JP2551206B2 - Control method of reactive power compensator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control method for a reactive power compensator installed for the purpose of suppressing voltage flicker in an arc furnace or the like.

[Conventional technology]

In the flicker compensation reactive power compensator such as an arc furnace,
Corresponding to the rapid flicker phenomenon, high-speed control by open loop is essential.

 FIG. 2 shows a conventional reactive power compensator of this type.

A bus line 1 is connected to a system power source 0 having a power source impedance, and a reactor switching circuit (hereinafter TCR unit) by a thyristor in which a reactor 141 and an antiparallel connection thyristor 142 are connected in series is connected to the bus line 1 in order to suppress voltage fluctuations due to a variable load 4. Said) and circuit breaker 143 through filter 144
Are connected, and the TCR main circuit 14 is configured by the TCR section and the filter.

A load current including harmonics is taken out by the current transformer 3, and the taken load current signal is a bandpass filter 8
to go into. On the other hand, a bus voltage signal is taken out from the bus 1 through the transformer 2, the signal is input to the 90 ° delayed phase shift circuit (voltage toulon circuit) 7, and subtraction is performed by the adder 9, and the output signal is , Enters the rectifying circuit 10, and further passes through the coefficient unit 11,
Output to the comparator 12.

Further, the bus voltage signal from the transformer 2 is input to the averaging circuit 6 via the rectifying circuit 5, and the output signal from the averaging circuit 6 and the output signal from the coefficient unit 11 are corrected by a correction circuit (dead zone formation). Circuit) Comparator with voltage signal from 20
Enter 12

The output signals from the 90 ° delay phase circuit 7, the bandpass filter 8, the averaging circuit 6 and the coefficient unit 11 for the synchronous power source Vl are shown in the waveform diagram of FIG.

Here, the bandpass filter 8 limits the frequency band to be passed through the fundamental waves having frequencies of 50 Hz and 60 Hz.

Usually, the fluctuation of the energizing current of the TCR unit is controlled by generating a constant reactive current on the bus 1 together with the fluctuation of the load reactive current. That is, when the reactive current of the load increases,
It operates so as to reduce the energizing current of the TCR part and cancel the fluctuation of the bus voltage.

If the load current signal increases, the load current signal from the bandpass filter increases, and at the same time, the voltage signal from the 90 ° delayed phase shift circuit 7 decreases, so that the load current signal from the coefficient unit 11 passes through the adder 9 and the rectifier circuit 10. The voltage signal will be at a lower level than before the load current increased. On the other hand, the level from the voltage averaging circuit 6 is adjusted by the voltage signal from the voltage averaging circuit 6 and the correction signal from the correcting circuit 20, and the adjusted voltage signal is adjusted by the comparator 12 and the coefficient unit 11 If the control pulse 13 is generated at the coincidence point with the output signal of, the pulse firing phase control angle β after the previous pulse firing phase control angle β
Occurs in the delayed direction, so that the current flowing through the TCR section is reduced, the bus voltage shifts to an increase, and voltage fluctuation due to load can be suppressed.

[Problems to be solved by the invention]

By the way, in the control method as described above, there is originally no linearity between the thyristor firing phase control angle and the reactor current due to its characteristics, and the firing phase angle upper limit (β ≈ 30 °) to lower limit (β ≈ 80 °). Within the range, even if there is a slight difference in the ignition phase, the energizing current fluctuates greatly, so it is difficult to perform precise control. This is a feature of open loop control.

[Structure of Invention]

The present invention solves the above-mentioned problem, and uses a load current with power factor correction as a control signal for high-speed TCR by open loop control.
By controlling the parts, the control can be improved without being adversely affected by the conventional harmonic current and the like.

Hereinafter, the present invention will be described with reference to the embodiment shown in FIG. 2 are indicated by the same reference numerals. The load current signal is taken out from the current transformer 3 connected to the circuit of the load 4. This signal is a signal containing harmonics. This load current signal is input to the power factor correction circuit 16 and converted into a fundamental wave current.

The power factor correction circuit consists of a power factor correction IC that detects the difference between the sinusoidal line voltage of the periodic power source and the instantaneous value of the pulsating current, and as a result, the line current It is an IC circuit that can be modified to.

By passing through the power factor correction circuit 16, the load current is converted into a fundamental wave current signal having a power factor cosφ≈1.

The fundamental wave delay reactive current signal output from the power factor correction circuit 16 is input to the squarer 17 and converted. Is calculated. Here, (i _L ) ² = i ² _L + i ² _L cos2ωt is output, and this output is supplied to the filter 17 ′, for example, twin T
Passing through the circuit (2ωt removal circuit), i ² _L is obtained. This i ² _L is square _rooted in the square root opener 18 and subtracted from the reference voltage signal 20 ′ in the adder 21. This reference voltage signal 20 'is set on the basis that the TCR section supplies the maximum allowable current 1 PU at the firing phase control angle β = 0 when the load current is zero. That is, when the load current i _L is zero, a delayed current is passed through the TCR section, and when the load current i _L is the maximum reactive current, the TCR section has a value that stops its energizing operation at approximately β = 90 °. Is.

FIG. 5 is an example of a characteristic diagram showing the relationship between the thyristor firing phase control angle β and the reactor current. As shown, the thyristor firing phase control angle β and the reactor current are not in a linear proportional relationship. The figure shows the magnitude of the resulting current through the reactor with respect to the thyristor firing phase control angle β.

Due to the subtraction in the adder 21, the output signal is
It is a signal corresponding to the magnitude of the delayed reactive current to be compensated generated by the TCR unit control. The signal input 19 is a non-linear correction circuit that stores the characteristics of the reactor current vs. thyristor firing phase control angle β obtained in advance by an actual machine as shown in the waveform of FIG. 5, and the signal corresponding to the subtracted compensation current. Is passed through this non-linear correction circuit to output a signal indicating the thyristor firing phase control angle.

On the other hand, a sawtooth wave is output from the power supply synchronizing circuit 15 as shown in FIG. 3, but this sawtooth wave is present at α = 90 ° to 180 ° and α = 270 ° to 360 ° of the half-sine wave. , 0 indicates the position where β is zero, and h ′ indicates the position where β is 90 °. The sawtooth wave rises when the ignition phase control angle β is zero, the β is 90 °, and the wave height hh 'is made to correspond to the allowable current 1PU, and the wave heights hh' and β have a width of 0 to 90 °.
If 0h 'is made equal, the output signal corresponding to the ignition phase control angle by the output from the non-linear correction circuit 19 and the sawtooth wave are input to the comparator 12, and the level required by the TCR section is the same. The signals X ₁ , X ₂ , X ₃ ... Indicating the ignition phase control angle β are sequentially generated so as to generate a reactive current with a delay of, and the signals are amplified in the control pulse generating circuit 13 and the thyristor is ignited. If it is applied to the pole, a predetermined compensation current will be applied to the TCR.
It is possible to perform a highly accurate fluctuation suppression control with respect to load fluctuations by making the reactive current of the delay that flows in the power supply impedance constant by making it constant.

[Effects of the Invention] In the present invention, a distorted load current can be converted into a fundamental wave current by using a correction circuit composed of a power factor correction IC, and thereafter, a non-linear characteristic matched to the reactor conduction characteristic by the thyristor firing phase control angle β is obtained. Since the thyristor firing phase control angle is obtained using a sawtooth wave without being adversely affected by a high frequency current or the like through the correction circuit, the voltage fluctuation suppression control can be performed with high accuracy and at high speed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a block diagram showing an example of a conventional flicker countermeasure reactive power compensator. FIG. 3 shows an operation waveform chart of each part of the embodiment shown in FIG. FIG. 4 shows an operation waveform diagram of each part by the conventional apparatus of FIG. FIG. 5 shows the relationship between the thyristor firing phase control angle of the TCR section and the energizing current. 5, 10 ... Rectifier circuit, 6 ... Voltage averaging circuit, 7 ... Voltage 90 ° delay phase circuit, 8 ... Bandpass filter, 9 ...
… Adder, 11 …… Coefficient unit, 12 …… Comparator, 13…
… Control pulse generator, 14 …… TCR main circuit, 15 …… Power supply synchronization circuit, 16 …… Power factor correction circuit, 17 …… Square multiplier, 17 ′ ……
Filter, 18 ... Square rooter, 19 ... Non-linear correction circuit of reactor current vs. thyristor firing phase control angle

Claims (1)

(57) [Claims] 1. An open-loop reactive power compensator for the purpose of compensating for voltage flicker in an arc furnace or the like, in which a load current is instantaneously converted into a fundamental wave delay reactive current having a power factor cosφ≈1 through a power factor correction circuit, The delayed reactive current is converted to a DC signal corresponding to the load current through a squarer, a filter and a square root circuit, the DC signal is subtracted from a reference voltage signal based on the allowable current of the reactor switching circuit by the thyristor, and the subtracted A signal equivalent to the compensating current is input to the non-linear correction circuit of the reactor current vs. thyristor firing phase control angle and taken out as an output signal equivalent to the thyristor firing phase control angle, synchronized with the output signal and the power supply phase, and the firing phase is A control angle β rises at zero, β is 90 °, and a sawtooth wave whose wave height is equal to the allowable current is input to the comparator, and the comparator is input to the comparator. The method of the reactive power compensation apparatus and determines the ignition phase control angle point of the thyristor in that the level of the output signal and the sawtooth wave of the thyristor firing phase control angle corresponding matches to have.