Fuel cell system and charging method

Abstract

To provide a fuel cell system for charging a high voltage side power storage device and a low voltage side power storage device with power supplied from a fuel cell, where the low voltage side power storage device is inhibited from being in an overdischarged state while reducing an uncomfortable feeling given to a user.SOLUTION: A fuel cell system 1 is configured to comprise a fuel cell FC, a high voltage side power storage device BH to be charged with power supplied from the fuel cell FC, a low voltage side power storage device BL to be charged with power supplied from the fuel cell FC or the high voltage side power storage device BH, and a control unit 3 for performing charging control on the high voltage side power storage device BH and the low voltage side power storage device BL. The control unit 3 makes power be supplied from the fuel cell FC to the high voltage side power storage device BH when a charged amount CL of the low voltage side power storage device BL is equal to or lower than a low voltage threshold CLth in a first specific condition and makes power be supplied from the high voltage side power storage device BH to the low voltage side power storage device BL in a second specific condition.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system that charges a high-voltage side power storage device and a low-voltage side power storage device with power supplied from a fuel cell, and a charging method thereof. [Background technology]

[0002] There is a fuel cell system that, when the charge amount of the high-voltage side power storage device is relatively large and the charge amount of the low-voltage side power storage device is relatively small during an ignition-off period of a vehicle equipped with the fuel cell system, supplies power from the high-voltage side power storage device to the low-voltage side power storage device to prevent the low-voltage side power storage device from becoming over-discharged.

[0003] However, when the charge amount of the high-voltage side storage device is relatively small and power cannot be supplied from the high-voltage side storage device to the low-voltage side storage device, it is necessary to supply power from the fuel cell to the high-voltage side storage device to increase the charge amount of the high-voltage side storage device.

[0004] Therefore, in the above fuel cell system, if the charge level of the high-voltage side storage device is relatively small and power cannot be supplied from the high-voltage side storage device to the low-voltage side storage device, the fuel cell will generate power while the vehicle's ignition is off, which may cause discomfort to the user. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-52189 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of one aspect of the present invention is to prevent the low-voltage side storage device from becoming over-discharged while reducing discomfort felt by the user in a fuel cell system in which a high-voltage side storage device and a low-voltage side storage device are charged with power supplied from a fuel cell. [Means for solving the problem]

[0007] A fuel cell system according to one embodiment of the present invention includes a fuel cell, a high-voltage side storage device that is charged with power supplied from the fuel cell, a low-voltage side storage device that is charged with power supplied from the fuel cell or the high-voltage side storage device, and a control unit that controls the charging of the high-voltage side storage device and the low-voltage side storage device.

[0008] The control unit causes the fuel cell to supply power to the high-voltage side power storage device when the charge amount of the low-voltage side power storage device is equal to or less than a low-voltage threshold under a first specific condition, and causes the high-voltage side power storage device to supply power to the low-voltage side power storage device under a second specific condition.

[0009] As a result, when a first specific condition is met in which the fuel cell generating power does not cause the user to feel uncomfortable, power can be supplied from the fuel cell to the high-voltage power storage device, and when a second specific condition is met in which the fuel cell generating power may cause the user to feel uncomfortable, power can be supplied from the high-voltage power storage device to the low-voltage power storage device without the fuel cell generating power, thereby reducing the user's discomfort and preventing the low-voltage power storage device from entering an over-discharge state.

[0010] In addition, the control unit may be configured to determine whether the charge amount of the low-voltage side storage device is below a low-voltage threshold every time a certain period of time elapses under the second specific condition, and if the charge amount of the low-voltage side storage device is below the low-voltage threshold, to supply power from the high-voltage side storage device to the low-voltage side storage device.

[0011] This makes it possible to prevent the low-voltage side power storage device from entering an over-discharge state even if the state where the second specific condition is met remains for a relatively long period of time.

[0012] In addition, the control unit may be configured to stop the supply of power from the high-voltage side storage device to the low-voltage side storage device when the charge amount of the high-voltage side storage device falls below a high-voltage threshold while power is being supplied from the high-voltage side storage device to the low-voltage side storage device.

[0013] This makes it possible to prevent the high-voltage side battery device from being over-discharged.

[0014] Furthermore, the fuel cell system may be mounted on a vehicle, and the control unit may be configured to supply power from the fuel cell to the high-voltage side storage device at the time of switching from ignition on to ignition off if the charge amount of the low-voltage side storage device is below the low-voltage threshold at the time of switching from ignition off to ignition on.

[0015] This makes it possible to determine whether the charge amount of the low-voltage side power storage device is equal to or less than the low-voltage threshold when the ignition-off period is relatively long and the charge amount of the low-voltage side power storage device is relatively stable.

[0016] Furthermore, one embodiment of the present invention provides a charging method for a high-voltage side power storage device and a low-voltage side power storage device in a fuel cell system including a fuel cell, a high-voltage side power storage device charged with power supplied from the fuel cell, a low-voltage side power storage device charged with power supplied from the fuel cell or the high-voltage side power storage device, and a control unit that controls charging of the high-voltage side power storage device and the low-voltage side power storage device, wherein the control unit causes the fuel cell to supply power to the high-voltage side power storage device when the charge amount of the low-voltage side power storage device is equal to or less than a low-voltage threshold under a first specific condition, and causes the high-voltage side power storage device to supply power to the low-voltage side power storage device under a second specific condition.

[0017] As a result, when a first specific condition is met in which the fuel cell generating power does not cause the user to feel uncomfortable, power can be supplied from the fuel cell to the high-voltage power storage device, and when a second specific condition is met in which the fuel cell generating power may cause the user to feel uncomfortable, power can be supplied from the high-voltage power storage device to the low-voltage power storage device without the fuel cell generating power, thereby reducing the user's discomfort and preventing the low-voltage power storage device from entering an over-discharge state. [Effects of the Invention]

[0018] According to the present invention, in a fuel cell system in which a high-voltage side storage device and a low-voltage side storage device are charged with power supplied from a fuel cell, it is possible to prevent the low-voltage side storage device from becoming over-discharged while reducing the discomfort felt by the user. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a diagram illustrating an example of a fuel cell system according to an embodiment. [Figure 2] 1 is a diagram showing an example of a connection configuration between a high-voltage side DC-DC converter and a high-voltage side power storage device, and a connection configuration between a low-voltage side DC-DC converter and a low-voltage side power storage device; [Figure 3] 10 is a flowchart illustrating an example of the operation of a control unit. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0021] FIG. 1 is a diagram illustrating an example of a fuel cell system according to an embodiment.

[0022] 1 is mounted on a vehicle Ve, such as an industrial vehicle such as a forklift, an automobile, etc. The vehicle Ve is equipped with an external load Lo, such as an inverter that drives a traction motor, and power is supplied from the fuel cell system 1 to the external load Lo.

[0023] The fuel cell system 1 also includes a fuel cell FC, a fuel tank T, a main stop valve SV, an injector INJ, a gas-liquid separator GLS, a circulation pump HP, an exhaust drain valve EDV, a diluter DIL, an air compressor ACP, an air pressure regulating valve ARV, and an air shutoff valve ASV.

[0024] The fuel cell system 1 further includes a radiator R, a fan F, a water pump WP, an intercooler IC, a high-voltage side DCDC converter CNVH, a low-voltage side DCDC converter CNVL, a high-voltage side power storage device BH, a low-voltage side power storage device BL, a current sensor Sif, a voltage sensor Svf, a memory unit 2, and a control unit 3.

[0025] A fuel cell FC is a fuel cell made up of multiple fuel cell units connected in series with each other, and generates electricity through an electrochemical reaction between hydrogen contained in a fuel gas (such as hydrogen gas) and oxygen contained in an oxidant gas (such as air).

[0026] The fuel tank T is a storage container for fuel gas. The fuel gas stored in the fuel tank T is supplied to the fuel cell FC via the main stop valve SV and the injector INJ.

[0027] The main stop valve SV is configured by an electromagnetic valve or the like, and supplies fuel gas to the injector INJ. The main stop valve SV is controlled by the control unit 3 to cut off the supply of fuel gas to the injector INJ.

[0028] The injector INJ adjusts the flow rate of the fuel gas so that the pressure of the fuel gas supplied to the fuel cell FC is constant.

[0029] The gas-liquid separator GLS separates the fuel gas and liquid water discharged from the fuel cell FC.

[0030] The circulation pump HP supplies the fuel gas separated by the gas-liquid separator GLS back to the fuel cell FC.

[0031] The exhaust drain valve EDV sends the liquid water separated by the gas-liquid separator GLS to the diluter DIL. The liquid water sent to the diluter DIL accumulates in a tank inside the diluter DIL. In addition, the fuel gas and oxidant gas discharged from the fuel cell FC join together in the diluter DIL and are discharged outside the fuel cell system 1.

[0032] The air compressor ACP compresses the oxidant gas present around the fuel cell system 1 and supplies it to the fuel cell FC via the intercooler IC and the air shutoff valve ASV. The compression rate of the air compressor ACP is controlled by adjusting the opening of the air pressure regulating valve ARV provided downstream of the fuel cell FC.

[0033] The intercooler IC exchanges heat between the oxidant gas, which has been heated by compression, and a refrigerant such as cooling water flowing through the intercooler IC.

[0034] The air shutoff valve ASV cuts off the supply of oxidant gas to the fuel cell FC under the operational control of the control unit 3. It is assumed that the air shutoff valve ASV is fully open when the ignition is on and the vehicle Ve is in operation (when loading and unloading operations and driving are possible).

[0035] The air pressure regulating valve ARV adjusts the pressure and flow rate of the oxidant gas supplied to the fuel cell FC.

[0036] The radiator R exchanges heat between the refrigerant, which has been heated by the heat generated by the fuel cell FC, and the outside air.

[0037] Fan F increases the amount of heat dissipated by radiator R.

[0038] The water pump WP supplies the refrigerant cooled by the radiator R to the fuel cell FC via the intercooler IC.

[0039] The high-voltage side DC-DC converter CNVH is connected downstream of the fuel cell FC and converts the voltage Vfc (e.g., 90 [V]) output from the fuel cell FC into a voltage Vch (e.g., 48 [V]). The power output from the high-voltage side DC-DC converter CNVH is supplied to an external load Lo, a high-voltage side internal load LiH, and a high-voltage side power storage device BH. The high-voltage side internal load LiH is the circulation pump HP, the air compressor ACP, and the water pump WP.

[0040] The high-voltage side power storage device BH is configured by a lithium ion capacitor or the like, and is connected between the high-voltage side DC-DC converter CNVH and the external load Lo.

[0041] The low-voltage side DCDC converter CNVL is connected after the high-voltage side DCDC converter CNVH and the high-voltage side battery BH, and converts the voltage Vch output from the high-voltage side DCDC converter CNVH or the voltage Vbh of the high-voltage side battery BH to a voltage Vbl (for example, 12 V). The power output from the low-voltage side DCDC converter CNVL is supplied to the low-voltage side internal load LiL and the low-voltage side battery BL. The low-voltage side internal load LiL includes the main stop valve SV, the fan F, the air shutoff valve ASV, and the air pressure regulating valve ARV.

[0042] The low-voltage side power storage device BL is configured by a lead battery or the like, and is connected to the rear stage of the low-voltage side DC-DC converter CNVL.

[0043] When the supply power corresponding to the difference between the power output from the high-voltage side DC-DC converter CNVH and the total value of the power supplied to the high-voltage side internal load LiH and the low-voltage side internal load LiL is greater than the power required by the external load Lo, the power corresponding to the required power is supplied to the external load Lo, and the remaining power is supplied to the high-voltage side power storage device BH and the low-voltage side power storage device BL. When power is supplied from the high-voltage side DC-DC converter CNVH to the high-voltage side power storage device BH, the high-voltage side power storage device BH is charged, and the charge amount CH of the high-voltage side power storage device BH increases. Furthermore, when the supply power corresponding to the difference between the power output from the high-voltage side DC-DC converter CNVH and the total value of the power supplied to the high-voltage side internal load LiH and the low-voltage side internal load LiL is less than the power required by the external load Lo, the supply power is supplied to the external load Lo, and the shortfall in power is supplied from the high-voltage side power storage device BH to the external load Lo. When power is supplied from the high-voltage side power storage device BH to the external load Lo, the high-voltage side power storage device BH is discharged, and the charge amount CH of the high-voltage side power storage device BH decreases. Note that the charge amount CH may be the charge rate [%] of the high-voltage side power storage device BH (the ratio of the remaining capacity to the full charge capacity of the high-voltage side power storage device BH), the open-circuit voltage [V] of the high-voltage side power storage device BH when no current is flowing through the high-voltage side power storage device BH, the closed-circuit voltage [V] of the high-voltage side power storage device BH when current is flowing through the high-voltage side power storage device BH, or the integrated value [Ah] of the current flowing through the high-voltage side power storage device BH, etc.

[0044] When the power output from the low-voltage side DCDC converter CNVL is greater than the power consumed by the low-voltage side internal load LiL, the remaining power output from the low-voltage side DCDC converter CNVL other than the power consumed by the low-voltage side internal load LiL is supplied to the low-voltage side storage device BL. When power is supplied to the low-voltage side storage device BL from the high-voltage side DCDC converter CNVH or the low-voltage side DCDC converter CNVL, the low-voltage side storage device BL is charged and the charge amount CL of the low-voltage side storage device BL increases. Also, when the power output from the low-voltage side DCDC converter CNVL is less than the power consumed by the low-voltage side internal load LiL, the power output from the low-voltage side DCDC converter CNVL is supplied to the low-voltage side internal load LiL, and the shortfall in power is supplied from the low-voltage side storage device BL to the low-voltage side internal load LiL. When power is supplied from the low-voltage side storage device BL to the low-voltage side internal load LiL, the low-voltage side storage device BL is discharged, and the charge amount CL of the low-voltage side storage device BL decreases. Note that the charge amount CL may be the charge rate [%] of the low-voltage side storage device BL (the ratio of the remaining capacity to the full charge capacity of the low-voltage side storage device BL), the open circuit voltage [V] of the low-voltage side storage device BL when no current is flowing through the low-voltage side storage device BL, the closed circuit voltage [V] of the low-voltage side storage device BL when current is flowing through the low-voltage side storage device BL, or the integrated value [Ah] of the current flowing through the low-voltage side storage device BL, etc.

[0045] The current sensor Sif is configured with a shunt resistor, a Hall element, etc., and detects the current Ifc flowing from the fuel cell FC to the high-voltage side DC-DC converter CNVH, and sends the detected current If to the control unit 3.

[0046] The voltage sensor Svf is configured with a voltage dividing resistor and the like, detects the voltage Vfc of the fuel cell FC, and sends the detected voltage Vfc to the control unit 3.

[0047] The storage unit 2 is configured by a RAM (Random Access Memory), a ROM (Read Only Memory), and the like.

[0048] The control unit 3 is configured by a microcomputer and the like.

[0049] Furthermore, when the fuel cell system 1 is operating, the control unit 3 changes the target generated power Pt in stages according to the charge amount CH of the high-voltage side power storage device BH.

[0050] Furthermore, the control unit 3 controls the operation of the high-voltage side internal load LiH and the low-voltage side internal load LiL so that the power generated by the fuel cell FC follows the target power generation power Pt when the fuel cell system 1 is operating. For example, when the fuel cell system 1 is operating, the control unit 3 controls the operation of the high-voltage side internal load LiH and the low-voltage side internal load LiL by PI (Proportional-Integral) control so that the difference between the power generated by the fuel cell FC and the target power generation power Pt becomes zero.

[0051] FIG. 2 is a diagram showing an example of a connection configuration between the high-voltage side DC-DC converter CNVH and the high-voltage side power storage device BH, and a connection configuration between the low-voltage side DC-DC converter CNVL and the low-voltage side power storage device BL.

[0052] The high-voltage side DCDC converter CNVH shown in Figure 2 includes a high-side switch SWH, a diode DH connected in parallel to the switch SWH, a low-side switch SWL connected in series to the switch SWH, a diode DL connected in parallel to the switch SWL, an inductor L connected between the connection point of the switches SWH and SWL and the fuel cell FC, and a capacitor C connected in parallel to the switches SWH and SWL. For example, if the switches SWH and SWL are each configured with MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), the diodes DH and DL are parasitic diodes of the switches SWH and SWL. The low-voltage side DCDC converter CNVL has the same configuration as the high-voltage side DCDC converter CNVH, and its description will be omitted.

[0053] When the fuel cell system 1 is operating, if the voltage Vfc of the fuel cell FC is lower than the voltage of the external load Lo, the control unit 3 alternately turns on and off the switches SWH and SWL to boost the voltage Vfc of the fuel cell FC and output it to the external load Lo. Also, when the fuel cell system 1 is operating, if the voltage Vfc of the fuel cell FC is higher than the voltage of the external load Lo, the control unit 3 constantly turns off the switches SWH and SWL to lower the voltage Vfc of the fuel cell FC and output it to the external load Lo.

[0054] The control unit 3 may turn on the switch SWH and output the voltage Vfc of the fuel cell FC to the external load Lo in a state where the diode DH and the switch SWH are connected in parallel.

[0055] The switch SWH may also be omitted. In this case, when the switch SWH is omitted, the anode terminal of the diode DH is connected to the connection point between the inductor L and the switch SWL, and the cathode terminal of the diode DH is connected to one end of the capacitor C. Furthermore, when the fuel cell system 1 is operating, if the voltage Vfc of the fuel cell FC is lower than the voltage of the external load Lo, the control unit 3 repeatedly turns the switch SWL on and off to boost the voltage Vfc of the fuel cell FC and output it to the external load Lo. Furthermore, when the fuel cell system 1 is operating, if the voltage Vfc of the fuel cell FC is higher than the voltage of the external load Lo, the control unit 3 constantly keeps the switch SWL off to lower the voltage Vfc of the fuel cell FC and output it to the external load Lo.

[0056] The high-voltage side relay RH is configured by an electromagnetic relay or the like. One terminal of the high-voltage side relay RH is connected to the output terminal (capacitor C) of the high-voltage side DC-DC converter CNVH via the high-voltage side internal load LiH and the external load Lo, and the other terminal of the high-voltage side relay RH is connected to the high-voltage side power storage device BH. When the high-voltage side relay RH is connected (conducted) by operation control of the control unit 3, the high-voltage side DC-DC converter CNVH, the external load Lo, the high-voltage side internal load LiH, and the high-voltage side power storage device BH are electrically connected. On the other hand, when the high-voltage side relay RH is disconnected by operation control of the control unit 3, the high-voltage side DC-DC converter CNVH, the external load Lo, and the high-voltage side internal load LiH are electrically disconnected from the high-voltage side power storage device BH.

[0057] The connection relay RC is composed of an electromagnetic relay or the like. One terminal of the connection relay RC is connected to the high-voltage side power storage device BH, and the other terminal of the connection relay RC is connected to the input terminal of the low-voltage side DCDC converter CNVL. When the connection relay RC is connected (conducted) under the operational control of the control unit 3, the high-voltage side DCDC converter CNVH and the high-voltage side power storage device BH are electrically connected to the low-voltage side DCDC converter CNVL. On the other hand, when the connection relay RC is disconnected under the operational control of the control unit 3, the high-voltage side DCDC converter CNVH and the high-voltage side power storage device BH are electrically disconnected from the low-voltage side DCDC converter CNVL. In other words, the connection relay RC connects or disconnects the high-voltage system consisting of the high-voltage side DCDC converter CNVH, the high-voltage side internal load LiH, etc., to the low-voltage system consisting of the low-voltage side DCDC converter CNVL, the low-voltage side internal load LiL, etc.

[0058] The low-voltage side relay RL is configured by an electromagnetic relay or the like. One terminal of the low-voltage side relay RL is connected to the output terminal of the low-voltage side DCDC converter CNVL via the low-voltage side internal load LiL, and the other terminal of the low-voltage side relay RL is connected to the low-voltage side battery BL. When the low-voltage side relay RL is connected (conducted) by operation control of the control unit 3, the low-voltage side DCDC converter CNVL and the low-voltage side internal load LiL are electrically connected to the low-voltage side battery BL. On the other hand, when the low-voltage side relay RL is disconnected by operation control of the control unit 3, the low-voltage side DCDC converter CNVL and the low-voltage side internal load LiL are electrically disconnected from the low-voltage side battery BL.

[0059] That is, when the high-voltage side relay RH, the connection relay RC, and the low-voltage side relay RL are connected, power can be supplied from the fuel cell FC to the high-voltage side power storage device BH and the low-voltage side power storage device BL. Also, when the high-voltage side relay RH is disconnected and the connection relay RC and the low-voltage side relay RL are connected, power can be supplied from the high-voltage side power storage device BH to the low-voltage side power storage device BL.

[0060] The monitoring relay RM is configured by an electromagnetic relay or the like. One terminal of the monitoring relay RM is connected to a monitoring unit 31 provided in the control unit 3, and the other terminal of the monitoring relay RM is connected to the low-voltage side power storage device BL. When the monitoring relay RM is connected by operational control of the control unit 3, the monitoring unit 31 and the low-voltage side power storage device BL are electrically connected. On the other hand, when the monitoring relay RM is disconnected by operational control of the control unit 3, the monitoring unit 31 and the low-voltage side power storage device BL are electrically disconnected.

[0061] When control unit 3 receives a signal from vehicle Ve indicating that the ignition has been switched from off to on, it starts power generation control of fuel cell FC and connects high-voltage side relay RH, connection relay RC, low-voltage side relay RL, and monitoring relay RM. It is assumed that the ignition is switched from off to on by a user operating an ignition switch (not shown) provided on vehicle Ve. It is also assumed that control unit 3 is constantly powered by power supplied from low-voltage side power storage device BL (during the ignition-on period (while vehicle Ve is in operation) and the ignition-off period (while vehicle Ve is stopped)). When connecting low-voltage side relay RL, control unit 3 may be configured to first connect connection relay RC to reduce the potential difference across low-voltage side relay RL to a relatively low level, and then connect low-voltage side relay RL, in order to prevent an inrush current from flowing through low-voltage side relay RL.

[0062] Furthermore, when control unit 3 receives a signal from vehicle Ve indicating that the ignition has been switched from on to off, it terminates power generation control of fuel cell FC and disconnects high-voltage side relay RH, connection relay RC, low-voltage side relay RL, and monitoring relay RM. It is assumed that the ignition is switched from on to off by a user operating an ignition switch (not shown) provided in vehicle Ve. By disconnecting high-voltage side relay RH and connection relay RC during the ignition-off period, dark current is prevented from flowing from high-voltage side power storage device BH to external load Lo or high-voltage side internal load LiH via high-voltage side relay RH, and dark current is prevented from flowing from high-voltage side power storage device BH to low-voltage side internal load LiL via connection relay RC and low-voltage side DC-DC converter CNVL. This prevents high-voltage side power storage device BH from entering an over-discharge state. Furthermore, by cutting off the low-voltage side relay RL during the ignition-off period, it is possible to prevent dark current from flowing from the low-voltage side power storage device BL to the low-voltage side internal load LiL via the low-voltage side relay RL, thereby preventing the low-voltage side power storage device BL from entering an over-discharge state. Furthermore, by cutting off the high-voltage side relay RH, the connection relay RC, and the low-voltage side relay RL during the ignition-off period, it is possible to cause the high-voltage side internal load LiH and the low-voltage side internal load LiL to consume the charges stored in the capacitors C of the high-voltage side DC-DC converter CNVH and the low-voltage side DC-DC converter CNVL.

[0063] Furthermore, when a notification that the ignition has been switched from off to on is received, monitoring unit 31 determines whether or not the charge amount CL of low-voltage side power storage device BL is equal to or less than low-voltage threshold value CLth.

[0064] Furthermore, when the control unit 3 receives notification that the ignition has been switched from off to on and determines that the charge amount CL is equal to or less than the low-voltage threshold CLth, it switches the charge flag from off to on. If the charge amount CL of the low-voltage side power storage device BL is relatively small when the ignition is switched on, it is expected that not only the ignition-on period but also the ignition-off period will be relatively short, and therefore it is necessary to forcibly charge the low-voltage side power storage device BL. Therefore, when the charge amount CL of the low-voltage side power storage device BL is equal to or less than the low-voltage threshold CLth, the control unit 3 switches the charge flag from off to on so that it recognizes that it is necessary to forcibly charge the low-voltage side power storage device BL until the time when the ignition is switched from on to off. Note that when charging of the high-voltage side power storage device BH is completed during the ignition-off period, the control unit 3 switches the charge flag from on to off.

[0065] Furthermore, when the charging flag is off at the timing of switching from ignition on to ignition off, the control unit 3 does not need to forcibly charge the low-voltage side power storage device BL, and sets the charge amount CH of the high-voltage side power storage device BH as the charge termination condition to the charge amount CH1.

[0066] In addition, if the charging flag is on at the time of switching from ignition on to ignition off, the control unit 3 needs to forcibly charge the low-voltage side storage device BL, so it causes the fuel cell FC to generate electricity and charge the high-voltage side storage device BH and the low-voltage side storage device BL.

[0067] Furthermore, if the charge flag is on when the ignition is switched from on to off, the control unit 3 sets the charge amount CH of the high-voltage side power storage device BH as a charge end condition to a charge amount CH2 that is greater than the charge amount CH1, since it is necessary to forcibly charge the low-voltage side power storage device BL. This makes it possible to prevent the high-voltage side power storage device BH from entering an over-discharge state, even when the low-voltage side power storage device BL is forcibly charged using only the high-voltage side power storage device BH when the fuel cell FC is not generating power.

[0068] Furthermore, the control unit 3 temporarily connects only the monitoring relay RM every time a certain period of time (for example, every 24 hours) elapses during the ignition-off period.

[0069] Furthermore, during an ignition-off period, when the monitoring relay RM is connected, the monitoring unit 31 determines whether or not the charge amount CL of the low-voltage side power storage device BL is equal to or less than the low-voltage threshold value CLth.

[0070] Furthermore, when the control unit 3 determines that the charge amount CL is equal to or less than the low voltage threshold CLth during the ignition-off period, it keeps the high-voltage side relay RH disconnected and connects the connection relay RC and the low-voltage side relay RL, and then supplies power from the high-voltage side storage device BH to the low-voltage side storage device BL via the connection relay RC, the low-voltage side DCDC converter CNVL, and the low-voltage side relay RL to charge the low-voltage side storage device BL.

[0071] Furthermore, control unit 3 may determine that the contacts in high-voltage side relay RH are welded if the potential difference across both ends of high-voltage side relay RH is zero or nearly zero after switching off high-voltage side relay RH. Furthermore, control unit 3 may determine that the contacts in connection relay RC are welded if the potential difference across both ends of connection relay RC is zero or nearly zero after switching off low-voltage side relay RL. Furthermore, control unit 3 may determine that the contacts in low-voltage side relay RL are welded if the potential difference across both ends of low-voltage side relay RL is zero or nearly zero after switching off low-voltage side relay RL.

[0072] However, when the charge amount CH of the high-voltage side storage device BH is relatively small and power cannot be supplied from the high-voltage side storage device BH to the low-voltage side storage device BL, it is necessary to supply power from the fuel cell FC to the high-voltage side storage device BH to increase the charge amount of the high-voltage side storage device BH.

[0073] Therefore, if the charge amount CH of the high-voltage side storage device BH is relatively small during the ignition-off period and power cannot be supplied from the high-voltage side storage device BH to the low-voltage side storage device BL, the charge amount CH of the high-voltage side storage device BH will increase by generating power from the fuel cell FC, which may cause the user to feel uncomfortable when the fuel cell FC generates power while the vehicle Ve is stopped.

[0074] Therefore, in the fuel cell system 1 of the embodiment, when the charge amount CL of the low-voltage side storage device BL is equal to or less than the low-voltage threshold CLth under a first specific condition, power is supplied from the fuel cell FC to the high-voltage side storage device BH, and when the second specific condition is met, power is supplied from the high-voltage side storage device BH to the low-voltage side storage device BL.

[0075] As a result, when a first specific condition is met in which the user will not feel uncomfortable even if the fuel cell FC is generating electricity (for example, when the ignition is switched from on to off, during the period when fuel gas is being filled into the fuel tank T, or during the period when liquid water accumulated in the tank in the diluter DIL is being discharged), power is supplied from the fuel cell FC to the high-voltage power storage device BH, and when a second specific condition is met in which the user may feel uncomfortable if the fuel cell FC is generating electricity (for example, during the ignition is off), power is supplied from the high-voltage power storage device BH to the low-voltage power storage device BL without the fuel cell FC generating electricity. This makes it possible to reduce the discomfort felt by the user while preventing the low-voltage power storage device BL from entering an over-discharge state.

[0076] In addition, in the fuel cell system 1 of the embodiment, under the second specific condition, it is determined every certain time that the charge amount CL of the low-voltage side storage device BL is equal to or less than the low-voltage threshold value CLth, and if the charge amount CL of the low-voltage side storage device BL is equal to or less than the low-voltage threshold value CLth, power is supplied from the high-voltage side storage device BH to the low-voltage side storage device BL.

[0077] This allows the low-voltage side storage device BL to be charged periodically even if the state of the second specific condition is relatively long (for example, even if the ignition-off period is relatively long and the period during which dark current flows from the low-voltage side storage device BL to the control unit 3 is relatively long), thereby preventing the low-voltage side storage device BL from entering an over-discharge state.

[0078] In addition, in the fuel cell system 1 of the embodiment, when power is being supplied from the high-voltage side storage device BH to the low-voltage side storage device BL, if the charge amount CH of the high-voltage side storage device BH becomes equal to or less than the high-voltage threshold CHth, the power supply from the high-voltage side storage device BH to the low-voltage side storage device BL is stopped.

[0079] This makes it possible to prevent high-voltage side power storage device BH from entering an over-discharge state.

[0080] In addition, in the fuel cell system 1 of the embodiment, if the charge amount CL of the low-voltage side power storage device BL is less than or equal to the low-voltage threshold CLth at the timing when the ignition switches from off to on, power is supplied from the fuel cell FC to the high-voltage side power storage device BH at the timing when the ignition switches from on to off.

[0081] This makes it possible to determine whether the charge amount CL of the low-voltage side power storage device BL is equal to or less than the low-voltage threshold value CLth when the ignition has been off for a relatively long time and the charge amount CL of the low-voltage side power storage device BL is relatively stable.

[0082] 3 is a flowchart showing an example of the operation of the control unit 3. It is assumed that the high-voltage side relay RH, connection relay RC, low-voltage side relay RL, and monitoring relay RM are connected during the ignition-on period.

[0083] First, when the control unit 3 determines that the ignition has been switched from ON to OFF (step S1: Yes), it determines whether the charge flag is ON (step S2).

[0084] Next, when the control unit 3 determines that the charging flag is on (step S2: Yes), it starts power generation in the fuel cell FC and charges the high-voltage side storage device BH and the low-voltage side storage device BL with the power output from the fuel cell FC (step S3).

[0085] Next, the control unit 3 continues power generation by the fuel cell FC until the charge amount CH of the high-voltage side power storage device BH becomes equal to or greater than the charge amount CH2 (step S4: No). When the charge amount CH becomes equal to or greater than the charge amount CH2 (step S4: Yes), the control unit 3 stops power generation by the fuel cell FC (step S5). Note that the control unit 3 may be configured to stop power generation by the fuel cell FC when the charge amount CH of the high-voltage side power storage device BH becomes greater than a high-voltage threshold CHth and the charge amount CL of the low-voltage side power storage device BL becomes greater than a low-voltage threshold CLth. For example, the high-voltage threshold CHth is set to the minimum value of the charge amount CH of the high-voltage side power storage device BH that can drive the high-voltage side internal load LiH. Furthermore, for example, the low-voltage threshold CLth is set to the minimum value of the charge amount CL of the low-voltage side power storage device BL that can drive the low-voltage side internal load LiL. Furthermore, after power generation by the fuel cell FC stops in step S5, the connection relay RC and the low-voltage side relay RL are in a connected state, so power is supplied from the high-voltage side storage device BH to the low-voltage side storage device BL via the connection relay RC, the low-voltage side DCDC converter CNVL, and the low-voltage side relay RL, and the low-voltage side storage device BL is charged and the high-voltage side storage device BH is discharged.

[0086] Next, if the charge amount CL of the low-voltage side power storage device BL is equal to or less than the low-voltage threshold CLth and the charge amount CH of the high-voltage side power storage device BH is greater than the high-voltage threshold CHth (step S6: No), control unit 3 continues to charge the low-voltage side power storage device BL and discharge the high-voltage side power storage device BH. Note that the period from when the charge amount CH becomes equal to or greater than the charge amount CH2 during the ignition-off period until the ignition is switched to on is set as a second specific condition. In this case, since charging the low-voltage side power storage device BL using the fuel cell FC under the second specific condition may cause discomfort to the user, the low-voltage side power storage device BL is charged using only the high-voltage side power storage device BH.

[0087] On the other hand, when the charge amount CL of the low-voltage side power storage device BL becomes larger than the low-voltage threshold CLth, or when the charge amount CH of the high-voltage side power storage device BH becomes equal to or smaller than the high-voltage threshold CHth (step S6: Yes), control unit 3 interrupts the high-voltage side relay RH, connection relay RC, low-voltage side relay RL, and monitoring relay RM to stop the power supply from the high-voltage side power storage device BH to the low-voltage side power storage device BL, thereby stopping the charging of the low-voltage side power storage device BL and stopping the discharging of the high-voltage side power storage device BH (step S7). Note that the period from when the ignition is switched from on to off until the charge amount CH becomes equal to or greater than the charge amount CH2 is set as the first specific condition. In this case, even if the fuel cell FC is forcibly caused to generate power to charge the high-voltage side power storage device BH and the low-voltage side power storage device BL under the first specific condition, the user can be made to believe that the ignition-on period has been slightly extended, and therefore, the user does not feel uncomfortable.

[0088] Next, when a certain time has elapsed since the control unit 3 disconnected the high-voltage side relay RH, the connection relay RC, the low-voltage side relay RL, and the monitoring relay RM (step S8: Yes), it connects only the monitoring relay RM (step S9) and then determines whether the charge amount CL of the low-voltage side storage device BL is equal to or less than the low-voltage threshold CLth (step S10).

[0089] Next, if the charge amount CL is greater than the low voltage threshold CLth (step S10: No), the control unit 3 executes the processes of steps S7 to S10 again.

[0090] On the other hand, when the charge amount CL becomes equal to or less than the low voltage threshold CLth (step S10: Yes), the control unit 3 connects the connection relay RC and the low voltage side relay RL to supply power from the high voltage side storage device BH to the low voltage side storage device BL via the connection relay RC, the low voltage side DCDC converter CNVL, and the low voltage side relay RL, thereby charging the low voltage side storage device BL and discharging the high voltage side storage device BH (step S11).

[0091] Next, the control unit 3 returns to step S6, and if the charge amount CL of the low-voltage side storage device BL is less than or equal to the low-voltage threshold CLth and the charge amount CH of the high-voltage side storage device BH is greater than the high-voltage threshold CHth (step S6: No), it continues charging the low-voltage side storage device BL and continues discharging the high-voltage side storage device BH.

[0092] On the other hand, when the charge amount CL of the low-voltage side power storage device BL becomes larger than the low-voltage threshold CLth, or when the charge amount CH of the high-voltage side power storage device BH becomes equal to or smaller than the high-voltage threshold CHth (step S6: Yes), control unit 3 interrupts the high-voltage side relay RH, connection relay RC, low-voltage side relay RL, and monitoring relay RM to stop the power supply from the high-voltage side power storage device BH to the low-voltage side power storage device BL, thereby stopping the charging of the low-voltage side power storage device BL and stopping the discharging of the high-voltage side power storage device BH (step S7), and then transitions to the processing of step S8 and subsequent steps. That is, during the ignition-off period, from the time when power generation by the fuel cell FC stops until the ignition is turned on, charging of the low-voltage side power storage device BL by supplying power from the high-voltage side power storage device BH to the low-voltage side power storage device BL is periodically and repeatedly performed. This makes it possible to prevent the low-voltage side power storage device BL from becoming over-discharged during the ignition-off period.

[0093] After determining that the ignition has switched from on to off (step S1: Yes), if the control unit 3 determines that the charging flag is off (step S2: No), it does not perform the charging process for the high-voltage side storage device BH and the low-voltage side storage device BL using the power output from the fuel cell FC, and repeatedly performs the processes of steps S6 to S11 until the ignition switches from off to on.

[0094] Furthermore, when control unit 3 determines in step S6 that the charge amount CL of low-voltage side power storage device BL becomes larger than low-voltage threshold CLth and the charging time of low-voltage side power storage device BL becomes equal to or longer than a predetermined charging time, control unit 3 may transition to processing in step S7 to stop charging of low-voltage side power storage device BL, and then transition to processing in step S8 and subsequent steps. For example, the predetermined charging time may be the charging time when the charging current becomes relatively large when the low-voltage side power storage device BL is a power storage device such as a lead battery that has a relatively low charging efficiency and makes it difficult for current to flow at the beginning of charging. This makes it possible to determine whether the charge amount CL becomes larger than low-voltage threshold CLth at a timing when the charging current becomes relatively large (a timing when the N / S ratio of the charging current can be improved).

[0095] In the example of operation of the control unit 3 shown in FIG. 3, when the charge flag is on, the high-voltage side power storage device BH and the low-voltage side power storage device BL are forcibly charged at the beginning of the ignition-off period, and then the low-voltage side power storage device BL is charged periodically during the ignition-off period. When the ignition-on period or the ignition-off period is relatively short, or when the ignition-off period is relatively long, it is possible to reduce the discomfort felt by the user while preventing the low-voltage side power storage device BL from becoming over-discharged.

[0096] 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.

[0097] <Variation 1> When the charge amount CH of the high-voltage side storage device BH is relatively small and power cannot be supplied from the high-voltage side storage device BH to the low-voltage side storage device BL, the control unit 3 may display this fact on a display (not shown) provided in the vehicle Ve.

[0098] <Variation 2> The fuel cell system 1 in the above embodiment is configured as a generator that supplies power to an external load Lo mounted on a vehicle Ve, but the fuel cell system 1 may also be configured as a stationary generator that cooperates with a commercial power source to supply power to an external load Lo located outside the fuel cell system 1. [Explanation of symbols]

[0099] 1. Fuel cell system 2 Storage section 3. Control Unit 31 Monitoring Department Vehicle Lo external load FC fuel cell T Fuel Tank SV Main stop valve INJ injector GLS gas-liquid separator HP Circulation Pump EDV Exhaust Drain Valve DIL Diluter ACP Air Compressor ARV Air Pressure Regulating Valve ASV Air Shutoff Valve R radiator F Fan WP water pump IC intercooler CNVH High Voltage Side DCDC Converter CNVL Low voltage side DC / DC converter BH High-voltage side storage device BL Low voltage side storage device Sif current sensor SVF voltage sensor

Claims

1. A fuel cell system mounted on a vehicle, comprising: A fuel cell; a high-voltage side power storage device that is charged by power supplied from the fuel cell; a low-voltage side power storage device that is charged with power supplied from the fuel cell or the high-voltage side power storage device; a control unit that controls charging of the high-voltage side power storage device and the low-voltage side power storage device; Equipped with The control unit controls the fuel cell to supply power to the high-voltage power storage device when the ignition of the vehicle is switched from on to off if the charge amount of the low-voltage power storage device is equal to or less than a low-voltage threshold at the timing when the ignition of the vehicle is switched from off to on, which is a first specific condition, and controls the high-voltage power storage device to supply power to the low-voltage power storage device under a second specific condition. A fuel cell system characterized by:

2. 2. The fuel cell system according to claim 1, The control unit determines whether the charge amount of the low-voltage side power storage device is equal to or less than the low-voltage threshold every time a certain time period elapses under the second specific condition, and when the charge amount of the low-voltage side power storage device is equal to or less than the low-voltage threshold, causes the high-voltage side power storage device to supply power to the low-voltage side power storage device. A fuel cell system characterized by:

3. 3. The fuel cell system according to claim 1, wherein: When the amount of charge of the high-voltage side power storage device becomes equal to or less than a high voltage threshold while power is being supplied from the high-voltage side power storage device to the low-voltage side power storage device, the control unit stops the power supply from the high-voltage side power storage device to the low-voltage side power storage device. A fuel cell system characterized by:

4. A fuel cell; a high-voltage side power storage device that is charged by power supplied from the fuel cell; a low-voltage side power storage device that is charged with power supplied from the fuel cell or the high-voltage side power storage device; a control unit that controls charging of the high-voltage side power storage device and the low-voltage side power storage device; a monitoring relay connected between a monitoring unit provided in the control unit and the low-voltage side power storage device; Equipped with the control unit temporarily connects the monitoring relay every time a certain time period elapses under a second specific condition, the monitoring unit determines whether or not the amount of charge of the low-voltage side power storage device is equal to or less than a low-voltage threshold when the monitoring relay is connected under the second specific condition; When the charge amount of the low-voltage side power storage device is equal to or less than the low-voltage threshold under a first specific condition, the control unit causes the fuel cell to supply power to the high-voltage side power storage device, and when it is determined that the charge amount of the low-voltage side power storage device is equal to or less than the low-voltage threshold under the second specific condition, causes the high-voltage side power storage device to supply power to the low-voltage side power storage device. A fuel cell system characterized by:

5. a fuel cell; and a high-voltage side power storage device that is charged by power supplied from the fuel cell; A method for charging a high-voltage side power storage device and a low-voltage side power storage device in a fuel cell system including: a low-voltage side power storage device that is charged with power supplied from the fuel cell or the high-voltage side power storage device; and a control unit that controls charging of the high-voltage side power storage device and the low-voltage side power storage device, The fuel cell system is mounted on a vehicle, The control unit controls the fuel cell to supply power to the high-voltage power storage device when the ignition of the vehicle is switched from on to off if the charge amount of the low-voltage power storage device is equal to or less than a low-voltage threshold at the timing when the ignition of the vehicle is switched from off to on, which is a first specific condition, and controls the high-voltage power storage device to supply power to the low-voltage power storage device under a second specific condition. A charging method characterized by:

6. A fuel cell, a high-voltage side power storage device that is charged by power supplied from the fuel cell, A method for charging the high-voltage side power storage device and the low-voltage side power storage device in a fuel cell system including: a low-voltage side power storage device that is charged with power supplied from the fuel cell or the high-voltage side power storage device; a control unit that controls charging of the high-voltage side power storage device and the low-voltage side power storage device; and a monitoring relay connected between a monitoring unit provided in the control unit and the low-voltage side power storage device, the control unit temporarily connects the monitoring relay every time a certain time period elapses under a second specific condition, the monitoring unit determines whether or not the amount of charge of the low-voltage side power storage device is equal to or less than a low-voltage threshold when the monitoring relay is connected under the second specific condition; When the charge amount of the low-voltage side power storage device is equal to or less than the low-voltage threshold under a first specific condition, the control unit causes the fuel cell to supply power to the high-voltage side power storage device, and when it is determined that the charge amount of the low-voltage side power storage device is equal to or less than the low-voltage threshold under the second specific condition, causes the high-voltage side power storage device to supply power to the low-voltage side power storage device. A charging method characterized by:

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