JPH08321319A - Power converter for fuel cell power plant - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for a fuel cell power generator which converts DC power generated by a fuel cell into commercial AC power and supplies the power to a power system.

[0002]

2. Description of the Related Art An inverter is generally used as a power conversion device for a fuel cell power generator described above, and in order to further improve the power conversion efficiency of the inverter, a booster chopper is combined with the front end of the inverter, and a fuel cell is used. It is known that the output voltage of is boosted by chopper control and input to the inverter.

FIG. 4 is a circuit diagram (single line diagram) of a power converter for a fuel cell power generator combined with such a step-up chopper. In the figure, 1 is a fuel cell, 2 is an inverter, and 3 is a front stage of the inverter 2. Connected boost chopper, 4 commercial power system (3 phase), 5 system power supply, 6 system load, 7
Is a interconnection switch, and the boost chopper 3 is composed of a combination of a reactor L, a semiconductor switching element Tr, a diode D, and a capacitor C as is well known. In addition,
Reference numeral 8 is a discharge resistance of the capacitor C, and 9 is a discharge switch which is turned on when the fuel cell 1 is stopped.

[0004]

By the way, in the power converter in which the step-up chopper is combined with the inverter as described above, the following problems occur especially in the starting process of the fuel cell. That is, the fuel cell 1 shifts to the "cooperative operation" with the power system 4 through the operation modes of "startup" and "standby operation". In this case, in the starting process of the fuel cell 1,
After preheating the fuel cell without supplying the reaction gas (hydrogen, air), the hydrogen-rich fuel gas and air are introduced into the hydrogen electrode and the air electrode of the fuel cell with the inverter 2 stopped to start power generation, The output voltage VFC of the fuel cell is adjusted to a predetermined open voltage VFCopen by gradually increasing the supply amount of fuel gas.
The fuel cell itself is heated up to a predetermined operating temperature by the cell reaction heat accompanying power generation, and the startup is established. Next, the inverter 2 is operated as a stand-alone operation to shift to a standby operation state, and then the inverter 2 is controlled to match the voltage and phase before and after the interconnection switch 7,
The interconnection switch 7 is turned on and the power system 4 is also connected.

In this case, when the fuel gas is introduced into the fuel cell 1 as shown in FIG. 5 in the above-mentioned starting process, the output voltage VFC of the fuel cell 1 is almost in proportion to the increase of the gas supply amount. Ascend to VFCopen. On the other hand, the charging voltage VC for the capacitor C of the boost chopper 3 also rises in proportion to the output voltage VFC of the fuel cell 1, and the capacitor C
The charging current IC of is flowing through the reactor L and the diode D.

By the way, the diode D is not energized while the forward applied voltage does not exceed the armpit voltage (rising voltage) VD, and the charging current IC of the capacitor C is also zero during this period. Then, when the output voltage VFC of the fuel cell reaches the armpit voltage VD of the diode D, the charging of the capacitor C starts, and a rush current that causes the output current IFC of the fuel cell 1 to rapidly increase from zero flows.

On the other hand, since the amount of fuel gas supplied to the fuel cell 1 is still small at the initial stage of starting the start-up, when the inrush current flows, the fuel gas consumption at the hydrogen electrode increases and the gas utilization rate increases. The fuel gas becomes extremely high, and therefore, the fuel gas temporarily becomes insufficient until the supply amount of the fuel gas increases, which causes a so-called gas shortage. Moreover, in this gas shortage state, a portion where the cell reaction occurs locally and a portion where the cell reaction does not occur in the electrode surface area of the fuel cell, which causes a large thermal stress to the electrode, This may cause deterioration of the catalyst and damage to the fuel cell such as deterioration of characteristics. Particularly, in the case of an on-site fuel cell power generator that is operated and stopped in accordance with the power demand on the system side, the fuel cell may be greatly damaged by repeated startups.

The present invention has been made in view of the above points, and an object of the present invention is to solve the above problems by implementing a power conversion device in which a step-up chopper is combined in the preceding stage of an inverter, and a capacitor of the step-up chopper is used in the starting process of a fuel cell. An object of the present invention is to provide a power conversion device for a fuel cell power generation device, which is capable of skillfully preventing occurrence of a gas shortage state due to inrush current to the fuel cell and damage to the fuel cell due to the gas shortage.

[0009]

In order to achieve the above object, according to the present invention, a capacitor of a step-up chopper circuit receives power from a power system in a state where an inverter is stopped at the time of starting a fuel cell to form a capacitor. An initial charging circuit for charging to a predetermined operating voltage is provided. Then, the initial charging circuit described above can be specifically implemented with the following circuit configuration.

1) A rectifier circuit for connecting the initial charging circuit to a power system to convert the system voltage into a direct current, a charging resistor connected between the rectifying circuit and a capacitor of a step-up chopper, and a charging switch. Composed of combinations. 2) In 1) above, the discharging resistance of the capacitor of the boost chopper circuit is used as the charging resistance of the initial charging circuit.

3) In the above item 1), a flywheel diode connected to a switching element of an inverter circuit is used as a rectifier circuit of an initial charging circuit.

[0012]

With the above structure, at the time of starting the fuel cell, the charging switch of the initial charging circuit is turned on before starting the introduction of the reaction gas into the cell electrode, and the capacitor of the step-up chopper circuit performs a predetermined operation by receiving power from the power system side. Charge to voltage. Therefore, even when the output voltage of the fuel cell reaches the bottom layer voltage of the diode built into the boost chopper after the reaction gas is supplied to the fuel cell, the capacitor is already in the charged state, so no rush current flows, and It is possible to prevent the gas from running out of the cell and the damage to the fuel cell due to the deterioration of the characteristics caused by the gas out.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings of each embodiment, the same members corresponding to those in FIG. 4 are designated by the same reference numerals. Embodiment 1 FIG. 1 shows an embodiment corresponding to claim 2 of the present invention, in which an initial charging circuit 10 for the capacitor C is newly provided between the capacitor C of the boost chopper 3 and the power system 4. Is additionally equipped with. The initial charging circuit 10 includes a rectifier circuit (three-phase full-wave rectifying circuit) 11 that converts AC of the system 4 into DC, a charging switch 12,
The circuit is composed of a combination with the charging resistor 13. Then, when the fuel cell 1 is started, the charging switch 12 is turned on before starting the introduction of the reaction gas into the fuel cell. As a result, the capacitor C of the step-up chopper 3 is charged with a predetermined charging voltage VC by flowing the charging current IC from the power system 4 side through the rectifier circuit 11 and the charging resistor 13.

In this case, the average value of the DC output voltage VDC of the rectifier circuit 11 for full-wave rectifying AC is expressed as VDC = VS × 1.35, where the voltage (effective value) of the power system 4 is VS. To be done. Here, if the system voltage VS is 200V, the average value VDC of the DC output voltage of the rectifier circuit, and thus the charging voltage VC of the capacitor C, is 270V. On the other hand, the fuel cell 1 using the step-up chopper 3 is generally designed so that its DC output voltage (open voltage) has a lower output voltage value than the system voltage. As a result, even when the fuel gas is started to be introduced into the fuel cell 1 and the output voltage due to the power generation thereof rises, the inrush current due to the charging current of the capacitor does not flow, and thus the fuel gas is out of gas due to the inrush current. And the damage to the fuel cell due to lack of gas can be prevented.

Embodiment 2 FIG. 2 shows an application embodiment corresponding to claim 3 of the present invention. In this embodiment, the charging resistor 13 in the above-mentioned Embodiment 1 is omitted, and instead it is used. The initial charging circuit 10 is configured so that the discharging resistor 8 connected to the capacitor C of the step-up chopper 3 also serves as a charging resistor. As a result, the number of circuit components can be reduced and the circuit configuration can be simplified.

Embodiment 3 FIGS. 3 (a) and 3 (b) show another application embodiment corresponding to claim 4 of the present invention. In this embodiment, the rectifying circuit 11 in the first embodiment described above is used.
Instead, the flywheel diode incorporated in the inverter 2 is used to convert the alternating current received from the power system 4 into direct current to charge the capacitor C of the step-up chopper 3. That is, in the circuit of the inverter 2 shown in FIG. 2B, the flywheel diode FD is connected in parallel for each semiconductor switching element Tr that forms a three-phase bridge circuit with a thyristor, a power transistor (IGBT, etc.). Therefore, by using this flywheel diode FD as a three-phase full-wave rectification circuit of the initial charging circuit 10, the AC received from the power system 4 can be rectified to charge the capacitor C of the boost chopper 3. Charging circuit 10
The configuration of is simpler.

[0017]

As described above, according to the configuration of the present invention, before the start of the introduction of the reaction gas into the fuel cell at the time of start-up, the capacitor of the boost chopper combined with the preceding stage of the inverter is initially connected to the power system. It can be charged to a predetermined operating voltage through the charging circuit. Therefore, in the process of starting the reaction gas introduction at the time of starting the fuel cell and increasing the output voltage of the cell as in the conventional case, it is possible to prevent the inrush current due to the charging of the capacitor of the boost chopper, and the occurrence of gas shortage of the fuel cell due to this inrush current. It is possible to improve the reliability of the fuel cell by preventing damage such as characteristic deterioration due to the gas shortage.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an initial charging circuit corresponding to a first embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of an initial charging circuit corresponding to a second embodiment of the present invention.

3A and 3B are circuit configuration diagrams corresponding to a third embodiment of the present invention, in which FIG. 3A is a circuit diagram of an initial charging circuit, and FIG. 3B is a circuit diagram of an inverter in FIG.

FIG. 4 is a circuit diagram of a conventional power conversion device for a fuel cell power generator combined with a boost chopper.

5 is a time chart showing the relationship between the introduction of fuel gas and the change in cell output voltage, capacitor charging current, and charging voltage at the time of starting the fuel cell in FIG.

[Explanation of symbols]

 1 Fuel Cell 2 Inverter 3 Boost Chopper 4 Power System 8 Discharge Resistance 10 Initial Charging Circuit 11 Rectifier Circuit 12 Charging Switch 13 Charging Resistance C Boost Capacitor Capacitor FD Chopper Flywheel Diode

Claims (4)

[Claims] 1. A power converter for a fuel cell power generator that converts direct-current power generated by a fuel cell into commercial alternating-current power and supplies the power to a power system. The power converter is an inverter and a pre-stage of the inverter. In the combination with the connected boost chopper, the initial charge that charges the capacitor of the boost chopper circuit from the power system with the inverter stopped when the fuel cell starts up to charge the capacitor to a specified operating voltage. An electric power converter for a fuel cell power generator, comprising a circuit. 2. The power converter according to claim 1, wherein the initial charging circuit is connected between the rectifier circuit which is connected to the power system and converts the system voltage into a direct current, and the rectifier circuit and the capacitor of the step-up chopper. A power conversion device for a fuel cell power generator, comprising a combination of a charging resistor and a charging switch. 3. The power converter for a fuel cell power generator according to claim 2, wherein a discharge resistance of a capacitor of a boost chopper circuit is used as a charging resistance of an initial charging circuit. 4. The power converter for a fuel cell power generator according to claim 2, wherein a flywheel diode connected to a switching element of an inverter circuit is used as a rectifier circuit of an initial charging circuit. apparatus.