JPH0833784B2 - Control system of reactive power compensator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention compensates for reactive power generated by a fluctuating load connected to an AC system to suppress voltage fluctuations in this AC system. The present invention relates to a control system for a reactive power compensator.

[Conventional technology]

FIG. 5 is a single-line connection diagram showing a conventional example for compensating for reactive power in an AC system. Fluctuations that cause large fluctuations, such as an AC power supply 1 that supplies AC power to a bus bar 2, an arc furnace, or a welding machine. A load 3 and a reactive power compensator 6 for compensating the reactive power generated from the variable load 3 are connected.

The voltage of the bus 2 is detected by the voltage transformer 5, and the current of the fluctuating load 3 is detected by the current transformer 4. The detected voltage and the current are input to the control circuit 7, the reactive power is obtained from them, and the reactive power compensator 6 is controlled according to this reactive power. The one shown in FIG. 5 is the thyristor phase. This is called a control reactor system, and in response to the reactive power detected by the control circuit 7, the thyristor switch of this reactive power compensator 6 is ignition-controlled to phase-control the reactor current and disable it. Power is being adjusted.

[Problems to be solved by the invention]

By the way, in the conventional circuit for reactive power compensation shown in FIG. 5, the thyristor switch can be controlled to be fired only once for each half cycle of the frequency of the AC power supply 1 (for example, 100 times per second in the 50 Hz area). The resolution of the compensation cannot be improved, and a large error occurs in the reactive power value detected from the load current and the bus voltage due to the waveform distortion of the current flowing through the variable load 3 and the like.
There is a major drawback that it is difficult to perform accurate reactive power compensation. Furthermore, since the reactive power compensation by the thyristor phase control reactor system is an adjustment of only the reactive power, it has a problem that even if the active power of the load is unbalanced, it cannot be compensated.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to perform highly accurate reactive power compensation without causing an error due to waveform distortion or the like, and also to compensate for imbalance of active power.

[Means for solving problems]

In order to achieve the above object, the control system of the present invention is
By compensating the reactive power generated corresponding to the fluctuation of the load connected to the AC system by the self-excited reactive power compensating means,
In the control system of the reactive power compensator that suppresses the voltage fluctuation of the AC system, the instantaneous value of the voltage of each phase of the AC system and the instantaneous value of the load current of each phase are multiplied, and the multiplication of each phase is performed. From the sum of the results, find the average active power of the load,
The current waveform of the active power component for each phase obtained by multiplying the average active power by the reference sine waveform for each phase, and the waveform obtained by the difference calculation between the load current instantaneous value, It is assumed that a current target value is set and control is performed for each phase so that the actual value of the current flowing through the reactive power compensating device matches the current target value.

[Action]

The present invention detects the average active power of each phase of a fluctuating load from the bus voltage and the load current, and multiplies the average active power by the reference sine waveform of each phase to obtain the instantaneous current value waveform of the active power component. Is calculated for each phase, and the waveform obtained by calculating the difference between this and the load current instantaneous value waveform detected for each phase is the current flowing in the self-excited reactive power compensator connected to the busbar. The target value of. Therefore, by controlling the reactive power compensator so that the actual value of the current flowing through the reactive power compensator matches the current target value, without causing an error due to current waveform distortion or the like,
It not only performs highly accurate reactive power compensation, but also balances active power.

〔Example〕

FIG. 1 is a single line connection diagram showing the principle of the present invention.
The AC power supply 1 and the variable load 3 are connected to the bus bar 2 as in the case of the conventional circuit described above in FIG. 5, but in the present invention, the reactive power of the thyristor phase control reactor method is used. Instead of the compensating device 6, for example, a self-excited invalid device composed of a thyristor switch (or a self-extinguishing type semiconductor switch element such as a gate turn-off thyristor) provided with a forced commutation circuit and a capacitor. A power compensator 11 is connected to the bus 2, and a control circuit for controlling the reactive power compensator 11
The current of the fluctuating load 3 detected by the current transformer 4, the bus voltage detected by the voltage transformer 5 and the current of the reactive power compensating device 11 detected by the current transformer 13 are input to 12. It is supposed to be done.

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, and calculates the current waveform of the active power component by multiplying this by the reference sine wave,
The reactive power compensator is calculated by calculating the difference between this and the load current.
Create the target current value to be applied to 11. Further, in the control circuit 12, a control signal for making the actual current value of the var compensator input to the control circuit 12 coincide with the above-mentioned current target value is created, and this control signal is given to the var compensator. ing.

FIG. 2 is a block diagram showing a first embodiment of the control circuit of the reactive power compensating device according to the present invention, and shows the case where the AC system has three phases.

Assuming that the phase voltage effective value is E, the power source angular velocity is ω, and the time is t, the voltages e _R , e _S , e _T of the R, S, T phases of the bus 2 are as follows (1), (2), ( It can be expressed by equation (3).

On the other hand, each phase current i _R1 , i _S1 , i _T1 flowing in the variable load 3 is
When I _R , I _S , and I _T are the effective values of each phase current, and the power factor angle of each phase is φ _R , φ _S , and φ _T , the following equations (4), (5), and (6) are obtained. Become.

Therefore, in the multiplier 21R, the voltage e _R shown in the equation (1) is multiplied by the current i _R1 shown in the equation (4) to calculate the R-phase active power of the variable load 3. 21S,
The 21T calculates the active powers of the S phase and T phase of the variable load 3, respectively, and the ripple component is removed by the adder 22 and the low-pass filter 23, and the three-phase average active power P ^* shown in the equation (7) is calculated ^. To get (At this time, the gain of the low-pass filter 23 is 1/3.) By multiplying the three-phase effective average power P ^* and the R-phase reference sine wave in the multiplier 24R, the R-phase instantaneous current waveform i _AR of the active power component is obtained as shown in equation (8). Similarly, by the multipliers 24S and 24T, the S-phase and T-phase current instantaneous waveforms i _AS and i _{AT of the} active power components shown in the equations (9) and (10) can be obtained.

If the difference between the instantaneous current value of the active power component and the instantaneous value of the current flowing through the fluctuating load 3 is calculated, this becomes the target current value to be passed through the reactive power compensator 11, and therefore the above (4), ( 5) Calculate the difference between the instantaneous current value obtained by the equations (6) and the instantaneous current value obtained by the equations (8), (9), (10) with the adders 25R, 25S, 25T. As a result, current target values i _R2 ^* , i _S2 ^* , i _T2 ^* for each phase are obtained as shown in the following equations (11), (12) and (13).

i _R2 ^* = i _R1 -i _AR ...... (11) i _S2 ^* = i _S1 -i _AS ...... (12) i _T2 ^* = i _T1 -i _AT ...... (13) Detected by current transformer 13 In order to match the actual current values i _R2 , i _S2 , and i _T2 of the reactive power compensator 11 to the above-described current target values, adders 26R, 26S, and 27T calculate the deviation between the two,
When this calculation result is input to the current regulators 27R, 27S, and 27T, these current regulators 27R, 27S, and 27T generate control signals for zeroing the respective input deviations, and the pulse generator 28 of the next stage.
Output to R, 28S, 28T. Therefore, by controlling the on / off of the thyristor switch of the reactive power compensator 11 with the outputs of these pulse generators 28R, 28S, 28T, the actual current value becomes the current target value. That is, i _R2 ≈ i _R2 ^* , i _S2
≈i _S2 ^* , i _T2 ≈i _T2 ^* can be realized.

If the system currents of each phase flowing from the AC power supply 1 to the bus 2 are i _R3 , i _S3 , and i _T3 , respectively, Therefore, the reactive power is completely compensated, and only the current of the active power component in which the three phases are balanced flows in 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 shows the current angular velocity ω, but FIG. The phase voltage waveform is shown in Fig. 3 (b), the waveform of each phase flowing through the variable load 3, Fig. 3 (c) is the active power of the variable load 3, and Fig. 3 (d) is the reference sine of each phase. The waveform and the current waveform of the active power component are shown in FIG. 3 (e), which shows the current target value waveform of each phase, and FIG. 3 (f) which shows the system current waveform of 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. The multipliers 21R, 21S, 21T, the adder 22 and the multiplier 24 in FIG.
R, 24S, 24T, adder 25R, 25S, 25T, 26R, 26S, 26T, current regulator 27R, 27S, 27T and pulse generator 28R, 28
Since S and 28T have the same names, uses, and functions as those of the circuit of the first embodiment described above in FIG. 2, their description 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 as an integrator 31R, 31.
S, 31T performs integral calculation for a predetermined period such as 1 cycle or half cycle, and the final value of the calculation is sampled by sample hold circuits 32R, 32S, 32T to calculate the average value and average the active power for each phase. Value P ^*
_{Since R} , P ^* _S , and P ^* _T are obtained, the operation thereafter is the same as that of the first embodiment circuit.

〔The invention's effect〕

According to the present invention, a self-excited reactive power compensator is connected to an AC system to which a load with large fluctuations is connected, and by multiplying the average value of each phase of the active power of this fluctuating load by a reference sine waveform. The current instantaneous value of the active power component of each phase obtained, and the difference between the load current instantaneous value is calculated, the difference calculation result as the target value of the current flowing through the reactive power compensator,
Since the control is performed so that the actual value of the current flowing through this reactive power compensator matches the current target value, no error occurs even if the current waveform is distorted,
Since the reactive power is compensated with high accuracy, the voltage fluctuation of the AC system can be suppressed, and the active power of each phase can be prevented from being unbalanced.

[Brief description of drawings]

FIG. 1 is a single line connection diagram showing the principle of the present invention, FIG. 2 is a block diagram showing a first embodiment of a control circuit of a reactive power compensating device according to the present invention, and FIG. 3 is a diagram showing in FIG. FIG. 4 is a block diagram showing a second embodiment of the control circuit of the reactive power compensating apparatus according to the present invention, and FIG. 5 shows the reactive power of the AC system. It is a single-line connection diagram showing a conventional example for compensation. 1 ... AC power supply, 2 ... Busbar, 3 ... Variable load, 4,13 ...
… Current transformer, 5 …… Instrument transformer, 6,11 …… Reactive power compensator, 7,12 …… Control circuit, 21R, 21S, 21T, 24R, 24S, 24T…
… Multiplier, 22,25R, 25S, 25T, 26R, 26S, 26T …… Adder, 23
...... Low pass filter, 27R, 27S, 27T ...... Current regulator, 2
8R, 28S, 28T …… Pulse generator, 31R, 31S, 31T ……
Integrator, 32R, 32S, 32T ... Sample and hold circuit.

Claims (1)

[Claims] 1. A self-excited reactive power compensating means compensates the reactive power generated in response to the fluctuation of a load connected to the AC system, thereby suppressing the voltage fluctuation of the AC system.
In the control system of the reactive power compensator, the instantaneous value of the voltage of each phase of the AC system and the instantaneous value of the load current of each phase are multiplied, and from the sum of the multiplication results of each phase, the average active power of the load is calculated. Then, the waveform obtained by calculating the difference between the current waveform of the active power component for each phase obtained by multiplying the average active power by the reference sine waveform for each phase and the load current instantaneous value is used as the reactive power compensation. A control method for a reactive power compensating device, characterized in that a control is performed for each phase so that a current target value of the device is set, and an actual value of a current flowing through the reactive power compensating device is made to match the current target value.