JPH071700B2 - Fuel cell power generation system - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a fuel cell power generation system, and more particularly to a fuel cell power generation system including control means for controlling the flow rate of an oxidant supplied to an oxidant electrode.

[Technical Background of the Invention] Conventionally, a fuel cell power generation system has been known as a device that directly converts the energy of a fuel into electrical energy. In this fuel cell power generation system, usually, a pair of electrodes of a fuel electrode and an oxidant electrode are arranged with an electrolyte layer sandwiched between them, fuel such as hydrogen is brought into contact with the back surface of the fuel electrode, and air or the like is contacted with the back surface of the oxidant electrode. Oxidizer is contacted, and the electrochemical reaction that takes place at this time is used to take out electrical energy from between the pair of electrodes, and the electrical energy generated by this fuel cell is converted into an electrical energy corresponding to the load command value by the power converter. It is configured to be converted into a quantity (for example, electric power) and supplied to a load, and as long as the fuel and the oxidant are supplied, electric energy can be extracted with high conversion efficiency.

By the way, in this type of fuel cell power generation system,
The electric energy generated in the fuel cell is controlled by the power converter so that the amount of electricity is commensurate with the load command value.As a result, the changing battery output current is detected by the current detector and is oxidized according to its magnitude. Obtain the agent supply flow rate command value,
And this is compared with the flow rate detection value from the flow rate detector that detects the flow rate of the oxidant flowing through the oxidant supply line, and the valve of the control valve provided on the above oxidant supply line according to the deviation value. The flow rate of the oxidant supplied to the oxidant electrode is controlled by adjusting the opening degree. The fuel is supplied to the fuel electrode in proportion to the amount of power generated by the cell.

[Problems of Background Art] However, in the above-described conventional fuel cell power generation system, the cell output voltage during the low load operation of the fuel cell is
Since the upper limit voltage, which is important for maintaining the life and performance of the fuel cell, is exceeded and concentrated phosphoric acid, etc. is used as the electrolyte of the fuel cell, if the temperature or voltage exceeds a certain value, the Corrosion of the platinum catalyst causes permanent deterioration of battery performance, which is not preferable. FIG. 2 shows the output current-output voltage characteristics of such a fuel cell. From the figure, it is understood that the upper limit voltage Vm of the cell is exceeded in a cell output state in which the output current is less than Il.

[Object of the Invention] The present invention has been made to solve the above problems, and an object of the present invention is to suppress the battery output voltage to the upper limit voltage or lower even during low load operation of the battery to improve the battery performance. It is an object of the present invention to provide a fuel cell power generation system capable of preventing the deterioration and improving the life.

[Summary of the Invention] In order to achieve the above object, in the present invention, a pair of electrodes of a fuel electrode and an oxidant electrode are arranged with an electrolyte layer sandwiched between them, and a fuel is applied to the fuel electrode and an oxidant is applied to the oxidant electrode. A fuel cell for supplying electric power to each of the electrodes, which takes out electric energy from between the electrodes by utilizing an electrochemical reaction occurring at this time, and a power conversion device for converting the electric energy generated by the fuel cell into an electric quantity corresponding to a load command value. A control valve provided on the oxidant supply line, a flow rate detector for detecting the flow rate of the oxidant flowing through the oxidant supply line, and a current detector for detecting the output current of the fuel cell. An arithmetic unit that obtains the oxidant supply flow rate command value according to the magnitude of the output current detected by the current detector, and compares the command flow rate from this arithmetic unit with the detection flow rate from the flow rate detector. Flow rate control means consisting of means for giving a control signal to adjust the valve opening to the control valve based on the comparison result, a voltage detector for detecting the output voltage of the fuel cell,
A voltage rise detection means for comparing the detection voltage from the voltage detector with the upper limit voltage of the battery, and a load command correction value based on the comparison result of the voltage rise detection means, and the load command correction value and the load Load command correction means for obtaining a corrected load command value by comparing with a command value; first flow rate correction means for obtaining a first supply flow rate correction value based on the comparison result of the voltage rise detection means; An electricity quantity detector for detecting the electricity quantity output from the converter, comparing the electricity quantity detection value from the electricity quantity detector with the load command value, and based on the comparison result, a second supply flow rate correction value. And a second flow rate correction means for obtaining the flow rate, and at least one of the first and second supply flow rate correction values is given to the supply flow rate command value as a correction value thereof. .

[Embodiment of the Invention] First, the concept of the present invention will be described with reference to FIG. 3 and FIG. FIG. 3 shows the cell output voltage characteristics with respect to the oxidant utilization rate in a state where the cell output current and the fuel utilization rate are maintained at a certain constant value. Further, FIG. 4 shows the cell output voltage characteristics with respect to the fuel utilization rate in the state where the cell output current and the oxidant utilization rate are held at a certain constant value. In the above, the utilization rate of the fuel or the oxidant is the cell output current with respect to the actual fuel and the oxidant amount supplied to the cell, and the electrochemical theoretical fuel amount and the theoretical oxidant amount determined by the Faraday constant. Is expressed as a percentage.

According to the present invention, as shown in FIGS. 3 and 4, the output voltage decreases as the utilization rate increases, and the oxidant utilization rate is more strongly manifested by the fact that the oxidant utilization rate appears more strongly when the degree is compared. As one of the control amounts, it is intended to perform the upper limit voltage suppression control during battery low load operation.

An embodiment of the present invention based on the above concept will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a fuel cell power generation system according to the present invention. In the figure, reference numeral 1 is a fuel cell in which a pair of electrodes of a fuel electrode 2 and an oxidizer electrode 3 are arranged with an electrolyte layer sandwiched between them, and a fuel such as hydrogen is supplied to the fuel electrode 2 through a fuel supply line 4. Further, an oxidant such as air is supplied to the oxidant electrode 3 through an oxidant supply line 5, and direct current electric power, which is electric energy, is generated between the electrodes by utilizing an electrochemical reaction occurring at this time. I try to take it out. 6
Is an inverter as a power converter that converts DC power generated in the fuel cell 1 into AC power based on a corrected load command value 7 described later. Further, 8 is a control valve provided on the oxidant supply line 5, 9 is a flow rate detector for detecting the flow rate of the oxidant flowing through the oxidant supply line 5,
Reference numeral 10 is a current detector for detecting the output current I of the fuel cell 1. Further, 11 is a calculator for obtaining a supply flow rate command value 12 of the oxidizer by a function according to the magnitude of the output current I detected by the current detector 10, and 13 is a supply flow rate command from the calculator 11. A subtracter 16 for comparing the value 12 with a supply flow rate correction value 14 described later to obtain a deviation signal 15 as a corrected supply flow rate command value, 16 is a deviation signal 15 from the subtracter 13 and a detection signal from the flow rate detector 9 A subtractor 19 for comparing with 17 to obtain a deviation signal 18, and a first PID 19 for giving a control signal 20 for adjusting the valve opening degree to the control valve 8 according to the deviation signal 18 from the subtractor 16. It is an arithmetic unit, and constitutes flow rate control means from these.

On the other hand, 21 is a voltage detector for detecting the output voltage of the fuel cell 1, and 22 is a subtraction for obtaining a deviation signal 23 by comparing the detected voltage V from the voltage detector 21 with the above-mentioned upper limit voltage Vm of the battery. And constitutes a voltage rise detecting means. Further, 24 is a PID calculator with a reset windup prevention function that obtains a load command correction value according to the deviation signal 23 from the subtractor 22 and outputs this as a 26 via a lower limit zero limiter 25. It is an adder that compares the load command correction value 26 and the load command value P ₀ from the load command setter 28 to obtain a deviation signal as the corrected load command value 7, and constitutes a load command correction means. . Further, 31 is a PID calculator with a reset windup prevention function that obtains a first supply flow rate correction value in accordance with the deviation signal 23 from the subtractor 22 and outputs this as a 33 via a lower limit zero limiter 32. Yes, these constitute the first flow rate correction means. Further, 34 is an electric power detector as an electric quantity detector that detects the output electric quantity (for example, electric power Ps) from the inverter 6, and 35 is the electric power detection value Ps from the electric power detector 34 and the load command setter 28. , A subtracter for obtaining a deviation signal 36 by comparing with a power instruction value P ₀ as a load instruction value from 37, 37 obtains a second supply flow rate correction value in accordance with the deviation signal 36 from the subtractor 35, and This is a PID calculator with a reset windup prevention function that outputs this as 39 via the lower limit zero limiter 38, and these constitute the second flow rate correction means. Furthermore, 40 is an adder for adding the first and second supply flow rate correction values 33 and 39, and the addition signal is output as the supply flow rate correction value 14.

In the above, the function in the arithmetic unit 11 is set as follows. That is, in the case of a fuel cell, the cell electromotive force tends to decrease as the oxidant utilization rate increases, and therefore the voltage must be lower than the allowable lower limit voltage in order to prevent phenomena such as reversal. So, if you decide the usage rate below a certain value,
The oxidant supply flow rate with respect to the battery output current can be obtained from the following equation.

I × N × 3600 × 22.4 4 × 96 500 × 1000 × 0.21 × η where F: oxidizer supply flow rate (Nm / H), I: cell output current (A), N: number of fuel cells connected in series, η : Oxidizing agent utilization rate, Faraday constant is 96500 (c / mol), and oxygen concentration in the oxidizing agent is 0.21.

Next, the operation of the fuel cell power generation system having such a configuration will be described with reference to FIG. FIG. 5 shows the battery output voltage-output current characteristics during normal operation.
First, suppose that point a on the characteristic curve (load command value P ₀ :
Considering the case where the load command value P ₀ decreases to P ₂ during operation at P ₀ ), the battery output voltage V shifts to point b on the characteristic curve of and exceeds the upper limit voltage Vm of the battery. Then, due to this voltage increase, a positive voltage deviation 23 with respect to the upper limit voltage Vm is obtained by the subtractor 22, and according to this deviation signal 23
The load command correction value 26 is obtained via the PID calculator 24 and the lower limit zero limiter 25, and the load command value is increased by adding it to the load command value P ₀ from the load command setter 28 by the adder 27. The corrected load command value 7 is obtained by applying the corrected load command value 7 to the inverter 6, and the output is increased to the point c where the voltage deviation becomes zero, and is controlled to be equal to or lower than the upper limit voltage.

However, in this state, the actual output power does not match the target load command value P ₂ . Therefore, the PID calculator 31 obtains the first supply flow rate correction value according to the deviation signal 23 from the subtractor 22 and outputs it to the adder 40 as 33 via the lower limit zero limiter 32. A second supply flow rate correction value is obtained according to the deviation signal 36 between the actual output power P ₁ and the load command value P ₂ obtained by the subtractor 35, and this is supplied via the lower limit zero limiter 38.
By outputting it to the adder 40 as 39, the adder 40 adds the first and second supply flow rate correction values 33 and 39, and the addition signal is supplied as the supply flow rate correction value 14 to the subtracter 13
To correct the supply flow rate command value 12 from the arithmetic unit 11 to obtain a corrected supply flow rate command value 15. Then, the difference signal 18 between the corrected supply flow rate command value 15 and the flow rate detection value 17 from the flow rate detector 9 is obtained by the subtractor 16 and is obtained.
By giving it to the PID calculator 19, the PID calculator 19 gives the control valve 8 a control signal 20 for adjusting its valve opening in the closing direction in accordance with the deviation signal 18 from the subtractor 16 to oxidize it. The amount of oxidizing agent supplied to the agent electrode 3 is reduced. As a result, the battery output voltage drops increasingly oxidant utilization, finally output voltage shown similar in Figure 5 - conform to the load command value P ₂ by shifting the current characteristics, and a battery The operation can be continued stably by shifting to the point d, which is the operating point of the upper limit voltage Vm or less.

As described above, the present fuel cell power generation system has a pair of electrodes of the fuel electrode 2 and the oxidizer electrode 3 with the electrolyte layer sandwiched therebetween, and hydrogen or the like is supplied to the fuel electrode 2 via the fuel supply line 4. Is supplied to the oxidant electrode 3 via the oxidant supply line 5, respectively, and an oxidant such as air is supplied to the oxidant electrode 3 to generate electric energy from between the electrodes by utilizing an electrochemical reaction occurring at this time. A fuel cell 1 for extracting DC power,
An inverter 6 as a power converter for converting the DC power generated in the fuel cell 1 into AC power based on the corrected load command value 7; a control valve 8 provided on the oxidant supply line 5; A flow rate detector 9 for detecting the flow rate of the oxidant flowing through the oxidant supply line 5, a current detector 10 for detecting the output current I of the fuel cell 1, and an output current I detected by the current detector 10. Calculating the supply flow rate command value 12 of the above oxidant by a function according to the size of the calculation unit 11, comparing the supply flow rate command value 12 from this calculation unit 11 with the supply flow rate correction value 14, and calculating the deviation signal 15 thereof. From the subtracter 13 that obtains the corrected supply flow rate command value, the deviation signal 15 from this subtractor 13 and the detection signal 17 from the above flow rate detector 9 to obtain the deviation signal 18, and from this subtracter 16 The valve opening of the control valve 8 should be adjusted according to the deviation signal 18 of A flow rate control means comprising a first PID calculator 19 for giving a node signal 20, a voltage detector 21 for detecting the output voltage of the fuel cell 1, a detection voltage V from this voltage detector 21 and an upper limit voltage of the battery. A voltage rise detection means consisting of a subtractor 22 that obtains a deviation signal 23 by comparing with Vm, and a load command correction value is obtained according to the deviation signal 23 from the subtractor 22, and this is also passed through a lower limit zero limiter 25. PID with reset windup prevention function that outputs as 26
A load consisting of an adder 27 that obtains a deviation signal as the corrected load command value 7 by comparing the load command correction value 26 with the power command value P ₀ as the load command value from the load command setting device 28. A command correcting means, a power detector 34 as an electric quantity detector for detecting an output electric power Ps which is an output electric quantity from the inverter 6, a detected electric power value Ps from the electric power detector 34 and the load command setter 28. Subtractor 35 that obtains the deviation signal 36 by comparing the load command value P ₀ from No. 2, the second supply flow rate correction value is obtained according to the deviation signal 36 from this subtractor 35, and this is the lower limit zero limiter 38. A second flow rate correction means composed of a PID calculator 37 with a reset windup prevention function for outputting 39 as a supply flow rate correction value, and the second supply flow rate correction value 39 is given to the subtractor 13 as the supply flow rate correction value 14. It is configured.

Therefore, in any low load operation range of the battery, not only the output voltage of the battery is suppressed to the upper limit limit voltage Vm or less, it is possible to prevent the performance of the battery from being deteriorated and also to improve the life, but also the load command value. It is possible to control the battery operating state in which the actual load output value is always matched. In addition to the above configuration, a first supply flow rate correction value is obtained according to the deviation signal 23 from the subtractor 22, and this is also set as the lower limit zero limiter 32.
A first flow rate correction means provided with a PID calculator 31 having a reset windup prevention function for outputting as a signal 33 via the first flow rate correction means and the second flow rate correction means. The second supply flow rate correction values 33 and 39 are added by the adder 40, and the addition signal is added to the supply flow rate correction value.
It is configured such that 14 is given to the subtractor 13.

With such a configuration, when the detected voltage exceeds the upper limit voltage, the first supply flow rate correction value first acts to decrease the oxidant supply flow rate to the battery, and at the same time the load on the inverter 6 is reduced. The command correction value is output, the output of the inverter 6 works in the direction of increasing, and the battery voltage is returned to the upper limit voltage or less like the function of the first supply flow rate correction value described above.

However, if the battery voltage is left as it is, the battery voltage can be promptly suppressed to the upper limit voltage or lower, but the output electricity amount of the inverter 6 continues to be in the operating state while being increased from the load command value. Therefore, when the detected amount of electricity exceeds the load command value, the battery voltage is made equal to the first supply flow rate correction value by the second supply flow rate correction value that works to decrease the oxidant supply flow rate to the battery. The battery is operated so that the load command value and the output electricity amount match when the battery output voltage is equal to or lower than the upper limit voltage.

Therefore, the voltage upper limit is suppressed by the battery output control with a fast response, and then the pullback control to the steady operation state of the upper limit voltage Vm or less is performed by the supply oxidant flow rate control with a relatively slow response. It is possible to operate the battery in a state where the upper limit voltage Vm is not exceeded as much as possible throughout the change period.

Although the inverter 6 for controlling the AC power is used as the power converter in the above embodiment, the invention is not limited to this, and a device such as a chopper device or a variable resistance device for controlling the DC power may be applied. .

[Effects of the Invention] As described above, according to the present invention, it is possible to suppress the battery output voltage to the upper limit voltage or less even during low load operation of the battery, prevent the performance of the battery from decreasing, and improve the life of the battery. It is possible to provide an extremely reliable fuel cell power generation system capable of achieving the above.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing output current-output voltage characteristics of a battery, FIGS. 3 and 4 are diagrams for explaining the concept of the present invention, FIG. 5 is a diagram for explaining the operation of the embodiment. 1 ... Fuel cell, 2 ... Fuel electrode, 3 ... Oxidizer electrode, 4 ...
… Fuel supply line, 5 …… Oxidizer supply line, 6 …… Inverter, 8 …… Control valve, 9 …… Flow rate detector, 10 …… Current detector, 11 …… Calculator, 13,16,22, 35 …… Subtractor, 19,
24,31,37 …… PID calculator, 21 …… Voltage detector, 25,32,38
...... Lower limit zero limiter, 27,40 …… Adder, 28 …… Load command setter, 34 …… Power detector.

Claims (2)

[Claims] 1. A load command value for an electric energy generated in a fuel cell provided with a fuel electrode supplied with fuel through a fuel supply line and an oxidant electrode supplied with oxidant through an oxidant supply line. In a fuel cell power generation system that converts and outputs the corresponding amount of electricity, a current detector that detects the output current of the fuel cell, and the oxidizer of the oxidizer according to the magnitude of the output current detected by the current detector. An arithmetic unit that obtains a supply flow rate command value, compares the supply flow rate command value from this arithmetic unit with a detected value of the oxidant flow rate flowing through the oxidant supply line, and is provided in the oxidant supply line based on the deviation. Flow control means for giving a valve opening adjustment signal to the control valve, a voltage detector for detecting the output voltage of the fuel cell, a detection voltage of the voltage detector and an upper limit limiting voltage of the fuel cell. And load command correction means for outputting a load command correction value for increasing the load command value to the power converter when the detected voltage exceeds the upper limit voltage, and the detected voltage of the voltage detector is the fuel cell. Flow rate correction means for outputting a supply flow rate correction value for decreasing the supply flow rate command value obtained by the flow rate control means due to a deviation between the output electric quantity of the power converter and the load command value when the upper limit voltage is exceeded. A fuel cell power generation system comprising: 2. A power converter converts electric energy generated in a fuel cell having a fuel electrode supplied with fuel through a fuel supply line and an oxidant electrode supplied with oxidant through an oxidant supply line into a load command value by a power converter. In a fuel cell power generation system that converts and outputs the corresponding amount of electricity, a current detector that detects the output current of the fuel cell, and the oxidizer of the oxidizer according to the magnitude of the output current detected by the current detector. An arithmetic unit that obtains a supply flow rate command value, compares the supply flow rate command value from this arithmetic unit with a detected value of the oxidant flow rate flowing through the oxidant supply line, and is provided in the oxidant supply line based on the deviation. Flow control means for giving a valve opening adjustment signal to the control valve, a voltage detector for detecting the output voltage of the fuel cell, a detection voltage of the voltage detector and an upper limit limiting voltage of the fuel cell. And load command correction means for outputting a load command correction value for increasing the load command value to the power converter when the detected voltage exceeds the upper limit voltage, and the detected voltage of the voltage detector is the fuel cell. When a voltage exceeds the upper limit voltage of the above, the first flow rate correction means for outputting the first supply flow rate correction value for decreasing the supply flow rate command value, and the output electric quantity from the power conversion device are detected, and the electric quantity is detected. When the value exceeds the load command value, the oxidant supply flow rate to the fuel cell is decreased, and the load command value and the output electricity amount match when the output voltage of the fuel cell is equal to or lower than the upper limit voltage. A fuel cell power generation system, comprising: a second flow rate correction means for outputting a second supply flow rate correction value to be added to the supply flow rate correction value.