JPH01152518A - Control system for reactive power compensator - Google Patents

Abstract

PURPOSE:To attain the reactive power compensation of high accuracy by preparing a current aimed value to flow to a reactive power compensator and controlling so that a current actual value to flow to the reactive power compensator may correspond to the current aimed value. CONSTITUTION:The current of a fluctuating load 3 detected by a current transformer 4, a bus voltage detected by a potential transformer 5 and the current of a reactive power compensator 11 detected by a current transformer 13 are inputted to a control circuit 12. The circuit 12 operates the average of the effective power of the load 3 from the bus voltage and the load current, operates the current waveform of an effective power component by the multiplication of the average and a reference sine wave, practices the difference operation of the current waveform and a load current and prepares a current aimed value to flow to the device 11. Moreover, in the circuit 12, a control signal to correspond the current actual value of the inputted device 11 to the current aimed value is generated and given to the device 11. Consequently, even when a deformation is generated to the power waveform, an error is not generated and the reactive power compensation of high accuracy can be executed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a static type system that suppresses voltage fluctuations in an AC system by compensating for reactive power generated by a fluctuating load connected to the AC system. The present invention relates to a control method for a reactive power compensator.

[Conventional technology]

5th i! 1 is a single-line diagram showing a conventional example of compensating reactive power in an AC system, in which a bus 2 includes an AC power source 1 that supplies AC power, and a variable load 3 that causes large fluctuations such as an arc furnace or a welding machine. and a reactive power compensator N6 for compensating the reactive power generated from the variable load 3.

The voltage of the bus 2 is detected by a potential transformer 5, and the current of the variable load 3 is detected by a current transformer 4. The detected voltage and current are manually input to the control circuit 7 to obtain reactive power from them, and the reactive power compensator 6 is controlled in accordance with this reactive power. This is called a control reactor system, and the control circuit 7
In response to the detected reactive power, the reactive power is adjusted by controlling the phase of the reactor current by controlling the firing of the si-risk switch of the reactive power compensator 6.

[Problems to be solved by the invention] By the way, in the conventional reactive power compensation circuit shown in FIG.
Because the thyrisk switch can only be controlled to fire once every half cycle of the frequency of the AC power supply 1 (for example, 5
(100 times per second in the 0 Hz area), the resolution of reactive power compensation cannot be improved, and the reactive power value detected from the load current and bus voltage may be affected by waveform distortion of the current flowing through the variable load 3. This causes a large error, so there is a major problem in that it is difficult to perform accurate reactive power compensation. Furthermore, since the reactive power compensation using the SIRISK phase control reactor system adjusts only the reactive power, it also has the disadvantage that even if an unbalance occurs in the active force of the load, it cannot compensate for this.

Therefore, the purpose of this invention is to perform highly accurate reactive power compensation without causing errors due to waveform distortion, etc.
The object is to be able to compensate for the unbalance of active power as well.

[Means for solving problems]

In order to achieve the above object, the control method of the present invention compensates for the voltage fluctuations in the AC system by compensating for the reactive power generated in response to the fluctuations in the load connected to the AC system using a self-excited reactive power compensation means. In a control method of a reactive power compensator that suppresses The waveform obtained by calculating the difference between the current waveform of the active power component for each phase obtained by and the instantaneous value of the load current is set as the current target value of the reactive power compensator, and the actual value of the current flowing through the reactive power compensator is set as the current target value of the reactive power compensator. It is assumed that control is performed for each phase to make the current match the current target value.

[Operation] This invention detects the average active power of each phase of a fluctuating load from the bus voltage and load current, and multiplies this average active power by a reference sine waveform for each phase to determine the current of the active power component. A self-excited reactive power compensator connected to the bus bar calculates the instantaneous value waveform for each phase and calculates the difference between this and the load current instantaneous value waveform detected for each phase. The target value of the current flowing through the Therefore, by controlling the reactive power compensator so that the actual value of the current flowing through the reactive power compensator matches this current target value, high-precision reactive power It performs power compensation and also balances the active power.

〔Example〕

FIG. 1 is a single line diagram showing the principle of the present invention, and the connection of the AC type tA1 and the variable load 3 to the bus 2 is different from the conventional circuit described in FIG. The same, but
In the present invention, instead of the reactive power compensator 6 of the Thyrisk phase control reactor type, for example, a Thyrisk switch equipped with a forced commutation circuit (or a self-extinguishing semiconductor switching element such as a gate turn-off thyristor) may be used. A self-excited reactive power compensator 11 composed of a capacitor and a capacitor is connected to the bus 2, and a control circuit 12 for controlling the reactive power compensator 11 includes a current transformer 4 that detects The current of the variable load 3 to be
Bus voltage detected by instrument transformer 5 and current transformer 1
The current of the reactive power compensator 11 detected at step 3 is inputted.

The control circuit 12 calculates the average value of the active power of the variable load 3 from the input bus voltage and load current, calculates the current waveform of the active power component by multiplying this by a reference sine wave,
A difference calculation between this and the load current is performed to create a target value of current to be passed through the reactive power compensator 11. Furthermore, this control circuit 12 generates a control signal that makes the actual current value of the reactive power compensator inputted therein coincide with the above-mentioned current target value, and supplies this control signal to the reactive power compensator. ing.

FIG. 2 is a block diagram showing a first embodiment of a control circuit for a reactive power compensator according to the present invention, in which an AC system has three
It is raining the case of the phase.

If the effective value of the phase voltage is E, the angular velocity of the power source is ω, and the time is t, then the voltage of each phase of R, S, and T of bus 2 is e.

el and ea can be calculated using the following formulas (1), (2), and (3).

el = r d・E −s in ωt =−−−−−
−−−−−−−−−−−−−−(1)es””F
E −5in ((1) t −g) “−(2) el
=(T--E-5in ((11t-W)-
(3) On the other hand, each phase current 111+ flowing through variable load 3
til+jul+ is (■), Is, It is the effective value of each phase current, and the power factor angle of each phase is φ, and φ8. When φd is assumed, the following equations (4), (5), and (6) are obtained.

i +++ = 汀・I a −5tn(ωL−φm
) −−−−−−−(4) is+=ff ・Is
・5in(ωt K-φg )-----
...
・5in(ωt−□π−φT)−・−1−−−−・−・
-.-(6) Therefore, the voltage e shown in equation (1) in the multiplier 21R.

R of variable load 3 is obtained by multiplying by the current i□ shown in equation (4).
To calculate the phase active power, multiplier 2
1S and 21T calculate the active powers of the S phase and T phase of the variable load 3, respectively, and remove ripples from these using the adder 22 and the low-pass filter 23 to obtain the three-phase average active power shown in equation (7). Get P1. (At this time, the gain of the low-pass filter 23 is set to 1/3.) P" = (E-1++ ・cos φ1
+E°1s-cos φ.

+E-17・cos φT) ---(7) This 3
A multiplier 24 multiplies the phase effective average power P0 and the reference sine wave of the R phase.
By multiplying each other in H, the R phase current instantaneous waveform i of the active power component is obtained as shown in equation (8).
Similarly, multipliers 24S and 24T are used to form instantaneous S-phase and T-phase current waveforms iAs and iA? of the active power components shown in equations (9) and 0m? is obtained.

(T −p 0 i 4 @ x sin ωt −
−−−−−−−−−−−−−−−=−−−(8) ff
-P'' 4 If we calculate the difference between the instantaneous value of the current of this active power component and the instantaneous value of the current flowing through the variable load 3, this becomes the target value of the current that should be passed through the reactive power compensator 11. 4), (5
), the instantaneous current value obtained by equation (6), and this (8),
(9) By calculating the difference with the instantaneous current value obtained by the 0ff1 formula using the adders 25R, 25S, and 25T, the current target value ixz of each phase as shown in the following (IQ, 021.09 formula) is calculated. .+'"+ITt" is obtained.

18□Umbrella=f＋＋＋fAe −・・−１−−−−−−−
−−−・・−・−−−−−−・−・−・・−・・・・θ
! )1 sz"=is+tAs"---
−−−−・−・・−−−−−−−・・−・−・−・−・
−・−・−Q2) f T t ” = t t +
j s t ”−’−’−−−−−−−”’−−−”
−'−'−−−−−−−−−−−−”−'−'−031
Actual current value i of the reactive power compensator 11 detected by the current transformer 13. r'! ! + I TZ to match the above-mentioned current target value, adders 26R, 26S, 27
When the deviation between the two is calculated at T and the calculation result is manually input to the current regulators 27R, 275, and 27T, these current regulators 27R, 27S, and 27T transmit control signals to the next stage to make their respective input deviations zero. pulse generator 28
Output to R, 28S, 28T. Therefore, by controlling the sirisk switch of the reactive power compensator 11 on and off using the outputs of these pulse generators 28R, 28S, and 28T, the actual current value matches the current target value. In other words, i@tζi, ge.

i,ζts*” 1 172ζitz can be realized.

If the system current of each phase flowing from the AC ili source 1 to the bus 2 is 1131 1 ms+ i ts, then j
si=1st 15g 1tsIII It+ Its, the reactive power is completely compensated, and only the current of the active power component in which the three phases are balanced flows through the AC system.

FIG. 3 is a time chart showing the operation of each part of the circuit of the first embodiment shown in FIG. 2, and the horizontal axis is the current angular velocity ω.
However, Figure 3 (A) shows the voltage waveform of each phase of bus 2, Figure 3 (B) shows the waveform of each phase flowing to variable load 3, and Figure 3 (C) shows the voltage waveform of each phase flowing to variable load 3. The effective power of 3 is shown in Figure 3 (
d) shows the quasi-sine waveform of each phase and the current waveform of the active power component, Fig. 3(e) shows the waveform of the current target value of each phase, and Fig. 3(e) shows the waveform of the current target value of each phase.
) shows the waveforms of the grid current for each phase.

FIG. 4 is a block diagram showing a second embodiment of the control circuit of the reactive power compensator according to the present invention. , 24S, 24T and adders 25R, 2
5S, 25T, 26R, 263, 26T, current regulators 27R, 27S, 27T and pulse generator 2
8R, 28S, and 2BT have the same names, uses, and functions as those of the circuit of the first embodiment already described in FIG. 2, so their explanations will be omitted.

In the second embodiment circuit shown in FIG. 4, instead of obtaining the three-phase active power average value P'' by the low-pass filter 23, the value of the active power P obtained by the adder 22 is used by the integrator 31.
R, 313, 31T perform integral calculation for a predetermined period such as one cycle or half cycle, and the final value of the calculation is sampled in sample hold circuits 32R, 32S, 32"r to perform average value calculation. The average value of active power P ``II+ P ''S
+P''T is obtained, and the subsequent operations are the same as in the first embodiment circuit.

〔Effect of the invention〕

According to this invention, a self-excited reactive power compensator is connected to an AC system to which a highly fluctuating load is connected, and the multiplication of the average value of each phase of the active power of this fluctuating load by a reference sine waveform is performed. The obtained instantaneous current value of the active power component of each phase,
Calculate the difference with the instantaneous value of the load current, use this difference calculation result as the target value of the current flowing through the reactive power compensator, and set the current value such that the actual value of the current flowing through the reactive power compensator is one match with this current target value. I'm trying to control it, so
Since it compensates for reactive power with high precision without causing errors even if the current waveform is distorted, it has the effect of suppressing voltage fluctuations in the AC system, and also eliminates unbalance in the active power of each phase. It also has the effect of preventing this from occurring.

[Brief explanation of the drawing]

FIG. 1 is a single line diagram showing the principle of the present invention, FIG. 2 is a block diagram showing a first embodiment of a control circuit for a reactive power compensator according to the present invention, and FIG. FIG. 4 is a block diagram showing the operation of each part of the circuit of the first embodiment, FIG. 4 is a block diagram showing the second embodiment of the control circuit of the reactive power compensator according to the present invention, and FIG. FIG. 2 is a single-line diagram showing a conventional example of compensation. 1...AC power supply, 2...bus bar, 3...variable load,
4゜13... Current transformer, 5... Instrument transformer, 6.1
1... Reactive power compensator, 7.12... Control circuit,
21R, 213° 21T, 24R, 24S, 24T...
・Multiplier, 22.25R. 25S, 25T, 26R, 26S, 26T...Adder, 23...Low pass filter, 27R, 27S, 27
T... Current regulator, 28R, 28S, 28T... Pulse generator, 31R231S, 31T... Integrator, 32R, 32S, 32T... Sample hold circuit. ■ 1 Figure 3 Figure 4

Claims (1)

[Claims] 1) A control method for a reactive power compensator that suppresses voltage fluctuations in an AC system by compensating the reactive power generated in response to fluctuations in the load connected to the AC system using a self-excited reactive power compensation means. , the average active power of the load is determined from the voltage and load current of the AC system, and the current waveform of the active power component for each phase is obtained by multiplying the reference sine waveform for each phase by this average active power. The waveform obtained by calculating the difference between the current value and the instantaneous load current value is set as the current target value of the reactive power compensator, and control is performed for each phase to make the actual value of the current flowing through the reactive power compensator match the current target value. A control method for a reactive power compensator, characterized in that the control is performed at each time.