JP2001210345A - Output control device of fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a output control device of a fuel cell system, which can supply an electric power generated in the fuel cell to a load system ideally, and in which a sufficient operation performance can be brought about. SOLUTION: To have set to detect input voltage and output voltage of both input side and output side of DC/DC converter 21 by voltage detection parts 23, 25, in the case a voltage difference between the input voltage and the output voltage is within a predetermined range, by controlling to fix the output voltage of a stuck 7 in constant value (step S40), even when the DC/DC converter 21 works in a switch region of pressure up conversion and pressure down conversion, the output voltage can be fixed by the one of the conversion action.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output control device for a fuel cell system, and more particularly to an output of a fuel cell system capable of optimally supplying electric power generated by a fuel cell to a load system to derive sufficient operation performance. It is to provide a control device.

[0002]

2. Description of the Related Art In a fuel cell vehicle configured to supply electric power generated by a fuel cell system to a driving motor, the output of the fuel cell generally changes according to the operation of a driver. At the same time, in order to generate electric power to be supplied to the drive motor to the stack, the amount of hydrogen generated in the reformer is controlled to change, but the response speed of the reformer tends to be lower than the load fluctuation.

For this reason, if power is drawn from the stack in accordance with the increase in the load by the driving motor, the amount of hydrogen supplied to the stack becomes insufficient, causing a problem that the stack voltage drops abnormally. Therefore, the power corresponding to the amount of hydrogen and the amount of air supplied to the stack should be drawn out, and an excess or deficiency of the power from the stack and the power required by the load occurs only for the response delay of the stack. The power difference is absorbed by charging and discharging from the secondary battery.

Conventionally, in an output control device of a fuel cell system mounted on a fuel cell vehicle, a step-up / step-down DC / DC having a basic configuration as shown in FIG. The converter 121 is arranged between the stack and the load. In the DC / DC converter 121, the step-up conversion and the step-down conversion
The switching elements to be operated are different from each other,
A desired voltage is generated according to the duty ratio of a control signal applied to the bases of the transistors Tr101 and Tr103. FIG. 11 shows transistors Tr101 and Tr10.
3 is a graph showing a relationship between a duty ratio of a control signal applied to a base No. 3 and a step-up / step-down ratio.

At the time of boosting, an ON control signal (1) is applied to the CNT 101 to turn on the transistor Tr101, and a control signal having a desired duty ratio is applied to the CNT 103 to turn the transistor Tr103 on and off, so that the input voltage Vin or more. Is controlled to output a voltage of On the other hand, when stepping down, the CNT 103 is turned off.
The control signal (0) is applied to turn on the transistor Tr103.
F operation, and apply a control signal of a desired duty ratio to CNT101 to turn on transistor Tr101.
It is controlled so as to perform a −OFF operation and output a voltage equal to or lower than the input voltage Vin.

[0006]

However, FIG.
As shown in (1), the output voltage that can be extracted from the DC / DC converter 121 does not always have continuity. In particular, when the input / output voltages are almost equal and switching is performed from step-up conversion to step-down conversion, or when switching is performed from step-down conversion to step-up conversion, it is difficult to convert the power stably by the DC / DC converter 121. Can be

That is, when a voltage sensor is used to detect the voltage of a secondary battery or a load provided on the output side of the DC / DC converter 121, the sensor itself has some detection error. A / D of sensor output signal
Even if the signal is input to the converter and quantized, the resolution and error of the A / D converter itself are added. Therefore, for example, 2
The voltage of the next battery or load is compared with the output voltage from the stack, and even if the conversion function of the DC / DC converter 121 is switched based on the magnitude relationship between the two, the above-described detection error is added and an error occurs in the switching determination. Therefore, it is considered that an appropriate conversion function cannot be selected.

As described above, in the boundary region where the DC / DC converter switches between step-up conversion and step-down conversion, appropriate switching control is impeded by detection errors of input / output voltage, stack current, and the like, which are information for determining switching control. As a result, it may be difficult to secure desired driving performance.

[0009] The present invention has been made in view of the above,
An object of the present invention is to provide an output control device of a fuel cell system capable of optimally supplying electric power generated by a fuel cell to a load system and extracting sufficient operation performance.

[0010]

According to the first aspect of the present invention,
In order to solve the above problems, a reformer that reforms fuel to generate a reformed gas containing hydrogen, a compressor that compresses air,
A fuel cell that generates electricity using reformed gas supplied from a reformer and air supplied from a compressor, and power control means that performs step-up or step-down conversion of power output from the fuel cell according to a request command Power storage means for storing the power output from the power control means, and a load connected in parallel with the power storage means and consuming the power output from the power control means in accordance with an operating condition; Voltage detecting means for detecting an input voltage and an output voltage on the input side and output side of the control means; calculating means for calculating a voltage difference between the input voltage and the output voltage detected by the voltage detecting means; A fixed control means for controlling the output voltage of the fuel cell to be fixed at a constant value when the voltage difference is within a predetermined range.

According to a second aspect of the present invention, in order to solve the above problems, the fixed control means controls the output current of the fuel cell so as to have a constant value.

According to a third aspect of the present invention, in order to solve the above-mentioned problem, the power control means may be configured to fix an output voltage of the fuel cell to a constant value and then to obtain a desired output of the fuel cell. A voltage estimating means for estimating an output voltage; and a voltage difference calculating means for calculating a voltage difference between an estimated output voltage estimated by the voltage estimating means and an output voltage value of the power control means. When the calculated voltage difference is equal to or larger than a predetermined value, the gist of the invention is to release the control for fixing the output voltage of the fuel cell to a constant value.

According to a fourth aspect of the present invention, there is provided an exhaust hydrogen combustor provided in the reformer for burning hydrogen discharged from a fuel cell, and detecting a temperature of the exhaust hydrogen combustor. Temperature fixing means, the fixed control means,
The gist of the present invention is to release the control for fixing the output voltage of the fuel cell to a constant value when the temperature of the exhaust hydrogen combustor is outside a predetermined temperature range.

According to a fifth aspect of the present invention, there is provided a hydrogen amount detecting means for detecting the amount of hydrogen on an input side and an output side of the fuel cell; A hydrogen utilization rate calculating means for calculating a hydrogen utilization rate in the fuel cell based on the hydrogen amount on the output side, wherein the fixed control means determines that the hydrogen utilization rate calculated by the hydrogen utilization rate calculating means is a predetermined value. In this case, the control for fixing the output voltage of the fuel cell to a constant value is released when the value exceeds the limit.

[0015]

According to the first aspect of the present invention, the input voltage and the output voltage of the input side and the output side of the power control means are detected, and the voltage of the detected input voltage and output voltage is detected. By controlling the output voltage of the fuel cell to a fixed value when the difference is within a predetermined range,
Even when the power control means operates in the switching region between the step-up conversion and the step-down conversion, the output voltage can be fixed by one of the conversion operations. As a result, it is possible to prevent appropriate switching control from being disturbed by detection errors of the input / output voltage and the stack current, etc., which serve as the switching control determination information, and to obtain sufficient driving performance.

Further, according to the present invention, the output voltage of the fuel cell can be fixed at a constant value by controlling the output current of the fuel cell to a constant value.

According to the third aspect of the present invention, the power control means estimates an output voltage when a desired output of the fuel cell is obtained after fixing the output voltage of the fuel cell to a constant value. When the voltage difference between the estimated output voltage and the output voltage value of the power control means is equal to or larger than a predetermined value, the power control means cancels the control for fixing the output voltage of the fuel cell to a constant value, so that the power control means It is possible to shift from the conversion operation to the other conversion operation.

According to the present invention, hydrogen discharged from the fuel cell provided in the reformer is burned in the exhaust hydrogen combustor, and the temperature of the exhaust hydrogen combustor is detected. Keep it. Here, when the temperature of the exhaust hydrogen combustor is out of the predetermined temperature range, by canceling the control for fixing the output voltage of the fuel cell to a constant value, the fuel cell generates power according to the required power value. By consuming the amount of hydrogen, the amount of hydrogen entering the exhaust hydrogen combustor can be returned to the original, and the temperature of the exhaust hydrogen combustor can be prevented from exceeding a predetermined range.

According to the present invention, the amounts of hydrogen on the input side and the output side of the fuel cell are detected in advance.
Based on the detected amount of hydrogen, the hydrogen utilization rate in the fuel cell is calculated, and when the hydrogen utilization rate exceeds a predetermined value, the control for fixing the output voltage of the fuel cell to a constant value is released. The power control means can shift from one conversion operation to the other conversion operation.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a diagram showing a system configuration of a power control device of a fuel cell system according to a first embodiment of the present invention.

In FIG. 1, a fuel tank 1 stores methanol as a fuel. The methanol is sent to a reformer 3 to be reformed into a reformed gas containing hydrogen gas, and further supplied to a stack 7. Is done. At the same time, compressor 5
Sucks air, compresses it, and supplies it to the stack 7.
The stack 7 is an assembly of a large number of fuel cells, and obtains electric energy by reacting the inflowing hydrogen gas with oxygen in the air.

The remaining hydrogen not used for the reaction in the stack 7 is discharged to a waste hydrogen combustor (not shown) in the reformer 3.
The fuel is returned and burned, and is used as a heat source in the reformer 3. Further, exhaust air is exhausted from the stack 7 to the outside of the vehicle.
The electric current generated from the stack 7 is power-controlled by the power control unit 9 and supplied to a chargeable / dischargeable power storage unit 11 composed of, for example, a secondary battery, and a load 13 composed of an inverter, a driving motor, and a fuel cell system device. Is done.

The system control unit 15 stores a control program and control data for controlling the entire apparatus.
M and RAM that always stores control data, control flags, etc.
And a CPU that controls the entire apparatus according to a control program stored in the ROM. The temperature sensor 17 detects the temperature of the exhaust hydrogen combustor provided in the reformer and outputs the detected temperature to the system control unit 15.

FIG. 2 shows a DC / D which constitutes the power control unit 9.
FIG. 3 is a diagram showing a specific configuration of a C converter 21. This D
The input side and the output side of the C / DC converter 21
Input voltage Vin and output voltage Vout of DC converter 21
Are provided, and the output voltage detected by the voltage detection units 23 and 25 is output to the system control unit 15. Then, the DC / DC converter 21 performs switching operation of the transistors Tr1 and Tr3 based on the command values CNT1 and CNT3 given from the system control unit 15, and controls the output current to a desired value.

Next, the operation of the power control device of the fuel cell system according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a flowchart showing the main control flow. FIG. 4 is a flowchart of a subroutine representing details of the output holding determination process. FIG. 5 is a flowchart of a subroutine showing details of the output holding release determination processing. FIG. 6 is a graph showing current-voltage characteristics of the stack. FIG. 7 is a diagram illustrating an example of a change over time of the stack output power (a), the stack voltage (b), and the exhausted hydrogen amount (c) when the required power amount increases. FIG. 8 is a diagram illustrating an example of a change over time of the stack output power (a), the stack voltage (b), and the amount of discharged hydrogen (c) when the required power amount decreases.

First, in FIG. 3, in step S10, it is determined whether or not the power drawn from the stack 7 is kept at a constant value irrespective of a change in the required power value. here,
The output holding determination processing will be described in detail with reference to a subroutine shown in FIG.

Referring to FIG. 4, first, in step S110, the input voltage and the output voltage of the DC / DC converter 21 are detected by the voltage detectors 23 and 25, respectively. Next, in step S120, an absolute value is obtained for the detected voltage difference between the input voltage Vin and the output voltage Vout, and it is determined whether the difference is less than a predetermined reference value ΔV. That is, it is determined whether the input / output voltage difference is within the reference range (−ΔV to ΔV).

| Vin−Vout | ≦ ΔV It is desirable that the reference value ΔV used for the above-described determination is set to be larger than a voltage width that makes the determination of step-up / step-down erroneous due to a detection error of the control system. In other words, for a boundary region where the magnitude relationship between the input and output voltages of the DC / DC converter 21 is considered to be reversed, the time during which the two are substantially equal due to the detection error of the input and output voltages by the voltage detection units 23 and 25 is determined. It is desirable to set the time during which the resolution of the A / D converter in the CPU constituting the system control unit 15 is lower than the resolution to be shorter than the sampling period.

If the absolute value of the input / output voltage difference of the DC / DC converter 21 is equal to or larger than the reference value ΔV, it is determined that it is not necessary to hold the value, and the subroutine is terminated without setting the holding flag. I do. The power command value drawn from the stack 7 includes the accelerator opening degree, the brake pedal force, the amount of power required from a load, for example, an inverter, a driving motor (not shown), and system equipment, and the charge / discharge of the power storage unit 11. It is a command value of the total power required for the stack 7 determined in consideration of the possible amount, and in the present embodiment, is calculated by the system control unit 15.

On the other hand, in step S130, if the absolute value of the input / output voltage difference is smaller than the reference value ΔV, since the magnitude relationship between the input / output voltages is in a boundary area where it is likely to be reversed after a while, the stack 7 The holding flag is set (1) to hold the power command value drawn from

Next, referring to FIG. 3, in step S20,
It is determined whether to hold or cancel the held power command value. Here, the output hold release determination processing will be described in detail with reference to a subroutine shown in FIG.
First, in step S210, the DC / DC converter 2
The first output voltage Vout is detected by the voltage detection unit 25.

In step S220, the input voltage input from the stack 7 to the DC / DC converter 21 when the holding of the power command value is released, that is, the output voltage of the stack 7, is estimated. Specifically, while maintaining the power command value, the power command value originally requested is monitored, and the voltage value Vin ′ when the power is drawn from the stack 7 is represented by the current-voltage characteristic shown in FIG. Estimate by referring to.

The current-voltage characteristic of the stack 7 shows a tendency that the voltage V decreases as the current I increases, as shown in FIG. FIG. 6 shows an example in which hydrogen and air required for power generation are sufficiently supplied. Further, the current-voltage characteristics shown in FIG. 6 may be corrected by using the amount of hydrogen and / or the amount of air supplied to the stack 7 or the pressure of both, but the detailed description thereof is not directly related to the present invention. Is omitted.

Then, in step S230, DC / D
The absolute value of the voltage difference between the output voltage Vout of the C converter 21 and the estimated input voltage Vin ′ is determined, and it is determined whether the difference is less than a predetermined reference value ΔV. If the voltage difference is equal to or greater than the reference value ΔV, it is determined that it is not necessary to maintain the power command value drawn from the stack 7 and step S3
At 00, the holding flag is cleared (0).

On the other hand, if the input / output voltage difference is less than the reference value ΔV, it is determined that it is not necessary to release the holding of the power command value yet, and the process proceeds to step S240. In step S240, the temperature T of the exhaust hydrogen combustor is detected by the temperature sensor 17 provided in the exhaust hydrogen combustor (not shown) in the reformer 3.

The exhaust hydrogen combustor burns the exhaust hydrogen not consumed in the stack 7 to maintain the temperature in the reformer 3, and maintains the amount of hydrogen consumed in the stack 7 at a certain value. As a result, the power drawn from the stack 7 is held at a certain value.

Now, the response speed of the reformer 3 is
So that when the output hold is released, sufficient output can be drawn from the stack 7.
Consider that the amount of hydrogen generated in the reformer 3 is changed according to the power required for the fuel cell system regardless of the amount of hydrogen consumed in the stack 7. In this case, the amount of exhausted hydrogen not consumed in the stack 7 will differ from the required amount scheduled for combustion in the exhausted hydrogen combustor. If the amount of exhausted hydrogen is excessive, the temperature T of the exhausted hydrogen combustor becomes If the amount of exhaust hydrogen is insufficient and the amount of exhausted hydrogen is insufficient, the temperature T tends to decrease.

Therefore, in step S250, it is determined whether the temperature T of the exhaust hydrogen combustor detected by the temperature sensor 17 exceeds a predetermined range from the upper limit temperature Tlow to the lower limit temperature Thi.

Tlow ≦ T ≦ Th If it is determined that the temperature T of the exhaust hydrogen combustor exceeds this range, the process proceeds to step S300, the holding flag of the power command value is cleared (0), and the stack 7 Generates power in accordance with the required power value and consumes the amount of hydrogen, thereby returning the amount of hydrogen entering the exhaust hydrogen combustor and preventing the temperature T from exceeding this range.

As shown in FIG. 7B, at time t1 when the stack voltage (input voltage) approaches the battery voltage (output voltage), the current drawn from the stack 7 starts to be controlled to a constant value. In this case, as shown in FIG. 7 (b), the amount of hydrogen consumed in the stack 7 becomes a constant value, and the reformer 3 generates hydrogen in accordance with the required amount of power. Increase. Further, when the holding flag is cleared (0) at time t2 and the output holding is released and the required power amount is drawn from the stack 7, the voltage decreases according to the power value, and the hydrogen consumption increases. As shown in FIG. 7C, the discharged hydrogen amount also returns to a value close to the original value.

As shown in FIG. 8B, at time t3 when the stack voltage (input voltage) approaches the battery voltage (output voltage), the current drawn from the stack 7 starts to be controlled to a constant value. In this case, as shown in FIG. 8B, the amount of hydrogen consumed in the stack 7 becomes a fixed amount, and the reformer 3
In order to reduce the amount of generated hydrogen in accordance with the required amount of power, the amount of discharged hydrogen is reduced. Further, when the holding flag is cleared (0) at time t4 and the output holding is released and the required power amount is drawn from the stack 7, the voltage decreases according to the power value, and the hydrogen consumption also decreases. FIG.
As shown in (c), the discharged hydrogen amount also returns to a value close to the original value.

Referring to FIG. 5, in step S260, it is determined whether the required power has the same tendency even after the holding determination. That is, after it is estimated that the magnitude relationship between the input / output voltages of the DC / DC converter 21 intersects, it is estimated whether the direction of change in the required power value is reversed and the intersection does not occur.

More specifically, a time change of the required power change amount is calculated, and if the current value and the previous value have the same sign, that is, if the current value continuously increases or decreases, the stack voltage also tends to decrease or increase, respectively. It is determined that the tendency continues, and the power from the stack 7 is maintained without clearing the holding flag.

If the sign has been reversed, in step S270, the stack voltage at the time of holding release is estimated in order to determine the release of the power holding from the stack 7. In addition,
The content of this step is the same as step S220 described above.

Then, in a step S280, it is determined whether or not the input / output voltages have already crossed. If they have already crossed, the holding is continued until they cross again. Then, when it is estimated that the magnitude relationship between the input and output voltages does not intersect, the process proceeds to step S290, where it is determined whether the holding flag is cleared (0) and released. That is, in step S280, when the change direction of the required power value is reversed and the change tendency of the stack voltage is also reversed, it is considered that the magnitude relationship between the input and output voltages does not change as it is. If it has, flip it again and wait for it to return to its original relationship.

In step S290, it is determined whether the absolute value of the voltage difference between the output voltage Vout and the estimated input voltage Vin 'is within a predetermined reference value ΔV. If the absolute value of the input / output voltage difference exceeds the reference value, step S30
0, clear (0) and release the output holding flag,
It returns to the main routine shown in FIG.

On the other hand, when the absolute value of the input / output voltage difference is equal to or smaller than the reference value, the process returns to the main routine shown in FIG. Referring to FIG. 3, in step S30, it is determined whether the holding flag is in the set state (1). If the holding flag is (1), the process proceeds to step S40, where output holding control is performed, and the magnitude relationship between the input and output voltages is performed. Wait for him to come back.

On the other hand, if the holding flag is not in the set state (1), the process proceeds to step S50, where normal control is performed, and
The process ends. That is, as the normal control, DC /
The input voltage Vin and the output voltage Vout detected by the voltage detection units 23 and 25 provided on the input / output side of the DC converter 21.
Compare.

When Vin <Vout, and the input voltage Vin is lower than the output voltage Vout, the DC / DC converter 21 can perform a boosting operation. The CNT3 composed of a rectangular wave having a certain duty ratio is output to the transistor Tr3 so that I flows so as to perform a switching operation. As a result, when the transistor Tr3 is turned on, the power input from the stack 15 is charged in the inductor L1 and the transistor Tr3 is turned on.
When the switch 3 is OFF, power is discharged from the inductor L1 and added to the voltage between the terminals of the capacitor C3 to be boosted.

On the other hand, the input voltage Vin is compared with the output voltage Vout, and it becomes Vin> Vout. If the input voltage Vin is higher than the output voltage Vout, the DC / DC converter 21 can perform a step-down operation. First, the transistor Tr3 is turned off by CNT3.
F control is performed, and CNT1 composed of a rectangular wave having a certain duty ratio is output to the transistor Tr1 to perform a switching operation so that a desired current I flows. As a result, when the transistor Tr1 is turned on, the power input from the stack 15 is charged into the capacitor C3 via the inductor L1 and the diode D3. When the transistor Tr1 is turned off, the power is discharged from the capacitor C3 and the capacitor C3 is discharged. The voltage between terminals is reduced.

The effect of the first embodiment is that DC /
The input voltage and the output voltage on the input side and the output side of the DC converter 21 are detected by the voltage detection units 23 and 25, and the voltage difference between the detected input voltage and the output voltage is within a predetermined range. In addition, by controlling the output voltage of the stack 7 to be fixed to a constant value, even when the DC / DC converter 21 is operating in the switching region between the step-up conversion and the step-down conversion, the output voltage is controlled by one of the conversion operations. Can be fixed. As a result, it is possible to prevent appropriate switching control from being disturbed by detection errors of the input / output voltage and the stack current, etc., which serve as the switching control determination information, and to obtain sufficient driving performance.

Further, by controlling the output current of the stack 7 to a constant value, the output voltage of the stack 7 can be fixed at a constant value. Further, after fixing the output voltage of the stack 7 to a constant value, the DC / DC converter 21 estimates an output voltage when a desired output is obtained for the stack 7, and the estimated output voltage and the DC / DC converter 2
In the case where the voltage difference from the output voltage value of the stack 1 is equal to or more than the predetermined value, the control for fixing the output voltage of the stack 7 to a constant value is released, so that the DC / DC converter 21 switches from one conversion operation to the other conversion operation. Move to operation.

Further, the exhaust hydrogen discharged from the stack 7 provided in the reformer 3 is burned by the exhaust hydrogen combustor, and the temperature of the exhaust hydrogen combustor is detected by the temperature sensor 17. Here, when the temperature of the exhaust hydrogen combustor is out of the predetermined temperature range, by canceling the control for fixing the output voltage of the stack 7 to a constant value, the stack 7 generates power according to the required power value. By consuming the amount of hydrogen, the amount of hydrogen entering the exhaust hydrogen combustor can be returned to the original, and the temperature of the exhaust hydrogen combustor can be prevented from exceeding a predetermined range.

(Second Embodiment) A power control device for a fuel cell system according to a second embodiment of the present invention is shown in FIG.
Has the same basic configuration as the power control device of the fuel cell system corresponding to the first embodiment shown in FIG.

Next, a part of the control operation of the power control device will be described with reference to a flowchart of a subroutine for the output holding release determination processing shown in FIG. Note that the control flowchart shown in FIG. 9 has the same basic procedure as the control flowchart shown in FIG. 5, and the same procedure is denoted by the same reference numeral. The control flowchart shown in FIG. 9 is also stored as a control program in the internal ROM of the system control unit 15.

As shown in FIG. 8A, when the output from the stack 7 is held while the required power value is decreasing, the amount of hydrogen discharged from the stack 7 decreases. This is because while the hydrogen reformed in the reformer 3 is reduced in accordance with the required electric energy, the output power of the stack 7 is converted to electric power for the hydrogen supplied to the stack 7 in order to maintain the output power of the stack 7 at a certain value. That is, the ratio of consumed hydrogen (hereinafter, referred to as hydrogen utilization rate) increases.

When the hydrogen utilization exceeds a certain limit, the voltage characteristics such as a decrease in the output voltage of the stack 7 due to the reason that the pressure and amount of hydrogen are not evenly distributed to all the cells constituting the stack 7 are considered. It is conceivable that it will decrease.

Therefore, a feature of the second embodiment is that the hydrogen utilization is prevented from rising beyond the limit. Specifically, in FIG. 9, in step S253, the hydrogen utilization rate Sr is calculated. That is, a hydrogen flow meter (not shown) is provided in each of a hydrogen path supplied to the stack 7 from the reformer 3 and a hydrogen path of hydrogen discharged from the stack 7 shown in FIG. Is used to calculate the utilization rate Sr.

Then, in a step S255, it is determined whether or not the calculated hydrogen utilization rate Sr exceeds a predetermined reference value Sr '. Here, when the hydrogen utilization rate Sr exceeds the predetermined reference value Sr ′, the step S
Proceeding to 300, the output holding flag of the stack 7 is cleared (0) and released.

On the other hand, if the hydrogen utilization ratio Sr does not exceed the predetermined reference value Sr ', the output holding flag is kept in the set state (1). Step S25
3. Instead of S255, a change in the output voltage of the stack 7 may be detected to estimate that the hydrogen utilization rate has risen beyond the limit. This is a case where the output current of the stack 7 is maintained at a constant value. When a sufficient amount of hydrogen is supplied to the stack 7, the output voltage of the stack 7 is also maintained at a constant value. This is based on the fact that when the amount of hydrogen supplied from the vessel 3 relatively decreases, the voltage characteristics such as the output voltage of the stack 7 decreases.

While the output of the stack 7 is being held, a change in the output voltage of the stack, that is, a change in the input voltage Vin of the DC / DC converter 21 is detected. Judge that it has risen above a certain limit. In steps S253 & S255, the hydrogen utilization rate Sr is set to a predetermined reference value Sr '.
Is selected to clear (0) and release the output holding flag of the stack 7 when it is determined that the
The amount of hydrogen supplied to the stack 7 from the reformer 3 may be maintained at the amount of hydrogen at that time.

More specifically, a threshold value Sr "smaller than the hydrogen usage rate Sr used for the determination when releasing the output holding of the stack 7 is separately set, and it is determined that the hydrogen usage rate Sr has exceeded this threshold value. At this time, the control of the reformer 3 in accordance with the required power value is temporarily stopped, and the operation of the reformer 3 is continued with the hydrogen generation amount at that time, whereby the hydrogen utilization rate Sr is reduced to the threshold value Sr. It is possible to keep the value before and after "", and the output holding of the stack 7 can be continued.

When estimating the hydrogen utilization rate Sr from the output voltage of the stack 7, a threshold of a voltage change width smaller than the voltage change width for judging release of stack output holding is separately set. Is expressed by keeping the amount of hydrogen generated. In this case, it is appropriate to control the reformer 3 to return the target value of the generation amount to a value corresponding to the required power value obtained from the system when the output holding of the stack 7 is released.

The effect of the second embodiment is the same as the effect of the first embodiment. In addition, the amounts of hydrogen on the input side and the output side of the stack 7 are detected, and based on the detected amount of hydrogen. , The hydrogen utilization rate in the stack 7 is calculated, and when the hydrogen utilization rate exceeds a predetermined value, the control for fixing the output voltage of the stack 7 to a constant value is released, whereby DC
The / DC converter 21 can shift from one conversion operation to the other conversion operation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a system configuration of a power control device of a fuel cell system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a specific configuration of a DC / DC converter 21 constituting the power control unit 9;

FIG. 3 is a flowchart illustrating a main control flow.

FIG. 4 is a flowchart of a subroutine representing details of an output holding determination process.

FIG. 5 is a flowchart of a subroutine representing details of an output holding release determination process.

FIG. 6 is a graph showing current-voltage characteristics of a stack.

FIG. 7 is a diagram showing an example of a change over time of a stack output power (a), a stack voltage (b), and a discharged hydrogen amount (c) when a required power amount increases.

FIG. 8 is a diagram illustrating an example of a change over time of a stack output power (a), a stack voltage (b), and a discharged hydrogen amount (c) when a required power amount decreases.

FIG. 9 is a flowchart of a subroutine showing details of an output holding release determination process.

FIG. 10 is a diagram showing a specific configuration of a conventional DC / DC converter.

FIG. 11 is a graph showing a relationship between a duty ratio of a control signal applied to bases of transistors Tr101 and Tr103 constituting a conventional DC / DC converter and a step-up / step-down ratio.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel tank 3 Reformer 5 Compressor 7 Stack 9 Electric power control part 11 Electric power storage part 13 Load 15 System control part 17 Temperature sensor 21 DC / DC converter 23, 25 Voltage detection part

Continued on the front page F term (reference) 5H027 BA01 BA09 KK31 KK41 KK54 MM26 5H115 PG04 PI16 PI18 PI29 PU01 PV02 PV23 QN03 SE06 SJ12 SJ13 TI10 TO13 TO21 TO23 5H420 BB12 CC03 DD01 EA10 EB26 EB37 FF03 FF22 FF26 GG

Claims (5)

[Claims] 1. A reformer for reforming a fuel to generate a reformed gas containing hydrogen, a compressor for compressing air, a reformed gas supplied from the reformer, and supplied from the compressor. A fuel cell that generates power using air, a power control unit that performs step-up or step-down conversion of the power output from the fuel cell according to a request command, and a power storage unit that stores the power output from the power control unit. A load connected in parallel with the power storage means and consuming power output from the power control means in accordance with an operating condition; detecting an input voltage and an output voltage on an input side and an output side of the power control means; Voltage detecting means, calculating means for calculating a voltage difference between the input voltage and the output voltage detected by the voltage detecting means, and when the voltage difference calculated by the calculating means is within a predetermined range, Output voltage Output control device of the fuel cell system is characterized in that a fixed control means for controlling so as to fix the value. 2. The output control device for a fuel cell system according to claim 1, wherein the fixed control unit controls the output current of the fuel cell to be a constant value. 3. The power control means, comprising: a voltage estimation means for fixing an output voltage of the fuel cell to a constant value, and then estimating an output voltage when a desired output of the fuel cell is obtained; And a voltage difference calculating means for calculating a voltage difference between the estimated output voltage estimated by the above and the output voltage value of the power control means. When the voltage difference calculated by the voltage difference calculating means is equal to or more than a predetermined value, 2. The output control device for a fuel cell system according to claim 1, wherein the control for fixing the output voltage of the fuel cell to a constant value is released. 4. An exhaust hydrogen combustor provided in the reformer for burning hydrogen exhausted from a fuel cell, and a temperature detecting unit for detecting a temperature of the exhaust hydrogen combustor, wherein the fixed control unit comprises: 4. The output control of the fuel cell system according to claim 3, wherein the control for fixing the output voltage of the fuel cell to a constant value is released when the temperature of the exhaust hydrogen combustor is out of a predetermined temperature range. apparatus. 5. A fuel cell, comprising: a hydrogen amount detector for detecting an amount of hydrogen on an input side and an output side of the fuel cell; and a hydrogen amount on the input side and an output side detected by the hydrogen amount detector. A hydrogen utilization rate calculating means for calculating the hydrogen utilization rate of the fuel cell, wherein the fixed control means, when the hydrogen utilization rate calculated by the hydrogen utilization rate calculating means exceeds a predetermined value, the output voltage of the fuel cell 4. The control according to claim 3, wherein the control for fixing the fixed value is released.
Or an output control device for a fuel cell system according to item 4.