JPS6223323A - 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. This invention relates to an active filter that is installed at the power input terminal of a harmonic-generating load to inject 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. 3 to 7.

This active filter is constructed by combining an injection circuit and a voltage source inverter, and controls the switching elements of the voltage source inverter on and off depending on the level and polarity of the sum of the harmonic current of the harmonic generation load and the harmonic current of the injection circuit. It is something to do.

That is, as shown in FIG. 3, this active filter is installed between the power system 1 and a 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 2.
an active filter that injects harmonic current into the power system 1 for canceling harmonic current flowing from the power system 1 into the power system 1, and includes first and second impedance elements 3A connected to the power system 1; , 3B series circuit, and a harmonic 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 having a predetermined negative value as a lower threshold value, a predetermined positive value as an upper threshold value, and inputting the output Δi of the harmonic current detection circuit 4; An output voltage is applied to the connection point between the first and second impedance elements 3A and 3B of the injection circuit 3, and the sum of the two harmonic currents reaches a predetermined bipolar value according to the output of the hysteresis comparator 5. The configuration includes a voltage source inverter 6 that turns on and off the switching elements in a direction in which the sum of both harmonic currents approaches zero when the harmonic current exceeds the current.

In this case, the first impedance element 3A of the injection circuit 3
is composed of a capacitor (-j
is selected so that Z2 = jXL2- jX(2-0 or z21IIIO) for the fundamental wave of power system 1. With this injection circuit 3,
It becomes possible to significantly reduce the inverter rating.

The harmonic current detection circuit 4 is composed of current transformers 7 and 8, an adder 9, and a fundamental wave removal filter (for example, a notch filter) 10, and the current transformer 7 extracts the load current IL and outputs the current i. 1 is taken out by a current transformer 8, and both are added by an adder 9, and then passed through a fundamental wave removal filter 10 to obtain a harmonic current i and a current i in the load current IL. The sum Δl of the harmonic currents ich in 1 is output.

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

As shown in FIG. 4, the hysteresis comparator 5 has an upper threshold value ■o/
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. .

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

FIG. 5 shows a circuit diagram for explaining the operation of the three-phase voltage source inverter 6. In the figure, Ql and Q2 are A-phase switching elements, Q3 and Q4 are B-phase switching elements, Q5 and Q6 are C-phase switching elements, E is a DC power supply, and D1 to D.

are diodes connected in antiparallel to the switching elements Q1 to Q6, Tr is a harmonic transformer, and L in to Lie are reactors.

FIG. 6 shows an enlarged view of one channel of harmonic current, and the operation will be explained in more detail based on this diagram.

In the case of 1 channel < -11, when Δi = -(1/2) IO is reached as shown in 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 A phase is turned on. Let it be.

As a result, the harmonic current tch increases, and ich>-i. After this, when Δi-(1/2) IO is reached as at point (2), the output of the hysteresis comparator 5 becomes high level, turning on the switching element Q1 of the upper arm of the A phase, for example. As a result, the harmonic @tXicb decreases to icl<-1, and changes in the same manner thereafter. Therefore, the harmonic current i. is 1. It changes along the harmonic current -1rb while changing in a zigzag manner with a width of +8m.

FIG. 7 shows a waveform diagram of each part of FIG. 3.

The figure (A) shows the system current l, and the figure (B) shows the load current i.
(C) is the current flowing through the capacitor C1 -'C
(D) is the current i flowing through the capacitor C2. 2
Is the figure (E) the output type of voltage source inverter 6? tt+
It shows Nv.

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

Problems to be Solved by the Invention The above active filter has a harmonic current detection circuit 4.
If the fundamental wave removal in 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. Since it is set to resonate at a frequency near the fundamental wave of the power system 1, the impedance element 3B short-circuits the output end of the voltage source inverter 6 with respect to the frequency near the fundamental wave, and the impedance element 3B is connected to the voltage source inverter 6. A large current with a frequency near the fundamental wave will flow to 3B, that is, as shown in Fig. 7(E).
As shown in the figure, the output current i+wv 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.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an active filter that can reduce the current having a frequency near the fundamental wave flowing from the voltage source inverter to the injection circuit.

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 current, the active filter comprising a first impedance element connected to the power system and comprising a first capacitor, and a second impedance element comprising a second capacitor and a reactor. an injection circuit consisting of a series circuit of two impedance elements; and harmonic current detection for detecting the sum of a harmonic current flowing from the harmonic generation load to the power system and a harmonic current flowing from the injection circuit to the power system. a hysteresis comparator having a predetermined negative value as a lower threshold value, a predetermined positive value as an upper threshold value, and inputting the output of the harmonic current detection circuit; According to the output of the hysteresis comparator, the sum of the harmonic current of the harmonic generation load and the harmonic current of the injection circuit reaches a predetermined bipolar value. a voltage source inverter that turns on and off a switching element in a direction in which the sum of the harmonic currents approaches zero when the voltage exceeds the first voltage source; A first subtracter that subtracts the capacitor voltage of the second impedance element at a ratio according to its reactance ratio, and the output of the first subtracter is inputted to the output of the harmonic current detection circuit to the hysteresis comparator. As described above, the active filter of the present invention subtracts the sum of the harmonic current of the harmonic generation load and the harmonic current of the injection circuit. At the same time, the harmonic current detection circuit detects the voltage, and the difference between the output of the harmonic current detection circuit and the output of the first subtracter is input to a hysteresis comparator, and the voltage of the first and second capacitors is detected. Since the value subtracted by the ratio of the capacitance is used as the correction signal, the harmonic current for compensating the harmonic current of the harmonic generation load is passed through the injection circuit, and the voltage source inverter is
It is possible to suppress the flow of a large current having the same wave number near the fundamental wave to the impedance element, and it is possible to reduce the inverter capacity.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 and 2.

The circuit shown in FIG. 1 has a compensating arithmetic circuit 1 in addition to the circuit shown in FIG.
2 has been added, and the other parts are the same as in FIG. 3, so a description of the same parts will be omitted.

Specifically, the compensation arithmetic circuit 12 changes the reactance ratio X of the capacitor C2 to the capacitor CI from the voltage VC2 of the capacitor C2 to the voltage Vat of the capacitor C1. 2
The voltage multiplied by / 15.16.

Next, it will be explained in detail that by providing the compensating arithmetic circuit 12, a large current near the fundamental wave included in the inverter capacitance flow can be suppressed.

In order to prevent a current with a frequency near the fundamental wave from flowing from the voltage source inverter 6 to the impedance element 3B of the injection circuit 3, a signal that detects the fundamental wave component in the output of the voltage source inverter 6 and cancels it is generated. It is sufficient to feed it back to the input of the hysteresis comparator 5.

Therefore, an attempt is made to detect only the fundamental wave component in the output voltage of the voltage source inverter 6 without using a bandpass filter that causes a delay.
It is.

Voltage V across capacitor C2. 2, the output of the voltage source inverter 6 and the voltage of the power system 1 appear in a superimposed manner, so it is necessary to remove the influence of the voltage of the power system 1. Voltage ■. 1 is the reactance ratio X of capacitors C, C2
The product multiplied by c2/X01 is subtracted, and the output of the subtracter 15 corresponds only to the fundamental wave in the output of the voltage source inverter 6.

Of course, the voltage V. 1. VC2 contains not only the fundamental wave component but also harmonic components, and by inputting this harmonic component to the hysteresis comparator 5, the harmonic compensation function will be slightly degraded, but this can be ignored. This is as much as possible.

This point will be explained below. n flowing to C1 and C2
For the harmonic current component 1CIR+iC*n (n includes non-integer values), the correction term (below the margin) −j−KXc2 ・ □ =K ′ □ Therefore, this correction term is the low frequency component It has a large effect on harmonic components, and has a small effect on harmonic components.

Therefore, when the fundamental wave component is corrected by 100, the fifth harmonic component is corrected by 20, and although the performance as an active filter is slightly degraded, this is not a particularly problematic amount.

Figure 2 shows waveform diagrams of each part in Figure 1, where (A) shows the grid current i, and (B) shows the load current LL.
) is the current i in capacitor C1. 1, (D) of the same figure shows the output Δi3 of the constant circuit 14, that is, the above-mentioned correction term, and (E) of the same figure shows the output current i+sv of the voltage source inverter 6.

As is clear from this figure, the fundamental wave component input to the hysteresis comparator 5 is compensated by the correction term in FIG. It will no longer be included. Therefore, almost no current with a frequency near the fundamental wave flows from the voltage source inverter 6 into the injection circuit 3, and as a result, the capacity of the voltage source inverter 6 can be reduced.

Effects of the Invention The active filter of the present invention detects the sum of the harmonic current of the harmonic generation load and the harmonic current of the injection circuit with a harmonic current detection circuit, and detects the sum of the harmonic current of the harmonic current detection circuit and the harmonic current of the injection circuit. The difference between the output of the subtracter No. 1 and the output of the subtracter No. 1 is input to a hysteresis comparator, and according to the output of the hysteresis comparator, when the output of the harmonic current detection circuit exceeds a predetermined bipolar value, the output of the harmonic generation load is determined. A harmonic current injection circuit for compensating the harmonic current of the harmonic generation load by turning on and off the switching elements of the voltage source inverter in a direction in which the sum of the harmonic current and the harmonic current of the injection circuit approaches zero. In addition to the method of flowing to
Since the difference between the capacitor voltage of the first impedance element and the capacitor voltage of the second impedance element is determined according to the reactance ratio and is input to the hysteresis comparator, the voltage near the fundamental wave included in the output of the harmonic current detection circuit is Frequency components can be canceled, and current at frequencies near the fundamental wave from the voltage source inverter can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a waveform diagram of each part in Figure 1, Figure 3 is a circuit diagram of an active filter that is the basis of this invention, Figure 4 is an operating characteristic diagram of a hysteresis comparator, and Figure 5 is a circuit for explaining the operation of a voltage source inverter. Similarly, FIG. 6 is an enlarged waveform diagram for explaining the operation, and FIG. 7 is a waveform diagram of each part of FIG. 3.

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. an injection circuit comprising a series circuit of a first impedance element comprising a first capacitor connected to the power system and a second impedance element comprising a second capacitor and a reactor; a harmonic current detection circuit that detects the sum of a harmonic current flowing from the wave generation load to the power system and a harmonic current flowing from the injection circuit to the power system, and a predetermined negative value as a lower threshold value; and applying an output voltage to a connection point between a hysteresis comparator having a predetermined positive value as an upper threshold and inputting the output of the harmonic current detection circuit, and the first and second impedance elements of the injection circuit. None When the sum of the harmonic current of the harmonic generation load and the harmonic current of the injection circuit exceeds a predetermined bipolar value according to the output of the hysteresis comparator, the sum of both harmonic currents becomes zero. a voltage source inverter that turns on and off the switching element in the approaching direction; a first subtracter that subtracts the capacitor voltage of the first impedance element and the capacitor voltage of the second impedance element at a ratio according to their reactance ratio; and a second subtracter that subtracts the output of the first subtracter when inputting the output of the harmonic current detection circuit to the hysteresis comparator.