JPS6046782B2 - Fuel cell voltage regulator - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] The present invention relates to a voltage regulator for a fuel cell, and in particular to a voltage regulating device for a fuel cell that is combined with a passive inverter to perform parallel operation with an AC system to configure a fuel cell power generation system. The present invention relates to a battery voltage regulator.

[Prior art and its problems] When supplying power to an AC system from a fuel power generation system consisting of a fuel cell and a passive inverter, the following is required based on the voltage-current characteristics of the fuel cell and the control characteristics of the inverter. There are issues to be solved.

That is, the voltage-current characteristic curve m of the fuel cell is as shown in FIG. 1, while the voltage-current characteristic curve 1 of the inverter is illustrated as 1, 10, 1, in FIG. The control angle (control advance angle) β is changed as a parameter. In this case, the intersection of curve m and curve 1 provides a common steady-state operating point for the fuel cell and the passive inverter. Therefore, the inverter current Id can be controlled by the control angle β. However, cos β corresponds to the power factor of the inverter, so if the control angle β is increased in order to increase the inverter current Id, the power factor deteriorates, and the inverter requires a large amount of reactive power from the AC system. The above problem is to eliminate the negative impact on the grid caused by this reactive power and to suppress the rush current when starting the inverter. In passive inverters, a minimum value βMin is set for the control angle β to ensure safe commutation, but β
Let us first consider the case where the voltage-current characteristic curve of a separately excited inverter under the condition of = βMin is designed to be, for example, curve 11 in Figure 1 or a curve at a level above this. Make it. In this case, by gradually increasing the control angle β n when starting the inverter, the inverter current 1d can be adjusted from 0 to the rated value 1.0 [P.
Since UJ can be raised smoothly, no problem regarding inrush current occurs. However, in order to obtain the characteristic curve 13 in the constant operation range (Id″.1.0 [P.U.] after startup is complete), the control angle β must be made considerably large, and the inverter has a large effect on the AC system. In order to solve this problem, conventionally, the output transformer of a separately excited inverter is equipped with an on-load tap changer, so that the inverter AC voltage is gradually reduced as the current increases. A method has been considered in which the control angle β does not need to be increased by performing tap switching.In addition, under the condition of β = βMin, the voltage-current characteristic curve of the separately excited inverter becomes the curve shown in Fig. 1. 13, instead of maintaining a high power factor in the constant operating range, the current suddenly increases due to the large difference between the fuel cell output voltage and the inverter DC reverse voltage at startup, resulting in overshoot. Conventionally, a resistor for suppressing inrush current is inserted between the fuel cell and the inverter at startup, and the value of this resistor is decreased as the output current increases. However, in the case of the conventional method mentioned above,
In order to suppress the inrush current when starting the inverter and to enable the inverter to operate at a high power factor in the constant operation range, a transformer with an on-load tap changer or a variable resistor for inrush current suppression is required. It requires expensive and large-scale additional equipment such as containers.

As a result of various studies on other methods that simultaneously satisfy inrush current suppression at the time of inverter startup and high power factor operation of the inverter, the inventors of the present invention found that the inverter control characteristic curve 1
We have found a method to start the inverter while suppressing inrush current by changing the voltage-current characteristic curve m of the fuel cell while keeping the changes within a range that guarantees high power factor operation of the inverter.

In other words, by keeping the inverter control angle β at a small value, for example βMin, when starting the inverter and adjusting the voltage of the fuel cell itself, the inverter can be started while suppressing inrush current, and the inverter can also operate at a high power factor. That is something that can be guaranteed. [Object of the Invention] An object of the present invention is to provide a voltage regulator that can provide a voltage control function to a fuel cell using as simple and inexpensive means as possible.

SUMMARY OF THE INVENTION The gas supplied to a fuel cell typically contains some impure gas (eg, inert nitrogen).

In particular, when air is used as the oxidant gas, nearly 80% of the total amount is inert nitrogen (N2). For this reason, in order to prevent inert gas from accumulating in the gas chamber within the fuel cell during operation of the fuel cell, some gas is always purged to the outside. The present invention connects the inlet and outlet of a fuel cell with a return pipe, and provides a fan in a pipe other than the return pipe in a reaction gas circulation path formed by the return pipe and a reaction gas chamber. By providing a flow rate adjustment means on the discharge pipe other than the circulation route on the outlet side of the
This is characterized in that the output voltage of the battery is adjusted by changing the inert gas concentration within the battery while keeping the amount of gas supplied into the battery constant. In other words, if the purge gas flow rate is reduced, the exhaust gas is supplied to the battery again through the gas return pipe, which increases the inert gas concentration within the battery and decreases the oxygen concentration.As a result, the voltage of the fuel cell decreases, and the purge gas Increasing the flow rate will do the opposite. The voltage regulator according to the present invention, which changes the inert gas concentration in the cell by adjusting the flow rate of purge gas, is suitable for adjusting the purge gas flow rate of air in fuel cells that use air as an oxidant gas. However, it is also applicable to fuel cells that use oxygen gas as an oxidant gas, and can be applied not only to the oxidant gas side but also to the fuel gas side.

This is because inert gas is not limited to air, but is also generally included in oxygen and hydrogen gas. The voltage of the fuel cell can also be adjusted by mixing hydrogen gas and inert gas and supplying the mixture to the fuel gas chamber and adjusting the mixing ratio. Requires a gas source and its delivery system.

On the other hand, in the case of the present invention, the concentration of inert gas in the cell is reduced by mixing a part of the pannizi gas with the supply gas by using the inert gas contained in the oxidizing gas or fuel gas. The method is to adjust the voltage by changing the
There is no need to provide a special inert gas source. The advantage of the voltage regulator according to the invention is that the additional equipment means required to provide the voltage regulation function are thus simple, and not only that, but also that battery life is not adversely affected. There is also a point where there is no. That is, although it is theoretically possible to adjust the voltage by changing the gas pressure (without adjusting the purge gas flow rate), in this case, however, it is difficult to obtain the desired voltage adjustment range. This requires a large change in gas pressure, which is difficult to implement in terms of battery life. In the case of the present invention, since the voltage can be adjusted by changing the inert gas concentration within the battery while keeping the gas pressure substantially constant, there is no adverse effect on the battery life. According to the present invention, the new gas, which is supplied in a known manner so that the pressure is kept approximately constant, is mixed with the gas with increased inert concentration, which is returned via the gas return pipe, and the gas is mixed into the battery. The purge gas flow rate is adjusted, for example, by operating a damper as an adjusting means provided in the purge outlet pipe.

This changes the gas flow rate in the return pipe. Although the gas supply flow rate into the cell hardly changes, the mixing ratio of the fresh gas and the gas circulating through the return pipe changes, resulting in a change in the inert gas concentration within the cell. For this reason, the pressure in the gas passage of the fuel cell is always kept constant, and there is a risk that one gas will leak into the other gas passage and cause a crossover, where the electrode surface burns and consumes fuel and oxidizer. There is no such thing. [Embodiments of the Invention] Preferred embodiments of the present invention will be described below with reference to the drawings.

According to the embodiment of the present invention shown in FIG. 2, the fuel cell 1 constitutes a fuel cell system together with a separately excited inverter 2,
It is operated in parallel with AC system 3.

The separately excited inverter 2 has a DC reactor 4 on the DC input side.
It is connected between the DC output buses 5 and 6 of the fuel cell 1 via the AC output side, and is connected to the AC system 3 via the transformer 7 on the AC output side. Hydrogen gas is supplied to the fuel gas chamber of the fuel cell 1 through a supply pipe 8 at a constant pressure, and the gas that has passed through the fuel gas chamber comes out through a discharge pipe 9. Air ΔIr is supplied as an oxidant to the oxidant gas chamber of the fuel cell 1 through a supply pipe 10 at a constant pressure. The air that has passed through this gas chamber exits through the exhaust pipe 11. The discharge pipe 11 is the return pipe 12
and a purge pipe 13, and the return pipe 12 and the oxidant gas chamber form a circulation path for the reaction gas. Return pipe 12
open into the supply pipe 10 and allow air to circulate with the aid of a fan 14. A damper 15 as an adjusting means is disposed within the purge pipe 13, and the damper 15 is operated by a motor 16. Note that in this embodiment, the fan 14 is provided in the supply pipe 10;
The present invention is not limited to this, and for example, any pipe other than the return pipe 12 in the circulation path may be provided in the discharge pipe 11. When the motor 16 is driven by a control device (not shown), the opening degree of the damper 15 changes.

The purge gas flow rate increases or decreases by increasing or decreasing the opening degree of the damper 15, and accordingly, a part of the air discharged from the battery with an increased concentration of inert gas and new air are mixed and supplied into the battery. . For example, if the opening degree of the damper 15 is reduced to reduce the purge gas flow rate, the return pipe 12
The air flow rate inside the battery increases, and the inert gas concentration within the battery increases. As a result, the output voltage increases for the same output current. In Fig. 3, a plurality of purge pipes 131 to 133 of different diameters are provided as adjustment means instead of the damper 15 in Fig. 2, and the purge gas flow rate is adjusted in stages by the solenoid valves 151 to 153 of the pipes. This is an example in which the system is configured to do this, and this example has better responsiveness than the example shown in FIG.

If the solenoid valve operates instantaneously, the response speed of the cell is determined by the volume of the gas system and the circulation speed; for example, when circulating at 500e/min in a battery with a gas system volume of 5', the response speed of the cell is about 0.6 seconds. . Note that the illustration of the fan 14 is omitted in FIG. 3. In both the embodiments shown in FIGS. 2 and 3, the inert gas concentration inside the battery can be changed by keeping the gas supply flow rate into the battery almost constant, so that the air distribution to each unit battery can be improved. Since there is no need to worry about unevenness in the gas flow, and because the pressure in the gas passage of the battery can always be kept constant, there is no risk of crossover occurring.

FIG. 4 shows the characteristics when a fuel cell power generation system configured by combining a fuel cell 1 and a separately excited inverter 2 is operated in parallel with an AC system.

The separately excited inverter 2 is operated with an almost fixed control characteristic curve 1, whereas the fuel cell 1 is operated with a variable voltage-current characteristic curve. FIG. 4 illustrates two curves Ml and m2 among the variable voltage-current characteristic curves of the fuel cell 1. Voltage control by adjusting the purge gas flow rate of the fuel cell 1 is performed to enable substantially constant high power factor operation of the separately excited inverter 2 despite changes in the output or output current of the separately excited inverter 2. Furthermore, the current limiting loop can also control the fuel cell voltage so that, for example, the fuel cell output current (inverter input current) smoothly increases according to a predetermined pattern at startup. [Effects of the Invention] As described above, the fuel cell voltage control device according to the present invention can adjust the output voltage of the cell by changing the inert gas concentration within the cell while keeping the amount of gas supplied into the cell constant. This is very effective for a fuel power generation system configured with a separately excited inverter, since high power factor operation and suppression of inrush current at start-up can be simultaneously achieved by extremely simple means.

[Brief explanation of the drawing]

Fig. 1 is an operating characteristic diagram when a general control method is applied to a fuel cell power generation system configured in combination with a separately excited inverter, and Figs. 2 and 3 are principles showing different embodiments of the present invention. FIG. 4 is an operational characteristic diagram when the present invention is applied to a fuel cell power generation system configured in combination with a separately excited inverter. 1... Fuel cell, 2... Separately excited inverter, 3... AC system, 4... DC reactor, 5, 6... DC bus, 7... Transformer, 8... Fuel gas supply pipe, 9... Fuel gas discharge pipe, 10... Oxidizing gas supply pipe, 11.
... Oxidizing gas discharge pipe, 12 ... Exhaust gas return pipe, 13,131-133 ... Purge pipe, 14 ... Fan, 15 ...・Damper, 1
6...Operating motor, 151-153...
solenoid valve.

Claims (1)

[Claims] 1. A return pipe connecting the inlet and outlet of the reaction gas chamber of the fuel cell, and a fan installed in a pipe other than the return pipe in the reaction gas circulation path formed by the return pipe and the reaction gas chamber. A voltage regulating device for a fuel cell, comprising: a flow rate regulating means provided on an outlet side of the reaction gas chamber and in a discharge pipe other than the circulation route.