratio, and controls the operation of the air compressor ACP and the operation of the air pressure regulating valve ARV so that the air stoichiometric ratio obtained from the flow rate detected by the flow sensor Sf becomes the target air stoichiometric ratio. This allows the air stoichiometric ratio to be reduced during state recovery control.

[0067] In this way, when the air stoichiometric ratio is reduced during state recovery control, the flow rate of air supplied to the fuel cell stack FCS is reduced, making it possible to suppress the amount of moisture carried away by the air near the air-side inlet INa. This prevents the amount of moisture carried away by the air near the air-side inlet INa from exceeding the amount of moisture generated by the electrochemical reaction, making it possible to reduce the dry region DRY near the air-side inlet INa, and therefore preventing the inside of the fuel cell stack FCS from becoming partially dry.

[0068] Another example of a state recovery process is to increase the pressure of the air supplied to the fuel cell stack FCS.

[0069] FIG. 4(b) is a diagram showing an example of information associating target currents with tire pressures. The horizontal axis of the two-dimensional coordinate system shown in FIG. 4(b) represents current, and the vertical axis represents tire pressure. The dashed line in FIG. 4(b) represents information Dp1 indicating the correspondence between target currents and tire pressures during normal power generation control, and the solid line in FIG. 4(b) represents information Dp2 indicating the correspondence between target currents and tire pressures during state recovery control. The tire pressures corresponding to all target currents shown in information Dp2 are assumed to be higher than the tire pressures shown in information Dp1.

[0070] During normal power generation control, the control unit Cf references information Dp1 shown in Figure 4(b) and sets the air pressure corresponding to the current target current as the target air pressure, and controls the operation of the air compressor ACP and the operation of the air pressure regulating valve ARV so that the air pressure calculated based on the pressure detected by the pressure sensor Sp becomes the target air pressure. Furthermore, during state recovery control, the control unit Cf references information Dp2 shown in Figure 4(b) and sets the air pressure corresponding to the current target current as the target air pressure, and controls the operation of the air compressor ACP and the operation of the air pressure regulating valve ARV so that the air pressure calculated based on the pressure detected by the pressure sensor Sp becomes the target air pressure. This allows the air pressure to be increased during state recovery control.

[0071] In this way, when the air pressure is increased during the state recovery process, the rate of the electrochemical reaction in the fuel cell stack FCS can be increased, and the amount of liquid water generated by the electrochemical reaction can be increased. This prevents the amount of water carried away by the air near the air-side inlet INa from exceeding the amount of water generated by the electrochemical reaction, and reduces the dry region DRY near the air-side inlet INa, preventing the inside of the fuel cell stack FCS from becoming partially dry.

[0072] Furthermore, as another state recovery process, for example, there is a method of lowering the temperature of the coolant supplied to the fuel cell stack FCS (hereinafter referred to as the coolant temperature).

[0073] FIG. 4(c) is a diagram showing an example of information associating target currents with refrigerant temperatures. The horizontal axis of the two-dimensional coordinate system shown in FIG. 4(c) represents current, and the vertical axis represents refrigerant temperatures. The dashed line in FIG. 4(c) represents information Dt1 indicating the correspondence between target currents and refrigerant temperatures during normal power generation control, and the solid line in FIG. 4(c) represents information Dt2 indicating the correspondence between target currents and refrigerant temperatures during state recovery control. The refrigerant temperatures corresponding to all target currents shown in information Dt2 are assumed to be lower than the refrigerant temperatures shown in information Dt1.

[0074] During normal power generation control, the control unit Cf references information Dt1 shown in FIG. 4(c) to set the refrigerant temperature corresponding to the current target current as the target refrigerant temperature, and controls the operation of the water pump WP so that the refrigerant temperature calculated based on the temperature detected by the temperature sensor St becomes the target refrigerant temperature. Furthermore, during state recovery control, the control unit Cf references information Dt2 shown in FIG. 4(c) to set the refrigerant temperature corresponding to the current target current as the target refrigerant temperature, and controls the operation of the water pump WP so that the refrigerant temperature calculated based on the temperature detected by the temperature sensor St becomes the target refrigerant temperature. This allows the refrigerant temperature to be lowered during state recovery control.

[0075] In this way, when the refrigerant temperature is lowered during the state recovery process, the amount of moisture in the fuel cell stack FCS can be increased. This prevents the amount of moisture carried away by the air near the air inlet INa from exceeding the amount of moisture generated by the electrochemical reaction, and reduces the dry region DRY near the air inlet INa, preventing the inside of the fuel cell stack FCS from becoming partially dry.

[0076] Another example of state recovery control is to increase the rotational speed of the motor M of the hydrogen circulation pump HP compared to the rotational speed during normal power generation control. For example, the control unit Cf sets the target rotational speed of the motor M to rotational speed N0 during normal power generation control, and sets the target rotational speed of the motor M to rotational speed N1 during state recovery control. For example, rotational speed N0 is set to any rotational speed within a range from the minimum value Nmin of the rotational speed of the motor M when the output power of the fuel cell stack FCS is made to track the power value to a predetermined value that is smaller than the maximum value Nmax. Furthermore, rotational speed N1 is set to the maximum value Nmax of the rotational speed of the motor M when the output power of the fuel cell stack FCS is made to track the power command value.

[0077] In this way, when the rotation speed of the motor M is increased during state recovery control, the flow rate of hydrogen gas supplied to the fuel cell stack FCS increases, which increases the amount of liquid water produced by the electrochemical reaction. This prevents the amount of water carried away by the air near the air-side inlet INa shown in Figure 2 from exceeding the amount of water produced by the electrochemical reaction, and reduces the dry region DRY near the air-side inlet INa, preventing the inside of the fuel cell stack FCS from becoming partially dry.

[0078] The control unit Cf may be configured to increase the rotation speed N1 as the charge transfer resistance Ic increases during the state recovery process.

[0079] When configured in this manner, hydrogen gas can be supplied to the fuel cell stack FCS at an appropriate flow rate according to the charge transfer resistance Ic, thereby preventing excess power consumption by the motor M and preventing a decrease in the efficiency of the fuel cell module FCM.

[0080] Furthermore, as another state recovery process, for example, there is a method of intermittently reducing the output power of the fuel cell stack FCS during the above-mentioned predetermined time T1. For example, during normal power generation control, the control unit Cf controls the operation of each auxiliary device so that the output power of the fuel cell stack FCS becomes the required power Pt during the predetermined time T1. On the other hand, during state recovery control, the control unit Cf controls the operation of each auxiliary device so that the output power of the fuel cell stack FCS becomes the power Pt' during the predetermined time T1, and then repeats controlling the operation of each auxiliary device so that the output power of the fuel cell stack FCS becomes the power Po. Note that power Pt' > required power Pt > power Po, and power Po is set to zero, for example.

[0081] Here, Figure 5(a) shows the output power of the fuel cell stack FCS during normal power generation control, Figure 5(b) shows the input / output power of the storage device B during normal power generation control, Figure 5(c) shows the output power of the upper system STM during normal power generation control, Figure 5(d) shows the output power of the fuel cell stack FCS during state recovery control, Figure 5(e) shows the input / output power of the storage device B during state recovery control, and Figure 5(f) shows the output power of the upper system STM during state recovery control.

[0082] During normal power generation control, as shown in Figures 5(a) to 5(c), when power equivalent to the required power Pt is output from the fuel cell stack FCS and power equivalent to the required power Pt is supplied from the upper system STM to the load Lo, no power is supplied from the storage device B to the load Lo.

[0083] On the other hand, during state recovery control, as shown in FIGS. 5(d) to 5(f), when power equivalent to power Pt' is output from the fuel cell stack FCS, thereby supplying power equivalent to the required power Pt to the load Lo from the higher-level system STM, power equivalent to the difference between power Pt' and the required power Pt (power in the hatched portion) is supplied from the power storage device B to the load Lo, and the power storage device B is charged. Thereafter, when power equivalent to power Po is output from the fuel cell stack FCS, thereby supplying power equivalent to the required power Pt from the higher-level system STM to the load Lo, power equivalent to the required power Pt is supplied from the power storage device B to the load Lo. In other words, during state recovery control, the fuel cell stack FCS repeatedly outputs power equivalent to power Pt' and then outputs power equivalent to power Po. Furthermore, during state recovery control, when the output power of the fuel cell stack FCS is insufficient to meet the required power Pt, the power storage device B outputs the power that makes up the shortfall.

[0084] As a result, even if the output power of the fuel cell stack FCS is intermittently reduced during state recovery control, it is possible to continuously supply power equivalent to the required power Pt to the load Lo. Furthermore, during state recovery control, when power equivalent to the power Po is output from the fuel cell stack FCS, that is, when the output power of the fuel cell stack FCS is reduced, power generation by the fuel cell stack FCS is suppressed, so moisture moves from the wet region WET within the fuel cell SEL to the dry region DRY, reducing the dry region DRY within the fuel cell SEL and preventing the fuel cell stack FCS from becoming partially dry.

[0085] The control unit Cf may be configured to perform at least two of the following depending on the state recovery control, the configuration of the upper system STM, and the ambient environment of the fuel cell stack FCS: reducing the air stoichiometric ratio, increasing the air pressure, lowering the refrigerant temperature, increasing the rotation speed of the motor M, and intermittently reducing the output power of the fuel cell stack FCS.

[0086] In addition, one method of restoring the state when the fuel cell stack FCS is partially dry is to install a humidifier in the supply path FP that supplies air to the fuel cell stack FCS. However, there is a concern that installing a humidifier in the supply path FP will result in the fuel cell module FCM becoming larger.

[0087] Therefore, in the fuel cell module FCM of this embodiment, a humidifier is not provided in the supply path FP, and when the state monitoring timing occurs during normal power generation control of the fuel cell stack FCS, the charge transfer resistance Ic of the fuel cell stack FCS is measured, and if the measured charge transfer resistance Ic is equal to or greater than a threshold value Icth, a transition is made from normal power generation control to state recovery control. Note that the state monitoring timing may be generated repeatedly at regular intervals (for example, every few minutes, hours, days, weeks, months, or years), or may be generated in response to an instruction from the control unit Cs of the higher-level system STM.

[0088] <Operation of control unit Cf> FIG. 6 is a flowchart showing an example of the operation of the control unit Cf at the state monitoring timing.

[0089] First, when the state monitoring timing arrives, the control unit Cf determines whether a charge transfer resistance measurement permission flag is on (step Stp11). The charge transfer resistance measurement permission flag is a flag for identifying whether or not the charge transfer resistance Ic can be measured. When the charge transfer resistance measurement permission flag is on, the charge transfer resistance Ic can be measured. When the charge transfer resistance measurement permission flag is off, the charge transfer resistance Ic cannot be measured. For example, in a case where a boost circuit including an inductor, a switching element, a diode, and the like is configured as the DC-DC converter CNV, during normal power generation control, if the voltage of the fuel cell stack FCS is higher than the voltage of the power storage device B and current can flow from the fuel cell stack FCS to the power storage device B without switching the switching element, the charge transfer resistance measurement permission flag is turned on because there is no risk of the switching noise of the switching element reducing the measurement accuracy of the charge transfer resistance Ic. On the other hand, when the voltage of the fuel cell stack FCS is lower than the voltage of the power storage device B and the switching element needs to be switched, the charge transfer resistance measurement permission flag is turned off because there is a risk of the switching noise reducing the measurement accuracy of the charge transfer resistance Ic. Alternatively, if there is a risk that the efficiency of the entire fuel cell module FCM will decrease significantly due to the transition from normal power generation control to state recovery control, the charge transfer resistance measurement permission flag is turned off, and if there is no risk that the efficiency of the entire fuel cell module FCM will decrease significantly due to the transition from normal power generation control to state recovery control, the charge transfer resistance measurement permission flag is turned on.

[0090] Next, if the charge transfer resistance measurement permission flag is off (step Stp11: No), the control unit Cf ends the state monitoring process at this state monitoring timing. Note that, during normal power generation control, if the charge transfer resistance measurement permission flag is off, the control unit Cf continues to perform normal power generation control, and during state recovery control, if the charge transfer resistance measurement permission flag is off, the control unit Cf continues to perform state recovery control.

[0091] On the other hand, if the charge transfer resistance measurement permission flag is on (step Stp11: Yes), the control unit Cf measures the charge transfer resistance Ic (step Stp12) and determines whether the charge transfer resistance Ic measured in step Stp12 is equal to or greater than the threshold value Icth (step Stp13).

[0092] Next, if the charge transfer resistance Ic is smaller than the threshold value Icth (step Stp13: No), the control unit Cf ends the state monitoring process at this state monitoring timing. Note that, during normal power generation control, if the charge transfer resistance Ic is smaller than the threshold value Icth, the control unit Cf continues to perform normal power generation control, and during state recovery control, if the charge transfer resistance Ic is smaller than the threshold value Icth, the control unit Cf continues to perform state recovery control.

[0093] On the other hand, if the charge transfer resistance Ic is equal to or greater than the threshold value Icth (step Stp13: Yes), the control unit Cf sends an abnormality notification to the host system STM (control unit Cs) to the effect that the fuel cell stack FCS is in an abnormal state (step Stp14).

[0094] Next, if the control unit Cf does not receive a state recovery command from the control unit Cs within the lapse of the predetermined time Tc1, i.e., if a timeout occurs after sending the abnormality notification (step Stp15: No, step Stp16: Yes), the control unit Cf ends the state monitoring process for the current state monitoring timing. Note that, during normal power generation control, if a timeout occurs after sending the abnormality notification, the control unit Cf continues normal power generation control, and during state recovery control, if a timeout occurs after sending the abnormality notification, the control unit Cf continues state recovery control. Also, during state recovery control, if a timeout occurs after sending the abnormality notification, the control unit Cf may transition from state recovery control to normal power generation control.

[0095] On the other hand, when the control unit Cf receives a state recovery command from the control unit Cs during the lapse of the predetermined time Tc1 (step Stp15: Yes), it performs state recovery control (step Stp17) and ends the state monitoring process at the current state monitoring timing. Note that, during normal power generation control, when the control unit Cf receives a state recovery command from the control unit Cs during the lapse of the predetermined time Tc1, it transitions from normal power generation control to state recovery control, and during state recovery control, when the control unit Cf receives a state recovery command from the control unit Cs during the lapse of the predetermined time Tc1, it continues to perform the state recovery control.

[0096] <Operation of control unit Cs> FIG. 7 is a flowchart showing an example of the operation of the control unit Cs.

[0097] First, when the control unit Cs determines that it has received an abnormality notification (step Stp21: Yes), it notifies the user that the fuel cell stack FCS is in an abnormal state (step Stp22). For example, the control unit Cs displays information indicating that the fuel cell stack FCS is in an abnormal state on a display (not shown). Alternatively, the control unit Cs outputs a sound indicating that the fuel cell stack FCS is in an abnormal state from a speaker (not shown).

[0098] Next, if the control unit Cs does not receive a state recovery instruction from the user within the lapse of a predetermined time Tc2, that is, if a timeout occurs after notifying the user (step Stp23: No, step Stp24: Yes), the control unit Cs returns to step Stp21 and determines again whether or not an abnormality notification has been received, and if a state recovery instruction is received from the user within the lapse of the predetermined time Tc2 (step Stp23: Yes), it sends a state recovery command to the control unit Cf (step Stp25). Note that the predetermined times Tc1 and Tc2 are shorter than the above-mentioned predetermined time T1.

[0099] In this way, the fuel cell module FCM of this embodiment is configured to send an abnormality notification to the host system STM when the charge transfer resistance Ic of the fuel cell stack FCS becomes equal to or greater than the threshold value Icth during normal power generation control.

[0100] As a result, even if the fuel cell stack FCS becomes partially dry by continuously generating power for a relatively long period of time, the user can be prompted to restore the state of the fuel cell stack FCS, and when a state restoration instruction is received from the user, it is possible to transition from normal power generation control to state restoration control. Therefore, by continuously generating power for a relatively long period of time, it is possible to prevent the fuel cell stack FCS from becoming partially dry. Furthermore, because it is possible to prevent the fuel cell stack FCS from becoming partially dry, it is possible to suppress a decrease in the output voltage of the fuel cell stack FCS.

[0101] Furthermore, the fuel cell module FCM of the embodiment is configured to continue normal power generation control after sending an abnormality notification to the host system STM.

[0102] This makes it possible to notify the user that the fuel cell stack FCS is in an abnormal state without reducing the power supplied to the load Lo.

[0103] Furthermore, the fuel cell module FCM of the embodiment is configured to transition from normal power generation control to state recovery control when it receives a state recovery command from the host system STM.

[0104] This makes it possible to restore the state of the fuel cell stack FCS according to the user's convenience, the state of the load Lo, etc. For example, if the maintenance period for the fuel cell module FCM is relatively close, the state restoration control can be performed to coincide with that maintenance period.

[0105] Furthermore, the fuel cell module FCM of the embodiment is configured such that a humidifier is not provided in the supply path FP that supplies air to the fuel cell stack FCS.

[0106] This allows the fuel cell module FCM to be made smaller by the amount corresponding to the absence of a humidifier.

[0107] The present invention is not limited to the above-described embodiments, and various improvements and modifications can be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0108] FCM Fuel Cell Module Lo load FCS fuel cell stack HT fuel tank INJ injector HP Hydrogen Circulation Pump INV Inverter circuit Medium motor P pump GLS gas liquid separator EDV Exhaust Drain Valve ACP Air Compressor ARV Air Pressure Regulating Valve DIL Diluter R radiator WP water pump CNV DC / DC converter B Energy storage device Sf flow sensor Sp pressure sensor St temperature sensor Str storage Cf, Cs control section

Claims

1. A fuel cell module provided in a host system that supplies power to a load, a fuel cell stack for supplying power to the load; a control unit that controls power generation by the fuel cell stack based on a power command value from the host system; Equipped with When the charge transfer resistance of the fuel cell stack reaches or exceeds a threshold value during normal power generation control, the control unit sends an abnormality notification to the host system indicating that the state of the fuel cell stack is abnormal. Fuel cell module.

2. 10. The fuel cell module of claim 1, The control unit continues the normal power generation control after sending the abnormality notification to the host system. A fuel cell module characterized by:

3. 10. The fuel cell module of claim 1, When the host system receives a state recovery instruction from a user to recover the state of the fuel cell stack, the host system sends a state recovery command to the control unit, When the control unit receives the state recovery command from the host system, the control unit transitions from the normal power generation control to the state recovery control. A fuel cell module characterized by:

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