JPH0357116Y2 - - Google Patents

Description

[Detailed description of the invention] (Technical field to which the invention belongs) This invention relates to a synchronization control circuit that smoothly matches the phase when synchronizing the AC output of an inverter with another AC power source.

(Prior art and its problems) In order to connect multiple AC power supplies in parallel, for example, two sets of AC power supplies, it is natural that the phase rotation directions of both power supplies must be the same. Prior to this, it is necessary to synchronize both power supplies, but in order to do so, the voltages of both power supplies must be equal, the frequencies must be the same, and the phases must be aligned. Among these conditions, if the voltages are not equal, a reactive cross current will flow between the two power supplies when they are connected in parallel, which is inconvenient. This problem can be resolved by controlling it, and it is easy to control the voltages to be equal.

On the other hand, if the frequencies are not equal, an imbalance will occur in the active power shared by both power sources, so frequency control is related to the degree of load sharing, but at the same time it is also related to the phase difference between the two power sources. In other words, if there is a difference in the frequencies of the two power supplies, the phase difference will change from moment to moment. However, even if the frequencies are exactly the same, the phase difference may be large.

In order to synchronize the AC power output by the inverter with other AC power sources, the above-mentioned conditions must be satisfied, and in particular, frequency and phase control will be described below.

FIG. 1 is a circuit diagram showing a conventional inverter phase control circuit. In FIG. 1, AC power from an AC power supply 1 is insulated and transformed by a transformer 2, and then applied to a thyristor rectifier 3. The DC output of this thyristor rectifier 3 is smoothed by a DC reactor 4 and a smoothing capacitor 5 and then applied to a thyristor inverter 6. This thyristor inverter 6 converts the input DC into the desired constant voltage constant frequency AC power, and the above-mentioned thyristor rectifier 3, DC reactor 4, smoothing capacitor 5, and thyristor inverter 6 constitute a so-called CVCF inverter 10. . The constant voltage, constant frequency AC power output from the CVCF inverter 10 is supplied to the AC load 8 via the inverter side switch 7, but if the CVCF inverter 10 breaks down, the AC power is supplied to the AC load 8. Therefore, in order to ensure continuity of power supply, the AC power from the AC power source 1 is connected in parallel with the AC output of the thyristor inverter 6 via a separate power supply side switch 9 to connect the AC power to the AC load. 8 or leave the separate power supply switch 9 open, but the AC power of the AC power supply 1 and the AC output of the thyristor inverter 6 are always kept in synchronization, so that the AC power supply can be switched on at any time. In many cases, power can be supplied from load 8 to load 8.

In order to synchronize the AC output of the thyristor inverter 6 and the AC power of the AC power supply 1, it is necessary to match the voltage, frequency, and phase of both power supplies as described above, but it is easy to match the voltages. Therefore, in FIG. 1, illustration of a circuit for matching voltages is omitted, and only a control circuit for matching frequencies and phases is shown. In other words, the voltage transformer 1 is connected to the output AC side of the thyristor inverter 6.
1 is connected, and its detection voltage is applied to the phase difference detector 15 via the synchronous switch 13.
An instrument transformer 12 is also connected to the AC power supply 1, and its detected voltage is also applied to a phase difference detector 15 via a synchronization switch 14. A signal corresponding to the phase difference is output to the frequency adjuster 16. Therefore, if there is a difference in the frequencies of the two power supplies, the signal corresponding to the phase difference between the two sets of voltages output from the phase difference detector 15 will change from moment to moment, and the rate of change of this phase difference is large. This shows that the frequency difference is large. Further, even if the frequency difference is zero, if there is a phase difference, a signal corresponding to the phase difference is output from the phase difference detector 15, but since there is no difference in frequency, there is no change in the phase difference signal.

The frequency adjuster 16, which is a PI adjuster, receives this phase difference signal and sends a signal to the frequency oscillator 17 to determine the output frequency of the CVCF inverter 10.
This signal is sent to the pulse distributor 18 and the pulse amplifier 1.
The signal is applied to the thyristor inverter 6 via the inverter 9, and outputs AC power at a desired frequency.

Synchronization switch 13 to synchronize both power supplies
It has already been mentioned that when closing and 14, if there is a difference in the frequencies of the two power supplies, the output signal of the phase difference detector 15 changes, but even if there is no difference in the frequency of the two power supplies, there is a phase difference. The output frequency of the thyristor inverter 6 is changed to correct the phase difference. The larger the above-mentioned phase difference is, the larger the frequency fluctuation range becomes. Therefore, even if the frequency difference is adjusted to zero and the synchronization switches 13 and 14 are closed, a large frequency fluctuation may occur. load 8
If it is an electronic computer or the like, there are various disadvantages such as the risk of malfunction due to the above-mentioned frequency fluctuations.

(Purpose of the invention) This invention is a synchronous control of an inverter that prevents large fluctuations in frequency due to phase difference when synchronizing the AC output of an inverter with other AC power sources, and achieves smooth synchronization control. The purpose is to provide circuits.

(Key points of the invention) In order to achieve this purpose, the invention
In order to synchronize the AC output of the inverter with another AC power supply, phase difference detection compares the AC voltage phase output by the inverter with the AC voltage phase of the other AC power supply and outputs a phase difference signal between the two voltages to the frequency adjuster. In an inverter synchronous control circuit, the inverter synchronous control circuit is equipped with a frequency regulator and a frequency oscillator that receives the output signal of the frequency adjuster, and uses the output signal of the frequency oscillator to align the output frequency of the inverter with the frequency of another AC power supply. A minute phase difference generator that outputs a signal corresponding to the phase difference, a switch that connects the output signal of the minute phase difference generator to a frequency adjuster when synchronizing the inverter with another AC power supply, and an output signal of the phase difference detector. a slight phase difference detector that detects that the slight phase difference becomes less than a predetermined value; and a changeover switch that switches the input signal of the frequency adjuster from the minute phase difference generator to the phase difference detector based on the output signal of the slight phase difference detector. It is characterized by comprising the following.

In other words, when the synchronization switch is closed to enter the synchronized state, the present invention sends a signal corresponding to the minute phase difference to the frequency adjuster instead of the output signal of the phase difference detector that detects the phase difference between the two power supplies. By creating a slight frequency difference between the two power supplies, the phase difference between the two power supplies is gradually changed, and when this phase difference becomes smaller than a predetermined value, the input signal of the frequency adjuster is detected as a regular phase difference. The purpose is to perform synchronous control smoothly by switching to the output signal of the device.

For example, assume that the phase difference between the inverter and the separate AC power source is Φ. At this time, the minute phase difference △ψ
A signal corresponding to , is given from the minute phase difference generator to the frequency adjuster. As a result, the phase difference between the inverter and another AC power source is (Φ-△ψ) after one cycle of the AC voltage frequency, and (Φ-△ψ) after two cycles of the AC voltage frequency.
2Δψ), and after n cycles it becomes (Φ−nΔψ), resulting in a slight phase difference. Assuming that this slight phase difference (Φ-n△ψ) is within the detection value δ of the small phase difference detector (that is, δ>Φ-n△ψ), this is detected by the small phase difference detector, and the Based on the detection, the input signal of the frequency adjuster is switched from the microphase difference generator to the phase difference detector.

Note that if this switching is not performed, the phase difference between the inverter and the separate AC power source will be (Φ - (n - 1) △ψ) after n+1 cycles, and after that, contrary to the above explanation, it will become larger. After 2n cycles, the phase difference becomes Φ, and then the above-described phase difference decreasing operation is repeated.

(Embodiment of the invention) FIG. 2 is a circuit diagram showing an embodiment of the invention,
The content of the present invention will be explained in detail with reference to FIG.

In Fig. 2, a transformer 2 is connected to an AC power supply 1, and the AC power insulated and transformed by the transformer 2 is converted to DC power by a thyristor rectifier 3, and this DC power is smoothed by a DC reactor 4. After being smoothed by a capacitor 5, it is applied to a thyristor inverter 6, where it is converted into desired AC power. In Fig. 2, a thyristor rectifier 3, a DC reactor 4, a smoothing capacitor 5, and a thyristor inverter 6 form a CVCF inverter 10, which converts AC power from an AC power source 1 into constant voltage constant frequency AC power. There is.

The AC power output from this CVCF inverter 10 is supplied to an AC load 8 via an inverter side switch 7, but the output of the CVCF inverter is supplied to a separate AC power source, for example, a separate power source side switch 9 in FIG. Although the inverter can be operated in parallel with the AC power supply 1 by closing the AC power supply 1, it is of course possible to operate in parallel with another CVCF inverter instead of the AC power supply 1.

Prior to parallel operation, it is necessary to synchronize the AC output of the CVCF inverter 10 and the AC power supply 1. Even if the voltage and frequency of both power supplies are controlled to be equal, if the phase difference is large, synchronization will occur. As already mentioned, inconveniences arise when trying to change the state.

Therefore, in the present invention, the voltage detected by the potential transformer 11 connected to the inverter side and the voltage detected by the potential transformer 12 connected to the AC power source 1 are input to the phase difference detector 15. Even if the synchronous switches 13 and 14 are closed to detect the phase difference between the two voltages, the output signal of the phase difference detector 15 is not input to the frequency adjuster 16 because the changeover switch 24 is in the open state. Instead, the signal generated by the minute phase difference generator 21, which generates a signal corresponding to a minute phase difference, passes through the synchronous switch 22, which is closed in conjunction with the synchronous switches 13 and 14, and the changeover switch 23, which is in the closed state. A frequency adjuster 16 is provided. In other words, even if the phase difference between the two power supplies is large,
When the synchronization switches 13, 14, 22 operate,
The signal input to the frequency adjuster 16 has a value corresponding to a minute phase difference.

Since the input signal to the frequency adjuster 16 is small for the above-mentioned reason, the output frequency of the thyristor inverter 6 is slightly deviated from the AC power supply 1 by the signals given through the frequency oscillator 17, pulse distributor 18, and pulse amplifier 19. frequency. Therefore, a phase difference detector 15 detects the phase difference between the two power supplies.
Since the output signal changes very slowly, for example, a slight phase difference detector 25 having a built-in comparator receives the output signal of the phase difference detector 15 and detects a predetermined very slight phase difference. When the value becomes less than a value corresponding to , the slight phase difference detector 25 operates to switch the states of the changeover switches 23 and 24. In other words, the changeover switch 23 changes from closed to open, and the changeover switch 24 changes from open to closed, so the input signal of the frequency adjuster 16 changes from the minute phase difference generator 21 to the output signal of the phase difference detector 15. Switch. The output signal of this frequency adjuster 16 is applied to the thyristor inverter 6 via a frequency oscillator 17, a pulse distributor 18, and a pulse amplifier 19.
Since the AC power source 1 and the AC power source 1 are controlled so that their frequencies and phases are aligned, if the voltages of both power sources are made equal, parallel operation becomes possible.

(Effect of the invention) According to this invention, when aligning the voltage phases of each power supply in order to synchronize multiple AC power supplies,
Instead of the actual phase difference, a signal corresponding to a predetermined minute phase difference is input to the frequency adjuster of the inverter, so it is not possible to input a signal due to a large phase difference to this frequency adjuster. do not have. Therefore, the output frequency of the inverter has a very small difference compared to the frequency of the partner power source, so the speed of change in the phase difference between the two power sources is slow, and the frequency is prevented from changing significantly. Therefore, the load on the inverter is not adversely affected, and the control to achieve the synchronized state proceeds smoothly.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional phase control circuit for an inverter, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. 1... AC power supply, 2... Transformer, 3... Thyristor rectifier, 4... DC reactor, 5... Smoothing capacitor, 6... Thyristor inverter, 7...
...Inverter side switch, 8...AC load, 9...
Separate power supply side switch, 10...CVCF inverter, 1
1, 12...Instrument transformer, 13,14,22...
...Synchronization switch, 15...Phase difference detector, 16...
...Frequency adjuster, 17...Frequency oscillator, 18...
...Pulse distributor, 19...Pulse amplifier, 21...
...Small phase difference generator, 23, 24...Selector switch, 25...Small phase difference detector.

Claims (1)

[Claims for Utility Model Registration] In order to synchronize the AC output of the inverter with another AC power source, the AC voltage phase outputted by the inverter and the AC voltage phase of the separate AC power source are compared to signal a phase difference between the two voltages. and a frequency oscillator 17 that receives the output signal of the frequency adjuster, and the output frequency of the inverter is adjusted to the frequency of the separate AC power source by the output signal of the frequency oscillator. In a synchronization control circuit for an inverter that is aligned with the AC voltage, the micro phase difference generator 21 outputs a signal corresponding to the micro phase difference between the two AC voltages, and the micro phase difference generator 21 outputs a signal corresponding to the micro phase difference between the two AC voltages; a switch 22 that connects the output signal of the phase difference detector to the frequency adjuster; a slight phase difference detector 25 that detects that the output signal of the phase difference detector is below a predetermined value; and an output signal of the slight phase difference detector. a changeover switch 2 for switching the input signal of the frequency adjuster from the minute phase difference generator to the phase difference detector;
A synchronous control circuit for an inverter, comprising: 3, 24;