JPS60223436A - Method of operating fuel battery generator system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention converts the DC output of a fuel cell into AC using an inverter circuit, or a power conversion device consisting of a chopper circuit and an inverter circuit, and supplies power to a power system or a load. The present invention relates to a method of operating a fuel cell system that supplies fuel.

[Technical background of the invention]

Against the backdrop of the increasingly severe energy situation in recent years, fuel cell power generation systems can effectively utilize fossil fuel resources such as natural gas and coal, and achieve high power conversion efficiency.
Furthermore, since it has the advantage of producing less pollutants such as exhaust gas, ideas are being advanced for large-scale centralized power generation systems or medium-sized and small-scale decentralized power generation systems as replacements for thermal power plants. Incidentally, one characteristic of fuel cells is that voltage fluctuations are relatively large in response to changes in load. As shown in FIG. 1, the general discharge characteristics of a fuel cell are that as the current increases and as the load on the battery increases, the battery voltage decreases significantly. For example, in the case of a phosphoric acid fuel cell, the cell voltage at no load increases 1.4 to 1.6 times the voltage at rated load. Particularly, this voltage fluctuation is remarkable in the light load range of about 0 to 25-25. Therefore, since the direct current power generated from the fuel cell has limited uses as it is, it is generally used after converting it into a predetermined stabilized direct current voltage or alternating current power. In order to connect a fuel cell as a power generation system to an AC power system (hereinafter referred to as power system) or an AC load, a power converter that converts DC power to AC power is generally required. C: A power conversion device used in a fuel cell power generation system is required to have a system design that fully takes into account the battery characteristics shown in FIG.

[Problems with background technology]

However, when voltage fluctuations occur as shown in Figure 1, when designing power conversion equipment, increasing the withstand voltage of semiconductor elements in order to handle the entire wide range of voltage fluctuations forces the ratings of the parts used to be increased more than necessary. It had been. Therefore, in the case of , the capacity of the device is larger than necessary, and there are various problems in terms of cost and efficiency, and the output characteristics are also deteriorated. On the other hand, in a high voltage region near the no-load voltage for a fuel cell, a voltage difference occurs between the multiple layers of elements that make up the fuel cell, which promotes the melting of the catalyst that promotes chemical reactions, which is one of the elements. This has the disadvantage that the battery's useful life is compromised. These drawbacks increase as the capacity of the fuel cell power generation system increases, both in terms of cost and lifespan, and are one of the challenges of increasing capacity.

As a countermeasure to these shortcomings of fuel cells, it has been proposed to forcibly drop the fuel cell voltage by inserting a voltage suppression resistor into the DC circuit during light loads of the fuel cell system between 0 and 25%. . A block diagram of the fuel cell power generation system in this first case is shown in Figure 2.

In FIG. 2, reference numeral 1 denotes a fuel cell that directly outputs DC power by causing an electrochemical reaction between hydrogen obtained by reforming fuel such as natural gas or coal and oxygen in the atmosphere. 2
is a power converter that converts DC power to AC power,
This power converter 2 generally includes a DC breaker 4, an inverter 5, a transformer 6, and a switch 7 that opens and closes connection to a power system 8.
It is composed of etc. Further, 3 is a backflow prevention diode, 9 is a voltage suppressing resistor inserted in the DC circuit between the fuel cell and the power converter 2, and 10 is a switch for turning on/off the voltage suppressing resistor 9. . The voltage suppressing resistor 9 is used in the initial power generation state of the fuel cell 1, in the event of an accident in the power converter 2, or when the switch 7 is opened, that is, when the current value in FIG. 1 is in the range of 0 to 11. , the switch 10 is closed and operates to suppress the battery voltage E1 of the fuel cell 1 to a predetermined value or less.

During this voltage suppressing resistor 9 is turned on, the fuel cell 1 is generally
By rapidly flowing air into the air electrode, the output of the multi-fuel cell 1 is rapidly increased by C double; conversely, by rapidly suppressing the air, the output of the fuel cell 1 is rapidly reduced. Control takes place. However, according to the method shown in FIG. 2, all the power consumed by the voltage suppression resistor 9 during startup and shutdown becomes a loss and reduces the efficiency of the multi-fuel cell power generation system, and although the power-on time is short, As the resistance capacity, 20q6 or more of the system capacity is required, and the voltage suppression resistor 9 itself becomes large.

Further, such a fuel cell power generation system has a drawback in that it is difficult to perform a unit test of the converter 2 when the fuel cell 1 cannot be used.

That is, it requires a separate DC power supply device such as a rectifier as testing equipment, and it also has the drawback of requiring more time than necessary for maintenance and adjustment.

[Purpose of the Invention] The present invention stabilizes the power conversion device by suppressing the voltage of the fuel cell from increasing without impairing the power generated by the fuel cell at the time of starting/stopping the power conversion device 2 or an accident. It is an object of the present invention to provide a method for operating a fuel cell power generation system that can be operated in a timely manner and that can also perform a unit test of a power conversion device.

[Summary of the invention]

In order to achieve this object, the present invention has developed a fuel cell power generation system that uses a fuel cell as a DC power source to supply power to a power grid or load via an inverter circuit or a power conversion device consisting of a chopper circuit and an inverter circuit. In I:, the fuel cell is connected to another power converter capable of transmitting and receiving power from the power system, and when the fuel cell starts up or has low output, the other power converter operates as a forward converter, and the fuel cell When the power generation system is operating at an output higher than a predetermined value, other power converters are stopped or operated with reduced output, and if a power converter fails while the fuel cell power generation system is in operation, other power converters are The power converter is equipped with C2 to operate as an inverse converter.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

In FIG. 3C, parts with the same symbols as in FIG. 2 have the same functions. The difference from FIG. 2 is that the voltage suppression resistor 9 and the switch 10 are not included, and the power system 12 is separate from the power system 8, and the fuel cell 1 is connected to the power conversion device 11, which is separate from the power conversion device 2.
These points are connected by .

The power conversion device 11 includes a switch 13 for connecting and disconnecting the power to the power system 12, a transformer 14, a separately excited converter 15, and a polarity reversing circuit 16, and is connected to the DC output of the fuel cell 1. In this case, the power converter 11 is not limited to a separately-excited converter, but may be configured as a self-excited converter, and the intended point of the present invention remains the same.

Next, two operations of the present invention will be explained.

When starting up the fuel cell power generation system (second is the power converter 11
The polarity reversing circuit 16 of the switch is switched so that power can be supplied from the power system 12 to the DC circuit, and the switch 13 and the DC breaker 4 of the power converter 2 are turned on. This state f
In step 2, we start up the separately excited converter 15. For example, if the power converter 2 is configured with a voltage-type self-excited inverter, the DC input circuit is equipped with a capacitor (not shown), and the inrush of this capacitor It is necessary to suppress the current. For this purpose, the separately excited converter 15 of the power converter 11 is
The rectifier operates to gradually raise the DC voltage.

After confirming that the voltage has risen to the specified DC voltage, the inverter 5 is started, and the AC side switch 7 is turned on and connected to the power grid 8 to enter grid-connected operation and output the specified power. Supply to system 8. The power at this time is suppressed below the capacity of the power converter 11. Moreover, the power conversion device 1
The DC voltage when the rectifier No. 1 is in operation is set lower than the battery voltage at the rated output of the fuel cell shown in the vN1 diagram.

Next, fuel is supplied to the fuel cell 1, and the battery voltage of the fuel cell 1 is gradually raised. When the DC voltage value controlled by the power converter 11 is exceeded, the fuel cell 1 gradually supplies power to the power converter 2. C2 You will have to bear the burden.

Thereafter, when the fuel cell 1 is fully activated, the battery voltage of the fuel cell 1 reliably exceeds the DC voltage value controlled by the power converter 11, and all the power to the power converter 2 is borne. When this state is reached, the power converter 11 becomes unnecessary and is therefore stopped.

Furthermore, when the fuel cell power generation system is stopped, the power conversion device 11 is operated again for forward conversion to throttle the fuel in the fuel cell 1], and the DC voltage is kept constant until the generated power is suppressed, thereby stabilizing the power conversion device 2. be in proper operating condition. In addition, when an abnormality occurs in the power system 8 or the power converter 2 and it becomes necessary to stop the power converter 2 during operation of the fuel cell power generation system, the power converter 2 is controlled to reduce the power generated by the fuel cell, and the power converter 11, the fuel cell 1 is operated to supply the generated power to the power grid 12. That is, in the event of an accident in the power converter 2, the polarity reversing circuit 16 of the power converter 11 is switched so that power can be supplied from the DC circuit to the power grid 12, and the separately excited converter 15 is caused to perform a reverse conversion operation. Power converter device 2 converts generated power into multi-fuel cell 10
Power can be transferred so that power that was being supplied to the power grid 8 via the power converter 11 is now supplied to the power grid 12 via the power conversion device 11.

Furthermore, by providing the power converter 11, it is possible to use it as a power source for testing the stain force converter 2), the power converter 2 can be easily maintained, and the repair time in the event of an accident can be reduced. can also be shortened.

In addition to the power conversion device 2 for constantly converting the electromotive force of the fuel cell 1 into AC power, other power conversion devices capable of transmitting and receiving power to and from the power grid 12 are connected to the fuel cell 1. By doing so, the fuel cell power generation system can be operated accurately even during startup and shutdown processes where the fuel cell 1 does not have sufficient electromotive force, and in the event of an accident or failure of the power converter 2. Even in the event of a power failure in the power system 8, overvoltage to the fuel cell 1 can be prevented, and voltage ratings can be appropriately selected when selecting main circuit components of the power converter 2.

Next, other embodiments of the present invention will be described. In the embodiment shown in FIG. 3, the power conversion device 2 has been described as a self-excited inverter, but the same effect can be obtained by using an opposite-side inverter. Further, the present invention can also be applied to a power conversion device 2 in which a chopper circuit is arranged on the DC input side and combined with an inverter circuit. Moreover, it goes without saying that the same effect can be obtained even if the power converter 11 is a self-excited power converter that has a control function that allows it to exchange power with the power grid.

In the embodiment shown in FIG. 3, the power conversion device 1 is
1 is stopped, but by controlling the power consumption to be suppressed without stopping the power converter 1 and allowing the power converter 2 to continue operating, power can be quickly transferred when an accident occurs in the power converter 2.

Furthermore, the power system 8 and the power system 12 may be completely the same. In addition, in order to suppress the voltage rise of the fuel cell 1 to below a predetermined value, it is generally sufficient to have a power loss of 30% in addition to the capacity of the fuel cell power generation system, that is, the rated capacity of the power converter 2. The rated capacity of No. 11 may be selected by adding the rated capacity of the power converter 2 to 30 clb+.

〔Effect of the invention〕

According to the present invention, in addition to a commonly used power conversion device for constantly converting the electromotive force of a fuel cell into alternating current power, another power conversion device capable of transmitting and receiving power to and from the power grid is connected to the fuel cell. This makes the fuel cell unstable at low output. When starting or stopping, other power converters are operated in a forward-converting manner so that transient fluctuations in the fuel cell are absorbed by the other power converters, thereby making it possible to start or stop the fuel cell stably. In addition, even when the fuel cell is operating at its rated output and there is an abnormality in the power converter or power system,
By inverting other power conversion devices and supplying fuel cell power to the power grid, the electromotive force of the fuel cell can be wasted and overvoltage of the fuel cell can be suppressed. can.

A fuel cell power generation system equipped with such other power conversion devices suppresses voltage jumps and prevents overvoltage damage to the fuel cell without installing an overvoltage suppression resistor that causes unnecessary power loss. By reducing the voltage duty of the commonly used power converter, the capacity of the device can be reduced, and a safe and economical fuel cell power generation system can be constructed. In addition, the test DC power source for the power converter, which is commonly used as a power generation facility, is built in-house, reducing the time spent on maintenance and adjustment.

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram of cell voltage versus current of a fuel cell, Fig. 2 is a block diagram of a conventional fuel cell power generation system, and Fig. 3 is a block diagram of a fuel cell power generation system showing an embodiment of the present invention. . 1... Fuel cell 2... Power converter 3... Backflow prevention diode 4... DC breaker 5... Inverter 6114.
...Transformer 7,13...Switch 8.12...Power system 9...Overvoltage suppression resistor lO...Switch 1
1... Power converter 15... Separately excited converter 16.
・Polarity reversal circuit (7317) Representative Patent Attorney Kensuke Norichika (and 1 other person) Figure 1 Ship's current 1 (-1 Figure 2 Figure 3 ゛//

Claims (2)

[Claims] (1) In a fuel cell power generation system that uses a fuel cell as a DC power source and supplies power to a power system or load via an inverter circuit or a commonly used power conversion device consisting of a chopper circuit and an inverter circuit, the fuel cell receives the power from the fuel cell. A fuel cell power generation system in which another power conversion device capable of transmitting and receiving power is connected to a power grid or another power system, and the other power conversion device is operated as a forward converter when the fuel cell starts up or when the output is low. When the power converter is operating at an output higher than a predetermined value, the other power converter is stopped or the output power is suppressed and the power converter is operated in good condition, and if the regular power converter fails while the fuel cell power generation system is in operation, I: A method of operating a fuel cell power generation system, comprising operating the other power converter as an inverter. (2) Operation of the fuel cell power generation system according to claim 1, characterized in that the required capacity of the other power converter is an addition of 30% to the required capacity of the commonly used power converter. Method.