JPH0621968B2 - Control circuit of reactive power compensator - Google Patents

Description

The present invention relates to a control circuit for a reactive power compensator.

[Prior Art] In order to suppress the power fluctuation caused by the operation of an arc furnace or the like, it is necessary to compensate the fluctuation of the reactive power, and as a side effect of such a purpose, application of a thyristor type reactive power compensator is required. Conceivable.

FIG. 2 is a schematic diagram for explaining the configuration of a thyristor type reactive power compensator.

The arc furnaces F1 and F2 are connected to the system via transformers T1 and T2, and a reactor Re and a conduction control element in which a thyristor Th is combined so as to be capable of bidirectionally conducting electricity are connected in series with the arc furnaces F1 and F2. And the delayed reactive power adjustment circuit
A phase advancing capacitor / filter circuit including a capacitor C and an inductance L is connected.

Then, the reactive power signal DD is calculated every moment in the reactive power detector DD by the current transformers CT1 and CT2 that detect the load current of the arc furnaces F1 and F2, and the voltage transformer PT, and the fluctuating reactive power signal is the reference. A control pulse generator PG which controls the phase of the pulse which is compared to the value and which is applied to the firing control terminal of the thyristor according to a magnitude which is more positive or negative than the reference value.
The output end of is connected to the ignition control terminal of thyristor Th,
Reactive power is controlled.

[Problems to be Solved by the Invention] By the way, in order to calculate the reactive power signal Q, it is obtained as follows by multiplying the 90-degree lag voltage v of the bus voltage and the load current i.

Q = VI {sin φ-sin (2ωt-φ)} (1) where V is the effective value of the voltage signal obtained by passing the bus voltage through the voltage transformer, and I is the load current obtained through the current transformer. The effective value of the applied current signal, φ is the phase angle.

From the above equation, the reactive power signal Q is expressed by a combination of the DC component and the double frequency ripple of the fundamental wave, and the reactive power value includes the second harmonic (double frequency component).

The load current signal I includes a reactive current signal Iq corresponding to the reactive power signal Q and an active current signal Ip corresponding to the active power signal P.

The active power signal P is expressed by the following equation.

P = VI {cosφ−cos (2ωt−φ)} (2) The active current signal Ip corresponding to this active power signal P is completely unnecessary in the reactive power signal Q detection, and the load current signal I becomes large. As it becomes clearer, the ripple of the double frequency is increased as is clear from the equations (1) and (2).

Further, the reactive current signal Iq includes a reactive current component signal (Iqav) corresponding to a quasi-stationary reactive power signal exhibiting a gentle movement, and a reactive current component signal exhibiting a sudden change,
An active current component signal (Ipav) corresponding to a quasi-stationary active power signal that also exhibits a gentle movement to the active current signal Ip.
And an active current component signal exhibiting abrupt changes.

As described above, conventionally, in the detection of the reactive power signal, the reactive current component signal Ipav corresponding to the quasi-stationary reactive power signal in the reactive current signal Iq and the quasi-stationary active power signal in the active current signal Ip are supported. Active current component signal Ipa
Since the load current signal including v is used as it is, when the variable reactive power signal is multiplied, the dynamic range of the necessary multiplier cannot be widened, and the reactive power signal detection accuracy can be improved. could not.

In the present invention, in detecting the reactive power signal Q, the active current signal Ip corresponding to the active power signal P is preferably as small as possible, and the reactive current signal Ip corresponding to the reactive power signal Q is preferable.
With respect to q as well, if there is a current component that is involved in voltage fluctuations, it is possible to rapidly respond to reactive power fluctuations, and the load current that is input to the multiplier that multiplies the reactive power signal Q is also reduced, thus increasing the dynamic range of the multiplier. It was made paying attention to the fact that it can be widely used and the detection accuracy can be improved.

[Means for Solving the Problems] In order to detect a variable reactive power signal, the present invention reduces the amplitude of a load current signal input to a multiplier that multiplies a reactive power signal, and leaves a rapid fluctuation as small as possible. Both the active current component signal Ipav corresponding to the quasi-stationary active power signal in the active current signal Ip and the reactive current component signal Ieav corresponding to the quasi-stationary reactive power signal in the reactive current component Iq. The current component signal is the load current signal I
It is characterized in that the current signal to be input to the multiplier for subtracting from the above to calculate the reactive power signal is narrowed down.

[Examples] The present invention will be described below based on examples shown in the drawings.

As shown in FIG. 1, a voltage transformer PT, a variable load LV, a series circuit of antiparallel-connected thyristors Th that bidirectionally conduct electricity to a reactor Re, and a capacitor C for phase advancing and filtering are connected in parallel to the bus bar. It Note that L1 represents the inductance of the power supply line.

The secondary side of the voltage transformer PT is connected to the 90-degree phase shifter PS, and is connected to the multiplier X1 on the output side of the 90-degree phase shifter PS.

A current transformer CT for detecting the current I of the variable load LV is coupled to the variable load LV, the secondary side of the current transformer CT is connected to the subtractor S and the multiplier X2, and the multiplier X2 is connected to the voltage transformer PT. It is connected to the secondary side.

The output side of the multiplier X2 is connected to the multiplier X3 via the low pass filter LPF1, and is connected to the secondary side of the multiplier X3 voltage transformer PT.

On the other hand, the multiplier X4 is connected to the secondary side of the AC device CT and 90
Is connected to the output side of the phase shifter PS, the output side of the multiplier X4 is connected to the multiplier X5 via the low-pass filter LPF2,
The multiplier X5 is connected to the output side of the 90-degree phase shifter PS.

The output sides of the multipliers X3 and X5 are the adder A2.
To the multiplier S, and the output side of the subtractor S is connected to the multiplier X1.

Here, on the output side of the multiplier X2, the active power signal P is output by the equation (2), but since it contains the second harmonic, it is converted by the low-pass filter LPF1. It is removed and smoothed to obtain a slow-moving active power signal P '. This P'is called a quasi-stationary active power signal.

Since the waveform in phase with the load voltage waveform and proportional to the quasi-stationary active power signal P'is the active current component signal in the load current signal I corresponding to the quasi-stationary active power signal, the load voltage waveform in the multiplier X3 It is generated by multiplication of the signal and the quasi-stationary active power signal P '.

Assuming that the active current signal I′p corresponds to the quasi-stationary active power signal P ′, I′psinωt∝P ′ × Vsinωt active power signal P is passed through the low-pass filter LPF1 as described above. , The active current signal I'p has a gradual change I in accordance with the change of the quasi-steady active power signal P '.
Appears as pav.

On the other hand, the reactive current component in the load current I corresponding to the quasi-stationary reactive power signal is obtained as follows.

The 90 degree delayed phase voltage signal and the load current signal are multiplied by the multiplier X4 to output the reactive power signal Q, and the second harmonic wave contained therein is removed and smoothed by the low pass filter LPF2. In this case, by selecting the characteristic of the low-pass filter LPF2 to have a long time constant of about 1 to several seconds, the rapid fluctuation component of the reactive power signal Q does not appear as an average, and the reactive power signal of gentle movement is not displayed. Q'can be obtained. This Q'is called a quasi-stationary reactive power signal.

Since the waveform that is delayed by 90 degrees from the load voltage waveform and whose amplitude is proportional to the quasi-stationary reactive power signal Q'is the reactive current signal I'q corresponding to the quasi-stationary reactive power signal, The lagging load voltage waveform and the quasi-stationary reactive power signal are input to the multiplier X5, and the average reactive current component signal Iqav contained in the load current signal is I'qsinωt∝Q 'with a gentle movement. × Vsin (ωt−90 °)

Then, both outputs of the multiplier X3 and the multiplier X5 are input to the adder A2, the output of the adder A2 is input to the subtractor S, and the active current component signal Ipav and the reactive current component signal are calculated from the load current signal I. Iqav is subtracted and input to the multiplier X1.

In the illustrated example, the quarter-cycle delay circuit TC is used on the output side of the multiplier X1 which is the final reactive power signal detector, but a filter for removing the second harmonic may be used.

In the event of a sudden change in the reactive power, the circuit for obtaining the active current component signal corresponding to the quasi-stationary active power signal and the circuit for obtaining the reactive current component signal corresponding to the quasi-stationary reactive power signal as described above Is a low-pass filter L with a large time constant
PF is used, and such abrupt fluctuation is smoothed, and the waveforms of the average active current component signal Ipav and reactive current component signal Iqav appear only as gentle fluctuations.

When the active current component signal Ipav and the reactive current component signal Iqav are subtracted from the load current signal I, I- (Ip
The remaining reactive power signal Δq due to av + Iqav) can be caused by almost abrupt changes.

This reactive power signal Δq is input to the control pulse generator PG via the reactive power phase conversion circuit QPS, and its output controls the reactive power by controlling the firing phase of the thyristor Th connected to the reactor Re.

[Effects of the Invention] As described above, in the present invention, in the multiplier for determining the reactive power, the active current component signal corresponding to the quasi-stationary active power signal from the load current signal and the reactive power corresponding to the quasi-stationary reactive power signal Since both current component signals of the current component signal are subtracted and input, the amplitude of the load current signal is reduced and the current signal input to the multiplier that calculates unscented power is converted to the current signal corresponding to the reactive power fluctuation. The second harmonic ripple generated in the multiplication output can be made smaller than that in which the load current signal is directly input to the multiplier, and the dynamic range of the multiplier for obtaining the reactive power can be widened. Therefore, the detection accuracy of reactive power detection can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional reactive power compensator. PT ... voltage transformer, CT ... current transformer, LV ... fluctuating load, PS ... phase shifter, X1, X2, X3, X4, X5 ...
... Multiplier, LPF1, LPF2 ... Low-pass filter, A1,
A2 ... Adder, S ... Subtractor, TC ... Delay circuit, QP
S ... Reactive power phase conversion circuit, PG ... Control pulse generator, Re ... Reactor, Th ... Thyristor.

 ─────────────────────────────────────────────────── --Continued from the front page Judgment panel for referee Judge Koichi Uyama Judge Ryoji Iio Judge Mitsuaki Hara (56) References JP53-66550 (JP, A) JP54-7978 (JP, A) JP-A-52-5452 (JP, A)

Claims (1)

[Claims] 1. A lagging reactive power adjusting circuit in which an energization control element and a reactor connected in anti-parallel are connected in series in parallel with a fluctuating load connected to a bus, and a phase advancing filter. In a control circuit of a reactive power compensator to which a circuit is connected, a voltage transformer for detecting a load voltage signal, a current transformer for detecting a load current signal, and a 90-degree voltage phase shifter for the load voltage are provided. A circuit for multiplying a load current signal and a load voltage signal to obtain a quasi-stationary active power signal through a low pass filter; and a circuit for multiplying the quasi-stationary active power signal and a load voltage waveform signal by the quasi-stationary A circuit for obtaining an active current component signal in a load current signal corresponding to an active power signal, and a quasi-steady state through a low-pass filter by multiplying the detected load current signal and a load voltage 90 ° delayed phase load voltage signal. A static reactive power signal A circuit for calculating a reactive current component signal in a load current signal corresponding to the quasi-stationary reactive power signal by multiplying the quasi-stationary reactive power signal and the 90-degree lag load voltage waveform signal. A subtractor circuit for subtracting both the current component signals of the effective current component signal and the reactive current component signal from the load current signal, and a circuit for multiplying the output current signal from the subtractor circuit by the 90-degree delayed phase load voltage signal. A control circuit for a reactive power compensator, comprising: