Fuel cell system, and method for controlling fuel cell system

Abstract

To provide a fuel cell system which is excellent in output stability and also lightened in weight and compact, and a method for controlling a fuel cell system.SOLUTION: A fuel cell system 1 mainly comprises a fuel cell 2, a first DC-DC converter 3, and a control circuit 5. The control circuit 5 in which a capacitor 51 and a discharge resistance 52 are connected through a relay 53 can switch to a first mode in which power generated by the fuel cell 2 is charged to the capacitor 51 depending on a load operating condition, a second mode in which a load is operated by only the output of the fuel cell 2, and a third mode in which a load is operated by output power from both the fuel cell 2 and the capacitor 51. Thus, a load can be stably operated even when the fuel cell 2 has low power.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fuel cell system and a control method for a fuel cell system, and more particularly to a lightweight, compact fuel cell system with excellent output stability, and a control method for a fuel cell system. [Background technology]

[0002] In the railway industry, it is desirable to carry out regular safety checks in order to detect any abnormalities on the tracks that may hinder the safe operation of trains at an early stage and to promptly take necessary measures, such as maintenance work, on any abnormal parts.

[0003] Various types of track maintenance equipment are used depending on the purpose of the track maintenance work, such as a nail driver for driving in the nails that fasten the rails to the sleepers, a bolt loosening machine for loosening the bolts that fasten the rails, and a single-head rail grinding machine that rolls over the rail and uses a grinding stone or milling cutter to grind down any unevenness on the top surface of the rail.

[0004] Many of these track maintenance devices require a power source, and so far, portable engine generators have been used as the power source, as shown in Patent Document 1. However, engine generators use fossil fuels such as gasoline to drive the engine, which not only causes carbon dioxide emissions due to the combustion reaction and air pollution from exhaust gases, but also creates noise problems for the surrounding area.

[0005] Therefore, in recent years, instead of engines as a driving source, generators using fuel cells, which are devices that directly convert energy generated by chemical reactions into electrical energy, have been adopted (Patent Document 2). In this way, by adopting fuel cells as a driving source, it is possible to solve the above-mentioned problems of carbon dioxide and exhaust gas emissions, as well as noise problems. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-14246 A [Patent Document 2] JP 2017-27766 A Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, there are various types of track maintenance equipment used for track maintenance work depending on the purpose, and there are many types of track maintenance equipment that require a large amount of power instantaneously. Therefore, a low-output generator may not be able to drive some track maintenance equipment due to insufficient output, so the generator output must be above a certain level.

[0008] Meanwhile, according to regulations for track maintenance work, there is a weight limit for equipment used on the tracks so that it can be quickly removed from the tracks in an emergency. Specifically, the total weight of the track maintenance equipment and the generator must be less than 60 kg. Here, in order to ensure a certain level of output from a fuel cell-type generator, the fuel cells must be made into a multi-layer structure. However, if the fuel cells are made into a stacked structure, the weight of the entire generator becomes heavy, and there is a risk that it will exceed the weight limit for equipment used in track maintenance work. On the other hand, if the output of the generator is limited to meet the weight limit, the amount of track maintenance equipment that can be used will be limited due to insufficient output.

[0009] The present invention has been devised in consideration of the above points, and aims to provide a fuel cell system that is lightweight, compact, and has excellent output stability and that can be mounted on a generator used, for example, in track maintenance work, and a control method for the fuel cell system. [Means for solving the problem]

[0010] In order to achieve the above-mentioned objective, the fuel cell system of the present invention has a fuel cell that generates power to be supplied to a load, a power converter that converts the output voltage of the power generated by the fuel cell, and a power storage device that stores the power to be supplied to the load, and is switchable between a first mode in which the power output from the fuel cell is charged to the power storage device when the load is not operating, a second mode in which power is supplied to the load only from the fuel cell when the power consumption when the load is operating is less than a predetermined threshold, and a third mode in which power is supplied to the load from both the fuel cell and the power storage device when the power consumption when the load is operating is equal to or greater than a predetermined threshold, and is equipped with a control circuit connected downstream of the power converter.

[0011] Here, the fuel cell system is equipped with a fuel cell that generates electricity to be supplied to the load, and can generate electricity to be supplied to the load through a chemical reaction between hydrogen and oxygen, resulting in high power generation efficiency. In addition, since no harmful substances or noise are produced during power generation, the environmental burden can be reduced.

[0012] In addition, by providing a power converter that converts the output voltage of the power generated by the fuel cell, the power generated by the fuel cell can be adjusted to a voltage range in which a load connected to the generator can operate.

[0013] Furthermore, by providing a control circuit having a power storage device that stores the power to be supplied to the load, a portion of the power generated by the fuel cell can be stored in the power storage device and the power can be supplied to the load as needed. Therefore, since there is no need to stack fuel cells in multiple layers to ensure output power, the entire fuel cell can be made smaller and lighter.

[0014] In addition, the control circuit has a first mode in which the power output from the fuel cell is charged to the power storage device when the load is not operating, so that when there is no need to supply power to the load, the power generated by the fuel cell can be charged to the power storage device.

[0015] In addition, the control circuit has a second mode in which power is supplied to the load only from the fuel cell when the amount of power consumed during load operation is less than a predetermined threshold, thereby making it possible to operate the load using only the power generated by the fuel cell, without using the power stored in the power storage device.

[0016] In addition, the control circuit has a third mode in which power is supplied to the load from both the fuel cell and the power storage device when the power consumption during load operation is equal to or greater than a predetermined threshold, making it possible to compensate for insufficient output from the fuel cell with the power storage device. By switching between the first, second, and third modes, the required power can be supplied to the load at the required timing, making it possible to stably operate the load even with a low-output fuel cell.

[0017] In addition, if a diode is connected between the power converter and the control circuit to prevent reverse current flow from the power storage device to the fuel cell, the reverse current flow from the power storage device to the fuel cell can be prevented, thereby protecting the fuel cell.

[0018] In addition, the control circuit includes a discharge resistor connected in parallel to the storage device, and when the output from the fuel cell to the control circuit is stopped, the storage device and the discharge resistor are electrically connected by a relay circuit, and when the control circuit has a fourth mode in which the remaining power of the storage device is consumed by the discharge resistor, the power stored in the storage device is consumed by the discharge resistor, thereby preventing electric shock due to the remaining power in the storage device.

[0019] Furthermore, when the power storage device is made up of a plurality of capacitors connected in parallel, it can be charged in a short period of time, and therefore it is possible to supply power from the power storage device to the load at the required timing.

[0020] In order to achieve the above-mentioned objective, the control method for a fuel cell system of the present invention includes the steps of starting power generation by the fuel cell, charging the power generated by the fuel cell to a power storage device when the load is not operating, supplying power to the load only from the fuel cell when the amount of power consumed when the load is operating is less than a predetermined threshold, and supplying power to the load from both the fuel cell and the power storage device when the amount of power consumed when the load is operating is equal to or greater than a predetermined threshold.

[0021] Here, by providing a step of starting power generation in the fuel cell, it is possible to generate the power required to operate the load.

[0022] In addition, by including a step of charging the power generated by the fuel cell to the power storage device when the load is not operating, the power generated by the fuel cell can be charged to the power storage device when there is no need to supply power to the load.

[0023] In addition, by providing a step of supplying power to the load only from the fuel cell when the amount of power consumed during load operation is less than a predetermined threshold, the load can be operated using only the power generated by the fuel cell, without using the power stored in the storage device.

[0024] In addition, by providing a step of supplying power to the load from both the fuel cell and the power storage device when the amount of power consumed during load operation is equal to or greater than a predetermined threshold, the power storage device can compensate for any output deficiency of the fuel cell.

[0025] In addition, if there is a step of stopping the supply of power from the storage device and supplying power to the load only from the fuel cell when the amount of power consumed during load operation falls below a predetermined threshold after the step of supplying power to the load from both the fuel cell and the storage device, the load can be operated using only the power generated by the fuel cell, without using the power stored in the storage device.

[0026] In addition, if there is a step of consuming the remaining power of the storage device through a discharge resistor when the output of the fuel cell is stopped, the power stored in the storage device is consumed through the discharge resistor, thereby preventing electric shock due to the remaining power in the storage device.

[0027] As a result, it is not necessary for the fuel cell to generate all of the power to be supplied to the load, so there is no need to increase the output of the fuel cell, and the entire fuel cell can be made smaller and lighter.

[0028] The fuel cell system and the control method for the fuel cell system according to the present invention can be made lightweight and compact, with excellent output stability. [Brief description of the drawings]

[0029] [Figure 1] 1 is a schematic diagram of a fuel cell system according to an embodiment of the present invention. [Diagram 2] 3 is a control flow of a fuel cell system according to an embodiment of the present invention. [Diagram 3] 4 is a time chart of a fuel cell system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] A fuel cell system and a control method for the fuel cell system according to an embodiment of the present invention will be described below with reference to the drawings to facilitate understanding of the present invention. Note that in the following description, an example in which the fuel cell system is applied to a generator used in track maintenance work will be described, but the present invention is not limited to this, and the fuel cell system can be applied to any type of generator.

[0031] 1 is a diagram showing a schematic configuration of a fuel cell system 1 according to an embodiment of the present invention. The fuel cell system 1 is mounted on a generator used for track maintenance work, for example, and generates and controls the output of electric power required to drive track maintenance equipment (load) for track maintenance work connected to the generator.

[0032] The fuel cell 2 generates electricity through an electrochemical reaction between hydrogen contained in a fuel gas (such as hydrogen gas) and oxygen contained in an oxidant gas. The fuel cell 2 is a known configuration and will not be shown in detail, but is made up of a plurality of fuel cell units connected in series, and has an electrolyte membrane, an anode disposed on one side of the electrolyte membrane, and a cathode disposed on the other side of the electrolyte membrane.

[0033] Specifically, catalyst layers are disposed on both sides of the electrolyte membrane, a diffusion layer is disposed on the outside of the catalyst layers, and a separator with a hydrogen gas flow path HL is disposed on the outside of the diffusion layer. Here, the catalyst layer and the diffusion layer function as the anode or cathode in the fuel cell.

[0034] The electrolyte membrane, catalyst layer, diffusion layer, and separator arranged in the fuel cell 2 are not limited to specific specifications, and known materials can be used. For example, an ion exchange membrane made of a solid polymer material can be used as the electrolyte membrane, a platinum-based catalyst can be used as the catalyst layer, and a porous material such as a carbon material can be used as the diffusion layer. In addition, a metal material such as stainless steel or a carbon material such as a carbon composite material can be used as the separator.

[0035] In the fuel cell 2, hydrogen, which is a fuel gas, is supplied to the anode, and oxygen is supplied to the cathode, causing an electrochemical reaction to occur and generating electricity. In Fig. 1, a hydrogen tank HT is a supply device for hydrogen gas (H2), which is an example of a fuel gas, and stores hydrogen gas under high pressure inside. When a hydrogen tank valve HV of the hydrogen tank HT is opened, hydrogen gas is supplied from the hydrogen tank HT, and is supplied to the anode side of the fuel cell 2 after being adjusted to a predetermined pressure by a pressure regulating valve (not shown).

[0036] Residual gas (unreacted hydrogen and nitrogen) containing liquid water generated by the chemical reaction in the fuel cell 2 passes through the exhaust path EL and is discharged from the system through the exhaust port EP. At this time, the exhaust port EP has an exhaust valve EV, and the amount of residual gas discharged from the exhaust port EP is adjusted by controlling the opening and closing amount and opening and closing timing of the exhaust valve EV.

[0037] The first DC-DC converter 3 is a power converter connected downstream of the fuel cell 2, which steps down or steps up (in this embodiment of the present invention, converts to 24V DC) the DC voltage supplied from the fuel cell 2 and outputs it to a load. The first DC-DC converter 3 includes a switching element, and converts the output voltage of the fuel cell 2 by controlling the switching of the switching element. The first DC-DC converter 3 is classified into forward type, push-pull type, flyback type, etc., and all of these are applicable to this embodiment.

[0038] A circuit breaker 4 is connected between the fuel cell 2 and the first DC-DC converter 3. The circuit breaker 4 is driven by switching a mechanical switch on and off, and when in the on state, it outputs the power generated by the fuel cell 2 to the first DC-DC converter 3, and when in the off state, it stops the supply of power to the first DC-DC converter 3.

[0039] The circuit breaker 4 is not necessarily required and may be omitted as necessary. In addition to being switched on and off by a mechanical switch, the circuit breaker 4 may also be automatically operated when, for example, a short-circuit fault in the switching element of the first DC-DC converter 3 is detected, to separate the switching element from the circuit. This can reliably prevent a short-circuit current from flowing through the circuit.

[0040] A control circuit 5 is connected to the rear stage of the first DC-DC converter 3. The control circuit 5 is mainly composed of a first relay circuit 50a, a second relay circuit 50b, and a third relay circuit 50c. A capacitor 51 that stores the power output from the first DC-DC converter 3 and functions as a power storage device that outputs a part of the stored power to a load, and a discharge resistor 52 for discharging the power stored in the capacitor 51 are connected to each relay circuit 50 via a relay 53. In addition, a diode 54 is provided to prevent the power stored in the capacitor 51 from flowing into the fuel cell 2.

[0041] Here, it is not essential to have the diode 54. However, by having the diode 54, it is possible to prevent a current from flowing back from the capacitor 51 to the fuel cell 2, thereby protecting the fuel cell 2.

[0042] First, the first relay circuit 50a is connected to a first capacitor 51a and a first discharge resistor 52a corresponding to the first capacitor 51a via a first relay 53a. The second relay circuit 50b is connected to a second capacitor 51b and a second discharge resistor 52b corresponding to the second capacitor 51b, and a third capacitor 51c and a third discharge resistor 52c corresponding to the third capacitor 51c, respectively, via a second relay 53b. The third relay circuit 50c is connected to a fourth capacitor 51d and a fourth discharge resistor 52d corresponding to the fourth capacitor 51d, and a fifth capacitor 51e and a fifth discharge resistor 52e corresponding to the fifth capacitor 51e, respectively, via a third relay 53c.

[0043] Here, the relay circuit 50 does not necessarily have to be divided into three, the first relay circuit 50a to the third relay circuit 50c, and within the range of the allowable current output from the first DC-DC converter 3, the relay circuit 50 can be increased or decreased as appropriate from the standpoint of efficiency in charging and discharging power. For example, the relay circuit 50 may be only one, or may be divided into four or more.

[0044] It is not necessary to provide a total of five capacitors 51, the first capacitor 51a to the fifth capacitor 51e, and five discharge resistors 52, the first discharge resistor 52a to the fifth discharge resistor 52e, as the capacitors 51. The numbers of capacitors 51 and discharge resistors 52 can be appropriately increased or decreased based on the maximum output of the fuel cell system 1.

[0045] In the above configuration, when the power supply of the generator is turned on and power generation by the fuel cell 2 begins, the power output from the first DC-DC converter 3 is input to the control circuit 5, and at this time the first relay 53a to the third relay 53c are turned on.

[0046] Since no electricity is stored in capacitor 51 for a predetermined time immediately after the generator is powered on, first, a portion of the current input from first DC-DC converter 3 is stored in first capacitor 51a to fifth capacitor 51e for a predetermined time (first mode).

[0047] Then, when a load connected to the generator is operated after a predetermined time has elapsed from the first mode, if the amount of power consumed when the load is operating is less than a predetermined threshold (1000 W in this embodiment of the present invention), the load is operated only by the output current from the fuel cell 2 (second mode).

[0048] On the other hand, when the power consumption of the load exceeds a certain threshold, the output current from the fuel cell 2 alone is insufficient, so that in order to make up for the insufficient output, electricity stored in the capacitor 51 in addition to the fuel cell is supplied to the load (third mode).

[0049] Furthermore, when the circuit breaker 4 is turned off after the load operation is completed and the current supply from the first DC-DC converter 3 to the control circuit 5 is cut off, the first relay 53a to the third relay 53c are turned off. At this time, the electricity stored in the first capacitor 51a to the fifth capacitor 51e is discharged by the first discharge resistor 52a to the fifth discharge resistor 52e (fourth mode). As a result, electricity is not stored in the capacitor 51 and the power stored in the capacitor 51 is consumed by the discharge resistor 52, so that electric shock due to the remaining power in the capacitor 51 can be prevented.

[0050] A storage battery may be used as the power storage device instead of the capacitor 51. However, since a storage battery takes a long time to charge, for example, when a load is operated at high output in a short time after the generator is turned on, there is a risk that the battery will not be charged enough and will not function as an output supplement for the fuel cell 2. Therefore, when the load is used for track maintenance work in which high output operation is repeated in a short time after the generator is turned on, such as track maintenance equipment, it is preferable to use the capacitor 51, which is capable of storing a predetermined amount of electricity in a short time, as the power storage device.

[0051] A second DC-DC converter 6 is connected to the power line of the control circuit 5, and an exhaust fan EF is connected downstream of the second DC-DC converter 6. The voltage of 24 VDC converted by the first DC-DC converter 3 is stepped down to 12 VDC by the second DC-DC converter 6 to operate the exhaust fan EF. As described above, the exhaust fan EF guides the residual gas containing liquid water produced by the chemical reaction in the fuel cell 2 to the exhaust port EP, where it is discharged outside the system.

[0052] An exhaust valve EV that opens and closes the exhaust port EP is connected to the power line of the control circuit 5 via a timer circuit 7, and a voltage of 24 V DC is input from the first DC-DC converter 3. The timer circuit 7 is set so that the exhaust valve EV opens at intervals of, for example, once every 60 seconds, and residual gas in the fuel cell 2 that has been guided to the exhaust port EP by the exhaust fan EF is discharged outside the system at the same time that the exhaust valve EV opens.

[0053] Here, it is not necessary to control the exhaust valve EV in the opening direction at the timing set in the timer circuit 7 as described above, and the control timing of the exhaust valve EV can be set arbitrarily.

[0054] Furthermore, an intake fan IF is connected to the power line of the control circuit 5, and the intake fan IF is driven when the 24V DC voltage output from the first DC-DC converter 3 is input. The intake fan IF is a fan for cooling and for taking in outside air to supply oxygen to the fuel cell, and while the generator is operating, it constantly takes in outside air as cooling air, supplies oxygen to the fuel cell system 1, and prevents the fuel cell system 1 from becoming too hot.

[0055] A DC-AC inverter 8 is connected to the rear of the control circuit 5, and converts the direct current from the first DC-DC converter 3 and the control circuit 5 into an alternating current. The DC-AC inverter 8 converts the current by controlling the on / off of a switching element based on a known PWM (Pulse Width Modulation) control method. The output current of the DC-AC inverter 8 is output to a load connected to an outlet 10 via a noise filter 9.

[0056] The above is the configuration of the fuel cell system 1 according to the embodiment of the present invention. Next, the control method of the fuel cell system according to the embodiment of the present invention will be described with reference to the flow chart of Fig. 2. The control method of the fuel cell system is mainly controlled based on the following steps.

[0057] First, when the generator is powered on, the hydrogen tank valve HV of the hydrogen tank HT is opened to supply hydrogen to the fuel cell 2. This starts power generation through a chemical reaction in the fuel cell 2 as described above (S101).

[0058] Next, when the circuit breaker 4 is turned on (S102), the current generated by the fuel cell 2 is input from the circuit breaker 4 to the first DC-DC converter 3. At this time, the first DC-DC converter 3 converts the direct current output from the fuel cell 2 into a voltage of 24 V. The current output from the first DC-DC converter 3 is input from the control circuit 5 to the exhaust fan EF, exhaust valve EV, and intake fan IF, respectively, and each device operates accordingly.

[0059] When a current is input from the first DC-DC converter 3 to the control circuit 5, the first relay 53a to the third relay 53c in the first relay circuit 50a to the third relay circuit 50c are turned on, respectively. As a result, the current input to the control circuit 5 is input to the first capacitor 51a to the fifth capacitor 51e, and the first mode is entered in which power storage begins (S103).

[0060] Next, it is determined whether the amount of charge (E) of the capacitor 51 is equal to or greater than a predetermined threshold value (E1) (S104). In determining the amount of charge, the amount of charge of each of the first capacitor 51a to the fifth capacitor 51e may be detected, or the time (charging time) from the start of the first mode may be measured. If the result of the determination in S104 is that the amount of charge is less than a predetermined amount, it is determined that the charge in the capacitor 51 is insufficient, and the first mode is continued.

[0061] On the other hand, if it is determined in S104 that the amount of stored electricity in capacitor 51 is equal to or greater than a predetermined amount, the on / off state of the power supply to the generator is determined (S105), and if the power supply remains on, it is determined whether the power consumption (P) of the load connected to the generator is less than a predetermined threshold value (P1) (in this embodiment of the present invention, P1 is defined as 1000 W) (S106).

[0062] The power consumption determination threshold (1000 W) mentioned above is an example, and the determination threshold can be increased or decreased as appropriate depending on the power generation capacity of the fuel cell 2 or the power storage capacity of the capacitor 51.

[0063] If the power consumption of the load is less than 1000 W in S106, the load is operated only by the output power from the fuel cell 2 as the second mode (S107). On the other hand, if it is determined in S106 that the power consumption of the load is 1000 W or more, the load cannot be operated by the power generated by the fuel cell 2 alone, so the load is operated in the third mode by the output power from both the fuel cell 2 and the capacitor 51 (S108). This makes it possible to operate the load stably even if the power consumption of the load temporarily increases.

[0064] When the load is operated in the third mode in S108, the amount of charge stored in the capacitor 51 decreases. Therefore, after the load is operated in the third mode, the process returns to S104, and if the amount of charge stored in the capacitor 51 is less than a predetermined amount, the process switches back to the first mode and the capacitor 51 is charged.

[0065] On the other hand, when the power supply of the generator is turned off in S105, the first relay 53a to the third relay 53c of the relay circuit 50 are also turned off. Accordingly, the current remaining in the capacitor 51 is discharged by the discharge resistor 52 in the fourth mode for a predetermined time (S109), and then the flow ends.

[0066] 3 is a diagram showing a time chart in the fuel cell system 1 according to an embodiment of the present invention, in which the horizontal axis represents the time from the start to the end of power generation by the fuel cell 2, and the vertical axis represents the power consumption of the load (the amount of power output by the fuel cell 2 and the capacitor 51).

[0067] The power consumption of the load is zero for a predetermined time from the start of power generation by the fuel cell 2, and during this time, the current generated by the fuel cell 2 is input to the capacitor 51, and electricity is stored in the capacitor 51. Then, when the load starts to operate and the power consumption of the load is less than 1000 W, the load is operated only by the output power from the fuel cell 2.

[0068] On the other hand, when the power consumption of the load exceeds 1000 W, the electricity stored in the fuel cell 2 and the capacitor 51 are output to the load. In this way, by supplying output power only from the fuel cell 2 or from both the fuel cell 2 and the capacitor 51 based on the power consumption of the load, it is possible to operate the load stably even with a low-output fuel cell.

[0069] As described above, the fuel cell system and the control method for the fuel cell system according to the present invention are lightweight, compact, and have excellent output stability. [Explanation of symbols]

[0070] 1. Fuel cell system 2 fuel cell 3. First DC-DC Converter 4. Circuit Breaker 5 Control circuit 50 Relay Circuit 501 First relay circuit 502 Second Relay Circuit 503 3rd relay circuit 51 Capacitor 51a First capacitor 51b Second capacitor 51c 3rd capacitor 51d 4th capacitor 51e 5th capacitor 52 Discharge resistor 52a 1st discharge resistor 52b 2nd discharge resistor 52c 3rd discharge resistor 52d 4th discharge resistor 52e 5th discharge resistor 53 Relay 53a 1st Relay 53b 2nd Relay 53c 3rd Relay 54 Diode 6 Second DC-DC converter 7 Timer Circuit 8 DC-AC inverter 9. Noise Filter 10 Power Outlets HL Hydrogen gas flow path HT Hydrogen Tank HV Hydrogen tank valve EL exhaust duct EP exhaust port EV Exhaust Valve EF Exhaust Fan IF intake fan

Claims

1. A fuel cell that generates power to be supplied to a load; a power converter that converts an output voltage of the power generated by the fuel cell; a control circuit connected to a downstream stage of the power converter, the control circuit being switchable between a first mode in which the power output from the fuel cell is charged to the power storage device when the load is not in operation, a second mode in which power is supplied to the load only from the fuel cell when the amount of power consumption when the load is in operation is less than a predetermined threshold, and a third mode in which power is supplied to the load from both the fuel cell and the power storage device when the amount of power consumption when the load is in operation is equal to or greater than a predetermined threshold; Fuel cell system.

2. A diode is connected between the power converter and the control circuit to prevent a reverse current flow from the power storage device to the fuel cell. The fuel cell system according to claim 1 .

3. The control circuit includes: a fourth mode including a discharge resistor connected in parallel to the power storage device, wherein when the output from the fuel cell to the control circuit is stopped, the power storage device and the discharge resistor are electrically connected by a relay circuit, and the remaining power of the power storage device is consumed by the discharge resistor; 3. The fuel cell system according to claim 1 or 2.

4. The power storage device is composed of a plurality of capacitors connected in parallel.

3. The fuel cell system according to claim 1 or 2.

5. starting power generation in the fuel cell; charging a power storage device with the power generated by the fuel cell while a load is not in operation; supplying power to the load only from the fuel cell when the amount of power consumed during operation of the load is less than a predetermined threshold; supplying power to the load from both the fuel cell and the power storage device when the amount of power consumption during load operation is equal to or greater than a predetermined threshold. A method for controlling a fuel cell system.

6. and after the step of supplying power from both the fuel cell and the power storage device to the load, when the amount of power consumed during operation of the load falls below a predetermined threshold, stopping the supply of power from the power storage device and supplying power to the load only from the fuel cell. The method for controlling a fuel cell system according to claim 5 .

7. and consuming the remaining power of the power storage device through a discharge resistor when the output of the fuel cell is stopped.

7. A method for controlling a fuel cell system according to claim 5.

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