JPS60219920A - Method of controlling fuel battery generator system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a fuel cell that performs power control by connecting an inverter circuit connected to a fuel cell or a power conversion device consisting of a chopper circuit and an inverter circuit to a power system. The present invention relates to a power generation system, and relates to a control method for a fuel cell power generation system that can appropriately control overvoltage when starting or stopping a fuel cell.

[Technical background of the invention and its problems]

In recent years, against the backdrop of the increasingly severe energy situation, fuel cells are an excellent option that can directly convert the chemical energy of fuel into electricity, and can be expected to have high power conversion efficiency, while also having the potential to keep environmental pollution to a minimum. It is attracting attention as a new energy source. Incidentally, it is known that one of the characteristics of fuel cells is that voltage fluctuations are relatively large with respect to changes in load.

As shown in FIG. 1, a typical discharge characteristic of a fuel cell is that as the current increases, that is, as the load on the fuel cell increases, the cell voltage decreases significantly. For example, in the case of a phosphoric acid fuel cell, the cell pressure at no load and the cell voltage at rated load (load voltage) are 50 to 80% of the rated voltage.
There is a close difference. This voltage rotation rate is remarkable in the light load range, which varies from 0 to 25%. Therefore, since the @ current power generated from the fuel cell has limited uses as it is, it is generally used after being stabilized to a certain level and converted into DC voltage or current power. In order to connect a fuel cell to a current power system (hereinafter referred to as a power system) as a power generation system, a power conversion device that converts direct current power to current power is generally used. That is, a power converter used in a power generation system using fuel cells is required to design a system that fully takes into account the voltage fluctuation rate as shown in FIG.

However, voltage fluctuations as shown in FIG. 1 cause an increase in output harmonics in a self-excited inverter, and cause a deterioration in the operating power factor in a separately-excited inverter. Also, for fuel cells, a voltage difference occurs between the multi-AvM elements that make up the centrifugal charge cell in a region near the no-load voltage of the fuel cell itself, which promotes the chemical reaction that is one of the elements. This results in a meltdown of IQ and suffering.

In other words, the voltage fluctuation of a fuel cell exhibiting the characteristics shown in Fig. 1 causes the device capacity to be larger than necessary for the power converter, which not only causes problems in terms of cost and efficiency, but also affects the output characteristics. It also makes things worse. On the other hand, fuel cells have the disadvantage of shortening their useful life as a battery. This drawback increases both in cost and lifespan as the capacity of the fuel cell system increases, and has been one of the problems faced by human control. As a countermeasure against these drawbacks of fuel cells (2), the fuel cell power generation system has a
It has also been proposed that a voltage suppressing resistor be inserted on the DC side to forcibly lower the fuel cell voltage between 5% and 5%. A block diagram of a fuel cell power generation system in this case is shown in FIG.

Figure 2 (where 2, l is a fuel cell, 2 is a power converter, 3 is a fuel cell,
4 is a switch for closing and opening the voltage suppressing resistor 5; 6 is a transformer; and 7 is a switch for closing and opening the output of the power converter 2 and the power system 8. In the initial power generation state of the voltage suppressor resistance 5F of the fuel cell l, or in the event of an accident in the power converter 2, or when the switch 7 is opened, that is, when the current I in FIG. .

The switch t4 is turned on, and the fuel cell 1 operates to suppress the battery voltage E of the fuel cell 1 to a predetermined value E. While the voltage suppressing resistor 5 is turned on, the output of the fuel cell 1 is generally rapidly increased by rapidly injecting air into the air electrode of the fuel cell 1, or conversely, the nitrogen gas is rapidly suppressed. From g2, control is performed to rapidly reduce the output of the fuel cell l. however,
According to the means shown in FIG. 2, not only all the power consumed by the voltage suppressing resistor 5 during startup and stopping becomes a loss, but also the switch F4, which turns on and off the voltage suppressing resistor 5, operates at high speed. Moreover, there is a drawback that unnecessary transient fluctuations are caused in the fuel cell when the voltage suppressing resistor 5 is turned on and off.

[Purpose of the invention]

Therefore, in consideration of the above-mentioned points, the present invention provides power control of the power conversion device 2 in a light load state when the fuel cell power generation system is started or when it is stopped, that is, in a state in which the fuel cell l is also controlled to suppress its output. The fuel cell is controlled by switching to blood flow constant voltage control so that the blood flow input of the power conversion device 2, that is, the DC output of the fuel cell 1, is kept constant at a predetermined voltage, voltage E shown in FIG. An object of the present invention is to provide a control method for a fuel cell power generation system that can suppress the voltage of 1.

[Summary of the invention]

The present invention aims to achieve this objective. ! ! An inverter circuit uses the output of the DC power source as a DC power source,
Alternatively, in a control method for a fuel cell power generation system configured by connecting a power conversion device consisting of a chopper circuit and an inverter circuit to a power system, if the electromotive force of the fuel cell is less than a predetermined value, the @flow of the power conversion device is DC constant voltage control is performed to keep the input constant (secondary operation is performed in connection with the power grid, and when the electromotive force of the fuel cell reaches a predetermined value or higher, the DC constant voltage control is switched to the predetermined power control, and the fuel It is designed to control power between the battery and the power grid.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

Components in FIG. 3 with the same symbols as in FIG. 2 have the same functions. Although the control circuit lOO of the power liquid exchanger &2 is shown in FIG. 3 as a control circuit for an individually excited inverter, the purpose of the present invention is the same for a control circuit for a separately excited inverter.

Furthermore, the details of the function of controlling reactive power in the control circuit lOO are well known and will therefore be omitted.

Generally, when the power converter 2 and the power system 8 are operated in parallel, the power system 8 cannot be controlled, so the gravity converter 2 generates reactive power by the voltage difference between the two power sources, and active power by the phase difference between the two power sources. It is known that each can be controlled.

In the control circuit 100 shown in FIG. 3, based on an active power control system generally used for power control, the amount of power (not shown) has decreased, that is, below the 1JL flow I, l2 in FIG. A changeover switch 47 is operated by a signal from a detection circuit that detects this, and the power control system is switched to the DC constant voltage control system. Here, the active power control system will be briefly explained.

The active power reference 40 is compared with the output of the active power quadrature transducer f41, and the deviation is added to the input of the error amplifier 42, and the outputs of the four error amplifiers are connected to a phase-locked loop (Phase 1ocked 1oop), so-called PL.
It serves as one input Roy of the L circuit 43.

It is necessary to use a divider to divide the output frequency of the PLL circuit 43,
The power becomes the other input 1/N' of the PLL circuit 43. The other input 60"C2 of the PLL circuit 43 is given as a phase reference to the power system voltage 22 of the power system 8. Here, the PLL circuit 43μ is a well-known circuit, but will be briefly explained. FIG. This is an example of a block diagram of a PLL circuit @43, and the configuration of the PLL circuit 43 is a phase error detector PH.
D, a low-pass P wave generator LPF, and a voltage controlled oscillator vCO. To give an overview of each of these elements, the phase error detector PHD has a phase reference signal "output 1" and a phase feedback signal "output 1".
Generates a signal "2" proportional to the phase difference with the noise. The signal "2" proportional to this phase difference C2 becomes an input to the low-pass p-wave filter LPF, which removes harmonic components and amplifies the phase error. Then, the voltage controlled oscillator vCO outputs a frequency proportional to the output "H" of the low frequency PL&
is added to the splitter 44. If the frequency division ratio of the frequency divider 44 is N, the oscillation frequency of the voltage controlled oscillator vCO will be N times that of the phase reference signal "M". Here, N is selected as an arbitrary integer depending on the number of phases of the inverter. Since the output of the splitter 44 is phase feedback No. 48 "C" of the phase error detector PHD, the resonance frequency of the voltage controlled oscillator vCO is such that the phases of the phase reference signal 10" and the phase feedback signal "C" match. Here, the function of one input "A" of the PLL circuit 43 is to provide a signal to the low-pass p-wavelength filter LPF to output the phase reference signal "口" and the phase feedback signal "HA". It is possible to arbitrarily set the phase difference between the

Returning to FIG. 3 again to explain its operation, since the phase of the power system 8 is applied to the phase reference signal of the PLL circuit 43, the output frequency of the PLL circuit 43 is equal to the phase of the power system 8. Therefore, the phase of the gravity converter 2 is also synchronized with the phase of the power system 8. When the switch 7 is in the closed state, the input and output of the error amplifier 42 are short-circuited by a switch (not shown). An automatic control circuit for controlling the power and the phase of the replacement ri2 is not formed.When the switch 7 is closed, the input and output of the error amplifier 42 are short-circuited, and the deviation 47a or 47b as an input, the error amplifier 42 operates to perform predetermined control.This changeover switch 47 switches the flow tortoise pressure detection circuit 46 when the electromotive force of the fuel cell l is below a predetermined value.
Select the deviation 47b between the output signal detected by the voltage reference 45 and the output signal of the active power transducer 41 and the active power reference 40. In other words, by having a DC voltage (not shown) that has sufficient capacity to start the power and conversion R2 even when the fuel cell 1 is in a stopped state, it is possible to select the bias M 47M in advance when starting the fuel cell 1. The gravity converter it2 is activated, and (while the electromotive force of the thermal battery l is below a predetermined value, the changeover switch 47 selects DC constant voltage, and the output signal of the DC voltage detection circuit 46 and the voltage reference 45 are The phases of the power converter 2 are controlled so that they are equal to each other.In other words, this DC constant voltage control is performed even when the fuel cell 1 is stopped. When the capacitor (not shown) is charged, excess power is returned to the power system 8 through the power converter 2, good voltage switch 6, and switch 7 by direct current constant voltage control.As a result, the power Only the no-load loss of the power converter 2 is supplied from the grid 8, and the power converter 12 can continue parallel operation with the power grid 8.At this point, the power converter 2, which is not shown, is no longer connected to the power converter 2. This DC constant voltage control (parallel operation of the converter 2 and the power system 8 is performed until the fuel cell l has a predetermined electromotive force, that is, By continuing the currents Q and I in Fig. 1, the phase is controlled so that the current of the fuel cell I is outputted corresponding to the electromotive force of the fuel cell during this time. The voltage jump of the fuel cell 1 during light load is suppressed, and the voltage E1 is always controlled to be equal to the DC constant voltage setting value.Furthermore, when the electromotive force of the fuel cell 1 reaches a predetermined value or more, that is, DC constant voltage control allows the first
When the current l shown in the figure is exceeded, the output signal of the detection circuit (not shown) causes the recirculation switch Y-47 to switch to select the deviation 47a, and power control is performed so that the effective quadrature duplex f41 and the active power reference 40 become equal. be done. Here, the functions of the DC constant voltage control system and power control system using the error amplifier 42 shown in FIG. When the voltage becomes larger than the voltage reference 45, the phase of the power converter 2 is advanced relative to the power system 8C2 in order to extract more power from the fuel cell 1, and in the case of a power control system, the effective quadrature transducer 41 is activated. The output signal of the active power standard 4
When it becomes larger than 0, the phase of the power conversion device 2 is delayed with respect to the power system 8 so as to suppress the power from the fuel cell.

Conversely, when stopping the fuel cell power generation system by reducing the electromotive force from the rated output of the fuel cell,
Power control is performed until the electromotive force is below a predetermined value,
By switching to DC constant voltage control when the voltage falls below a predetermined value, the voltage can also be suppressed when the fuel cell I is stopped.

In other words, by starting the power conversion device 2 connected to the fuel cell 1 in advance and operating it in parallel with the power grid 8, the fuel cell power generation system can be started accurately even during the startup process when the fuel cell 1 does not have an electromotive force. In addition, it is possible to prevent overvoltage for the fuel cell 1 and to appropriately select the high pressure rating when selecting circuit components of the power converter 2. Also, as conventionally done, the output of the fuel cell l (=
It can be realized with an inexpensive and simple control circuit without requiring expensive and large attached equipment such as a resistor for controlling the dragon pressure.

Next, other embodiments of the present invention will be described. In the embodiment shown in FIG. 3, the power converter 2 has been described as a self-excited inverter circuit, but a separately excited inverter circuit having a DC power source with sufficient capacity to start the power converter 2 can be similarly controlled. Can be done.

Furthermore (in the case of the power converter 2 consisting of two self-excited inverter circuits, the power consumption is 1M3 ka - without the need for a separate DC power supply)
.

7 before starting the power and conversion fiiiit2,
It is also possible to charge a capacitor of a DC circuit (not shown) and start the inverter circuit during a predetermined pulse. In addition, the conditions for switching between flow chamber voltage control and power control are not only the flow current of the fuel cell l, but also the condition that the FM power or AC power exceeds a predetermined value (it may be switched when the two are connected.Similarly, the condition for switching between flow chamber voltage control and power control is When the electromotive force of the L pond reaches a predetermined value or more, the power control is switched, but the same effect can be obtained by using DC current control instead of this power control.Also, a power converter with a chopper circuit It is obvious that similar effects can be obtained for device 2 as well.

[Effects of the Invention] Thus, according to the present invention, a fuel cell is provided in which a fuel cell is used as a DC power source and the output of the DC power source is connected to an inverter circuit, or a power conversion device consisting of a chopper circuit and an inverter circuit, and a power system. In a power generation system, when starting up a fuel cell, the power conversion device is started in advance using a DC auxiliary power source, and even in normal operating conditions, if the electromotive force of the fuel cell does not reach a predetermined value, , performs continuous operation with the gravity system using DC constant voltage control, and when the electromotive force of the fuel cell reaches a predetermined value or more, switches to the predetermined power control, thereby controlling the voltage when starting and stopping the fuel cell or under light loads. This may cause the voltage rating of the power converter to be increased more than necessary, reduce the service life due to melting of the catalyst caused by the overvoltage generated in the fuel cell itself, or cause expensive and unnecessary A simple control circuit board can be used without installing a voltage suppression resistor that causes power loss; it is possible to control an efficient power conversion device that is cheaper and has a longer service life.

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram of cell voltage versus current of a fuel cell, Fig. 2 is a block diagram of a control device of a conventional fuel cell power generation system,
FIG. 3 is a block diagram of a fuel cell power generation system showing one embodiment of the present invention, the fourth factor is a block diagram showing the detailed configuration of the phase-locked loop portion in FIG. 3, and the fifth factor is the battery voltage of the present invention. FIG. 3 is a characteristic diagram of current versus current. l... Fuel cell 2... Power converter 3... Diode for backflow prevention 4... Switch 5... Resistor for voltage suppression 6... Pressure regulator 7... Switch 8... Power system 20... Output flow 21... Output voltage 22... Power system voltage 30... Reactive power control circuit 31... Voltage control circuit 40... Active power reference 41... Effective Type Cadrance Dieu 9 42...
Error amplifier 43...PLL circuit 44...Counter 45...
Voltage reference 46...DC voltage detection circuit 47...Selector switch 47a, 47b...Difference (7317) Agent Patent attorney Noriyuki Chika Kei (and 1 other person) Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] In a fuel cell power generation system configured by using a fuel cell as a DC power source and connecting the output of the DC power source to an inverter circuit, or a power conversion device consisting of a chopper circuit and an inverter circuit, and a power system, the electromotive force of the fuel cell is If the voltage is below a predetermined value, the DC input to the power converter is controlled to be connected to the power grid by constant voltage control to keep the DC input constant, and if the electromotive force of the fuel cell reaches a predetermined value or higher, the @pressure 1. A method of controlling a fuel cell power generation system, characterized by switching from constant voltage control to power control to control power between the fuel cell and the power grid.