JPH06283187A - Fuel cell power generation system and operation thereof - Google Patents

Abstract

PURPOSE:To restrict increase in the interpole differential pressure in a fuel cell at the time of cutting off in a fuel cell power generation plant. CONSTITUTION:A capacity type load 10 for accumulating the superfluous gas energy in a fuel cell 1 at the time of cutting off the fuel cell as electric energy, and an external resistance circuit 13 for consuming the energy accumulated in the capacity type load 10 are provided between a d.c. circuit breaker 6 for cutting off the circuit between the fuel cell 1 and an external electric circuit and a d.c. circuit breaker 7 provided on the input circuit of an inverter 8. Energy can be drawn by a required amount when required and can be utilized effectively by accumulating the superfluous gas energy in the fuel cell at the time of cutting off the fuel cell as electric energy in an external electric element. Bad effect is not given externally, while increase in the interpole differential pressure of the fuel cell can be restricted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power generation system and a method of operating the same, and more particularly, when an energy imbalance occurs between a process flow other than an electric system and an electric system process in a fuel cell power plant. The present invention relates to a fuel cell power generation system and an operating method thereof capable of suppressing an increase in differential pressure between cell electrodes that occurs without causing a transient shock.

[0002]

2. Description of the Related Art In a fuel cell plant in which a DC output of a fuel cell is converted into an AC output by an inverter, when an abnormality occurs in an external line system such as a power transmission system, the inverter circuit is first opened, and then continued. In general, the valves of the process system of the fuel cell are shut off or the load is narrowed down. However, since the shutoff operation of the valve itself generally takes time in seconds, the battery tries to continue the power generation reaction until the shutoff valve is closed after the electric circuit is opened. However, electricity as a product loses its destination due to the open circuit of the electric circuit, and the battery has a high voltage value as the open circuit voltage with no load, and the actual power generation reaction is blocked. As a result, the flow rate balance of fuel gas or the like as a reaction group is lost in each electrode of the battery. At this time, as is apparent from the chemical reaction formula, the gas mole fraction at the pole portion is changed, so that the pressure at the pole portion fluctuates, and as a result, the differential pressure between the electrodes increases. This causes many inconveniences such as impairing the mechanical strength of the battery.

In a fuel cell power plant in which a DC output of a fuel cell is converted into an AC output by an inverter, a conventional fuel cell is used as a method for eliminating the energy imbalance between the cell mechanical system and the cell electrical system. Between the inverter and the inverter, a dummy resistor that can be turned on and off via a switch for the purpose of keeping the input voltage of the inverter below a predetermined value is used. The dummy resistor is used to electrically consume the surplus gas of the fuel cell that accompanies the shutdown, thereby reducing the differential pressure between the electrodes. Has been proposed (Japanese Patent Publication No. 63-411).
93, etc.).

[0004]

When an energy imbalance between the mechanical system and the electrical system occurs in the fuel cell power plant, the energy release to the external system is consumed at once by the resistor as described above. It is thought that the method of reducing the differential pressure between the electrodes by means of the method works effectively without causing any particular problems when the scale of the power generation plant is relatively small, but when the capacity of the plant increases, the resistance The calorific value of the vessel becomes non-negligible, and radiating it to the external system in a short time causes not only thermal loss but also disaster prevention. In other words, it is an uncontrolled emission of energy to the external system and waste of electric power, which may cause a rapid thermal shock to the surroundings of the power plant and, in some cases, cause a large temperature change. There is.

An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art, and more specifically, a fuel cell plant in which a DC output of a fuel cell is converted into an AC output by an inverter. In order to obtain a fuel cell power generation system and an operating method thereof, which can suppress an increase in the inter-electrode differential pressure of the fuel cell at the time of device shutdown due to an abnormality or the like, in a state in which the impact on the external system is minimized. It is an object.

[0006]

The present invention basically provides an energy buffer mechanism between a fuel cell and an electric system after the inverter, and gradually releases buffered energy in an external resistance circuit. Solve problems and achieve objectives. That is, a capacitive load (for example, a capacitor) having a predetermined capacity or an inductive load (for example, a coil) having a predetermined inductance is arranged in parallel between the fuel cell and the inverter, and the deviation between the DC output of the cell and the AC output of the inverter is set. After storing a part or all of them as electrostatic energy or magnetic energy in those loads, it is gradually released to the outside process system so that the transient impact on the mechanical system and thermal system is mitigated. To do.

That is, according to the present invention, in a fuel cell power generation system having a fuel cell and an inverter for converting a DC output of the fuel cell into an AC output, a gas cutoff valve used for at least the fuel cell is provided between the fuel cell and the inverter. A capacitive load or an inductive load having a capacity capable of storing the energy due to the reaction of the surplus gas due to the time required for the shutoff operation in the form of electric energy or magnetic energy is arranged in parallel with the inverter as viewed from the fuel cell, Further, a switch for turning on / off the capacitive load or the inductive load is provided, and it is possible to store the electric energy in the capacitive load or the magnetic energy in the inductive load by operating the switch. Disclosed is a fuel cell power generation system.

The energy stored in the capacitive load or the inductive load is gradually consumed by an internal resistance of the circuit itself or an external resistance circuit provided separately. As such an external resistance circuit, a part of a display circuit provided for monitoring the fuel cell power generation system or a cooling circuit of an auxiliary machine can be effectively used. Further, the capacitive load or the inductive load may be a single element or a composite element.

The present invention is also the above-mentioned method for operating a fuel cell power generation system, wherein the timing of turning on the capacitive load or the inductive load is such that the gas shutoff valve is shut off during an emergency stop during operation of the fuel cell. Also disclosed is a method of operating the above fuel cell power generation system, which is linked with a command or when an open circuit occurs when an abnormality occurs in an external line system after the inverter while the power plant is operating, and the open circuit is generated.

[0010]

In the fuel cell power generation system and the method of operating the same according to the present invention, the above-described dynamic pole phenomenon of the cell, that is, a pole accompanied by a change in the gas mole fraction of the pole due to the closing delay of the shutoff valve. In contrast to the phenomenon that the pressure difference between the electrodes increases as a result of the fluctuation of the internal pressure, which causes unnecessary mechanical stress inside the battery, the operation of the switch that turns on the load circuit is very short. Since it can be performed in time, it can be considered that it is almost equivalent to the fact that the electric load is not interrupted when viewed from the battery. Therefore, as a result, the rise in the differential pressure between the electrodes of the battery is suppressed, and it becomes possible to perform the function of the mechanical protection operation of the battery, and at the same time, the capacitive load or inductive load is used as a buffer, so that the thermal load is reduced. The transient impact on the system can be mitigated.

[0011]

1 and 2 show an embodiment of a fuel cell power generation system to which the present invention is applied. In FIG. 1, a fuel gas a from a fuel gas inlet valve 2 and a fuel gas b from a fuel gas inlet valve 3 are sent to a fuel cell 1 to generate electricity by a chemical reaction.
The power generation output is guided to the electric circuit connected to the electrode of the fuel cell 1. Unreacted fuel gas and reaction products are discharged to the outside of the fuel cell 1 from the fuel gas outlet valve 4, and similarly, the fuel gas b is discharged from the fuel gas outlet valve 5 after the electrode reaction. On the other hand, the power output of the fuel cell 1 is converted into AC power by closing the DC circuit breaker 6 and then closing the DC circuit breaker 7 to drive the inverter 8. The electric power is supplied to an external electric load (not shown) through the container 9.

When a short-circuit accident or the like occurs in the external electric circuit, the fuel cell power generation system is disconnected from the external electric circuit and power generation is stopped. When stopping the fuel cell power generation system, the fuel gas inlet valves 2 and 3 and the fuel gas outlet valves 4 and 5 are mechanically closed to stop the chemical reaction of the fuel cell 1 and the direct current circuit breaker 7 is opened. The inverter 8 is stopped and the DC circuit breaker 6 is opened. Here, the electric circuit instantaneously cuts off the current due to the stop of the inverter 8 or the like, but there is a slight time delay in the cutoff of the fuel cell process system system because the cutoff valve is a mechanical operation. Then, the pressure difference between the electrodes in the fuel cell 1 temporarily rises. This inter-electrode differential pressure leads to mechanical damage to the fuel cell 1, which is not preferable.

Therefore, as a means for suppressing the rise in the inter-electrode differential pressure as much as possible, the fuel cell 1 is installed in the electric circuit of the fuel cell.
In view of this, a capacitor 10 as a capacitive load is connected in parallel with the inverter 8 to extract and consume excess gas in the fuel cell 1 as electric energy due to the time delay between the opening of the electric circuit and the cutoff of the shutoff valve. . Specifically, at the same time when the operation is stopped, that is, the fuel gas inlet valve 2,
3. The switch 11 of the capacitor 10 is connected to the contact 11 to the inverter side by interlocking with the transmission of the valve shutoff command to the fuel gas outlet valves 4, 5, or interlocking with the opening of the external electric circuit.
The contact is switched from the side a to the side of the capacitor 11b, the DC breaker 7 is opened, and the inverter 8 is stopped. Switching of this switch is an electrical operation and is instantaneously performed. Since the DC circuit breaker 6 remains closed at this time, the energy due to the reaction of the surplus gas accumulated in the fuel cell 1 is stored in the capacitor 10 as electric energy until the respective shutoff valves are closed. .

Next, the voltage on the fuel cell 1 side and the capacitor 1
The DC circuit breaker 6 is opened when the 0-side voltage has settled down to a substantially constant value, and the switch 12 is closed at an appropriate time. As a result, the electric energy stored in the capacitor 10 is gradually consumed by the external resistor 13. The capacity of the condenser 10 is at least the energy due to the expected reaction of the surplus gas in the fuel cell 1, that is, each valve 2, 3, 4,
It is desirable that the energy due to the reaction of the excess gas caused by the delay time of the valve shutoff operation of No. 5 and the like be set as the capacity that can be stored as electrostatic energy. In practice, it is recommended that the optimum capacity be determined in consideration of external conditions such as a limit value for strength against excessive voltage difference between battery electrodes, space saving, and a manufacturable range of the element.

FIG. 2 shows another embodiment of the fuel cell system according to the present invention, in which a capacitor 14 and a switch 15 are further connected in parallel with the capacitor 10. The load capacity at this time may be half of the capacity of the capacitor 10 described in FIG. The electric energy stored in the capacitor 14 first closes the switch 12 and the external resistance 13
Then, the electric energy stored in the capacitor 10 is gradually consumed by the external resistor 13 by closing the switch 15.

FIG. 3 shows another embodiment of the fuel cell system according to the present invention. In this example, a coil 3 is used instead of the capacitor 10 in the system described in FIG.
0 is used. That is, the required amount of electric energy generated by the reaction of the excess gas due to the time required for the shutoff operation of the gas shutoff valve can be stored in the coil 30 in the form of magnetic energy rather than as electrostatic energy.

Also in this system, when a short-circuit accident or the like occurs in the external electric circuit, the fuel cell system is disconnected from the external electric circuit and power generation is stopped.
The same operation is performed. At that time, the energy due to the reaction of the excess gas is stored in the coil 30 as magnetic energy. After the operation of the shutoff valve of the fuel cell is completed, when the charge amount to the coil 30 has also settled down to a constant level, the DC circuit breaker 6 is circuited as in the system of FIG. 1, and the switch 12 is closed at an appropriate time. The following operations are performed in the same manner as in the system of FIG. The capacity of the coil 30 can be determined under the same conditions as the capacity of the capacitor 10 is determined.

In each of the above-mentioned aspects, the capacitive load and the inductive load may be constituted by a single unit or plural units. Further, the external resistance 13 may be a pure resistance or a resistance including an inductive component. The external resistance circuit may be a solenoid valve drive source on the purge gas piping of the power plant of the fuel cell power generation system or a display power supply circuit to the central panel / monitor panel, and it may also be a cooling fan to promote heat dissipation. May be. It is also effective to use it as a DC power supply for a DC power supply load that operates in a short time in case of emergency. In a special case such as when the capacity of the power generation system is relatively small, the energy stored in the load may be consumed by its own internal circuit resistance without providing an external resistance circuit.

Although the embodiment of the basic operation of the present invention has been described above, the advantage of the present invention is supported by the fact that the energy loss due to transient resistance consumption in the charge / discharge characteristics centering on the capacitor is demonstrated. Explain the tendency.
FIG. 4 shows an example of the R-C circuit in FIG. 1 and shows what kind of tendency the energy at the time of charging / discharging generally has according to the value of C. The solid line in the figure is the capacitor charging energy, and the solid line is the total energy consumption in the RC circuit through the charging and discharging of the capacitor.
Is the corresponding energy when a plurality of circuit elements are arranged in parallel. It should be noted that this tendency is under certain conditions, such as assuming that the battery characteristic is a constant voltage source and setting the resistance value of the circuit arbitrarily. The electrostatic energy of the capacitor (charging) for the line that estimates a lot of possible energy is
It is shown that a sufficient value can be accumulated as a relative value.

That is, the capacitance C of the selected capacitor
In contrast to (line), it is shown that the electrostatic energy corresponding to line segment A can be discharged (heat radiation) over a sufficient time by circuit resistance (R + R '), and line segment B
It is possible to design to minimize the heat generation by the charging resistance (R ') corresponding to, and the contribution of the increase in the battery electrode differential pressure for the energy corresponding to the line segment C (A + B + C)
It is shown that it is possible to keep the value relatively small.

[0021]

According to the present invention, when the shut-off valve is fully closed when shutting down the process system of the fuel cell, the surplus gas capable of chemically reacting and accumulated in the cell increases the inter-electrode differential pressure in the fuel cell. It can be suppressed, and the energy from the surplus gas is extracted as electric energy or magnetic energy, which is stored electrically or magnetically separately from the mechanical system of the fuel cell, so that it can be controlled for a relatively long time. The accumulated energy can be taken out and used effectively. As a result, it is possible to avoid a situation where energy is simply and unnecessarily released as heat as in the case where the resistance is consumed in a short time, resulting in a sudden rise in the ambient temperature as in the conventional case.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a fuel cell power generation system that stores excess gas energy in a fuel cell in one capacitive load.

FIG. 2 is a schematic configuration diagram of a fuel cell power generation system in which surplus gas energy in the fuel cell is stored in two capacitive loads.

FIG. 3 is a schematic configuration diagram of a fuel cell power generation system that stores excess gas energy in the fuel cell in an inductive load.

FIG. 4 is a diagram showing a capacity characteristic of energy during charging / discharging in an RC circuit.

[Explanation of symbols]

1 ... Fuel cell, 2, 3, 4, 5 ... Valve, 8 ... Inverter,
10 ... Capacitive load (capacitor), 13 ... External resistance, 3
0 ... Inductive load (coil)

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Shoji Takahashi 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Tadashi Takashima 3-chome, Saiwaicho, Hitachi-shi, Ibaraki No. 1 Stock Company, Hitachi, Ltd., Hitachi Plant (72) Inventor, Nobuhiro Kiyoki, No. 502, Kandachi-cho, Tsuchiura, Ibaraki Prefecture

Claims (8)

[Claims] 1. A fuel cell power generation system having a fuel cell and an inverter for converting a DC output of the fuel cell into an AC output, and at least a shutoff operation of a gas shutoff valve used in the fuel cell between the fuel cell and the inverter. A capacitive load having a capacity capable of storing the required amount of electric energy generated by the reaction of the surplus gas due to the required time in the form of electrostatic energy is arranged in parallel with the inverter as seen from the fuel cell, and the capacitive load is further provided. 2. A fuel cell power generation system, comprising: a switch for switching on and off, and enabling the electrostatic energy to be stored in a capacitive load by operating the switch. 2. In a fuel cell power generation system having a fuel cell and an inverter for converting a DC output of the fuel cell into an AC output, at least a shutoff operation of a gas shutoff valve used in the fuel cell is provided between the fuel cell and the inverter. An inductive load having a capacity capable of storing the required amount of electric energy generated by the reaction of the surplus gas due to the required time in the form of magnetic energy is arranged in parallel with the inverter as viewed from the fuel cell, and the inductive load A fuel cell power generation system having an on / off switch, wherein the magnetic energy can be stored in an inductive load by operating the switch. 3. The fuel cell power generation system according to claim 1, further comprising an external resistance circuit for gradually consuming the energy stored in the capacitive load or the inductive load. 4. The fuel cell power generation system according to claim 3, wherein the external resistance circuit is a part of a display circuit or a part of an auxiliary circuit provided for monitoring the fuel cell power generation system. system. 5. The fuel cell power generation system according to claim 4, wherein a cooling fan is used as an auxiliary machine of the auxiliary machine circuit in order to prevent a temperature rise due to heat generation in the external resistance circuit or the like. 6. The capacitive load or the inductive load is
The fuel cell power generation system according to claim 1 or 2, wherein the fuel cell power generation system is configured by a single element or a composite element. 7. The method according to any one of claims 1 to 6, wherein the timing of inputting the capacitive load or the inductive load is linked with a shutoff command of the gas shutoff valve at the time of an emergency stop of the fuel cell during operation of the power plant. The method for operating the fuel cell power generation system according to any one of the above. 8. The method according to any one of claims 1 to 6, wherein the timing of inputting to the capacitive load or the inductive load is linked to the occurrence of an open circuit due to an external line system abnormality after the inverter during operation of the power plant. A method for operating the described fuel cell power generation system.