Fuel cell system

Abstract

To provide a fuel cell system capable of quickly increasing the output of a fuel cell after refresh control is terminated.SOLUTION: A fuel cell system 1 has a fuel cell 2 that is configured to make it possible to generate power by reacting a liquid fuel with an oxidant. The fuel cell system 1 has a control device 3 that is configured to make it possible to switch between supplying the liquid fuel to the fuel cell 2 and stopping the supply of the liquid fuel and a heating element 4 arranged in a position where at least a portion of the fuel cell 2, a supply path of the liquid fuel to the fuel cell 2, and a supply path of the oxidant to the fuel cell 2 can be heated. The control device 3 is configured to electrically connect the fuel cell 2 to the heating element 4 while the supply of the liquid fuel to the fuel cell 2 is stopped.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A fuel cell such as a solid polymer fuel cell has a membrane electrode assembly (so-called MEA) including an electrolyte membrane, an anode provided on one surface of the electrolyte membrane, and a cathode provided on the other surface of the electrolyte membrane. The fuel cell can cause an electrode reaction to occur at each electrode by supplying fuel to the anode of the MEA and an oxidant to the cathode. As a result of these electrode reactions, an electromotive force is generated between the anode and the cathode, and power generation can be performed.

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

[0004] In order to increase the output of the fuel cell, it is desirable to keep the temperatures of the anode and the cathode within a range where the electrode reaction occurs efficiently. For example, Patent Document 1 describes a fuel cell including a temperature raising unit that heats a liquid fuel supplied from a tank, a fuel electrode to which the liquid fuel heated by the temperature raising unit is supplied, an air electrode to which air is supplied, and a cell unit having an electrolyte membrane sandwiched between the fuel electrode and the air electrode, wherein the temperature raising unit is installed on the fuel electrode side of the cell unit and heats the liquid fuel by waste heat from the cell unit.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] In fuel cells using liquid fuel, a phenomenon may occur where the fuel cell output gradually decreases if power generation is continued. To recover from this output decrease, fuel cells using liquid fuel perform an operation called refresh control after power generation has been continued for a predetermined period of time. In refresh control, the positive and negative electrodes of the fuel cell are short-circuited to discharge the fuel cell, and the supply of liquid fuel to the MEA is temporarily stopped.

[0007] However, even when the supply of liquid fuel to the MEA is stopped by refresh control, unreacted liquid fuel remains in the fuel cell. Therefore, after refresh control is initiated, electrode reactions continue until the remaining liquid fuel in the fuel cell reacts with the continuously supplied oxidizer and is consumed. In fuel cells using liquid fuel, the electrode reaction at the anode is an endothermic reaction, and the electrode reaction at the cathode is an exothermic reaction. When these reaction heats are added together, the overall reaction is slightly endothermic. Therefore, when refresh control is performed, the temperature of the MEA decreases due to the electrode reaction between the remaining liquid fuel in the fuel cell and the continuously supplied oxidizer, and there is a risk that the reaction efficiency of the electrode reaction will decrease when power generation is restarted after the refresh control is completed. As a result, this may lead to a decrease in the output of the fuel cell after refresh control.

[0008] This invention has been made in view of the above problems, and aims to provide a fuel cell system that can quickly increase the output of a fuel cell after the refresh control has been completed. [Means for solving the problem]

[0009] One aspect of the present invention is a fuel cell system having a fuel cell configured to generate electricity by reacting a liquid fuel with an oxidizer, A control device configured to switch between supplying and stopping the supply of the liquid fuel to the fuel cell, The fuel cell, the supply path for the liquid fuel to the fuel cell, and the supply path for the oxidizer to the fuel cell are all heated by a heating element positioned at a location that can heat at least a portion of them. The control device is located in a fuel cell system and is configured to electrically connect the fuel cell and the heating element while the supply of the liquid fuel to the fuel cell is stopped. [Effects of the Invention]

[0010] The fuel cell system is configured such that, while refresh control is performed and the supply of liquid fuel to the fuel cell is temporarily stopped, the control device electrically connects the fuel cell to the heating element. As described above, even when the supply of liquid fuel to the fuel cell is stopped due to refresh control, the electrode reaction continues for a certain period of time due to the liquid fuel and oxidizer remaining in the fuel cell.

[0011] The fuel cell system can generate heat by supplying the electricity generated during the refresh control to a heating element. By heating at least a portion of the aforementioned parts of the fuel cell system with the heating element, the decrease in the temperature of the fuel cell during the refresh control can be suppressed, or the temperature of the fuel cell can be rapidly increased when power generation is restarted. As a result, when the refresh control is completed and liquid fuel and oxidizer are supplied to the fuel cell again, the reaction efficiency of the electrode reaction can be rapidly improved.

[0012] As described above, according to the above embodiment, it is possible to provide a fuel cell system that can quickly increase the output of the fuel cell after the refresh control is completed. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is an explanatory diagram showing the schematic configuration of the fuel cell system in Embodiment 1. [Figure 2] Figure 2 is a block diagram of the fuel cell system in Embodiment 1. [Figure 3] Figure 3 is an explanatory diagram showing the time chart of the fuel cell system in Embodiment 1. [Figure 4] Figure 4 is a block diagram of the fuel cell system in Embodiment 2. [Figure 5] Figure 5 is an explanatory diagram showing a flowchart of the operation of the fuel cell system in Embodiment 2. [Figure 6] Figure 6 is a block diagram of the fuel cell system in Embodiment 3. [Figure 7] Figure 7 is an explanatory diagram showing a flowchart of the operation of the fuel cell system in Embodiment 3. [Figure 8] Figure 8 is an explanatory diagram showing a flowchart of the operation of the fuel cell system in Embodiment 4. [Modes for carrying out the invention]

[0014] (Embodiment 1) Embodiments of the fuel cell system described above will be explained with reference to Figures 1 to 3. As shown in Figures 1 and 2, the fuel cell system 1 of this embodiment has a fuel cell 2 configured to generate electricity by reacting a liquid fuel with an oxidizer. The fuel cell system 1 also has a control device 3 configured to switch between supplying and stopping the supply of liquid fuel to the fuel cell 2, and a heating element 4 positioned to heat at least a portion of the fuel cell 2, the supply path for liquid fuel to the fuel cell 2, and the supply path for oxidizer to the fuel cell 2. The control device 3 is configured to electrically connect the fuel cell 2 and the heating element 4 while the supply of liquid fuel to the fuel cell 2 is stopped. Hereinafter, specific examples of the configuration of the fuel cell system 1 will be described.

[0015] As shown in FIG. 1, the fuel cell system 1 includes a fuel cell 2, a fuel tank 5 that holds a liquid fuel supplied to the fuel cell 2, a fuel pump 52 that sends the liquid fuel from the fuel tank 5 to the fuel cell 2, and a blower 6 that supplies an oxidant to the fuel cell 2. The fuel tank 5 and the fuel pump 52, and the fuel pump 52 and the fuel cell 2 are connected by fuel supply pipes 51 and 53. The blower 6 and the fuel cell 2 are connected by an oxidant supply pipe 61.

[0016] The fuel cell system 1 may have a fuel recovery tank 55 that recovers the liquid fuel used in the electrode reaction at the anode of the fuel cell 2. In the fuel cell system 1 of this embodiment, the fuel cell 2 and the fuel recovery tank 55 are connected by a fuel recovery pipe 54.

[0017] Further, the fuel cell system 1 may have a drain tank 63 that recovers the generated water produced by the electrode reaction at the cathode of the fuel cell 2. In the fuel cell system 1 of this embodiment, the fuel cell 2 and the drain tank 63 are connected by a water recovery pipe 62.

[0018] The fuel cell 2 has a MEA 21 including an electrolyte membrane, an anode provided on one surface of the electrolyte membrane, and a cathode provided on the other surface of the electrolyte membrane. The fuel cell 2 is configured to be able to generate electricity by supplying a liquid fuel to the anode of the MEA 21 and an oxidant to the cathode. As the fuel supplied to the fuel cell 2, for example, liquid fuels such as formic acid and methanol can be used. Also, as the oxidant, for example, oxidizing gases such as air and oxygen gas can be used.

[0019] The liquid fuel supplied to fuel cell 2 is preferably formic acid. In other words, fuel cell 2 is preferably a direct formic acid fuel cell. When formic acid is used as the liquid fuel, the amount of heat lost in the overall electrode reaction is large, and the temperature of MEA21 tends to drop more easily during refresh control. Even in such a situation, as described above, by heating a part of the fuel cell system 1 with the power generated during refresh control, the output of fuel cell 2 can be more reliably increased after the refresh control is completed.

[0020] As shown in Figure 1, the fuel cell 2 of this embodiment has a plurality of single cells 24, each containing an MEA 21, an anode-side separator 22 provided on the anode of the MEA 21, and a cathode-side separator 23 provided on the cathode of the MEA 21. A fuel passage (not shown in the figure) is provided between the MEA 21 and the anode-side separator 22 in each single cell 24. The fuel passage is configured to allow liquid fuel supplied from the fuel tank 5 to come into contact with the anode. Additionally, an oxidizer passage (not shown in the figure) is provided between the MEA 21 and the cathode-side separator 23 in each single cell 24. The oxidizer passage is configured to allow oxidizer supplied from the blower 6 to come into contact with the cathode.

[0021] If the fuel cell 2 has multiple single cells 24, these single cells 24 may be stacked on top of each other to form a cell stack 25. In the fuel cell system 1 of this embodiment, the single cells 24 constituting the cell stack 25 are arranged such that the anode-side separator 22 of each single cell 24 and the cathode-side separator 23 of the single cell 24 adjacent to that single cell 24 are in contact with each other. As a result, multiple single cells 24 are electrically connected in series via the anode-side separator 22 and the cathode-side separator 23.

[0022] A pair of holders 251 (251p, 251n) for holding single cells 24 may be arranged at both ends of the cell stack 25 in the stacking direction. In this embodiment of the fuel cell 2, a fastening member 252 is inserted into the holder 251p of the pair of holders 251 that is in contact with the cathode-side separator 23. The fastening member 252 penetrates the cell stack 25 in the stacking direction of the single cells 24, and the holder 251p in contact with the cathode-side separator 23 and the holder 251n in contact with the anode-side separator 22 are fastened together by the fastening member 252. As a result, the single cells 24 constituting the cell stack 25 are held between the pair of holders 251.

[0023] Furthermore, one of the pair of holders 251, the holder 251n in contact with the anode-side separator 22, is provided with a negative terminal 253n, and the holder 251p in contact with the cathode-side separator 23 is provided with a positive terminal 253p. The positive terminal 253p and the negative terminal 253n are used to supply the power generated in the fuel cell 2 to an external load 7 (see Figure 2) and a heat-generating element 4.

[0024] As shown in Figures 1 and 2, the fuel pump 52 and blower 6 of the fuel cell system 1 are electrically connected to the control device 3. The control device 3 is configured to switch between supplying and stopping the supply of liquid fuel and oxidizer to the fuel cell 2 by controlling the operation of the fuel pump 52 and blower 6.

[0025] In the fuel cell system 1, the heating element 4 is positioned to heat at least a portion of the fuel cell 2, the liquid fuel supply path to the fuel cell 2, and the oxidizer supply path to the fuel cell 2. For example, in this embodiment, the heating element 4 is a coil-shaped heater and, as shown in Figure 1, is wrapped around the fuel supply pipe 53 that connects the fuel pump 52 and the fuel cell 2 in the liquid fuel supply path to the fuel cell 2. The heating element 4 is also electrically connected to the positive terminal 253p and the negative terminal 253n of the fuel cell 2. A circuit switch 32, which will be described later, is provided between the heating element 4 and the positive terminal 253p.

[0026] The specific form of the heating element 4 is not limited to the form described here, and can take various forms depending on its placement.

[0027] For example, the heating element 4 may be configured to heat at least one of the liquid fuel and the oxidizer. In this case, for example, the heating element 4 can be attached to at least one of the fuel supply pipes 51, 53 and the oxidizer supply pipe 61. The heating element 4 attached to the fuel supply pipes 51, 53 and the oxidizer supply pipe 61 can take various forms, such as a sheet, film, or coil. Furthermore, some or all of these pipes can be made up of the heating element 4. In addition, the connector for connecting these pipes may also be the heating element 4.

[0028] The heating element 4 can also be attached to the fuel tank 5. In this case, the heating element 4 may be located outside or inside the fuel tank 5. The heating element 4 attached to the fuel tank 5 can take various forms, such as a sheet, film, or coil. Furthermore, part or all of the fuel tank 5 may be composed of the heating element 4.

[0029] In this way, by positioning the heating element 4 in a location that can heat at least one of the liquid fuel and the oxidizer, the temperature of the liquid fuel and the oxidizer can be increased during refresh control. Then, when the refresh control is completed, the liquid fuel and / or oxidizer heated by the heating element 4 can be supplied to the fuel cell 2. As a result, when power generation is restarted after the refresh control is completed, the temperature of the MEA 21 can be rapidly increased, and consequently, the output of the fuel cell 2 can be increased more easily.

[0030] From the viewpoint of more easily raising the temperature of the liquid fuel and / or oxidizer, and more reliably supplying the liquid fuel and / or oxidizer to the fuel cell 2 in a heated state, it is preferable that the heating element 4 is attached to at least one of the fuel supply pipes 51, 53 and the oxidizer supply pipe 61, and more preferably wrapped around at least one of the fuel supply pipes 51, 53 and the oxidizer supply pipe 61. Furthermore, from the viewpoint of more easily raising the temperature of the fuel cell 2, it is preferable that the heating element 4 is provided so as to be able to heat a liquid fuel with a large heat capacity, and more preferably attached to the fuel supply pipes 51, 53 or the fuel tank 5.

[0031] Furthermore, the heating element 4 may be attached to the fuel cell 2. The heating element 4 attached to the fuel cell 2 can take various forms, such as a sheet or a film. Also, some or all of the components of the fuel cell 2, such as the holder 251 of the fuel cell 2, can be made from the heating element 4.

[0032] In this way, by attaching the heating element 4 to the fuel cell 2, the decrease in the temperature of the fuel cell 2 due to electrode reactions during refresh control can be suppressed. As a result, it is easier to avoid a decrease in the output of the fuel cell 2 when restarting power generation after the refresh control is completed. From the viewpoint of more reliably obtaining these effects, it is preferable that the holder 251 of the fuel cell 2 is made of the heating element 4.

[0033] Preferably, the heating element 4 is configured to heat the portion to which it is attached to a temperature of 40°C to 70°C. By setting the temperature of the portion to which the heating element 4 is attached within the specified range, the reaction efficiency of the electrode reaction in the MEA 21 can be rapidly increased when liquid fuel is supplied to the fuel cell 2 after the refresh control is completed. As a result, the output of the fuel cell 2 after the refresh control can be increased more rapidly.

[0034] The operation of the fuel cell system 1 in this embodiment is controlled by a control device 3. As shown in Figures 1 and 2, the control device 3 includes a power generation control unit 31 that is electrically connected to the fuel pump 52 and the blower 6 and configured to control their operation, and a circuit switch 32 that is electrically connected to the positive terminal 253p of the fuel cell 2. The power generation control unit 31 is configured to switch between a power generation mode in which the fuel pump 52 is operated and liquid fuel and oxidizer are supplied to the fuel cell 2, and a refresh control mode in which the fuel pump 52 is stopped and the supply of liquid fuel to the fuel cell 2 is stopped. The power generation control unit 31 is also configured to operate the blower 6 to supply oxidizer to the fuel cell 2 while the fuel cell system 1 is in operation. The operation of the power generation control unit 31 can be realized, for example, by an electronic circuit provided in the power generation control unit 31 or a program for operating the power generation control unit 31.

[0035] The power generation control unit 31 switches between the power generation mode and the refresh control mode based on preset conditions. For example, the power generation control unit 31 in this embodiment is configured to switch from the power generation mode to the refresh control mode when the duration of the power generation mode reaches a preset value. The power generation control unit 31 is also configured to switch from the refresh control mode to the power generation mode when the duration of the refresh control mode reaches a preset value.

[0036] As shown in Figure 2, the circuit switch 32 has two contacts: a first contact 321 and a second contact 322. An external load 7 is electrically connected to the first contact 321 of the circuit switch 32. A heating element 4 is electrically connected to the second contact 322.

[0037] The circuit switch 32 is configured to switch between a state in which the positive terminal 253p and the first contact 321 are electrically connected and a state in which the positive terminal 253p and the second contact 322 are electrically connected. More specifically, the circuit switch 32 in this embodiment is configured to electrically connect the positive terminal 253p and the first contact 321 while the power generation control unit 31 is operating the fuel pump 52, that is, while the power generation mode is being executed, and to electrically connect the positive terminal 253p and the second contact 322 while the power generation control unit 31 is stopping the operation of the fuel pump 52, that is, while the refresh control mode is being executed.

[0038] Therefore, in this embodiment of the fuel cell system 1, while the fuel pump 52 and blower 6 are operating and liquid fuel and oxidizer are being supplied to the fuel cell 2, the power generated from the fuel cell 2 is supplied to the external load 7. Also, when refresh control is performed and the supply of liquid fuel to the fuel cell 2 is stopped, the power generated from the fuel cell 2 is supplied to the heat-generating element 4.

[0039] Next, the operation of the fuel cell system 1 of this embodiment will be described with reference to Figure 3. The fuel cell system 1 of this embodiment is configured so that the power generation control unit 31 of the control device 3 repeatedly performs a power generation mode in which the supply of liquid fuel and oxidizer to the fuel cell 2 is continued for a predetermined time, and a refresh control mode in which the supply of liquid fuel to the fuel cell 2 is stopped for a predetermined time. The duration of the power generation mode and the refresh control mode is not particularly limited, but for example, the duration of the power generation mode can be appropriately set from the range of 5 to 20 minutes. The duration of the refresh control mode can also be appropriately set from the range of 30 to 120 seconds.

[0040] As shown in Figure 3, in power generation mode, both liquid fuel and oxidizer are supplied to the fuel cell 2. This causes an electrode reaction in the MEA 21, generating electricity from the fuel cell 2. In addition, in power generation mode, the circuit switch 32 electrically connects the fuel cell 2 and the external load 7, so that the electricity generated by the fuel cell 2 is supplied to the external load 7 and the external load 7 can be operated. However, if the electrode reaction is continued for a long time in power generation mode, the reaction efficiency of the electrode reaction gradually decreases, and as shown in Figure 3, the voltage and current of the fuel cell 2 may gradually decrease.

[0041] The power generation control unit 31 stops the power generation mode and starts the refresh control mode when the duration of liquid fuel supply to the fuel cell 2 reaches a predetermined time. When the refresh control mode is started, the operation of the fuel pump 52 stops, and the supply of liquid fuel to the fuel cell 2 is stopped. In addition, along with the cessation of liquid fuel supply, the circuit switch 32 electrically connects the positive terminal 253p and the heating element 4.

[0042] As mentioned above, even if the supply of liquid fuel to the fuel cell 2 is stopped, unreacted liquid fuel remains in the fuel cell 2. Also, since the blower 6 is operating even in refresh control mode, the oxidizer is supplied to the fuel cell 2. Therefore, as shown in Figure 3, electrode reactions occur in the MEA 21 until the liquid fuel remaining in the fuel cell 2 reacts with the oxidizer and is consumed, generating electricity from the fuel cell 2. By supplying this electricity to the heating element 4, heat can be generated from the heating element 4. In this embodiment of the fuel cell system 1, as shown in Figure 1, the heating element 4 is attached to the fuel supply pipe 53, so the temperature of the liquid fuel in the fuel supply pipe 53 can be increased by performing refresh control.

[0043] As shown in Figure 3, when the supply of liquid fuel to the fuel cell 2 is stopped for a predetermined period of time, the power generation control unit 31 stops the refresh control mode and restarts the power generation mode. When the power generation mode starts, the fuel pump 52 operates and the supply of liquid fuel to the fuel cell 2 is resumed. At this time, as mentioned above, the temperature of the fuel in the fuel supply pipe 53 is high, so the temperature of the MEA 21 in contact with the high-temperature liquid fuel rises rapidly. As a result, the reaction efficiency of the electrode reaction in the MEA 21 increases, and the output of the fuel cell 2 can be rapidly improved. In addition, in the power generation mode, along with the resumption of the liquid fuel supply, the circuit switch 32 electrically connects the positive terminal 253p to the external load 7. As a result, the power generated from the fuel cell 2 is supplied to the external load 7.

[0044] As described above, with this embodiment of the fuel cell system 1, the output of the fuel cell 2 can be rapidly increased after the refresh control is completed.

[0045] (Embodiment 2) In this embodiment, an example of a fuel cell system 102 equipped with a power storage device 42 that recovers power generated from the fuel cell 2 during refresh control is described. In this embodiment and subsequent embodiments, any reference numerals identical to those used in previously described embodiments represent the same components as those in the previously described embodiments, unless otherwise specified.

[0046] As shown in Figure 4, the fuel cell system 102 in this embodiment includes a fuel cell 2, a fuel tank 5, a fuel pump 52, and a blower 6. The fuel tank 5 and the fuel pump 52, and the fuel pump 52 and the fuel cell 2 are connected by fuel supply pipes 51 and 53. The blower 6 and the fuel cell 2 are connected by an oxidizer supply pipe 61. Although not shown in the figure, the fuel cell system 102 also includes a fuel recovery tank connected to the fuel cell 2 via a fuel recovery pipe, and a drain tank connected to the fuel cell 2 via a water recovery pipe.

[0047] Furthermore, a heating element 4 is attached to the fuel supply pipe 53 between the fuel pump 52 and the fuel cell 2. In Figure 4, for convenience, the heating element 4 is shown in a different location from the fuel supply pipe 53, but the position of the heating element 4 in Figure 4 is unrelated to the actual position of the heating element 4 in the fuel cell system 102.

[0048] As shown in Figure 4, the fuel pump 52 and blower 6 are electrically connected to the power generation control unit 31 of the control device 3. The operation of the fuel pump 52 and blower 6 is controlled by the power generation control unit 31. In addition, the positive terminal 253p of the fuel cell 2 is electrically connected to the circuit switch 32 of the control device 3. The first contact 321 of the circuit switch 32 is electrically connected to the external load 7. In addition, the heating element 4 is electrically connected to the second contact 322 of the circuit switch 32.

[0049] As shown in Figure 4, the fuel cell system 102 in this embodiment includes a temperature sensor 26 connected to a control device 3 and configured to acquire the temperature of the fuel cell 2, and a power storage device 42 configured to charge at least a portion of the power output from the fuel cell 2. The control device 3 is configured to charge the power storage device 42 with the power output from the fuel cell 2 when the temperature of the fuel cell 2 acquired by the temperature sensor 26 exceeds a preset temperature target value and the supply of liquid fuel to the fuel cell 2 is stopped.

[0050] The energy storage device 42 is not particularly limited as long as it is a device capable of storing electricity. For example, a capacitor or a secondary battery can be used as the energy storage device 42. There can be various methods for recovering electricity during refresh control by the energy storage device 42. For example, the fuel cell system 102 in this embodiment is configured to recover the heat generated from the heat-generating element 4 during refresh control as electricity again and charge the energy storage device 42.

[0051] More specifically, as shown in Figure 4, a thermoelectric conversion element 41 is provided near the heat-generating element 4 in the fuel cell system 102 of this embodiment. The thermoelectric conversion element 41 is configured to convert the heat generated from the heat-generating element 4 into electricity, which can then be recovered as electricity.

[0052] Furthermore, the control device 3 in this embodiment has a charge changeover switch 33, and the thermoelectric conversion element 41 is electrically connected to the energy storage device 42 via the charge changeover switch 33. The charge changeover switch 33 is configured to switch between an ON state, which electrically connects the energy storage device 42 to the thermoelectric conversion element 41, and an OFF state, which electrically disconnects the energy storage device 42 from the thermoelectric conversion element 41. Therefore, by setting the charge changeover switch 33 to the ON state, the power recovered in the thermoelectric conversion element 41 can be used to charge the energy storage device 42.

[0053] The use of the power stored in the energy storage device 42 is not particularly limited. For example, the energy storage device 42 may be configured to supply power to the external load 7 by superimposing the power stored in the energy storage device 42 onto the power generated from the fuel cell 2 in the power generation mode. In this case, as shown in Figure 4, for example, a discharge changeover switch 34 is provided between the energy storage device 42 and the external load 7, which is configured to switch between an ON state in which the energy storage device 42 is electrically connected to the external load 7 and an OFF state in which the energy storage device 42 is electrically disconnected from the external load 7, and the energy storage device 42 and the external load 7 are electrically connected via the discharge changeover switch 34. Although not shown in the figure, a boost circuit or the like can be provided between the energy storage device 42 and the external load 7 as needed. By electrically connecting the energy storage device 42 in this way and setting the discharge changeover switch 34 to the ON state, the power recovered in the energy storage device 42 can be supplied to the external load 7.

[0054] The operation of the fuel cell system 102 in this embodiment will be explained with reference to Figure 5. When the operation of the fuel cell system 102 in this embodiment is started (step S1), the power generation control unit 31 operates the blower 6 and starts the power generation mode, and continues to supply liquid fuel to the fuel cell 2 for a predetermined time (step S2). In the power generation mode, electricity is generated from the fuel cell 2 by the liquid fuel and oxidizer supplied to the fuel cell 2. The electricity generated from the fuel cell 2 in the power generation mode is supplied to the external load 7 via the first contact 321 of the circuit switch 32.

[0055] When the duration of the power generation mode reaches a predetermined time, the power generation control unit obtains the temperature T of the fuel cell 2 from the temperature sensor 26 (step S3). Next, the power generation control unit 31 terminates the power generation mode and starts the refresh control mode (step S4). When the refresh control mode starts, the operation of the fuel pump 52 is stopped. As a result, the supply of liquid fuel to the fuel cell 2 is stopped. In addition, along with stopping the supply of liquid fuel, the power generation control unit 31 electrically connects the positive terminal 253p and the second contact 322 in the circuit switch 32. As a result, the fuel cell 2 and the heating element 4 are electrically connected, and the power generated by the reaction between the liquid fuel remaining in the fuel cell 2 and the oxidizer continuously supplied from the blower 6 is supplied to the heating element 4. As a result, heat is generated from the heating element 4.

[0056] In this configuration, when the refresh control mode is started, the power generation control unit 31 compares the temperature T of the fuel cell 2 obtained in step S3 with a preset temperature target value Tth (step S5). If the temperature T of the fuel cell 2 is less than the temperature target value Tth (step S5, "Yes"), the power generation control unit 31 determines that it is necessary to raise the temperature of the fuel cell 2 and turns off the charge changeover switch 33. As a result, power is supplied to the heating element 4 by the reaction between the liquid fuel remaining in the fuel cell 2 and the oxidizer continuously supplied from the blower 6, and the liquid fuel in the fuel supply pipes 51 and 53 is heated (step S51).

[0057] On the other hand, if the temperature T of the fuel cell 2 is equal to or greater than the temperature target value Tth (step S5, "No"), it is determined that the temperature of the fuel cell 2 is sufficiently high and there is no need to raise the temperature of the fuel cell 2, and the charge changeover switch 33 is turned ON. In this case, the power generated from the fuel cell 2 is first converted into heat in the heating element 4 and then converted into power by the thermoelectric conversion element 41. The power converted by the thermoelectric conversion element 41 is then charged into the energy storage device 42 (step S52). The charge changeover switch 33 remains ON until a preset condition is met, and then turns OFF after the condition is met. For example, the power generation control unit 31 in this embodiment is configured to keep the charge changeover switch 33 ON while the refresh control mode is in progress and to turn it OFF when the refresh control mode ends.

[0058] When the supply of liquid fuel to the fuel cell 2 has been stopped for a predetermined period of time, the power generation control unit 31 restarts the power generation mode (step S6). When the power generation mode starts, the fuel pump 52 operates and the supply of liquid fuel to the fuel cell 2 is resumed. The circuit switch 32 also electrically connects the positive terminal 253p and the first contact 321. As a result, the power generated from the fuel cell 2 is supplied to the external load 7.

[0059] The power generation control unit 31 determines whether the energy storage device 42 is charged or not after the power generation mode has resumed (step S7). If the energy storage device 42 is charged (step S7, "Yes"), the power generation control unit 31 turns on the discharge changeover switch 34. This causes the energy storage device 42 to discharge (step S71). The power discharged from the energy storage device 42 is superimposed on the power generated from the fuel cell 2 and supplied to the external load 7. After the discharge from the energy storage device 42 is complete, the power generation control unit 31 turns off the discharge changeover switch 34. On the other hand, if the energy storage device 42 is not charged (step S7, "No"), the power generation control unit 31 keeps the discharge changeover switch 34 in the off state.

[0060] Subsequently, the power generation control unit 31 determines whether or not to stop operation (step S8). If the operation of the fuel cell system 102 is to continue (step S8, "No"), the power generation control unit 31 repeatedly performs the aforementioned power generation mode and refresh control mode. On the other hand, if the operation of the fuel cell system 102 is to be stopped (step S8, "Yes"), the power generation control unit 31 stops the fuel pump 52 and blower 6 to stop the operation of the fuel cell system 102 (step S100).

[0061] In this embodiment, the fuel cell system 102 is configured to supply power generated during refresh control to either the heating element 4 or the energy storage device 42 based on the temperature of the fuel cell 2. This prevents an excessive rise in the temperature of the fuel cell 2 and allows for more efficient use of the power generated during refresh control.

[0062] (Embodiment 3) In this embodiment, an example of a fuel cell system 103 configured to directly recover power generated from the fuel cell 2 during refresh control is described.

[0063] As shown in Figure 6, the fuel cell system 103 in this embodiment includes a fuel cell 2, a fuel tank 5, a fuel pump 52, and a blower 6. The fuel tank 5 and the fuel pump 52, and the fuel pump 52 and the fuel cell 2 are connected by fuel supply pipes 51 and 53. The blower 6 and the fuel cell 2 are connected by an oxidizer supply pipe 61. Although not shown in the figure, the fuel cell system 103 also includes a fuel recovery tank 55 connected to the fuel cell 2 via a fuel recovery pipe, and a drain tank connected to the fuel cell 2 via a water recovery pipe.

[0064] Furthermore, a heating element 4 is attached to the fuel supply pipe 53 between the fuel pump 52 and the fuel cell 2. In Figure 6, for convenience, the heating element 4 is shown in a different location from the fuel supply pipe 53, but the position of the heating element 4 in Figure 6 is unrelated to the actual position of the heating element 4 in the fuel cell system 103.

[0065] As shown in Figure 6, the fuel pump 52 and blower 6 are electrically connected to the power generation control unit 31 of the control device 3. The operation of the fuel pump 52 and blower 6 is controlled by the power generation control unit 31. In addition, the positive terminal 253p of the fuel cell 2 is electrically connected to the circuit switch 32 of the control device 3. The first contact 321 of the circuit switch 32 is electrically connected to the external load 7. Furthermore, the heating element 4 and the energy storage device 42 are connected in parallel to each other at the second contact 322 of the circuit switch 32.

[0066] In this embodiment of the fuel cell system 103, the control device 3 has a heating changeover switch 35 provided between the second contact 322 and the heating element 4. The heating changeover switch 35 is configured to switch between an ON state, which electrically connects the heating element 4 to the second contact 322 and the energy storage device 42, and an OFF state, which electrically disconnects the heating element 4 from the second contact 322 and the energy storage device 42. By setting the heating changeover switch 35 to the ON state, power can be supplied from the fuel cell 2 or the energy storage device 42 to the heating element 4, and heat can be generated from the heating element 4.

[0067] Furthermore, a charge changeover switch 33 provided on the control device 3 is interposed between the second contact 322 and the energy storage device 42. The charge changeover switch 33 is configured to switch between an ON state, which electrically connects the energy storage device 42 to the second contact 322 and the heating element 4, and an OFF state, which electrically disconnects the energy storage device 42 from the second contact 322 and the heating element 4. By setting the charge changeover switch 33 to the ON state, the power generated from the fuel cell 2 during refresh control can be used to charge the energy storage device 42.

[0068] Furthermore, the energy storage device 42 is electrically connected to the external load 7 via the discharge changeover switch 34.

[0069] The operation of the fuel cell system 103 in this embodiment will be described with reference to Figure 7. The fuel cell system 103 in this embodiment operates in the same manner as the fuel cell system 102 of Embodiment 2 from the start of operation (step S1) until the step of comparing the temperature T of the fuel cell 2 with a preset temperature target value Tth (step S5).

[0070] In the power generation control unit 31, the temperature T of the fuel cell 2 is compared with the target temperature Tth (step S5). If the temperature T of the fuel cell 2 is less than the target temperature Tth (step S5, "Yes"), the power generation control unit 31 determines that it is necessary to raise the temperature of the fuel cell 2. In this case, the power generation control unit 31 turns on the heating switch 35 and turns off the charging switch 33. As a result, power is supplied to the heating element 4 by the reaction between the liquid fuel remaining in the fuel cell 2 and the oxidizer continuously supplied from the blower 6, and the temperature of the liquid fuel in the fuel supply pipe 53 rises (step S513). The heating switch 35 remains on until a preset condition is met, after which it turns off. For example, in this embodiment, the power generation control unit 31 is configured to keep the heating switch 35 on while the refresh control mode is in progress and to turn it off when the refresh control mode ends.

[0071] On the other hand, if the temperature T of the fuel cell 2 is equal to or greater than the temperature target value Tth (step S5, "No"), the power generation control unit 31 determines that the temperature of the fuel cell 2 is sufficiently high and there is no need to raise the temperature of the fuel cell 2. In this case, the power generation control unit 31 turns off the heating switch 35 and turns on the charging switch 33. As a result, the power generated from the fuel cell 2 is directly supplied to the energy storage device 42, and the energy storage device 42 is charged (step S523). The charging switch 33 remains on until a preset condition is met, and then turns off. For example, the power generation control unit 31 in this embodiment is configured to keep the charging switch 33 on while the refresh control mode is in progress and turn it off when the refresh control mode ends.

[0072] In this embodiment, the fuel cell system 103 operates similarly to the fuel cell system 102 of Embodiment 2 from the end of the refresh control mode and the start of the power generation mode again (step S6) until a decision is made as to whether or not to stop operation (step S8). In the step of deciding whether or not to stop operation (step S8), if the operation of the fuel cell system 103 is to be continued (step S8, "No"), the power generation control unit 31 repeatedly performs the aforementioned power generation mode and refresh control mode. On the other hand, if the operation of the fuel cell system 103 is to be stopped (step S8, "Yes"), the power generation control unit 31 stops the fuel pump 52 and the blower 6 to stop the operation of the fuel cell system 103 (step S100).

[0073] In this embodiment, the fuel cell system 103 is configured to directly charge the energy storage device 42 with the power generated during refresh control. Therefore, power loss during refresh control can be further reduced.

[0074] (Embodiment 4) This embodiment describes another method for distributing power generated from the fuel cell 2 during refresh control. The fuel cell system of this embodiment has a configuration similar to that of the fuel cell system 103 of Embodiment 3 shown in Figure 6.

[0075] The operation of this fuel cell system will be explained with reference to Figure 8. When the operation of this fuel cell system is started (step S1), the power generation control unit 31 operates the blower 6 to supply oxidizer to the fuel cell 2 and starts the power generation mode, continuing to supply liquid fuel to the fuel cell 2 for a predetermined time (step S2). When the duration of the power generation mode reaches the predetermined time, the power generation control unit 31 obtains the temperature T of the fuel cell 2 from the temperature sensor 26 (step S3). Next, the power generation control unit 31 terminates the power generation mode and starts the refresh control mode (step S4). When the refresh control mode is started, the operation of the fuel pump 52 is stopped. As a result, the supply of liquid fuel to the fuel cell 2 is stopped.

[0076] In this fuel cell system configuration, the power generation control unit 31 turns off the heating switch 35 and turns on the charging switch 33 when the refresh control mode is started. As a result, the electricity generated by the reaction between the liquid fuel remaining in the fuel cell 2 and the oxidizer continuously supplied from the blower 6 is first used to charge the energy storage device 42 (step S504).

[0077] After a predetermined time has elapsed since the refresh control mode started, the power generation control unit 31 compares the temperature T of the fuel cell 2 acquired in step S3 with a preset temperature target value Tth (step S604). For example, the power generation control unit 31 may be configured to compare the temperature T of the fuel cell 2 with a preset temperature target value Tth when half the duration of the refresh control mode has elapsed from the time the refresh control mode started.

[0078] If the temperature T of the fuel cell 2 is less than the temperature target value Tth (step S604, "Yes"), the power generation control unit 31 determines that it is necessary to raise the temperature of the fuel cell 2 and turns on the heating switch 35 and the charging switch 33. As a result, the power stored in the energy storage device 42 is supplied to the heating element 4, and the temperature of the liquid fuel in the fuel supply pipe 53 rises (step S614).

[0079] On the other hand, if the temperature T of the fuel cell 2 is equal to or greater than the temperature target value Tth (step S604, "No"), the power generation control unit 31 determines that the temperature of the fuel cell 2 is sufficiently high and there is no need to raise the temperature of the fuel cell 2, and turns off the heating switch 35 and the charging switch 33. As a result, the power stored in the energy storage device 42 is maintained.

[0080] When the supply of liquid fuel to the fuel cell 2 is stopped for a predetermined period of time, the power generation control unit 31 restarts the power generation mode (step S704). When the power generation mode is started, the power generation control unit 31 turns off the heating switch 35 and the charging switch 33.

[0081] Furthermore, after the power generation mode is started, the power generation control unit 31 determines whether or not the energy storage device 42 is charged (step S804). If the energy storage device 42 is charged (step S804, "Yes"), the power generation control unit 31 turns on the discharge changeover switch 34. This allows the power generated from the fuel cell 2 to be superimposed with the power recovered by the energy storage device 42 and supplied to the external load 7 (step S814). After the discharge from the energy storage device 42 is complete, the power generation control unit 31 turns off the discharge changeover switch 34. On the other hand, if the energy storage device 42 is not charged (step S804, "No"), the power generation control unit 31 keeps the discharge changeover switch 34 in the off state.

[0082] Subsequently, the power generation control unit 31 determines whether or not to stop operation (step S904). If the operation of the fuel cell system is to continue (step S904, "No"), the power generation control unit 31 repeatedly performs the aforementioned power generation mode and refresh control mode. On the other hand, if the operation of the fuel cell system is to be stopped (step S904, "Yes"), the power generation control unit 31 stops the fuel pump 52 and the blower 6 to stop the operation of the fuel cell system (step S100).

[0083] In this embodiment of the fuel cell system, the power generated during refresh control is first used to charge the energy storage device 42, and then used to heat the fuel cell 2, etc., as needed. Therefore, when power generation is restarted after the refresh control is completed, the temperature of the fuel cell 2 can be more easily brought within the desired range.

[0084] The present invention is not limited to the embodiments described above, and can be applied to various embodiments without departing from its spirit. [Explanation of Symbols]

[0085] 1, 102, 103 Fuel cell systems 2 fuel cell 3. Control device 4. Heating element

Claims

1. A fuel cell system having a fuel cell configured to generate electricity by reacting a liquid fuel with an oxidizer, A control device configured to switch between supplying and stopping the supply of the liquid fuel to the fuel cell, The fuel cell, the supply path for the liquid fuel to the fuel cell, and the supply path for the oxidizer to the fuel cell are all heated by a heating element positioned at a location that can heat at least a portion of them. A fuel cell system in which the control device is configured to electrically connect the fuel cell and the heating element while the supply of the liquid fuel to the fuel cell is stopped.

2. The fuel cell system according to claim 1, wherein the heating element is positioned to heat at least one of the liquid fuel and the oxidizer.

3. The fuel cell system according to claim 2, wherein the fuel cell system includes a fuel supply pipe for supplying the liquid fuel to the fuel cell and an oxidizer supply pipe for supplying the oxidizer to the fuel cell, and the heating element is attached to at least one of the fuel supply pipe and the oxidizer supply pipe.

4. The fuel cell system according to claim 3, wherein the heating element is wrapped around at least one of the fuel supply pipe and the oxidizer supply pipe.

5. The fuel cell system according to claim 1, wherein the fuel cell system has a fuel tank that holds the liquid fuel supplied to the fuel cell, and the heating element is attached to the fuel tank.

6. The fuel cell system according to claim 1, wherein the heat-generating element is attached to the fuel cell.

7. The fuel cell system according to claim 6, wherein the fuel cell comprises a single cell having an anode, a cathode, and a separator interposed between the anode and the cathode, and a holder for holding the single cell, the holder being composed of the heating element.

8. The fuel cell system according to claim 1, comprising: a temperature sensor connected to the control device and configured to acquire the temperature of the fuel cell; and a power storage device configured to charge at least a portion of the power output from the fuel cell, wherein the control device is configured to charge the power output from the fuel cell to the power storage device while the temperature of the fuel cell acquired by the temperature sensor exceeds a preset temperature target value and the supply of the liquid fuel to the fuel cell is stopped.

9. The fuel cell system according to any one of claims 1 to 8, wherein the heating element is configured to heat the portion to which the heating element is attached to a temperature of 40°C or more and 70°C or less.

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