JPH0748933B2 - Active filter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power source from a power system to a harmonic generation load, wherein the harmonic component generated by the harmonic generation load is applied to another load connected to the power system. The present invention relates to an active filter which is installed at a power source input terminal of a harmonic generation load and injects a compensation current in order to prevent an adverse effect, and prevents harmonics from flowing out to a power system.

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

This active filter is configured by combining an injection circuit and a voltage source inverter, and controls the switching element of the voltage source inverter on / off by the level and polarity of the difference between the harmonic current of the harmonic generating load and the harmonic current of the injection circuit. To do.

That is, as shown in FIG. 4, the active filter is installed between the electric power system 1 and the harmonic generating load 2 fed from the electric power system 1, and the harmonic generating load 2 is installed.
An active filter for injecting a harmonic current for canceling a harmonic current flowing from the power system 1 into the power system 1, the first and second impedance elements 3A being connected to the power system 1. , 3B in series circuit, and a harmonic for detecting the sum of the harmonic current flowing from the harmonic generating load 2 to the power system 1 and the harmonic current flowing from the injection circuit 3 to the power system 1. A wave current detection circuit 4, a hysteresis comparator 5 having a negative predetermined value as a lower threshold value and a positive predetermined value as an upper threshold value, and an output Δi of the harmonic current detection circuit 4 as an input; An output voltage is not applied to the connection point of the first and second impedance elements 3A and 3B of the injection circuit 3, and the sum of the both harmonic currents is calculated according to the output of the hysteresis comparator 5. The sum of Sozo Re said two harmonic current is configured to include a voltage source inverter 6 for turning on and off the switching element in a direction approaching to zero when it exceeds a predetermined value polarity.

In this case, the first impedance element 3A of the injection circuit 3 is composed of the capacitor (−jX _C1 ) C ₁ , and the second impedance element 3B is the series circuit of the capacitor C ₂ and the reactor L ₂ (jX _L2 -jX _C2 ). The impedance Z ₂ of the second impedance element 3B is selected such that Z ₂ = jX _L2 -jX _C2 = 0 or Z ₂ ≈0 with respect to the fundamental wave of the power system 1.

The harmonic current detection circuit 4 includes current transformers 7 and 8, an adder 9, and a fundamental wave removal filter (notch filter) 10. The load current i _L is taken out by the current transformer 7 and the current i _C1 is output. Take out by current transformer 8 and filter both by fundamental wave removal filters 10A, 10B
The summation Δi of the harmonic current i _Lh in the load current i _L and the harmonic current i _{ch in} the current i _C1 is output by the addition by the adder 9 passed through.

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

As shown in FIG. 5, the hysteresis comparator 5 changes its output level from a low level to a high level when the output Δi of the harmonic current detection circuit 4 exceeds the upper threshold value I _O / 2, and the lower side. The output level changes from high level to low level when it falls below the threshold −I _O / 2.

By the output of this hysteresis comparator 5, the sixth
Each switching element Q ₁ ~ of the voltage source inverter 6 shown in the figure
By turning Q _{6 on} and off, a harmonic current i _ch (having a polarity opposite to i _Lh ) for compensating the harmonic current i _lh flowing in the harmonic generating load 2 is supplied to the injection circuit 3.

FIG. 6 shows a circuit diagram of the three-phase voltage source inverter 6. In the figure, Q ₁ and Q ₂ are A-phase switching elements, Q ₃ and Q ₄ are B-phase switching elements, and Q ₅ and Q ₆
Is a C-phase switching element, E is a DC power supply, D _{1 to} D ₆ are diodes connected in reverse parallel to switching elements Q _{1 to} Q ₆ , 11
Is a harmonic transformer.

FIG. 7 shows an enlarged version of the harmonic current i _ch , and the operation will be described in more detail based on this figure.

In the case of i _ch <−i _Lh , when Δi = − (1/2) I _O is reached like the point, the output of the hysteresis comparator 5 becomes low level, and for example, the switching element of the lower arm of the A phase
Turn on Q ₂ .

As a result, the harmonic current i _ch increases and i _ch > −i _Lh . After this, when Δi = (1/2) I _O is reached as shown by the point, the output of the hysteresis comparator 5 becomes high level, and for example, the switching element of the upper arm of phase A
Turn on Q ₁ . As a result, the harmonic current i _ch decreases, i _ch <−i _Lh , and so on. Therefore, the harmonic current
i _ch is the harmonic current −i while changing zigzag with the width of I _O.
It will change along _Lh .

FIG. 8 is a waveform diagram of each part in FIG. 4 when the load amount of the harmonic generation load 2 transiently increases. Same figure (A)
Is the voltage V _A at the power receiving end, (B) is the load current i _L , (C) is the harmonic current i _Lh in the load current i _L , and (D) is the same.
Shows the current i _C1 of the capacitor C ₁ , FIG. 6 (E) shows the output current i _INV of the voltage source inverter 6, and FIG. 6 (F) shows the system current i _S.

The same applies to the B phase and the C phase.

Problems to be Solved by the Invention In the above-described active filter, when the load current i _L includes harmonics having a frequency near the fundamental wave of the power system 1 or the fundamental wave removal in the harmonic current detection circuit 4 is insufficient. , The voltage source inverter 6 also outputs the fundamental wave voltage, and this fundamental wave voltage is applied to the injection circuit 3, but the series circuit of the reactor L ₂ and the capacitor C ₂ of the injection circuit 3 is close to the fundamental wave of the power system 1. Since it is set so as to resonate at the frequency, the impedance element 3B short-circuits the output end of the voltage source inverter 6 with respect to the fundamental wave near frequency, and the voltage source inverter 6 shifts to the impedance element 3B from the fundamental wave near frequency. A considerable amount of current will flow, that is, the output current i _INV of the voltage source inverter 6 will contain many fundamental wave components, and as a result, the voltage source inverter 6 I had no choice but to increase the capacity.

In particular, when the load current i _L of the harmonic generation load 2 transiently increases as shown in FIG. 8 (B), the fundamental wave elimination filter 10A is driven by the response delay of several cycles of the fundamental wave elimination filter 10A. The fundamental wave passes, and the harmonic current i _Lh (FIG. 8 (C)) contains the fundamental wave component in the transient change section of the load current i _L (FIG. 8 (B)) and in the section of several cycles immediately after that. As a result, the output current of the voltage source inverter 6
Since i _INV (Fig. 8 (E)) contains an extremely large amount of fundamental wave components, as a result, the capacity of the voltage source inverter 6 had to be made extremely large.

The present invention has been made in view of the above problems, and it is possible to reduce the current of the frequency near the fundamental wave flowing out from the voltage source inverter to the injection circuit not only during the steady state of the harmonic generation load but also during the transient change. The object is to provide an active filter that can be used.

Means for Solving the Problems The active filter according to the present invention is installed between a power system and a harmonic generation load fed from the power system, and harmonics flowing out from the harmonic generation load to the power system. An active filter for injecting a harmonic current for canceling a current into the power system, the injection circuit including a series circuit of first and second impedance elements connected to the power system, and the harmonic generation A harmonic current detection circuit that detects the sum of the harmonic current that flows from the load to the power system and the harmonic current that flows from the injection circuit to the power system, and a negative predetermined value as the lower threshold value. A hysteresis comparator having a positive predetermined value as an upper threshold value and an output of the harmonic current detection circuit as an input, and first and second impedances of the injection circuit No output voltage is applied to the connection point of the element When the sum of the harmonic current of the harmonic generating load and the harmonic current of the injection circuit exceeds the predetermined value of both polarities according to the output of the hysteresis comparator. 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, and a current that flows from the current that flows to the second impedance element to the injection circuit in the absence of the harmonic generation load. Alternatively, a subtractor that subtracts a current flowing through the first impedance element, a first weighting function circuit that has an input / output characteristic in which a slope increases as the input increases, and an output of the subtractor is input, and an inverter. A second weighting function circuit having an input / output characteristic in which an electric current is detected, and when this value exceeds a certain value, the gradient sharply increases; Is obtained by the output of the current detection circuit to the structure and a calculator for subtracting the output of said first and second weighting function circuit when inputting to the hysteresis comparator.

Action As described above, the active filter of the present invention subtracts the current flowing through the injection circuit or the current flowing through the first impedance element with the subtracter from the current flowing through the second impedance element in the state where there is no harmonic generation load, The output of the subtractor is passed through the first weighting function circuit, the inverter current is passed through the second weighting function circuit, and the output of the harmonic current detection circuit is input to the hysteresis comparator. Since the output of the function circuit is subtracted, the frequency component near the fundamental wave contained in the output of the harmonic current detection circuit is reduced, and if the inverter becomes overcurrent due to the change in load current, that current Can be restricted.

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 and 2. 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, and flows out from the harmonic generation load 2 to the power system 1. An active filter for injecting a harmonic current for canceling a harmonic current into the power system 1 and comprising a series circuit of first and second impedance elements 3A, 3B connected to the power system 1. An injection circuit 3 and a harmonic current detection circuit 4'for detecting 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 negative predetermined value as a lower threshold value and a positive predetermined value as an upper threshold value and an output of the harmonic current detection circuit 4'as an input, and the injection circuit 3 The output voltage is not applied to the connection point between the first impedance element 3A and the second impedance element 3B. A voltage source inverter 6 for turning on / off a switching element in a direction in which the sum of the both harmonic currents approaches zero when the sum of the two exceeds a predetermined value of both polarities;
The current i _L2 flowing through the impedance element 3B of the injection circuit 3 (second
Of the impedance element 3B) for subtracting the current i _C0 , and the first weighting function circuit 15 to which the output of the subtractor 14 is input, which has an input / output characteristic in which the slope increases as the input increases. And a current transformer 17 for detecting the inverter current, and a second weighting function to which the output of the current transformer 17 is inputted, which has an input / output characteristic in which the gradient sharply increases when the input exceeds a certain value. A circuit 18 and a calculator 13 for subtracting the outputs Δi ₁ , Δi ₂ of the first and second weighting function circuits 15, 18 when the output of the harmonic current detection circuit 4'is input to the hysteresis comparator 5. It is configured to include.

The harmonic current detection circuit 4'comprises current transformers 7 and 8, a fundamental wave removal filter 10A, an adder 9 and an arithmetic unit 13. Although the configuration is slightly different from the circuit of FIG. 5, it has the same function. It has.

Next, it will be described in detail that the inverter current can be reduced by the current transformers 16 and 17, the subtractor 14, the weighting function circuits 15 and 18, and the arithmetic circuit 13.

The current i _L2 of the second impedance element 3B appears due to the output of the voltage source inverter 6 and the voltage of the power system 1 overlapping, so it is necessary to remove the effect of the voltage on the power system 1 side. , Therefore, the current i _L0 in the state without the harmonic generation load 2 is subtracted by the subtractor 14,
Further, it is passed through the weight function circuit 15. Therefore, the fundamental wave component included in the inverter current i _INV in the steady state is significantly reduced. In addition, the inverter current i _INV
It is detected by 17 and further passed through the weighting function circuit 18.The weighting function circuit 18 is designed to rise steeply when the input exceeds a certain value, so if the load current rises steeply, It is possible to limit the flow of a large basic current in the inverter current i _INV due to such transient fluctuations.

FIG. 2 is a waveform diagram of each part of FIG. 1, where (A) shows the system voltage V _S , (B) shows the load current i _L , and (C) shows the harmonic current of the load. i _Lh , (D) shows the current i _C1 of the capacitor C ₁ , (E) shows the output current i _INV of the voltage source inverter 6, and (F) shows the system current i _S. .

As is clear from this figure, the output current i of the voltage source inverter 6 is changed by the outputs Δi ₁ and Δi ₂ of the weight function circuits 15 and 18.
_INV (Fig. 2 (E)) contains almost no fundamental wave component in the steady state, and even when the load current i _L changes transiently, the output current of the voltage source inverter 6 is limited and the inverter current is Significantly reduced.

Although the second impedance element 3B is a series circuit of the capacitor C ₂ and the reactor L _{2 in} the above embodiment, as shown in FIG. 3, the second impedance element 3B is only the reactor L ₂ . In this case, the same effect can be obtained by applying the present invention. This prevents the fundamental wave component of the power system 1 from being applied to the voltage source inverter 6 in the injection circuit in which the first impedance element 3A is composed of the capacitor C ₁ and the second impedance element 3B is composed of the reactor L _2. In order to do so, on the basis of the fundamental wave, the impedance of the reactor L ₂ with respect to the impedance of the capacitor C ₁ ,
This is because it is set to 0.06pu to 0.15pu.

In addition, the current i _C1 is passed through the fundamental wave removal filter 10A and the current i
The fundamental wave component in _C1 is removed, but instead of this, the current
The fundamental wave may be removed from the current i _C1 by subtracting the current i _L2 (consisting only of the fundamental wave) flowing through the injection circuit 3 from i _{C1 in the} absence of the harmonic generation load 2.

EFFECTS OF THE INVENTION According to the active filter of the present invention, it is possible to limit the fundamental wave component of the output waveform of the voltage source inverter to a certain limit even at the time of harmonic generation negative transient change, and reduce the capacity of the voltage source inverter. it can.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing the structure of an embodiment of the present invention, and FIG.
FIG. 3 is a waveform diagram of each part of FIG. 1, FIG. 3 is a circuit diagram of a modified example,
FIG. 4 is a circuit diagram of an active filter which is the basis of the present invention, FIG. 5 is an operation characteristic diagram of a hysteresis comparator, FIG. 6 is a circuit diagram of a voltage type inverter, and FIG. 7 is an enlarged waveform for explaining the operation. FIG. 8 and FIG. 8 are waveform diagrams of the respective parts in FIG. 1 ... Power system, 2 ... Harmonic load, 3 ... Injection circuit, 3A, 3B ... Impedance element, 4 '... Harmonic current detection circuit, 5 ... Hysteresis comparator, 6 ...
Voltage source inverter, 13 ... Calculator, 14 ... Subtractor, 15,1
8 …… Weight function circuit

Claims (1)

[Claims] 1. A harmonic current for canceling a harmonic current flowing from the harmonic generating load to the power system, the harmonic current being installed between the power system and a harmonic generating load fed from the power system. An active filter for injecting into the power system, the injection circuit including a series circuit of first and second impedance elements connected to the power system, and a harmonic current flowing from the harmonic generating load into the power system. And a harmonic current detection circuit for detecting the sum of the harmonic current flowing from the injection circuit to the power system, and a negative predetermined value as a lower threshold value and a positive predetermined value as an upper threshold value, The output voltage of the harmonic current detection circuit is input to the hysteresis comparator, and the output voltage is applied to the connection point of the first and second impedance elements of the injection circuit. A direction in which the sum of the harmonic currents of the harmonic generating load and the harmonic current of the injection circuit exceeds a predetermined value of both polarities in accordance with the output of the sterisis comparator, and the sum of the harmonic currents approaches zero. A voltage source inverter for turning on and off a switching element, and the second
A subtractor that subtracts the current that flows in the injection circuit in the absence of the harmonic generation load from the current that flows in the impedance element, and the output of the subtractor that has an input / output characteristic in which the slope increases as the input increases. The input first weighting function circuit, the second weighting function circuit which detects the inverter current and has an input / output characteristic in which the gradient becomes steep when the value exceeds a certain value, and the harmonic current detection circuit An active filter comprising: an arithmetic unit that subtracts the outputs of the first and second weighting function circuits when the output is input to the hysteresis comparator.