JPH08205543A - Apparatus for parallel inverter operation - Google Patents

Abstract

PURPOSE: To eliminate the phase difference when a parallel operation is started by establishing the voltage waveform of an inverter according to a waveform correction signal, correcting a reference pulse from a PLL circuit according to the signal, and operating the inverters in parallel. CONSTITUTION: A zero-crossing detector 15 for forming a zero-crossing signal of a sine wave formed by a sine wave generator 12 is provided in the control circuit 10 of an inverter 1, and a zero-crossing detector 25 for forming a zero- crossing signal of a sine wave formed by a sine wave generator 22 is provided in the control circuit 20 of an inverter 2. The zero-crossing signals are input to a phase corrector 40 in a parallel operation control board 4 to form a phase correction signal, which is input to PLL circuits 11, 21 in the circuits 10, 20 to correct the reference pulses. Accordingly, the phase difference when the parallel operation is started can be eliminated, and a cross current or the distortion of the voltage waveform of the inverter can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter parallel operation system, and more particularly to an inverter parallel operation system provided with a function of correcting a phase difference between the inverters at the start of parallel operation. .

[0002]

2. Description of the Related Art In recent years, parallel operation of inverters by a parallel redundancy system has become widespread, in which one unit can be inspected or repaired while supplying electric power to a load having a capacity of (parallel number-1) units. Parallel operating devices are known.

When the inverters are operated in parallel by the parallel redundancy method described above, the output voltage difference, frequency deviation, phase difference, and polarity difference between the inverters are eliminated to prevent a cross current from flowing between the inverters. .

Further, the above-mentioned inverters which are operated in parallel by the parallel redundancy system are designed so that they can be switched to a commercial power source without interruption in the event of overload or an accident, and their reliability is improved.

In order to satisfy the above conditions, it is necessary to operate each inverter synchronously, and it is necessary to synchronize the output of each inverter and the commercial power source.

As a conventional example of the above-mentioned inverter parallel operation apparatus, as shown in FIG. 2, the inverter is provided in the control circuit 10 of the inverter 1 and the control circuit 20 of the inverter 2.
PLL circuits 11 and 21 that generate a reference pulse corresponding to the synchronization source signal, sine wave generation circuits 12 and 22 that generate a sine wave corresponding to the reference pulse, and correct the voltage waveform distortion of the inverter based on the sine wave. The parallel operation is started after the synchronous operation of each inverter is established by the waveform correction circuits 13 and 23 that create the waveform correction signal.

As the synchronization source signal, a commercial zero-cross signal from the commercial power source 3 or the control circuits 10 and 20 is used.
One of the reference zero-cross signals from the reference oscillators 14 and 24 in the internal power source 3 is transmitted.
The reference zero-cross signal from the reference oscillators 14 and 24 is transmitted as a synchronization source signal when the commercial zero-cross signal is lost due to the power failure.

[0008]

In the above-mentioned conventional inverter parallel operation system, the synchronous operation of each inverter is established by the commercial zero-cross signal as the synchronization source signal because of the steady frequency fluctuation of the commercial power supply 3. Phase difference may occur between the start of parallel operation and
As a result, there is a problem that a cross current flows and the voltage waveform of the inverter is distorted.

[0009]

In order to solve the above problems, the present invention relates to an inverter comprising a plurality of inverters having a control circuit and a parallel operation control panel for controlling parallel operation of these inverters. In the parallel operation device, the control circuit includes a PLL circuit that creates a reference pulse corresponding to the synchronization source signal, a sine wave generation circuit that creates a sine wave corresponding to the reference pulse, and a voltage of an inverter based on the sine wave. A waveform correction circuit that creates a waveform correction signal that corrects waveform distortion, and a zero-cross detection circuit that creates the zero-cross signal of the sine wave are provided, and the parallel operation control panel is a control circuit for one inverter before the start of parallel operation. Phase of the zero-cross signal from the zero-cross detection circuit in the inverter and the phase of the zero-cross signal from the zero-cross detection circuit in the control circuit of the other inverter A phase correction circuit that has a function of sending the phase correction signal that causes the phase correction signal to stop after the parallel operation is started, and establishes the voltage waveform of the inverter by the waveform correction signal. The reference pulse from the PLL circuit is corrected by the phase correction signal so that the inverters are operated in parallel.

[0010]

According to the present invention, the sine wave zero-cross signal corresponding to the synchronization source signal created by the zero-cross detection circuit in the control circuit of one inverter and the synchronization created by the zero-cross detection circuit in the control circuit of another inverter. When the parallel operation is started, the sine wave zero-cross signal corresponding to the original signal is sent to the phase correction circuit, and the reference pulse from the PLL circuit is corrected by the phase correction signal created by this phase correction circuit. It is possible to eliminate the phase difference between the two, and it is possible to prevent the cross current flowing therethrough and the resulting distortion of the voltage waveform of the inverter.

[0011]

EXAMPLES The present invention will be described below with reference to examples.

FIG. 1 is a block diagram of a parallel operating apparatus for inverters according to the present invention. The parts having the same functions as those in FIG.

A feature of the present invention is that the control circuit 10 of the inverter 1 is provided with the zero-cross detection circuit 15 for producing the zero-cross signal of the sine wave produced by the sine-wave generation circuit 12, and the control circuit 20 of the inverter 2 is provided. A zero-cross detection circuit 25 that creates a sine-wave zero-cross signal created by the sine-wave generation circuit 22 is provided, and each zero-cross signal is input to the phase correction circuit 40 in the parallel operation control panel 4 to create a phase correction signal, This phase correction signal is input to the PLL circuits 11 and 21 in the control circuits 10 and 20 to correct the reference pulse sent from the PLL circuits 11 and 21.

The parallel operation control panel 4 includes inverters 1,
Before the parallel operation of No. 2 is started, a phase correction signal is sent from the phase correction circuit 40 by the above-described operation, the reference pulse sent from the PLL circuits 11 and 21 is corrected by this phase correction signal, and the sine corresponding to this reference pulse is corrected. Create waves,
A waveform correction signal for correcting the voltage waveform distortion of the inverter is created based on this sine wave, the voltage waveform of the inverter is established by this waveform correction signal, and the phase correction signal is transmitted after the parallel operation of the inverters 1 and 2 is started. Operates to stop.

The zero-cross detection circuits 15 and 25 are
The sine wave zero-cross signal generated by the above is configured to be input to the phase correction circuit 40 via the isolated signal transmission circuits 16 and 26, and the phase correction signal sent from the phase correction circuit 40 is an isolated signal. It is configured to be input to the PLL circuits 11 and 21 via the transmission circuits 17 and 27.

Further, according to the present invention, the control circuit 10, when the commercial power source 3 has a power failure or when the frequency accuracy of the commercial power source 3 is low,
Although the reference zero-cross signals from the reference oscillators 14 and 24 in 20 are used as the synchronization source signals, the phase difference between the reference zero-cross signal from the reference oscillator 14 and the reference zero-cross signal from the reference oscillator 24 is small. Even if there is, it can be corrected by the phase correction circuit 40, so that the parallel operation of the inverters can be stably performed.

[0017]

As described above, the inverter parallel operation apparatus of the present invention can not only stably perform the parallel operation of each inverter, but also cause a cross current at the start of the parallel operation or the inverter voltage. The problem that the waveform is distorted can be solved.

[Brief description of drawings]

FIG. 1 is a block diagram of an inverter parallel operation device of the present invention.

FIG. 2 is a block diagram of a conventional inverter parallel operation device.

[Explanation of symbols]

 1, 2 Inverter 10, 20 Control circuit 11, 21 PLL circuit 12, 22 Sine wave generation circuit 13, 23 Waveform correction circuit 14, 24 Reference oscillator 15, 25 Zero cross detection circuit 4 Parallel operation control panel 40 Phase correction circuit

Claims (1)

[Claims] 1. In an inverter parallel operation apparatus comprising a plurality of inverters having a control circuit and a parallel operation control panel for controlling parallel operation of these inverters, the control circuit corresponds to a synchronization source signal. A PLL circuit that creates a reference pulse, a sine wave generation circuit that creates a sine wave corresponding to this reference pulse, and a waveform correction circuit that creates a waveform correction signal that corrects the voltage waveform distortion of the inverter based on this sine wave. , A zero-crossing detection circuit for creating the zero-crossing signal of the sine wave, the parallel operation control panel is the phase of the zero-crossing signal from the zero-crossing detection circuit in the control circuit of one inverter and the other inverter before the start of parallel operation. The phase correction signal that matches the phase of the zero-cross signal from the zero-cross detection circuit in the control circuit of After the start, it has a phase correction circuit having a function of stopping the phase correction signal, establishes the voltage waveform of the inverter by the waveform correction signal, and corrects the reference pulse from the PLL circuit by the phase correction signal. A parallel operation device for inverters, characterized in that the inverters are operated in parallel.