JPH0686560A - Self-excited inverter - Google Patents

Abstract

PURPOSE:To prevent damages on its own device and loads when changing over the isolated operation of a device into the linkage operation of devices. CONSTITUTION:In a loop filter 4 integrated into a synchronism sensing circuit, a maximum value limiter 11A and a minimum value limiter 11B for limiting respectively the output of the loop filter 4 are provided, and when changing over the isolated operation of a device into the linkage operation of devices, the loop filter 4 is opened gradually.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-excited inverter, and more particularly to a self-excited inverter having an improved synchronous detection circuit with an interconnected AC system.

[0002]

2. Description of the Related Art FIG. 3 is a main circuit single wire connection diagram showing an example of a conventional self-exciting inverter connected to an AC system. In FIG. 3, 21 is an AC system, 22 is a self-excited inverter, 23 is a circuit breaker that connects the self-excited inverter 22 and the AC system 21, 24 is a load connected to the AC system 21 and the self-excited inverter 22, and 25 is a self-excited load. Excitation-type inverter control device, 26 is a synchronization detection circuit incorporated in self-excitation-type inverter control device 25,
Reference numeral 27 denotes an instrument transformer that detects a synchronization signal for synchronizing the alternating current system 21 with the synchronization detection circuit 26.

In FIG. 1, when the power supply from the AC system 21 is lost, the circuit breaker 23 is provided to maintain the power supply to the load 24 connected to the AC system 21 until then. While opening, electric power is independently supplied to the load 24 from the self-excited inverter 22. After that, when the power supply of the AC system 21 is restored, the frequency of the output voltage of the self-excited inverter 22 is synchronized with the frequency of the AC system 21 again by the synchronization detection circuit 26,
The breaker 23 is turned on to connect the self-excited inverter 22 and the AC system 21, and the AC system 21 and the self-excited inverter 22 are operated in parallel to supply power to the load 24. In the following, the self-excited inverter 22 operates independently while it is supplying power to the load 24.
The state in which power is being supplied to the system is called interconnection operation.

Next, a block diagram showing an example of a conventional synchronization detection circuit is shown in FIG. This FIG. 4 is disclosed in Japanese Patent No. 131495, where 1 is a variable frequency oscillator that changes the output frequency according to the input voltage, 2 is a counter that counts the output of the variable frequency oscillator 1, and 3 is an input signal and an internal signal. A phase comparator for comparing the phase difference with the transmission signal, 34 is a loop filter for receiving the phase difference signal from the phase comparator 3 and adjusting the phase difference, 5 is an internal signal transmission for transmitting an internal signal with the data of the counter 2. Shows a container.

FIG. 5 is a connection diagram showing details of the loop filter 34 shown in FIG. In FIG. 5, the same elements as those in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted. In FIG. 5, 41 is a switch for zeroing the output signal of the loop filter 34 during islanding operation, 42 is a Zener diode that determines the maximum and minimum values of the output of the loop filter 34, and 33 is the synchronization detection circuit 26 6 shows a bias setter that determines the center frequency to be set.

In FIG. 5, the switch is operated during the isolated operation.
41 is closed, and the output of the loop filter 34 is set to zero and fixed to the frequency set by the bias setter 33. When switching from independent operation to interconnection operation, switch 41
Open, input the phase difference signal output from the phase comparator 3 shown in FIG. 4, adjust the oscillation frequency of the variable frequency oscillator 1, and synchronize with the power supply frequency of the AC system 21 shown in FIG. Then, the output of the loop filter 34 is operated.

[0007]

As described above, when switching from the state in which the self-excited inverter 22 alone supplies power to the load to the interconnection operation, the switch 41 of the loop filter 34 in FIG. 5 is closed. Open from the state.
Therefore, due to the phase difference between the input signal and the internal oscillation signal, the output signal of the loop filter 34 changes greatly, the frequency of the voltage output from the self-excited inverter 22 changes greatly, and the load 24 shown in FIG. There is a risk of damage or an accident such as magnetic bias of the transformer for the converter.

Therefore, a method of extremely slowing the operation of the loop filter 34 may be considered. However, in a steady state, if a situation in which the phase of the power supply of the system suddenly changes occurs, the self-excited inverter is used. I can't follow, so
A large current may flow from the AC system 21 to the self-excited inverter 22.

Therefore, in order to solve the above-mentioned problems, the present invention makes the operation of the loop filter fast at the steady state and delayed only when the operation is changed from the independent operation to the interconnection operation again, and the operation is changed from the independent operation to the interconnection operation. It is an object of the present invention to obtain a self-excited inverter that can prevent load and self-damage at the time.

[0010]

SUMMARY OF THE INVENTION The present invention switches between an interconnected operation in which electric power is supplied to a load by being connected to an AC system and an independent operation in which electric power is separately supplied to the AC system by disconnecting from the AC system. A variable frequency oscillator that changes the oscillation frequency according to the voltage of the input signal of the synchronous detection circuit of the self-excited inverter that operates, a counter that counts the output frequency of this variable frequency oscillator, and a predetermined value according to the output from this counter. It is composed of an internal signal oscillator that transmits the signal of, a phase comparator that detects the error between the output of this internal signal oscillator and the phase of the AC system, and a loop filter that extracts the DC component from the output signal of this phase comparator. In a self-excited inverter equipped with a synchronous detection circuit that uses the output signal of this loop filter as the input signal of the variable frequency oscillator and the phase of the AC system as the output signal of the counter. , Characterized in that by adding the maximum value limiter and minimum limiter for limiting the output of the loop filter to the synchronous detection circuit.

[0011]

[Operation] When switching from independent operation to interconnection operation,
The output signal of the loop filter spreads with the time constants for which the maximum value limiter and the minimum value limiter are set, and a large change in the frequency of the voltage output from the self-excited inverter is suppressed.

[0012]

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 connection diagram showing a loop filter incorporated in a synchronization detection circuit of a self-excited inverter according to the present invention, and is a diagram corresponding to FIG. 5 showing a conventional technique. Note that, in FIG. 1, the same elements as those in FIG.

In FIG. 1, 4 is a loop filter, 41 is a switch for resetting the limiter, 42 is a Zener diode for determining the upper limit of the limiter, 11A is a maximum value limiter of the loop filter 4, and 11B is a minimum value limiter of the loop filter 4. Is. FIG. 2 is a time chart for explaining the operation of the loop filter 4 shown in FIG.

The operation of the embodiment will be described below with reference to FIGS. 1 and 2. In FIG. 2, a time point t0 is a time point when the switch 41 is closed by switching from the interconnected operation to the isolated operation,
Time point t1 indicates a time point when the independent operation is switched to the interconnected operation and the synchronization detection circuit starts synchronizing with the AC system. C0 is
Output of the maximum value limiter 11A when the islanding operation command is ON,
Similarly, D0 represents the output of the minimum value limiter 11B when the islanding operation command is ON. The diagonal line C indicates the islanding operation command O.
The transition of the output of the maximum value limiter 11A when FF is shown, the shaded line D is the minimum value limiter 11B when the individual operation command is OFF.
Shows the transition of the output of. The curve B shows the transition of the output signal of the loop filter 4.

In FIG. 2, when the operation is switched from the isolated operation to the interconnection operation at the time T1, the output voltage of the inverter is out of phase with the AC system. Although an attempt is made to output with a high waveform, the output of the loop filter 4 is limited by the output signal C of the maximum value limiter 11A and the output signal D of the minimum value limiter 11B, so that the rising edge is gentle and gradually as shown by the curve B. The output is a waveform that is attenuated.

As described above, the maximum value limiter 11A and the minimum value limiter 11B for limiting the output of the loop filter 4 are added to the synchronization detection circuit, and the maximum value limiter 11A and the minimum value limiter 11B are connected to the self-excited inverter. The output of the loop filter 4 is set to a predetermined value during the isolated operation, and the values of the maximum value limiter 11A and the minimum value limiter 11B are respectively set before shifting the self-excited inverter from the independent operation to the interconnected operation. By gradually changing to a predetermined value, it is possible to prevent not only the load connected to the AC system at the time of shifting from the isolated operation to the interconnected operation but also the failure of its own body.

In the above embodiment, the loop filter, the maximum value limiter and the minimum value limiter are described as electronic circuits, but they may be implemented by software using a microcomputer or the like. In this case, by processing the maximum value limiter 11A and the minimum value limiter 11B by software, the loop filter incorporated in the synchronization detection circuit of the self-excited inverter of the present invention can be easily incorporated in the device.

[0018]

As described above, according to the present invention, it is possible to switch between an interconnected operation in which power is supplied to a load by being connected to an AC system and an independent operation in which power is separately supplied to the AC system by disconnecting from the AC system. A variable frequency oscillator that changes the oscillation frequency according to the voltage of the input signal of the synchronous detection circuit of the self-excited inverter that operates, a counter that counts the output frequency of this variable frequency oscillator, and a predetermined value according to the output from this counter. It is composed of an internal signal oscillator that transmits the signal of, a phase comparator that detects the error between the output of this internal signal oscillator and the phase of the AC system, and a loop filter that extracts the DC component from the output signal of this phase comparator. In a self-excited inverter equipped with a synchronous detection circuit that uses the output signal of this loop filter as the input signal of the variable frequency oscillator and the output signal of the counter for the phase of the AC system When by adding a maximum value limiter and minimum limiter for limiting the output of the loop filter to the synchronous detection circuit switched to interconnected operation of a single operation,
The output signal of the loop filter is expanded with the time constants for which the maximum value limiter and the minimum value limiter are set, and large changes in the frequency of the voltage output from the self-excited inverter are suppressed, allowing the self-excited inverter to operate from independent operation to interconnected operation. Since the maximum limiter and the minimum limiter values are gradually changed to predetermined values before shifting to, it is possible to prevent the load and self-damage at the time of shifting from isolated operation to interconnection operation. A self-excited inverter can be obtained.

[Brief description of drawings]

FIG. 1 is a connection diagram showing a main part of a synchronization detection circuit showing an embodiment of a self-excited inverter of the present invention.

FIG. 2 is a graph showing the operation of the self-excited inverter of the present invention.

FIG. 3 is a main circuit single wire connection diagram showing an example of a conventional self-excited inverter.

FIG. 4 is a block diagram showing an example of a synchronization detection circuit incorporated in a conventional self-excited inverter.

FIG. 5 is a connection diagram showing a loop filter of a synchronization detection circuit incorporated in a conventional self-excited inverter.

[Explanation of Codes] 1 ... Variable frequency oscillator, 2 ... Counter, 3 ... Phase comparator, 4 ... Loop filter, 5 ... Internal signal oscillator, 11A ...
Maximum value limiter, 11B ... Minimum value limiter, 33 ... Bias setter, 41 ... Switch, 42 ... Zener diode.

Claims (1)

[Claims] 1. A synchronization of a self-excited inverter that is switched between an interconnected operation in which electric power is supplied to a load by being connected to an AC system and an isolated operation in which electric power is independently supplied to the load by disconnecting from the AC system. A variable frequency oscillator that changes the oscillation frequency according to the voltage of the input signal of the detection circuit, a counter that counts the output frequency of this variable frequency oscillator, and an internal signal that emits a predetermined signal according to the output from this counter. The oscillator, a phase comparator that detects an error between the output of the internal signal oscillator and the phase of the AC system, and a loop filter that extracts a DC component from the output signal of the phase comparator, and the loop filter In a self-excited inverter equipped with a synchronization detection circuit that uses an output signal as an input signal of the variable frequency oscillator and the phase of the AC system as an output signal of the counter, A self-excited inverter characterized in that a maximum value limiter and a minimum value limiter for limiting the output of the loop filter are added to the synchronization detection circuit.