JP2671523B2 - Operation control method for fuel cell power generator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel gas supply system for reforming fossil fuels and hydrocarbon fuels into hydrogen-rich fuel gas for supply to a fuel cell, and supply of reaction air. System and a method for controlling the operation of a fuel cell power generator including a fuel cell output power converter system,
Particularly, the present invention relates to an operation control method when the load of the fuel cell increases.

[Conventional technology]

FIG. 3 is a schematic configuration diagram showing an example of a fuel cell power generator. The power generator is a fuel cell 1 including a stack of unit cells.
A fuel supply system 10 for supplying the fuel gas G ₁ to the fuel electrode 1a of the fuel cell, an air system 3 including a blower for supplying the reaction air A to the air electrode 1b, and the power generated by the fuel cell 1 to a load 11. It is composed of a power conversion system 4 that outputs the power after converting it to a corresponding power, and the control of the entire device is controlled by a command signal 5S that specifies the target power
The control system 5 receives the control signal.

The fuel supply system 10 includes a fuel reformer 6 having a reforming catalyst pipe 6A and a burner 6B, a raw material tank 7A, a raw material pump 7B, and a control valve.
Raw material supply system 7 having 7C, fuel tank 8A, fuel pump 8
B, a control valve 8C, an auxiliary fuel supply system 8 for supplying auxiliary fuel to the burner 6B, and a combustion air blower 9. The raw material supply system 7 mixes a predetermined amount of steam with fossil fuel or hydrocarbon fuel. The produced raw material gas G ₁ is supplied to the fuel reformer 6, and the fuel reformer 6 converts methane or hydrocarbons in the raw material gas into a hydrogen-rich fuel gas G ₂ based on a steam reforming reaction which is an endothermic reaction. The required heat of reaction is supplied from the burner 6B which uses the off gas G ₃ of the fuel cell 1 and the auxiliary fuel as fuel.

The control for the steady load fluctuation in the above-mentioned fuel cell power generator detects the output current I of the fuel cell 1, and based on the deviation between the detected current I and the target current, a control signal issued by the control system 5 causes the main flow rate to flow. Controlling control valves, pumps, blowers, etc. (flow rate of raw material gas G ₁ , reforming steam amount, auxiliary fuel flow rate, off gas G ₃ flow rate, off air flow rate, reformed gas G ₂ flow rate, reaction air A flow rate) Current value control is performed. Further, the target current is performed based on a command signal 5S designating the output power of the power conversion system 4, and the output current is greatly increased or decreased by updating the target current value.

When the load rises, the power conversion system responds to the load increase command from the outside at a speed of millisecond or less, but the response of the fuel cell is generally slow due to the response of the fuel processing system and the air system. Is. The response speed of the fuel supply system and the air system to the load increase command is slower than that of the power conversion system, for example, in the fuel processing system, a chemical reaction such as an increase in the reforming amount (increase in the reforming reaction) is included in the response process. The reason is that it includes a mass transfer process such as gas transfer in piping. Further, the temperature of the fuel cell does not rise immediately due to the increase in load, but there is a time delay. This is due to the heat capacity of the fuel cell and follows the load increase on the order of minutes to hours. The output characteristic of the fuel cell has temperature dependency as shown in the VI characteristic diagram of FIG. 4, the limiting current is small when the temperature is low, and the output voltage is low at the same load current.

FIG. 5 is a time chart showing a conventional operation control method during load increase, external output P ₁ by a command signal 5S
(KW) is commanded, and the control signal output by the control system based on this command causes steady operation with the output voltage V ₁ , output current I ₁ , reformed gas flow rate Q ₁ , and fuel cell temperature T ₁ of the fuel cell maintained. It is assumed that a command signal 5S that raises the output power target value to P ₂ is issued from the time t ₁ to the time t ₂ to the power generation device that is performing.
Receiving this command signal, the control system 5 increases the flow rate of the reformed gas G _{2 in} the fuel supply system 10 to its target value Q ₂ at time t ₂ and outputs the output voltage V and the output current I of the fuel cell 1 respectively. Target value V ₂
And a control signal for maintaining I ₂ is output, and current value control is performed after time t ₂ . However, at this point, the fuel cell 1
Temperature is lower than the operating temperature T ₂ corresponding to the target current I ₂
Since the target operating temperature T ₂ is not reached until t ₃ is reached, the operating points of the VI characteristic at the times t ₁ , t ₂ , and t ₃ are shown in FIG.
As shown by P ₁ , P ₂ , and P ₃ , at time t ₂ , the output current becomes larger than its target value I ₂ and the output voltage becomes lower than its target value V ₂ , and the control system is modified by the current value control. By requesting an increase in the gas G ₂ , the reformed gas flow rate Q becomes larger than its target value Q ₂ . Further, the deviation from this target value decreases as the temperature of the fuel cell approaches T ₂ , and at time t ₃ , the target value Q ₂ ,
V ₂ , I ₂ and the measured values Q, V, I coincide with each other.

[Problems to be solved by the invention]

In the conventional operation control method, a difference occurs between the target values I ₂ and V _{2 of the} fuel cell output current and output voltage generated by the control system based on the output power increase command, and the respective actual values, and By the time the temperature T reaches the target operating temperature T ₂ , the fuel cell is in the overcurrent state, and the fuel cell is exposed to the overcurrent state each time the output power of the fuel cell power generator is greatly increased or decreased. There is a problem that the deterioration of the characteristics of the unit cells that form the fuel cell stack is promoted. Since this characteristic deterioration is remarkable in the unit cells in which the flow of the reaction gas such as fuel gas and reaction air is bad among a plurality of unit cells, it has progressed to the situation where the power generation operation is hindered by the deterioration of a small number of unit cells. Therefore, it is an important issue that affects the life of the fuel cell.

An object of the present invention is to prevent the overcurrent state that occurs in the fuel cell when the load rises, thereby preventing the deterioration of the characteristics of the single cell and improving the life characteristics of the fuel cell.

[Means for solving the problem]

In order to solve the above problems, according to the present invention, a fuel cell, a fuel gas supply system for supplying a fuel gas to the fuel cell, a reaction air supply system for supplying a reaction air to the fuel cell, and the fuel A method for controlling the operation of a fuel cell power generator when a load rises, which includes a power conversion system that converts the battery output and supplies it to an external load, and a control system that controls each of these systems. At this time, the flow rate of the fuel gas and the reaction air supplied to the fuel cell is set to a predetermined amount (for maintaining the output voltage of the fuel cell to be equal to or higher than the target output voltage value, from the specified flow rate corresponding to the target power value determined by the increase command value). The fuel cell is operated for a period of time until the temperature of the fuel cell reaches a predetermined target operating temperature by supplying a large amount, and then the fuel supply system and reaction air supply based on the output current of the fuel cell. , Switching to current value control for controlling the fuel cell and power conversion system, and the output of the fuel cell during the period from when a predetermined amount of fuel gas and reactive air is supplied until the target operating temperature is reached, if necessary. The voltage value control based on the voltage is performed.

[Action]

It is noted that the above-mentioned means has a property that the output voltage of the fuel cell increases in proportion to the increase of the fuel cell temperature and increases in inverse proportion to the decrease of the hydrogen consumption rate or the oxygen consumption rate in the reaction gas. It has been configured. That is, when a load increase command is received, the amount of reformed gas and the amount of reaction air to be supplied to the fuel cell are increased by a predetermined amount to reduce the hydrogen consumption rate and the oxygen consumption rate from those during steady operation, thereby reducing the fuel consumption. It becomes possible to compensate for the drop in output voltage caused by the low battery temperature. When the output power is constant, an increase in the output voltage makes it possible to reduce the output current, so that the overcurrent state of the fuel cell can be avoided. Further, if the current value control by the control system is switched at the time when the fuel cell temperature reaches the target operating temperature, the target voltage, the target current, and the amount of reaction gas corresponding to the target voltage can be held to achieve efficient power generation operation. Can be moved to.

In addition, until the fuel cell temperature rises to a predetermined temperature,
If the output voltage of the fuel cell is detected and the control of the reaction gas amount based on this is configured to control the voltage value, the reaction gas amount can be controlled based on the deviation of the actual output value from the target voltage. Control that makes the actual value of the output current closer to the target value becomes possible.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

FIG. 1 is a time chart showing an operation control method supplement of a fuel cell power generator according to an embodiment of the present invention. An operation control method as an embodiment will be described with reference to the configuration diagram shown in FIG. When the command signal 5S for increasing the output power of the power converter system 4 from P ₁ to P ₂ is input to the control system 5 at time t ₁ , the control system 5 outputs the target voltage V ₂ corresponding to the power P ₂ , the target voltage V ₂ . to calculate the current I _2, the fuel supply system a control signal for supplying a predetermined quantity q by more amount Q ₃ from the supply amount Q ₂ of the fuel gas G ₂ required for this
In addition to the output toward 10, the air system 3 is also instructed to supply a large amount of reaction air A to the air system 3 as described above. If the predetermined amount q is a sufficient amount to compensate for the voltage drop V (see FIG. 5) caused by the fuel cell temperature T being lower than the target operating temperature T ₂ , the reaction gas amount Q reaches Q ₃ at time t ₂ In, the output voltage V of the fuel cell 1 once becomes equal to the target voltage V _2, and the output current I also becomes once equal to its target value I ₂ , after which the fuel cell temperature T rises toward its target operating temperature T _2. As the output voltage V rises, the voltage compensation becomes over-guaranteed and the output voltage V rises slightly above its target value V ₂ , and at the same time, the output current I becomes slightly smaller than its target value I _2. Value control is performed. Therefore, by switching the power value control to the current value control when the fuel cell temperature T rises to the target operating temperature T ₂ , the target flow rate Q ₂ , target voltage V ₂ , It is possible to shift to a steady operation state in which the target current I _{2 and the} like are held. The gas amount q to be supplied in a large amount can be determined in consideration of the gas consumption rate vs. output voltage characteristic determined by the type and structure of the fuel cell and the temperature dependency of the VI characteristic, and the calculation of the control system 5 is performed. Set as an arbitrary function or constant in the section.

FIG. 2 is a time chart showing a different embodiment of the present invention. The difference from the above-mentioned embodiment is that the operation control is performed at the time t ₂ when the amount of fuel gas reaches Q ₃ and the voltage value based on the output voltage V of the fuel cell. It is configured to switch to control. As a result, the time at which the fuel cell temperature T reaches the target operating temperature T ₂
During the period up to t _3, control is performed to maintain the output voltage V at its target value V ₂ , and the output current I is also controlled accordingly.
Since it is held at I ₂ , the target value is held from time t _{2 in} terms of the output characteristics of the fuel cell, the load response of the power generator can be greatly improved, and the waste of reaction gas can be suppressed. The advantage that can be obtained is obtained.

Since the dependence of the output voltage of the fuel cell on the fuel consumption rate shows different characteristic values for the hydrogen consumption rate and the oxygen consumption rate, it is preferable to perform an increase control of the reaction gas that maximizes the voltage compensation effect.

〔The invention's effect〕

As described above, according to the present invention, when the output increase command based on the power value control is issued, the reaction gas is supplied to the fuel cell by a predetermined amount more than that in the steady operation, and when the fuel cell temperature reaches the target operating temperature. It was configured to switch to current value control and shift to steady operation. As a result, it is possible to compensate for the decrease in the output voltage caused by the low temperature of the fuel cell by utilizing the voltage increase caused by increasing the reaction gas amount and lowering the hydrogen or oxygen consumption rate from that in the steady operation, It is possible to avoid the overcurrent state of the fuel cell, which is a problem in the conventional operation control method, and the characteristic deterioration of the unit cell caused by the repetition thereof, and thus it is possible to contribute to the improvement of the life characteristic of the fuel cell.

Further, if the control is switched to the voltage value control when the reaction gas supply amount reaches the predetermined increase level, the operation with the target voltage and the target current held from this time becomes possible.
The load followability of the fuel cell can be improved, and the waste of the reaction gas can be suppressed.

[Brief description of the drawings]

FIG. 1 is a time chart showing an operation control method of a fuel cell power generator according to an embodiment of the present invention, FIG. 2 is a time chart showing a different embodiment of the present invention, and FIG. 3 is an example of a fuel cell power generator. FIG. 4 is a schematic configuration diagram shown in FIG. 4, FIG. 4 is an output voltage vs. output current (VI) characteristic diagram of the fuel cell, and FIG. 5 is a time chart showing a conventional method. DESCRIPTION OF SYMBOLS 1 ... Fuel cell, 3 ... Air system, 4 ... Electric power conversion system, 5 ... Control system, 6 ... Fuel reformer, 7 ... Raw material supply system, 8 ... Auxiliary fuel supply system, 9 ... Fuel air blower, 10 ... Fuel Gas supply system, G ₁
... Source gas, G ₂ ... Reformed gas (fuel gas), A ... Reaction air, G ₃ ... Off gas, Q ₂ ... Target gas flow rate, V ₂ ... Target voltage value, I ₂ ... Target current value, P ₂ ... Target Electric power value, q ... Increased gas amount.

Claims (2)

(57) [Claims] 1. A fuel cell, a fuel gas supply system for supplying fuel gas to the fuel cell, a reaction air supply system for supplying reaction air to the fuel cell, and an external load for converting the output of the fuel cell. In the operation control method at the time of load increase of the fuel cell power generator including the power conversion system to be supplied to the fuel cell and the control system for controlling these systems, the fuel gas to be supplied to the fuel cell when a load increase command is issued, and The flow rate of the reaction air is supplied by a predetermined amount larger than the specified flow rate corresponding to the target electric power value determined by the increase command value, and the fuel cell is operated for a period until the temperature of the fuel cell reaches a predetermined target operating temperature, The predetermined amount of the case, the output voltage of the fuel cell is an amount required to maintain a target output voltage value or more, after the temperature of the fuel cell reaches a predetermined target operating temperature, Serial fuel cell output current the fuel gas supply system on the basis of the reaction air supply system, the operation control method of a fuel cell power generation system, wherein the switching the current control for controlling the power conversion system. 2. The voltage value control based on the output voltage of the fuel cell is performed during a period from when a predetermined amount of fuel gas and reaction air is supplied until the target operating temperature is reached. A method for controlling the operation of the fuel cell power generator described.