JPS6180314A - Power converter for fuel battery - Google Patents

Abstract

PURPOSE:To start an inverter circuit stably by outputting a DC output from an AC system or the like connected to the output side of the inverter circuit and using said DC output as an auxiliary power supply for driving the inverter circuit. CONSTITUTION:Fuel 2 and air 3 are supplied to a fuel battery stack 1 in a fuel battery power converter to obtain a DC output. In DC output is converted into an AC signal by the inverter circuit 10 through a security resistor 5, a switch 6 and a DC interrupter (diode) 9 for a main circuit to supply the AC signal to an AC system 13. In addition, an auxiliary power supply circuit 18 having the small capacity and supplying DC output obtained from a power supply 14 independent from said AC system 13 is connected to the input side of the inverter circuit 10. The inverter circuit 10 is started by the circuit 18, and at the starting time, a breaker 15 is turned on and the output side 4 of the stack 1 is terminated by the maintenance resistor 5. If the DC output voltage of the stack 1 is raised and reached to the same level as the output voltage of a rectifier circuit 17, a DC breaker 9 is connected and the DC output voltage is supplied from the stack 1 side to the inverter circuit 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to fuel cells, and particularly to improvements in a power converter for fuel cells that converts DC output from a fuel cell stack into AC and outputs the AC.

[Technical background of the invention and its problems] In recent years, in order to meet the increasing demand for electricity, in addition to the construction of hydroelectric power plants, thermal power plants, and nuclear power plants, The concept of constructing a power plant using fuel cells that converts energy into natural energy is being advanced. This fuel cell usually consists of a fuel cell stack consisting of a plurality of stacked battery cells each consisting of a pair of electrodes, a fuel electrode and an oxidizer electrode (hereinafter referred to as an air electrode), with an electrolyte layer in between. A fuel such as hydrogen is brought into contact with the back surface of the electrode, and an oxidizing agent such as air is brought into contact with the back surface of the air electrode, and the electrochemical reaction that occurs at this time is used to extract electrical energy from between the pair of electrodes. As long as the above fuel and oxidizer are supplied, electrical energy can be extracted with high conversion efficiency. An actual fuel cell power plant consists of the above-mentioned fuel cell stack, a fuel reformer that reforms natural gas or coal gas into hydrogen-based battery fuel, and converts the DC output from the fuel cell stack into alternating current. The main component is a power conversion device that converts the power and supplies it to an external AC system, and also includes a control 11 device, a water treatment device, an exhaust heat recovery device, etc.

Now, among the main components of this type of fuel cell power plant, the main component of the power conversion device is the orthogonal conversion circuit (hereinafter referred to as the inverter circuit). Generally, an initial closing resistance (hereinafter referred to as "preload") is provided in order to match the current.

FIG. 4 is a configuration diagram showing an example of this type of conventional power conversion device for fuel cells. In the figure, a fuel cell stack 1 is supplied with fuel 2 and air 3 at its fuel electrode and air electrode, respectively, and a direct current output is obtained by an electrochemical reaction.

Further, on the output side 4 of the fuel cell stack 1, a maintenance resistor 5 is connected and turned on and off. Switches 6 are connected in series, and in parallel with this series circuit, a series circuit of a preload 7 and a preload breaker 8 for opening and closing is connected via a main circuit DC breaker 9 in series. Furthermore, the input side of an inverter circuit 10 is connected to the output side 4 of the fuel cell stack 1, which converts the DC output to AC and outputs the AC output via an output transformer 11 and an AC breaker 12. It is supplied to an external AC system 13.

Note that the DC breaker 9 is usually constructed using a power conversion element such as a diode or a thyristor, and has a main circuit opening/closing function and a reverse conduction blocking function.

The inverter circuit 10 in such a fuel cell power converter is activated as follows.

That is, both the DC breaker 9 and the preload breaker 8 are initially in an open state, and the output side of the fuel cell stack 1 is open or terminated with the maintenance resistor 5. Further, the fuel cell stack 1 is supplied with a certain amount of fuel 2 necessary for its fuel electrode in advance. Then, when the supply of air 3 is started in this state, the DC output voltage of the fuel cell stack 1 starts to rise to a certain voltage value Vp.
When the preload breaker 8 is exceeded, the preload breaker 8 is closed and the preload 7 is applied. The voltage 'J stk, which once decreased due to the application of the preload 7, rises again as the supply flow rate of the air 3 increases, and when the supply flow rate of the air 3 becomes sufficiently large, the DC breaker 9 closes and the inverter circuit 10 is connected. be done. At this time, almost simultaneously, the preload breaker 8
is opened, and the preload 7 is released. Then, approximately at the same time as the inverter circuit 10 is turned on, the AC breaker 12 is turned on, and the DC output of the fuel cell stack 1 is converted into AC and supplied to the AC system 13. Figure 5 (
Figures a, b, and c show the relationship between the temporal changes in the DC output voltage V stk and the DC output current 1 stk of the fuel cell stack 1 as the air 3 supply flow rate increases as described above.

By the way, in such a power conversion device for a fuel cell, the preload 7 is normally used at the start-up time 1) f of the inverter circuit 10.
1, but its resistance capacity needs to satisfy the minimum rated operating characteristics of the battery within the operating voltage range of the inverter circuit 10, so it requires 20% to 30% of the total inverter capacity. In some cases, preload 7
As the number of people increases, not only does the equipment become larger, but it also causes losses.
- There are also problems. In addition, in order to shorten the application period of the preload 7 as much as possible, the air 3 may be rapidly introduced into the fuel cell stack 1 to raise the DC output voltage at a steep slope. A problem arises in that the three air flow suspension control and the battery interelectrode pressure differential control become very complicated.

[Object of the Invention] The present invention was made in order to solve the above-mentioned problems, and its purpose is to avoid increasing the size of the device and complicating air flow rate control and battery interelectrode differential pressure control. An object of the present invention is to provide an inexpensive power conversion device for a fuel cell that can stably start an impark circuit without causing any damage.

[Summary of the Invention] In order to achieve the above object, the present invention obtains a DC output from an AC system connected to the output side of an inverter circuit or from an in-house power supply of a separate system, without using the preload described above. The present invention is characterized in that it includes a small-capacity auxiliary power supply circuit that supplies this to the input side of the inverter circuit as an auxiliary power supply for driving the inverter circuit.

[Embodiments of the invention] An embodiment of the present invention shown in the drawings will be described below.

FIG. 1 shows an example of the configuration of a power converter for a fuel cell according to the present invention. The same parts as in FIG. . In other words, in FIG. 1, the preload 7 and the preload breaker 8 mentioned above are omitted, and instead, the AC system 1 connected to the output side of the inverter circuit 10 is
3 is provided with a small-capacity auxiliary power supply circuit 18 that obtains a DC output from an in-house power supply 14 of a separate system and supplies this to the input side of the inverter circuit 10 as an auxiliary power supply for driving the same. Here, the auxiliary power supply circuit 18 is configured to rectify the output of the station power supply 14 introduced via the breaker 15 and the transformer 1G with a rectifier circuit 17 to obtain a DC output. The output capacity of this auxiliary power supply circuit 18 may be the minimum capacity for driving the inverter circuit 10 alone (specifically, the loss during no-load operation of the inverter circuit 10). Furthermore, depending on the circuit configuration, the breaker 15 and the transformer 16 can be omitted.

In the fuel cell power conversion device configured as described above,
The inverter circuit 10 is activated as follows. That is, at the beginning of the rise of the DC output voltage of the fuel cell stack 1, the DC breaker 9 is in an open state, and the output side 4 of the fuel cell stack 1 is open or terminated with the maintenance resistor 5.

Further, the fuel cell stack 1 is supplied with a certain amount of fuel 2 necessary for its fuel electrode in advance. On the other hand, the breaker 15 of the auxiliary power supply circuit 18 is turned on, and the rectifier circuit 17 receives power from the station power supply 8!14 and converts it into direct current having a pulsating waveform with the output voltage Vr as the center value. Circuit 10 is being driven. In this case, the AC breaker 12 is in the ON state and the output side of the inverter circuit 10 is connected to the AC system 13, but the inverter circuit 10 is in a no-load operation state and no power is supplied to the AC system 13.

Next, when the supply of air 3 is started in the above state, the DC output voltage V stk of the fuel cell stack 1 starts to rise. Then, the DC breaker 9 is turned on before this DC output voltage V Stk reaches the level of the rectifier circuit 17 output voltage value Vr, but if Vstk<Vr, the reverse conduction prevention function of the DC breaker 9 , no current flows from the auxiliary power supply circuit 18 to the fuel F3I battery stack 1 side. Next, when the DC output voltage Vstk of the fuel cell stack 1 further increases and reaches approximately the same level as the rectifier circuit 17 output voltage value Vr, the DC output voltage Vstk instantaneously exceeds the rectifier circuit 17 output pulsating voltage value. Therefore, the DC breaker 9 conducts in the forward direction, and the output current f Stk of the fuel cell stack 1 is applied to the inverter circuit 10 . Then, the output current from the auxiliary power supply circuit 18 decreases by the amount of current shared by the battery side output. Furthermore, since the rectifier circuit 17 output has a pulsating voltage waveform and the battery output side voltage drops instantaneously when current is drawn,
The current waveform applied from the fuel cell stack 1 side to the inverter circuit 10 has a continuous pulse shape. After this, when the flow rate of air 3 supplied to the fuel cell stack 1 has risen sufficiently, the DC output voltage V stk continuously becomes a value larger than the output voltage value Vr of the rectifier circuit 17, so that the inverter circuit 10 All input terminals will be supplied from the fuel cell stack 1 side.

Note that at this point, the circuit breaker 15 of the auxiliary power supply circuit 18 may be opened. FIGS. 5(a), 5(d), and 5(e) show the DC output voltage V stk and DC output current I S of the fuel cell stack 1 as the air 3 supply flow rate increases as described above.
It shows the relationship of temporal changes in tk. Figure 5 (
According to e), it is clear that the DC output current l5tk increases gradually in average value, and the current value suddenly increases when using a preload as shown in Fig. 5(C). There will be no change.

As described above, in the fuel cell power converter of this embodiment, the small-capacity auxiliary power supply circuit 18 is used as the auxiliary power supply for driving the inverter circuit 10, that is, with no load, without using the large-capacity preload that is conventionally required. Since it is used for starting, the device does not become larger and costs can be reduced accordingly. In addition, in conventional devices using preload, it was necessary to rapidly increase the supply flow rate of air 3 to fuel cell stack 1 in order to keep the preload input time short, but with this configuration, this is not necessary. Therefore, it is possible to easily control the air supply flow rate and to control the differential pressure between battery electrodes, which is extremely effective in terms of control logic. In addition, according to this device configuration, there is no sudden change in the battery output current when preloading is applied, and the output current Tstk rises slowly on average, so the process exhaust flow rate and pressure do not change suddenly and are effective for control. It is.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can be similarly implemented in the following manner.

(a) As shown in FIG. 2, a chopper circuit 19 may be provided in series on the input side of the inverter circuit 10 to control the DC input voltage of the inverter circuit 10. In this case, the DC output of the auxiliary power supply circuit 18 is applied to the input side of the chopper circuit 19.

(b) As shown in FIG. 3, a plurality of fuel cell stacks 1
and a plurality of inverter circuits 10 may be configured to include an auxiliary power supply circuit 21 for sequentially driving the inverter circuits 10 that need to be activated by the changeover switch 20.

(C) In the above, the power input for the auxiliary power supply circuit 18 or 21 is obtained from the in-house power supply 14, but it may also be obtained from the AC system 13 connected to the output side of the inverter circuit 10. be.

(d) The auxiliary power supply circuit may be replaced by a secondary battery power supply.

(e) Auxiliary power supply circuit As the rectification circuit 17, not only a simple rectification circuit but also a controlled rectification circuit such as a thyristor that can control the voltage or power level of the output of the auxiliary power supply circuit may be applied.

(f) As a circuit element, a DC breaker 9 having a main circuit opening/closing function and a reverse conduction blocking function was used, but the present invention is not limited to this; a DC interrupter having a main circuit opening/closing function;
It may also be constructed from circuit elements having a reverse conduction blocking function and inserted in series in the circuit.

(q) In the above, the maintenance resistor 5 can be omitted.

(h) In the above, the inverter circuit 10 is started with no load, but the fuel cell stack 1 may start generating power with a small load in the power transmission state.

In addition, the present invention can be modified and implemented in various ways without changing the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, DC output is obtained from the AC system connected to the output side of the inverter circuit or from the in-house power supply of a system different from this, and is applied to the input side of the inverter circuit. Since it is equipped with a small-capacity auxiliary power supply circuit that supplies an auxiliary power supply for driving the navel, it is possible to achieve a stable inverter without increasing the size of the device and without complicating air flow control and battery electrode differential pressure control. It is possible to provide an inexpensive power conversion device for a fuel cell that can start up a circuit.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, FIGS. 2 and 3 are configuration diagrams showing further embodiments of the present invention, and FIG. 4 is a configuration diagram showing a conventional power conversion device for fuel cells. Figure, Figure 5 (a
) to (e) are diagrams showing the relationship between temporal changes in battery DC output voltage and DC output current as the air supply flow rate increases. DESCRIPTION OF SYMBOLS 1... Fuel cell stack, 2... Fuel, 3... Air, 4... Fuel cell stack output side, 5... Maintenance resistor, 6... Maintenance resistor switch, 7 ... Preload, 8... Preload breaker, 9... DC breaker, 10... Inverter circuit, 11... Output transformer, 12... AC breaker, 13... AC system, 14... In-house power supply, 15... Breaker, 16
...Transformer, 17... Rectifier circuit, 18.21...
Auxiliary power supply circuit, 19... chopper circuit, 20... selector switch.

Claims (8)

[Claims] (1) A battery cell is constructed by stacking a plurality of battery cells in which a pair of electrodes, a fuel electrode and an oxidizer electrode, are arranged with an electrolyte layer in between, and the fuel is brought into contact with the fuel electrode, and the oxidizer is brought into contact with the oxidizer electrode. An orthogonal conversion circuit converts the DC output from the fuel cell stack into alternating current by utilizing the electrochemical reaction that occurs when the electrodes are brought into contact, and an orthogonal conversion circuit that converts the DC output from the fuel cell stack into alternating current using the electrochemical reaction that occurs when the electrodes are brought into contact. DC output is obtained from a circuit element provided between the fuel cell stack and the orthogonal conversion circuit, and an AC system connected to the output side of the orthogonal conversion circuit or an in-house power supply of a separate system. A power conversion device for a fuel cell, comprising: an auxiliary power supply circuit that supplies this to the input side of the orthogonal conversion circuit as an auxiliary power source for driving the orthogonal conversion circuit. (2) The fuel cell power according to claim (1), characterized in that the circuit element is a direct current or disconnector having a main circuit opening/closing function and a reverse conduction blocking function. conversion device. (3) A patent characterized in that the circuit elements are composed of a direct current or disconnector that has a main circuit opening/closing function, and a circuit element that has a reverse conduction blocking function and is inserted in series in the circuit. A power conversion device for a fuel cell according to claim (1). (4) Claim No. 1 characterized in that a chopper circuit is provided in series on the input side of the orthogonal conversion circuit.
) A power conversion device for a fuel cell as described in item 2. (5) A plurality of battery cells are stacked in which a pair of electrodes, a fuel electrode and an oxidizer electrode, are arranged with an electrolyte layer in between, and the fuel is brought into contact with the fuel electrode, and the oxidizer is brought into contact with the oxidizer electrode. A plurality of orthogonal conversion circuits convert the DC output from the plurality of fuel cell stacks into alternating current by utilizing the electrochemical reaction that occurs when the electrodes are brought into contact, and a plurality of orthogonal conversion circuits convert the DC output from the plurality of fuel cell stacks into alternating current. A plurality of circuit elements having a conduction blocking function and provided between the fuel cell stack and the orthogonal conversion circuit, and an AC system or a separate system connected to the output side of each of the orthogonal conversion circuits. At least one auxiliary power supply circuit that obtains a DC output from a power source and supplies this to the input side of the orthogonal conversion circuit that needs to be activated as an auxiliary power source for driving the same. conversion device. (6) The fuel cell power according to claim (5), characterized in that the circuit element is a direct current or disconnector having a main circuit opening/closing function and a reverse conduction blocking function. conversion device. (7) A patent characterized in that the circuit elements are composed of a direct current or disconnector that has a main circuit opening/closing function, and a circuit element that has a reverse conduction blocking function and is inserted in series in the circuit. A power conversion device for a fuel cell according to claim (5). (8) Claim No. 5 characterized in that a chopper circuit is provided in series on the input side of the orthogonal conversion circuit.
) A power conversion device for a fuel cell as described in item 2.