JP2002063925A - Fuel cell system and operating method of fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent that a high voltage is applied to a DC equipment system at the start of a fuel cell, and protect the equipment. SOLUTION: This device has equipment 8a, 8b connected with the fuel cell 2, a breaker 4 to break the electric power of a fuel cell, a voltage monitor 12 to detect the voltage of the fuel cell, a voltage stabilizer 20 which protects the equipment so that the electric power of the appropriate voltage at a rated point can be supplied to the equipment based on the detected voltage information, a simulation load 31 which consumes the initial electric power of the fuel cell while the voltage of the fuel cell drops from the open-circuit voltage to the rated point region, and a control 10 which sends a close command signal to the breaker so that the initial electric power from the fuel cell does not flow into the equipment based on the detected voltage information, and which sends the electric supply command signal to the voltage stabilizer so that the initial electric power from the fuel cell may be consumed at the simulation load, ad then sends an open command signal to the breaker when the voltage of the fuel cell descends to the rated actuating point region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a fuel cell system connected to a device of a DC system and a fuel cell operating method.

[0002]

A fuel cell, as shown in FIG. 5, a high open-circuit voltage E _0, often the difference between the voltage E ₁ to E ₂ in the region of the rated operating point is large. For example, the voltage of the unit cell at the time of starting the fuel cell is 1.1 to 1.0 V, whereas it is 0.7 to 0.5 V at the rated operating point.
This produces a difference of 3 to 0.5V. If the rated operating point of the fuel cell is set to 12 V, 17 to 18 single cells will be incorporated into the fuel cell stack, but the open circuit voltage E ₀ reaches 17 to 18 V and the rated operating point Between 5
A difference of up to 6 V is produced.

[0003]

On the other hand, on the power consuming side, there are many devices whose allowable voltage range is limited to, for example, ± 10% of the rated voltage. which may open circuit voltage E ₀ of the battery side deviates greatly. For this reason, if the open circuit voltage E ₀ is directly applied to the equipment of the DC system, the equipment cannot withstand high voltage and is damaged. In an extreme case, the equipment is destroyed as soon as the switch is turned on. It can be lost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a fuel cell system capable of preventing a high voltage from being applied to a DC system device at the time of starting the fuel cell and protecting the device. An object of the present invention is to provide a fuel cell operation method.

[0005]

When starting up (starting power generation) or shutting down (stopping power generation) of a fuel cell, the open circuit voltage is reduced for the reason that the load on the battery electrode is reduced due to a sudden voltage change. It is desirable to start / stop the power generation.
However, the open-circuit voltage E ₀ of the fuel cell is high beyond the rated capacity of the apparatus power consumption side, there is a possibility that equipment damage. Therefore, it is necessary to consume the output from the fuel cell and reduce the voltage to a level at which connection to the DC system is possible between the time when the fuel cell is started and the time when the operation for supplying power to each device is performed. The present inventors have intensively studied a connection method of a fuel cell for protecting a device of a DC system, and have worked hard to develop it. As a result, the present invention described below has been completed.

A fuel cell system according to the present invention includes a DC system device connected to a fuel cell via a power supply circuit, and a power supply circuit provided in the power supply circuit to supply power from the fuel cell to the DC system device. A circuit breaker that shuts off, a voltage monitoring unit that detects the voltage of the fuel cell, and power of an appropriate voltage in a rated operating point region is applied to the DC system device based on the detected voltage information sent from the voltage monitoring unit. A voltage stabilizing device to be supplied so as to protect the DC system equipment;
A simulated load that is connected to the voltage stabilizing device and the power supply circuit and consumes initial power generated by the fuel cell while the voltage of the fuel cell falls from the open circuit voltage to the rated operating point region; The circuit breaker is connected to each of the circuit breaker, the voltage monitoring unit, and the voltage stabilizing device so that the initial power from the fuel cell does not flow to the DC system device based on the detected voltage information sent from the voltage monitoring unit. And sending a power supply command signal to the voltage stabilizing device so that the initial power from the fuel cell is consumed by the simulated load based on the detected voltage information sent from the voltage monitoring unit, And a control unit that sends an open command signal to the circuit breaker when the voltage of the fuel cell drops to the rated operating point region.

The fuel cell operating method according to the present invention is a fuel cell operating method for protecting a fuel cell from an initial output of the fuel cell when the fuel cell is connected to a device of a DC system. Starting fuel injection into the
(B) turning on the voltage stabilization system to cut off the power supply to the devices of the DC system, and supplying power to the simulated load to consume the initial output of the fuel cell; and (c) detecting the voltage of the fuel cell. The detected voltage has reached the rated operating point range,
Or, close the circuit breaker at a predetermined timing, connect the power supply circuit, and start power supply to DC system equipment,
Stopping the power supply to the simulated load.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIGS. 1 and 2, the solid oxide fuel cell (PFFC) 2 is connected to a plurality of DC system devices 8a and 8b via a power supply circuit. The power supply circuit includes a voltage stabilizer 20, a switch 4, and power buses 6a and 6b.
Are provided in this order.

The separator in the fuel cell 2 is a voltage monitor 1
2 are connected. The voltage monitoring unit 12 detects a potential difference between separators in the fuel cell 2. That is, a terminal is attached for each separator, for every other separator, or for every two separators, and the potential difference between the separators is detected.
Further, the voltage monitoring unit 12 is connected to the CPU board 11 in the control unit 10 via the analog input AI.

As shown in FIG. 3, the CPU board 11
24 and a control power source (not shown) via N24 (24
V) are connected to the plus side and the minus side, respectively. The digital out DO of the CPU board 11 functions as a voltage stabilizer operation command unit 14 and a power bus connection command unit 16, respectively. One DO is connected to a terminal of the voltage stabilizer 20 and the other DO is Induction coil of relay 5 and negative side N24 of control power supply
It is connected to the. The relay 5 is connected to the induction coil of the switch 4. The switch 4 as a circuit breaker is of a magnet conductor type that simultaneously shuts off the power supply circuits of the power supply buses 6a and 6b on the plus side and the minus side.

The voltage stabilizer 20 as a protection device has a circuit including a control terminal and a power terminal. Among them, the control terminal is connected to DO of the voltage stabilization device operation command section 14, the control terminal is connected to P24 and N24, the power terminal is connected to the power supply circuit of the fuel cell, and the power terminal is simulated. Heater 3 as load
1 connected.

The heater 31 is connected to the device 8 by the open circuit voltage.
a and 8b function as a simulated load that consumes the initial output generated by the fuel cell 2 in order to prevent destruction of the fuel cell 2 and 8b. Has the function of quickly shifting from the unsteady state to the steady state. That is, since the power generation in the fuel cell 2 is an exothermic reaction, cooling water is allowed to flow through the inside of the cell for cooling to prevent overheating. Since a higher predetermined temperature range is more advantageous, the cooling water at the beginning of power generation is preheated to the predetermined temperature range using the heater 31 as a simulated load. In addition, it is preferable that the hydrogen gas and the oxygen gas as fuels are similarly preheated by the heater 31.

Next, the internal circuit of the voltage stabilizer will be described in detail with reference to FIG.

The circled numbers in the figure indicate the terminals 21 to 21.
28, and corresponds to the reference numeral in FIG. Code P24
Denotes a plus side of the control power supply, and reference numeral N24 denotes a minus side of the control power supply. Terminals 21 and 22 of voltage stabilizer 20
() Is a voltage stabilizing device operation command section D of the control device 10.
It is connected to the O transistor Tr3 circuit. Also,
The control terminal 23 () is connected to the positive side P24 of the power supply line (DC24V) of the control power supply,
() Is connected to the minus side N24 of the power supply line of the control power supply.

On the other hand, the power terminals are connected to the positive side and the negative side of the power supply line (DC 120 V) of the fuel cell 2, respectively. The power terminal is connected to a heater 31 as a simulated load.

The control circuit and the power circuit of the voltage stabilizing device 20 are connected via a comparator 29. The plus input side of the comparator 29 is P24 / terminal 23 / R2 / R
3 / Connected to a control circuit including a terminal 28 / N24, and the negative input side is connected to a power circuit including a terminal 25 / R4 / R9 / R5 / terminal 27. The former control circuit and the latter power circuit are connected via a shared circuit.

On the other hand, the output side of the comparator 29 is R7 / Tr2
/ Terminal 21 / Tr3 / terminal 22 / Tr1 / terminal 26 / heater 31 / terminal 25 and a loop circuit including R10 / R6.

The third transistor Tr3 in the control device 10
Is connected to the base of the first transistor Tr1, the collector of the first transistor Tr1 is connected to the heater 31, and the emitter of the first transistor Tr1 is connected to the above shared circuit. Also, the second transistor T
The emitter of r2 is also connected to the shared circuit. The base of the second transistor Tr2 is connected to the output side of the comparator 29, and the collector of the second transistor Tr2 is connected to the collector of the third transistor Tr3 in the control device 10. Further, a circuit connecting the third transistor Tr3 and the first transistor Tr1 is connected to the above-described shared circuit via a resistor R8.

Next, the operation will be described with reference to FIGS.

FIG. 5 is a diagram showing current-voltage characteristics when the fuel cell is operated, with the horizontal axis representing current and the vertical axis representing voltage. Launch fuel cell and occur electromotive force first open-circuit voltage E ₀ is generated between the cells. When the current reaches the voltage E ₁ of the sudden voltage drop to the rated operating point region with the start of flow of the feed circuit, a current increase rate is increased, the voltage drop rate decreases. This rated operating point region (voltage E ₁ to
E _2, the current I ₁ ~I ₂₎ in the device 8a, 8b may be stably operated without being damaged. When the voltage further drops, the devices 8a and 8b cannot withstand the current load and are destroyed.

[0022] For example, 17 pieces of the unit cells to activate the series-connected solid oxide fuel cell (PFFC), the open circuit voltage E ₀ of per unit cell is approximately 1.0~1.1V, and the fuel The battery as a whole produces an electromotive force of about 17 volts. If the open circuit voltage E ₀ is directly applied to the devices 8a and 8b of the DC system, the devices may not be able to withstand a high voltage, and may be damaged or destroyed. Therefore, until the electromotive force of the fuel cell 2 reaches the rated operating point, the initial electromotive force immediately after the fuel cell is started is supplied to the simulated load (preheating heater) to protect the DC system equipment from the high voltage load, and Prevent the destruction of. In this case electromotive force per unit cell is dropped from approximately 1.0~1.1V open circuit voltage E ₀ to about 0.5~0.7V the rated operating point region, as nominal operating point of the fuel cell Stabilizes at about 12 volts.

FIG. 6 is a timing chart when starting up the fuel cell.

When the main power switch of the fuel cell system is turned on, the computer of the control unit 10 starts up and sends an open command signal to a valve of a fuel gas supply device (not shown), so that hydrogen gas and oxygen gas are fed into the fuel cell 2 as fuel. Start flowing. When the supply of the fuel gas to the fuel cell 2 is started at the timing of time t1, an electromotive force is generated in each cell of the fuel cell 2 and the voltage of the entire fuel cell increases.

The voltage monitor 12 detects the increased voltage of the fuel cell, and outputs the detected voltage signal to the controller CPU board 1.
1 to the analog in AI. The CPU board 11 AD-converts the input signal and outputs a digitized command signal from the digital output DO 14 to the voltage stabilizing device 20.

At time t2, the voltage stabilizing device 2
When a digital command signal is input to the circuit via the 0 terminals 21 and 22, the potential on the negative side of the comparator 29 increases, and the comparator 29 is turned off. Accordingly, the base current of the second transistor Tr2 is turned off. Here, the control unit 10
When the DO of the voltage stabilization operation command section 14 is ON, a potential is applied to the base of the first transistor Tr1 and the first transistor Tr1 is turned ON, thereby supplying power to the simulated resistance heater 31. While power is being consumed by the heater 31, the voltage drops to the rated operating point due to the voltage-current characteristics of the fuel cell. Accordingly received high open-circuit voltage E ₀ at the time of start-up of the fuel cell device 8a, 8b can be prevented from being destroyed.

The cooling water flowing inside the fuel cell 2 is preheated to an appropriate temperature by the heater 31 as a simulated load. The temperature of the cooling water is preferably adjusted not to room temperature but to 60 to 80 ° C. in order to improve the power generation efficiency of the fuel cell. The reason is solid oxide fuel cell (PFFC)
Is operated at room temperature (20 to 23 ° C.), the internal resistance of the fuel cell is high, and the power generation efficiency is reduced. On the other hand, if the temperature of the cooling water is not adjusted to an appropriate temperature and the fuel cell is overheated to 120 ° C. or more, the water is evaporated and the reaction is not smoothly promoted, or the membrane is softened. Occurs.

Further, since the fuel gas is also preheated to an appropriate temperature by the heater 31, the fuel cell 2 starts up quickly.

The voltage monitoring unit 12 detects that the voltage of the fuel cell 2 has dropped and has reached the voltage E ₁ in the rated operating point region, and based on this, sends a close command signal from the DO to the relay 5 to turn on the circuit breaker 4. The circuit breaker 4 is closed and connected, or the circuit breaker 4 is closed and connected at time t3. The timing of the time t3 is set in advance based on the performance of the operating characteristics of the fuel cell 2. That is, the time from the start of power generation until the voltage of the fuel cell drops to the rated operating point region is actually measured, and the timing of the time t3 is determined based on the measured time. The time control may be performed in this manner, or the opening and closing of the circuit breaker 4 may be controlled in real time based on the voltage value measured and detected online.

In the above embodiment, the case of a solid oxide fuel cell (PFFC) has been described. However, the present invention is not limited to this, and the solid oxide fuel cell (SOFC)
FC), alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC)
The present invention can be applied to other types of fuel cells.

In the above embodiment, a heater for preheating fuel gas and cooling water is used as a simulated load. However, the present invention is not limited to this, and the preheating of equipment and systems other than the fuel cell is not limited to this. The heater can also be used as a simulated load.

[0032]

As described above in detail, according to the present invention, until the voltage of the fuel cell drops to the rated operating point region,
Since the initial power is consumed in the simulated resistance heater,
The device can be effectively prevented from being destroyed by the high open circuit voltage.

Further, since the cooling water of the fuel cell at the initial stage of startup is heated by the simulated resistance heater, the initial reaction in the cell portion is promoted, and a quick start-up is realized in a short time.

[Brief description of the drawings]

FIG. 1 is a conceptual block diagram schematically showing a fuel cell system according to an embodiment of the present invention.

FIG. 2 is a functional block diagram showing a fuel cell system according to the embodiment of the present invention.

FIG. 3 is an overall circuit diagram showing a fuel cell system according to an embodiment of the present invention.

FIG. 4 is a partial circuit diagram showing a part of the fuel cell system according to the embodiment of the present invention.

FIG. 5 is a characteristic diagram showing current-voltage characteristics of a fuel cell.

FIG. 6 is a timing chart when the fuel cell is started using the fuel cell operation method according to the embodiment of the present invention.

[Explanation of symbols]

 2 ... fuel cell, 4 ... switch (circuit breaker), 5 ... relay, 6a, 6b ... power bus, 8a, 8b ... equipment (to be protected), 10 ... control unit, 11 ... CPU board, 12 ... voltage monitoring unit, 14: voltage stabilization operation command section, 16: power bus connection command section, 20: voltage stabilization device (protection device), 21 to 28: terminal, 29: comparator, 31: heater (simulated load).

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ryutaro Fukumoto 5-717-1, Fukabori-cho, Nagasaki-shi, Nagasaki F-term (reference) 5H027 AA06 CC06 KK54 MM26

Claims (5)

[Claims] 1. A device of a DC system connected to a fuel cell via a power supply circuit; a circuit breaker provided in the power supply circuit, for interrupting supply of power from the fuel cell to the device of the DC system; A voltage monitoring unit that detects the voltage of the battery, based on the detected voltage information sent from the voltage monitoring unit, so that power of an appropriate voltage in a rated operating point region is supplied to the DC system device, A voltage stabilizing device that protects the DC system equipment, connected to the voltage stabilizing device and the power supply circuit, respectively, while the voltage of the fuel cell drops from the open circuit voltage to the rated operating point region, A simulated load that consumes the initial power to be generated, and an initial load from the fuel cell based on the detected voltage information sent from the voltage monitor, connected to the circuit breaker, the voltage monitor, and the voltage stabilizer, respectively. While sending a close command signal to the circuit breaker so that power does not flow to the DC system equipment, the initial power from the fuel cell is consumed by the simulated load based on the detected voltage information sent from the voltage monitoring unit. And a controller that sends a power supply command signal to the voltage stabilizing device and further sends an open command signal to the circuit breaker when the voltage of the fuel cell drops to the rated operating point region. Fuel cell system. 2. The voltage stabilizing device includes a comparator, a transistor Tr2 connected to an output side of the comparator, and a transistor Tr1 connected to the simulated load. Item 7. The method according to Item 1. 3. The fuel cell system according to claim 1, wherein the simulated load is a heater for preheating the cooling water for preventing overheating supplied to the fuel cell to an appropriate temperature. 4. The fuel cell system according to claim 1, wherein the circuit breaker is an ON / OFF switch that cuts off both a positive side and a negative side of a power supply circuit connected to the DC system equipment. . 5. A fuel cell operation method for protecting a fuel cell from an initial output of the fuel cell when the fuel cell is connected to a device of a DC system, comprising: (a) starting fuel supply to the fuel cell; (B) turning on the voltage stabilization system to cut off the power supply to the DC system equipment, and supplying power to the simulated load to consume the initial output of the fuel cell; and (c) detecting the voltage of the fuel cell. When the detected voltage reaches the rated operating point area or at a predetermined timing, the circuit breaker is closed and the power supply circuit is connected, and power supply to DC system equipment is started and power supply to the simulated load is performed. Stopping the fuel cell.