JP3318348B2 - Control circuit of active filter with passive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive filter in which a reactor and a capacitor connected in parallel to a load are connected in series to a power supply system, and a passive combined active in which a power converter constituted by a switching element is connected in series. The present invention relates to an improvement in a filter control circuit.

[0002]

2. Description of the Related Art A passive combined active filter, in which a passive filter formed of a series circuit of a reactor and a capacitor and a power converter formed of a switching element are connected in series, is known as the National Institute of Electrical Engineers of Japan in 1989.
89 is well known as described in "Harmonic Suppression Device Based on New Principle-Series Connection System of PWM Converter and LC Filter".

FIG. 3 is a block diagram of a main circuit of a passive active filter, and FIG. 4 is a block diagram of a control circuit thereof. In FIG. 3, an LC filter 3 is connected in parallel with the load 2 on a line that supplies power from a three-phase AC system power supply 1 to a load 2 such as a thyristor Leonard device.
The C filter 3 includes a fifth harmonic tuning filter including a series circuit of a capacitor 31 and a reactor 32, a seventh harmonic tuning filter including a series circuit of a capacitor 33 and a reactor 34, a parallel circuit of a resistor 35 and a reactor 36, and a capacitor. 37
And a higher-order filter composed of a series circuit.

The other end of each phase of the LC filter 3 is (YY)
The transformer 7 is connected to the primary side, the other end of the primary side of the transformer 7 is star-connected, one end of the secondary side is also star-connected, and the other end is connected to the AC reactor 4 in each phase. Are connected in series, and a capacitor 8 is connected to each phase connection point between the secondary side of the transformer 7 and the AC reactor 4.

[0005] On the anti-transformer side of the AC reactor 4, PWM is provided.
A converter 5 is connected, and a DC capacitor 6 is connected to a DC terminal side of the PWM converter 5, and a single-phase diode rectifier circuit 9 is connected to the DC capacitor 6 in parallel. The PWM converter 5 is a switching element that can be turned on and off.
Each form a three-phase bridge circuit connected in parallel to diode D1~D6 in S1 to S6, which is the switching element S1 to S6 by the trigger signal V _G generated by the control circuit shown in FIG. 4
Are turned on and off to perform harmonic suppression. The AC reactor 4 and the capacitor 8 are LC filters for suppressing switching ripple, and may not be provided when the switching frequency of the PWM converter 5 is high.

[0006] Such a harmonic suppression circuit is an LC filter 3
Part, transformer 7, AC reactor 4, capacitor 8,
The main components are a PWM converter 5, a DC capacitor 6, a single-phase diode rectifier circuit 9, and a control circuit shown in FIG.

When the LC filter 3 is operated as a phase-advancing capacitor and the PWM converter 5 is operated as zero impedance with respect to the fundamental wave, no fundamental wave voltage is applied to the PWM converter 5.

[0008] For harmonics, the PWM converter 5
Is to generate a harmonic voltage so as to block the harmonic component of the power supply current, and can suppress the anti-resonance which is a problem of the LC filter 3 and the inflow of the harmonic current from the upper system.

For this reason, the concept of real power and imaginary power is introduced by performing three-phase to two-phase conversion, and this will be described in detail below using mathematical expressions.

First, three-phase power supply currents I _SU , IS _SV , I _SW and power supply voltages V _U , V _V , V are expressed by the following equations (1) to (3).
_W is converted into two-phase voltages Vα and Vβ and currents Isα and Isβ.

(Equation 1) Here, [C] is a three-phase to two-phase conversion matrix.

From the two-phase voltage and current obtained by the equations (1) to (3), the instantaneous real power P is calculated by the following equation (4).
And the imaginary power Q are obtained.

(Equation 2)

The powers P and Q correspond to the conventional active power and reactive power, respectively. The instantaneous real power P and the imaginary power Q are expressed by the DC component P as shown in the following equations (5) to (6). It is decomposed into _DC and Q _DC and AC components P _AC and Q _AC .

P = P _DC + P _AC (5) Q = Q _DC + Q _AC (6) Here, the fundamental wave component of the two-phase power supply current Isα, Isβ is a DC component P
_DC and Q _DC , and the harmonic components are converted into _{AC components} P _AC and Q _AC . Actually, the separation of the DC component and the AC component is performed by a high-pass filter.

In FIG. 4, reference numeral 101 denotes a power calculation circuit;
Is a high-pass filter, 103 is a current command value calculation circuit, 104
Is an amplifier circuit, 105 is a triangular wave generation circuit, and 106 is a voltage suppression circuit.

The power calculation circuit 101 includes: a system voltage V _U ,
From the detected values of V _V , V _W and the power supply currents I _SU , I _SV , I _SW ,
The instantaneous real power P and the instantaneous imaginary power Q are calculated according to (1) to (4) and output to the high-pass filter 102. The high-pass filter 102 removes the DC component, and the AC component P _AC of the instantaneous real power P
And the AC component Q _AC of the instantaneous imaginary power Q is sent to the current command value calculation circuit 103 as the real power command signal P ^* and the imaginary power command signal Q ^* , respectively.

P ^* = P _AC (7) Q ^* = Q _AC (8)

The current command value calculation circuit 103 calculates the actual power command signal P ^* and the imaginary power command signal Q ^* and the system voltages V _U , V _V ,
It receives the V _W, to obtain a two-phase current command signal in accordance with equation (1) and the following equation (9) to (11), further subjected to two-phase-three phase conversion in accordance with Equation (10), three-phase current Command signal _IU ^* , I
_V ^* and _IW ^* are generated and sent to the amplifier circuit 104.

(Equation 5)

The amplifying circuit 104 includes current command signals I _U ^* , I _V
^* , I _W ^*, and multiply the gain by K to obtain the voltage command signal V _U
^* , V _V ^* , V _W ^* are generated and output to the voltage suppression circuit 106.

The voltage suppression circuit 106 includes a triangular wave carrier voltage S output from the triangular wave generation circuit 105 and a voltage command signal V
_U ^*, _V V ^*, enter and V _W ^*, voltage command signal V _U ^*
If ≧ triangle wave carrier voltage S, switching element S1 is turned on and switching element S6 is turned off, and voltage command signal V
_U ^* <If triangular wave carrier voltage S, switching element
S1 is turned off and switching element S6 is turned on.

Further, if the voltage command signals V _V ^* ≧ triangular carrier voltage S, and generates a trigger signal V _G so as to turn off the switching element S2 turns on the switching element S3. This trigger signal V _G, the switching element S1~S6 is turned on, is turned off, the voltage instantaneous value of each phase of the PWM converter 5 is controlled.

[0019]

When such a passive-use active filter is constructed by newly connecting a PWM converter 5 to an existing LC filter 3, a load 2
When the higher harmonic current increases and the current flowing through the LC filter 3 and the PWM converter 5 increases, the PWM converter 5 can be configured as a large-capacity converter because it is newly designed. Since the current rating of the LC filter 3 is limited, there is a problem that it is impossible to cope with an increase in the harmonic current of the load 2. The present invention has been made in view of the above points.

[0020]

SUMMARY OF THE INVENTION A control circuit for a passive-use active filter according to the present invention comprises a passive-use active filter in which an LC filter and a PWM converter connected in parallel to load equipment and a PWM converter are connected in series to a power supply system. In the control circuit, the control circuit detects a power supply current obtained by vectorially adding the load current and the LC filter current to calculate a harmonic current command, and multiplies the harmonic current command by a gain to obtain a harmonic. A means for outputting a voltage command; a means for calculating an effective value of a harmonic component of a power supply current, and outputting a fundamental voltage command such as reducing a fundamental wave of an LC filter when the effective value becomes a certain value or more; The harmonic voltage command and the fundamental wave voltage command are added and compared with a triangular wave signal, and PW
Means for outputting a switching command for the M converter.

[0021]

When the harmonic current included in the power supply current exceeds a certain value, that is, when the harmonic current flowing through the LC filter increases and the current flowing through the LC filter exceeds the rated value, the PWM converter operates with the power supply current. The harmonic current included in the LC filter is suppressed, and the harmonic voltage flowing through the LC filter is reduced, so that the fundamental voltage is generated in a vector manner. A large amount of harmonic current can flow through the filter.

[0022]

FIG. 1 is a block diagram showing an embodiment of a control circuit for a passive-use active filter to which the present invention is applied. Reference numeral 107 denotes an effective value calculation circuit, reference numeral 108 denotes an addition circuit, and the same as FIG. Reference numerals indicate the same components.

In FIG. 1, the power calculation circuit 101 and the high-pass filter 102 receive the power supply currents I _SU , I _SV , and I _SW of each phase and the power supply voltages V _U , V _V , and V _{W of} each phase, and obtain an equation ( 1) ~
According to (8), the AC component Q _AC of the instantaneous imaginary power Q is sent out as an instantaneous imaginary power command signal Q ^* to the current command value calculation circuit 103 and the effective value calculation circuit 107, and the AC component P _AC of the instantaneous real power P is transmitted. Is sent to the addition circuit 108 and the effective value calculation circuit 107.

The effective value calculating circuit 107 the effective value P _R calculated by Equation (12) from the AC component P _AC of the AC component Q _AC and instantaneous real power P of the instantaneous imaginary power Q,

[6] P _R = the ^{_{(P AC 2 + Q AC 2}} ) 1/2 (12) exceeds a certain value the effective value P _R, the fundamental wave power command P _F having values as shown in FIG. 2 Is sent to the adding circuit 108.

The adder circuit 108, the AC component and P _AC of the instantaneous real power P, the by adding the fundamental wave power command P _F, sends a real power command signal P ^* to the current command value calculating circuit 103.

From the instantaneous imaginary power command signal Q ^* , the actual power command signal P ^*, and the three-phase power supply voltages V _U , V _V , V _W , the current command value calculation circuit 103 calculates the equations (9) to (11). , The three-phase current command signals _IU ^* , _IV ^* , and _IW ^* are generated and sent to the amplifier circuit 104.

The amplifying circuit 104 includes current command signals I _U ^* , I _U ^*
_V ^* and _IW ^* are multiplied by a gain K and voltage command signals _VU ^* and VU ^*
_V ^* and _VW ^* are generated and sent to the voltage control circuit 106.

The voltage control circuit 106 includes a triangular wave generation circuit 105
Output carrier voltage S and voltage command signal V
_U ^*, V _V ^*, as inputs and V _W ^*, for example, if the voltage command signal V _U ^* ≧ triangular carrier voltage S, turns off the switching element (S6) by turning on the switching element S1, the voltage command signal V _U ^* <If the triangular wave carrier voltage S, so as to turn on the switching element (S6) and turns off the switching element S1, and generates a trigger signal V _G.

The switching element S1 by the trigger signal V _G
S6 are alternately turned on and off, and the instantaneous voltage of each phase of the PWM conversion carrier 5 is controlled.

The PWM converter 5 controlled in this way is:
When the harmonic current included in the power supply current is small, that is, L
When the harmonic current flowing through the C filter 3 is small, a harmonic voltage that suppresses the harmonic current flowing through the power supply is generated. When the harmonic current included in the power supply current exceeds a certain value,
A fundamental voltage such as reducing the fundamental current flowing in the LC filter and a harmonic voltage that suppresses the harmonic current flowing in the power supply are generated in a vector manner, and are generated in the LC filter 3 in excess of the rated current of the LC filter 3. A current obtained by adding the fundamental current and the harmonic current in a vector manner can be prevented from flowing. Thus, more harmonic currents can be suppressed by the existing LC filter 3.

In the above description, the harmonic current flowing in the LC filter is indirectly converted from the harmonic current included in the power supply current. However, the currents I _FU , _IF V, I _FW flowing directly in the LC filter or the load currents I _LU , I _LU , A harmonic current is detected from I _LV and I _LW , a fundamental wave voltage is similarly generated by the PWM converter 5, a fundamental wave current flowing through the LC filter 3 is reduced, and a harmonic current flowing through the LC filter 3 is increased. It is also possible to control so that

[0032]

As is apparent from the above description of the operation, according to the present invention, when the harmonic component of the power supply current exceeds a certain value, it becomes equivalent to an increase in the harmonic current flowing through the LC filter. Therefore, the fundamental current flowing in the LC filter can be reduced, and the harmonic current flowing in the LC filter can be increased by the reduced amount. It is possible to provide a passive combined active filter capable of performing wave compensation.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a control circuit for a passive-use active filter to which the present invention is applied.

FIG. 2 is a graph showing a fundamental power command to be generated for an instantaneous harmonic effective power used in the present invention.

FIG. 3 is a main circuit configuration diagram for explaining a passive-use active filter.

FIG. 4 is a block diagram of an example of a conventional control circuit of an active filter with a pattern.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Three-phase alternating current system power supply 2 Load such as thyristor leonard device 3 LC filter 4 AC reactor 5 PWM converter 6 DC capacitor 7 (Y-Y) transformer 8 Capacitor 9 Single-phase diode rectifier circuit 31, 33, 37 Capacitor 32, 34, 36 Reactor 35 Resistance 101 Power calculation circuit 102 High-pass filter 103 Current command value calculation circuit 104 Amplification circuit 105 Triangular wave generation circuit 106 Voltage suppression circuit 107 Effective value calculation circuit 108 Addition circuit

Claims (1)

(57) [Claims] An LC connected to a power system in parallel with a load facility.
A control circuit for a passive-use active filter comprising a filter and a PWM converter connected in series, wherein the control circuit detects a power supply current and calculates a harmonic current command, and multiplies the harmonic current command by a gain. Means for outputting a harmonic voltage command, and calculating the effective value of the harmonic component of the power supply current, and outputting a fundamental wave voltage command such as reducing the fundamental wave of the LC filter when the effective value exceeds a certain value. And a means for adding the harmonic voltage command and the fundamental voltage command, comparing the result with a triangular signal, and outputting a switching command for a PWM converter. .