JPH0775343A - Synchronous follow-up method of inverter - Google Patents

Abstract

PURPOSE:To improve synchronous follow-up by adding an analog signal corresponding to the difference between the detection period of a period detecting counter and a reference period to a phase differential signal obtained by converting the signal acquired by addition into a clock signal and varying the clock signal with a reference clock signal. CONSTITUTION:The output from an output counter 24 is converted into a three-phase signal whose phases differ by 120 deg.C, by a three-phase signal generating circuit 25, and the phase difference between the three-phase signal and the square wave signals of zero cross detectors 11-13 is detected by phase difference detectors(PD) 21-23. The outputs from the PDs 21-23 are added by an adder 3, and fed back as a phase difference signal. A frequency difference signal corresponding to the difference between the detection period of a ROM 14 and a reference period is converted into an analog signal by a D/A converter 15. The phase difference signal is adjusted with a reference value in an adder 20, and added to the frequency difference signal converted into an analog signal by an adder 17. The output from the adder 17 is added to the phase difference signal in an adder 18, converted into a clock signal by a V/F conversion circuit 22, and arithmetically operated with the reference clock signal of a voltage dividing circuit 32 by an OR circuit 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous follow-up method in an inverter that is interconnected with a commercial three-phase AC power supply.

[0002]

2. Description of the Related Art A conventional synchronous tracking method for an inverter, which operates in conjunction with a commercial three-phase AC power source, is one of three phases.
The phase was followed only in the phase. FIG. 5 is a flowchart showing a conventional single-phase synchronization tracking method. In FIG. 5, a voltage waveform detected from one phase of a commercial three-phase AC power supply is converted into a square wave in zero cross detection (103), and a voltage signal corresponding to the phase difference between two input signals in phase difference detection (104). Is output. This voltage signal is converted into a frequency signal corresponding to the input voltage signal in the V / F conversion (106) after removing a high frequency component in the low pass filter (105).
The reference frequency signal output from the reference oscillation (101) is divided (102) into the rated frequency signal of the commercial AC power source, and V
It is input to the clock addition / subtraction (107) together with the frequency signal from the / F conversion (106). When a phase difference from the reference frequency occurs due to the frequency fluctuation of the commercial power supply, a frequency signal corresponding to this phase difference is output from the V / F conversion (106) and differs from the reference frequency signal from the reference oscillation (101). Addition / subtraction is executed in the clock addition / subtraction (107), and a command signal for synchronizing the inverter to the commercial power source is output.

[0003]

Since the synchronous tracking method according to the prior art is a phase tracking method provided only in a single-phase circuit, the response speed is slow, and 100 to 1 in a 50 Hz system.
It took 50ms. Further, when the frequency of the commercial three-phase AC power supply deviates greatly from its rated frequency, the phase tracking alone is not sufficient and the inverter cannot be completely synchronized with the commercial three-phase AC power supply. The present invention has been made in order to solve the above-mentioned drawbacks in the prior art, and an object of the present invention is to provide a synchronous tracking method for an inverter having excellent tracking characteristics capable of coping with a wide range of frequency fluctuations. .

[0004]

In order to achieve the above-mentioned object, the synchronous tracking method for an inverter according to the present invention is
6 times the commercial frequency signal is used to speed up the response of synchronous tracking, and the phase difference detection signals for 3 phases are added and averaged so that tracking can be performed even when the commercial 3-phase AC power supply has imbalance. The generated phase difference signal is created and fed back to the command signal that causes the inverter to synchronously follow the commercial three-phase AC power supply. In addition, a frequency tracking method was added so that synchronous tracking can be performed even when the frequency of the commercial three-phase AC power supply deviates significantly from the rated frequency. For this purpose, the period detection counter is used to detect the difference between the period detected from the commercial three-phase AC power supply and the reference period, an analog signal corresponding to the difference is generated, and a phase difference signal is added. Synchronous tracking is performed by converting an analog signal into a clock signal and increasing or decreasing it with respect to a reference clock signal.

[0005]

Since the 6 times frequency signal is used, the response of the follow-up characteristic becomes fast, and the phase difference detection signals are averaged by adding the phase difference detection signals for each of the three phases.
It is also possible to deal with 3-phase imbalance in the target commercial 3-phase AC power supply. Further, since the frequency tracking is added, it is possible to follow the frequency fluctuation of the commercial three-phase AC power source with zero phase difference, and the tracking characteristic is smoothed by converting the frequency tracking signal into an analog signal.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of an inverter synchronous tracking method according to the present invention. In FIG. 1, U-phase, V-phase, W of commercial three-phase AC power supply
The voltage signal detected from the phase is the zero cross detection circuit 1 ₁ to 1
_{In 3 the} signal becomes a zero-cross converted square wave signal, is converted into a frequency signal of 6 times the commercial frequency (300 Hz in the commercial 50 Hz system) in the 6 × frequency generation circuit 5, and is input to the flip-flop 6. The reference oscillation frequency (for example, 6144 KHz) output from the reference oscillation circuit 31 is frequency-divided by the frequency dividing circuit 32 (for example, 512 KHz in the commercial 50 Hz system), and is output to the AND circuits 7 and 8 together with the two output signals of the flip-flop 6. input. The flip-flop 6, the two AND circuits 7 and 8, and the two 12-bit counters 10 and 11 constitute a cycle detection counter. The output signals of the AND circuits 7 and 8 are counted by the counters 10 and 11. .

Three-phase voltage waveforms B, C and D input to the 6-fold frequency generation circuit 5, signal waveforms E and F output from the flip-flop 6, and signal waveform G output from the AND circuits 7 and 8. H and the reference frequency signal waveform A input from the frequency dividing circuit 32 to the AND circuit 8 are as shown in FIGS. 3 and 4. In FIG. 3, U-phase, V-phase of commercial 3-phase AC power supply,
The W phase has voltage waveforms B, C, and D that are 120 ° out of phase with each other.
The two signal waveforms E and F output from the flip-flop 6 have different polarities.
The signal waveforms E and F in FIG. 4 are enlarged display of the signal waveforms in FIG. 3, and the signal waveforms E and F are AN.
The D circuits 7 and 8 are logically operated with the reference frequency signal waveform A to obtain output signal waveforms G and H from the AND circuits 7 and 8. The signal waveforms G and H are alternately counted by the counters 10 and 11, and the counted up values are latched by the latch circuits 12 and 13, respectively.
Input to 4.

Since the total number of counts latched by the latch circuits 12 and 13 corresponds to 1/6 cycle of the frequency signal detected from the commercial three-phase AC power source, RO
The difference between the input detection cycle and the 1/6 cycle of the reference cycle corresponding to the rated frequency of the commercial power supply preset in M14 is calculated. If the difference exceeds the set value, a frequency abnormality signal (alarm signal ) Is sent. If the alarm signal is not required, the frequency abnormality signal (alarm signal) is not sent.

A command signal for driving an inverter output from the 12-bit output counter 24 is converted into a three-phase signal generating circuit 2.
5, the phase difference is converted by 120 ° into three-phase signals, which are input to the phase difference detection circuits 2 ₁ to 2 ₃ and the phase difference with the square wave signal input from the zero-cross detection circuits 1 ₁ to 1 ₃ for each phase. To detect. Since the output signals of the phase difference detection circuits 2 _{1 to} 2 ₃ are added up in the adder 3, the output signal becomes an average value of the phase difference for three phases, and the ripple component included in the output signal is removed in the low pass filter 4. Then, it is fed back as a phase difference signal. Therefore, even if there is an imbalance in the phases between the three phases of the commercial three-phase AC power supply, the phase tracking characteristics are improved because the phase difference signal of the average value of the three phases is followed.

The frequency difference signal corresponding to the difference between the detection period detected in the ROM 14 and the reference period is converted into an analog signal in the D / A converter 15, and the proportional element 1
The gain is adjusted in 6 and then input to the adder 17. The phase difference signal fed back through the low pass filter 4 is adjusted by the reference value (0 ^V ) in the adder 20, and is added through the low pass filter 19.
At 7, it is added with the analogized frequency difference signal from the proportional element 16. The output signal of the adder 17 is added to the phase difference signal input via the proportional element 21 and the adder 1
8 is added and input to the V / F conversion circuit 22 and converted into a clock signal. The clock signal output from the V / F conversion circuit 22 is input to the OR circuit 23, logically operated with the reference clock signal output from the frequency dividing circuit 32, and input to the output counter 24 to drive the inverter. Is output.

Since the phase difference signal is added to the analog frequency difference signal in the adder 17 via the low-pass filter 19, it is possible to prevent the clock frequency from changing due to aging of the reference clock.

In the above description, the 6-fold frequency signal is formulated to speed up the response speed of the tracking characteristic, but it is not limited to the 6-fold frequency signal, and this frequency multiplication factor can be appropriately selected.

FIG. 2 is a block diagram showing a second embodiment according to the present invention. In FIG. 2, the difference between the detection cycle detected by the cycle detection counter and the reference cycle data 26 is detected by the adder 27 and converted into a frequency difference by the ROM 14. That is, in the first embodiment, the difference between the detection cycle and the reference cycle is detected in the ROM 14, and the subsequent processing is performed by using this cycle difference. However, in the second embodiment, the difference between the detection cycle and the reference cycle is detected. The difference from the reference cycle is ROM
It is detected before it is input to 14, and in the ROM 14, this period difference is converted into a frequency difference for subsequent processing.

[0014]

As described above, the inverter synchronous follow-up method according to the present invention uses a frequency six times as high as the commercial frequency in order to speed up the synchronous follow-up response, and the commercial three-phase AC power supply has an imbalance. At this time, the phase difference signals for three phases are detected so that they can be tracked and then added to create an averaged phase difference signal, which corresponds to the difference between the detection cycle detected by the cycle detection counter and the reference cycle. The phase difference signal is added to the signal and then converted into a clock signal, which is synchronized with the reference clock signal by increasing or decreasing. By taking the above measures, the response speed becomes faster, and it becomes 5 to 10 ms in the 50 Hz system, so that the range of commercial follow-up interconnection operation of the inverter expands,
It has become possible to connect to a power source with large frequency fluctuations such as an engine / generator. Also, by making the follow-up signal analog, the control response characteristics of the inverter were softened, and it became possible to freely turn on and off the follow-up operation during inverter operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of an inverter synchronous tracking method according to the present invention.

FIG. 2 is a block diagram showing a second embodiment according to the present invention.

FIG. 3 is a waveform diagram of a cycle detection counter.

FIG. 4 is a waveform diagram of a cycle detection counter.

FIG. 5 is a flowchart of a conventional inverter synchronous tracking method.

[Explanation of symbols]

1 ₁ to 1 ₃ zero-crossing detecting circuit 2 ₁ to 2 ₃ phase difference detecting circuit 3,17,18,20 adder 4 and 19 low-pass filter 5 6 times the frequency generating circuit 6 flip-flop 7, 8 the AND circuits 10 and 11 counter 12, 13 Latch circuit 14 ROM 15 D / A converter 16, 21 Proportional element 22 V / F conversion circuit 23 OR circuit 24 Output counter 25 Three-phase signal generation circuit

Claims (2)

[Claims] 1. A synchronous follow-up method for an inverter that is interconnected with a commercial three-phase AC power supply, wherein a zero-cross detection signal detected from the commercial three-phase AC power supply is converted into a 6-fold frequency signal and then input to a synchronous detection counter. Means for detecting the cycle of the 6-fold frequency signal using the reference frequency signal divided by the reference oscillation circuit, and detecting a difference from the reference cycle corresponding to 1/6 cycle of the rated frequency of the commercial AC power supply. And a phase difference between a three-phase frequency signal created from a command signal for controlling the inverter and a zero-crossing detection signal detected from the commercial three-phase AC power source, for each phase, and a detected three-phase phase difference signal Means for outputting an averaged phase difference signal through a low-pass filter by summing, and converting the difference between the detection cycle and the reference cycle into an analog signal, Signal to convert the clock signal into a clock signal, and increase / decrease this clock signal and the reference clock signal divided from the reference oscillation circuit to send a command signal for causing the inverter to follow the commercial three-phase AC power supply in synchronization. Means, to the analog signal converted from the difference between the detection period and the reference period, by adding the phase difference signal through a low-pass filter, means for preventing a change in the clock frequency due to aging of the reference clock signal, The synchronous follow-up method for an inverter characterized in that the inverter follows the commercial three-phase AC power supply synchronously by performing phase follow-up and frequency follow-up at the same time. 2. The detection cycle data detected by the cycle detection counter is converted into frequency difference data using a ROM,
The synchronous tracking is performed by increasing or decreasing a clock signal obtained by converting the frequency difference data into an analog signal and adding a phase difference signal to the converted clock signal and a reference clock signal divided by the reference oscillation circuit. The synchronous tracking method of the inverter described in.