Fuel cell module

Abstract

This prevents the inside of the fuel cell stack from becoming partially dry. [Solution] A fuel cell module FCM is configured comprising a fuel cell stack FCS, a cooling system auxiliary unit that dissipates the heat from the cooling water discharged from the fuel cell stack FCS and supplies it back to the fuel cell stack FCS, and a control unit Cf that controls the operation of the cooling system auxiliary unit. During normal power generation control, when the charge transfer resistance Ic of the fuel cell stack FCS exceeds a threshold Icth, the control unit Cf transitions from normal power generation control to state recovery control. During state recovery control, the operation of the cooling system auxiliary unit is controlled so that the temperature of the air-side inlet of the fuel cell stack FCS is lower due to the cooling water compared to when normal power generation control is performed.

Description

Technical Field

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

Background Art

[0002] As a fuel cell module, when the internal resistance of a fuel cell stack, which is obtained by an AC voltage superimposed on the output voltage of the fuel cell stack by flowing a relatively high-frequency alternating current through the fuel cell stack, is greater than or equal to a threshold value, it is determined that the inside of the fuel cell stack is overall dry, and the pressure of the air supplied to the fuel cell stack is increased to avoid drying inside the fuel cell stack. As a related technique, there is Patent Document 1.

[0003] By the way, when the fuel cell stack continues to generate electricity for a relatively long time, in the region near the inlet of the air inside the fuel cell stack, the amount of moisture carried away by the air exceeds the amount of moisture generated by the electrochemical reaction, resulting in a dry state, and in other regions, there is a possibility of becoming a wet state. That is, when the fuel cell stack continues to generate electricity for a relatively long time, there is a possibility that the inside of the fuel cell stack becomes partially dry.

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

[0005] Thus, in the above fuel cell module, it is not possible to determine that the inside of the fuel cell stack is partially dry, so there is a possibility that the inside of the fuel cell stack becomes partially dry. Further, when the inside of the fuel cell stack becomes partially dry, there is a concern that the output voltage of the fuel cell stack will decrease.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2008-146971 [Overview of the project] [Problems that the invention aims to solve]

[0007] One aspect of the present invention is to avoid the fuel cell stack becoming partially dry. [Means for solving the problem]

[0008] A fuel cell module in one embodiment of the present invention comprises a fuel cell stack, a cooling system auxiliary unit that dissipates heat from the cooling water discharged from the fuel cell stack and supplies it back to the fuel cell stack, and a control unit that controls the operation of the cooling system auxiliary unit. The control unit, during normal power generation control, transitions from normal power generation control to state recovery control when the charge transfer resistance of the fuel cell stack exceeds a threshold, and during state recovery control, controls the operation of the cooling system auxiliary unit so that at least the temperature of the air-side inlet of the fuel cell stack is lower than during normal power generation control.

[0009] This prevents the amount of moisture removed near the air-side inlet of the fuel cell stack due to the temperature rise from that area from exceeding the amount of liquid water produced by the electrochemical reaction. As a result, it is possible to change a dry area into a humid state, thus avoiding partial drying within the fuel cell stack.

[0010] Furthermore, the control unit may be configured to control the operation of the cooling system auxiliary equipment so that the amount of power generated by the fuel cell stack remains constant during the state recovery control.

[0011] As a result, temperature fluctuations in the fuel cell stack are reduced during state recovery control, enabling robust power generation control for the fuel cell stack.

[0012] Furthermore, the control unit may be configured to control the operation of the cooling system auxiliary equipment so that the amount of heat exchanged in the cooling system auxiliary equipment balances the amount of heat generated by the fuel cell stack during state recovery control.

[0013] Furthermore, the fuel cell module includes an air compressor that supplies air to the fuel cell stack, a radiator that exchanges heat between the cooling water discharged from the fuel cell stack and the outside air, and a water pump that resupplies the cooling water discharged from the radiator to the fuel cell stack. The air-side inlet of the fuel cell stack is adjacent to the cooling water-side inlet of the fuel cell stack, and the control unit may be configured to reduce the rotational speed of the water pump motor during state recovery control compared to during normal power generation control. [Effects of the Invention]

[0014] According to the present invention, it is possible to avoid the fuel cell stack becoming partially dry. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows an example of a fuel cell module according to an embodiment. [Figure 2] This diagram shows the state inside the fuel cell stack. [Figure 3] This figure shows an example of charge transfer resistance, fuel cell stack output voltage, and electrolyte membrane resistance. [Figure 4] This figure shows an example of the relationship between the temperature at the cooling water inlet of the fuel cell stack and the output voltage of the fuel cell stack. [Figure 5] This is a flowchart showing the operation of the control unit. [Figure 6] This diagram shows the state inside the fuel cell stack. [Modes for carrying out the invention]

[0016] The embodiments will be described in detail below based on the drawings.

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

[0018] The fuel cell module FCM shown in FIG. 1 is provided in the upper-level system STM and supplies power to the load Lo in cooperation with the power storage device B.

[0019] For example, when the upper-level system STM is a stationary generator such as an industrial stationary generator, a household 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 upper-level system STM as shown in FIG. 1.

[0020] Also, for example, when the upper-level 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 a cargo handling device or an inverter circuit that drives a traveling motor. In this case, the load Lo is assumed to be provided inside the upper-level system STM.

[0021] In addition to the fuel cell module FCM and the power storage device B, the upper-level system STM includes a control unit Cs, etc. Note that the devices and components provided in the fuel cell module FCM may change according to the type of the upper-level system STM. For example, when the upper-level system STM is a stationary generator, the fuel tank HT and the radiator R described later may be provided outside the fuel cell module FCM.

[0022] The control unit Cs, which is composed of a microcomputer or the like, sends a power command value to the fuel cell module FCM, which is determined from the power requested from the load Lo, the charge rate of the energy storage device B (the ratio of the remaining capacity to the full charge capacity of the energy storage device B [%]), and the maximum output power of the fuel cell module FCM. For example, if the power requested from the load Lo is greater than the maximum output power of the fuel cell module FCM, and the charge rate of the energy storage device B is a predetermined charge rate (for example, the charge rate of the energy storage device B when it is fully charged), the control unit Cs sends the maximum output power of the fuel cell module FCM as the power command value to the fuel cell module FCM. In this case, the fuel cell module FCM supplies power to the load Lo equivalent to the maximum output power of the fuel cell module FCM, and the energy storage device B supplies the remaining power to the load Lo (power equivalent to the difference between the power requested from the load Lo and the maximum output power of the fuel cell module FCM). Furthermore, if the power requested from load Lo is less than the maximum output power of the fuel cell module FCM, and the charge level of the energy storage device B is less than a predetermined charge level, the control unit Cs sends the sum of the power requested from load Lo and the power required to charge the energy 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 load Lo, and power required to charge the energy storage device B is also supplied from the fuel cell module FCM.

[0023] Energy storage device B is composed of, for example, a lithium-ion capacitor and is connected between the fuel cell module FCM and the load Lo. As described above, it works in cooperation with the fuel cell module FCM to supply power to the load Lo. When power is supplied from energy storage device B to the load Lo, energy storage device B is discharged and its charge level decreases. Conversely, when power is supplied from the fuel cell module FCM to energy storage device B, energy storage device B is charged and its charge level increases.

[0024] A fuel cell module (FCM) comprises a main unit, a fuel cell stack (FCS), and several types of auxiliary equipment for generating power for the fuel cell stack (FCS).

[0025] In other words, the fuel cell module (FCM) is equipped with hydrogen gas system auxiliary components such as a fuel tank (HT), an injector (INJ), a gas-liquid separator (GLS), a hydrogen circulation pump (HP), and an exhaust / drain valve (EDV).

[0026] Furthermore, the fuel cell module (FCM) is equipped with air system auxiliary equipment such as an air compressor (ACP), an air pressure regulating valve (ARV), and a diluent (DIL).

[0027] Furthermore, the fuel cell module (FCM) includes cooling system auxiliary components such as a radiator (R), fan (F), water pump (WP), intercooler (IC), and temperature sensor (St).

[0028] Furthermore, the fuel cell module (FCM) is equipped with a DC-DC converter (CNV) as an electrical auxiliary component.

[0029] Furthermore, the fuel cell module (FCM) also includes a memory unit (Str) and a control unit (Cf).

[0030] A fuel cell stack (FCS) consists of multiple fuel cell cells connected in series, and generates electricity through an electrochemical reaction between hydrogen gas (anode gas) and oxygen (cathode gas) in the air. A fuel cell cell is, for example, a polymer electrolyte fuel cell (PEFC).

[0031] The fuel tank (HT) is a storage container for hydrogen gas. The hydrogen gas stored in the fuel tank (HT) is supplied to the fuel cell module (FCM) via the injector (INJ).

[0032] The injector (INJ) regulates the flow rate of hydrogen gas supplied from the fuel tank (HT) to the fuel cell stack (FCS).

[0033] The gas-liquid separator (GLS) separates unreacted hydrogen gas from liquid water discharged from the fuel cell stack (FCS).

[0034] The hydrogen circulation pump (HP) resupplies the hydrogen gas separated by the gas-liquid separator (GLS) back to the fuel cell stack (FCS).

[0035] The exhaust drain valve (EDV) sends the liquid water separated by the gas-liquid separator (GLS) to the diluent (DIL). The liquid water sent to the diluent (DIL) is stored in a tank within the DIL. In addition, hydrogen gas and air discharged from the fuel cell stack (FCS) merge in the diluent (DIL) and are discharged to the outside or inside of the fuel cell module (FCM).

[0036] The air compressor (ACP) compresses air supplied from outside the fuel cell module (FCM) and delivers it to the fuel cell stack (FCS).

[0037] The air pressure regulating valve (ARV) adjusts the pressure and flow rate of air supplied to the fuel cell stack (FCS).

[0038] The radiator R exchanges heat between the coolant discharged from the fuel cell module (FCM) and the outside air. For example, the coolant is a liquid such as water containing additives such as antifreeze, rust inhibitors, and antioxidants.

[0039] Fan F increases the amount of heat exchanged between the coolant and the outside air in the radiator R. The rotation speed of fan F is changed by the control unit Cf, which adjusts the temperature of the coolant supplied to the fuel cell stack FCS. When the rotation speed of fan F decreases, the amount of heat exchanged in the radiator R decreases, so the temperature of the coolant supplied to the fuel cell stack FCS becomes relatively higher. On the other hand, when the rotation speed of fan F increases, the amount of heat exchanged in the radiator R increases, so the temperature of the coolant supplied to the fuel cell stack FCS becomes relatively lower.

[0040] The water pump WP supplies the cooling water, which has been heated by the radiator R, to the fuel cell stack FCS via the intercooler IC. In other words, the water pump WP comprises a pump P that sends the cooling water discharged from the radiator R to the intercooler IC, a motor M that drives the pump P, and an inverter circuit INV that drives the motor M. The rotation speed of the motor M is changed by the operation control of the inverter circuit INV by the control unit Cf, thereby adjusting the flow rate of the cooling water passing through the fuel cell stack FCS and radiator R. When the rotation speed of the motor M decreases, the flow rate of the cooling water passing through the fuel cell stack FCS and radiator R decreases, and the flow rate of the cooling water passing through the fuel cell stack FCS and radiator R increases, so the amount of heat exchange by the cooling water in the fuel cell stack FCS and radiator R increases, and the temperature change of the cooling water becomes relatively large. On the other hand, as the rotational speed of the motor M increases, the flow velocity of the cooling water passing through the fuel cell stack FCS and radiator R increases, and the flow rate of the cooling water passing through the fuel cell stack FCS and radiator R decreases. As a result, the amount of heat exchange by the cooling water in the fuel cell stack FCS and radiator R decreases, and the temperature change of the cooling water becomes relatively small.

[0041] The intercooler IC supplies air, which has been compressed and heated to a high temperature by the air compressor ACP, to the fuel cell stack FCS after exchanging heat with the cooling water flowing through the intercooler IC.

[0042] The temperature sensor St detects the temperature of the cooling water 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 to a predetermined voltage. The power output from the DC-DC converter CNV is supplied to each auxiliary unit, load Lo, and energy storage device B.

[0044] The memory unit Str is composed of non-volatile memory such as ROM (Read Only Memory) and flash memory.

[0045] The control unit Cf, composed of a microcomputer and other components, 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. Also, during normal power generation control of the fuel cell stack (FCS), the control unit Cf controls the rotation speed of the fan F so that the temperature of the fuel cell stack (FCS) follows an appropriate temperature. Furthermore, during normal power generation control, the control unit Cf decreases the rotation speed of the motor M when the power generation (heat generation) of the fuel cell stack (FCS) increases, and increases the rotation speed of the motor M when the power generation (heat generation) of the fuel cell stack (FCS) decreases, in order to maintain the temperature of the fuel cell stack (FCS) at an appropriate temperature.

[0046] Furthermore, when the higher-level system STM is a stationary generator, the control unit Cf may, during normal power generation control and during state recovery control (described later), repeatedly cause the fuel cell stack FCS to continuously generate power for a predetermined time T1, and then cause the fuel cell stack FCS to continuously stop generating power for a predetermined time T2. In other words, the control unit Cf causes the fuel cell stack FCS to intermittently generate power during normal power generation control or state recovery control. For example, predetermined times T1 and T2 may each be several hours, with predetermined time T1 > predetermined time T2. Alternatively, predetermined time T1 may be the period from Monday to Friday of a week, and predetermined time T2 may be the period from Saturday to Sunday of a week. Alternatively, predetermined time T1 may be several hours of a day, and predetermined time T2 may be the remaining several hours of a day.

[0047] <Regarding the state of the fuel cell stack (FCS) when generating power for a relatively long period of time> Figure 2 shows the state inside an arbitrary fuel cell cell SEL when the fuel cell stack FCS is generating power continuously for a relatively long period of time. The "relatively long period of time" refers to, for example, the predetermined time T1. Furthermore, during normal power generation control of the fuel cell stack FCS, the air supplied to the fuel cell stack FCS is supplied into the fuel cell cell SEL via the air-side inlet INa and then discharged to the outside of the fuel cell stack FCS via the air-side outlet OUTa. The hydrogen gas supplied to the fuel cell stack FCS is supplied into the fuel cell cell SEL via the hydrogen gas-side inlet INh and then discharged to the outside of the fuel cell stack FCS via the hydrogen gas-side outlet OUTh. The cooling water supplied to the fuel cell stack FCS passes through the inside of the fuel cell cell SEL via the cooling water-side inlet INw and then discharged to the outside of the fuel cell stack FCS via the cooling water-side outlet OUTw. In addition, the solid arrows in Figure 2 indicate the airflow inside the fuel cell cell SEL, the dashed arrows in Figure 2 indicate the hydrogen gasflow inside the fuel cell cell SEL, and the dotted arrows in Figure 2 indicate the cooling waterflow inside the fuel cell cell SEL. Furthermore, the wet region (WET) shown in Figure 2 represents an area within the fuel cell cell SEL with a relatively high moisture content, while the dry region (DRY) shown in Figure 2 represents an area within the fuel cell cell SEL with a relatively low moisture content.

[0048] When a fuel cell stack (FCS) containing a fuel cell cell (SEL) with this configuration 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). As a result, 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, and as shown in Figure 2, the dry region (DRY) near the air-side inlet (INa) may expand. In addition, generally, when the dry region (DRY) in a fuel cell cell (SEL) increases, the internal resistance of the fuel cell cell (SEL) increases, and the output voltage of the fuel cell stack (FCS) decreases. In other words, when the fuel cell stack (FCS) continues to generate power, the inside of 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 the performance of the fuel cell module (FCM).

[0049] Therefore, if the inside of the fuel cell stack (FCS) is partially dry, it is conceivable 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 hereafter referred to as state recovery control. When the fuel cell stack (FCS) is generating power continuously for a relatively long period of time, even if the inside of the fuel cell stack (FCS) becomes partially dry, state recovery control can change the dry state inside the fuel cell stack (FCS) to a wet state. As a result, even when the fuel cell stack (FCS) is generating power continuously for a relatively long period of time, it is possible to avoid the inside of the fuel cell stack (FCS) becoming partially dry, 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] <Method for determining whether the inside of a fuel cell stack (FCS) is dry or not> One method for determining whether the inside of a fuel cell stack (FCS) is dry is the AC impedance method. The AC impedance method measures the internal resistance of the fuel cell stack (FCS), and if the measured internal resistance is above a threshold, it is determined that the fuel cell cell (SEL) is dry.

[0051] For example, if the electrolyte membrane resistance Ie, one of several types of internal resistances of the fuel cell stack (FCS), is measured by applying a relatively high frequency AC input (AC voltage or AC current) (e.g., several hundred Hz to several kHz) to the FCS, and is above the threshold Ieth, it can be determined that the inside of the FCS is generally dry. Also, if the charge transfer resistance Ic, one of several types of internal resistances of the FCS, is measured by applying a relatively low frequency AC input (AC voltage or AC current) (e.g., several Hz to several tens of Hz), and is above the threshold Icth, it can be determined that the inside of the FCS is partially dry. In other words, the frequency of the AC input applied to the FCS to measure the charge transfer resistance Ic should be lower than the frequency of the AC input applied to the 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 defines the internal resistance obtained from the ratio of these AC currents to AC voltages as the charge transfer resistance Ic. Then, if the charge transfer resistance Ic is greater than or equal to the threshold Icth, the control unit Cf transitions from normal power generation control to state recovery control.

[0053] Furthermore, when the inside of the fuel cell stack (FCS) is partially dry, the fluctuation range of the electrolyte membrane resistance Ie per unit time is small. Therefore, this characteristic of the electrolyte membrane resistance Ie can be used to determine whether or not the inside of the fuel cell stack (FCS) is partially dry. In other words, by using the electrolyte membrane resistance Ie in addition to the charge transfer resistance Ic as a parameter for determining whether or not the inside of the fuel cell stack (FCS) is partially dry, the accuracy of determining whether or not the inside of the fuel cell stack (FCS) is partially dry can be improved. For example, if the charge transfer resistance Ic is greater than or equal to the threshold Icth, and the fluctuation range of the electrolyte membrane resistance Ie per unit time is less than or equal to the threshold Ieth, it can be considered that the inside of 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 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 high frequency AC voltage is applied to the fuel cell stack FCS, and defines the internal resistance obtained from the ratio of these AC currents to AC voltages as the electrolyte membrane resistance Ie. Then, if the charge transfer resistance Ic is greater than or equal to the threshold Icth, and the fluctuation range of the electrolyte membrane resistance Ie per unit time is less than or equal to the threshold Ieth, the control unit Cf transitions from normal power generation control to state recovery control.

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

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

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

[0058] Furthermore, in the two-dimensional coordinate system shown in Figure 3(c), the horizontal axis represents time, and the vertical axis represents resistance. The solid line in Figure 3(c) shows the electrolyte membrane resistance Ie when the fuel cell stack (FCS) is powered by normal power generation control during the period from time t0 to time t1. The dashed line in Figure 3(c) shows the electrolyte membrane resistance Ie when the fuel cell stack (FCS) is powered by state recovery control during the period from time t1 to time t2. The dashed line in Figure 3(c) shows the electrolyte membrane resistance Ie when the fuel cell stack (FCS) is powered by normal power generation control from time t2 onward.

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

[0060] Next, at time t1, when the charge transfer resistance Ic exceeds the threshold 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 Figures 3(a) and 3(b) become values ​​corresponding to the control parameters. Examples of control parameters include the air stoichiometric ratio of the fuel cell stack FCS (the ratio of the actual air flow rate 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 cooling water. For example, when the air stoichiometric ratio decreases, the output voltage of the fuel cell stack FCS decreases. Also, when the air pressure increases, the output voltage of the fuel cell stack FCS increases. Furthermore, a decrease in the cooling water temperature leads to a decrease in the output voltage of the fuel cell stack (FCS). However, even if the cooling water temperature decreases, the output voltage of the fuel cell stack (FCS) may increase. In the example shown in Figure 3(a), the charge transfer resistance Ic during the period from time t1 to time t2 is greater than the threshold Ict, and in the example shown in Figure 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 Vmin. As shown in Figure 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 approximately constant. The threshold Icth is defined as the charge transfer resistance Ic corresponding to the minimum allowable voltage (threshold Vmin) of the output voltage of the fuel cell stack (FCS).

[0061] Then, at time t2, when the system switches from state recovery control to normal power generation control, the output voltage of the fuel cell stack FCS decreases again due to the increase in charge transfer resistance Ic. Note that the electrolyte membrane resistance Ie remains approximately constant even after time t2.

[0062] Thus, when the fuel cell stack (FCS) is generating power continuously for a relatively long period of time, the system can transition from normal power generation control to state recovery control when the charge transfer resistance Ic exceeds the threshold Icth.

[0063] Furthermore, since the timing at which the output voltage of the fuel cell stack (FCS) falls below the minimum voltage (threshold Vmin) can be delayed from time t1 to time t2, the operating time at load Lo can be extended.

[0064] <An example of state recovery control> As shown in Figure 2, we assume that the air-side inlet INa is adjacent to the cooling water-side inlet INw.

[0065] For example, during normal power generation control, the control unit Cf controls the rotation speed of the fan F to rotation speed Nf1 and the rotation speed of the motor M to rotation speed Nw1 so that the temperature of the cooling water outlet OUTw becomes temperature tH and the temperature change of the cooling water inside the fuel cell stack FCS becomes temperature Δt1. The temperature change of the cooling water inside the fuel cell stack FCS is determined by the amount of power generated (heat generated) by the fuel cell stack FCS.

[0066] Furthermore, during state recovery control, the control unit Cf controls the rotation speed of the fan F to rotation speed Nf1 and the rotation speed of the motor M to rotation speed Nw2, which is lower than rotation speed Nw1, so that the temperature of the cooling water outlet OUTw becomes temperature tH and the amount of temperature change of the cooling water in the fuel cell stack FCS becomes temperature Δt2, which is greater than temperature Δt1. In other words, during state recovery control, by decreasing the rotation speed of the motor M without changing the rotation speed of the fan F, it is possible to lower the temperature of the cooling water supplied from the fuel cell stack FCS to the radiator R without changing the temperature of the cooling water supplied from the radiator R to the fuel cell stack FCS, thereby lowering only the temperature of the cooling water inlet INw.

[0067] Furthermore, the control unit Cf may be configured to reduce the rotational speed of the motor M as the charge transfer resistance Ic increases during state recovery control.

[0068] In this configuration, cooling water at an appropriate flow rate corresponding to the charge transfer resistance Ic can be supplied to the radiator R and fuel cell stack FCS, thereby suppressing the consumption of excess power by the motor M and preventing a decrease in the efficiency of the fuel cell module FCM.

[0069] Alternatively, during state recovery control, the control unit Cf controls the rotation speed of the fan F to a rotation speed Nf2, which is higher than rotation speed Nf1, and the rotation speed of the motor M to rotation speed Nw1, so that the temperature of the cooling water outlet OUTw becomes a temperature tL, which is lower than temperature tH, and the amount of temperature change of the cooling water in the fuel cell stack FCS becomes a temperature Δt1. In other words, during state recovery control, by increasing the rotation speed of the fan F without changing the rotation speed of the motor M, the temperature of the cooling water supplied from the fuel cell stack FCS to the radiator R and the temperature of the cooling water supplied from the radiator R to the fuel cell stack FCS can be lowered, thereby lowering the temperatures of the cooling water inlet INw and the cooling water outlet OUTw.

[0070] Furthermore, the control unit Cf may be configured to increase the rotation speed of the fan F as the charge transfer resistance Ic increases during state recovery control.

[0071] In this configuration, cooling water at an appropriate flow rate corresponding to the charge transfer resistance Ic can be supplied to the radiator R and fuel cell stack FCS, thereby suppressing the consumption of excess power by the fan F and preventing a decrease in the efficiency of the fuel cell module FCM.

[0072] Thus, during state recovery control, the temperature of at least the cooling water inlet INw can be lowered compared to normal power generation control, and the temperature of the air inlet INa adjacent to the cooling water inlet INw and its surroundings can also be lowered. As a result, the amount of moisture removed due to the temperature rise near the air inlet INa is suppressed to exceed the amount of moisture generated by electrochemical reactions, the dry region (DRY) near the air inlet INa can be reduced, and the fuel cell stack (FCS) can be prevented from becoming partially dry.

[0073] Furthermore, the control unit Cf is configured to control the rotation speed of the motor M and fan F so that the amount of power generated by the fuel cell stack FCS remains constant during state recovery control.

[0074] As a result, temperature changes in the fuel cell stack (FCS) are reduced during state recovery control, enabling robust power generation control for the fuel cell stack (FCS).

[0075] Furthermore, the control unit Cf is configured to control the rotation speed of the motor M and fan F so that the amount of heat exchanged in the radiator R is balanced with the amount of heat generated in the fuel cell stack FCS during state recovery control.

[0076] Furthermore, during state recovery control, a configuration that lowers only the temperature of the cooling water inlet INw can improve the performance of the fuel cell stack (FCS) compared to a configuration that lowers the temperatures of both the cooling water inlet INw and the cooling water outlet OUTw.

[0077] Figure 4 shows an example of the correspondence between the temperature of the cooling water inlet INw of the fuel cell stack (FCS) and the output voltage of the fuel cell stack (FCS). In the two-dimensional coordinate system shown in Figure 4, the horizontal axis represents temperature and the vertical axis represents voltage. The solid line in Figure 4 is an example of a curve CH showing the correspondence between the temperature of the cooling water inlet INw and the output voltage of the fuel cell stack (FCS) when a constant current Iα flows through the fuel cell stack (FCS) and the temperature of the cooling water outlet OUTw is temperature tH (e.g., 65°C). The dashed line in Figure 4 is an example of a curve CL showing the correspondence between the temperature of the cooling water inlet INw and the output voltage of the fuel cell stack (FCS) when a constant current Iα flows through the fuel cell stack (FCS) and the temperature of the cooling water outlet OUTw is temperature tL (e.g., 60°C). Assume that temperature t1 > temperature t2 and voltage V1 > voltage V2 > voltage V3. Furthermore, the operating point P1 shown in Figure 4 indicates that when the temperature of the cooling water inlet INw on the curve CH is temperature t1 (e.g., 55°C), the output voltage of the fuel cell stack FCS becomes voltage V1. Also, the operating point P2 shown in Figure 4 indicates that when the temperature of the cooling water inlet INw on the curve CH is temperature t2 (e.g., 50°C), the output voltage of the fuel cell stack FCS becomes voltage V2. Furthermore, the operating point P3 shown in Figure 4 indicates that when the temperature of the cooling water inlet INw on the curve CL is temperature t2, the output voltage of the fuel cell stack FCS becomes voltage V3.

[0078] For example, let's consider a case where the operating point P1 shown in Figure 4 is the operating point at any control timing during normal power generation control.

[0079] In this case, in a configuration where, at any control timing during state recovery control after transitioning from normal power generation control to state recovery control, the rotation speed of motor M is reduced to a lower rotation speed (e.g., 3000 rpm) than the rotation speed during normal power generation control (e.g., 5000 rpm) without changing the rotation speed of fan F, only the temperature of the cooling water inlet INw can be reduced, thus allowing the operating point P1 on the curve CH to transition to the operating point P2.

[0080] Alternatively, in a configuration where, at any control timing during state recovery control after transitioning from normal power generation control to state recovery control, the rotation speed of fan F is increased above the rotation speed during normal power generation control without changing the rotation speed of motor M, the temperatures at both the cooling water inlet INw and the cooling water outlet OUTw can be reduced, thereby allowing the operating point P1 on the curve CH to transition to the operating point P3.

[0081] In other words, during state recovery control, a configuration that lowers only the temperature of the cooling water inlet INw is more effective than a configuration that lowers the temperatures of both the cooling water inlet INw and the cooling water outlet OUTw, because it allows for a relatively higher voltage of the fuel cell stack FCS when a constant current Iα is flowing through the fuel cell stack FCS, thereby improving the performance of the fuel cell stack FCS.

[0082] Furthermore, one method to restore the condition of the fuel cell stack (FCS) when it is partially dry is to install a humidifier in the air supply path to the FCS. However, there are concerns that this method would increase the size of the fuel cell module (FCM).

[0083] Therefore, in the fuel cell module FCM of this embodiment, a humidifier is not provided. 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. If the measured charge transfer resistance Ic is greater than or equal to a threshold Icth, the system transitions from normal power generation control to state recovery control. The state monitoring timing may be repeatedly generated at regular intervals (for example, several minutes, several hours, several days, several weeks, several months, or several years), or it may be generated by an instruction from the control unit Cs of the higher-level system STM.

[0084] <About the operation of the control unit Cf> Figure 5 is a flowchart showing an example of the operation of the control unit Cf during the status monitoring timing.

[0085] First, when the state monitoring timing arrives, the control unit Cf determines whether the charge transfer resistance measurement permission flag is on or off (step Stp1). The charge transfer resistance measurement permission flag is used to identify whether or not it is possible to measure the charge transfer resistance Ic. When the charge transfer resistance measurement permission flag is on, it is possible to measure the charge transfer resistance Ic, and when the charge transfer resistance measurement permission flag is off, it is not possible to measure the charge transfer resistance Ic. For example, when a boost circuit consisting of an inductor, switching element, and diode is configured as a 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 energy storage device B, and current can flow from the fuel cell stack FCS to the energy 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 measurement accuracy of the charge transfer resistance Ic decreasing due to switching noise from the switching element. On the other hand, if the voltage of the fuel cell stack FCS is lower than the voltage of the energy storage device B, and it is necessary to switch the switching element, the charge transfer resistance measurement permission flag is turned off because there is a risk of the measurement accuracy of the charge transfer resistance Ic decreasing due to switching noise. Alternatively, if transitioning from normal power generation control to state recovery control could significantly reduce the overall efficiency of the fuel cell module (FCM), the charge transfer resistance measurement permission flag is turned off. If transitioning from normal power generation control to state recovery control does not pose a significant risk of reducing the overall efficiency of the fuel cell module (FCM), the charge transfer resistance measurement permission flag is turned on.

[0086] Next, if the charge transfer resistance measurement permission flag is off (step Stp1: No), the control unit Cf terminates the state monitoring process for the current 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 normal power generation control. Similarly, during state recovery control, if the charge transfer resistance measurement permission flag is off, the control unit Cf continues state recovery control.

[0087] On the other hand, if the charge transfer resistance measurement permission flag is on (step Stp1: Yes), the control unit Cf measures the charge transfer resistance Ic (step Stp2) and determines whether the charge transfer resistance Ic measured in step Stp2 is greater than or equal to the threshold Icth (step Stp3).

[0088] Next, if the charge transfer resistance Ic is less than the threshold Icth (step Stp3: No), the control unit Cf performs normal power generation control (step Stp4) and terminates the state monitoring process at this state monitoring timing.

[0089] On the other hand, the control unit Cf determines whether the cooling water flow rate can be reduced (whether there is sufficient heat exchange capacity in the radiator R) if the charge transfer resistance Ic is greater than or equal to the threshold Icth (step Stp3: Yes) (step Stp5). For example, the control unit Cf determines that the cooling water flow rate can be reduced if the estimated heat dissipation amount of the cooling water in the radiator R is greater than or equal to the estimated heat generation amount of the cooling water by the fuel cell stack FCS and intercooler IC, and determines that the cooling water temperature cannot be reduced if the estimated heat dissipation amount is less than the estimated heat generation amount. The estimated heat dissipation amount is a value obtained by calculating, for example, the heat dissipation coefficient [kW / K] × (cooling water temperature [K] - ambient temperature of the radiator R [K]). The heat dissipation coefficient is a value proportional to the rotational speed of the motor M of the water pump WP and the rotational speed of the fan F. The estimated heat generation amount is a value obtained by calculating, for example, the heat generation amount of the fuel cell stack FCS [kW] + the heat dissipation amount of the intercooler IC [kW].

[0090] Next, if the control unit Cf determines that it can reduce the flow rate of the cooling water (Step Stp5: Yes), it performs state recovery control (Step Stp6). If it determines that it cannot reduce the flow rate of the cooling water (Step Stp5: No), it performs normal power generation control (Step Stp4) and terminates the state monitoring process for this state monitoring timing.

[0091] Furthermore, during normal power generation control, if the charge transfer resistance Ic is less than the threshold Icth, the control unit Cf continues normal power generation control. During state recovery control, if the charge transfer resistance Ic becomes less than the threshold Icth, or if it is determined that the cooling water flow rate cannot be reduced, it transitions from state recovery control to normal power generation control. Also, during normal power generation control, if the charge transfer resistance Ic becomes greater than or equal to the threshold Icth and it is determined that the cooling water flow rate can be reduced, the control unit Cf transitions from normal power generation control to state recovery control. During state recovery control, if the charge transfer resistance Ic is greater than or equal to the threshold Icth and it is determined that the cooling water flow rate can be reduced, it continues state recovery control.

[0092] As described above, the control unit Cf of this embodiment is configured such that, during normal power generation control, when the charge transfer resistance Ic of the fuel cell stack FCS exceeds a threshold Icth, it transitions from normal power generation control to state recovery control, and during state recovery control, it controls the operation of the cooling system auxiliary equipment so that at least the temperature of the air-side inlet INa of the fuel cell stack FCS is lower than during normal power generation control. For example, during state recovery control, the control unit Cf is configured to reduce the rotation speed of the motor M of the water pump WP compared to during normal power generation control without changing the rotation speed of the fan F.

[0093] As a result, during state recovery control, lowering the temperature of the cooling water inlet INw also lowers the temperature of the air inlet INa adjacent to the cooling water inlet INw and its surroundings. This prevents the amount of moisture removed due to the temperature rise near the air inlet INa from exceeding the amount of moisture generated by the electrochemical reaction, thereby reducing the dry region (DRY) near the air inlet INa and preventing the fuel cell stack (FCS) from becoming partially dry.

[0094] Furthermore, the fuel cell module (FCM) of this embodiment is configured in which a humidifier is not provided in the supply path that supplies air to the fuel cell stack (FCS).

[0095] This allows for a smaller fuel cell module (FCM) by eliminating the need for a humidifier.

[0096] It should be noted that the present invention is not limited to the embodiments described above, and various improvements and modifications are possible without departing from the spirit of the invention.

[0097] For example, in the above embodiment, as shown in Figure 2, the air-side inlet INa is adjacent to the cooling water-side inlet INw, but as shown in Figure 6, the air-side inlet INa may be adjacent to the cooling water-side outlet OUTw.

[0098] In this configuration, during state recovery control, the control unit Cf increases the rotation speed of the water pump WP motor M compared to normal power generation control without changing the rotation speed of the fan F. This allows the temperature of the coolant supplied from the radiator R to the fuel cell stack FCS to be lowered without changing the temperature of the coolant, thus lowering only the temperature of the coolant outlet OUTw.

[0099] Alternatively, during state recovery control, the control unit Cf increases the rotation speed of the fan F compared to normal power generation control without changing the rotation speed of the motor M. This lowers the temperature of the coolant supplied from the fuel cell stack FCS to the radiator R and the temperature of the coolant supplied from the radiator R to the fuel cell stack FCS, thereby lowering the temperatures of the coolant inlet INw and the coolant outlet OUTw.

[0100] Thus, during state recovery control, the temperature of at least the cooling water outlet OUTw can be lowered compared to normal power generation control, and the temperature of the air inlet INa adjacent to the cooling water outlet OUTw and its surroundings can also be lowered. As a result, the amount of moisture removed due to the temperature rise near the air inlet INa is suppressed to exceed the amount of moisture generated by electrochemical reactions, the dry region DRY near the air inlet INa can be reduced, and the fuel cell stack FCS can be prevented from becoming partially dry.

[0101] [Note] The technical concepts that can be understood from the above embodiments and modified examples are described below. <Note 1> Fuel cell stack and A cooling system auxiliary unit that dissipates the heat from the cooling water discharged from the fuel cell stack and supplies it back to the fuel cell stack, A control unit that controls the operation of the cooling system auxiliary equipment, Equipped with, During normal power generation control, if the charge transfer resistance of the fuel cell stack exceeds a threshold, the control unit transitions from normal power generation control to state recovery control. During state recovery control, the control unit controls the operation of the cooling system auxiliary equipment so that at least the temperature of the air-side inlet of the fuel cell stack is lower than during normal power generation control. Fuel cell module. <Note 2> The fuel cell module described in Appendix 1, The control unit controls the operation of the cooling system auxiliary equipment so that the amount of power generated by the fuel cell stack remains constant during the state recovery control. Fuel cell module. <Note 3> A fuel cell module as described in Appendix 1 or 2, The control unit controls the operation of the cooling system auxiliary equipment during state recovery control so that the amount of heat exchanged in the cooling system auxiliary equipment balances the amount of heat generated by the fuel cell stack. Fuel cell module. <Note 4> A fuel cell module as described in any of the appendices 1 to 3, An air compressor that supplies air to the fuel cell stack, A radiator that exchanges heat between the cooling water discharged from the fuel cell stack and the outside air, A water pump that supplies the cooling water discharged from the radiator back to the fuel cell stack, Equipped with, The air-side inlet of the fuel cell stack is adjacent to the cooling water-side inlet of the fuel cell stack. The control unit reduces the rotational speed of the water pump motor during state recovery control compared to the normal power generation control. Fuel cell module. [Explanation of symbols]

[0102] FCM Fuel Cell Module Lo load FCS Fuel Cell Stack HT fuel tank INJ Injector HP Hydrogen Circulation Pump GLS gas liquid separator EDV Exhaust Drain Valve ACP Air Compressor ARV Air Pressure Regulating Valve DIL Diluent R Radiator F Fan WP Water Pump P Pump M Motor INV Inverter Circuit CNV DC-DC converter B Energy storage device St temperature sensor Str storage Cf, Cs control unit

Claims

1. Fuel cell stack and A cooling system auxiliary unit that dissipates the heat from the cooling water discharged from the fuel cell stack and supplies it back to the fuel cell stack, A control unit that controls the operation of the cooling system auxiliary equipment, Equipped with, During normal power generation control, if the charge transfer resistance of the fuel cell stack exceeds a threshold, the control unit transitions from normal power generation control to state recovery control. During state recovery control, the control unit controls the operation of the cooling system auxiliary equipment so that at least the temperature of the air-side inlet of the fuel cell stack is lower than during normal power generation control. Fuel cell module.

2. A fuel cell module according to claim 1, The control unit controls the operation of the cooling system auxiliary equipment so that the amount of power generated by the fuel cell stack remains constant during the state recovery control. Fuel cell module.

3. A fuel cell module according to claim 1, The control unit controls the operation of the cooling system auxiliary equipment during state recovery control so that the amount of heat exchanged in the cooling system auxiliary equipment balances the amount of heat generated by the fuel cell stack. Fuel cell module.

4. A fuel cell module according to claim 1, An air compressor that supplies air to the fuel cell stack, A radiator that exchanges heat between the cooling water discharged from the fuel cell stack and the outside air, A water pump that supplies the cooling water discharged from the radiator back to the fuel cell stack, Equipped with, The air-side inlet of the fuel cell stack is adjacent to the cooling water-side inlet of the fuel cell stack. The control unit reduces the rotational speed of the water pump motor during state recovery control compared to the normal power generation control. Fuel cell module.

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