JP2001229943A - Fuel cell system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell system capable of simplified construction as a whole system for preventing occurrence of an overcurrent during change-over of a power supply system. SOLUTION: A fuel cell stack 1 is connected to a DC/DC converter 25 via a diode 21. The target value for the output voltage of the DC/DC converter 25 during boosting operation is set to be smaller than a value obtained by subtracting a value for the on-voltage of the diode 21 from a value for the opening voltage of the fuel cell stack 1 and to be larger than a value for the output voltage of the fuel cell stack 1 at a perfect balance state, when the entire power required for starting the fuel cell stack 1 is supplied from the fuel cell stack 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell system and, more particularly, to a fuel cell system using a fuel cell stack as a main power source and supplying air using a separate power source when starting up the fuel cell stack. The present invention relates to a fuel cell system for starting the fuel cell.

[0002]

2. Description of the Related Art As a conventional fuel cell system, for example, a system shown in FIG. 7 is known. In this fuel cell system, the fuel gas supply means 3 and the air compressor 7 supply a fuel gas containing a large amount of hydrogen and an air containing oxygen to the fuel cell stack 1 from the fuel gas supply means 3 and the air compressor 7, respectively. I do. At this time, for example, air is pumped to the fuel cell stack 1 by driving the air compressor 7. The drive power of the air compressor 7 varies depending on the system, but when it is about several kW or more, a low-voltage secondary battery of about 12 V, which is generally used for supplying power to vehicle auxiliary equipment, is used as a power supply. Than the vehicle drive motor (load 3
The current value can be reduced by using a high-voltage power supply of, for example, about 350 V to supply power in 1). This is preferable in that the diameter of a harness for supplying electric power to the air compressor 7 and the size of other associated devices can be reduced.

Therefore, when the fuel cell stack 1 is started before the fuel cell stack 1 can generate high-voltage power, the output voltage of the secondary battery 13 for the vehicle accessory 15 is converted to the DC / DC converter 25. High-voltage power obtained by boosting is supplied to the air compressor 7, and after the start of the fuel cell stack 1, the power supply system is switched so that the air compressor 7 is driven by the power from the fuel cell stack 1. I have.

[0004]

However, in such a conventional fuel cell system, after the start of the fuel cell stack 1 is completed, the power supply of the air compressor 7 is changed from the boosted power of the secondary battery 13 to the fuel cell stack 1. It is necessary to exchange information densely between the sub-units of the fuel cell system before detecting the start-up state of the fuel cell stack 1 and notifying the result to the DC / DC converter 25 when switching to the above-mentioned power. Therefore, the configuration of the control system and, consequently, the overall configuration of the fuel cell system are complicated. For example, in the example shown in FIG. 7, the control device 5 of the fuel gas supply means 3, the control device 11 of the air compressor 7, the control device 33 of the load 31 (vehicle drive motor or the like), the control device 101 of the DC / DC converter 25, And switching means 10 such as a relay
3 are all connected to the control unit 105.

When the power supply system is switched by the mechanical switching means 103 such as a relay after the start of the fuel cell stack 1 is completed, the output voltage of the fuel cell stack 1 and the voltage of the air compressor 7 immediately before switching are large. If they are different, there is a problem that an overcurrent may flow through the switching means 103.

[0006] The present invention has been made in view of the above,
An object of the present invention is to provide a fuel cell system capable of simplifying the overall configuration of the system and preventing occurrence of overcurrent when switching the power supply system.

[0007]

According to the first aspect of the present invention,
In order to solve the above problems, a fuel cell stack that generates power using fuel gas and air, a secondary battery that generates power at a voltage lower than the voltage of power generated by the fuel cell stack, Boosting the voltage of the power generated by the secondary battery to supply power to the power supply destination of the battery stack to the voltage of the power generated by the fuel cell stack, or charging the secondary battery A voltage conversion unit that steps down a voltage of the power generated by the fuel cell stack to a voltage of the power generated by the secondary battery, and a control unit that controls switching between a step-up operation and a step-down operation in the voltage conversion unit. When the fuel cell stack is started, the voltage conversion means is switched to a step-up operation, and the fuel cell system supplies power required for starting the fuel cell stack using the secondary battery. Wherein the fuel cell stack and the voltage conversion means are connected via a diode, and a target value of an output voltage at the time of a boosting operation of the voltage conversion means is calculated based on an open voltage value of the fuel cell stack. Is smaller than the value obtained by subtracting the value of the ON voltage of the fuel cell stack, and is smaller than the value of the output voltage of the fuel cell stack at the time of equilibrium when all the power required for starting the fuel cell stack is supplied from the fuel cell stack. The gist is that a large value is set.

According to a second aspect of the present invention, in order to solve the above-mentioned problem, there is provided a voltage detecting means for detecting an output voltage of the fuel cell stack, and the control means controls the output voltage of the fuel cell stack for a predetermined time. When the voltage is equal to or more than the predetermined reference value, the gist of the present invention is to switch the voltage conversion means from a boosting operation to a step-down operation.

According to a third aspect of the present invention, in order to solve the above-mentioned problem, there is provided a current detecting means for detecting an output current of the voltage converting means, and the control means controls the output current of the voltage converting means for a predetermined time. When the voltage is equal to or less than the predetermined reference value, the gist of the present invention is to switch the voltage conversion means from a boosting operation to a step-down operation.

In order to solve the above-mentioned problems, the invention according to claim 4 includes voltage detecting means for detecting an output voltage of the fuel cell stack, and current detecting means for detecting an output current of the voltage converting means. The control means is configured to perform the voltage conversion when the output voltage of the fuel cell stack is equal to or more than a predetermined reference value for a predetermined time or more and the output current of the voltage conversion means is equal to or less than a predetermined reference value for a predetermined time or more. The gist is to switch the means from the step-up operation to the step-down operation.

According to a fifth aspect of the present invention, to solve the above-mentioned problem, there is provided a charge state detecting means for detecting a charge state of the secondary battery, and the control means is adapted to determine whether the charge state of the secondary battery is electric power. When it is not suitable for supplying
The gist of the present invention is to switch the voltage conversion means from a step-up operation to a step-down operation.

[0012]

According to the first aspect of the present invention, the fuel cell stack and the voltage converting means are connected via the diode, and the target value of the output voltage at the time of the boosting operation of the voltage converting means is set as follows.
The fuel cell stack at equilibrium when the power required to start the fuel cell stack is all supplied from the fuel cell stack, which is smaller than the value obtained by subtracting the diode on-voltage value from the value of the open circuit voltage of the fuel cell stack By setting the output voltage to a value larger than the value of the output voltage, it is possible to determine whether or not the activation of the fuel cell stack has been completed, using only information in a single subunit including the voltage conversion means, Since there is no need to exchange information between sub-units as in the related art, the overall configuration of the system can be simplified. At the same time, the fuel cell stack and the power supply destination of the fuel cell stack are already electrically connected via a diode, and mechanical switching means such as a relay is not required as in the related art. When the power supply system is switched after the start of the battery stack is completed, occurrence of an overcurrent can be prevented.

According to the second aspect of the present invention, voltage detecting means for detecting the output voltage of the fuel cell stack is provided, and when the output voltage of the fuel cell stack is higher than a predetermined reference value for a predetermined time or more. By switching the voltage converting means from the step-up operation to the step-down operation, it is possible to determine with a very simple configuration whether or not the activation of the fuel cell stack has been completed.

According to the third aspect of the present invention, current detecting means for detecting the output current of the voltage converting means is provided,
When the output current of the voltage conversion means is equal to or more than a predetermined time and equal to or less than a predetermined reference value, by switching the voltage conversion means from the step-up operation to the step-down operation, the start-up of the fuel cell stack is completed with a very simple configuration. Can be determined.

According to the present invention, a voltage detecting means for detecting an output voltage of the fuel cell stack and a current detecting means for detecting an output current of the voltage converting means are provided. When the output voltage is equal to or more than a predetermined reference value for a predetermined time or more, and the output current of the voltage conversion means is equal to or less than a predetermined reference value for a predetermined time or more, the voltage conversion means is switched from a step-up operation to a step-down operation, thereby Compared with the case where either one of the detection means and the current detection means is used, the accuracy of the determination of the completion of the startup of the fuel cell stack can be improved.

According to the present invention, there is provided a charging state detecting means for detecting a charging state of the secondary battery,
When the state of charge of the secondary battery is in a state that is not suitable for supplying power, by switching the voltage conversion means from the step-up operation to the step-down operation, consumption of the power stored in the secondary battery is prohibited, It is possible to prevent a situation where the operation of the power supply destination of the secondary battery must be stopped.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a diagram showing a configuration of a fuel cell system according to a first embodiment of the present invention. Here, a fuel cell system mounted on a fuel cell vehicle will be described as an example.

In FIG. 1, a fuel cell stack 1 is a main power supply of the fuel cell system, and generates high-voltage power using a fuel gas containing a large amount of hydrogen and air containing oxygen. Here, the fuel gas is supplied from the fuel gas supply means 3 to the fuel cell stack 1. The fuel gas supply means 3 stores a fuel gas containing a large amount of hydrogen and can adjust the temperature and pressure of the fuel gas. The fuel gas supply means 3 is controlled by the control device 5. By the fuel gas supply means 3 and the control device 5, the fuel gas having the optimum temperature and pressure is supplied to the fuel cell stack 1.

Air is supplied (pressurized) from the air compressor 7 to the fuel cell stack 1 through the air pipe 9. The air compressor 7 is controlled by the control device 11. Although not shown, the air pipe 9 includes:
A heat exchanger for adjusting the temperature of the air may be provided.

The secondary battery 13 is chargeable and dischargeable, and at the time of discharging, generates a power having a voltage lower than that of the power generated by the fuel cell stack 1. The secondary battery 13 stores the surplus power generated by the fuel cell stack 1 and the regenerative power generated by the vehicle drive motor when the fuel cell vehicle decelerates, and a high-voltage unit driven by a high voltage, for example, a vehicle. When the fuel cell stack 1 does not generate enough power to cover the power consumed by the drive motor, the air compressor 7, and the like, the fuel cell stack 1 discharges to make up for the insufficient power. In particular, in a fuel cell vehicle, the secondary battery 13
Preferably, the power is also supplied to a low-electricity unit driven at a low voltage, for example, various control devices, and vehicle accessories 15 such as vehicle electric components. The secondary battery 13 is provided with a battery sensor 17 for detecting a state of charge (SOC) of the secondary battery 13.

The fuel cell stack 1 and the secondary battery 13 are both connected to the power distribution means 19. The power distribution unit 19 includes a diode 21 for preventing a current from flowing into the fuel cell stack 1,
And a DC / DC converter 25 for converting DC power of a certain voltage into DC power of a higher or lower voltage according to selection. The power distribution means 19 is controlled by the control device 27. The voltmeter 23 and the battery sensor 17 are connected to the control device 27, and output respective detection signals to the control device 27. Here, the voltmeter 2
3 is provided on the anode side of the diode 21.

In this case, the DC / DC converter 25
The power voltage (output voltage of the secondary battery) generated by the secondary battery 13 is boosted to the level of the power voltage (output voltage of the fuel cell stack) generated by the fuel cell stack 1 after the start-up is completed (boosting operation). ), The power supply to the power supply destination of the fuel cell stack 1 connected to the cathode side of the diode 21 is enabled, and the output voltage of the fuel cell stack 1 passing through the diode 21 is output from the secondary battery 13 (Step-down operation), and the secondary battery 13 can be charged. The step-up operation and the step-down operation in the DC / DC converter 25 can be arbitrarily selected, and are switched by a command from the control device 27 described above.

Here, the target value of the output voltage during the step-up operation of the DC / DC converter 25 is smaller than the value obtained by subtracting the value of the on-voltage of the diode 21 from the value of the open voltage of the fuel cell stack 1 and The value is set to a value larger than the value of the output voltage of the fuel cell stack 1 at the time of equilibrium when all the electric power required for starting the fuel cell stack 1 is supplied from the fuel cell stack 1.

The power distribution means 19 is connected to the air compressor 7 and the load 31 to which the fuel cell stack 1 is supplied with power via the power cutoff means 29.
The power cutoff means 29 is for cutting off the supply of power in the event of an abnormality or the like, and is composed of, for example, a suitable switch. In the case of a vehicle, the load 31 is, for example, the above-described vehicle drive motor. Here, the air compressor 7 and the load 31 which are the power supply destinations of the fuel cell stack 1 are both high-power units driven by high voltage.

When starting the fuel cell stack 1, D
The high voltage power obtained by switching the C / DC converter 25 to the boosting operation and boosting the output voltage of the secondary battery 13 is
Drive power for the air compressor 7 and the like (fuel cell stack 1
Power required to start up). After the startup of the fuel cell stack 1 is completed, the DC / DC converter 2
5 is switched to a step-down operation, and the air compressor 7 and the like are driven by the electric power from the fuel cell stack 1.

The control device 27 has a control ROM in which a control program is stored, and an R which is a work area for control.
And a DC / DC based on a signal value from the voltmeter 23 (output voltage of the fuel cell stack 1) and a signal value from the battery sensor 17 (charging rate of the secondary battery 13).
The switching between the step-up operation and the step-down operation in the DC converter 25 is controlled.

Next, the control operation for switching the power system of the fuel cell system will be described with reference to the control flowchart shown in FIG. Note that the control flowchart shown in FIG. 2 is stored as a control program in the internal ROM of the control device 27. Further, this control flowchart is repeatedly executed at predetermined short time intervals.

First, in step S100, the control device 2
7 checks the value of a flag indicating that the activation of the fuel cell stack 1 has been completed (hereinafter referred to as “activation completion flag”), and determines whether or not this activation completion flag has been set. When the activation of the fuel cell stack 1 has been completed, the activation completion flag is set to a value of “1”, and
If the activation of the fuel cell stack 1 has not been completed, the activation completion flag has been cleared to a value of “0”. This startup completion flag is “0” in the initial setting, and is thereafter set in step S180 and step S150.
Is cleared. Therefore, the setting condition of the startup completion flag will be described later. As a result of this determination, if the startup completion flag is set (S100: YES), it is determined that the startup of the fuel cell stack 1 has been completed. Then, the process proceeds to step S190. In this step S190, an output restriction flag, which will be described later, is cleared to “0”, and this is indicated by the control device 3 of the load 31.
3 and the process proceeds to step S220. The control device 33 that has received the notification that the output restriction flag has been cleared releases the restriction on the power consumption of the load 31.

On the other hand, if the startup completion flag has not been set (S100: NO), it is determined that the startup of the fuel cell stack 1 has not been completed, and step S is executed.
Proceed to 110. In step S110, a signal value (charge rate of the secondary battery 13) from the battery sensor 17 provided in the secondary battery 13 is read, and the charge state of the secondary battery 13 is acquired.

More specifically, when the startup of the fuel cell stack 1 is not completed, as described above, the DC / DC converter 25 is switched to the boosting operation, and the high voltage obtained by boosting the output voltage of the secondary battery 13 is obtained. Voltage power is supplied as driving power for the air compressor 7 and the like, but the charging state of the secondary battery 17 is not suitable for supplying power, for example, the charging rate of the secondary battery 17 is low. If the power from the secondary battery 13 continues to be consumed in such a state, there is a possibility that the operation of the various control devices for controlling the system and the operation of the vehicle auxiliary equipment 15 must be stopped. is there. Thus, in order to prevent such a situation, in step S110, the state of charge of the secondary battery 13 is acquired, and it is determined whether or not to allow the boosting of the secondary battery 13 to be permitted. Operate the boost prohibition flag. That is, for example, when it is determined that the state of charge of the secondary battery 17 is not suitable for supplying power because the charge rate of the secondary battery 17 is lower than a preset threshold value, In order to prohibit power supply by boosting of the secondary battery 13, the boosting prohibition flag is set to a value of "1". on the other hand,
When it is determined that the state of charge of the secondary battery 17 is in a state suitable for supplying power because the charging rate of the secondary battery 17 is equal to or higher than the threshold value, the boosting of the secondary battery 13 is performed. In order to permit the power supply by the power supply, the boosting prohibition flag is cleared to a value of “0”.

Then, in step S120, the value of the boost prohibition flag is checked to determine whether or not this boost prohibition flag is set. If the result of this determination is that the boost prohibition flag has been set (S120: YE
S), it is determined that power supply by boosting of the secondary battery 13 is prohibited, and the process proceeds to step S200. In this step S200, an output restriction flag indicating that the power consumption of the load 31 should be restricted is set to "1", and the fact is notified to the control device 33 of the load 31 and the step S22 is performed.
Go to 0. The control device 33 that has received the notification that the output restriction flag has been set restricts the power consumption of the load 31. Here, the reason why the power consumption of the load 31 is limited is that the secondary battery 13 is charged by the fuel cell stack 1 at a stage where the activation of the fuel cell stack 1 is not completed in this case (step S220). This is because power consumption is limited to only necessary ones (driving power of the air compressor 7 and the like and charging power of the secondary battery 13) as much as possible.

On the other hand, if the boosting prohibition flag is not set (S120: NO), it is determined that power supply by boosting of the secondary battery 13 is permitted, and the process proceeds to step S130. In step S130, a signal value (output voltage of the fuel cell stack 1) from the voltmeter 23 provided on the anode side of the diode 21 in the power distribution unit 19 is read.

In step S140, the voltmeter 2
It is determined whether or not the output voltage of the fuel cell stack 1 read from the fuel cell stack 3 is higher than a preset reference value. The reference value here is a threshold value for determining whether or not the start-up of the fuel cell stack 1 is completed. After the start-up is completed, the diode 21 is turned on, and the current flows from the fuel cell stack 1 in the forward direction, that is, from the fuel cell stack 1. Will flow, so D
It is desirable that the output voltage is set to a value obtained by adding the value of the ON voltage of the diode 21 to the target value of the output voltage at the time of the boosting operation of the C / DC converter 25.

If the result of this determination is that the output voltage of the fuel cell stack 1 is equal to or lower than the reference value (S140: NO), it is determined that the activation of the fuel cell stack 1 has not yet been completed, and the process proceeds to step S150. move on. This step S15
In step S2, the activation completion flag is reset, and step S2
Go to 10.

On the other hand, when the output voltage of the fuel cell stack 1 is higher than the reference value (S140: YES),
Proceed to step S160. In this step S160,
The fuel cell stack 1 is controlled by a built-in timer of the control device 27.
, The elapsed time from when the output voltage exceeds the reference value is counted, and the process proceeds to step S170.

In step S170, it is determined whether or not the count value of the timer is equal to or longer than a predetermined time. The predetermined time here is after the supply of the fuel gas and the air to the fuel cell stack 1 is started, that is, after the voltage of the fuel cell stack 1 starts rising, the temperature rise and the humidification of the main body of the fuel cell stack 1 are sufficient for the power generation. Time until it becomes
Obtained in advance by experiments, etc., and taking this result into account,
After the output voltage of the fuel cell stack 1 exceeds the reference value,
The elapsed time is set such that it can be determined that the activation of the fuel cell stack 1 has been completed. In addition, this predetermined time is
Means for detecting the ambient temperature of the fuel cell system may be provided, and the temperature may be changed according to the detected ambient temperature.

If the result of this determination is that the count value of the timer is equal to or greater than the predetermined time (S170: YES), the fuel cell stack 1 has exceeded the predetermined time since the output voltage exceeded the reference value. It is determined that the activation of the battery stack 1 has been completed, and the process proceeds to step S180. In step S180, a start completion flag is set, and the process proceeds to step S220.

On the other hand, if the count value of the timer is less than the predetermined time (S170: NO), since the predetermined time has not elapsed since the output voltage of the fuel cell stack 1 exceeded the reference value, the fuel cell It is determined that the activation of the stack 1 has not been completed, and the process immediately proceeds to step S210. In step S210, in short, since the activation of the fuel cell stack 1 has not been completed, the DC / D
The C converter 25 is boosted. That is, the output voltage of the secondary battery 13 is boosted to the target value level, and the power of the secondary battery 13 is supplied to the power supply destination (the air compressor 7, the load 31, etc.) of the fuel cell stack 1. An operation for activating the stack 1 is performed.

In step S220, in short,
When the activation of the fuel cell stack 1 is completed, or
Since the activation of the fuel cell stack 1 has not been completed, but the state of charge of the secondary battery 13 is not suitable for power supply, the DC / DC converter 25 is stepped down. That is, the electric power generated by the fuel cell stack 1 is transferred to the electric power supply destination (the air compressor 7 and the load 3) of the fuel cell stack 1.
1), the voltage is reduced to the level of the output voltage of the secondary battery 13 and supplied to the secondary battery 13 to charge the secondary battery 13.

Next, referring to the characteristic diagram shown in FIG.
Fuel cell stack 1 during execution of the control flowchart shown in FIG.
And the relationship between current and voltage in the DC / DC converter 25 will be described. FIG. 3 is a diagram showing an example of the current-voltage characteristics of the fuel cell stack 1. When a current is taken out from the fuel cell stack 1, the voltage characteristics shown in FIG. 3 are obtained.

Here, the point M0 is an operating point when nothing is connected to the fuel cell stack 1, and the voltage and current at this operating point are V0 and I0, respectively. At this time, since I0 = 0, the output (power) P0 which is the product of the two is obtained.
Is also 0. V0 is the above open voltage value.

FIG. 3 shows two characteristic curves A and B. The state of the fuel cell stack 1 differs between the characteristic A and the characteristic B. That is, the characteristic A is a case where the temperature and the humidity of the fuel cell stack 1 are in an optimum state, and the fuel gas and the air are also supplied to the fuel cell stack 1 at a desired pressure and flow rate. The characteristic B is an example during the operation of the fuel cell stack 1, and since the temperature and the humidity of the fuel cell stack 1 are not in an optimum state, when a current is taken out, the voltage drop is large and the output is reduced. The state which cannot be taken is shown.

The point M2 is an operating point indicating the electric power required to drive the air compressor 7 when the fuel cell stack 1 is started. If all of this electric power is supplied from the fuel cell stack 1, The voltage and current are V2 and I2, respectively.

In this embodiment, the target value of the output voltage during the step-up operation of the DC / DC converter 25 is set to V1. At this time, if the power capacity of the DC / DC converter 25 is equal to or greater than the power consumption of the air compressor 7 at the time of starting the fuel cell stack 1, the voltage of the fuel cell stack 1 can be maintained at the same value as the target value V1. Become. That is, the diode 2 connected to the fuel cell stack 1
1 can be clamped with the same value as the target value V1. Therefore, the fuel cell stack 1 does not flow a current at a voltage smaller than the value V1. Therefore, even if the fuel cell stack 1 is in the state of the characteristic B during startup, the voltage of the fuel cell stack 1 becomes V
Since it is clamped at 1, the current will flow by I1a. Further, even when the startup of the fuel cell stack 1 is completed and the state of the characteristic A is reached, the current flows by I1b, and this value becomes the maximum value of the current flowing from the fuel cell stack 1 at the time of startup.

When the target value of the output voltage during the step-up operation of the DC / DC converter 25 is set to V2 or less,
While current flows from the fuel cell stack 1 by I2, no current flows from the DC / DC converter 25, and therefore, depending on the state of the fuel cell stack 1,
There is a possibility that sufficient electric power cannot be supplied to the air compressor 7.

Therefore, the target value of the output voltage during the step-up operation of the DC / DC converter 25 is smaller than the value obtained by subtracting the value of the on-voltage of the diode 21 from the value of the open voltage V0 of the fuel cell stack 1, and When the power required for driving the air compressor 7 at the start of the fuel cell stack 1 is supplied from the fuel cell stack 1, the output voltage V2 of the fuel cell stack 1 at equilibrium is set to a value as large as possible. Thus, even when the fuel cell stack 1 is started, the fuel cell stack 1, the air compressor 7, and the load 3
It is possible to keep the current flowing from the fuel cell stack 1 low while keeping the electrical connection with the fuel cell stack 1.

When the power supplied to the air compressor 7 and the like after the start of the fuel cell stack 1 is completed is switched from the power of the secondary battery 13 to the power of the fuel cell stack 1,
No mechanical switching means such as a relay is required, and the fuel cell stack 1 and the power supply destination (such as the air compressor 7 and the load 31) of the fuel cell stack 1 are already electrically connected via the diode 21. In this state, the occurrence of overcurrent can be prevented.

As a result, the effect of the first embodiment is that the fuel cell stack 1 is connected to the DC / DC converter 25 via the diode 21 so that the output voltage of the DC / DC converter 25 during the boost operation is increased. The target value was smaller than the value obtained by subtracting the value of the on-voltage of the diode 21 from the value of the open-circuit voltage of the fuel cell stack 1, and all the power required for starting the fuel cell stack 1 was supplied from the fuel cell stack 1. By setting the output voltage of the fuel cell stack 1 to a value larger than the value of the output voltage of the fuel cell stack 1 at the time of equilibrium, whether the activation of the fuel cell stack 1 is completed is determined by a single subunit including the DC / DC converter 25 Since it is possible to make a determination only with the information in the area 19, it is not necessary to exchange information between sub-units as in the prior art, so that the overall configuration of the system is simplified. Rukoto can. At the same time, the fuel cell stack 1 and the power supply destination (such as the air compressor 7 and the load 31) of the fuel cell stack 1 are already electrically connected via the diode 21. When the power supply system is switched after the start-up of the fuel cell stack 1 is completed,
The occurrence of overcurrent can be prevented.

(Second Embodiment) FIG. 4 is a diagram showing a configuration of a fuel cell system according to a second embodiment of the present invention. Note that the second embodiment has the same basic configuration as the fuel cell system corresponding to the first embodiment shown in FIG. 1, and the same components are denoted by the same reference numerals. , The description of which will be omitted.

The feature of the second embodiment is that, as shown in FIG. 4, a diode 21 for preventing a current from flowing into the fuel cell stack 1 is provided near the fuel cell stack 1 outside the power distribution means 19a. 1. In addition to the voltmeter 23 shown in FIG.
That is, an ammeter 35 for detecting the output current of the converter 25 is provided. The ammeter 35 is connected to the power distribution unit 19a.
, And sends a detection signal (output current of the DC / DC converter 25) to the control device 27. In the present embodiment, for example, the diode 21 is arranged near the fuel cell stack 1 due to the mounting method of the subsystem, and therefore, the voltmeter 2 for detecting the output voltage of the fuel cell stack 1 is used.
3 is effective when the power distribution unit 3 cannot be provided in the power distribution unit 19a.

Next, the control operation for switching the power system of the fuel cell system will be described with reference to the control flowchart shown in FIG. The control flowchart shown in FIG. 5 is stored as a control program in the internal ROM of the control device 27. In the present embodiment, as shown in FIG. 5, steps S230, S240, and S250 are inserted into the flowchart shown in FIG.
And step S140 are deleted. That is, FIG.
In the control flowchart corresponding to the first embodiment shown in FIG. 5, steps S130 (step of reading the output voltage of the fuel cell stack 1) and step S140 (step of comparing the read output voltage of the fuel cell stack 1 with a reference value) ), The determination of whether the activation of the fuel cell stack 1 has been completed can be made by reading the output current of the DC / DC converter 25.

Steps S100 to S120 are:
Since each step is the same as that in the flowchart shown in FIG. 2, the description thereof is omitted. Then, in step S230, a signal value (output current of the DC / DC converter 25) from the ammeter 35 provided in the power distribution means 19a is read.

In step S240, the value of the output current of the DC / DC converter 25 read this time in step S230 from the value of the output current of the DC / DC converter 25 at the time when the start of the fuel cell stack 1 is started. Is subtracted to calculate the amount of change in the output current.

Then, in step S250, it is determined whether or not the calculated amount of change in the output current of DC / DC converter 25 is greater than a preset reference value. This is equivalent to determining whether the output current of the DC / DC converter 25 is below a predetermined threshold.
If the result of this determination is that the amount of change in the output current of the DC / DC converter 25 is less than or equal to the reference value (S250: NO),
It is determined that the activation of the fuel cell stack 1 has not been completed yet, and the process proceeds to step S150. On the other hand, DC / DC
If the amount of change in the output current of converter 25 is larger than the reference value (S250: YES), the process proceeds to step S160.

According to the configuration of the present embodiment, the DC / DC power increases as the starting state of the fuel cell stack 1 progresses.
The fact that the output current of the DC converter 25 decreases is used. That is, referring to FIG. 3, the current-voltage characteristic of fuel cell stack 1 has characteristic B with the progress of the starting state.
From the current value I1a to the characteristic A, the current from the fuel cell stack 1 of the current value I2 consumed by the air compressor 7 when the fuel cell stack 1 starts It increases toward the value I1b. As a result, the current value to be shared by the DC / DC converter 25 decreases. By detecting a decrease in the output current of the DC / DC converter 25 at this time, it is possible to determine whether or not the activation of the fuel cell stack 1 has been completed.

Steps S150 to S220 are
Since each step is the same as that in the flowchart shown in FIG. 2, the description thereof is omitted. In this embodiment, steps S160 to S170 may be omitted.

As a result, the effect of the second embodiment is the same as that of the first embodiment.
An ammeter 35 for detecting the output current of the DC / DC converter 25 is provided in the power distribution means 19a.
By determining whether the activation of the fuel cell stack 1 has been completed based on the output current of the converter 25,
For example, the diode 21 may be arranged near the fuel cell stack 1 due to the mounting method of the subsystem, and the voltmeter 23 for detecting the output voltage of the fuel cell stack 1 may be provided in the power distribution means 19a. It is possible to cope with cases where it is not possible.

(Third Embodiment) FIG. 6 is a diagram showing a configuration of a fuel cell system according to a third embodiment of the present invention. The third embodiment has the same basic configuration as the fuel cell system corresponding to the first embodiment shown in FIG. 1, and the same components are denoted by the same reference numerals. , The description of which will be omitted.

The feature of the third embodiment is that, as shown in FIG. 6, an ammeter 35 for detecting the output current of the DC / DC converter 25 is provided in the power distribution means 19 shown in FIG. . That is, in the present embodiment, the diode 21, the voltmeter 23 and the ammeter 35 are provided in the power distribution means 19b.
Is provided. That is, the present embodiment is different from the first embodiment in that the start-up completion determination based on the output voltage of the fuel cell stack 1 and the DC / D in the second embodiment are performed.
The start completion determination based on the decrease in the output current of the C converter 25 is performed simultaneously.

The control operation for switching the power system of the fuel cell system can be described according to a flowchart obtained by appropriately combining the steps of the control flowcharts shown in FIGS. 2 and 5, and the contents of each step are as follows. Since the contents are the same as those described in the first and second embodiments, description thereof will be omitted.

As a result, the effect of the third embodiment is the same as that of the first embodiment.
Start completion judgment based on the output voltage of the fuel cell stack 1;
By simultaneously performing the activation completion determination based on the decrease in the output current of the DC / DC converter 25, it is determined that the activation of the fuel cell stack 1 has been completed when both of these conditions are simultaneously satisfied. It is possible to improve the determination accuracy of the start-up completion.

In the above embodiments, the power consumption of the air compressor 7 has been described as an example of the power consumption when the fuel cell stack 1 is started. Is provided, the power consumption of these subsystems must be considered.

[Brief description of the drawings]

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

FIG. 2 is a control flowchart for explaining a control operation of power system switching of the fuel cell system according to the first embodiment.

FIG. 3 is a diagram illustrating an example of a current-voltage characteristic of a fuel cell stack.

FIG. 4 is a diagram showing a configuration of a fuel cell system according to a second embodiment of the present invention.

FIG. 5 is a control flowchart for explaining a control operation of power system switching of the fuel cell system according to the second embodiment.

FIG. 6 is a diagram showing a configuration of a fuel cell system according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of an example of a conventional fuel cell system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel cell stack 3 Fuel gas supply means 7 Air compressor 13 Secondary battery 17 Battery sensor 19, 19a, 19b Power distribution means 21 Diode 23 Voltmeter 25 DC / DC converter 27 Control device 35 Ammeter

Claims (5)

[Claims] 1. A fuel cell stack for generating electric power using fuel gas and air; a secondary battery for generating electric power having a voltage lower than a voltage of electric power generated by the fuel cell stack; and the fuel cell stack. Boosting the voltage of the power generated by the secondary battery to supply power to the power supply destination to the voltage of the power generated by the fuel cell stack, or charging the fuel cell to charge the secondary battery A voltage conversion unit that steps down a voltage of power generated by the stack to a voltage of power generated by the secondary battery; anda control unit that controls switching between a step-up operation and a step-down operation in the voltage conversion unit. A fuel cell system that switches the voltage converting means to a boosting operation at the time of starting the battery stack and supplies electric power required for starting the fuel cell stack using the secondary battery; Connecting the fuel cell stack and the voltage conversion means via a diode, and setting the target value of the output voltage during the boosting operation of the voltage conversion means from the value of the open-circuit voltage of the fuel cell stack to the ON voltage of the diode. And a value larger than the value of the output voltage of the fuel cell stack at the time of equilibrium when all the power required for starting the fuel cell stack is supplied from the fuel cell stack. A fuel cell system, wherein the fuel cell system is set. 2. The fuel cell system according to claim 1, further comprising a voltage detecting unit configured to detect an output voltage of the fuel cell stack, wherein the control unit performs the voltage conversion when the output voltage of the fuel cell stack is equal to or more than a predetermined reference value for a predetermined time or more. 2. The fuel cell system according to claim 1, wherein the means is switched from a step-up operation to a step-down operation. A current detection unit for detecting an output current of the voltage conversion unit, wherein the control unit detects the voltage conversion when an output current of the voltage conversion unit is equal to or less than a predetermined reference value for a predetermined time or more. 2. The fuel cell system according to claim 1, wherein the means is switched from a step-up operation to a step-down operation. 4. A fuel cell system comprising: a voltage detection means for detecting an output voltage of the fuel cell stack; and a current detection means for detecting an output current of the voltage conversion means. The control means includes an output voltage of the fuel cell stack. Is greater than or equal to a predetermined reference value for a predetermined time or more, and when the output current of the voltage conversion means is equal to or less than a predetermined reference value for a predetermined time or more, switching the voltage conversion means from a step-up operation to a step-down operation. The fuel cell system according to claim 1, wherein 5. The battery according to claim 1, further comprising: a charging state detecting unit configured to detect a charging state of the secondary battery, wherein the control unit determines that a charging state of the secondary battery is not suitable for supplying power. 2. The fuel cell system according to claim 1, wherein the voltage conversion unit switches from a step-up operation to a step-down operation.