JPH05217588A - Fuel cell control system - Google Patents

Abstract

PURPOSE:To prevent the breakage of a fuel cell by the load fluctuation without using a commercial electric power. CONSTITUTION:When the increase of load is detected by a load electric current detector 19, an automatic electric current adjustor 11 reduces the frequency of a three-phase inverter 6 for receiving and supplying electric power and allows an induction motor 5 to act as a dynamo, and the rotational energy of a flywheel 4 is converted to an electric energy, and supplied to a load 3. Further, when the reduction of load is detected by the load electric current detector 19, the automatic electric current adjustor 11 increases the frequency of the three-phase inverter 6 for receiving and supplying electric power and allows the induction motor 5 to act as motor, and the electric energy supplied from a fuel cell 1 is converted into a rotational energy and stored in the flywheel 4. Further, when the load fluctuation is not detected by the load electric current detector 19, the automatic electric current adjustor 11 controls the number of revolution of the flywheel 4 according to the magnitude of the load.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell control system suitable for avoiding shortening of the life of a fuel cell due to a sudden load change.

[0002]

2. Description of the Related Art When a load connected to a fuel cell suddenly increases, the fuel cell instantaneously follows the load fluctuation and generates a large current. At this time, since the fuel supply cannot be rapidly increased, the carbon as the base material of the electrode is corroded and damaged, which shortens the life of the fuel cell. It is also known that the fuel cell deteriorates even when the load is rapidly reduced.

Therefore, conventionally, a DC power supply obtained by rectifying a commercial power supply is connected to a DC power supply line connecting a fuel cell and an inverter so that a sudden power fluctuation at the time of load fluctuation is imposed on the commercial power supply. A power supply system stabilizing system "(Japanese Patent Laid-Open No. 59-230435) is proposed.

Further, when the load changes abruptly, or when the electric power to be supplied to the load increases above a predetermined value,
A "DC hybrid power supply system" has also been proposed in which the output of the fuel cell is limited and the shortage of power supplied to the load is supplied from a commercial power supply.

[0005]

However, since all of them utilize commercial power sources, not independent power sources of fuel cells alone, there is no commercial power source for vehicles such as automobiles, remote areas, and remote islands. There was a problem that it could not be placed in place.

The present invention has been made in view of the above problems, and an object thereof is to prevent damage to a fuel cell due to load fluctuations without using a commercial power supply.

[0007]

In order to achieve the above object, a fuel cell control system according to the present invention includes a flywheel rotated by an induction motor and a direct current output line of the induction motor and the fuel cell. A power transfer inverter that transfers power, a load change detection unit that detects a change in the load connected to the DC output line of the fuel cell, and a load increase detected by the load change detection unit, By lowering the frequency of the power transfer inverter and causing the induction motor to function as a generator, the rotational energy of the flywheel is converted into electrical energy and supplied to the load, and the load fluctuation detection means reduces the load. If detected, increase the frequency of the power transfer inverter to drive the induction motor. Functioning as a controller to convert electric energy from the fuel cell into rotational energy and store the energy in the flywheel, and the load fluctuation detection means detects no load fluctuation, and Second control means for controlling the number of rotations of the wheel according to the magnitude of the load is provided.

[0008]

[Operation] When the load change detection means detects an increase in load, the first control means lowers the frequency of the power transfer inverter and causes the induction motor to function as a generator to rotate the flywheel. It converts energy into electrical energy and supplies it to the load. Further, when the load change detection means detects a decrease in load, the first control means increases the frequency of the power transfer inverter to cause the induction motor to function as a motor, and thereby the electric energy from the fuel cell. Is converted into rotational energy and stored in the flywheel. in this way,
By charging / discharging the flywheel when the load changes, the change in the electric power output from the fuel cell becomes slow, and damage and deterioration of the fuel cell can be avoided.

The second control means controls the rotational speed of the flywheel according to the magnitude of the load when the load variation is not detected by the load variation detecting means, that is, when the load is large, the flywheel is controlled. The number of revolutions of the flywheel is reduced, and the number of revolutions of the flywheel is increased when the load is small to prevent over-discharge and overcharge of the flywheel.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a system configuration diagram of a fuel cell control system according to an embodiment of the present invention. This fuel cell control system includes a fuel cell 1, a three-phase inverter 2, a load 3,
Flywheel 4, induction motor 5, power transfer inverter 6, delay circuit 7, first subtraction circuit 8, second
A subtraction circuit 9, a third subtraction circuit 10, an automatic current regulator 11,
A / D conversion circuit 12, ROM 13, D / A conversion circuit 1
4, a fourth subtraction circuit 15, a charging current target value output unit 16, a gate drive circuit 17, a rotation speed sensor 18, a load current detector 19, and a flywheel output current detector 20. When the fuel cell 1 is supplied with fuel and air, the fuel cell 1 oxidizes the fuel through an electrochemical process and directly outputs the oxidation energy generated at that time in the form of electric energy (electric power). This electric power is direct current, which is converted into alternating current by the three-phase inverter 2 and supplied to the load 3.
The fuel cell 1 may be any of phosphoric acid type, molten carbonate type, solid electrolyte type, and solid polymer electrolyte type.

The flywheel 4 is connected to an induction motor 5 which is driven and controlled by an electric power transfer inverter 6, and accumulates the electric power generated in the fuel cell 1 (this is also called charging). It is utilized to supply the accumulated power to the three-phase inverter 2 (this is also referred to as discharging). Such switching between charging and discharging is performed by controlling the gate of the three-phase power transfer inverter 6 by the gate drive circuit 17 to change the frequency and changing the slip of the induction motor 5 by the frequency change.

That is, when power is supplied (discharged) from the flywheel 4, the power transfer three-phase inverter 6 is used.
When operating the induction motor 5 as a generator by making the slip of the induction motor 5 negative and increasing the operating frequency of the power transfer three-phase inverter 6 when supplying (charging) power to the flywheel 4. , The slip of the induction motor 5 is made positive, and the induction motor 5 acts as a motor.

When the load current detected by the load current detector 19 is input, the delay circuit 7 delays the load current and outputs it to the minus input terminal of the first subtraction circuit 8.
The delay circuit 7 is connected to the positive input terminal of the first subtraction circuit 8.
The load current is input without going through. In this case, the first
The subtraction result of the subtraction circuit 8 is used as a discharge current value or a charge current value to be output by the power transfer three-phase inverter 6 that drives and controls the induction motor 5 connected to the flywheel 4. It

For example, when the load current sharply increases as shown in FIG. 2A, the delayed load current output by the delay circuit 7 becomes as shown in FIG. 2B. Then, the output of the first subtraction circuit 8, that is, the subtraction result obtained by subtracting the delayed load current from the load current is as shown in FIG. When the subtraction result of the first subtraction circuit 8 is positive as shown in FIG. 2C, the subtraction result is a three-phase power transfer inverter for driving and controlling the induction motor 5 connected to the flywheel 4. It has a meaning as a discharge current value of 6.
When the discharge current of FIG. 2 (c) is output, the output current of the fuel cell 1 gradually increases as compared to the load current, as shown in FIG. 2 (d).

When the load current sharply decreases as shown in FIG. 3 (a), the delayed load current output by the delay circuit 7 becomes as shown in FIG. 3 (b). And the first
The output of the subtraction circuit 8, that is, the subtraction result obtained by subtracting the delayed load current from the load current is as shown in FIG. In addition,
As shown in FIG. 3C, when the subtraction result of the first subtraction circuit 8 is negative, the subtraction result is obtained by the three-phase inverter 6 for power transfer for driving and controlling the induction motor 5 connected to the flywheel 4. It has a meaning as a charging current value. Figure 3
When the charging current of (c) is input, the output current of the fuel cell 1 gradually decreases as compared with the load current as shown in FIG. 3 (d).

The discharge current and charging current actually input and output by the three-phase inverter 6 for power transfer for driving and controlling the induction motor 5 connected to the flywheel 4 are the windage of the flywheel 4 and the rotation due to rotational friction. A flywheel output current detector 2 of a three-phase inverter 6 for exchanging electric power for driving and controlling a charging current or an induction motor 5 connected to the flywheel 4 in anticipation of energy decay.
Taking into account the current output (discharge) current detected at 0,
The second subtraction circuit 9 and the third subtraction circuit 10 are determined. In this case, the charging current in anticipation of the attenuation of the rotational energy of the flywheel 4 is the A / D conversion circuit 12, the ROM 13,
It is obtained by utilizing the D / A conversion circuit 14, the fourth subtraction circuit 15, the rotation speed sensor 18, and the like.

Since the ROM 13 determines the charging current in consideration of the attenuation of the rotational energy of the flywheel 4 according to the load current, the rotation of the flywheel 4 is necessary and sufficient corresponding to the load current and corresponding to the load current. The number is stored, and when the load current is input, the corresponding rotation number is output. The correspondence relationship between the load current and the number of revolutions is inversely proportional when the load current is large, the number of revolutions is small, and when the load current is small, the number of revolutions is large. This has the following significance. That is, when the load current is large, the load current is likely to become smaller thereafter.Therefore, by setting the rotation speed to a low value, it is possible to obtain a large charging current for charging that should be performed when the load current becomes small. I'm preparing. By thus allowing a large charging current, overcharging can be prevented. On the other hand, if the load current is small, the load current is likely to increase after that.Therefore, by setting a high rotation speed, it is possible to obtain a large discharge current for the discharge that should be performed when the load current becomes large. I have to. Thus, by preparing so that a large discharge current can be obtained, over-discharge can be prevented.

The automatic current regulator 11 includes a flywheel 4
When a discharge current and a charge current to be actually input / output by the three-phase power transfer inverter 6 for controlling the drive of the induction motor 5 connected to the are calculated, the gate drive circuit 17 is controlled on the basis of the discharge current and the charge current to control the transfer of power. The frequency of the three-phase inverter 6 for the
Change the slip of. Due to this change, the function of the induction motor 5 is switched to the generator or the motor.

Next, the power supply control will be described with reference to the flowchart of FIG.

The first subtraction circuit 8 outputs the subtraction value C obtained by subtracting the delayed load current B delayed by the delay circuit 7 from the load current A to the second subtraction circuit 9 (steps F1 to F4). This subtraction value C is the value of the discharge current to be discharged from the three-phase power transfer inverter 6 for driving and controlling the induction motor 5 connected to the flywheel 4 or the charge to be charged when the load current changes. The current value is shown.

On the other hand, when the load current A digitally converted by the A / D converter 12 is input to the ROM 13, the rotational speed H (digital data) of the flywheel 4 necessary and sufficient for the load current A is input. Is read (steps F5 to F
6), and output to the D / A converter 14. Then, the D / A converter 14 determines the rotation speed H given as digital data.
Is converted into analog data and given to the positive input terminal of the fourth subtraction circuit 15. The current rotational speed G of the flywheel 4 detected by the rotational speed sensor 18 is input to the negative input terminal of the fourth subtraction circuit 15 (step F7). Therefore, the fourth subtraction circuit 15 subtracts the present rotation speed G of the flywheel 4 from the necessary and sufficient rotation speed H for the load current A, and gives the subtraction result to the charging current target value output unit 16. Then, the charging current target value output unit 16
If the given subtraction result is greater than 0, that is, if the current rotational speed G of the flywheel 4 is equal to or lower than the necessary and sufficient rotational speed for the load current A, the flywheel 4 must be rotated sufficiently. In order to achieve the desired number of revolutions,
The charging current target value of (about) is given to the second subtraction circuit 9 (step F11). As described above, the target charging current value is used as the charging current for preventing the reduction in the rotation speed of the flywheel 4 due to windage loss, etc., but the charging is gradually performed by reducing it to about 1 KW. It is possible to avoid a sudden increase in the fuel cell load due to this charging. On the other hand, when the given subtraction result is 0 or less, that is, when the current rotation speed G of the flywheel 4 is larger than the necessary and sufficient rotation speed, the rotation of the flywheel 4 is maintained as it is (step F10). In this case, “0” is actually given to the second subtraction circuit 9 as the charging current target value.

In this way, when the charging current target value is given, the second subtraction circuit 9 causes the charging / discharging current for the power transfer three-phase inverter 6 for driving and controlling the induction motor 5 connected to the flywheel 4. The charging current target value is subtracted from C (step F4), and the subtraction result is given to the plus input terminal of the third subtraction circuit 10 as the flywheel output current target value F. At this time, the flywheel output current E is applied to the negative input terminal of the third subtraction circuit 10. Therefore, the third subtraction circuit 10 changes the flywheel output current E from the flywheel output current target value F.
Is subtracted and the subtracted value is given to the automatic current regulator 11 (step F12).

When the given subtraction result is greater than 0, that is, the flywheel output current target value F is the flywheel output current E.
If it is larger, the gate drive circuit 17 is controlled so as to lower the frequency of the three-phase power transfer inverter 6 in order to cause the induction motor 5 to function as a generator and perform discharging (step F15). On the other hand, when the given subtraction result is 0 or less, that is, when the flywheel output current E is equal to or more than the flywheel output current target value F, the induction motor 5 functions as a motor and is charged with electric power. Three-phase inverter for transfer 6
The gate drive circuit 17 is controlled so as to increase the frequency (step F16).

As is clear from the above description, when there is no load change, the subtraction result in step F3 becomes "0", so that the automatic current regulator 11 is exclusively based on the charging current target value. The frequency of the power transfer three-phase inverter 6 is controlled.

Next, based on the time chart of FIG.
The control of FIG. 4 will be specifically described.

Assuming that the load current suddenly increases from 0 kW to 35 kW at the timing T1 in FIG. 5, the period T
In 1 to T2, the subtraction result in step F3 of FIG. 4 becomes positive, and the flywheel 4 is discharged. Then, this discharge current is given to the load 3 via the three-phase inverter 2, so that the output current of the fuel cell 1 can be reduced accordingly. That is, the output current of the fuel cell 1 faithfully follows the sudden increase in the load current, does not increase sharply, and gradually increases, so that the increase in the fuel supply amount in time with the increase in the load current is in time. It is possible to avoid the situation where the fuel cell 1 runs out, and to prevent the fuel cell 1 from being damaged. Since the rotational energy of the flywheel 4 is consumed by such discharge, the rotational speed is reduced.

In the periods T2 to T3, step F3 in FIG.
The subtraction result at is 0, and charging is performed based on the charging current target value. As a result, the rotation speed of the flywheel 4 gradually increases.

In the periods T3 to T4, the rotation speed of the flywheel 4 becomes a necessary and sufficient rotation speed corresponding to the load current, and neither charging nor discharging is performed in order to maintain the rotation speed of the flywheel 4 at present. In this period, charging that was done in the previous period is stopped and the load decreases, so that
The output current of the fuel cell 1 decreases.

At timing T4, the load current is 35 kW
If it suddenly decreases from 0 kW to 0 kW, the period T4 to T5
In, the subtraction result in step F3 of FIG. 4 becomes negative, and the flywheel 4 is charged. That is, even if the load current suddenly decreases, the flywheel 4
Since the current output by the fuel cell 1 is used for charging by charging, the output current of the fuel cell 1 does not decrease sharply but gradually decreases. It is possible to prevent deterioration. Due to such charging, the rotation speed of the flywheel 4 increases.

In the periods T5 to T6, step F3 in FIG.
The subtraction result at is 0, and charging is performed based on the charging current target value. As a result, the rotation speed of the flywheel 4 further increases. In this period, since it is necessary to charge the battery, the output current of the fuel cell 1 does not become "0" even if the load current is "0".

In the periods T6 to T7, the charging which was performed in the previous period is stopped and the load is completely eliminated, so that the output current of the fuel cell 1 becomes "0" and the rotational speed of the flywheel 4 becomes constant. Become.

The present invention is not limited to the above embodiment, but the rotation control of the induction motor 5 can be performed by software instead of a hardware circuit.

[0034]

As described above, according to the fuel cell control system of the present invention, damage to the fuel cell due to load fluctuations can be avoided without using a commercial power source, and moving bodies such as automobiles, remote areas, remote islands, etc. It can also be installed in places where there is no commercial power supply.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a method of calculating a discharge current to be discharged by the flywheel when the load increases.

FIG. 3 is a diagram showing how to calculate a charging current for charging a flywheel when a load is reduced.

FIG. 4 is a flowchart showing a control operation of the fuel cell control system.

FIG. 5 is a time chart showing a control operation example of the fuel cell control system.

[Explanation of symbols]

 1 Fuel Cell 2 Three-Phase Inverter 3 Load 4 Flywheel 5 Induction Motor 6 Power Transfer Inverter 7 Delay Circuit 8 First Subtraction Circuit 9 Second Subtraction Circuit 10 Third Subtraction Circuit 11 Automatic Current Regulator 12 A / D Converter 13 ROM 14 D / A converter 15 Third subtraction circuit 16 Charging current target value output unit 17 Gate drive circuit 18 Rotation speed sensor 19 Load current detector 20 Flywheel output current detector

Claims (1)

[Claims] 1. A flywheel rotated by an induction motor, a power transfer inverter for transferring power between the induction motor and a DC output line of a fuel cell, and a DC output line of the fuel cell. Load fluctuation detection means for detecting fluctuations in the load, and when the load fluctuation detection means detects a load increase, the frequency of the power transfer inverter is lowered to cause the induction motor to function as a generator. As a result, the rotational energy of the flywheel is converted into electric energy and supplied to a load, and when a load decrease is detected by the load change detection means, the frequency of the power transfer inverter is increased to increase the induction motor. The electric energy from the fuel cell by operating the motor as a motor. A first control means for converting the load into a variable value and accumulating in the flywheel; and a load variation detecting means for controlling the rotational speed of the flywheel according to the magnitude of the load when the load variation is not detected. 2. A fuel cell control system comprising: two control means.