Fuel cell system

Abstract

A fuel cell system (1) comprises a fuel cell (10), a control device (20), an auxiliary power source (31) serving as a first electricity storage device, and a power reception electricity storage device (32) serving as a second electricity storage device. Furthermore, under the control of the control device (20), electric power output from the fuel cell (10) is supplied to an external load (C) and also charges the auxiliary power source (31), while liquid fuel is being supplied to the fuel cell (10). Furthermore, in addition to the electric power output from the fuel cell (10), post-shutdown electric power recovered by the power reception electricity storage device (32) is discharged and supplied to the external load (C). In a state in which the supply of liquid fuel to the fuel cell (10) has been stopped, the electric power with which the auxiliary power source (31) has been charged is discharged and supplied to the external load (C).

Description

fuel cell system

[0001] The present disclosure relates to fuel cell systems.

[0002] Fuel cells, which are the main components of fuel cell systems, particularly solid polymer fuel cells, generally have an electrode structure consisting of an anode electrode formed on one side of an electrolyte membrane and a cathode electrode formed on the other side. In solid polymer fuel cells, fuel is supplied to the anode electrode and an oxidant is supplied from the outside to the cathode electrode, causing an electrode reaction in the electrode structure to generate electricity.

[0003] In recent years, direct fuel cells have been developed that directly use liquid fuels such as methanol or formic acid as the fuel supplied to the anode electrode. Liquid fuels are easier to handle and have a higher energy density per unit volume than gaseous fuels such as hydrogen gas, making them extremely useful.

[0004] In such direct current fuel cells, a phenomenon may occur in which the output power due to power generation gradually decreases during continuous power generation operation. In order to suppress the decrease in output power and maintain the output power, direct current fuel cells periodically perform refresh control to stop the electrode reaction. When refresh control is performed, the electrode reaction in the direct current fuel cell is temporarily stopped, i.e., power generation is stopped, causing the output power to become unstable.

[0005] As a conventional configuration for stabilizing the output power, for example, Patent Document 1 discloses a configuration of a fuel cell system equipped with an auxiliary power supply that charges the power generated by the fuel cell. In the configuration disclosed in Patent Document 1, the fuel cell outputs power to the outside and charges the auxiliary power supply, and when the output power of the fuel cell decreases, the power charged (stored) in the auxiliary power supply is discharged, thereby stabilizing the power output to the outside.

[0006] Japanese Patent Application Laid-Open No. 2007-280741

[0007] In a fuel cell system equipped with a direct liquid fuel cell, when refresh control is performed on the fuel cell, the supply of liquid fuel to the anode electrode of the fuel cell is usually stopped. In this case, the electrode structure continues to generate power through an electrode reaction using the liquid fuel that has already been supplied, and then the electrode reaction is stopped.

[0008] Therefore, if it takes time for the supplied liquid fuel to be consumed by the electrode reaction in the electrode structure, the time during which the fuel cell stops generating power to output power to the outside due to the execution of refresh control will be long. As a result, even if the stored power is supplied to the auxiliary power supply, the power output to the outside will become unstable. Therefore, from the perspective of stabilizing the power output to the outside, it is desirable to keep the time during which the fuel cell stops generating power due to refresh control short.

[0009] Furthermore, normally, as a result of refresh control, the power output from the fuel cell continues until the liquid fuel already supplied is consumed, and is wasted by being grounded and discharging. Therefore, from the perspective of saving energy and improving efficiency of battery energy, it is desirable to recover the power that is wasted as a result of refresh control and to add this recovered power to the power output from the fuel cell to the outside.

[0010] The present disclosure aims to provide a fuel cell system that achieves both stabilization of the power output to the outside and improvement in the efficiency of power utilization.

[0011] One aspect of the present disclosure includes a fuel cell having an electrode structure having an anode electrode and a cathode electrode, the fuel cell generating electric power by supplying liquid fuel to the anode electrode and supplying an oxidant to the cathode electrode; a first power storage device that charges the first power storage device with a portion of the electric power output from the fuel cell when the supply of the liquid fuel to the fuel cell is being carried out; a second power storage device that charges the first power storage device with post-shutdown electric power generated by the fuel cell using the liquid fuel that has already been supplied when the supply of the liquid fuel to the fuel cell is stopped, and recovers the post-shutdown electric power generated by the fuel cell using the liquid fuel that has already been supplied; and a control device that controls the supply of liquid fuel to the fuel cell and the operation of the first power storage device and the second power storage device, the fuel cell being configured such that an electrode reaction in the electrode structure is stopped after the post-shutdown electric power is recovered by the second power storage device, and the control device controls the first power storage device to discharge and supply the electric power charged in the first power storage device to an external load when the supply of the liquid fuel to the fuel cell is stopped, The fuel cell system is configured such that, while the liquid fuel is being supplied to the fuel cell, in addition to the power output from the fuel cell, the post-shutdown power recovered in the second storage device is discharged and supplied to an external load.

[0012] According to the above-described aspect of the fuel cell system, the system includes a first power storage device and a second power storage device. The first power storage device is charged with a portion of the power generated by the fuel cell while the supply of liquid fuel to the fuel cell is ongoing, and discharges the power stored in the first power storage device to an external load while the supply of liquid fuel to the fuel cell is stopped. This allows the power supply to the external load to be maintained even during refresh control, when the supply of liquid fuel to the fuel cell is stopped, thereby stabilizing the power output to the outside.

[0013] In addition, the second power storage device stores and recovers post-shutdown power generated by the fuel cell using the liquid fuel already supplied when the supply of liquid fuel to the fuel cell is stopped, and the electrode reaction of the fuel cell is stopped after the second power storage device recovers the post-shutdown power. Then, in addition to the power output from the fuel cell when the supply of liquid fuel to the fuel cell is ongoing, the post-shutdown power recovered by the second power storage device is discharged to an external load. This allows the electrode reaction to be stopped quickly after the second power storage device recovers the post-shutdown power, thereby shortening the power generation stop time associated with refresh control and allowing the post-shutdown power that would previously have been wasted to be recovered by the second power storage device and used by discharging it to an external load. This improves power utilization efficiency.

[0014] As described above, according to the above aspect, it is possible to provide a fuel cell system that achieves both stabilization of the power output to the outside and improvement of the power utilization efficiency.

[0015] Note that the symbols in parentheses in the claims indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present disclosure.

[0016] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is a conceptual diagram showing the configuration of a fuel cell system according to a first embodiment, Fig. 2 is a conceptual diagram showing the configuration of a fuel cell according to the first embodiment, Fig. 3 is a conceptual diagram showing the configuration of a control device according to the first embodiment, Fig. 4 is a time chart illustrating the operation of the fuel cell system in a normal power generation mode according to the first embodiment, Fig. 5 is a time chart illustrating the operation of the fuel cell system in a refresh control mode according to the first embodiment, Fig. 6 is a time chart illustrating the operation of the fuel cell system in a power receiving storage device discharge mode according to the first embodiment, Fig. 7 is a time chart illustrating the operation of the fuel cell system in a normal power superposition mode according to the first embodiment, Fig. 8 is a time chart illustrating the operation of the fuel cell system in a refresh power superposition mode according to the first embodiment, Fig. 9 is a time chart illustrating the operation of the fuel cell system in another refresh power superposition mode according to the first embodiment, and Fig. 10 is a conceptual diagram illustrating the configuration of a control device according to a second embodiment.

[0017] (Embodiment 1) An embodiment of the fuel cell system will be described with reference to FIGS. 1 to 9. As shown in FIG. 1, the fuel cell system 1 of embodiment 1 mainly includes a fuel cell 10, a control device 20, an auxiliary power supply 31 as a first power storage device, and a receiving power storage device 32 as a second power storage device. The configuration of the fuel cell 10 is not limited, but a solid polymer fuel cell can be used as an example. In the solid polymer fuel cell 10, an anode electrode is formed on one side of an electrolyte membrane, and a cathode electrode is formed on the other side of the electrolyte membrane. The electrolyte membrane, anode electrode, and cathode electrode form an MEA (Membrane-Electrode-Assembly), which is an electrode structure. The anode electrode and cathode electrode are formed by coating, for example, a metal catalyst such as platinum (Pt) or palladium (Pd), carbon to which the metal catalyst is added, and an electrolyte. A fuel diffusion layer made of a conductive structure having a fuel supply structure is located between the MEA and the electrode (a fuel supply and electricity extraction structure called a separator in the case of a multilayer cell).

[0018] The fuel supplied to the anode electrode of the polymer electrolyte fuel cell 10 is formic acid (HCOOH), methanol (CH ３ OH), ethanol (C ２ H ５ In the first embodiment, the fuel cell 10 is a direct formic acid fuel cell (DFAFC) that directly uses formic acid as the liquid fuel. The oxidant (oxidant gas) supplied to the cathode electrode of the fuel cell 10 may be oxygen (O ２ In the first embodiment, air is used as an oxidizing agent, that is, an oxidizing gas, supplied to the fuel cell 10.

[0019] 1, a polymer electrolyte fuel cell 10 in this embodiment 1 includes a fuel cell stack 11. The fuel cell stack 11 is formed by stacking a plurality of unit cells U, each of which includes an MEA (not shown), an anode-side separator (not shown) that supplies liquid fuel to the anode electrode of the MEA, a cathode-side separator (not shown) that supplies an oxidant (oxidant gas) to the cathode electrode of the MEA, and a fuel diffusion layer (not shown).

[0020] As shown in FIG. 2 , the fuel cell stack 11 is formed by stacking a plurality of unit cells U, and the stacked unit cells U are held in place by holders H and bolts B. A first pump 14, which pressurizes and supplies formic acid, a liquid fuel stored in a supply tank 13, is connected to the fuel cell stack 11 via a pipe at a connection K1. A blower 15 (pressurization pump), which pressurizes and supplies air as an oxidant (oxidant gas), is also connected to the fuel cell stack 11 via a pipe at a connection K2. A second pump 17, which serves as a water supply device and pressurizes and supplies water stored in a supply tank 16 (e.g., water produced on the cathode side), is also connected to the connection K1 via a pipe. As shown in FIG. 1 , the operations of the first pump 14, the blower 15, and the second pump 17 are controlled by a control device 20.

[0021] Here, formic acid pressurized by the first pump 14 and water (produced water) pressurized by the second pump 17 are supplied to the anode electrode via a switching valve (not shown). That is, when the fuel cell stack 11 generates electricity, formic acid is supplied to the anode electrode by switching the switching valve. Then, when refresh control is performed, that is, when the electrode reaction in the MEA is stopped, the supply of formic acid is stopped. Water (produced water) from the supply tank 16 is supplied to the anode electrode by switching the switching valve when adjusting the concentration of formic acid. Furthermore, after the supply of formic acid is stopped during refresh control, the inside of the fuel cell stack 11 may be cleaned by switching the switching valve to supply water (produced water) from the supply tank 16 to the anode electrode. The switching valve may be provided at the connection part K1.

[0022] 1 and 3, the control device 20 mainly includes a control unit 21 and a control circuit 22. The control unit 21 is a microcomputer whose main components include a CPU, a ROM, a RAM, and an interface.

[0023] The control circuit 22 is an electric circuit controlled by the control unit 21. As shown in Fig. 1 , the control circuit 22 electrically connects the fuel cell stack 11 and an external load C. The control circuit 22 also electrically connects the fuel cell stack 11 and an auxiliary power supply 31, and also electrically connects the auxiliary power supply 31 and the external load C. The control circuit 22 also electrically connects the fuel cell stack 11 and a power receiving storage device 32, and also electrically connects the power receiving storage device 32 and the external load C.

[0024] As a result, under the control of the control unit 21, the control circuit 22 realizes each of the following states: a state in which the power generated by the fuel cell stack 11 is supplied to an external load C; a state in which the power generated by the fuel cell stack 11 is charged (stored) in the auxiliary power supply 31; a state in which the power charged (stored) in the auxiliary power supply 31 is supplied to the load C; a state in which the post-shutdown power generated by the fuel cell stack 11 is charged (stored) in the power receiving storage device 32; and a state in which the power charged (stored) in the power receiving storage device 32 is supplied to the load C.

[0025] As shown in FIG. 3 , the control circuit 22 mainly includes a first switch 22 a, a boost circuit 22 b, a second switch 22 c, a third switch 22 d, and a DC regulator circuit 22 e. The operation of these components is controlled by the control unit 21. In this embodiment, the control unit 21 is configured to control the operation of the fuel cell system by switching between multiple operating modes. The multiple operating modes include a normal power generation mode in which power generated by the fuel cell 10 is supplied to an external load C and charged (stored) in the auxiliary power supply 31; a refresh control mode in which power generated by the fuel cell 10 (including post-shutdown power) is charged in the power receiving storage device 32 and the power stored in the auxiliary power supply 31 is supplied to the external load C; and a power receiving storage device discharge mode in which power generated by the fuel cell 10 and power stored in the power receiving storage device 32 are supplied to the external load C. Note that the multiple operating modes may also include other operating modes, which will be described later.

[0026] 3, the first switch 22a is formed from two N-channel MOSFETs (N-ch MOSFETs) having parasitic diodes, and is disposed between the fuel cell stack 11 and the DC regulator circuit 22e and auxiliary power supply 31. The first switch 22a opens and closes when the two N-channel MOSFETs are switched on or off in synchronization under the control of the control unit 21, thereby supplying or cutting off high-voltage power output from the fuel cell stack 11 to the DC regulator circuit 22e and auxiliary power supply 31. The auxiliary power supply 31 and DC regulator circuit 22e are connected in parallel.

[0027] In the following description, when the two N-channel MOSFETs in the first switch 22a are synchronized to the on state, the first switch 22a is considered to be in the on state (closed state), and permits current to flow from the fuel cell stack 11 to the DC regulator circuit 22e and the auxiliary power supply 31. On the other hand, when the two N-channel MOSFETs in the first switch 22a are synchronized to the off state, the first switch 22a is considered to be in the off state (open state), and cuts off current to the fuel cell stack 11 from the DC regulator circuit 22e and the auxiliary power supply 31.

[0028] The boost circuit 22b may be any circuit capable of boosting the input voltage, and may be, for example, a chopper circuit, a switching regulator, or a linear regulator. In this embodiment, the boost circuit 22b is a boost chopper circuit including a choke coil, a capacitor, a diode, and an N-channel MOSFET switch 22b1, as shown in Fig. 3. In the boost circuit 22b, the switch 22b1 is periodically and rapidly switched between an on state and an off state under the control of the control unit 21, thereby boosting the power (voltage) supplied from the fuel cell stack 11 and outputting it to the power-receiving storage device 32.

[0029] In the following description, when the switch 22b1 is in the on state or switching state (repeatedly switching between the on state and the off state), the boost circuit 22b is in the on state. When the switch 22b1 is in the off state, the boost circuit 22b is in the off state. When the switch 22b1 is maintained in the on state, the power supplied from the fuel cell stack 11 is grounded via the switch 22b1 and discharged.

[0030] 3, the second switch 22c is formed of two N-channel MOSFETs, and is disposed between the boost circuit 22b and the power-receiving storage device 32. The second switch 22c opens and closes when the two N-channel MOSFETs are switched on or off in synchronization under the control of the control unit 21, thereby supplying or cutting off the high-voltage power output from the boost circuit 22b to the power-receiving storage device 32.

[0031] In the following description, when the two N-channel MOSFETs in the second switch 22c are synchronized to the on state, the second switch 22c is considered to be in the on state (closed state), and permits the flow of current from the boost circuit 22b to the power-receiving storage device 32. When the two N-channel MOSFETs in the second switch 22c are synchronized to the off state, the second switch 22c is considered to be in the off state (open state), and interrupts the flow of current from the boost circuit 22b to the power-receiving storage device 32.

[0032] 3, the third switch 22d is formed of two N-channel MOSFETs, and is disposed between the power receiving storage device 32 and the DC regulator circuit 22e. The third switch 22d opens and closes when the two N-channel MOSFETs are switched on or off in synchronization under the control of the control unit 21, thereby supplying or cutting off the power output from the power receiving storage device 32 to the DC regulator circuit 22e.

[0033] In the following description, when the two N-channel MOSFETs in the third switch 22d are synchronized to the on state, the third switch 22d is considered to be in the on state (closed state), and permits the flow of current from the power receiving storage device 32 to the DC regulator circuit 22e. When the two N-channel MOSFETs in the third switch 22d are synchronized to the off state, the third switch 22d is considered to be in the off state (open state), and cuts off the flow of current from the power receiving storage device 32 to the DC regulator circuit 22e.

[0034] As described above, the first switch 22a, the second switch 22c, and the third switch 22d are all configured to open and close the circuit by interlocking two N-channel MOSFETs, but this is not limited to this, and each switch may be configured to be capable of switching between supplying and cutting off power.

[0035] The DC regulator circuit 22e shown in Fig. 3 is a so-called well-known switching regulator that stabilizes the power (voltage) supplied from the fuel cell stack 11, the auxiliary power supply 31, and the power-receiving storage device 32. In the following description, when a switch (not shown) in the DC regulator circuit 22e is turned on, the DC regulator circuit 22e is considered to be in the on state, and when the switch (not shown) is turned off, the DC regulator circuit 22e is considered to be in the off state. The DC regulator circuit 22e has multiple output channels, and may have, for example, a 12V output channel for supplying power to an external load C and a 5V output channel for control. The voltage level output from each output channel may be variable.

[0036] The auxiliary power supply 31 serving as the first power storage device shown in FIG. 3 may be configured to be capable of charging and discharging power. Examples of the auxiliary power supply 31 include batteries such as Li-ion batteries, NiH batteries, Na batteries, and Pb batteries, and capacitors such as Li-ion capacitors and electric double-layer capacitors. It is preferable to use a battery with a relatively large capacity as the auxiliary power supply 31 so that it can charge and discharge sufficient power. The auxiliary power supply 31 includes a charge / discharge control circuit (not shown) for charging and discharging the auxiliary power supply 31, and is capable of shifting (boosting) the voltage level during discharging.

[0037] 3 is in the on state (closed state), the auxiliary power supply 31 is charged (stored) with part of the power generated by the fuel cell stack 11. When the first switch 22a provided in the control circuit 22 of the control device 20 is controlled to be in the off state (open state), the auxiliary power supply 31 discharges the charged (stored) high-voltage power to the DC regulator circuit 22e.

[0038] In the first embodiment, as will be described later, when the fuel cell stack 11 is in a normal power generation mode in which it is generating electricity normally, the auxiliary power supply 31 is charged (stored) with a portion of the power output from the fuel cell stack 11. When the charge state of the auxiliary power supply 31 reaches a predetermined state (for example, a fully charged state), charging of the auxiliary power supply 31 is stopped by the above-mentioned charge / discharge control circuit (not shown).

[0039] Furthermore, when the fuel cell stack 11 is in a refresh control mode in which the supply of power from the fuel cell stack 11 to the DC regulator circuit 22e is stopped, the auxiliary power supply 31 supplies power to the DC regulator circuit 22e by discharging the power charged in the auxiliary power supply 31 to the DC regulator circuit 22e.

[0040] Furthermore, when the voltage of the output power of the fuel cell stack 11 drops or the external load C increases, the auxiliary power supply 31 can discharge the power charged in the auxiliary power supply 31 to the DC regulator circuit 22e, thereby superimposing the power on the output power of the fuel cell stack 11 and supplying power to the DC regulator circuit 22e.

[0041] The power receiving storage device 32 serving as the second power storage device shown in FIG. 3 may be configured to be capable of charging and discharging power. For example, a battery such as a Li-ion battery, a NiH battery, a Na battery, or a Pb battery, or a capacitor such as a Li-ion capacitor or an electric double layer capacitor, can be used as the power receiving storage device 32. It is preferable to use a capacitor as the power receiving storage device 32. Capacitors generally have low internal resistance, allowing for rapid charging during charging (storage) and rapid discharge during discharging. Therefore, using a capacitor as the power receiving storage device 32 can improve the charge / discharge responsiveness of the power receiving storage device 32. The power receiving storage device 32 has a charge / discharge circuit (not shown) for charging and discharging the power receiving storage device 32, allowing for a voltage level shift (boost) during discharging.

[0042] When the second switch 22c provided in the control circuit 22 of the control device 20 is in the on state (closed state) and the third switch 22d provided in the control circuit 22 of the control device 20 is in the off state (open state), the power receiving storage device 32 is charged (stored) with high-voltage power boosted by the boost circuit 22b provided in the control circuit 22 of the control device 20. Furthermore, when the power receiving storage device 32 has been charged (stored) to a predetermined voltage, the third switch 22d provided in the control circuit 22 of the control device 20 is controlled to the on state (closed state), thereby discharging the charged (stored) high-voltage power to the DC regulator circuit 22e.

[0043] When the fuel cell stack 11 is in a refresh control mode in which it discharges power after the supply of liquid fuel is stopped in accordance with refresh control, the power receiving storage device 32 charges (stores) as post-stop power at least a portion of the power discharged from the fuel cell stack 11. When the fuel cell stack 11 transitions to a power receiving storage device discharging mode while generating power, the power receiving storage device 32 can discharge (store) the power charged (stored) in the power receiving storage device 32 to supply to the DC regulator circuit 22e.

[0044] In this way, the power receiving storage device 32 can recover at least a portion of the post-stop power discharged by the fuel cell stack 11 through refresh control by charging (storing) it. The power receiving storage device 32 can then supply the recovered post-stop power to the load C in addition to the power being generated by the fuel cell stack 11. This allows the power receiving storage device 32 to recover and reuse power.

[0045] Next, the operation of the fuel cell system 1 of this embodiment 1 will be described. The fuel cell system 1 of this embodiment 1 is configured to operate in each of the operation modes of the normal power generation mode shown in Fig. 4, the refresh control mode shown in Fig. 5, and the power receiving storage device discharge mode shown in Fig. 6, under the control of the control unit 21 in the control device 20. In this embodiment, the fuel cell system 1 is also configured to operate in the normal power superimposition mode shown in Fig. 7 and the refresh power superimposition mode shown in Figs. 8 and 9. Each operation mode will be described below in order.

[0046] First, the normal power generation mode is an operating mode in which the fuel cell stack 11 outputs the electric power generated by the fuel cell stack 11 to an external load C and charges the auxiliary power supply 31. In the normal power generation mode, as shown in Fig. 1, the control unit 21 of the control device 20 operates the first pump 14 to start supplying liquid fuel to the fuel cell 10, thereby turning on the output of the fuel cell stack 11 and controlling the outputs of the auxiliary power supply 31 and the power-receiving storage device 32 to be off, turning on the first switch 22a of the control circuit 22, and controlling the second switch 22c, the third switch 22d, and the boost circuit 22b to be off, as shown in Fig. 4.

[0047] As a result, in the normal power generation mode, the power generated by the fuel cell stack 11 is supplied to the DC regulator circuit 22e and the auxiliary power supply 31. The power supplied to the DC regulator circuit 22e is controlled to a predetermined voltage level by the DC regulator circuit 22e, and then output from a predetermined output channel and supplied to an external load C. Meanwhile, the power supplied to the auxiliary power supply 31 charges the auxiliary power supply 31. Note that when the auxiliary power supply 31 is fully charged, no power is supplied to the auxiliary power supply 31 and the auxiliary power supply 31 is not charged.

[0048] In the normal power generation mode, the second switch 22c is maintained in the OFF state, thereby cutting off the power supply from the fuel cell stack 11 to the power receiving storage device 32. Furthermore, the third switch 22d is maintained in the OFF state, thereby cutting off the power supply from the power receiving storage device 32 to the DC regulator circuit 22e.

[0049] Next, the refresh control mode shown in Fig. 5 is an operating mode in which refresh control is performed on the fuel cell stack 11 in the fuel cell 10. The refresh control mode is entered from the normal power generation mode when refresh control start timing t1 arrives in the normal power generation mode, as shown in Fig. 5. First, at refresh control start timing t1, the control unit 21 of the control device 20 turns on the output of the auxiliary power supply 31 and turns off the first switch 22a.

[0050] Thereafter, when the fuel supply stop timing t2 arrives, the control unit 21 of the control device 20 stops the supply of liquid fuel to the fuel cell stack 11 by stopping the first pump 14, and turns on the second switch 22c. As a result, after the supply of liquid fuel (formic acid) by the first pump 14 is stopped, post-stop power generated in the fuel cell stack 11 by the liquid fuel that was supplied to the fuel cell stack 11 before the first pump 14 was stopped is supplied to the boost circuit 22b. Note that the third switch 22d remains in the off state.

[0051] 5, when boost start timing t3 arrives, control unit 21 of control device 20 turns boost circuit 22b on and quickly switches switch 22b1 on and off to perform boost switching control. As a result, the post-shutdown power supplied to boost circuit 22b is boosted to a predetermined voltage by boost circuit 22b and supplied to power-receiving storage device 32. Note that refresh control start timing t1, fuel supply stop timing t2, and boost start timing t3 may occur simultaneously.

[0052] 5, when charging of the power receiving storage device 32 ends at timing t4, the switch 22b1 of the boost circuit 22b is maintained in the ON state. The charging end timing t4 can be set to the timing when the post-stop power has dropped and charging of the power receiving storage device 32 is no longer possible. By maintaining the switch 22b1 of the boost circuit 22b in the ON state, the boosting of the boost circuit 22b is terminated and the post-stop power is discharged until the post-stop power reaches approximately 0 V, which is the reference potential.

[0053] When refresh control end timing t5 arrives, the control unit 21 of the control device 20 keeps the switch 22b1 of the boost circuit 22b in the OFF state. Then, the control unit 21 turns the second switch 22c to the OFF state, and then drives the first pump 14 to resume the supply of liquid fuel to the fuel cell stack 11. Thereafter, the control unit 21 turns the first switch 22a to the ON state and stops the output of the auxiliary power supply 31. This ends the refresh control mode.

[0054] In the refresh control mode, after the fuel cell stack 11 has been controlled to stop power generation, i.e., after the supply of liquid fuel (formic acid) has been stopped, at least a portion of the post-stop power generated from the liquid fuel that had been supplied to the fuel cell stack 11 before the supply was stopped is boosted and charged (stored) in the power receiving storage device 32, and then recovered. Note that in the refresh control mode, the third switch 22d is maintained in the off state, and therefore the power supply from the power receiving storage device 32 to the DC regulator circuit 22e is cut off.

[0055] Next, the power receiving storage device discharge mode shown in Fig. 6 is an operation mode in which the power charged (stored) in the power receiving storage device 32 is output to the external load C, together with the power generated by the fuel cell stack 11. In the power receiving storage device discharge mode, as shown in Fig. 6, when discharge start timing t6 arrives, the control unit 21 of the control device 20 turns on the third switch 22d, thereby turning on the output of the power receiving storage device 32. As a result, the power charged (stored) in the power receiving storage device 32 is output to the external load C via the DC regulator circuit 22e.

[0056] The power output from the power receiving storage device 32 is boosted to a voltage equal to or higher than the power output from the fuel cell stack 11 by a charge / discharge control circuit (not shown) provided in the power receiving storage device 32. This allows the power output from the power receiving storage device 32 to be consumed preferentially.

[0057] In the power receiving storage device discharge mode, the first switch 22a is maintained in the ON state, and the second switch 22c and the boost circuit 22b are maintained in the OFF state, as shown in Fig. 6. As a result, at least a portion of the post-shutdown power generated by the refresh control is not discarded but is charged to the power receiving storage device 32, and then discharged from the power receiving storage device 32 and output to the external load C.

[0058] As shown in Fig. 6, when discharge end timing t7 arrives at which the output voltage of the electric power charged (stored) in the electric power receiving storage device 32 falls below a predetermined value, the control unit 21 of the control device 20 turns off the third switch 22d, turning off the output of the electric power receiving storage device 32. This ends the electric power receiving storage device discharge mode, and the system can transition to the normal power generation mode shown in Fig. 5. In the fuel cell system 1 of embodiment 1, the output from the DC regulator circuit 22e is maintained in the on state throughout the above-mentioned operation modes.

[0059] In the first embodiment, when power is stored in the auxiliary power supply 31, the operation mode of the fuel cell system 1 can be set to the normal power superimposition mode shown in Fig. 7. The normal power superimposition mode is an operation mode in which the power stored in the auxiliary power supply 31 is superimposed on the power supplied from the fuel cell stack 11 to the DC regulator circuit 22e.

[0060] For example, in the normal power superposition mode, if, at timing t8 shown in Fig. 7, the output current value in the 12V channel of the DC regulator circuit 22e increases to a predetermined current value or more, or if the power from the fuel cell stack 11 drops below a predetermined reference value, the control circuit 22 turns on the output of the auxiliary power supply 31 to discharge the power stored in the auxiliary power supply 31, which is then superimposed on the power from the fuel cell stack 11 and supplied to the DC regulator circuit 22e. This makes it possible to further stabilize the power output.

[0061] In this embodiment 1, the first switch 22a is formed by connecting N-channel MOSFETs having parasitic diodes in series, so that even when the power of the auxiliary power supply 31 is superimposed on the power from the fuel cell stack 11 as described above, the power of the auxiliary power supply 31 is prevented from being transmitted to the fuel cell stack 11 via the first switch 22a.

[0062] 6 , the power stored in the power receiving storage device 32 is discharged and output to the external load C, but the timing for discharging the power stored in the power receiving storage device 32 is not limited to this. For example, if the power output from the auxiliary power supply 31 falls below a predetermined reference value due to deterioration of the auxiliary power supply 31 or if the output current value in the 12V channel of the DC regulator circuit 22e increases during refresh control and exceeds a predetermined current value, it is possible to stabilize the power output by discharging the power stored in the power receiving storage device 32 during refresh control and outputting it to the external load C.

[0063] 8 and 9 show examples of operation modes in which the power receiving storage device 32 is discharged during refresh control. First, in the refresh power superposition mode shown in Fig. 8, when the charging end timing t4 for the power receiving storage device 32 arrives during refresh control, the switch 22b1 of the boost circuit 22b is maintained in the on state to terminate charging of the power receiving storage device 32, and the second switch 22c is turned off and the third switch 22d is turned on to discharge the power stored in the power receiving storage device 32, superimpose the discharged power on the power from the auxiliary power supply 31, and supply the superimposed power to the DC regulator circuit 22e. This makes it possible to stabilize the power output during refresh control even when the power output from the auxiliary power supply 31 falls below a predetermined reference value or when the output current value in the 12V channel of the DC regulator circuit 22e increases and exceeds a predetermined current value during refresh control.

[0064] Thereafter, as shown in FIG. 8, when the refresh control end timing t5 arrives, the switch 22b1 of the boost circuit 22b is maintained in the OFF state, and the supply of liquid fuel to the fuel cell stack 11 is resumed by driving the first pump 14 by the control unit 21, and then the first contactor 22a is turned ON and the output of the auxiliary power supply 31 is stopped, and the third contactor 22d is turned OFF and the output of the power receiving storage device 32 is stopped, thereby ending the refresh control.

[0065] Furthermore, when the power output from the auxiliary power supply 31 has decreased due to deterioration of the auxiliary power supply 31 or the like and it is predicted in advance that the auxiliary power supply 31 will be short of power during the next refresh control, it is also possible to employ the refresh power superimposition mode shown in FIG. 9 . In the refresh power superimposition mode shown in FIG. 9 , during refresh control, the second switch 22c remains in the OFF state, and after the fuel supply stop timing t2, the switch 22b1 is rapidly switched on and off, and then maintained in the ON state, thereby grounding and discharging the post-stop power until the post-stop power reaches approximately 0 V. This prevents the post-stop power from being charged into the power-receiving storage device 32. Alternatively or additionally, the second switch 22c may remain in the OFF state and the switching valve may be switched to supply water (produced water) from the supply tank 16 to the anode electrode, thereby cleaning the inside of the fuel cell stack 11 and rapidly stopping the electrode reaction.

[0066] Then, at timing t9 shown in FIG. 9 , when the power from the auxiliary power supply 31 drops below a predetermined reference value, the control circuit 22 turns on the output of the power receiving storage device 32 and turns on the third switch 22d to discharge the power stored in the power receiving storage device 32, superimposing the power on the power from the auxiliary power supply 31 and supplying it to the DC regulator circuit 22e. As a result, post-stop power recovery is not performed in this refresh control, but instead, power output in this refresh control can be stabilized. Thereafter, as shown in FIG. 9 , when the refresh control end timing t5 arrives, the control unit 21 drives the first pump 14 to resume the supply of liquid fuel to the fuel cell stack 11, and then turns on the first switch 22a to stop the output of the auxiliary power supply 31, and turns off the third switch 22d to stop the output of the power receiving storage device 32, thereby ending the refresh control.

[0067] Next, the effects of the fuel cell system 1 of this embodiment will be described in detail. The fuel cell system 1 of this embodiment includes an auxiliary power supply 31 as a first power storage device and a power-receiving storage device 32 as a second power storage device. The auxiliary power supply 31 is charged with a portion of the power generated by the fuel cell 10 when liquid fuel is being supplied to the fuel cell 10, and discharges the power charged in the auxiliary power supply 31 to an external load C when the supply of liquid fuel to the fuel cell 10 is stopped. This makes it possible to maintain the power supply to the external load C even during refresh control when the supply of liquid fuel to the fuel cell 10 is stopped, thereby stabilizing the power output to the outside.

[0068] At the same time, the power receiving storage device 32 is charged with and recovers post-shutdown power generated by the fuel cell 10 using the liquid fuel already supplied when the supply of liquid fuel to the fuel cell 10 is stopped, and the electrode reaction of the fuel cell 10 is stopped after the power receiving storage device 32 recovers the post-shutdown power. Then, in a state where the supply of liquid fuel to the fuel cell 10 is being carried out, the post-shutdown power recovered by the power receiving storage device 32, in addition to the power output from the fuel cell 10, is discharged to the external load C. This allows the electrode reaction to be stopped quickly after the power receiving storage device 32 recovers the post-shutdown power, thereby shortening the time during which power generation is stopped due to refresh control, and allowing the post-shutdown power that would previously have been wasted to be recovered by the power receiving storage device 32 and discharged to the external load C for use. This improves power utilization efficiency.

[0069] Furthermore, in the first embodiment, a boost circuit 22b is provided that boosts the post-stop power that is charged to the power-receiving storage device 32 as the second storage device. This allows a larger amount of post-stop power to be charged to the power-receiving storage device 32, thereby further improving the efficiency of power use.

[0070] In the first embodiment, the control device 20 is configured to control the operation of the fuel cell system 1 by switching between a plurality of operation modes. The plurality of operation modes include a normal power generation mode, a refresh control mode, and a second power storage device discharge mode (i.e., a power receiving storage device discharge mode). The normal power generation mode is set to supply at least a portion of the power generated by the fuel cell 10 to an external load C, and to charge a portion of the power generated by the fuel cell 10 to an auxiliary power source 31 serving as a first power storage device. The refresh control mode is set to stop the supply of liquid fuel to the fuel cell 10 to refresh control the fuel cell 10, charge at least a portion of the power generated after the stoppage to a power receiving storage device 32 serving as a second power storage device, and supply the power charged in the auxiliary power source 31 to the external load C.

[0071] In the power receiving storage device discharge mode, at least a portion of the power generated by the fuel cell 10 is supplied to the external load C, and the power charged in the power receiving storage device 32 is also supplied to the external load C. In this embodiment 1, by switching between the normal power generation mode, the refresh control mode, and the power receiving storage device discharge mode, refresh control of the fuel cell 10 can be performed without stopping the supply of power to the external load C, and power can be smoothly recovered after the supply is stopped and used to supply power to the external load C. This makes it possible to further stabilize the power supplied to the external load C while improving the efficiency of power utilization.

[0072] In the first embodiment, the plurality of operating modes further includes a power superimposition supply mode that is set to supply the power generated by the fuel cell 10 and the power charged in the first power storage device 31 to an external load C. As a result, when the output current value increases and exceeds a predetermined current value or when the power from the fuel cell stack 11 falls below a predetermined reference value, the control circuit 22 can discharge the power stored in the auxiliary power supply 31 and superimpose it on the power from the fuel cell stack 11 to supply to the DC regulator circuit 22e, thereby further stabilizing the power output.

[0073] As described above, according to this aspect, it is possible to provide a fuel cell system 1 that achieves both stabilization of the power output to the outside and improvement in the efficiency of power utilization.

[0074] (Embodiment 2) In the above-described embodiment 1, a boost chopper circuit is used as the boost circuit 22b as shown in Fig. 3. However, instead of this, in the present embodiment 2 shown in Fig. 10, the boost circuit 22b is configured by a switching regulator that converts DC current to AC current, boosts the voltage using a transformer, and reconverts it to DC current. Also, in the above-described embodiment 1, when the charging end timing t4 for the power receiving storage device 32 arrives as shown in Fig. 5, the switch 22b1 of the boost circuit 22b is maintained in the on state, so that the power is discharged to earth until the post-stop power becomes approximately 0 V.

[0075] In the second embodiment, instead, a discharge unit 22f including a switch 22f1 made of an N-channel MOSFET is connected in parallel between the fuel cell stack 11 and the boost circuit 22b. The control circuit 22 turns on the switch 22f1 of the discharge unit 22f (i.e., a state in which current can be passed) so that when the charging end timing t4 for the power receiving storage device 32 arrives, the discharge unit 22f discharges until the post-stop power reaches the reference potential of approximately 0 V. Note that the control circuit 22 keeps the discharge unit 22f off (i.e., a state in which current is cut off) in all other states.

[0076] Among other components in the second embodiment, components equivalent to those in the first embodiment are denoted by the same reference numerals and descriptions thereof are omitted. In addition, in Fig. 7, the switches 22a, 22c, and 22d have the same configuration as those in the first embodiment, and descriptions thereof are simplified.

[0077] In the second embodiment, a switching regulator using a transformer is used as the boost circuit 22b, which improves the power conversion efficiency and the responsiveness of the power conversion, thereby further improving the efficiency of power utilization. Note that the second embodiment also achieves the same effects as the first embodiment.

[0078] As described above, the first embodiment employs a step-up chopper circuit as the step-up circuit 22b, and the second embodiment employs a step-up transformer circuit, but instead, a step-up / step-down chopper circuit can also be employed. In this case, the same effects as those of the first and second embodiments can be achieved.

[0079] Furthermore, a step-down circuit that steps down the input voltage may be used instead of the step-up circuit 22b in the first and second embodiments. The step-down circuit may have a known configuration, such as a step-up / step-down chopper circuit or a step-down chopper circuit. When the step-down circuit is used, if the power output from the fuel cell stack 11 has an excessively high peak current, the peak current can be reduced to protect the circuit.

[0080] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A fuel cell (10) having an electrode structure having an anode electrode and a cathode electrode, the anode electrode being supplied with a liquid fuel and the cathode electrode being supplied with an oxidant to generate electric power; a first power storage device (31) for storing a part of the electric power output from the fuel cell while the liquid fuel is being supplied to the fuel cell; a second electricity storage device (32) that, when the supply of the liquid fuel to the fuel cell is stopped, stores and recovers post-stop electricity generated by the fuel cell using the liquid fuel that has already been supplied; a control device (20) that controls the supply of liquid fuel to the fuel cell and the operation of the first power storage device and the second power storage device; a DC regulator circuit (22e) for stabilizing voltage, which is provided immediately before an external load (C) and connected in parallel to the first power storage device; a switch (22d) provided between the second power storage device and the DC regulator circuit, for switching between supplying and cutting off power from the second power storage device to an external load (C) via the DC regulator circuit; Equipped with the fuel cell is configured such that an electrode reaction in the electrode structure is stopped after the post-shutdown power is recovered by the second power storage device, supplying at least a portion of the electric power output from the fuel cell other than the electric power charged to the first power storage device to an external load (C) via the DC regulator circuit while the liquid fuel is being supplied to the fuel cell; By the control of the control device, discharging the electric power stored in the first power storage device to an external load (C) while the supply of the liquid fuel to the fuel cell is stopped; When the liquid fuel is being supplied to the fuel cell, in addition to the power output from the fuel cell, the switch is switched to a state enabling power supply to an external load (C), and the post-shutdown power recovered in the second storage device is discharged and supplied to the external load (C) via the DC regulator circuit.

2. 2. The fuel cell system according to claim 1, further comprising a boost circuit (22b) that boosts the post-shutdown power that is charged to the second power storage device.

3. the control device is configured to switch between a plurality of operation modes to control the operation of the fuel cell system; The multiple operation modes include: a normal power generation mode in which at least a portion of the electric power generated by the fuel cell is supplied to the external load, and a portion of the electric power generated by the fuel cell is charged to the first power storage device; a refresh control mode in which the supply of the liquid fuel to the fuel cell is stopped to refresh control the fuel cell, and at least a portion of the power generated after the supply of the liquid fuel to the fuel cell is charged to the second power storage device, and the power charged in the first power storage device is supplied to the external load; a second power storage device discharge mode in which at least a portion of the power generated by the fuel cell is supplied to the external load, and the power charged in the second power storage device is supplied to the external load; The fuel cell system according to claim 1 or 2, comprising:

4. 4. The fuel cell system according to claim 3, wherein the plurality of operating modes further includes a normal power superimposition supply mode set to supply the power generated by the fuel cell and the power charged in the first power storage device to the external load.