JPH0461464B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell plant equipped with control means for operating a plurality of fuel cells.

[Technical background of the invention and its problems]

Normally, electric power is generated by rotating a generator with a prime mover such as a steam turbine, generating this driving energy as AC power in the generator, and sending it to the demand side as AC power, which reduces consumption rather than power generation. Until now, it has been adopted as the most convenient method, and most current power systems are AC systems.

On the other hand, the steam that drives steam turbines, etc. is generated from the thermal energy of burning fuel such as oil and gas in boilers, etc., but this fuel energy is extracted as thermal energy, converted to steam energy, and then used to generate electricity. Since extracting energy as energy is disadvantageous in terms of efficiency, in recent years fuel cell power generation methods have been developed as an energy-saving power generation method, which involves chemically changing the fuel and directly extracting electrical energy from the flow of electrons generated during this chemical change. It has come to be adopted as one.

These fuel cells chemically change the supplied fuel to generate electricity, but the output is direct current, and if it is consumed as is in a specific area, it will be consumed as direct current, and as part of energy conservation policy, large amounts of electricity will be generated. In the case of electricity, it is converted to alternating current using a DC-AC converter and connected to the power grid.

FIG. 1 is an explanatory diagram of a typical conventional fuel cell plant and its control method. The operation control of a conventional fuel cell plant will be explained below with reference to FIG.

In the figure, the part indicated by the dashed line 1 is the fuel cell plant. The fuel enters the reformer 4 with its flow rate controlled by a fuel control valve 8. The fuel that has entered the reformer 4 is heated and reformed here to become reformed fuel with a high hydrogen content. The flow rate of the reformed fuel is controlled by the reformed fuel control valve 9, and it flows into the hydrogen electrode 5A of the fuel cell 5, where part of it is consumed as electrical energy, and the rest is combusted in the combustion section of the reformer 4 mentioned above. The gas becomes high-temperature gas for heating the reformer 4, merges with the exhaust gas from the oxygen electrode 5B of the fuel cell 5, flows into the turbine 2 of the turbo compressor via the combustor 7, and drives the compressor 3 connected thereto. do.

The air discharged from the compressor 3 is controlled in flow rate by an air control valve 10 and enters the oxygen electrode 5B of the fuel cell 5. A part of the oxygen that entered the oxygen electrode 5B is transferred to the hydrogen electrode 5
The remaining part reacts with hydrogen in A and is consumed, and the remaining part is discharged from the oxygen electrode 5B, joins with the combustion gas from the combustion section of the reformer 4, and passes through the combustor 7 to the turbo compressor. It is used to drive the turbine 2.

The fuel cell 5 generates electrical energy such that the oxygen electrode 5B becomes a positive electrode and the hydrogen electrode 5A becomes a negative electrode through a catalytic reaction between hydrogen at the hydrogen electrode 5A and oxygen at the oxygen electrode 5B, and the fuel cell 5 is connected between the two electrodes. Supplying the electrical energy to an electrical load. At this time, in approximately proportion to the electrical energy absorbed by the electrical load, the hydrogen and oxygen supplied to the inlets of both poles react to form water, and the unreacted portion is discharged from the outlet of each pole.

In the fuel cell plant, the DC output of the fuel cell 5 is supplied to a converter 6, where it is converted into AC power, and sent to the power grid as AC power.

The basic configuration and general operation of the fuel cell plant have been described above. Next, a conventional control method for this plant will be explained. Basically, the control is performed by first controlling the alternating current output using the converter 6, and then controlling the amount of hydrogen and oxygen flowing into the battery so that the fuel cell 5 generates an output commensurate with this output. The amount of fuel supplied to the reformer 4 and the air discharged from the compressor 3 are controlled so as to compensate for the inflow of oxygen.

The converter active power setting signal Ps is subjected to a deviation calculation from the output signal Pa of the actual active power detector 21 by the comparator 26, and the active power control calculation section 33 performs control calculation using this deviation signal as input, and adjusts the converter AC output. The phase command is output to the converter output controller 35.

The converter reactive power setting signal Qs is subjected to a deviation calculation from the output signal Qa of the actual reactive power detector 20 by the comparator 27, and the reactive power control calculation section 34 performs control calculation using this deviation signal as input, and adjusts the converter AC output. A voltage command is output to the converter output controller 35. The converter output controller 35 controls the converter 6 by its output signal.
Controls the phase and voltage of the AC output. The voltage phase difference between the output of the converter 6 and the grid mainly contributes to the active power of the converter, and the output voltage of the converter 6 mainly contributes to the reactive power. Therefore, the active power setpoint Ps
The active power and the reactive power are adjusted depending on the magnitude of the deviation signal between the reactive power set value Qs and the actual values Pa and Qa, and the converter 6 outputs a predetermined output to the power system.

Next, control of reformed fuel to the fuel cell 5 will be described. Since the AC output energy of the exchanger 6 is sent from the fuel cell 5, the DC output current of the fuel cell is approximately proportional to the AC output of the converter 6.
Current detector 19 outputs a generated DC current signal I that is proportional to this DC output current.

The direct current signal I generated by the fuel cell is computed by the reformed fuel control computing section 30, and outputs a reformed fuel request command corresponding to this direct current load to the adder 24. The adder 24 sends an output signal of a reforming temperature control calculation section 29 and a signal of a reformed fuel control calculation section 30, which will be described later, to an output control calculation section 36, and the output control calculation section 36 performs reforming according to the magnitude of the output. The opening degree of the reformed fuel control valve 9 is controlled to control the amount of reformed fuel flowing into the fuel cell 5. The reformed fuel that has flowed into the fuel cell 5 is consumed within the cell in an amount corresponding to the DC output of the fuel cell, and the remainder is combusted in the combustion section of the reformer 4, but the reformer 4 is heated by this combustion. Temperature rises.

The reformer 4 has an operating temperature suitable for reforming. This operating temperature setting signal TRs is subjected to a deviation calculation from the actual temperature signal TRa of the temperature detector 17 by a comparator 23.
This deviation calculation signal is given to the reforming temperature control calculation section 29, where it is calculated and the reformed fuel request command is sent to the adder 2.
Send to 4. The adder 24 adds this signal to the output signal of the reformed fuel control calculation unit 30 corresponding to the generated DC current, and controls the inflow of the reformed fuel into the fuel cell 5 through the output control calculation unit 36. become.
To summarize the above operation, first, the amount of reformed fuel flowing into the fuel cell 5 is controlled in advance using the DC current generated by the fuel cell 5, and the excess or deficiency of the reformed fuel consumed within the fuel cell 5 is determined. This is detected as a temperature change in the reformer 4, and the inflow amount of reformed fuel is further corrected and controlled so that the temperature of the reformer 4 reaches the target value.

Next, fuel control to the reformer 4 will be explained.
Excess or deficiency of fuel to the reformer 4 is understood as a pressure change in the piping system between the fuel control valve 8 and the reformed fuel control valve 9. In other words, if there is too much fuel supply, the pressure will increase,
If the fuel supply is insufficient, the pressure will drop. This system also has an operating pressure suitable for the reaction. Operating pressure setting signal
PFs is the output signal PFa of pressure detector 18 and comparator 2
2, the deviation signal is given to the pressure control calculation unit 28, and the pressure control calculation unit 28 controls the opening of the fuel control valve 8 based on the calculation output to control the fuel supply amount. The amount of heat supplied to the reformer 4 is heated here and becomes reformed fuel with a high hydrogen content.

Next, air supply control to the fuel cell 5 will be explained. The generated DC current signal I is given to the air amount control calculation section 31. The air amount control calculation unit 31 controls the air control valve 10 to supply a predetermined excess amount of oxygen to the amount of oxygen commensurate with the generated DC current. By supplying this excess oxygen, the reaction within the fuel cell progresses, and the remaining oxygen joins the combustion gas from the reformer 4 mentioned above and is used for combustion in the combustor 7, which drives the turbine 2. Consumed for driving.

Next, the discharge control of the compressor 3 will be described. The compressor 3 is driven by the turbine 2 and supplies compressed air, but this air passes through the air control valve 10, the fuel cell 5, and immediately before the combustor 7, where it is fed with fuel via the reformer 4 as described above. It merges with the battery exhaust gas, and at this point the pressure in the air system line and the pressure in the fuel system line are equal. This is to keep the pressure difference between the hydrogen electrode 5A side and the oxygen electrode 5B side of the fuel cell 5 low, and the pressure at both electrodes is the pressure at this junction plus the slight pressure loss of each gas system. Become. Therefore, if the discharge pressure of the compressor 3 has a constant differential pressure at the confluence point of both systems, it will be easier to control the air inflow to the fuel cell 5 by the air control valve 10, and it will be easier to control the air flow into the fuel cell 5 when the air control valve 10 is fully opened. This is desirable in terms of preventing excessive differential pressure between the two poles. A differential pressure regulating valve 11 is provided to control this differential pressure.

The difference between the differential pressure setting signal DPs and the actual differential pressure signal DPa of the differential pressure detector 16 is calculated by the comparator 25, and this deviation signal is calculated by the differential pressure calculating section 32 to control the opening degree of the differential pressure regulating valve 11. Depending on the situation, the pressure difference before and after the valve can be adjusted. That is, the control is performed in the opening direction when the differential pressure on the discharge side is too high, and in the closing direction when the pressure on the discharge side is too low.

The valve 13 is a fuel humidification steam control valve, and is normally controlled in conjunction with the fuel control valve 8. Valve 1
4 is an air humidifying steam control valve, which is normally controlled in conjunction with the air control valve 10. control valve 12
is for replenishing fuel for driving the turbine 2 to control the pressure at the junction of the air system and fuel system mentioned above, and the turbine 2 and The compressor 3 connected to this is driven and controlled to control the air discharged from the compressor. Further, the valve 15 is a safety discharge valve, and when the system pressure rises abnormally, it is controlled to open by a control device (not shown) to discharge excess air to the outside.

Through the above operations, the fuel cell plant maintains and controls the reformation of fuel, the generation of compressed air, the supply of reformed fuel and oxygen to the fuel cell, and the supply of electrical energy to the power system by the converter. .

The amount of power generated by such a single fuel cell is still small compared to conventional thermal power plants and the like. Therefore, in order to realize a large-capacity power generation plant, it is possible to install multiple fuel cells and operate them in parallel, and even if one of the fuel cells fails, the power plant can continue to supply electricity. A fuel cell plant is being considered as a possible plant.

However, when multiple fuel cells are operated simultaneously, due to variations in the characteristics of each fuel cell, the generated power (current and voltage) of each fuel cell is not necessarily the same even if the fuel, air, and flow rate are the same. There was a problem that the load distribution of each battery was different, and the lifespan was different as well as the maintenance cycle was different, so a complicated maintenance plan had to be implemented.

In addition, when operating batteries with different capacities in parallel, batteries with different remaining lives, or batteries with different degrees of deterioration, the required full load current
It was not possible to share the burden according to each person's ability.

Further, there is an invention disclosed in Japanese Patent Application Laid-Open No. 57-204927 that uses a plurality of fuel cells to evenly share the load. However, in this invention, the electric power extracted from the electric circuit is controlled to be constant, so the voltage-current characteristics are determined by each battery, and therefore each battery is operated at a different voltage-current. Therefore, there was a risk of operation due to overvoltage and overcurrent.

[Purpose of the invention]

The object of the present invention is that when multiple fuel cells are operated in parallel, each fuel cell can be operated with uniform voltage and good current without being operated with overcurrent or overvoltage, and all fuel cells can be operated in parallel. An object of the present invention is to provide a fuel cell plant equipped with a control means that allows batteries to be operated uniformly or with a required load sharing.

[Summary of the invention]

The present invention provides a fuel flow rate and an air flow rate supplied to a fuel cell based on a deviation between a predetermined sharing ratio per unit of the total generated DC current of a plurality of fuel cells and the generated DC current of each individual fuel cell. At least one of the fuel cells is controlled to operate the direct current generated by the plurality of fuel cells at a predetermined sharing ratio.
Here, the predetermined sharing ratio can be a different sharing ratio for each fuel cell, or an equal sharing ratio (simply an average value).

[Embodiments of the invention]

Next, an embodiment of the present invention will be described in detail using FIG. Figure 2 relates to parallel operation of multiple units, and focuses on the k-th battery among them, and the symbols are the same as those in Figure 1, and those corresponding to the k-th battery are the same as those in Figure 1. Furthermore, I added a k at the end. In Fig. 2, an adder 101 is used to calculate the total generated DC current of n units from the generated DC current (I ₁ , . . . I _{o )} of each fuel cell; A divider 102 that calculates the average current per fuel cell, a comparator 103k that calculates the deviation amount between the average current per unit that is the output from the divider 102 and the DC current generated by each fuel cell, and a comparison Vessel 1
A control calculation unit 104k inputs the deviation amount, which is an output signal from the control calculation unit 104, and performs control calculation, and a fuel correction calculation unit 105k receives the output signal from the control calculation unit 104 and creates a correction signal for reformed fuel control. Similarly, an air correction calculation unit 106k inputs the output signal from the control calculation unit 104 and creates a correction signal for air volume control, and the output signal of the air correction calculation unit 106k is added to the output signal of the air volume control calculation unit 31k. An adder 107k is added for adding . Furthermore, for n fuel cells, there is one converter 6 that converts the direct current generated from the fuel cells into alternating current. Therefore, the DC power generated from the n fuel cells is connected to a common bus on the input side to the converter 6 and is input to the converter 6.

The adder 101 adds the generated DC currents from n fuel cells, and the divider 102 calculates the average generated DC current per fuel cell, which is input to the comparator 103k. It is input to the reformed fuel control calculation section 30k and the air amount control calculation section 31k. In FIG. 1, the actual generated DC current signal from the current detector 19 is input to the calculation units 30k and 31k.
However, in FIG. 2, the average generated DC current from n fuel cells is used as the advance control signal for the amount of reformed fuel and air. That is, the present invention attempts to equalize the DC current generated by the n fuel cells by controlling the amount of reformed fuel and air based on the average DC current generated by the n fuel cells.

Furthermore, the average generated DC current is calculated by the comparator 103k.
A deviation signal from the DC current generated by each fuel cell is created, and this deviation signal is added as a correction signal to the reformed fuel and air amount control system to further equalize the generated DC current. It is characterized by the ability to That is, the deviation signal created by the comparator 103k is input to the control calculation unit 104k, and the control signal subjected to control calculation by the calculation unit is sent to the fuel correction calculation unit 105k and the air correction calculation unit 106.
At step k, the DC current generated by the fuel cell is corrected so that it becomes the average DC current generated by n units, and the amounts of reformed fuel and air are controlled as correction signals, respectively.

In the embodiment described above, the correction signal from the deviation amount, which is the output signal of the comparator 103k, is applied to the reformed fuel and air amount control systems by the adders 24k and 107k shown in FIG. Even if only either the reformed fuel or the amount of air is changed as a characteristic of the battery, the direct current generated by the battery will change.
Therefore, even by using only one of the correction signals, it is possible to equalize the DC currents generated by n fuel cells, which is the object of the present invention.

Further, in the above description, the correction signal to the reformed fuel control system is added by the adder 24k, but the correction signal may be added by the adder 23k.

In Fig. 2, the average generated DC current of n units is used as the input signal of the reformed fuel control calculation unit 30k and the air amount control calculation unit 31k, and the output is set to either or both of them as the input signal. It may also be possible to use a signal obtained by multiplying the value by a coefficient.

In FIG. 2, this is also possible by controlling the control valve 12k to control the confluence pressure on the inlet side of the combustor 7k. That is, by controlling the control valve 12k, the confluence pressure on the inlet side of the combustor 7k is controlled, and this confluence pressure determines the system operating pressure of the fuel cell, which in turn determines the direct current generated by the fuel cell. For the same purpose, a bias may be added to the differential pressure setting signal DPs, which is one input signal of the comparator 25.

In the above explanation, we have explained by having each battery share the load uniformly, but due to the difference in capacity of each fuel cell,
If you want to change the sharing ratio due to differences in deterioration, etc., use multiple coefficient multipliers 102-1 to 102n according to the respective sharing ratios instead of the average current calculation divider 102 in FIG.
It is sufficient to provide the respective output signals to the comparators 103-1 to 103n corresponding to the corresponding batteries.

〔Effect of the invention〕

According to the present invention, at least one of the fuel flow rate and the air flow rate is controlled to reduce the voltage of the fuel cell itself.
Since the current characteristics are adjusted, each fuel cell connected in parallel is not operated with overcurrent or overvoltage, and can be operated with uniform voltage and good current.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional system configuration, and FIG. 2 is a block diagram showing an embodiment of the present invention. 1k... Fuel cell plant, 5k... Fuel cell, 6... Converter, 9k... Reformed fuel control valve, 1
0k...Air control valve, 19k...Current detector, 2
4k...Adder, 30k...Reformed fuel control calculation section, 31k...Air amount control calculation section, 36k...Output control calculation section, 101, 107k...Adder, 1
02...Divider, 103k...Comparator, 104k
...Control calculation section, 105k...Fuel correction calculation section,
106k...Air correction calculation section.

Claims (1)

[Claims] 1. In a fuel cell plant in which a plurality of fuel cells are connected in parallel and the generated DC current is converted into AC power by a power converter, the generated DC current from each of the fuel cells and the total generated DC current of the plurality of fuel cells The fuel is characterized by comprising means for controlling at least one of the fuel flow rate and the air flow rate of each fuel cell based on the amount of deviation from the amount corresponding to a predetermined sharing ratio of each fuel cell. battery plant.