JPS5913152B2 - How to start a fuel cell power generation system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for starting a thermal power generation system that supplies power from a fuel cell to an AC system via an inverter.

FIG. 1 shows the basic configuration of this type of fuel cell power generation system.

The fuel cell 1 is schematically shown here as a fuel cell of the type that uses hydrogen gas as the fuel gas and air as the oxidant gas. An inverter 2 is connected between the positive and negative terminals of the fuel cell via a DC reactor 20.
An AC output terminal of this inverter 2 is connected to an AC system 3 via a transformer 30. The inverter 2 can be configured as a separately excited inverter including, for example, three-phase bridge-connected thyristors. The control advance angle β of this inverter is controlled by a current regulator 21 that functions to match, for example, the DC current Id with a target value Id.The target value Id is controlled by a potentiometer or a power regulator (not shown). The output signal of the regulator 21 that determines the control advance angle β is the maximum control advance angle βm steep x determined in the inverse conversion operation region and the minimum control determined according to the inverse conversion operation commutation limit. The control advance angle is limited to be changed only between the advance angle β and the lead angle β.The system voltage on the DC side of the inverter 2 is
appears as a DC reverse voltage E2 opposing the fuel cell 1
A direct current 11 is caused to flow due to the voltage difference E1-E2 between the inverter and the inverter.

Inverter DC reverse voltage E2 is in'S■, control advance angle β
It is a function of , and the smaller the control advance angle β', the larger the b value. In a typical separately-excited inverter, the control and advance angle β is started from the maximum value '1 and then gradually increased at the time of startup, thereby controlling the rising speed of the DC current. A so-called soft start is being performed. In order to enable a soft start,
Maximum possible reverse voltage of inverter 2 (E when β = βi
2) is required to be larger than the no-load voltage of the fuel cell 1 (the value of E1 when Id=0). However,
The fuel cell 1 has a drooping characteristic and the fuel cell voltage under rated load drops considerably compared to the no-load voltage value. If you choose the voltage value on the AC side of the inverter so that it can produce an inverter DC reverse voltage that can counter the
At the operating point where the rated current is given, the control advance angle β becomes considerably large. Since the control advance angle β corresponds to the inverter's operating power factor, an increase in the control advance angle β means that the inverter's operating power factor becomes worse and the inverter's inert power generated in the AC system increases. It means that. In order to avoid this inconvenience, if the voltage value on the AC side of the inverter is selected so that the inverter operating power factor at rated load is good, the inverter can generate a DC reverse voltage that can sufficiently counter the no-load voltage of the fuel cell. As a result, soft start becomes impossible and current inrush occurs at startup. Therefore, various methods have been studied in order to satisfy both soft start and good inverter power ratio at rated load.

One method is to switch the voltage value on the AC side of the inverter according to the load condition, thereby making soft start possible and at the same time maintaining a good inverter operating power factor over the entire range from no load to rated load. be. However, in order to carry out this method, a very expensive transformer with an on-load tap changer must be used as the transformer 30. In addition, by inserting a thyristor chopper and a voltage smoothing filter into the DC circuit between the fuel cell and the inverter, even if the fuel cell voltage changes depending on the load, a smoothed voltage that remains constant is maintained as a direct current. A method of applying power to the imperter 2 via the reactor 20 has also been considered. However, this method also has the disadvantage of requiring expensive additional equipment. Furthermore, there is a method of starting while limiting the current by inserting a starting resistor consisting of multiple resistors into a DC current generator and short-circuiting those resistors one after another, or a method of starting while limiting the current. Consideration has been given to a method of starting the engine while minimizing fluctuations in the fuel cell voltage by connecting a dummy load to the fuel cell to lower the fuel cell voltage and sequentially disconnecting the resistors. However, these methods also require the provision of a resistor group and a switching device for sequentially shorting or opening them, which requires considerable expense and has the disadvantage of requiring large-scale additional equipment. In view of the above, an object of the present invention is to provide a small-scale, inexpensive additional device, or without any special additional device, without sacrificing the inverter operating power factor at rated load. The object of the present invention is to provide a method that enables smooth startup.

This object is achieved according to the invention by a starting method comprising the features specified in the claims.

What is important in the startup method according to the present invention is to first start supplying the reactant gas to at least one of the gas chambers in the fuel cell while the gas chamber is placed in an inert gas atmosphere.

As a result, the fuel cell voltage starts from zero or a low value and gradually increases as the inert gas concentration decreases due to the supply of the corresponding reactant gas. Nitrogen gas can be used as the inert gas. The gas chamber filled with inert gas can be both an oxidizer gas chamber and a fuel gas chamber, but either one is sufficient, especially if an external inert gas supply is provided. The amount of inert gas required each time is small. The inert gas source added to create the inert gas atmosphere can not only be small and inexpensive compared to the additional equipment required in traditional solutions, but also A special inert gas source can be omitted. That is, if an inert gas source is installed, for example, to inject inert gas into the fuel gas chamber at the time of an emergency stop in order to enable an emergency stop of the fuel cell, this can be used. Furthermore, in the case of fuel cells that use air as the oxidant gas, if the shutdown is performed by cutting off the air supply, only the oxygen in the air in the gas chamber will be discharged after the air supply is cut off. Since the inert gas is consumed by and remains in the gas chamber,
When starting the engine next time, there is no need to supply inert gas from outside. Therefore, in this case it is sufficient to have a small nitrogen cylinder available for initial startup or just in case. However, if there is a suitable load that can be directly connected to the fuel cell, if the load is connected and the fuel cell is pre-operated with the air supply cut off, the oxidizer gas chamber will be in an inert gas atmosphere. It can be done. Therefore, the starting method according to the present invention can be carried out without an inert gas source by disconnecting the load as necessary and then proceeding to normal operation using the inverter. Another important point in the starting method according to the present invention is that immediately after the start of supply of inverter control pulses, the fuel cell voltage E1 changes from the inverter DC reverse voltage E2 generated at this time.
The start of the supply of the inverter control pulses must not be delayed so much that it essentially undermines the current flow, ie, an unacceptable current inrush occurs. If the value of the inverter control advance angle β at the time of starting the supply of inverter control pulses is determined, the control pulses are supplied to the inverter as soon as the fuel cell voltage exceeds the value of the corresponding inverter DC reverse voltage. Ideally, start. However, for this purpose, it is necessary to monitor the fuel cell voltage, which is troublesome, and even if the supply of control pulses to the inverter is started at the same time as the supply of reactant gas (for example, air) to the fuel cell, there will be no problem. does not occur, so this is sufficient. In this case, when the fuel current voltage rises to a value corresponding to the inverter DC reverse voltage corresponding to the inverter control advance angle, the DC current 1d starts flowing. FIG. 2 shows an example of the time course of voltage E1 and direct current 1d of an air-hydrogen fuel cell in an experimental example conducted by the present inventors.

The inverter 2 is controlled by the current regulator 2 as shown in FIG.
Constant current control is based on 1, and a constant value 2 is set as the target value 1d*.
0A was set. The oxidant gas chamber of the fuel cell 1 was placed in a nitrogen atmosphere and a command was given to start the air supply and the inverter-controlled pulse supply at time t=o. At a time t1 delayed from this time, the fuel cell voltage E1 begins to rise. At this time, the output signal of the regulator 21 is the maximum control advance angle βMax(
(set to about 80 degrees).
As soon as the fuel cell voltage E1 exceeds the inverter DC reverse voltage E2 (time T2), the DC current 1d starts to rise.
Then, the DC current 1d increases as the fuel cell voltage E1 increases, and at time T3, the target value 1d*=
It reaches 20A. From this point on, the constant current control loop by the current regulator 21 works, and as the fuel cell voltage E1 increases, the control advance angle β, which had been stuck at the maximum control advance angle βMax, shifts toward the minimum control advance angle βi. Moving on. Time T4 - The gas condition in the CWilating agent gas reaches a steady state and the start-up process is completed. In this state, the control advance angle β is small and the inverter is operated with a good power factor. As described above, according to the starting method according to the present invention, it is only necessary to prepare a small-scale inert gas source as an additional device necessary to start the fuel cell power generation system, or as an inert gas source. A considerable additional amount can be added by reusing equipment already provided for other purposes, or by creating an inert gas atmosphere by supplying air during shutdown, cutting off the air supply, or pre-operating with an appropriate load. No equipment required.

[Brief explanation of the drawing]

FIG. 1 shows the basic configuration of a fuel cell power generation system, and FIG. 2 shows an example of the time course of the fuel cell voltage and direct current when started by the method according to the present invention. 1...Fuel cell, 2...Inverter,
3...AC system, 21...Current regulator, E1...Fuel cell voltage, Id...DC current.

Claims (1)

[Claims] 1. In a fuel cell power generation system that supplies power from a fuel cell to an AC system via an inverter, supply of reactant gas to the gas chamber is started with at least one gas chamber in the fuel cell in an inert gas atmosphere. By doing so, the fuel cell voltage is gradually raised, and the control pulse supply to the inverter is started before the fuel cell voltage substantially exceeds the value equivalent to the inverter DC reverse voltage that appears immediately after the control pulse supply starts. A method for starting a fuel cell power generation system characterized by: