JPH0467742A - Instantaneous voltage drop compensator - Google Patents

Abstract

PURPOSE:To prevent excessive increase of DC capacitor charging voltage by suppressing the amplitude of a reference voltage determining the waveform of output voltage when the level of current flowing from an inverter into the DC capacitor in the charging direction exceeds a predetermined level. CONSTITUTION:A voltage corresponding to the DC component of current on DC side of an inverter detected through a current detector appears on the output side of a lowpass filter 11 and compared with a set value by means of a comparator 14. When it is lower than the set value, an analog switch 13 is turned OFF. 1pu voltages are applied through a subtractor 15 onto one input terminals of multipliers 16-18 having the other input terminals to be applied with reference voltages VA, VB, VC for respective phases which are outputted while being multiplied by 1. The analog switch 13 is turned ON when the voltage corresponding to DC component of current on DC side of inverter detected through the current detector exceeds the set value.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is designed to generate a compensation voltage that is inserted in series in a power supply path from an AC power supply to a load and compensates for the voltage drop when the AC power supply voltage drops instantaneously. , relates to an instantaneous voltage drop compensator that adds the AC voltage in series and applies it to the load.

[Traditional techniques]

FIG. 3 shows a schematic block diagram of a conventional example of an instantaneous voltage drop compensator. In FIG. 3, 1 is an AC power supply, and 2 is a load supplied with power from the AC power supply 1.

3B is an instantaneous voltage drop compensation (with Ii filling device, DC capacitor 4 that stores compensation energy, and DC capacitor 4
an inverter 5 that generates a compensation voltage using stored energy; a press-fit transformer 6 that adds the output voltage of the inverter 5 in series to the voltage of the AC power supply 1; and a reference voltage generation circuit 10 that generates a reference voltage vR. and reference voltage ■8
and triangular gear rear voltage ■. The main component is a pulse width modulation circuit 7, which compares the output voltage and the pulse width modulation circuit 7 and turns on and off the switching elements of the inverter 5 based on the comparison result.

In such an instantaneous voltage drop compensator 3B, the AC power supply 1
When the voltage of the DC capacitor 4 momentarily drops due to lightning or the like, the energy stored in the DC capacitor 4 is used to perform a compensation operation. In other words, when the voltage of AC type #1 drops momentarily,
A compensation voltage corresponding to the drop is generated from the inverter 5, added in series with the voltage of the AC power supply 1 by the injection transformer 6, and applied to the load 2, so that even if the voltage of the AC power supply 1 momentarily drops,
The normal voltage before the instantaneous voltage drop is continuously applied to the load 2.

In this case, the reference voltage generation circuit 10 generates a voltage signal as the reference voltage (8) by eliminating the output of the detection means for detecting the voltage of the AC power supply 1 from the reference sine wave voltage corresponding to the AC power supply voltage during normal operation. , this reference voltage VR and the triangular wave carrier voltage■. By comparing the values, the target compensation voltage is generated from the inverter 5.

[Problems to be Solved by the Invention] However, in this instantaneous voltage drop compensator 3B, for example, when the load 2 is inductive, the phase of the output current ■ is delayed with respect to the output voltage V of the inverter 5, and the inverter 5 A regeneration mode occurs in which the polarities of the output voltage (■) and the output current (■) are reversed, and a regeneration current flows through the inverter 5. In such a regenerative motor, from the AC side of the inverter 5 to the DC side,
Regenerative power P of V-1 flows in, and at this time, the DC capacitor 4 is charged.

If the regenerative power P continues to flow from the load side of the inverter 5 to the power source side during the regenerative mode, there is a problem that the charging voltage ED of the DC capacitor 4 on the Nll side of the inverter 5 becomes excessive.

Therefore, an object of the present invention is to provide an instantaneous voltage drop compensator that can prevent the charging voltage of a DC capacitor on the power source side of an inverter from becoming excessive due to the inflow of regenerative power from the load side of the inverter to the power source side. It is to be.

[Means to solve the problem]

The instantaneous voltage drop compensator of the present invention is inserted in series in a power supply path from an AC power source to a load, and generates a compensation voltage to compensate for a voltage drop in the AC power source. Then, for compensation, a DC capacitor, a reference voltage generating means,
It includes an inverter, current detection means, and reference voltage suppression means.

The DC capacitor stores compensation energy, the reference voltage generation circuit detects the voltage drop of the AC power supply and generates a reference voltage corresponding to the voltage drop, and the inverter is supplied with power from the DC capacitor to generate a reference voltage corresponding to the voltage drop. A compensation voltage is generated in an additive manner with respect to the voltage of the AC power supply.

The current detection means has a function of detecting a current flowing from the inverter into the DC capacitor in a charging direction. Further, the reference voltage suppressing means has a function of suppressing the amplitude of the reference voltage when the value of the current flowing in the charging direction from the inverter to the DC capacitor exceeds a predetermined value based on the output of the current detecting means.

[For production]

According to the configuration of the present invention, in the case of a regenerative mote in which the polarity of the output voltage and output current of the inverter are reversed, when the current flowing from the inverter to the DC capacitor in the charging direction exceeds a predetermined value, the reference voltage The amplitude of is suppressed to be lower than the value corresponding to the voltage drop, and the compensation voltage generated from the in-hark becomes lower than the original compensation voltage. Therefore, less regenerative power flows from the inverter to the DC capacitor. As a result, it is possible to prevent the charging voltage of the DC capacitor from becoming excessive due to the flow of regenerative power into the DC capacitor.

〔Example〕

An embodiment of the present invention will be described based on FIGS. 1 and 2. This instantaneous voltage drop compensator 3A is for a three-phase circuit, and as shown in FIG. In the regeneration mode, a current detector 9 is added to detect the current ID flowing from the inverter 5 to the DC capacitor 4 in the charging direction, and based on the detection output of the current detector 9, the current ID flows from the inverter 5 to the DC capacitor 4 in the charging direction. A reference voltage suppression circuit 8 for suppressing the amplitude of the reference voltage VR when the value of the inflowing current TD exceeds a predetermined value is added, and the other configuration is the same as that of FIG. 3.

In this instantaneous voltage drop compensator 3A, the current detector 9 constantly detects the current flowing between the inverter 5 and the DC capacitor 4, and is normally created according to the voltage drop of the AC type #i1. Since the reference voltage suppression circuit 8 directly sends the reference voltage vR to the pulse width modulation circuit 7, the same compensation operation as the conventional one is performed.

However, when the output voltage ■ of the inverter 5 and the output current I are in regeneration mode in which the polarities are reversed, if the current ID flowing in the charging direction from the inverter 5 to the DC capacitor 4 exceeds a predetermined value, the reference voltage is suppressed. Since the circuit 8 sends the reference voltage V to the pulse width modulation circuit 7 with an amplitude smaller than the original amplitude corresponding to the voltage drop of the AC power source 1,
The compensation voltage generated from the inverter 5 is lower than the original compensation voltage. Therefore, the regenerative power flowing from the inverter 5 to the DC capacitor 4 is reduced.

Next, the specific configuration and operation of the reference voltage suppression circuit 8 will be explained based on FIG. 2.

In FIG. 2, 11 is a low-pass filter (LPF) that extracts the DC component of the inverter DC side current detected by the current detection means 9, 12 is a coefficient multiplier that multiplies the output of the low-pass filter 11, and 13 is an analog switch. . 14
is a comparator that compares the output voltage of the low-pass filter 11 with a predetermined set value, and when the output voltage of the low-pass filter 11 is smaller than the set value, the analog switch 13
is turned off, and when the output voltage of the low-pass filter 11 is larger than the set value, the analog switch 13 is turned on. 15 is a subtracter, and 16 to 18 are multipliers.

Although the above circuit is a three-phase circuit, the DC side of the three-phase inverter 5 has a configuration in which a compensation voltage is generated using a three-phase DC capacitor 4 as a Tamana energy source. Therefore, the reference voltage suppression circuit 8 is also of a three-phase-discarded type.

In the above configuration, a voltage corresponding to the DC component of the inverter DC side current detected by the current detector 9 appears on the output side of the low-pass filter 11, and this voltage is compared with a set value by the comparator 14. When the above voltage is smaller than the set value, the analog switch 13 is off.

At this time, since the voltage lpu is applied to one input terminal of each of the multipliers 16 to 18 via the subtracter 15, the reference voltage V of each phase is applied to the other input terminal of each of the multipliers 16 to 18. ,,V8. Each Vo is multiplied by 1 and output.

However, the voltage corresponding to the DC component of the inverter DC side current detected by the current detector 9 becomes thicker than the set value (when this happens, the analog switch 13 turns on. At this time,
1. The voltage of pu and the voltage of kpU (0 < k × 1) are input to the subtracter 15, and the voltage of (1k) pu is applied to one input terminal of each of the multipliers 16 to 18, so the multiplication The reference voltage of each phase applied to the other input terminal of each of the circuits 16 to 18 is V8. Vo is each (
1-k) is multiplied and output. As a result, inverter 5
The output voltage decreases to (1-k) ・■, and the regenerative power P determined by the inverter current ■ becomes P= (1k)・V・1, which decreases as the value increases, that is, the current 1 increases. Therefore, due to the inflow of regenerative power P from the load side of the inverter 5 to the power supply side, the charging voltage of the DC capacitor 4
This can prevent the amount from becoming too large.

〔Effect of the invention〕

According to the instantaneous voltage drop compensator of the present invention, when the value of the current flowing in the charging direction from the inverter to the DC capacitor exceeds a predetermined value, the amplitude of the reference voltage that determines the waveform of the output voltage of the inverter is suppressed. Therefore, it is possible to prevent the charging voltage of the DC capacitor from becoming excessive due to the inflow of regenerative power from the load side of the inverter to the power source side.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an instantaneous voltage drop compensator according to an embodiment of the present invention, FIG. 2 is a block diagram showing the specific configuration of the main parts of FIG. FIG. 2 is a circuit diagram showing the configuration of a conventional example. DESCRIPTION OF SYMBOLS 1... AC power supply, 2... Load, 4... DC capacitor, 5... Inverter, 6... Press-fit transformer, 7...
...Pulse width modulation circuit, 8...Reference voltage suppression circuit, 9
...Current detector, 10...Reference voltage generation circuit diagram

Claims (1)

[Claims] An instantaneous voltage drop compensator that is inserted in series in a power supply path from an AC power source to a load and generates a compensation voltage to compensate for a voltage drop in the AC power source, the device comprising: a DC capacitor that stores compensation energy; a reference voltage generating means for detecting a voltage drop of the AC power supply and generating a reference voltage corresponding to the voltage drop; and a compensation voltage supplied from the DC capacitor and corresponding to the reference voltage to the voltage of the AC power supply. an inverter that generates an additive polarity, a current detecting means for detecting a current flowing from the inverter to the DC capacitor in the charging direction, and a current flowing from the inverter to the DC capacitor in the charging direction based on the detection output of the current detecting means. An instantaneous voltage drop compensator comprising: reference voltage suppressing means for suppressing the amplitude of the reference voltage when the value of the flowing current exceeds a predetermined value.