JPS6223325A - Active filter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention is intended to prevent harmonic components generated by the harmonic generation load from adversely affecting other loads connected to the power system when power is supplied from the power system to a harmonic generation load. In order to prevent harmonic generation loads from causing harmonics, This field relates to an active filter that is installed at the input end of a power source and injects a compensation current to prevent harmonics from flowing into the power system.

2. Description of the Related Art An active filter, which is the basis of the present invention, will be explained with reference to FIGS. 4 to 8.

This active filter is configured by combining an injection circuit and a voltage source inverter, operates the voltage source inverter in current control mode, and measures the level of the difference between the harmonic current of the harmonic generation load and the harmonic current of the injection circuit. The switching elements of the voltage source inverter are controlled on and off depending on the polarity and polarity.

That is, as shown in FIG. 4, this active filter is installed between the power system 1 and the harmonic generation load 2 supplied with power from the power system 1, and is installed between the power system 1 and the harmonic generation load rt.
an active filter that injects harmonic current into the power system 1 for canceling harmonic current flowing from I2 to the power system 1, the series circuit comprising a capacitor C and a reactor L connected to the power system 1; and a harmonic current detection circuit 4 that detects the sum of the harmonic current flowing from the harmonic generation load 2 to the power system 1 and the harmonic current flowing from the injection circuit 3 to the power system 1. a hysteresis comparator 5 which has a predetermined negative value as a lower threshold value, a predetermined positive value as an upper threshold value, and which receives the output Δi of the harmonic current detection circuit 4 as an input; and a capacitor of the injection circuit 3. According to the output of the hysteresis comparator 5, when the sum of the two harmonic currents exceeds a predetermined value of both polarities, the output voltage is applied to the connection point of C and the reactor L. This configuration includes a voltage source inverter 6 that turns on and off the switching elements in a direction where the sum approaches zero.

In this case, the impedance of the capacitor C of the injection circuit 3 is -jXc, and the impedance of the reactor L is jXL
It is set to about XL-6% with respect to XC-100%, and the reactor is set to have a low impedance for low frequencies such as the fundamental wave or lower frequencies, and the voltage ■9 is prevented from being applied to the voltage source inverter 6.

The harmonic current detection circuit 4 includes a current transformer 7.8, an adder 9, and a fundamental wave removal filter (non-chi filter) 10^.

10B, the load current iL is taken out by a current transformer 7, and the current i (is taken out by a current transformer 8), and both are subjected to a fundamental wave removal filter IOA.

10B and then added by adder 9 to obtain harmonic current 10 in load current IL and harmonic current tc in current IC.
The sum Δi of k is output.

The output Δi of this harmonic current detection circuit 4 is input to a hysteresis comparator 5.

As shown in FIG. 5, the hysteresis comparator 5 has the output Δi of the harmonic current detection circuit 4 at an upper threshold value I. /
When the output level exceeds 2, the output level changes from low level to high level, and when it falls below the lower threshold value -IO,/2, the output level changes from high level to low level. There is.

The output of this hysteresis comparator 5 determines the sixth
Each switching element Q1 of the voltage source inverter 6 shown in the figure
~By turning Q6 on and off, harmonic current 1ck is generated to compensate for the harmonic current flowing through harmonic generation load 2.
(opposite polarity to i) will flow into the injection circuit 3.

FIG. 6 shows a circuit diagram of a three-phase voltage source inverter 6. In FIG. 6, Ql and Q2 are A-phase switching elements, Q3 and Q4 are B-phase switching elements, and Q5
and Q6 is a C-phase switching element, E is a DC power supply,
D1 to D6 are switching elements Q and diodes connected in antiparallel to -06, and 11 is a harmonic transformer.

FIG. 7 shows an enlarged view of the harmonic current 'Ch, and the operation will be explained in more detail based on this figure.

In the case of i ch <-i th, when Δi=-(1/2) IO is reached, such as the 0 point, the output of the hysteresis comparator 5 becomes a low level, and for example, the switching element Q2 of the lower arm of the human figure is turned on. Let it be.

As a result, the harmonic current 'ch increases and becomes 'ch>jLk. Thereafter, when Δi = (1/2) IO is reached as shown at point (■), the output of the hysteresis comparator 5 becomes high level, turning on the switching element Q1 of the upper arm of the human figure, for example. As a result, the harmonic current 'ch decreases so that ich<-i, and the same changes thereafter. Therefore, the harmonic current i. changes along the harmonic current -1- while changing in a zigzag manner with a width of 10.

FIG. 8 shows a waveform diagram of each part of FIG. 4.

The same figure (A) shows the voltage ■9, the same figure (B) shows the load current IL, the same figure (C) shows the harmonic current i+h in the load current 11-, and the same figure (D) shows the injection circuit 3. The current 1 of the capacitor C (in the figure (E) is the output current i+Nv of the voltage source inverter 6).
In the same figure, (F) is the system current i.

It shows.

Note that the same applies to the B phase and C phase.

Problems to be Solved by the Invention The above-mentioned active filter has problems when the load current iL contains harmonics near the fundamental frequency of the power system I, or when the fundamental wave removal in the harmonic current detection circuit 4 is insufficient. The voltage source inverter 6 also outputs a fundamental wave voltage, and this fundamental wave voltage is applied to the injection circuit 3, but since the impedance of the reactor L of the injection circuit 3 is set to be extremely small at low frequencies, The reactor L almost short-circuits the output end of the voltage source inverter 6 with respect to the frequency near the fundamental wave, and a considerable amount of Ti current at the frequency near the fundamental wave flows from the voltage source inverter 6 to the reactor.
That is, the output current i+sv of the voltage source inverter 6 contains many fundamental wave components, and as a result, the capacity of the voltage source inverter 6 has to be increased.

Moreover, since this current flows through the reactor, overload of the reactor L may occur.

In particular, the load current i of harmonic generation load 2 is as shown in Fig. 8(B).
When the transient increase occurs, as shown in FIG. A fundamental wave component is included in the transient change section of the current iL (Fig. 8 (B)) and the period of several cycles immediately after it, and as a result, the output current 1Isv of the voltage source inverter 6 < Fig. 8 (E)). A very large number of fundamental wave components are included, and as a result, the capacity of the voltage source inverter 6 has to be made very large.

This invention has been made in view of the above problems, and aims to reduce the current at a frequency near the fundamental wave flowing from the voltage source inverter to the injection circuit not only when the harmonic generating load is steady but also when there is a transient change. The purpose is to provide an active filter that can.

Means for Solving the Problems The active filter of the present invention is installed between a power system and a harmonic generation load supplied with power from the power system to prevent harmonics flowing from the harmonic generation load to the power system. An active filter that injects harmonic current into the power system for canceling the current, the injection circuit comprising a series circuit of a capacitor and a reactor connected at one end to the power system, and the harmonic current flowing into the harmonic generation load. a current detection circuit that detects the sum of a harmonic current and a current obtained by subtracting the current flowing through the injection circuit when there is no harmonic generation load from the current flowing through the injection circuit; a hysteresis comparator which has a predetermined positive value as an upper threshold and receives the output of the current detection circuit as an input; and an output voltage is applied to the other end of the injection circuit according to the output of the hysteresis comparator. and the sum of the harmonic current flowing through the harmonic generation load and the current flowing through the injection circuit minus the current flowing through the injection circuit when there is no harmonic generation load exceeds a predetermined bipolar value. switching in a direction in which the sum of the harmonic current flowing through the harmonic generation load and the current flowing through the injection circuit minus the current flowing through the injection circuit when there is no harmonic generation load approaches zero. This configuration includes a voltage type inverter that turns on and off the elements.

As described above, the active filter of the present invention calculates the sum of the harmonic current flowing through the harmonic generating load and the current flowing through the injection circuit minus the current flowing through the injection circuit when there is no harmonic generating load. The current is detected by a detection circuit, and the output of this current detection circuit is input to a hysteresis comparator, and according to the output of this hysteresis comparator, the harmonic current flowing to the harmonic generation load and the current flowing to the injection circuit are used to generate harmonics. When the sum of the current after subtracting the current flowing through the injection circuit exceeds a predetermined value for both polarities, the switching elements of the voltage source inverter are turned on and off in the direction in which the sum of the currents approaches zero. A constant fundamental current (current that flows through the injection circuit when there is no harmonic generating load) is passed through the injection circuit, and at the same time, a harmonic current is passed through the injection circuit to compensate for the harmonic current of the harmonic generating load. Become.

As a result, when performing harmonic compensation, a large current with a frequency close to the fundamental wave does not flow through the reactor, so the reactor is not overloaded, and there is no need to increase the capacity of the voltage source inverter.

In addition, since the output of the voltage source inverter is injected through a series circuit of a capacitor and a reactor, all of the output of the voltage source inverter is injected into the receiving end of the harmonic generation load. Even if a large low-frequency current such as a fundamental wave component is input from the harmonic current detection circuit to the hysteresis comparator due to a transient increase in the voltage and a large low-frequency current flows to the voltage source inverter and injection circuit, the response remains low. Frequency current can be controlled by 1.

Embodiment An embodiment of the present invention will be explained with reference to FIGS. 1 to 3. As shown in FIG. 1, this active filter is installed between a power system 1 and a harmonic generation load 2 fed from the power system 1.
An active filter injects harmonic current into the power system 1 for canceling harmonic current flowing from the power system 1 into the power system 1, the active filter comprising a capacitor C and a reactor L connected in series with one end connected to the power system 1. An injection circuit 3 consisting of a circuit, a harmonic current i+h flowing through the harmonic generation load 2, and a current jC flowing through the injection circuit 3. A current I flows through the injection circuit 3 when the harmonic generation load 2 is not present. A current detection circuit 4' that detects the sum of the electric current 7 and iX obtained by subtracting 0; A hysteresis comparator 5 inputs the output Δi' of the injection circuit 3, and an output voltage is applied to the other end of the injection circuit 3. 1, and the current i flowing through the injection circuit 3.

When the harmonic generation load 2 is not present, the injection circuit 3
Current i flowing through. When the sum of the current IX obtained by subtracting 0 exceeds a predetermined bipolar value, the harmonic current i flowing to the harmonic generation load 2 and the current j flowing to the injection circuit 3 (from the harmonic generation load 2 The voltage type inverter 6 turns the switching element on and off in a direction such that the sum of the current i, which is obtained by subtracting 0 from the current i flowing through the injection circuit 3 when there is no current i, approaches zero.

In this case, the current detection circuit 4' detects the load current IL with the current transformer 7, passes it through the fundamental wave removal filter 10A, and detects the harmonic current i in the load current i. , a current 1c flowing through the injection circuit 3 is detected by a current transformer 8, and this current i. The current (fundamental wave current) ico flowing through the injection circuit 3 in the absence of the harmonic generation load 2 is subtracted from the harmonic current Lh by the subtractor 10C, and the harmonic current Lh and the output 18 of the subtractor 10C are obtained.
are added by an adder 9, and the output Δi' of the adder 9 is input to the hysteresis comparator 5.

This active filter has no harmonic generation load 2,
When the harmonic current is not compensated for, the load current iL is zero and the harmonic current i is also zero, so the current 1c and the current i. 0, that is, the current i
. The harmonic current 1cb (in the explanation of FIG. (same as described above) will be controlled to flow a current that is the sum of

The fundamental wave current ico can be obtained by shifting the phase of the system voltage (1)9 by 90 degrees and dividing this by the impedance of the series circuit of the capacitor C and the reactor L. Further, the hysteresis comparator 5 and other operations are similar to those in FIG. 4.

FIG. 2 shows an example of a three-phase circuit, in which L1 to L3 are reactors and C1 to C3 are capacitors.

FIG. 3 is a waveform diagram of each part when the load amount of the harmonic generation load 2 increases transiently. The figure (A) shows the grid voltage ■9
The figure (B) shows the load current iL, and the figure (C) shows the load current i. (D) shows the current 1° of the injection circuit 3, that is, the output type QR of the voltage source inverter 6.
(E) shows the system current i.

As is clear from this figure, when the load current iL increases, the fundamental wave component of the output current iI□ of the voltage source inverter 6 hardly increases.

Thus, in this embodiment, the harmonic current i flowing through the harmonic generating load 2 and the current i flowing through the injection circuit 3. The current 'c flowing through the injection circuit 3 when there is no harmonic generation load 2 from
A current detection circuit 4' detects the sum of current ix obtained by subtracting o, and inputs the output Δi' of this current detection circuit 4' to a hysteresis comparator 5, and generates harmonics according to the output of this hysteresis comparator 5. Harmonic current i+h flowing through load 2 and current i flowing through injection circuit 3. The current i flowing through the injection circuit 3 when there is no harmonic generation load 2. . The injection circuit 3 A constant fundamental wave current (current 1c flowing through the injection circuit 3 when there is no harmonic generation load 2)
o), and at the same time, a harmonic current for compensating the harmonic current of the harmonic generation load 2 is caused to flow through the injection circuit 3.

As a result, when performing harmonic compensation, a large current with a frequency near the fundamental wave does not flow through the reactor L.
Therefore, the reactor L will not be overloaded, and there is no need to increase the capacity of the voltage source inverter 6.

In addition, since the output of the voltage source inverter 6 is injected through the series circuit of the capacitor C and the reactor L, all of the output of the voltage source inverter 6 is injected into the power receiving end of the harmonic generation load 2, which generates harmonics. When the amount of load increases transiently, low frequency components such as fundamental wave components are input from the harmonic current detection circuit 4' to the hysteresis comparator 5, and a large low frequency current flows to the voltage source inverter 6 and injection circuit 3. Even if there is a problem, low frequency current can be suppressed with good responsiveness.

Also, when using a voltage source inverter as a current control type,
In a method in which a switching element is turned on and off in comparison with a carrier of a constant frequency, a phase delay of, for example, about 30 degrees occurs, but in this embodiment, there is no phase delay and an instantaneous response can be expected. Furthermore, the injection circuit 3 also allows reduction of the inverter rating.

Effects of the Invention In the active filter of the present invention, a large current with a frequency close to the fundamental wave does not flow through the reactor, so the reactor is not overloaded, and there is no need to increase the capacity of the voltage source inverter.

In addition, since the output of the voltage source inverter is injected through a series circuit of a capacitor and a reactor, all of the output of the voltage source inverter is injected into the receiving end of the harmonic generating load, which reduces the load amount of the harmonic generating load. Even if low-frequency components such as fundamental wave components are input to the hysteresis comparator from the harmonic current detection circuit due to transient increase, and a large low-frequency current flows to the voltage source inverter and injection circuit, the low-frequency current can be detected with good response. Current can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a detailed circuit diagram of the main parts of Figure 1, Figure 3 is a waveform diagram of each part of Figure 1, Figure 4 is a circuit diagram of the active filter that is the basis of this invention, and Figure 5 is a diagram of the hysteresis comparator. FIG. 6 is a circuit diagram of the voltage source inverter, FIG. 7 is an enlarged waveform diagram for explaining the operation, and FIG. 8 is a waveform diagram of each part of FIG. 4. ■...Power system, 2...Harmonic generation load, 3...
injection circuit, 4'... current detection circuit, 5... hysteresis comparator, 6... [regular inverter, C...
・Capacitor, L...Reactor Figure 4 Figure 6

Claims (1)

[Claims] A harmonic current is installed between a power system and a harmonic generation load supplied from the power system, and injects a harmonic current into the power system to cancel a harmonic current flowing from the harmonic generation load to the power system. The active filter includes an injection circuit consisting of a series circuit of a capacitor and a reactor, one end of which is connected to the power system, and a harmonic current flowing through the harmonic generation load and a current flowing through the injection circuit. a current detection circuit that detects the sum of the current obtained by subtracting the current flowing through the injection circuit when there is no load; a hysteresis comparator which receives the output of the current detection circuit as an input; and an output voltage is applied to the other end of the injection circuit; a harmonic current flows to the harmonic generation load in accordance with the output of the hysteresis comparator; and the injection circuit. When the sum of the current flowing through the injection circuit when there is no harmonic generation load from the current flowing through the injection circuit exceeds a predetermined bipolar value, the harmonic current flowing through the harmonic generation load and the An active filter comprising: a voltage source inverter that turns on and off a switching element in a direction in which the sum of the current flowing through the injection circuit minus the current flowing through the injection circuit when there is no harmonic generation load approaches zero from the current flowing through the injection circuit.