JPH06243882A - Protection/suspension method for fuel cell power plant - Google Patents

Abstract

PURPOSE:To prevent a fuel cell from being damaged by detecting a gas shortage condition which locally takes place in a cell stack when a command is directed to increase fuel cell loading, and thereby suspending the operation of the fuel cell for protecting the cell. CONSTITUTION:A fuel cell stack 1 is divided into a plurality of cell blocks 1a, 1b, 1c,...1f and the like while plural unit cells are made to be one unit, so that each voltage Va, Vb, Vc,...Vf and the like in each cell block is thereby detected by a voltage detector 22. Detected voltage is compared by a judging means, with a protection level set value Vp determined in advance when either one of respective voltages Va, Vb, Vc,...Vf and the like for the cell blocks is found to have been lowered to the protection level set value Vp in a process that the output electric power of fuel cell stack is quickly increased by a load change command 9s, it is judged that gas shortage takes place in some cell blocks, so that the fuel cell is suspended in operation so as to be protected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power generation apparatus which is out of gas due to insufficient supply of fuel gas when a load increase command is received during its operation to rapidly increase the output power, and a fuel cell The present invention relates to a protection stop method for avoiding damage.

[0002]

2. Description of the Related Art FIG. 5 is a general system configuration diagram of a fuel cell power generation system. A fuel cell power generation system including a fuel cell stack 1 composed of a unit cell stack uses fossil fuel and hydrocarbon fuel as fuel. A fuel processing device 2 for reforming to hydrogen-rich fuel gas as an anode gas for a cell, an air supply device 3 for supplying air as an oxidant to the fuel cell, and an external load demanding output DC power of the fuel cell. A power conversion device 4 for converting the electric power into a form of electricity, a control device 5 for controlling each of these parts, and the like.

The rise and fall of the electric power supplied to the external load during the operation of the fuel cell power generator configured as described above is as follows.
The control device 2 receives the external load change command 9S and outputs the control signal 2 to the fuel processing device 2 and the air supply device 3.
S, 3S, control signal 4S issued to the power conversion device 4
And the like, and the supply amounts of the fuel gas and air and the electric power supplied to the external load are controlled so as to match the respective target values corresponding to the external load change command 9S.

When the external load change command 9S commands a load increase during the operation of the fuel cell power generator, the power conversion device 4 attempts to output the power corresponding to the command value at a response speed of millisecond or less. The fuel cell 1 is limited by the response speeds of the fuel processing device 2 and the air supply device 3, and there is a delay in increasing the supply of fuel gas and air in response to the increase command. Note that the response speed of the fuel processing device 2 and the air supply device 3 is slower than that of the power conversion device 4, for example, in the fuel processing device, a chemical reaction of increasing the reforming amount (increasing the reforming reaction) occurs in the response process. This is because it includes the process of mass transfer such as gas transfer in the pipe.

[0005]

When the load is increased by the electric power control by the external load change command in the fuel cell power generator,
The following problems occur. That is, when the fuel cell power generator is feed-forward controlled by the external load change command 9S, the control device sets the target value corresponding to the external load change command, and the power conversion device 4 responds to the target value by the control signal 4S. The output of the generated electric power, and the control signals 2S, 3S
Thus, the fuel processing device 2 and the air supply device 3 are instructed to supply the fuel gas and the air in the amounts corresponding to the target values.
However, as described above, the supply speed of the fuel gas and air is lower than the increase in the electrical output, so that the supply amount of the fuel gas and air to the fuel cell 1 increases in response to the sudden load increase command. Without doing so, a gas shortage state temporarily occurs in the fuel electrode and the air electrode of the fuel cell 1.

[0006] Once a gas shortage state occurs in the fuel cell, the power generation voltage of the fuel cell drops, so the power conversion device 4 tries to increase the output current of the fuel cell to match the output power with the target value, which is the cause. Then, a vicious cycle occurs in which the voltage of the fuel cell 1 further decreases, and the fuel cell eventually reaches a gas shortage state. In this case, a delay in the temperature rise due to the heat capacity of the fuel cell also leads to an increase in the current when the load rises because the fuel cell has temperature dependence of the power generation characteristics. As a result, among a large number of stacked unit cells, due to variations in the cross-sectional shape of the reaction gas passages formed in each electrode, the cell voltage is reversed from the unit cell in which the reaction gas does not flow easily, or the gas applied between the electrodes There is a problem that the pressure difference increases and gas blows between the electrodes causing damage to the fuel cell, which eventually leads to a situation where continuous operation of the fuel cell becomes impossible. Therefore, it is required to establish a protection stop method that can prevent the fuel cell from being damaged by stopping the power generation operation of the fuel cell upon detection.

FIG. 6 is an explanatory diagram of a protection operation in the conventional protection stopping method of the fuel cell power generator, and in order to detect the gas shortage state of the fuel cell stack 1 by the decrease of the output DC voltage, the fuel cell stack 1 With respect to the planned IV characteristic curve (planned current-voltage characteristic curve) 10 of the above, a constant voltage VL is set as the protection stop judgment curve 11 regardless of the magnitude of the current I, and the output DC voltage V of the fuel cell stack 1 is set.
When i falls to the determination level VL, it is determined that a gas shortage state has occurred in the fuel cell, and for example, the output of the power conversion device 4 is narrowed to perform a protective stop for stopping the power generation of the fuel cell stack 1. The method is known. There is also known a method in which the fuel cell stack 1 is divided into a plurality of cell sections having a plurality of unit cells as one block, the voltage of each cell section is detected, collated with a constant voltage VL, and protection is stopped.

However, the judgment curve 1 for starting the protection stop
1 is fixed to the constant voltage VL irrespective of the output current I of the fuel cell, the difference voltage ΔV = V from the planned IV curve
VO-VL (corresponding to the amount of decrease in the output voltage) becomes large in the low current (low power) region, and if a gas shortage occurs in this region, the detection will be greatly delayed and damage to the unit cell cannot be avoided. The problem occurs. Further, even when the fuel cell stack 1 is divided into a plurality of cell sections to detect the voltage, assuming that a voltage drop occurs only in a certain unit cell in a transient state, even in the low current region. The large difference voltage ΔV becomes an obstacle, the detection of the gas shortage state in this region is significantly delayed, and there arises a problem that damage to the unit cell cannot be sufficiently avoided.

An object of the present invention is to avoid damage to the fuel cell by early detecting a gas shortage condition locally generated in the fuel cell stack at the time of a load increase command of the fuel cell and stopping the protection. .

[0010]

In order to solve the above-mentioned problems, according to the present invention, a fuel cell stack comprising a unit cell stack, a fuel processor for supplying a fuel gas to the fuel cell stack, and In a fuel cell power generation device including an air supply device, a power conversion device that converts the output DC power of the fuel cell stack into load power and outputs the load power, and a control device that interconnect-controls the above-mentioned parts, a fuel cell power generation device generates when a load increase command is issued. A method of detecting a gas shortage state by detecting a decrease in the output voltage of the fuel cell stack and stopping protection, wherein the output voltage of the fuel cell stack is detected for a plurality of cell sections with a plurality of unit cells as a cell section, and a detection voltage is detected. Protection shall stop when the minimum value of voltage drops by a certain voltage regardless of the load power.

Further, a curve obtained by moving the planned IV curve in the cell section in parallel to the lower side of the constant voltage is used as a judgment curve of voltage drop, and the minimum value of the detected voltage with respect to a predetermined command power value is the command power on the judgment curve. When the voltage value corresponding to the value decreases, it is determined that the minimum value of the cell section voltage has decreased by a certain voltage, and the protection is stopped. Further, the average value of the detection voltage of a plurality of cell sections and the difference voltage between this average value and each detection voltage are obtained, and the maximum value of the sum of the obtained difference voltage and the correction voltage determined for each cell section is a constant voltage. When the voltage exceeds the threshold value, it is determined that the minimum value of the cell section voltage has decreased by a certain voltage, and the protection is stopped.

[0012]

In the present invention, the gas shortage state in the low current region cannot be detected early because the protection stop is performed when the output voltage of the fuel cell stack drops by a constant voltage regardless of the magnitude of the load power. The problem of the prior art is eliminated, and the function of preventing damage to the fuel cell by early detection of a gas shortage condition in all load regions can be obtained. In addition, by using a plurality of unit cells as a cell section, a voltage drop is detected for a plurality of cell sections, and protection is stopped when the minimum value of the detected voltage drops by a certain voltage. It is possible to obtain the function of preventing damage to the unit cell by detecting an insufficient state quickly and with high sensitivity.

Further, a curve obtained by moving the planned IV curve in the cell section in parallel to the lower side of the constant voltage is used as a judgment curve of voltage drop, and the minimum value of the detected voltage with respect to a predetermined command power value is the command power on the judgment curve. If the protection is stopped when the voltage drops to the voltage value corresponding to the value, the protection stop judgment level lower than the constant voltage is applied to all load regions based on the planned IV curve compensated as the initial characteristic of the fuel cell stack. It is possible to set with high accuracy over the whole range, and the protection voltage value corresponding to the command power value of the power rise command can be easily selected from the judgment curve, so the minimum output voltage of the cell section voltage drops to the selected protection voltage value. When this happens, protection stop is performed to detect the occurrence of gas shortage at an early stage for each cell section,
The function of preventing damage to the unit cell is obtained, and the plan I-
Depending on how to determine a constant voltage difference held between the V curve and the judgment curve, a function of adjusting the degree of the gas shortage state in which the protection is stopped can be obtained.

Further, an average value of the detection voltages in a plurality of cell sections and a voltage difference between the average value and each detection voltage are obtained,
If the maximum value of the sum of the obtained difference voltage and the correction voltage determined for each cell section exceeds a certain voltage, it is determined that the minimum value of the cell section voltage has decreased by a certain voltage, and protection is stopped. , A cell section with the slowest voltage rise is detected based on the average value of the detected voltage in each cell section in the descending process which is inversely proportional to the increase in the output power due to the load increase command, and the cell temperature in that cell section, Voltage fluctuation factors such as the ease of fuel gas flow are corrected by adding a correction voltage, and protection stops when the voltage difference (voltage drop) from the average value exceeds a certain voltage. The excess or deficiency state of the supply gas that occurs in 1) can be monitored in real time for each cell section as a transient change in voltage, and it becomes possible to perform protection stop based on a detailed situation judgment. A function to quickly detect the deterioration of cell characteristics over time to minimize damage to the cell is obtained, and there is no need to worry about damage to the fuel cell due to gas shortage without the need to stop the protection. The function of keeping the generator set in a safe continuous operation state is obtained.

[0015]

EXAMPLES The present invention will be described below based on examples. FIG. 1 is an explanatory diagram of a protection operation in a protection stop method for a fuel cell power generator according to an embodiment of the present invention, and FIG. 2 is a system configuration diagram showing a protection stop method according to an embodiment. Are denoted by the same reference numerals, and redundant description will be omitted. In the method for stopping and protecting the fuel cell power generator according to the embodiment, the fuel cell stack 1 is divided into a plurality of cell sections 1a, 1b, 1c ,. , A plurality of voltage detectors 22 are used to detect the voltages Va and V in the respective cell sections.
b, Vc, ... Vn, etc. 1i are detected, each detection voltage is compared with the preset protection level set value Vp in the judgment unit 23, and in the process of suddenly increasing the output power of the fuel cell stack by the load change command 9s, Cell section voltage Va, Vb, Vc,
-When any of Vf etc. falls to the protection level set value, it is judged that a gas shortage condition has occurred in any of the cell sections and the protection is stopped.

In the case of this embodiment, the set value V of the protection level is
As a method of determining p, as shown in FIG. 1, a planned IV curve 20 corresponding to the initial cell section voltage is used as a reference, and a curve obtained by moving this curve in parallel to the lower side of the constant voltage ΔV is a determination curve 21 for the voltage drop. Set as. If the predetermined command power value by the load change command 9s is Is × Vs, the current Is
The voltage value Vp on the judgment curve 21 corresponding to is automatically set in the judgment unit 23 as the protection level setting value, and the voltage detector 22
Detection voltage Va, Vb, Vc, ... Vf and protection level set value V
p and are matched respectively.

A load increase command 9 for increasing the current to Is in the load region where the output current of the fuel cell stack 1 is smaller than Is.
When s is received, the power converter 4 is instructed to output the power corresponding to the target value by the control signal 4S issued by the control unit 5 (see FIG. 5), and the fuel processor 2 and the air are controlled by the control signals 2s and 3s. By instructing the supply device 3 to supply the amount of fuel gas and air corresponding to the target value, as the output current of the fuel cell stack 1 increases, the voltages Va, Vb, Vc ,. Changes toward the target voltage Vs. However, there are variations in the temperature rise of the unit cells between the cell sections, and variations in the cross-sectional shape of the reaction gas passages, and gas shortages occur in the unit cells under adverse conditions. The decrease width of the cell section voltage including the unit cell increases and approaches the determination curve 21. Therefore,
If the voltage difference ΔV between the planned IV curve 20 and the judgment curve 21 is set so that the cell section voltage in the gas shortage state matches the set value Vp of the judgment level, the minimum value of the detected voltage is set. It becomes possible to detect and stop the fuel cell stack early by detecting it, and it is possible to minimize damage to the unit cell, and in the state where protection stop does not occur, the fuel cell power generator can be operated safely with confidence A highly effective protection stop method can be obtained. In addition, if the constant voltage difference ΔV held between the planned IV curve and the judgment curve is made variable, there is an advantage that the degree of the gas shortage state in which the protection is stopped can be adjusted.

FIG. 3 is a system block diagram showing a protection stop method of a fuel cell power generator according to a different embodiment of the present invention, and FIG. 4 is an explanatory view of a protection operation in the protection stop method according to a different embodiment. In the figure, the fuel cell stack 1 is divided into n cell sections such as 1a, 1b, 1c, ... 1n, and the cell section voltages Va, Vb, Vc, Vd, Ve, respectively detected by the voltage detector 22 are divided. The average value calculation unit 32 calculates the average value of the n detected values such as Vf Vave = Va + Vb + Vc + Vd + Ve + V
f ··· / n is required. Next, the voltage drop calculator 3
In 3, the decrease amount of each detection voltage with respect to the average value Vave of the detection voltage and its correction (Vave-Vi) + Vki (subscript i indicates an arbitrary cell section) are calculated. However, the correction voltage Vki is determined in advance in consideration of the influence of the difference in initial conditions such as the temperature difference between the cell sections and the easiness of fuel gas flow on the cell section voltage. The calculation of the decrease amount of the detection voltage may be performed only for the detection voltage lower than the average value Vave.

The calculation result is sent to the judgment unit 34 and collated with the judgment voltage ΔVj preset in the protection level setting unit 35. As shown in FIG. 4, for example, the cell section 1f is (Vave-
When the condition of (Vf) + Vkf ≧ ΔVj is satisfied, it is determined that the gas shortage condition has occurred in the cell section 1f, and the determination unit issues a protection stop command. In the protection stop method configured as described above, the cell section with the slowest voltage rise is based on the average value Vave of the detected voltage in each cell section that is in the descending process in inverse proportion to the increase in the output power due to the load increase command. (1f in the figure) is detected as the amount of decrease in the detection voltage with respect to the average value Vave (Vave-Vi), and the correction voltage Vki is added to the voltage variation factors such as the cell temperature in that cell section and the easiness of fuel gas flow. The voltage difference (Vave
Since the protection is stopped when -Vi) + Vki exceeds the judgment voltage ΔVj, the excess or deficiency state of the supply gas that occurs transiently immediately after the load increase command is monitored in real time as a transient change of the voltage for each cell section, and fine grained. It becomes possible to stop the protection based on the situation judgment, and it is possible to obtain the function to minimize the damage of the cell by detecting the local and time-dependent deterioration of the cell characteristics. There is an advantage that the load can be controlled to rise and fall without fear of running out of gas or damage to the fuel cell due to this, and the fuel cell power generator can be safely operated continuously.

[0020]

As described above, the present invention detects the output voltage of the fuel cell stack for a plurality of cell sections using a plurality of unit cells as a cell section, and the minimum value of the detected voltage is constant regardless of the magnitude of the load power. The protection stop method when the load of the fuel cell is increased is configured to stop the protection when the voltage drops. As a result, the problem of the prior art that the gas shortage condition in the low current region cannot be detected early, the gas shortage condition can be detected early in all the load regions, and the fuel cell can be prevented from being damaged. It is possible to provide a method for stopping and protecting a fuel cell power generation device that can detect a gas shortage state that transiently occurs in a given unit cell with high sensitivity and prevent deterioration of the characteristics of the unit cell.

Further, in the state where the protection stop is not applied, there is an advantage that the load increase / decrease can be controlled without fear of gas shortage and damage to the fuel cell due to this, and the fuel cell power generator can be continuously operated safely. To be

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a protection operation in a protection stop method for a fuel cell power generator according to an embodiment of the present invention.

FIG. 2 is a system configuration diagram showing a protection stop method according to an embodiment.

FIG. 3 is a system configuration diagram showing a protection stop method for a fuel cell power generator according to a different embodiment of the present invention.

FIG. 4 is an explanatory diagram of a protection operation in a protection stop method according to another embodiment.

FIG. 5 is a general system configuration diagram of a fuel cell power generator.

FIG. 6 is an explanatory diagram of a protection operation in a conventional protection stop method for a fuel cell power generator.

[Explanation of Codes] 1 fuel cell stack 1i cell section 2 fuel processor 3 air supply device 4 power converter 5 controller 9s load change command 10 planned IV characteristic curve 11 judgment curve 20 planned IV characteristic curve 21 judgment Curve 22 Voltage detector 23 Judgment part 32 Average value calculation part 33 Voltage drop calculation part 34 Judgment part 35 Protection level setter Vs Cell section voltage (command value) Is Output current (command value) Vp Protection level set value ΔV Voltage drop Width (judgment voltage) Vave Average value of detection voltage Vf Cell section voltage (detection value of cell section 1f) Vkf Correction voltage of cell section 1f ΔVj Voltage drop width (judgment voltage)

Claims (3)

[Claims] 1. A fuel cell stack comprising a stack of unit cells, a fuel processing device for supplying a fuel gas to the fuel cell stack, an air supply device, and output DC power of the fuel cell stack converted to load power. In a fuel cell power generation device including a power conversion device that outputs the power and a control device that interconnects controls the above-mentioned respective parts, a gas shortage state that occurs at the time of a load increase command is detected and protected by a decrease in the output voltage of the fuel cell stack. A method of stopping, wherein the output voltage of the fuel cell stack is detected for a plurality of cell sections using a plurality of unit cells as cell sections, and protection is performed when the minimum value of the detected voltage drops by a constant voltage regardless of the magnitude of load power. A method of protecting and stopping a fuel cell power generator, which is characterized by stopping. 2. A curve obtained by translating a planned IV characteristic curve in a cell section to a lower side of a constant voltage is used as a determination curve of voltage drop,
When the minimum value of the detected voltage for the predetermined command power value has dropped to the voltage value corresponding to the command power value on the judgment curve,
The protection stop method for a fuel cell power generator according to claim 1, wherein the protection stop is performed by determining that the minimum value of the cell section voltage has decreased by a constant voltage. 3. An average value of detection voltages in a plurality of cell sections and a difference voltage between the average value and each detection voltage is obtained, and a maximum value of a sum of the obtained difference voltage and a correction voltage determined for each cell section. Is above a certain voltage, it is judged that the minimum value of the cell section voltage has dropped by a certain voltage, and the protection is stopped, and the protection stopping method of the fuel cell power generator according to claim 1.