JPH07107656B2 - Reactive power regulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reactive power adjusting device for a three-phase AC circuit for preventing voltage flickering, improving power factor, reducing harmonic components, and the like. .

[Conventional technology]

It is well known to connect a lead current supply circuit composed of a capacitor, or a parallel circuit of a capacitor and a reactor, between each of the three-phase AC power supply lines in order to prevent flicker and / or improve the power factor. Further, Japanese Patent Application Laid-Open No. 56-159936 (Japanese Patent Application No. 55-61600) discloses that an instantaneous active current and an instantaneous reactive current are obtained and the power failure compensation circuit is controlled based on the obtained values. Further, in Japanese Patent Application No. 60-137499, the applicant of the present application has proposed a method for easily achieving power factor improvement of a three-phase unbalanced load based on line current detection. A method for controlling the reactive component using a three-phase PWM converter composed of transistors has already been proposed.

[Problems to be solved by the invention]

However, the above-mentioned Japanese Patent Application No. 60-137499 does not disclose a method for removing harmonic components. Further, the method of using the transistor three-phase PWM converter has a drawback that it is difficult to increase the capacity.

Therefore, an object of the present invention is to provide a device capable of easily achieving a medium or large capacity reactive power adjustment.

[Means for solving problems]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention for achieving the above object will be described with reference to the reference numerals of the drawings showing an embodiment. A capacitor or a reactor is connected to a three-phase AC power supply line through a switch to supply a fundamental component of a reactive current. And three-phase reactive current fundamental wave component supply circuits (3a) (3b) (3) configured to adjust the magnitude of the fundamental wave component of the reactive current.
c), and a three-phase pulse width modulation conversion circuit (62) connected to the three-phase AC power supply line and configured to be able to supply a harmonic component of the reactive current by on / off control of a semiconductor switch. And a line current detection for detecting the line currents (I _U , I _V , I _W ) of the first phase, the second phase and the third phase of the three-phase load (2) connected to the three-phase AC power supply line. Bowl (4a) (4
b) Based on (4c) and the line currents (I _U , I _V , I _W ) of the first, second and third phases, the first phase, the second phase and the third phase.
The instantaneous reactive currents (I _Uq , I _Vq , I _Wq ) of the phase are obtained, and the first, second and third instantaneous reactive currents (I _Uq , I _Vq , I _Wq ) are obtained.
Of the fundamental wave component (a, b, c) or a value proportional thereto, and the effective value (a, b, c) of the fundamental wave component of the instantaneous reactive current of each phase represented by the line current is obtained. Alternatively, a value proportional to this is converted into a phase current (x, y, z), and the phase current (x, y
y, z) of the reactive current fundamental wave component supply circuits (3a) (3b) (3c) so as to compensate all or a part of the reactive current fundamental wave component of the three-phase load (2). The harmonic components (a2, b2, c2) of the first, second and third instantaneous reactive currents (I _Uq , I _Vq , I _Wq ) are _calculated by controlling the switch, and the harmonic components (a2 , B2, c2), and a reactive power adjusting device comprising arithmetic and control means for controlling the three-phase pulse width modulation conversion circuit (62) so as to remove this harmonic component (a2, b2, c2). Related to.

The calculation and control means are, for example, reference numeral 5 in FIG.
It is a circuit shown by 6, 7, 8, 60, 61, a microcomputer, or the like.

[Action]

According to the above invention, the fundamental wave component and the harmonic wave component are substantially separated and compensated based on the detection of the line current. Since the harmonic component has a higher frequency than the fundamental component, it is compensated by the pulse width modulation (PWM) conversion circuit (62). At this time, if necessary, part of the fundamental wave component can be converted to a PWM converter (6
You may compensate in 2). The PWM conversion circuit (62) has a function of compensating for the fundamental wave component, but if it is configured to correct all the fundamental wave components here, the semiconductor switch becomes unavailable in the case of a large capacity, or High cost. Therefore, in the present invention, the fundamental wave component supply circuit (3a) of the reactive current is used.
(3b) (3c) supplies all or most of the fundamental component of the reactive current. This makes it possible to easily and satisfactorily achieve suppression of harmonic current, prevention of flickering, and power factor improvement.

[First Embodiment] Next, a reactive power adjusting method of a three-phase AC circuit according to a first embodiment of the present invention will be described with reference to the drawings.

(Explanation of FIG. 1) In FIG. 1, three power supply lines (1u, 1v, 1w) for the first phase (U phase), the second phase (V phase), and the third phase (W phase) are Ai Heihei load (2) is connected. This three-phase unbalanced load (2) is, for example, a single-phase load (2a) (2b) (2c) of a welding machine or the like having almost the same power factor connected between the lines,
The loads (2a) (2b) (2c) between the lines are not fixed loads, but their magnitudes change. Therefore, if the power factor is not compensated, the fluctuation of the load (2) causes the voltage fluctuation (flicker) of the power line (1u) (1v) (1w),
And the power factor gets worse. (3a) (3b) (3c) are the fundamental wave component supply circuits of the forward reactive current for power factor adjustment, which are connected to the three-phase power supply lines (1u) (1v) (1w). The fundamental component supply circuit reactive current (3a) (3b) (3c ) is a plurality of capacitors C _1a -C _1n between each line, C _2a ~C _2n, C _3a
~ C _3n as thyristors S _{1a to} S _1n as AC switches,
It is configured to be selectively connected via S _{2a to} S _2n and S _{3a to} S _3n . Reactive current fundamental wave component supply circuit (3
a) By adjusting the forward currents supplied in (3b) and (3c) according to the fluctuation of the load (2), the power factor of the three-phase AC circuit is compensated and the voltage fluctuation (flicker) is also prevented. In addition,
In this embodiment, since four capacitors having a capacitance ratio of 1: 2: 4: 8 are provided as the capacitors C _{1a to} C _1n ,
With a combination of these four capacitors, a capacity of 15 stages can be obtained. The capacitors C _{2a to} C _2n and C _{3a to} C _3n have the same structure.

In this embodiment, since the loads (2a) (2b) (2c) between the lines as the three-phase load (2) are composed of a large number of loads, it is difficult to directly detect the phase current. Therefore, in order to detect the line currents I _U , I _V , and I _W , a current detector (4a) including a current transformer is provided on each power supply line (1u) (1v) (1w).
(4b) and (4c) are connected respectively.

(5) is a first arithmetic circuit for obtaining the instantaneous reactive current component, which outputs the instantaneous reactive currents I _Uq , I _Vq , I _Wq of the respective phases corresponding to the line currents I _U , _IV , I _W of the respective phases. To do. The specific configuration of the arithmetic circuit (5) will be described later.

(6) is a fundamental wave component extraction circuit, which is the effective value of the fundamental wave component of the instantaneous reactive currents I _Uq , I _Vq , and I _Wq obtained from the first arithmetic circuit (5), that is, the fundamental wave component of the instantaneous reactive current. The line currents a, b, and c (effective value) are output as direct current, and the fundamental wave component is output as alternating current.

(7) is a second arithmetic circuit for converting a line current into a phase current. That is, it is a circuit for converting the line currents a, b, c (effective value) of each phase of the fundamental wave component of the instantaneous reactive current into the phase currents x, y, z (effective value) of each phase. This second arithmetic circuit (7)
Will be explained in detail later.

(8) is a gate control circuit, and a second arithmetic circuit (7)
Based on the phase currents x, y, and z of each phase of the fundamental wave component of the instantaneous reactive current obtained from, the load (2) and the fundamental wave component supply circuit (3a) (3b) (3c) of the reactive current are combined. It is a circuit that generates a gate signal for controlling the thyristors S _{1a to} S _3n so that the power factor becomes 1.

(60) is a harmonic component extraction circuit, which is newly provided according to the present invention, and is connected to the first arithmetic circuit (5) and the fundamental wave component extraction circuit (6). This harmonic component extraction circuit (60) subtracts the fundamental wave components a ₁ , b ₁ and c ₁ from the instantaneous reactive currents I _Uq , I _Vq and I _{Wq in} each phase to obtain the harmonic components of each phase. It outputs a ₂ , b ₂ , and c ₂ .

(61) is a control signal forming circuit, which is a current detector (63a) (63b) for detecting the current supplied by the harmonic component extraction circuit (60) and the harmonic conversion compensating PWM conversion circuit (62). )
It is connected to the (63c), to generate a transistor Q ₁ to Q _{signals 6} to the on-off control of the PWM converter (62).

Harmonic compensation current supply for the PWM converter (62) includes transistors Q ₁ to Q ₆ as a self-turn-off semiconductor switch elements which are Buritsuji connected, each pair of transistors Q ₁ to Q ₆
AC power supply line (1u, 1v, 1w) is connected to the connection point of, and the reactor (64) serves as a load for the transistors Q _{1 to} Q ₆ of each pair.
Are connected. Bases of the transistors Q ₁ to Q ₆ is connected to the control signal forming circuit (61), each transistor Q
₁ to Q ₆ is driven pulse width modulation (PWM), and supplies a controlled harmonic compensation current. The capacitors C ₁₁ , C ₁₂ , and C ₁₃ are connected between the input lines of the PWM conversion circuit (62).

(Explanation of Instantaneous Reactive Current and FIG. 2) Instantaneous reactive current is described in the above-mentioned JP-A-56-159936.

The three-phase AC power supply voltages V _U , V _V , and V _W are represented by the following equations, assuming that they are balanced three-phase AC voltages having a maximum value V _m and an angular frequency ω.

Now, when the three-phase load currents I _U , I _V , and I _W are coordinate-converted by a conversion matrix that rotates by ω, the currents are represented by I _p and I _q ,
When there is no zero-phase current, the following equation is generally established.

Further, if the three-phase currents I _U , I _V , and I _W are represented by I _p and I _q , the following equation is obtained.

Here, since only the reactive current I _q is calculated, (2)
When I _p = 0 in the equation (3), the following equation is obtained.

Reactive current components I _Uq , I _Vq , I of load currents I _U , I _V , I _W
Wq is expressed by the following equation from equations (4) and (5).

FIG. 2 is a block diagram showing the first arithmetic circuit (5) for calculating the equation (7) in matrix display. (9u)
(9v) and (9w) are lines that give line currents I _U , I _V , and I _W ,
(10) is a line that gives information about ωt, (11) is sinωt
Generating circuit, (12) is a sin (ωt-2π / 3) generating circuit, (1
3) is a sin (ωt-4π / 3) generation circuit, (14) (15) (1
6) is a multiplier of the line currents I _U , I _V , I _W and the outputs of the circuits (11) (12) (13), and (17) is three multipliers (14) (15)
(16) output adder, (18) (19) (20) multipliers between the adder (17) output and the circuits (11) (12) (13) output, K ₁ , K ₂ , K ₃ is a coefficient unit of 2/3, from which instantaneous reactive currents I _Uq , I _Vq , and I _Wq are output. For example, the first
The instantaneous reactive current I _Uq of the phase is obtained based on the following equation.

The second- and third-phase instantaneous reactive currents I _Vq and I _Wq are similarly calculated. Since these instantaneous reactive currents I _Uq , I _Vq , and I _Wq are determined based on the line currents I _U , _IV , and I _W , they are instantaneous reactive current components of the line current. The instantaneous reactive currents I _Uq , I _Vq , and I _Wq are applied to the effective value of the fundamental wave component, that is, the line currents a, b, c (of the instantaneous reactive current component) by the fundamental wave component extraction circuit (6) in FIG. Rms value).

(Explanation of Fundamental Wave Component Extraction Circuit) The fundamental wave component extraction circuit (6) is a low pass filter for fundamental wave component extraction connected to the first arithmetic circuit (5) of FIG. 1 as is clear from FIG. (65) and RMS converter (6
6) consists of and. The effective value converter (66) is, for example, an AD536A RMS / DC converter of Analog Devices Co., Ltd., and sends out a current voltage corresponding to the effective value of alternating current. Although FIG. 3 shows only the circuit for the first phase, the second phase and the third phase are also constructed in exactly the same manner, so that the fundamental wave component extraction circuit (6) The effective value of the fundamental wave component of the phase, that is, the line currents a, b, c (DC) of the effective value display are output, and the fundamental wave components a ₁ , b ₁ , c ₁ of the reactive current are output from the low-pass filter (65). Output by alternating current.

(Description of Line Current-Phase Current Conversion) Next, referring to FIGS. 4 and 5, the line currents (instantaneous reactive currents) a, b, and c are converted into phase currents (instantaneous reactive currents) x, y, and z. The conversion method will be described.

Second operation circuit (7) for converting line current to phase current in FIG.
Next, based on the equations (8), (9) and (10), the line current a,
It is configured to convert b, c into phase currents x, y, z.

However, A is shown by the following equation.

It will be described that the phase currents x, y, and z are approximately obtained by the equations (8), (9), and (10). Each load in Figure 1 (2a)
If the power factors of (2b) and (2c) are the same, the summed phase currents x, y, z of the respective phases have a phase difference of 120 degrees, and
It can be represented by the vector diagram of the figure. Since the relationship between the phase currents x, y, z and the line currents a, b, c is also as shown in FIG. 5, the following equation (11) is established between them.

The following expression (13) is established by the expression (12).

2 (x + y + z) 2 -3 (xy + yz + zx) = b 2 + c 2 + a 2
(13) On the other hand, the following formula (14) is established by the formula.

3 (xy + yz + zx) 2 = 2 (b 2 c 2 + c 2 a 2 + a 2 b 2) -
(B ⁴ + c ⁴ + a ⁴ ) (14) From the equation (14), the following equation is obtained.

Substituting equation (15) into equation (13), the following equation is obtained.

Hereinafter, the expression (16) is referred to as A. Further, the following equation is established from the equation (12).

The following equation is established from the equation (18) and the relation of x + y + z = A.

From the equation (19), the above equations (8), (9) and (10) are obtained. Therefore, the equations (8), (9) and (10) represent the phase current of each phase.

The operation circuit (7) of FIG. 4 is connected to the fundamental wave component extraction circuit (6) of FIG. 1 to execute the operations of the expressions (8), (9) and (10). 21) (22) (2
In (3), the square operator (2
4) Has (25) (26). Each square calculator (24) (25)
The output stage of (26) has a ² in the equations (8), (9) and (10).
Adders (27), (28) and (29) are provided to perform the operation of + b ² , b ² + c ² , and c ² + a ² , and (8)
In order to obtain 2c ² , 2a ² and 2b ² of the expressions (9) and (10), double value calculators (30), (31) and (32) are provided. (33)
(34) and (35) are subtractors, and adders (27) (2
8) Subtract the outputs of the arithmetic units (30), (31) and (32) from the outputs of (29) to obtain a ² + b ² −2c ^{2 of} the equations (8), (9) and (10),
b ² + c ² −2a ² and c ² + a ² −2b ² are obtained. (3
6) is an adder, which adds the output b ² of the square operator (25) to the output c ² + a ² of the adder (29) to obtain (8) (9) (1
This is to obtain a ² + b ² + c ² included in A of the formula (0).
(37) (38) (39) are dividers, and subtractors (3
3) Divide the output of (34) (35) by the separately obtained 3A,
The second term of the equations (8), (9) and (10) is obtained.
(40) (41) (42) are adders, and the divider (3
7) (8) (9) (1 obtained separately from the output of (38) (39)
Add (8), (9), (10) by adding the value A / 3 of the first term of expression (0)
It outputs the phase currents x, y, and z of the equation.

The adders (43), (44) and (45) connected to the line current input lines (21), (22) and (23) are a + b in the formulas (8), (9) and (10) showing A. , B + c, c + a. The adder (46) adds (c) of the line (23) to the output a + b of the adder (43) to obtain (a + b
+ C). The subtractor (47) is the adder (4
The output of line (23) is subtracted from the output of 3) to obtain a + bc of the expression indicating A. The subtractor (48) subtracts the output of the line (21) from the output of the adder (44),
This is a circuit for obtaining (-a + b + c) in the formula showing A. The subtracter (49) is a circuit that subtracts the output of the line (22) from the output of the adder (45) to obtain (ab + c) of the expression indicating A. The multiplier (50) is connected to the output of the adder (46) and the subtractor (4
(A + b + c) of the formula showing A by multiplying with the output of 7)
This is a circuit for obtaining (a + b-c). The multiplier (51) multiplies the output of the multiplier (48) and the output of the subtractor (49) to obtain A
Is a circuit that obtains (-a + b + c) (a-b + c) in the equation. The multiplier (52) is the former two multipliers (50) (5
The two outputs of 1) are multiplied, and (a + b +
c) (-a + b + c) (a-b + c) (a + b-c)
(Hereinafter, referred to as B). The multiplier (53) is B × 3 based on the output B of the multiplier (52) in the previous stage.
Is a circuit to obtain. The square root calculator (54) is the output 3B square root of the multiplier (53) in the previous stage. Is a circuit to obtain. The adder (55) is the previous-stage arithmetic unit (54)
Of the formula showing A by adding the output of and the output of the adder (36) Is a circuit to obtain. The 1/2 divider (56) is the adder (5
This is a circuit that obtains 1/2 the output of 5). The square root calculator (57) obtains the square root of the output of the 1/2 divider (56) in the preceding stage, that is, the output of the expression indicating A. The multiplier (58) multiplies the output A of the arithmetic unit (57) at the preceding stage by 3 to obtain 3A, and supplies this to the multipliers (37) (38) (39) of the respective phases. The divider (69) is 1/3 of the output A of the square root calculator (57).
Is obtained and is supplied to the adders (40) (41) (42).

(Harmonic Component Compensation) The harmonic component extraction circuit (60) subtracts the fundamental wave component a ₁ from the instantaneous reactive current I _Uq as shown in FIG.
0a) is included. Since the second and third phases are also configured in the same manner, the harmonic components a ₂ , b ₂ and c ₂ of each phase are output as alternating current.

The control signal forming circuit (61) includes a hysteresis comparator (67) and a logic circuit (68). A harmonic component extraction circuit (60) is connected to one input terminal of the hysteresis comparator (67), and the AC harmonic component a _{2 which} is illustratively shown in FIG. 6 (A) is input thereto. Comparators (67)
The current detector (63a) of FIG. 1 is connected to the other input terminal of, and the current detection value a ₃ shown in FIG. 6 (A) is input. Comparator (67), the harmonic components a ₂ 2 two hysteresis levels V _L on the basis of, V _H is obtained, and this such a current detection value a ₃ are compared, each time a ₃ reaches V _L, V _H The output is inverted to obtain the comparison output shown in FIG. 6 (B). That is, a ₃ goes from the level V _H to the level V _L , t ₂ to t
_{In 3} sections, the comparison output is low level, and a ₃ is the level from _VL to _VH.
It becomes a high level in the period of t ₃ to t ₄ heading for.

The logic circuit (68) uses a transistor Q based on the comparison output.
It is a circuit that forms the control signals of ₁ and Q ₂ . Fig. 6 (C)
For the control signal of the transistor Q ₁ shown in FIG. 6, the comparison output of FIG. 6 (B) is selected as it is in the first half cycle of t ₁ to t ₅ of the harmonic component a ₂ , and the sixth half of the latter half cycle of t ₅ to t ₆ is selected. It is formed by inverting the comparison output of FIG. The control signal of the transistor Q _{2 in} FIG. 6 (D) is an inversion of the control pulse in FIG. 6 (C). Control signal of the transistor Q ₃ to Q ₆ of the second and third phases also forms exactly like the first phase.

(Operation) When the line currents I _U , I _V , and I _W including harmonic components and reactive components are flowing through the load (2) in FIG. 1, the current detector (4
a) (4b) and (4c) are detected and sent to the first arithmetic circuit (5). The first arithmetic circuit (5) uses the line currents I _U , I _V ,
The instantaneous reactive currents I _Uq , I _Vq , and I _Wq of I _W are detected. The fundamental wave component extraction circuit (6) uses the instantaneous reactive currents I _Uq , I _Vq , and I _Wq.
The fundamental wave component in is extracted, and the line currents a, b, and c composed of the DC voltage corresponding to this effective value are output. Reactive current fundamental wave component supply circuit (3a) (3b) (3c) is power line (1u)
Since they are connected between the lines (1v) and (1w), the line currents a, b, and c in the second arithmetic circuit (7) are changed to the phase current x,
It is converted into y, z (effective value) and a DC voltage indicating the phase currents x, y, z is supplied to the control circuit (8). The control circuit (8) supplies a reactive current fundamental wave component supply circuit (3a) (3b) (3c) so as to compensate the phase currents x, y, z of the reactive current fundamental wave component.
Is selected, and the thyristors S _{1a to} S _3n are turned on so that the capacitors are connected. Thyristor S
Since _1a to S _3n is not interrupted current also immediately supplied stops the gate signals, it is possible to supply the current lead of the fundamental wave, it is impossible to supply the high harmonic components of frequencies.

On the other hand, the harmonic compensating PWM conversion circuit (62) compensates for the component which cannot be compensated by the fundamental wave component supply circuits (3a) (3b) (3c) of the reactive current. That is, since the fundamental wave component supply circuits (3a) (3b) (3c) of the reactive current compensate the fundamental wave component of the reactive current and cannot compensate the harmonic component, the harmonic component extraction circuit (3 Harmonic component a in 60)
₂ , b ₂ and c ₂ are extracted, and the PWM conversion circuit (62) including the transistors Q _{1 to} Q ₆ is driven so as to compensate for this.
Since the transistor Q ₁ to Q ₆ is a self-extinguishing semiconductor switch, it is possible to perform the on-off at a commercial frequency or frequencies, it is possible to compensate for the harmonic components. Therefore, according to the method of FIG. 1, flickering prevention, power factor improvement, and harmonic current suppression are achieved.

[Second Embodiment] FIG. 7 shows a part of a reactive power compensation system according to a second embodiment of the present invention. The method of the second embodiment is the same as that of FIG. 1 except that a part of the method of the first embodiment is changed.
Most of the parts in common with the figure are not shown in FIG. In the method of FIG. 1, for the fundamental wave component supply circuit reactive current (3a) (3b) (3c ) connects the capacitor C _1a -C _3n stepwise and supplies 100% of the desired fundamental component Becomes impossible, resulting in shortage or oversupply. Therefore, in the circuit of FIG. 7, a signal for controlling the harmonic compensating PWM conversion circuit (62) of FIG. 1 is formed so as to compensate for the shortage or excess of the fundamental wave component. Therefore, a circuit (71) that forms a signal indicating the amount of compensation of the fundamental wave component is provided. The signal forming circuit (71) is compensated want phase current x, y, z and (effective value), the capacitor C _1a based on a signal indicating the number of connected capacitors C _1a -C _3n obtained from the control circuit (8) A fundamental wave component x ₁ that can be compensated for by C _3n ,
It has a circuit (72) for determining y ₁ and z ₁ . Since the compensable fundamental wave components x ₁ , y ₁ , z ₁ obtained here are obtained as the effective value (DC voltage) corresponding to the phase current, the phase current is calculated by the third arithmetic circuit (73). The current is converted into a current, and the line current (DC) obtained from the current is converted into a sine wave AC by the DC-sine wave conversion circuit (74), and the compensable fundamental wave components a ₁₁ , b ₁₁ , converted into the line current, c ₁₁ is a harmonic component extraction circuit (60)
Send to.

Since the harmonic component extraction circuit (60) has the same configuration as that in FIG. 1, the reactive currents I _Uq , I _Vq , I _Wq and the fundamental wave components a ₁₁ , b are obtained.
_11, and sends the signal corresponding to the difference between c ₁₁ a _2, b _2, a c ₂ FIG. 1 and the same control signal forming circuit (61). Therefore, the harmonic component extraction circuit (60) not only extracts the harmonic components, but also the fundamental wave component supply circuits (3a) (3b) (3
Also extract the fundamental wave component that was under-compensated or over-compensated in c). As a result, the harmonic compensation PWM conversion circuit (6
In 2), not only the harmonic component but also the fundamental component that is under-compensated or over-compensated by the reactive current fundamental component supply circuits (3a) (3b) (3c) are compensated. PWM conversion circuit (6
2) has a function of compensating not only the harmonic component but also the fundamental component, so in principle, a lead reactive current supply circuit (3a)
It is possible to omit (3b) and (3c) and supply all of the fundamental wave components with the PWM conversion circuit (62).
2) must operate at high frequency, and therefore must use self-turn-off type semiconductor switch elements such as transistors and GTO. Therefore, it is difficult to increase the capacity of the PWM conversion circuit (62). Therefore, in this embodiment, all or most of the fundamental wave components are compensated by the fundamental wave component supply circuits (3a) (3b) (3c) using an AC switch composed of a thyristor antiparallel or triac.

Note that FIG. 8 shows the third arithmetic circuit (73) in FIG.
This arithmetic circuit (73) executes the following arithmetic operations.

In FIG. 8, x ² is a squarer, x is a multiplier, and √ is a calculator for obtaining a square root.

(Modification) The present invention is not limited to the above-described embodiments, and the following modifications are possible, for example.

(1) Figure 9 shows reactive current fundamental wave component supply circuit (3a)
A modified example of (3b) and (3c) is shown. In this circuit, the reactors L ₁ , L ₂ and C ₂ in parallel with the capacitors C ₁ , C ₂ and C ₃ between the lines are used.
L ₃ is connected, it is the reactor _1, L _2, thyristors S ₁ in series with L _3, S _2, S ₃ are connected. Thyristor S ₁ ,
Phase control (conduction angle control) of S ₂ and S ₃ is performed so that the power factor becomes 1. Therefore, an effect equivalent to continuously controlling the capacitance of the capacitor can be obtained. Thyristor S ₁ , S ₂ , S ₃
The phase control angle of is determined based on the phase currents x, y, and z of the instantaneous reactive current.

(2) Instead of the thyristors S _{1a to} S _3n shown in FIG. 1, a mechanical switch such as an electromagnetic contactor is connected to slow down the response speed of control, and the force of the three-phase unbalanced load and unbalanced power factor is simply used. It may be a rate adjustment position. It may also be used GTO instead of the transistor Q ₁ to Q _6.

(3) The arithmetic circuits (5) and (7) may be digital arithmetic circuits using a microcomputer instead of the analog arithmetic units.

(4) The thyristors S _{1a to} S _3n and S _{1 to} S ₃ may be connected in anti-parallel with each other without using the triac.

(5) A capacitor may be connected instead of the reactor (64) in FIG. Moreover, when connecting this capacitor, you may connect a reactor in series with the three-phase input line of a PWM converter.

(6) Instead of obtaining the compensation shortage or excess of the fundamental wave component as shown in FIG. 7, when the shortage of compensation or excess is divided in advance, the fundamental wave components a ₁ , b ₁ , c This shortage or excess may be added to ₁ and input to the harmonic extraction circuit (60).

(7) The fundamental wave component extraction circuit (6) in FIG. 1 may be configured as shown in FIG. In FIG. 10, an average value conversion circuit (80) calculates an average value (proportional to the effective value) a of the instantaneous reactive current I ^Uq and sends it to the second arithmetic circuit (7). The average value conversion circuit (80) includes a full-wave rectifier (82), an integration circuit (83), and a sample hold circuit (84). The sine wave generation circuit (85) for obtaining the AC fundamental wave component is a ROM (86) containing a large number of sine wave data and a D (A) for converting the output of this ROM (86) into AC. / A converter (87) and. The ROM (86) is read-out controlled based on the multiplication circuit (88) and the counter (89) synchronized with the zero-point signal of the power supply voltage, and outputs the sine wave data corresponding to the output level of the average value conversion circuit (80). Output. This positive and negative cancellation occurs, and it has almost no relation to the average value output, and finally, the average value output corresponding to the fundamental wave component is obtained.

(8) The fundamental wave component extraction circuit (6) in FIG. 1 is a combination of the same effective value converter (66) as in FIG. 3 and the sine wave generation circuit (85) in FIG. 10 as shown in FIG. You may comprise.

〔The invention's effect〕

The present invention has the following effects (a) The pulse width modulation conversion circuit has a function of compensating the fundamental wave component. If the pulse width modulation conversion circuit is configured to compensate all the fundamental wave components, it becomes necessary to use a large capacity semiconductor switch, which increases the cost of the device. Therefore, in the present invention, in addition to the pulse width modulation conversion circuit, a fundamental wave component supply circuit composed of a capacitor or a reactor connected between lines of a three-phase AC power supply line via a switch is provided, whereby the fundamental wave component All or part is compensated. Since the switch of the fundamental wave component supply circuit does not need to be interrupted at high speed, when compared with the same current capacity, the cost is lower than that of the semiconductor switch of the pulse width modulation circuit. Therefore, according to the present invention, the cost of the reactive power adjusting device can be reduced.

(B) Since the three-phase line currents are detected and both the fundamental wave component supply circuit and the pulse width modulation conversion circuit are controlled by arithmetic processing based on the detected line currents, the configuration of the device becomes relatively simple.

[Brief description of drawings]

1 is a block diagram showing a three-phase reactive power regulator according to a first embodiment of the present invention, FIG. 2 is a block diagram showing the first arithmetic circuit of FIG. 1, and FIG. 3 is FIG. 4 is a block diagram showing in detail a part of FIG. 4, FIG. 4 is a block diagram showing the second arithmetic circuit of FIG. 1, and FIG. 5 is a block diagram showing the relationship between the line current and the phase current of a three-phase unbalanced load. FIG. 6 is a waveform diagram showing the state of each part of FIG. 3, FIG. 7 is a block diagram showing a part of the nullification adjusting device of the second embodiment of the present invention, and FIG. 8 is a third diagram of FIG. 9 is a circuit diagram showing a fundamental wave component supply circuit for a reactive current of a modified example, and FIGS. 10 and 11 are block diagrams showing a fundamental wave component extraction circuit of a modified example. . (1u) (1v) (1w) …… Power line, (2) …… Load, (3
a) (3b) (3c) ... fundamental wave component supply circuit of reactive current,
(4a) (4b) (4c) ... current detector, (5) ... first arithmetic circuit, (6) ... fundamental wave component extraction circuit, (7) ...
Second arithmetic circuit, (8) ... Gate control circuit, (60) ...
… Harmonic component extraction circuit, (62) …… PWM conversion circuit.

Claims (1)

[Claims] 1. A capacitor or a reactor is connected to a three-phase AC power supply line via a switch to supply a fundamental wave component of a reactive current and adjust the magnitude of a fundamental wave component of the reactive current. The three-phase reactive current fundamental wave component supply circuit (3a) (3b) (3c) configured and the reactive current harmonic component connected to the three-phase AC power supply line and the semiconductor switch ON / OFF control. A three-phase pulse width modulation conversion circuit (62) configured to be supplied, and a first phase, a second phase and a third phase load (2) connected to the three-phase AC power line. Three-phase line current (I _U , I _V , I _W )
Line current detectors (4a) (4b) (4c) for detecting the line current, and line currents (I _U , I _V , I _W ) of the first, second and third phases
The instantaneous reactive currents (I _Uq , I _Vq , I _Wq ) of the first phase, the second phase and the third phase are _{calculated based on}
Value of the fundamental wave component of the instantaneous reactive current (I _Uq , I _Vq , I _Wq ) of (a, b, c) or a value proportional thereto is obtained, and the instantaneous reactive current of each phase represented by the line current The effective value (a, b, c) of the fundamental wave component or a value proportional thereto is used as the phase current (x,
y, z), and based on the phase current (x, y, z), the fundamental of the reactive current so as to compensate all or part of the fundamental wave component of the reactive current of the three-phase load (2). The switches of the wave component supply circuits (3a) (3b) (3c) are controlled, and the first, second and third instantaneous reactive currents (I _Uq , I _Vq ,
I _Wq ) harmonic component (a2, b2, c2) is obtained, and based on the harmonic component (a2, b2, c2), this harmonic component (a2,
A reactive power adjusting device comprising arithmetic and control means for controlling the three-phase pulse width modulation conversion circuit (62) so as to remove b2, c2).