JP2009026529A - Fuel cell device, and control method of fuel cell device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell device and a control method thereof, which can start a fuel cell device while avoiding an abnormal drop of a voltage of the stack at low temperature. <P>SOLUTION: The fuel cell device 100 is provided with a temperature sensor 12 for detecting the temperature of a fuel cell stack 10 and an output controller 30 for controlling power outputted by the stack. The output controller 30 carries out a voltage control to maintain the voltage outputted by the stack 10 to a target voltage when the temperature detected by the temperature sensor 12 is lower than a threshold, and carries out a current control to maintain the current outputted by the stack 10 to a target current when the detected temperature is higher than the threshold. The stack 10 is maintained to a target voltage when the temperature is low. While carrying out voltage control, the temperature of the stack 10 is increased by its own heat generation. The fuel cell device 100 can be started while avoiding an abnormal drop of the voltage of the stack, even when the temperature of the stack 10 is low. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell device that can be activated while avoiding an abnormal drop in stack voltage at low temperatures, and a control method therefor.

The fuel cell device includes a fuel cell stack having at least one fuel cell. When the fuel cell stack has a plurality of fuel cells, the plurality of fuel cells in the fuel cell stack are electrically connected in series, and the entire fuel cell stack constitutes one battery unit. In the present specification, “fuel cell” and “fuel cell stack” are treated as synonymous. In the present specification, the “fuel cell stack” may be simply referred to as “stack”.
The stack (that is, the fuel cell) outputs a current by causing oxygen to react with fuel (typically hydrogen, but a substance other than hydrogen, such as carbon monoxide, may be used as fuel). When the amount of fuel to be supplied (especially the amount of hydrogen) is changed, the current output from the stack changes. Therefore, when a fuel cell device is used (typically when the fuel cell device is used as a power source), the stack is often current-controlled. The “current control” in the present specification refers to control for matching the current output from the stack with the target current. While performing “current control”, the voltage of the stack varies depending on the state of the stack. Usually, power is drawn from the stack with a constant current corresponding to the amount of fuel by a current regulator, and the power drawn from the plurality of stacks is converted to a constant voltage by an inverter circuit or the like and output from the fuel cell device.

When the current value drawn from the stack is gradually increased in a state where a predetermined amount of fuel is being supplied, the voltage drops rapidly without being able to react to the amount of fuel when a certain current value is exceeded. Therefore, if the target current for controlling the current of the stack is too large, the voltage of the stack is abnormally lowered. It is known that the stack deteriorates when the fuel cell device is continuously used in such a state.
Patent Document 1 discloses a technique for avoiding an abnormal drop in stack voltage. The technique disclosed in Patent Document 1 monitors a stack voltage, and lowers a target current for current control when the voltage drops to a predetermined voltage.

Japanese Patent Application Laid-Open No. 11-144749

The relationship between the current and voltage output by the stack is called the IV characteristic (current-voltage characteristic). It is known that the IV characteristic is highly temperature dependent. The lower the stack temperature, the lower the current value when the voltage drops rapidly. Therefore, when current control is performed with a constant target current, the above-described abnormal voltage drop tends to occur when the stack temperature is low.
In addition, when the fuel cell device is started in a state where the stack temperature is low, the IV characteristic of the stack rapidly increases while the stack temperature rises from a low temperature to a predetermined temperature (the lower limit temperature of the temperature range suitable for steady operation). To change. Since the temperature of the stack changes abruptly due to its own reaction heat, the temperature in the stack varies, and even when a current of the same magnitude is drawn, the voltage varies greatly. Therefore, when starting the fuel cell device in a state where the temperature of the stack is low, it is difficult to set a target current that avoids an abnormal drop in voltage. In a low temperature environment, the reaction heat of the self cannot be used, and it has been necessary to start the fuel cell device after raising the stack to a predetermined temperature (lower limit temperature range suitable for steady operation) with a heater or the like. The lower limit temperature in the temperature range suitable for steady operation is referred to as “operation lower limit temperature”.
There is a need for a fuel cell device that can be activated while avoiding an abnormal drop in stack voltage at low temperatures.

  As described above, when the fuel cell device operates in a steady state, the stack is current-controlled. However, the present invention dares to control the voltage of the stack until the temperature of the stack rises to the operation lower limit temperature. The voltage control referred to in this specification refers to control for matching the stack voltage with a target voltage. While “voltage control” is being executed, the current output from the stack varies depending on the stack temperature and the amount of fuel. By doing so, it is possible to avoid the phenomenon that the voltage drops abnormally when the temperature of the stack is low. On the other hand, even when the stack temperature is low, the stack is heated by its own reaction heat by operating the stack. A fuel cell device that can be started up while avoiding an abnormal drop in stack voltage at low temperatures can be realized.

The present invention can be embodied in a fuel cell device. This fuel cell device includes a stack having at least one fuel cell, a temperature sensor that detects the temperature of the stack, and an output controller that controls the power output by the stack. The output controller performs voltage control that maintains the voltage output by the stack at the target voltage when the temperature detected by the temperature sensor is lower than the threshold, and targets the current output by the stack when the detected temperature is higher than the threshold. Execute current control to maintain current. The “threshold value” corresponds to the above-described operating lower limit temperature. The “target voltage” is a value determined in advance from the characteristics of the stack, and is set to a value equal to or higher than a level at which the deterioration of the stack does not proceed rapidly. The “target current” is a value determined from the IV characteristics of the stack, and is set to a value at which the stack voltage is not at least zero. The “threshold value”, “target current”, and “target voltage” are set in advance and stored in the output controller.
The output controller may be one device capable of switching between current control and voltage control. Alternatively, the output controller may be a system including a current controller, a voltage controller, and a switching device that switches and operates two controllers with respect to the stack. The circuit that performs current control and the circuit that performs voltage control may typically be a current regulator and a voltage regulator, respectively.

  The fuel cell device may be various types of fuel cell devices such as a solid oxide type and a polymer electrolyte type. The term “low temperature” in the present specification means that the temperature is lower than the lower limit operating temperature of the fuel cell device. Therefore, the present invention is particularly suitable for a fuel cell device (so-called high temperature operation type fuel cell device) having a high operating minimum temperature such as a solid oxide type or a molten carbonate type.

According to the fuel cell device described above, when the stack temperature is lower than the threshold value, voltage control is performed to maintain the stack voltage at the target voltage. Since the stack is operated by voltage control, the stack is heated by its own heat generation. Since the stack is heated from the inside by its own heat generation, the heat generation of the stack can be used for raising the temperature of the stack, and the temperature of the stack can be raised more quickly than by heating from the outside with a heater or the like. When the temperature of the stack is low, the stack temperature can be quickly raised while avoiding the abnormal drop in the stack voltage.
When the temperature of the stack is higher than the threshold value, the control is switched to the current control that maintains the current output from the stack at the target current. The fuel cell device can be brought into a state where it can be normally used (typically, a state where it can be used as a power source).

The output controller of the fuel cell device preferably increases the target voltage as the temperature of the fuel cell stack increases while the voltage control is being performed (that is, when the temperature of the stack is lower than the threshold value).
The IV characteristic of the fuel cell stack has a characteristic that when the current of the same magnitude is output, the voltage increases as the temperature increases. Therefore, when voltage-controlling the fuel cell stack, the current output from the stack can be within a predetermined range by increasing the target voltage for voltage control as the stack temperature rises. That is, although the stack is actually voltage controlled, pseudo current control can be realized by increasing the target voltage as the temperature rises. Furthermore, when the target voltage is increased, the current output from the stack increases. The increase in current promotes chemical reactions in the stack, so the temperature of the stack rises quickly.

The fuel cell device may include a plurality of stacks. In the case of such a fuel cell device, each stack is provided with a temperature sensor, and the output controller can independently execute voltage control and current control for each stack, and the temperature of all the stacks can be controlled. Until the threshold is exceeded, it is preferable to maintain the target current of the stack whose temperature exceeds the threshold at zero.
When the fuel cell device includes a plurality of stacks, the temperature may vary among the stacks. Until the temperature of all the stacks becomes higher than the threshold value, the target current of the stack whose temperature has quickly exceeded the threshold value is maintained at zero. After all the stacks are in the same state (current control state with a target current of zero), normal use (use of the fuel cell device as a power source) can be started.

The present invention can also be embodied in a control method for a fuel cell device. This method performs voltage control to maintain a voltage output from the stack at a target voltage when the temperature of the stack having at least one fuel cell is lower than a threshold, and when the temperature of the stack is higher than the threshold, the stack Is a control method for performing current control for maintaining the current output from the target current. More simply, this method controls the voltage of the stack when the temperature of the stack having at least one fuel cell is lower than a threshold, and controls the current of the stack when the temperature of the stack is higher than the threshold. It can be expressed as a method.
This control method can also start the fuel cell device while avoiding an abnormal drop in the stack voltage at low temperatures.
In the fuel cell device or the control method thereof, when the stack temperature is equal to the threshold value, the stack may be controlled by either current control or voltage control.

  ADVANTAGE OF THE INVENTION According to this invention, when the temperature of a stack is low, the fuel cell apparatus which can be started while avoiding the abnormal fall of the voltage of a stack, and its control method can be provided.

The main features of the examples are listed.
(First Feature) The output controller increases the target voltage stepwise as the temperature of the fuel cell stack increases when voltage control is performed to maintain the stack voltage at the target voltage.

(First Embodiment) A fuel cell apparatus according to a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a block diagram of a fuel cell device 100 of the present embodiment. FIG. 1 shows only parts necessary for explaining the present invention, and illustration of parts (reformer and the like) included in a general fuel cell device is omitted.

The fuel cell device 100 according to this embodiment includes a plurality of stacks 10 a and 10 b, voltage / current controllers 14 a and 14 b, a general controller 20, and a power controller 16. The voltage / current controllers 14a and 14b and the overall controller 20 may be collectively referred to as an output controller 20.
A plurality of fuel cells (not shown) are stacked and accommodated in each of the stacks 10a and 10b. In each stack, the plurality of fuel cells are connected in series. Therefore, one stack includes a pair of electrodes.
The stack 10a is connected to a voltage / current controller 14a. The stack 10b is connected to the voltage / current controller 14b. The voltage / current controllers 14 a and 14 b are connected to the power controller 16. The voltage / current controller 14a has a transformer (not shown) inside, and outputs the power output from the stack 10a to the power controller 16 through the transformer. Similarly, the voltage / current controller 14b has a transformer (not shown), and outputs the power output from the stack 10b to the power controller 16 through the transformer. The power controller 16 sums the power output from the stacks 10 a and 10 b, holds the summed power at a predetermined voltage, and outputs it to the output terminal 40 of the fuel cell device 100. The fuel cell device 100 can supply power of a predetermined voltage to the outside via the output terminal 40. When the fuel cell device 100 is required to supply a predetermined amount of current, the power controller 16 may include a circuit that supplies the required amount of current to the outside. .

The voltage / current controller 14a is a device capable of selectively executing a voltage control function for maintaining the voltage of the stack 10a at a target voltage and a current control function for maintaining a current output from the stack 10a at a target current. Hereinafter, the “voltage control function” is simply referred to as “voltage control”, and the “current control function” is simply referred to as “current control”.
The voltage / current controller 14a functions as a so-called voltage regulator when executing voltage control, and functions as a so-called current regulator when executing current control. Which control the voltage / current controller 14 a executes is determined by a command from the overall controller 20. Also, the control target value of the voltage / current controller 14a (the target voltage for the voltage control and the target current for the current control) is also commanded from the overall controller 20. Specifically, the voltage / current controller 14a may be a DC / DC converter capable of selectively executing control for maintaining the voltage at the target voltage and control for maintaining the current at the target current.
The voltage / current controller 14b is a device that can selectively execute voltage control for maintaining the voltage of the stack 10b at the target voltage and current control for maintaining the current output from the stack 10b at the target current. Since the function of the voltage / current controller 14b is the same as that of the voltage / current controller 14a, the description thereof is omitted.
As will be described later, the voltage / current controllers 14 a and 14 b and the overall controller 20 work together as an output controller 30, and the outputs of the stacks 10 a and 10 b are controlled by the output controller 30. The target voltage and the target current are stored in advance in the overall controller 20.

The voltage / current controller 14a includes a voltage sensor 18a that detects the output voltage of the stack 10a. The voltage / current controller 14a includes a current sensor 19a that detects an output current of the stack 10a.
The voltage / current controller 14b includes a voltage sensor 18b that detects an output voltage of the stack 10b. The voltage / current controller 14b includes a current sensor 19b that detects an output current of the stack 10b.

  Temperature sensors 12a and 12b are installed in the stacks 10a and 10b, respectively. The temperature sensors 12a and 12b detect the temperatures of the stacks 10a and 10b, respectively.

The temperature sensors 12 a and 12 b and the voltage / current controllers 14 a and 14 b are electrically connected to the overall controller 20 via the signal line 50. The overall controller 20 receives detection results of the respective sensors (voltage sensors 18a and 18b, current sensors 19a and 19b, and temperature sensors 12a and 12b). Based on the input detection result, the overall controller 20 instructs the voltage / current controllers 14a and 14b to execute either current control or voltage control, and a target value for control (target in the case of current control). Current, and in the case of voltage control, command the target voltage).
The voltage / current controller 14a can execute voltage control for maintaining the voltage of the stack 10a at the target voltage based on the voltage detected by the voltage sensor 18a. Further, the voltage / current controller 14a can execute current control for maintaining the output current of the stack 10a at the target current based on the current detected by the current sensor 19a.
Similarly, the voltage / current controller 14b can perform voltage control for maintaining the voltage of the stack 10b at the target voltage and current control for maintaining the output current of the stack 10b at the target current.

Next, an outline of the operation of the fuel cell device 100 will be described. Hereinafter, the stacks 10a and 10b are collectively referred to as “stack 10”, and the voltage / current controllers 14a and 14b are collectively referred to as “voltage / current controller 14”.
When fuel (hydrogen and oxygen) is supplied to the stack 10, a current is generated by a chemical reaction. In order to perform this chemical reaction stably, it is necessary to maintain the stack 10 in an appropriate temperature range. The lower limit of the appropriate temperature range is referred to as the operating lower limit temperature. The fuel cell device 100 starts a steady operation (that is, an operation of supplying constant electric power to the outside) after raising the temperature of each of the stacks 10a and 10b to the operation lower limit temperature or higher.
The fuel cell device 100 is also provided with a cooler (not shown) that cools the stack 10 so that the stack 10 does not overheat.

As described above, the fuel cell device 100 performs a normal operation after the temperature of the stack 10 rises to the operation lower limit temperature or higher. Here, the normal operation refers to an operation of outputting power required from an external device to the outside. Therefore, when the fuel cell device 100 is started, it is necessary to raise the temperature of the stack 10 to the operation lower limit temperature or higher. The fuel cell device 100 does not supply the fuel after the stack 10 has been heated to the operation lower limit temperature or higher, but causes a chemical reaction to generate electricity by supplying fuel even during the temperature increase to the operation lower limit temperature. Let Since the stack 10 is heated from the inside due to the heat generated by the chemical reaction, the temperature rises faster than the outside is heated by a heater or the like.
When the temperature of the stack 10 is equal to or lower than the operation lower limit temperature, it is necessary to appropriately control the output of the stack 10 (power generated by a chemical reaction) (control so that the voltage of the stack 10 does not drop abnormally). When the fuel cell device 100 is activated, control of the output of the stack 10 until the temperature of the stack 10 becomes equal to or higher than the operation lower limit temperature is referred to as activation control.

Next, activation control of the fuel cell device 100 will be described. FIG. 2 is a flowchart of start control executed by the overall controller 20. When the fuel cell device 100 is activated, fuel supply to the stack 10 is started. FIG. 2 is a flowchart for controlling the electric power of the stack 10, and therefore, the process of supplying fuel is not shown.
The voltage / current controllers 14a and 14b are controlled by the general controller 20 in the same control state (current control state in which the current output from the stacks 10a and 10b is maintained at the target current, or the respective voltages of the stacks 10a and 10b. The voltage control state is maintained at the target voltage.
The magnitude relationship among the first temperature T0, the second temperature T1, and the operation lower limit temperature Tok that appears in the following description is T0 <T1 <Tok. The magnitude relationship among the first voltage V1, the second voltage V2, and the maximum voltage Vmax that appears in the following description is V1 <V2 <Vmax.

When the fuel cell device 100 is activated, the overall controller 20 first outputs a command for operating the voltage control to each voltage / current controller 14 (step S100). At this time, the target voltage Vset of the stack 10 is set to the maximum voltage Vmax. The maximum voltage Vmax is the maximum voltage value that can be generated by the stack 10. The reason for setting the target voltage Vset to the maximum voltage Vmax at the start of the fuel cell device 100 will be described later.
Since the voltage / current controller 14 is naturally in a stopped state before the fuel cell device 100 is started, both the voltage control and the current control are stopped when the process of step S100 is executed. Nevertheless, “current control OFF” is shown in step S100 of FIG. This is to clearly indicate that the overall controller 20 selectively causes the voltage / current controller 14 to execute either voltage control or current control.

The temperature of the stack 10 increases due to the heat of chemical reaction. The overall controller 20 causes the voltage / current controller 14 to maintain voltage control with the target voltage Vset set to Vmax until the temperature of the stack 10 exceeds the first temperature T0 (step S102: NO). The symbol Tx_min in FIG. 2 means the lower temperature of the stack 10a and the stack 10b. Therefore, step S102 in FIG. 2 means that the process proceeds to step S104 when both the temperature of the stack 10a and the temperature of the stack 10b exceed the first temperature T0.
When the temperatures of the stacks 10a and 10b both exceed the first temperature T0 (step S102: YES), the overall controller 20 determines whether or not the temperatures of the stacks 10a and 10b both exceed the operation lower limit temperature Tok ( Step S104). Here, the case where the temperatures of the stacks 10a and 10b both exceed the operation lower limit temperature Tok means that both the stacks 10a and 10b have reached a temperature at which steady operation is possible. In this case (step S104: YES), the activation control can be terminated, and the process proceeds to step S114. The process of step S114 will be described later.
When step S104 is NO, that is, when the temperature of at least one of the stacks 10a and 10b has not reached the operation lower limit temperature Tok, the voltage control target voltage Vset in the voltage / current controller 14 is set to the first voltage V1. Change (step S106). If the process of step S102 and the process of step S104 are combined and expressed by a mathematical expression, it can be expressed that step S106 is executed when T0 <T_min <Tok.

Next, the overall controller 20 causes the voltage / current controller 14 to maintain the voltage control while keeping the target voltage Vset at the first voltage V1 until the temperatures of the stacks 10a and 10b both exceed the second temperature T1 ( Step S108: NO).
When the temperatures of the stacks 10a and 10b both exceed the second temperature T1 (step S108: YES), the overall controller 20 changes the voltage control target voltage Vset in the voltage / current controller 14 to the second voltage V2. (Step S110).
The overall controller 20 causes the voltage / current controller 14 to maintain voltage control while setting the target voltage Vset to the second voltage V2 until the temperatures of the stacks 10a and 10b both exceed the operation lower limit temperature Tok (step S112). : NO).
When the temperatures of the stacks 10a and 10b both exceed the operation lower limit temperature Tok (step S112: YES), the overall controller 20 outputs the following command to the voltage / current controller 14. That is, a command to stop the voltage control, set the target current Iset to zero, and start the current control is output to the voltage / current controller 14 (step S114). As a result, the output current of the stack 10 (stack 10a and stack 10b) is maintained at the target current Iset = zero.

Since the temperatures of the stacks 10a and 10b both exceed the operation lower limit temperature Tok at the stage when step S114 is executed, the overall controller 20 ends the start control. Note that after the start-up control is completed, the overall controller 20 executes the following process in order to output from the output terminal 40 the voltage requested from the outside to the fuel cell device 100.
When the start control is completed, the overall controller 20 sets the target current Iset to a predetermined value according to the output voltage required for the fuel cell device 100. The voltage / current controller 14 performs current control for maintaining the current output from the stack 10 at Iset.

  The meaning of the start control by the overall controller 20 will be described with reference to FIG. FIG. 3 is a graph of the IV characteristics (current-voltage characteristics) of the stack 10. The vertical axis of the graph of FIG. 3 is the voltage of the stack 10, and the horizontal axis is the current output by the stack 10. In FIG. 3, the IV characteristics when the temperature of the stack 10 is the first temperature T0, the second temperature T1, and the operation lower limit temperature Tok are indicated by solid lines. In FIG. 3, the IV characteristic when the stack temperature is (T1−ΔT) is indicated by a broken line.

As shown in FIG. 3, the relationship between the current and voltage output by the stack 10 is such that the stack voltage decreases as the output current (current drawn from the stack 10) increases. In a region where the current output from the stack 10 is large, the voltage of the stack 10 rapidly decreases as the output current of the stack 10 increases.
Further, the IV characteristics of the stack 10 are strongly dependent on the temperature of the stack 10. That is, even when the same current is output, the lower the temperature, the lower the stack voltage and the greater the voltage variation.
The stack 10 outputs electrons generated when hydrogen in the supplied fuel is ionized as a current. Therefore, in a steady state, the stack is current controlled. Here, it is assumed that the stack is current-controlled by setting the target current Iset to I1. From FIG. 3, when the stack output current is I1, the stack voltage is the first voltage V1 if the stack temperature is the second temperature T1, and the stack voltage is (T1−ΔT) if the stack temperature is (T1−ΔT). Ve. The voltage change rate ΔV / ΔT with respect to the temperature change is large in the vicinity of the target current I1 and the stack temperature T1. Therefore, when the stack current is controlled by setting the target current Iset to I1, the stack voltage changes rapidly while the stack temperature rises to the second temperature T1. At this time, if the stack capacity is unexpectedly low with respect to the target current I1, the stack voltage is abnormally decreased (the stack voltage is decreased below a predetermined voltage). The ability of the stack to become unplanned is a factor in the stack voltage variation. It is known that a stack of fuel cells deteriorates when a current is continuously output with an abnormally low voltage. When current control of the stack is performed when the fuel cell device is started in a state where the temperature of the stack is low, the IV characteristic changes as the temperature of the stack rises, so that the target current for avoiding abnormal voltage drop It is difficult to determine.
There is also a temperature distribution inside one stack. For example, if there is a region where the temperature is T1 and a region where the temperature is (T1-ΔT) inside the stack, the voltage locally decreases to Ve in the region where the temperature is (T1-ΔT). When there is a temperature distribution of ΔT inside the stack, the electrical state distribution inside the stack (in this case, the voltage distribution) becomes non-uniform. The uneven electrical state inside the stack contributes to the deterioration of the stack.

In the fuel cell device 100 of the present embodiment, when the temperature of the stack is lower than the operation lower limit temperature Tok, the voltage of the stack is controlled. Specifically, when the temperature of the stack 10 is lower than the second temperature T1 (and when the temperature of the stack 10 is higher than the first temperature T0), the target voltage Vset is set to the first voltage V1 and the stack 10 is set. Is voltage controlled (step S106 in FIG. 2). The first voltage V1 (target voltage) is a value determined in advance from the characteristics of the stack, and is set to a value equal to or higher than a level at which deterioration of the stack does not proceed rapidly. Since the output current of the stack 10 is adjusted so that the voltage thereof matches the first voltage V1, the voltage of the stack 10 does not become lower than the first voltage V1 (however, although the voltage control is performed, some voltage fluctuations) Can happen). Since the temperature of the stack is low when the fuel cell device 100 is activated, it is possible to prevent the stack voltage from rapidly decreasing. Deterioration of the stack can be reduced.
Further, when voltage control is performed so that the voltage of the stack 10 becomes the target voltage Vset = V1, as shown in FIG. 3, if the temperature of the stack 10 rises to the second temperature T1, the current output by the stack 10 is I1. It becomes. When the temperature of the stack 10 is (T1−ΔT), the current output from the stack 10 is Ie. The current difference ΔI between I1 and Ie is small. Therefore, even when there is a temperature distribution of ΔT inside the stack 10, the non-uniformity of the distribution of electrical states (here, the current distribution) is reduced inside the stack. When the voltage of the stack 10 is controlled, the non-uniformity of the electrical state due to the temperature distribution inside the stack can be made smaller than the non-uniformity at the time of current control. When the voltage of the stack 10 is controlled, deterioration due to the temperature distribution inside the stack can be reduced.

When the stack temperature is lower than the operation lower limit temperature Tok, the following effects can be obtained by controlling the voltage of the stack.
As shown in FIG. 3, even when the stack is current-controlled, if the target current is set small, the voltage of the stack will not be extremely reduced. However, it is better to draw (output) a predetermined current from the stack. This is due to the following reason. As described above, the stack of the fuel cell device outputs electrons emitted when the fuel is ionized as a current. When the current output from the stack is reduced, non-ionized fuel burns locally in the stack, which may cause uneven temperature distribution and local degradation. In order not to cause such an event, it is better to draw a predetermined current from the stack. Furthermore, heat generated by a chemical reaction can be increased by drawing a predetermined current from the stack. By increasing the heat generation in the stack, the stack can be quickly heated. In a fuel cell device, it is desired to output a predetermined current while avoiding an abnormal voltage drop in the stack.
The fuel cell device 100 according to the present embodiment performs voltage control on the stack 10 when the temperature is equal to or lower than the operation lower limit temperature Tok. In the transition period until the temperature of the stack 10 rises to the operation lower limit temperature Tok, the fuel cell device 100 draws a predetermined current from the stack 10 even in voltage control if the target voltage of the stack 10 is appropriately selected. Can do. As a result, a predetermined current can be drawn from the stack 10 while avoiding an abnormal voltage drop of the stack 10.

In the fuel cell device 100 of the embodiment, the target voltage is increased stepwise as the temperature of the stack 10 rises. When the temperature Tx_min, which is the lower temperature of the stack 10a and the temperature of the stack 10b, satisfies T0 <Tx_min ≦ T1, the target voltage Vset is set to the first voltage V1 (step S106). When T1 <Tx_min ≦ Tok, the target voltage Vset is set to the second voltage V2.
The operating point on the IV curve of the stack 10 changes as follows until the temperature of the stack 10 rises to the operation lower limit temperature Tok. Note that only one stack is considered here. That is, in FIG. 2, the lower temperature of the plurality of stacks 10a and 10b is represented by Tx_min, but only the temperature Tx of one stack is considered here.
When the temperature Tx of the stack 10 reaches the first temperature T0, the target voltage Vset is set to the first voltage V1 (step S106). At this time, the operating point of the stack 10 is a point P1 in FIG. As the temperature of the stack 10 rises from the first temperature T0 to the second temperature T1, the operating point of the stack 10 moves from the point P1 to the point P2. When the temperature of the stack 10 exceeds the second temperature T1, the target voltage Vset is changed from the first voltage V1 to the second voltage V2 (step S108: YES and step S110). At this time, the operating point of the stack 10 moves from the point P2 to the point P3. As the temperature of the stack 10 rises from the second temperature T1 to the operation lower limit temperature Tok, the operating point of the stack 10 moves from the point P3 to the point P4.
The current output from the voltage-controlled stack 10 during start-up control is in the range from Imin to Imax in FIG. By appropriately adjusting the target voltage values (first voltage V1 and second voltage V2 in the above example) to be increased stepwise as the temperature of stack 10 rises, the current output by stack 10 during start-up control is adjusted. It can be within a predetermined range. This means that pseudo current control can be realized. In addition, since the stack is actually voltage-controlled, the voltage of the stack does not become lower than the target voltage (however, although the voltage is controlled, some voltage fluctuation may occur). While increasing the target voltage of the voltage control stepwise as the temperature of the stack 10 increases, the voltage of the stack 10 is prevented from becoming abnormally low (that is, while suppressing deterioration of the stack), and is simulated. Current control can be performed.
The “predetermined range” is preferably set to a current range corresponding to the amount of fuel (hydrogen) supplied to the stack 10. Even in the voltage control, the output current of the stack 10 can be within a range commensurate with the fuel supplied to the stack 10. This can suppress the phenomenon of non-ionized fuel burning locally in the stack.

  The fuel cell device 100 according to the embodiment includes a plurality of stacks (stacks 10a and 10b), and all the stacks are voltage-controlled until the temperature of all the stacks exceeds the operation lower limit temperature Tok. Then, when the temperature of all the stacks exceeds the operation lower limit temperature Tok, the control is switched to the current control in which the target current is set to zero (step S114). When all the stacks are capable of steady operation, all the stacks can be shifted from the same state (no output current) to the steady operation at the same time. Further, even if the temperature of each stack is different, the target voltage Vset is increased stepwise in accordance with the lowest temperature Tx_min (step S108). That is, voltage control is performed on the plurality of stacks with the same target voltage. As a result, the control instruction form can be simplified, and an abnormal drop in voltage in the stack having the lowest temperature can be avoided even if the temperatures of the plurality of stacks are different.

  Note that, when the temperature of the stack 10 is equal to or lower than the first temperature T0, the voltage is controlled as the target current Vset = Vmax for the following reason. As can be seen from FIG. 3, Vmax is the maximum voltage that the stack 10 can output, and no current flows when the voltage of the stack 10 is the maximum voltage Vmax. Voltage control with the target voltage Vset = Vmax effectively means that no current is drawn from the stack 10. The case where the temperature of the stack 10 is extremely low (when the temperature of the stack is equal to or lower than the first temperature T0) means immediately after the start of the chemical reaction in the stack. Immediately after the start of the chemical reaction, the temperature distribution inside the stack is large. This is because when the current is drawn from the stack in such a state, the electrical state inside the stack becomes extremely uneven and the stack is likely to deteriorate.

(Second Embodiment) Next, a fuel cell apparatus according to a second embodiment of the present invention will be described. The fuel cell apparatus of the second embodiment has basically the same configuration as the fuel cell 100 shown in FIG. Therefore, the description of the configuration of the fuel cell device of the second embodiment is omitted.

The fuel cell device of the second embodiment individually controls the voltage / current controllers 14a and 14b corresponding to the plurality of stacks 10a and 10b, respectively. The overall controller 20 of the second embodiment is for each of the stack and the voltage / current controller (the stack 10a and the voltage / current controller 14a, and the stack 10b and the voltage / current controller 14b). Then, the processing shown in FIG. 2 is executed individually. The overall controller 20 executes a process of replacing Tx_min with the temperature of the stack 10a in the flowchart of FIG. 2 for the set of the stack 10a and the voltage / current controller 14a. For the set of the stack 10b and the voltage / current controller 14b, a process in which Tx_min is replaced with the temperature of the stack 10b in the flowchart of FIG. 2 is executed.
Further, the overall controller 20 maintains the target current Iset at zero with respect to the stack whose temperature has previously exceeded the operation lower limit temperature Tok until both the temperatures of the stacks 10a and 10b exceed the operation lower limit temperature Tok.
According to the fuel cell device of the second embodiment, even if the temperature varies from stack to stack, it is possible to maintain the target voltage appropriate for the temperature of each stack. Further, among the plurality of stacks, the stack whose temperature has quickly exceeded the operation lower limit temperature is maintained in a state where the target current Iset is zero until all the stacks exceed the operation lower limit temperature. Accordingly, normal operation (use of the fuel cell device as a power source) can be started after all the stacks are in the same state (that is, a current control state in which the target current Iset is set to zero).
In the fuel cell device of the second embodiment, the voltage / current controllers 14a and 14b and the overall controller 20 also function as an output controller 30 that controls the outputs of the stacks 10a and 10b.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
For example, the fuel cell device may include a voltage controller and a current controller separately instead of the voltage / current controller 14 that switches between voltage control and current control.
In the above embodiment, the start control of the fuel cell device has been described with reference to FIG. The process of FIG. 2 is preferably executed not only at the time of start-up, but also when the temperature of the stack becomes lower than the operation lower limit temperature for some reason during the operation of the fuel cell device. That is, the present invention is effective not only at the time of start-up but also when the temperature of the stack becomes equal to or lower than the operation lower limit temperature.
In the above embodiment, the target voltage during the start-up control is changed in two stages (first voltage V1 and second voltage V2). When the target voltage is increased stepwise as the stack temperature rises, it may be increased more than three steps. Alternatively, the target voltage may be continuously increased as the stack temperature rises.

  The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

FIG. 1 is a block diagram of the fuel cell device of the first embodiment. FIG. 2 is a flowchart of start control of the fuel cell device. FIG. 3 is a schematic graph showing IV characteristics of the fuel cell stack.

Explanation of symbols

10a, 10b: Fuel cell stacks 12a, 12b: Temperature sensors 14a, 14b: Voltage / current controller 16: Power controller 18a, 18b: Voltage sensor 20: General controller 30: Output controller 40: Output terminal 100: Fuel Battery device

Claims (4)

A stack having at least one fuel cell;
A temperature sensor that detects the temperature of the stack;
When the temperature detected by the temperature sensor is lower than the threshold, voltage control is performed to maintain the voltage output from the stack at the target voltage, and when the detected temperature is higher than the threshold, the current output from the stack is maintained at the target current. An output controller for performing current control,
A fuel cell device comprising:   2. The fuel cell device according to claim 1, wherein the output controller increases the target voltage as the temperature of the stack increases while executing the voltage control. It has multiple stacks and each stack has a temperature sensor,
The output controller can execute voltage control and current control independently for each stack, and until the temperature of all stacks exceeds the threshold value, the target current of the stack whose temperature exceeds the threshold value is reduced to zero. The fuel cell device according to claim 1, wherein the fuel cell device is maintained.   When the temperature of the stack having at least one fuel cell is lower than a threshold, voltage control is performed to maintain the voltage output from the stack at a target voltage, and when the temperature of the stack is higher than the threshold, the current output from the stack A control method for a fuel cell device, wherein current control is performed to maintain the current at a target current.

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