JPS61128767A - Harmonic distortion compensator - Google Patents

Abstract

PURPOSE:To compensate the harmonic wave distortion of a power system by controlling the resonance operation of resonance means capable of supplying to the system by resonance control means. CONSTITUTION:A harmonic wave distortion compensator has resonance means 2a (having a coils 13 and a capacitor 4) which outputs a reverse phase resonance current i22 to a harmonic wave current by a resonance operation and its resonance control means 5. The means 5 has the first current detector 6 for detecting the current i22, the second current detector 7 for detecting them current i3 of a load 3, a filter 8 for extracting the third harmonic wave component from the current i3, a comparator 9, and a controller 10 for opening or closing a switch 11 which supplies a DC voltage from a DC power source 12 to both ends of the coil 13. Thus, the third harmonic wave component of the current i3 is compared by a comparator 9 with the output of the detector 6 to control to open or close the switch 11, thereby supplying reverse phase resonance voltage i22 to the system to cancel the third harmonic wave current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a harmonic distortion compensator that compensates for harmonic distortion in a power system.

[Technical background of Ring and its problems] Home electrical products such as televisions, radios, stereos, microwave ovens, etc. are equipped with a power supply unit W (AC/DC conversion circuit) that converts AC voltage to DC voltage.

Furthermore, with the recent development of power electronics, inverter circuits have come to be used to control the speed of induction motors, and an AC/DC converter circuit similar to the above is also disposed in the preceding stage of this inverter circuit.

A general circuit configuration of this AC/DC conversion circuit is shown in FIG. 1 is an AC power supply including a power transmission system, D is a rectifier (generally consisting of a group of bridge-connected silicon diodes) that performs full-wave rectification of the AC voltage from this AC power supply 1, and C is a full-wave rectifier that performs full-wave rectification of the AC voltage from this AC power supply 1. This is a smoothing capacitor that smoothes the rectified voltage, and the voltage across the smoothing capacitor C is applied to the load RL as a DC voltage.

By the way, as shown in FIG. 7, in an AC/DC conversion circuit in which a smoothing capacitor C is connected immediately after the rectifier, the impedance of the circuit becomes nonlinear with respect to the 1iii [t'R pressure. A harmonic current flows through the alternating current machine 1I11.

FIG. 8 is a waveform diagram showing the relationship between the current flowing through the AC power supply 1 and the power supply voltage in the circuit of FIG. 7.

Because harmonic current (odd order) is generated, the voltage waveform VL
In contrast, the current waveform becomes as shown by il-.

This harmonic current not only distorts the voltage waveform of the AC machine and i11, but also causes overheating of the power factor correction capacitor, burnout of the series reactor, and protective connections such as negative phase detectors and earth leakage circuit breakers!
This may cause various failures such as malfunction of the device. Therefore, measures to reduce harmonic current are extremely important.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its purpose is to provide a harmonic wave that can compensate for harmonic distortion in a power system by attenuating harmonic current. An object of the present invention is to provide a distortion compensation device.

[Summary of the Invention J The outline of the present invention for achieving the above object is to generate a resonance 1 having the same frequency and opposite phase to the harmonic current by resonance operation.
Along with generating flow, this one is also 1! Compensating for harmonic distortion in the power system, comprising a resonance means capable of supplying current to the power system, and a resonance control means for attenuating harmonic current by controlling the resonance operation of the resonance means. It is something to do.

[Embodiments of the invention] Hereinafter, the present invention will be specifically explained with reference to Examples.

First, the principle of the present invention will be explained with reference to FIG.

FIG. 2 is a diagram explaining the principle of the present invention. Figure 1a.

Reference numeral 1b denotes a power system line; 2, as will be described in detail later, is a resonant means formed by, for example, a coil and a capacitor connected in series and connected to the power system lines 1a, 1bl; 3, the power system lines 1a, 1b; It is a load to which power is supplied through. Here, the load 3 is not limited to the case of a device FI, but also includes a case where a plurality of devices are connected via, for example, power distribution equipment.

In the figure, the voltage between power system lines 1a and Ib is E
[V], its instantaneous value e is e − r d E si
It is expressed as n ωt − (1). It is assumed that the current flowing through the load 3 contains harmonic components, and the effective values of the current for each order are Il, I2, . , I3. .......

In, the current 13 (instantaneous value) flowing through the load 3 is: i 3- rT I t sin ωt + rT I2
sin (2ωt+02)+rTI3sin (3ω
t +03 )+…・-+C7In sin (n
ωt +θn )...(2) It is expressed as follows. However, in general, the harmonic components are of odd order, and since it is considered that there are few 9th or higher harmonic components among the odd order 7iI4wi wave components, the previous equation (2) is (hereinafter referred to as the margin) i 3 −ar'; l It sin ωt+(
T [3 sin (3 ωt +03) + C t l5
sin(5cc>t+θ5)+ffI7S
It can be transformed as in (7ωt +θ7) (3).

Therefore, the current i2 (instantaneous value of the resonant current) flowing through the resonant means 2 is expressed as i 2 =/7 I3 sin (
3ω t −)−θ 3 + π )+C71s
sin (5ω+85+π)+r′rIT sin
(7ωt +θ7+π) (4) If set as follows, the current i1 flowing through the power system
(Instantaneous value> is i1-i2+i3...
...Since (5), from the previous + 3) I41 formula, it - (dI t sin ωt
=·=(6), and since harmonic components can be removed, harmonic distortion in the power system can be compensated for.

Next, an embodiment of the present invention based on the above principle will be described.

To sufficiently compensate for harmonic distortion, the 3rd, 5th and 7th
It is preferable to reduce the next harmonic component, but here:
-For example, when reducing the third harmonic component,
This will be explained with reference to FIG.

FIG. 1 is a circuit diagram of a harmonic distortion compensator according to an embodiment of the present invention.

FIG. 2a shows a resonant means that can generate a resonant current 1u having the same frequency and opposite phase as the harmonic current by resonance operation, and can supply this resonant current 1u to the power system, for example, the power system lines 1a, 1bl. Coil 13. A so-called series resonant circuit consisting of a capacitor 4 is applied. Further, reference numeral 5 denotes a resonance 914m means for attenuating the harmonic 'R flow by controlling the resonance operation of the resonance means 2a according to the harmonic current flowing in the power system. 1st to detect izz
current detector (current transformer) 6 and the load 3
a second current detector (current transformer) 7 that detects the current i3 flowing in the second current detector 7, a filter 8 that extracts the third harmonic component from the output of the second current detector 7, and an output of the filter 8. a comparator 9 that compares the output of the first current detector 6 with the output of the first current detector 6 and outputs the comparison result; and an am circuit 10 that controls the opening/closing operation of a switch to be described later in accordance with the output of the comparator 9. a switch 11 connected to one end of the coil 13 and opened and closed by the MID of the control circuit 10;
3 and a series power supply 12 for supplying a DC voltage applied to both ends of the power supply.

Next, the operation of the embodiment device configured as described above will be explained.

For example, the third harmonic current i JJ generated by load 3
Assuming that the phase of is delayed by π [rad] with respect to the voltage ■ as shown in FIG. As shown in FIG.
It would be a good idea to stream io.

Therefore, in order to make the resonant frequency of the resonant means 2 equal to the frequency of the third harmonic current, the coil 13° capacitor 4
The value of 3ω-1/rUc (
Set up a satisfying relationship. Now, control circuit 1
0 control, when the switch 11 is switched only between the lower On@, the current IL flowing through the coil 13 is equal to the inductance of the coil I3, and if the voltage of the DC power supply 12 is Ed, then (L - (Ed / L) ) -Ton
It is expressed as ...--(8). And Figure 3 (b
), the switch 11 closes at time [0, and the time [
When the switch 11 is opened at 1, a resonance current 1u having an amplitude equal to the current value at time t1 is generated in the resonance means 2a. This resonant current in is generated by a circuit constant that satisfies the previous equation, so
Its frequency is equal to the third harmonic current, and its phase is opposite to the phase of the third harmonic current.

This resonant current iH cancels out the third harmonic component.

If there is no loss in the load 3 and the power system line, the resonant current i 22 of the resonant means 2a continues to flow, but in reality it is attenuated due to the loss in the circuit.

Therefore, the control circuit 10 continues the resonant operation of the resonant means 2a by closing the switch 11 again, and the comparator 9
control so that the output is zero.

When switch 11 is closed and this switch 110 is open, I! If f(Ton) is controlled according to the output of the comparator 9, the amplitude of the resonant current iH is determined by the time the switch 11 is closed, so the amplitude of the resonant current 1u and the third harmonic current are The amplitude can always be made equal, thereby making it possible to almost completely cancel out the third harmonic component.

In this way, in the device of this embodiment, the resonant operation of the resonant means 2 generates a resonant current that is equal to the frequency of the third harmonic current and has an opposite phase, and also supplies this resonant current to the power system. Therefore, the third harmonic current can be canceled and harmonic distortion of the power system can be compensated for.

Further, the output of the first current detector 6 and the output of the filter 8 are compared by a comparator 9, and the output of the comparator 9 is set to zero, in other words, the amplitude of the third harmonic current is The control circuit 10
Since the resonant operation of the resonant means 2 is controlled (sustained) through can be canceled out.

Although one embodiment of the present invention has been described above, it goes without saying that the present invention is not limited to the above-mentioned embodiment, and can be modified as appropriate within the scope of the gist of the present invention.

For example, in the above embodiment, the case where the 3rd harmonic bottom component is reduced is explained, but when the 5th and 7th harmonic components are also reduced, as shown in FIG. The resonant frequencies are 3rd and 5th, respectively.

Resonant means 2a, 2 equal to the frequency of the 7th harmonic current
b and 2c may be connected in parallel, and a resonance control means having the same function as the resonance control means 5 shown in FIG. 1 may be connected to each resonance means. In this case, at least the second current detector 7 could be shared.

Further, the resonance control means 5 can also be configured as shown in FIG.

FIG. 5 is a circuit diagram showing a modification of the resonance control means in the embodiment shown in FIG. 1.

In FIG. 5, parts having the same functions as those shown in FIG. 1 are given the same reference numerals.

What is shown in FIG. 5 is different from what is shown in FIG. 14 and a control circuit 15 that controls the opening/closing operation of the switch 11 according to the output of the filter 8.

In the above configuration, the basic operation is the same as that of the device shown in FIG. By controlling the operation, the resonant means 2
Control (sustain) the resonant operation of. Note that the control circuit 15 in this embodiment controls the switch 11 based on the output of the filter 8.
I'm trying to find the right time to close it.

Even with this configuration, since the resonance operation of the resonance means 2 can be controlled via the control circuit 15, the same effects as the embodiment shown in FIG. 1 can be achieved.

Furthermore, even if a harmonic current of the ninth or higher order or an even-numbered harmonic current becomes a problem, it can be easily dealt with by matching the resonant frequency of the resonant means to the frequency of the harmonic current. Particularly when a high-order harmonic current is generated, it is effective to use a low-pass filter 19 comprising a coil 17 and a capacitor 18, as shown in FIG.

In the above embodiment, the amplitude of the harmonic current and the amplitude of the resonance current are controlled to be equal to each other by the resonance control means 5. In cases where it is sufficient to reduce the harmonics 2) 11%E that are only generated to a certain extent, a method of presetting the amplitude of the resonant current to a predetermined value may be considered. Particularly in the latter case, a time switch or the like may be used to operate the device according to the present invention only during a specific time period. With this configuration, for example, in FIG. Second t4 current detectors 6, 7, filter 8, comparator 9, and in FIG. 5, current detector 7. Filter 8. The AC/DC conversion circuit 14 and the like are not required, and the control circuit 10.15 only needs to have the function of controlling the opening/closing operation of the switch 11 at predetermined intervals in order to maintain the resonant operation of the resonant means 2a. Therefore, it is extremely advantageous in terms of cost.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a harmonic distortion compensator that can compensate for harmonic distortion in a power system by attenuating harmonic current.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a harmonic distortion compensator which is an embodiment of the present invention, Fig. 2 is a diagram explaining the principle of the present invention, and Figs. 3 (a) and (b).
) is a waveform diagram for explaining the operation of the embodiment shown in FIG. 1, FIGS. 4 to 6 are circuit diagrams for explaining other embodiments of the present invention, and FIG. 7 is an AC/DC conversion diagram. FIG. 8 is a circuit diagram showing the general circuit configuration of the circuit. FIG. 8 is a waveform diagram showing the relationship between the current flowing through the AC power source and the power supply voltage in the circuit of FIG. 7. 2a, 2b, 2c...Resonance means, 5...
- Resonance control means. L --J Figure 2n (b)

Claims (2)

[Claims] (1) A harmonic distortion compensator that compensates for harmonic distortion in a power system by attenuating harmonic current, and generates a resonant current with the same frequency and opposite phase as the harmonic current through resonance operation. A harmonic distortion compensation system comprising: a resonant means capable of supplying the resonant current to the power system; and a resonant control means that attenuates the harmonic current by controlling the resonant operation of the resonant means. Device. (2) The resonance control means detects a harmonic current of the power system, and varies the amplitude of the resonance current of the resonance means based on the detection result. Harmonic distortion compensator.