JP5314364B2 - Fuel cell power generation system and fuel cell output control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out automatic voltage and current control at startup of a fuel cell. <P>SOLUTION: A fuel cell power generation system includes the fuel cell 1, a voltage detector 31 detecting output voltage of the fuel cell 1, and a control device 35 obtaining a current change rate corresponding to an output voltage detected by the voltage detector 31 from related information correlating an output voltage and the current change rate of the fuel cell 1 and setting a current command value based on the current change rate obtained. The system controls an output of the fuel cell 1 based on the current command value. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a fuel cell power generation system that generates power using a fuel cell, and a fuel cell output control method.

Conventionally, a power generation system using a solid oxide fuel cell (hereinafter referred to as “SOFC”) has been proposed. For example, in Patent Document 1, in a hybrid power generation system that combines a SOFC generator that generates power using a SOFC and a gas turbine generator that generates power using a gas turbine, the SOFC generator is changed to a SOFC generator while maintaining temperature constraints on the SOFC generator and the like. A control method for controlling the SOFC so as to satisfy the load requirements is disclosed. More specifically, the total required output required for the hybrid power generation system is assigned to the SOFC generator and the gas turbine generator so as to satisfy the temperature constraints of the SOFC, and the required output assigned to each is satisfied. Discloses that each generator is controlled. The output of the SOFC generator is determined by using not only demand current but also fuel utilization, temperature, and pressure as key parameters.
JP 2006-294621 A

By the way, in the above-described operation of the SOFC, a voltage limit value and a current limit value are set according to the temperature. For this reason, at the time of SOFC start-up where the temperature gradually increases, the temperature is always monitored, and the voltage limit value and the current limit value corresponding to the temperature are not controlled, and both are controlled well while being rated. I have to make it happen.
Conventionally, in this work, a skilled worker manually controls the voltage and current so as not to exceed the respective limit ranges while monitoring the temperature, voltage and current.

  The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a fuel cell power generation system and a fuel cell output control method capable of automatically performing voltage / current control at the time of startup of the fuel cell. And

In order to solve the above problems, the present invention employs the following means.
The present invention relates to a fuel cell, a voltage detection means for detecting the output voltage of the fuel cell, a table that is set based on the temperature characteristics of the fuel cell, and associates the output voltage of the fuel cell and the current change rate, or a calculation equation, the current change rate corresponding to the detected output voltage by the voltage detecting means obtained from the table or the mathematical expression, to set the current command value based on the current change rate, the fuel cell Control means for performing the output control process , wherein the table or the arithmetic expression is set so that the rate of change of the current decreases when the output voltage of the fuel cell falls below a predetermined threshold value. A fuel cell power generation system is provided.

According to such a configuration, a current change rate suitable for the output voltage is acquired based on a table or an arithmetic expression in which the output voltage of the fuel cell is associated with the current change rate, and a current command is obtained based on the current change rate. Value is set. Thereby, it becomes possible to perform optimal output control by controlling the output of the fuel cell based on the current command value.
The related information is set so as to decrease the current change rate when the output voltage of the fuel cell becomes equal to or lower than a predetermined threshold value. As a result, the change rate of the output current of the fuel cell gradually decreases, and the output voltage gradually increases in response to the decrease in the current change rate, and recovers to a voltage threshold value or more. By changing the rate of change of the current command value in accordance with the voltage in this way, the output voltage and output current can be automatically controlled within an appropriate current voltage range, and the burden on workers and the like can be reduced. It becomes possible.

  In the fuel cell power generation system, the table or the arithmetic expression is set so that the current change rate decreases as the output voltage decreases in a region where the output voltage of the fuel cell is equal to or less than a predetermined threshold. It is good.

According to the present invention, the current change rate corresponding to the output voltage of the fuel cell is calculated from a process in which the output voltage of the fuel cell is detected and a table or an arithmetic expression in which the output voltage of the fuel cell and the current change rate are associated in advance. Gets includes a process of setting the current command value based on the obtained said current change rate, and a step of controlling the output of the fuel cell based on the current command value, the table or the arithmetic expression, A fuel cell output control method that is set based on the temperature characteristics of the fuel cell and that is configured to decrease the current change rate when the output voltage of the fuel cell becomes a predetermined threshold value or less. I will provide a.

  According to the present invention, it is possible to automatically perform voltage / current control at the time of startup of the fuel cell, and it is possible to reduce the burden on the operator.

Hereinafter, an embodiment of a fuel cell power generation system and an operation control method thereof according to the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a fuel cell power generation system according to an embodiment of the present invention. As shown in FIG. 1, the fuel cell power generation system includes a fuel cell 1, a reformer 2, an air preheater 3, a combustor 4, a recirculation blower 5, and a preheater heater 6.

  The fuel cell 1 is, for example, a SOFC. The fuel cell 1 includes a fuel inflow portion 21 into which the fuel gas output from the reformer 2 flows, a fuel discharge portion 22 through which the fuel gas flowing through the fuel cell 1 is discharged, and air from the air preheater 3. The air inflow part 23 into which the air flows in and the air exhaust part 24 through which the air flowing through the fuel cell 1 is exhausted are provided.

The reformer 2 is configured such that high-temperature air discharged from the air discharge unit 24 of the fuel cell 1 circulates inside, and fuel gas (for example, city) supplied from the outside by this high-temperature air. Gas or natural gas) is heated and supplied to the fuel cell 1. The reformer 2 also has a function of reforming the fuel gas.
The air preheater 3 is configured to be supplied with high-temperature air that has passed through the reformer 2. The air preheater 3 preheats the air (oxidant gas) supplied from the outside with the high temperature air supplied from the reformer 2, supplies the fuel cell 1 with the high temperature air used for the preheating. Supply to the combustor 4.
The combustor 4 is supplied with the fuel exhaust gas discharged from the fuel discharge portion 22 and supplied with preheated air from the air preheater 3. The combustor 4 mixes and burns unburned fuel gas contained in the fuel exhaust gas discharged from the fuel discharge unit 22 of the fuel cell 1 and high-temperature air supplied from the air preheater 3.

The recirculation blower 5 branches a part of the fuel exhaust gas discharged from the fuel discharge part 22 of the fuel cell 1 and distributes it again to the reformer 2 to recycle unburned fuel gas contained in the fuel exhaust gas. Use.
The preheating heater 6 is a heater that is installed in the fuel cell 1 and generates heat upon receipt of electric power. When the fuel cell 1 is started, air and a fuel gas for temperature increase burn in the fuel cell 1. The fuel cells in the fuel cell 1 are heated until a predetermined temperature at which a reaction occurs in the catalyst is reached.
In the present embodiment, the preheating heater 6 is installed in the fuel cell 1 to generate heat by electric power. However, the air supplied to the fuel cell 1 is heated outside the fuel cell 1 by various methods. Any means may be used as long as the fuel cell in the fuel cell 1 can be heated. In the present embodiment, the reformer 2 is installed outside the fuel cell 1. However, the reformer 2 may be installed inside the fuel cell 1.

Next, a basic operation of the fuel cell power generation system having the above configuration will be described.
First, when the fuel cell 1 is started, the fuel cell in the fuel cell 1 is heated by the preheating heater 6 in the fuel cell 1. Then, when the fuel cell is heated to a temperature at which self-power generation is possible (for example, 600 ° C.), the fuel gas is supplied to the fuel supply unit 21 of the fuel cell 1 via the reformer 2, and the fuel cell 1 Power generation by the battery cell is started. The fuel cell is heated by generating power and generating heat (self-generated heat). Further, when the self-generated heat generation is started, the preheating heater 6 is stopped.

After the start of power generation by the fuel cell, the fuel gas supplied to the reformer 2 from the outside is reformed to hydrogen and carbon monoxide by the heat of the high-temperature air discharged from the air discharge unit 24 of the fuel cell 1. Then, the fuel flows into the fuel cell 1 through the fuel supply unit 21 of the fuel cell 1.
Further, the high-temperature air used for preheating the fuel gas in the reformer 2 is sent to the air preheater 3, and the air (oxidant gas) is heated using the high-temperature air in the air preheater 3. . The heated air (oxidant gas) flows from the air preheater 3 into the fuel cell 1 through the air inflow portion 23 of the fuel cell 1.
The fuel gas and heated air that have flowed into the fuel cell 1 are supplied to the fuel cell and used for power generation in the fuel cell.

  The fuel exhaust gas after being used for power generation is discharged from the fuel cell 1 via the fuel discharge portion 22 of the fuel cell 1. A part of the discharged fuel exhaust gas is reintroduced into the reformer 2 through the recirculation blower 5 and the unburned fuel gas is reused, and the rest is led to the combustor 4. 4, the unburned portion is combusted by mixing with high-temperature air supplied from the air preheater 3.

On the other hand, as described above, the electric power generated when the fuel cell 1 is started is supplied to the system 30 connected via the power line as shown in FIG. Here, the system 30 is shown as the power supply destination, but a load may be connected instead of the system. Between the fuel cell 1 and the system 30, there is provided a power conversion device 36 that converts DC power generated by the fuel cell 1 into three-phase AC power and outputs it.
The power supplied to the system 30, specifically, the voltage and current output from the fuel cell 1 are detected by the voltage detector 31 and the current detector 32, respectively, and input to the control device (control means) 35. .

The control device 35 outputs a current command to the power conversion device 36 based on the output voltage detected by the voltage detector 31 and the output current detected by the current detector 32, whereby the output voltage and output of the fuel cell 1 are output. Control the current.
Hereinafter, the output control process at the time of starting of the fuel cell 1 realized by the control device 35 will be described with reference to FIG.

  First, when the target load is input by the user when the fuel cell 1 is started, the target load is held (step SA1). Subsequently, the actual load is calculated from the detected values input from the voltage detector 31 and the current detector 32 (step SA2), and it is determined whether or not the actual load has reached the target load (step SA3). As a result, when the actual load has not reached the target load (“NO” in step SA3), a current command per cycle is set (step SA4). The current command is set by the following method.

As shown in FIG. 4, the control device 35 has a table in which the voltage and the current change rate are associated with each other. This table is created in consideration of the temperature characteristics of the fuel cell 1, and is set so as to reduce the current change rate when the voltage falls below a certain threshold value Vth. As described above, when the voltage decreases, the current change rate is decreased to suppress an increase in current, thereby recovering the temperature of the fuel cell 1.
Note that the information associating the voltage with the current change rate is not limited to the above table, and may be stored as an arithmetic expression using the voltage and the current change rate as parameters, for example.

The control device 35 obtains a current change rate corresponding to the voltage detection value input from the voltage detector 31 from the table, sets a current command value based on the current change rate, and sets the set current command value to the power conversion device. 36 (step SA5).
Thus, by driving the power conversion device 36 based on the current command value, the output current and the output voltage of the fuel cell 1 are controlled, and the actual load increases toward the target load.
When the control device 35 repeatedly performs the processing of steps SA2 to SA5 and determines in step SA3 that the actual load has reached the target load (“YES” in step SA3), the output control processing at the time of startup ends. .

  As described above, when the voltage becomes equal to or lower than the predetermined threshold value Vth, by controlling the current change rate according to the voltage, the increase in the output current of the fuel cell 1 is suppressed, and the output voltage Can be gradually recovered. When the voltage recovers to the threshold value Vth or higher, the control device 35 sets the change rate of the current command value to the normal value. Thus, for example, the current is controlled at an appropriate rate of change while automatically maintaining the output voltage at a certain value or higher until the fuel cell 1 is in a state of about 900 to 1000 ° C. (= rated operation state) and the start-up is completed. It becomes possible to do.

  FIG. 5 shows an example of the relationship between current density and voltage when the above control is performed. As described above, in the fuel cell operation control method according to the present embodiment, it is possible to avoid the output voltage from significantly lowering than the predetermined threshold value Vth.

  As described above, according to the fuel cell power generation system and the operation control method thereof according to the present embodiment, the output voltage of the fuel cell 1 is monitored, and the output current is controlled according to the value of the output voltage. The output voltage and output current can be automatically controlled within an appropriate current voltage range. As a result, it is possible to prevent the elements in the fuel cell from being destroyed due to a temperature rise, a voltage drop, or the like, and to reduce the burden on the operator. In addition, it is possible to smoothly control the power of the fuel cell when the load increases, and it is possible to reduce the time required for startup.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the specific structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

It is the figure which showed an example of schematic structure of the fuel cell power generation system which concerns on one Embodiment of this invention. It is the figure which showed an example of the electric system of the fuel cell power generation system which concerns on one Embodiment of this invention. 3 is a flowchart showing a process of output control at the time of starting the fuel cell. It is the figure which showed an example of the table which showed the correspondence of an output voltage and a current change rate. It is the figure which showed an example of the voltage-current characteristic acquired when the output control method of the fuel cell which concerns on one Embodiment of this invention is implemented.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Reformer 3 Air preheater 4 Combustor 5 Recirculation blower 6 Preheating heater 21 Fuel inflow part 22 Fuel discharge part 23 Air inflow part 24 Air discharge part 30 Electric load 31 Voltage detector 32 Current detector 35 Control Device 36 power conversion device

Claims (4)

A fuel cell;
Voltage detection means for detecting the output voltage of the fuel cell;
A table or an arithmetic expression that is set based on the temperature characteristics of the fuel cell and associates the output voltage and current change rate of the fuel cell;
Gets the current change rate corresponding to the output voltage detected by said voltage detecting means from the table or the mathematical expression, to set the current command value based on the current rate of change, the output control process of the fuel cell And a control means for performing
The fuel cell power generation system is configured such that the current change rate decreases when the output voltage of the fuel cell becomes equal to or less than a predetermined threshold . The fuel cell power generation system according to claim 1, wherein the fuel cell is a solid oxide fuel cell.   3. The table or the arithmetic expression is set such that a current change rate decreases as the output voltage decreases in a region where the output voltage of the fuel cell is equal to or less than a predetermined threshold. The fuel cell power generation system described. A step of detecting the output voltage of the fuel cell,
The current change rate corresponding to the output voltage of the fuel cell is acquired from a table or an arithmetic expression in which the output voltage of the fuel cell and the current change rate are associated in advance, and a current command value is obtained based on the acquired current change rate. The process of setting
Controlling the output of the fuel cell based on the current command value ;
Have
The table or the arithmetic expression is set based on the temperature characteristic of the fuel cell, and is set so as to decrease the current change rate when the output voltage of the fuel cell becomes a predetermined threshold value or less. output control method of the fuel cell has.

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