Fuel battery module

Abstract

To provide a fuel battery module in which a storage battery is directly connected between a fuel battery stack and a load, capable of suppressing a sudden increase in noise generated in an air compressor at a start of power generation of the fuel battery stack, and improving auditory performance of a user.SOLUTION: A fuel battery module FCM includes a storage battery B, the fuel battery stack FCS connected to the storage battery B without a power conversion circuit, an air compressor ACP supplying an oxidant gas to the fuel battery stack FCS, and a control part Cnt controlling an operation of the air compressor ACP so that a flow rate of the oxidant gas gradually increases until a voltage of the fuel battery stack FCS exceeds the voltage of the storage battery B at the start of the power generation of the fuel battery stack FCS.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 gradually changes the flow rate of oxidant gas output from an air compressor to prevent abrupt changes in the noise generated by the air compressor and improve the audibility of the user. Related technology is disclosed in Patent Document 1.

[0003] In some fuel cell modules, a storage battery is directly connected between the fuel cell stack and a load, and power generation by the fuel cell stack begins when the storage battery's charge rate falls below a threshold. In a fuel cell module configured in this manner, the voltage of the fuel cell stack decreases as the voltage of the storage battery decreases, causing an increase in the current flowing through the fuel cell stack. This increases the stoichiometric ratio of the oxidant gas supplied to the fuel cell stack (the ratio of the actual oxidant gas flow rate to the theoretical oxidant gas flow rate required to output a desired current from the fuel cell stack), and increases the rotation speed of the air compressor motor. As a result, when the fuel cell stack starts to generate power, the noise generated by the air compressor increases sharply, which may reduce the user's hearing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-085096 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one aspect of the present invention is to suppress a sudden increase in noise generated by an air compressor when the fuel cell stack starts generating power in a fuel cell module in which a storage battery is directly connected between the fuel cell stack and a load, thereby improving the audibility of the user. [Means for solving the problem]

[0006] One form of the fuel cell module according to the present invention comprises a fuel cell stack, a storage battery connected directly between the fuel cell stack and a load, an air compressor that supplies oxidant gas to the fuel cell stack, and a control unit that controls the operation of the air compressor, wherein the fuel cell stack is connected to the storage battery without going through a power conversion circuit, and the control unit controls the operation of the air compressor so that when the fuel cell stack starts to generate power, the flow rate of the oxidant gas gradually increases until the voltage of the fuel cell stack exceeds the voltage of the storage battery.

[0007] This prevents the noise generated by the air compressor from increasing suddenly when the fuel cell stack starts generating electricity, thereby improving the audibility to the user.

[0008] Furthermore, the control unit may be configured to, during power generation by the fuel cell stack, determine a stoichiometric ratio of the oxidant gas based on a target power generation output of the fuel cell stack, determine a required flow rate of the oxidant gas based on the determined stoichiometric ratio, determine a rotation speed command value for the motor of the air compressor based on the determined required flow rate, and linearly increase the stoichiometric ratio, the required flow rate, or the rotation speed command value.

[0009] Furthermore, the control unit may be configured to, during power generation by the fuel cell stack, determine a stoichiometric ratio of the oxidant gas based on a target power generation output of the fuel cell stack, determine a required flow rate of the oxidant gas based on the determined stoichiometric ratio, determine a rotation speed command value for the motor of the air compressor based on the determined required flow rate, and gradually increase the stoichiometric ratio, the required flow rate, or the rotation speed command value. [Effects of the Invention]

[0010] According to the present invention, in a fuel cell module in which a storage battery is directly connected between a fuel cell stack and a load, it is possible to suppress a sudden increase in noise generated by an air compressor, thereby improving the hearing performance for the user. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating an example of a fuel cell module according to an embodiment; [Figure 2] FIG. 10 is a diagram illustrating an example of the relationship between the charging rate of the storage battery, the switching threshold value, and the target generated power. [Figure 3] 10A to 10C are diagrams showing examples of current-power characteristics, current-voltage characteristics, information showing the relationship between a power command value and a stoichiometric ratio, information showing the relationship between a stoichiometric ratio and a required flow rate, and information showing the relationship between a required flow rate and a rotation speed command value in a fuel cell stack. [Figure 4] FIG. 10 is a diagram illustrating an example of a stoichiometric ratio, a required flow rate, and a rotation speed command value in a comparative example. [Figure 5] 5 is a diagram showing an example of a stoichiometric ratio, a required flow rate, and a rotation speed command value in the first embodiment. FIG. [Figure 6] 10 is a diagram showing an example of a stoichiometric ratio, a required flow rate, and a rotation speed command value in the second embodiment. FIG. [Figure 7] 11 is a diagram showing an example of a stoichiometric ratio, a required flow rate, and a rotation speed command value in the third embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0013] FIG. 1 is a diagram illustrating an example of a fuel cell module according to an embodiment.

[0014] The fuel cell module FCM shown in FIG. 1 is mounted on a vehicle such as a forklift, towing tractor, or automatic guided vehicle (AGV) serving as a host system STM, and supplies power to a load Lo mounted on the vehicle. In this configuration, the load Lo is, for example, an inverter circuit that drives a loading device or a travel motor. The fuel cell module FCM may also be provided in a stationary generator such as an industrial stationary generator, a home stationary generator, or an emergency stationary generator serving as the host system STM. In this configuration, the load Lo is, for example, industrial machinery or a home appliance. A control unit Cs of the host system STM controls applications such as the vehicle, industrial machinery, and home appliance, and also issues commands to the control unit Cnt.

[0015] The fuel cell module FCM also 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.

[0016] That is, the fuel cell module FCM includes fuel gas system accessories such as a fuel tank HT and an injector INJ.

[0017] The fuel cell module FCM also includes oxidant gas system accessories such as an air compressor ACP and an air pressure regulating valve ARV.

[0018] The fuel cell module FCM also includes cooling system accessories such as a radiator R, a fan F, and a water pump WP.

[0019] The fuel cell module FCM also includes, as electrical auxiliaries, a storage battery B, a relay Re, an inrush current prevention circuit Lim, a diode D, a voltage sensor Sv, a current sensor Si, etc. In addition to the relay Re, a relay that transitions from a conductive state to a cut-off state when the fuel cell module FCM goes from a normal state to an abnormal state may be connected between the fuel cell stack FCS and the diode D.

[0020] The fuel cell module FCM further includes a memory unit Str and a control unit Cnt.

[0021] A fuel cell stack (FCS) is composed of multiple fuel cell cells connected in series, and generates electricity through an electrochemical reaction between the hydrogen contained in a fuel gas (such as hydrogen gas) and the oxygen contained in an oxidant gas (such as air).

[0022] The fuel tank HT is a storage container for fuel gas. The fuel gas stored in the fuel tank HT is supplied to the fuel cell stack FCS via the injector INJ.

[0023] The injector INJ adjusts the flow rate of the fuel gas supplied to the fuel cell stack FCS.

[0024] The air compressor ACP compresses the oxidant gas present around the fuel cell module FCM and supplies it to the fuel cell stack FCS via the intercooler IC.

[0025] The air pressure regulating valve ARV adjusts the pressure and flow rate of the oxidant gas supplied to the fuel cell stack FCS.

[0026] The radiator R exchanges heat between the cooling water heated by the heat generated by the fuel cell stack FCS and the outside air.

[0027] Fan F increases the amount of heat dissipated by radiator R.

[0028] The water pump WP supplies the cooling water cooled by the radiator R to the fuel cell stack FCS via the intercooler IC.

[0029] Storage battery B is composed of a lithium-ion capacitor or the like and is connected to the junction point where the fuel cell stack FCS and the load Lo are directly connected via a relay Re rather than a power conversion circuit such as a DC-DC converter. In other words, storage battery B is connected directly between the fuel cell stack FCS and the load Lo without a power conversion circuit. Power output from the fuel cell stack FCS is supplied to auxiliaries such as the air compressor ACP and water pump WP, the load Lo, and storage battery B. If the supply power, which corresponds to the difference between the power output from the fuel cell stack FCS and the power supplied to each auxiliaries, is greater than the power required by the load Lo, a portion of the supplied power equal to the required power is supplied to the load Lo, and the remaining power is supplied to storage battery B. When power is supplied from the fuel cell stack FCS to storage battery B, storage battery B is charged, and the charging rate of storage battery B (the percentage [%] of the remaining capacity relative to the full charge capacity of storage battery B) increases. Furthermore, when regenerative power supplied from the load Lo to the fuel cell module FCM is supplied to storage battery B, storage battery B is charged, and the charging rate of storage battery B increases. Furthermore, if the supply power, which corresponds to the difference between the power output from the fuel cell stack FCS and the power supplied to each auxiliary device, is smaller than the power required by the load Lo, the supply power is supplied to the load Lo, and the shortfall in power is supplied to the load Lo from the storage battery B. When power is supplied from the storage battery B to the load Lo, the storage battery B is discharged and the charging rate of the storage battery B decreases.

[0030] The relay Re is connected between the connection point between the fuel cell stack FCS and the load Lo and the storage battery B, and when in a conductive state, it electrically connects the fuel cell stack FCS and the load Lo to the storage battery B, and when in a cut-off state, it electrically disconnects the fuel cell stack FCS and the load Lo from the storage battery B.

[0031] The inrush current prevention circuit Lim is configured with, for example, a resistor, a relay, etc., and is connected in parallel to the relay Re. The inrush current prevention circuit Lim prevents a relatively large inrush current from flowing through the relay Re when the relay Re transitions from a cut-off state to a conductive state.

[0032] The diode D is connected between the storage battery B and the load Lo and the fuel cell stack FCS, and prevents current from flowing from the storage battery B or the load Lo to the fuel cell stack FCS.

[0033] The voltage sensor Sv detects the voltage V of the storage battery B and sends the detected voltage V to the control unit Cnt.

[0034] The current sensor Si detects the current I flowing through the storage battery B and sends the detected current I to the control unit Cnt.

[0035] The storage unit Str is configured by a nonvolatile memory such as a ROM (Read Only Memory), a flash memory, etc. For example, the storage unit Str stores information D1 to D3, which will be described later.

[0036] The control unit Cnt is configured with a microcomputer and the like, and controls the operation of each auxiliary device to control the power generation of the fuel cell stack FCS.

[0037] For example, when the control unit Cnt receives a start instruction from the control unit Cs provided in the higher-level system STM, it transitions the relay Re from a cut-off state to a conductive state, and when it receives a termination instruction from the control unit Cs, it transitions the relay Re from a conductive state to a cut-off state.

[0038] Furthermore, for example, when controlling the power generation of the fuel cell stack FCS, the control unit Cnt changes the target power generation Pt in accordance with the result of comparing the state of charge of the storage battery B with multiple switching thresholds, and controls the operation of each auxiliary device using PI (Proportional-Integral) control or the like so that the power generated by the fuel cell stack FCS follows the target power generation Pt. In this embodiment, the target power generation Pt is changed in stages in accordance with the result of comparing the state of charge of the storage battery B with multiple switching thresholds. There may be one or more switching thresholds, and in this embodiment, an example is shown in which there are six switching thresholds.

[0039] 2 is a diagram showing an example of the relationship between the storage rate SOC of the storage battery B, the switching threshold SOCth, and the target power generation Pt. Note that the switching threshold SOCth1<switching threshold SOCth2<switching threshold SOCth3<switching threshold SOCth4<switching threshold SOCth5<switching threshold SOCth6. Also, the target power generation Pt0<target power generation Pt1<target power generation Pt2<target power generation Pt3.

[0040] When the storage battery B is being charged, if the storage rate SOC becomes equal to or greater than the switching threshold SOCth2, the control unit Cnt switches the target power generation Pt from the target power generation Pt3 to the target power generation Pt2.

[0041] Furthermore, when the storage battery B is being charged, if the storage rate SOC becomes equal to or greater than the switching threshold SOCth4, the control unit Cnt switches the target power generation Pt from the target power generation Pt2 to the target power generation Pt1.

[0042] Furthermore, when the storage battery B is being charged, the control unit Cnt switches the target power generation Pt from the target power generation Pt1 to the target power generation Pt0 when the storage battery B's charging rate SOC becomes equal to or greater than the switching threshold value SOCth6. For example, if the target power generation Pt0 is set to zero, the control unit Cnt stops power generation by the fuel cell stack FCS when the charging rate SOC becomes equal to or greater than the switching threshold value SOCth6.

[0043] Furthermore, when the storage battery B is discharging, the control unit Cnt switches the target power generation Pt from the target power generation Pt0 to the target power generation Pt1 when the storage battery B's charging rate SOC becomes equal to or lower than the switching threshold SOCth5. For example, if the target power generation Pt0 is set to zero, the control unit Cnt starts power generation by the fuel cell stack FCS when the charging rate SOC becomes equal to or lower than the switching threshold SOCth5.

[0044] Furthermore, when the storage battery B is discharging, if the storage rate SOC becomes equal to or lower than the switching threshold SOCth3, the control unit Cnt switches the target power generation Pt from the target power generation Pt1 to the target power generation Pt2.

[0045] Furthermore, when the storage battery B is discharging, if the storage rate SOC becomes equal to or lower than the switching threshold SOCth1, the control unit Cnt switches the target generated power Pt from the target generated power Pt2 to the target generated power Pt3.

[0046] Furthermore, when controlling the power generation of the fuel cell stack FCS, the control unit Cnt controls the rotation speed of the motor (not shown) of the air compressor ACP based on the target power generation Pt.

[0047] Here, Figure 3(a) is a diagram showing an example of the current-power characteristics and current-voltage characteristics of the fuel cell stack FCS. Note that the horizontal axis of the two-dimensional coordinate system shown in Figure 3(a) represents current, and the vertical axis represents power or voltage. Furthermore, the solid line shown in Figure 3(a) represents an example of the current-power characteristics of the fuel cell stack FCS, and the dashed line shown in Figure 3(a) represents an example of the current-voltage characteristics of the fuel cell stack FCS.

[0048] In the current-power characteristics (solid line) and current-voltage characteristics (dashed line) shown in FIG. 3(a), as the output current increases, the output voltage decreases and the generated power increases.

[0049] In a fuel cell stack FCS having these characteristics, the control unit Cnt controls the operation of the air compressor ACP so that, when the fuel cell stack FCS starts generating electricity, the flow rate of the oxidant gas supplied from the air compressor ACP to the fuel cell stack FCS gradually increases until the voltage of the fuel cell stack FCS exceeds the voltage of the storage battery B. For example, when the fuel cell stack FCS starts generating electricity, the control unit Cnt adjusts the rotation speed of the motor of the air compressor ACP so that the generated power of the fuel cell stack FCS approaches the target generated power and so that the stoichiometric ratio of the oxidant gas (the ratio of the flow rate of the oxidant gas actually supplied to the fuel cell stack FCS to the theoretical flow rate of the oxidant gas required to output the desired power from the fuel cell stack FCS) approaches the target stoichiometric ratio. As a result, the voltage of the fuel cell stack FCS gradually increases. When the voltage of the fuel cell stack FCS exceeds the voltage of the storage battery B, current naturally flows from the fuel cell stack FCS to the storage battery B. As the current flowing from the fuel cell stack FCS to the storage battery B increases, the voltage of the fuel cell stack FCS decreases, and the voltage of the fuel cell stack FCS and the voltage of the storage battery B become balanced.

[0050] FIG. 3(b) is a diagram showing an example of information D1, which is pre-stored in the memory unit Str and which associates a power command value with the stoichiometric ratio of the oxidant gas. FIG. 3(c) is a diagram showing an example of information D2, which is pre-stored in the memory unit Str and which associates a stoichiometric ratio with a required flow rate of the oxidant gas. FIG. 3(d) is a diagram showing an example of information D3, which is pre-stored in the memory unit Str and which associates a required flow rate with a rotation speed command value of the motor of the air compressor ACP. In FIG. 3(b), the horizontal axis of the two-dimensional coordinate system represents power, and the vertical axis represents the stoichiometric ratio of the oxidant gas. The solid line in FIG. 3(b) represents information D1. In FIG. 3(c), the horizontal axis of the two-dimensional coordinate system represents the stoichiometric ratio of the oxidant gas, and the vertical axis represents the flow rate of the oxidant gas. The solid line in FIG. 3(c) represents information D2. The horizontal axis of the two-dimensional coordinate system shown in Fig. 3(d) represents the flow rate of the oxidant gas, and the vertical axis represents the rotation speed of the motor. The solid line shown in Fig. 3(d) represents information D3.

[0051] For example, first, when the storage rate SOC becomes equal to or lower than a switching threshold SOCth5, the control unit Cnt switches the target generated power Pt from the target generated power Pt0 to the target generated power Pt1.

[0052] Next, control unit Cnt determines a power command value It1 from the target power generation Pt1, refers to information D1 to determine a stoichiometric ratio St1 as the stoichiometric ratio corresponding to power command value It1, refers to information D2 to determine a required flow rate Qt1 of oxidant gas corresponding to the stoichiometric ratio St1, and refers to information D3 to determine a rotation speed command value Nt1 as a motor rotation speed command value corresponding to the required flow rate Qt1. Note that control unit Cnt may be configured to determine, by calculation, the stoichiometric ratio corresponding to target power generation Pt1, the required flow rate of oxidant gas corresponding to the stoichiometric ratio, and the motor rotation speed command value for the required flow rate of oxidant gas.

[0053] The control unit Cnt then controls the operation of the motor so that the current rotation speed of the motor follows the rotation speed command value Nt1. Note that the lower the rotation speed of the motor, the lower the noise generated by the air compressor ACP.

[0054] FIG. 4(a) is a diagram showing an example of change in the stoichiometric ratio at the start of power generation in a comparative example (conventional example), FIG. 4(b) is a diagram showing an example of change in the required flow rate at the start of power generation in the comparative example, and FIG. 4(c) is a diagram showing an example of change in the rotation speed command value at the start of power generation in the comparative example. In FIG. 4(a), the horizontal axis of the two-dimensional coordinate system represents time, and the vertical axis represents the stoichiometric ratio. The solid line in FIG. 4(a) shows an example of change in the stoichiometric ratio over time. In FIG. 4(b), the horizontal axis represents time, and the vertical axis represents the flow rate. In FIG. 4(b), the solid line shows an example of change in the required flow rate over time, and the dashed line shows an example of change in the actual flow rate of the oxidant gas over time. In FIG. 4(c), the horizontal axis represents time, and the vertical axis represents the rotation speed. The solid line in FIG. 4(c) shows an example of change in the rotation speed command value over time.

[0055] In the comparative example shown in Figures 4(a) to 4(c), at the start of power generation t0 of the fuel cell stack FCS, the stoichiometric ratio is increased sharply from zero to the stoichiometric ratio St1, so the required flow rate increases sharply from zero to the required flow rate Qt1, and the rotation speed command value increases sharply from zero to the rotation speed command value Nt1.

[0056] Therefore, as shown in Figure 4(b), the actual flow rate of the oxidizer gas also increases sharply from zero to a flow rate equivalent to the required flow rate Qt1. When the flow rate of the oxidizer gas increases sharply like this, the rotation speed of the motor of the air compressor ACP also increases sharply, as shown in Figure 4(c), and the noise generated by the air compressor ACP increases sharply. For example, if the host system STM is a vehicle and the vehicle is traveling at a constant speed for a relatively long period of time, such as when traveling on a highway, if the noise generated by the air compressor ACP increases sharply while the user is barely changing the amount of depression of the accelerator pedal, this may degrade the user's hearing ability.

[0057] As another comparative example, when a DC-DC converter is connected between the fuel cell stack FCS and the storage battery B, the DC-DC converter can adjust the output voltage of the fuel cell stack FCS. When a DC-DC converter is provided in this way, the voltage of the fuel cell stack FCS does not depend on the voltage of the storage battery B, and the voltage of the fuel cell stack FCS can be made relatively high, so the power command value can be made relatively small and the rotation speed of the motor of the air compressor ACP can be reduced.

[0058] On the other hand, in the case of a fuel cell module FCM according to the embodiment, which does not include a DC-DC converter and in which the storage battery B is directly connected between the fuel cell stack FCS and the load Lo, the voltage of the fuel cell stack FCS varies depending on the voltage of the storage battery B. In particular, when the fuel cell stack FCS starts to generate power, the voltage of the storage battery B is relatively low, so the voltage of the fuel cell stack FCS also becomes relatively low, and the power command value becomes relatively large. This causes the motor rotation speed to become relatively high, and the noise generated by the air compressor ACP becomes relatively large.

[0059] Therefore, in this embodiment, the control unit Cnt controls the operation of the air compressor ACP so that, when the fuel cell stack FCS starts to generate electricity, the flow rate of the oxidant gas supplied from the air compressor ACP to the fuel cell stack FCS gradually increases until the voltage of the fuel cell stack FCS exceeds the voltage of the storage battery B. Whether the voltage of the fuel cell stack FCS exceeds the voltage of the storage battery B may be determined by monitoring the respective voltages using a voltage sensor or the like, or by determining whether a predetermined time experimentally determined at the design stage has elapsed.

[0060] As a result, when the fuel cell stack FCS starts generating electricity, the rotation speed of the air compressor ACP motor gradually increases, preventing the noise generated by the air compressor ACP from increasing suddenly, thereby improving the user's hearing performance.

[0061] Example 1 FIG. 5(a) is a diagram showing an example of a change in the stoichiometric ratio at the start of power generation in Example 1, FIG. 5(b) is a diagram showing an example of a change in the required flow rate at the start of power generation in Example 1, and FIG. 5(c) is a diagram showing an example of a change in the rotation speed command value at the start of power generation in Example 1. Note that the horizontal axis of the two-dimensional coordinate system shown in FIG. 5(a) represents time, and the vertical axis represents the stoichiometric ratio. The solid line shown in FIG. 5(a) represents an example of a change in the stoichiometric ratio over time. The horizontal axis of the two-dimensional coordinate system shown in FIG. 5(b) represents time, and the vertical axis represents the flow rate. The solid line shown in FIG. 5(b) represents an example of a change in the required flow rate over time, and the dashed line represents an example of a change in the actual flow rate of the oxidant gas over time. The horizontal axis of the two-dimensional coordinate system shown in FIG. 5(c) represents time, and the vertical axis represents the rotation speed. The solid line shown in FIG. 5(c) represents an example of a change in the rotation speed command value over time. Note that time t0 is set to be less than time t1. At time t1, the voltage of the fuel cell stack FCS is higher than the voltage of the storage battery B. The time from time t0 to time t1 is an arbitrary time that is shorter than the time from when the fuel cell stack FCS starts generating electricity until an abnormality such as water clogging occurs in the fuel cell stack FCS, while the stoichiometric ratio is maintained at a value smaller than the stoichiometric ratio St1. Furthermore, when the fuel cell stack FCS starts generating electricity, the control unit Cnt calculates the stoichiometric ratio St1, the required flow rate Qt1, and the rotation speed command value Nt1 based on the target generated power Pt1.

[0062] In the first embodiment, the control unit Cnt linearly increases the stoichiometric ratio from zero to St1 between time t0 when the fuel cell stack FCS starts generating electricity and time t1, as shown in FIG. 5(a). For example, the control unit Cnt increases the stoichiometric ratio from zero to St1 or greater by a constant value Sc1 every time unit time Tc1 elapses, and then maintains the stoichiometric ratio at St1. Note that the unit time Tc1 is set to an arbitrary time shorter than the time from time t0 when the fuel cell stack FCS starts generating electricity to time t1. The constant value Sc1 is set to an arbitrary value smaller than the stoichiometric ratio St1. As a result, between time t0 when the fuel cell stack FCS starts generating electricity and time t1, the required flow rate gradually increases from zero to Qt1, as shown in FIG. 5(b), and the rotation speed command value gradually increases from zero to Nt1, as shown in FIG. 5(c). 5(b), the actual flow rate of the oxidant gas can be gradually increased from zero to a flow rate corresponding to the required flow rate Qt1. That is, when the fuel cell stack FCS starts to generate electricity, the actual flow rate of the oxidant gas can be gradually increased from zero to a flow rate corresponding to the required flow rate Qt1.

[0063] The control unit Cnt of the first embodiment may be configured to linearly increase the required flow rate from zero to the required flow rate Qt1 or the rotation speed command value from zero to the rotation speed command value Nt1 during the period from the start of power generation t0 of the fuel cell stack FCS to time t1. Even with this configuration, when power generation by the fuel cell stack FCS starts, the actual flow rate of the oxidant gas can be gradually increased from zero to a flow rate equivalent to the required flow rate Qt1.

[0064] In this way, in the first embodiment, when the fuel cell stack FCS starts generating electricity, the stoichiometric ratio, the required flow rate, or the rotation speed command value is linearly increased, so that the actual flow rate of the oxidant gas can be made to gradually (smoothly) follow the flow rate corresponding to the required flow rate, and the actual rotation speed of the motor can be made to gradually follow the rotation speed command value. This makes it possible to further prevent the noise generated by the air compressor ACP from increasing suddenly, and further improves the audibility to the user.

[0065] <Example 2> FIG. 6(a) is a diagram showing an example of change in the stoichiometric ratio at the start of power generation in Example 2, FIG. 6(b) is a diagram showing an example of change in the required flow rate at the start of power generation in Example 2, and FIG. 6(c) is a diagram showing an example of change in the rotation speed command value at the start of power generation in Example 2. Note that the horizontal axis of the two-dimensional coordinate system shown in FIG. 6(a) represents time, and the vertical axis represents the stoichiometric ratio. The solid line shown in FIG. 6(a) represents an example of change in the stoichiometric ratio over time. The horizontal axis of the two-dimensional coordinate system shown in FIG. 6(b) represents time, and the vertical axis represents the flow rate. The solid line shown in FIG. 6(b) represents an example of change in the required flow rate over time, and the dashed line represents an example of change in the actual flow rate of the oxidant gas over time. The horizontal axis of the two-dimensional coordinate system shown in FIG. 6(c) represents time, and the vertical axis represents the rotation speed. The solid line shown in FIG. 6(c) represents an example of change in the rotation speed command value over time. Note that time t0 is set to be less than time t1. At time t1, the voltage of the fuel cell stack FCS is higher than the voltage of the storage battery B. Also, the stoichiometric ratio St1' is set to be less than the stoichiometric ratio St1, the required flow rate Qt1' is set to be less than the required flow rate Qt1, and the rotation speed command value Nt1' is set to be less than the rotation speed command value Nt1. The time from time t0 to time t1 is set to be an arbitrary time that is shorter than the time from when the fuel cell stack FCS starts generating electricity to when an abnormality such as water clogging occurs in the fuel cell stack FCS, while the stoichiometric ratio is maintained at a value smaller than the stoichiometric ratio St1. Also, when the fuel cell stack FCS starts generating electricity, the control unit Cnt calculates the stoichiometric ratio St1, the required flow rate Qt1, and the rotation speed command value Nt1 based on the target generation power Pt1.

[0066] The control unit Cnt of the second embodiment increases the stoichiometric ratio command value stepwise from zero to St1 between time t0 when the fuel cell stack FCS starts generating electricity and time t1. For example, the control unit Cnt changes the stoichiometric ratio from zero to St1' at time t0 when the fuel cell stack FCS starts generating electricity, and then maintains the stoichiometric ratio at St1' between time t0 when the power generation starts and time t1, and then changes the stoichiometric ratio from St1' to St1 at time t1, and then maintains the stoichiometric ratio at St1. As a result, between time t0 when the fuel cell stack FCS starts generating electricity and time t1, the required flow rate gradually increases from zero to required flow rate Qt1, as shown in FIG. 6(b), and the rotation speed command value gradually increases from zero to rotation speed command value Nt1, as shown in FIG. 6(c). 6(b), the actual flow rate of the oxidant gas can be gradually increased from zero to a flow rate corresponding to the required flow rate Qt1. That is, when the fuel cell stack FCS starts to generate electricity, the actual flow rate of the oxidant gas can be gradually increased from zero to a flow rate corresponding to the required flow rate Qt1.

[0067] The control unit Cnt of the second embodiment may be configured to increase the required flow rate stepwise from zero to the required flow rate Qt1, or the rotation speed command value stepwise from zero to the rotation speed command value Nt1, during the period from the start of power generation t0 of the fuel cell stack FCS to time t1. Even with this configuration, the actual flow rate of the oxidant gas can be gradually increased from zero to a flow rate equivalent to the required flow rate Qt1 when the fuel cell stack FCS starts power generation.

[0068] As described above, in Example 2, similarly to Example 1, the rotation speed of the motor of the air compressor ACP is controlled so that the flow rate of the oxidant gas gradually increases when the fuel cell stack FCS starts generating electricity, so that the rotation speed of the motor can be gradually increased. This makes it possible to prevent the noise generated by the air compressor ACP from increasing suddenly, thereby improving the audibility of the user.

[0069] Furthermore, in Example 2, the number of times the stoichiometric ratio, required flow rate, or rotation speed command value is changed can be reduced from the time t0 when the fuel cell stack FCS starts generating electricity to time t1, compared to Example 1, thereby reducing the load on the control unit Cnt. As a result, a relatively inexpensive control unit Cnt can be used, and an increase in the manufacturing cost of the fuel cell module FCM can be suppressed.

[0070] Example 3 FIG. 7(a) is a diagram showing an example of a change in the stoichiometric ratio at the start of power generation in Example 1. FIG. 7(b) is a diagram showing an example of a change in the required flow rate at the start of power generation in Example 1. FIG. 7(c) is a diagram showing an example of a change in the rotation speed command value at the start of power generation in Example 1. Note that the horizontal axis of the two-dimensional coordinate system shown in FIG. 7(a) represents time, and the vertical axis represents the stoichiometric ratio. The solid line shown in FIG. 7(a) represents an example of a change in the stoichiometric ratio over time. The horizontal axis of the two-dimensional coordinate system shown in FIG. 7(b) represents time, and the vertical axis represents the flow rate. The solid line shown in FIG. 7(b) represents an example of a change in the required flow rate over time, and the dashed line represents an example of a change in the actual flow rate of the oxidant gas over time. The horizontal axis of the two-dimensional coordinate system shown in FIG. 7(c) represents time, and the vertical axis represents the rotation speed. The solid line shown in FIG. 7(c) represents an example of a change in the rotation speed command value over time. Time t0 < time t11 < time t1 < time t12. At time t12, the voltage of the fuel cell stack FCS is higher than the voltage of the storage battery B. Also, the stoichiometric ratio St1' is set to be less than the stoichiometric ratio St1, the required flow rate Qt1' is set to be less than the required flow rate Qt1, and the rotation speed command value Nt1' is set to be less than the rotation speed command value Nt1. The time from time t0 to time t12 is set to be an arbitrary time that is shorter than the time from when the fuel cell stack FCS starts generating electricity to when an abnormality such as water clogging occurs in the fuel cell stack FCS, while the stoichiometric ratio is maintained at a value smaller than the stoichiometric ratio St1. Also, when the fuel cell stack FCS starts generating electricity, the control unit Cnt calculates the stoichiometric ratio St1, the required flow rate Qt1, and the rotation speed command value Nt1 based on the target generation power Pt1.

[0071] The control unit Cnt of the third embodiment linearly and stepwise increases the stoichiometric ratio from zero to the stoichiometric ratio St1 between the start of power generation t0 of the fuel cell stack FCS and time t12. For example, the control unit Cnt increases the stoichiometric ratio by a constant value Sc2 for each unit time Tc2 between the start of power generation t0 and time t11, or between the time when the stoichiometric ratio goes from zero to the stoichiometric ratio St1' or greater, and then maintains the stoichiometric ratio at St1' between time t11 and time t1, and then increases the stoichiometric ratio by a constant value Sc3 for each unit time Tc3 between time t1 and time t12, or between the time when the stoichiometric ratio goes from the stoichiometric ratio St1' to the stoichiometric ratio St1 or greater, and then maintains the stoichiometric ratio at St1 from time t12 onwards. Note that the unit time Tc2 is an arbitrary time shorter than the time from the start of power generation t0 to time t11, and the unit time Tc3 is an arbitrary time shorter than the time from time t1 to time t12. The constant value Sc2 is an arbitrary value smaller than the stoichiometric ratio St1′, and the constant value Sc3 is an arbitrary value smaller than the difference between the stoichiometric ratio St1 and the stoichiometric ratio St1′. As a result, between the start of power generation t0 of the fuel cell stack FCS and time t1, the required flow rate gradually increases from zero to the required flow rate Qt1, as shown in FIG. 7(b), and the rotation speed command value gradually increases from zero to the rotation speed command value Nt1, as shown in FIG. 7(c). Therefore, as shown in FIG. 7(b), the actual flow rate of the oxidant gas can be gradually increased from zero to a flow rate equivalent to the required flow rate Qt1. That is, at the start of power generation of the fuel cell stack FCS, the actual flow rate of the oxidant gas can be gradually increased from zero to a flow rate equivalent to the required flow rate Qt1.

[0072] The control unit Cnt of the third embodiment may be configured to linearly and stepwise increase the required flow rate from zero to the required flow rate Qt1 or the rotation speed command value from zero to the rotation speed command value Nt1 during the period from the start of power generation t0 of the fuel cell stack FCS to time t12. Even with this configuration, the actual flow rate of the oxidant gas can be gradually increased from zero to a flow rate equivalent to the required flow rate Qt1 when the fuel cell stack FCS starts power generation.

[0073] As described above, in Example 3, similarly to Examples 1 and 2, the rotation speed of the motor of the air compressor ACP is controlled so that the flow rate of the oxidant gas gradually increases when the fuel cell stack FCS starts generating electricity, so that the rotation speed of the motor can be gradually increased. This makes it possible to prevent the noise generated by the air compressor ACP from increasing suddenly, thereby improving the audibility of the user.

[0074] Furthermore, in the third embodiment, the stoichiometric ratio, required flow rate, or rotation speed command value is increased linearly and stepwise from the time t0 when the fuel cell stack FCS starts generating electricity to time t12, thereby reducing the load on the control unit Cnt and further improving the auditory performance for the user.

[0075] 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]

[0076] FCM Fuel Cell Module Lo load FCS fuel cell stack HT fuel tank INJ injector ACP Air Compressor ARV Air Pressure Regulating Valve R radiator WP water pump B. Storage battery Str storage STM upper system Cnt, Cs control section

Claims

1. a fuel cell stack; a storage battery connected directly between the fuel cell stack and a load; an air compressor for supplying an oxidant gas to the fuel cell stack; a control unit for controlling the operation of the air compressor; Equipped with the fuel cell stack is connected to the storage battery without an intermediary of a power conversion circuit; The control unit controls the operation of the air compressor so that the flow rate of the oxidant gas gradually increases when the fuel cell stack starts to generate electricity until the voltage of the fuel cell stack exceeds the voltage of the storage battery. Fuel cell module.

2. 10. The fuel cell module of claim 1, The control unit, when the fuel cell stack is generating power, determines a stoichiometric ratio of the oxidant gas based on a target generated power of the fuel cell stack, determines a required flow rate of the oxidant gas based on the determined stoichiometric ratio, determines a rotation speed command value for the motor of the air compressor based on the determined required flow rate, and linearly increases the stoichiometric ratio, the required flow rate, or the rotation speed command value. Fuel cell module.

3. 3. The fuel cell module according to claim 1, wherein: The control unit, when the fuel cell stack is generating power, determines a stoichiometric ratio of the oxidant gas based on a target generated power of the fuel cell stack, determines a required flow rate of the oxidant gas based on the determined stoichiometric ratio, determines a rotation speed command value for the motor of the air compressor based on the determined required flow rate, and gradually increases the stoichiometric ratio, the required flow rate, or the rotation speed command value. Fuel cell module.

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