JPH07104742B2 - Reactive power compensator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a reactive power compensator for a grid.

[Background Art] Fig. 2 (a) shows a reactive power compensator of the already proposed system. In the figure, 1 is an infinite bus, 2 is a power source impedance, 3 is a bus, 8 is a variable load connected to the bus 3, such as an arc furnace, and 4 is reactive power generated by the variable load 8. A high-impedance transformer for compensating for fluctuations, and 5 is a thyristor connected in anti-parallel and connected in series with the high-impedance transformer 4 to control energization of the high-impedance transformer 4. In addition,
Instead of the high impedance transformer 4, a series circuit of a transformer 41a and a reactor 42a may be used as shown in (b).

9 is a Q detector, 7 is a CT coupled to a variable load 8,
Reference numeral 6 is a PT coupled to the bus bar 3, and the bus voltage and fluctuating load current are input to the Q detector 9 by PT6 and CT7, and the reactive load power Q is calculated. A pulse generator 10 receives the output of the Q detector 9 and generates a control pulse signal for the thyristor 5 to form a reactive power control circuit. The current control in the thyristor 5 reduces the reactive power flowing to the high impedance transformer 4 when the reactive power of the variable load 8 increases, and reduces the reactive power of the variable load 8 when the reactive power decreases.
The reactive power flowing through the high impedance transformer 4 is increased to suppress power fluctuations in the system.

By the way, according to the Q detection reactive power control alone as described above, even when the voltage of the infinite bus 1 is dropping, the Q control is continued, and the control system itself creates a factor of further voltage drop. The same thing can be said when is rising.

In order to improve this, when the system voltage as shown in Fig. 3 is above a predetermined voltage upper limit value and below a predetermined voltage lower limit value, the energization amount of the high impedance transformer by thyristor control. We have proposed a reactive power compensator that can control the fluctuation of the system voltage by maximizing or cutting off.

The same parts as those in FIG. 2 are designated by the same reference numerals.

As shown in the figure, this device is equipped with the Q detection reactive power control system of FIG. 2 and includes a voltage detector 11, an upper / lower limit comparator 12, a dead zone circuit 15, and an upper limit setting device for the upper / lower limit comparator 12. 13, a lower limit setting device 14, and a voltage detection circuit in which a dead band circuit 15 is connected to the pulse generator 10.

If there is an output signal that exceeds the dead zone, this signal controls the pulse generator 10, and if the signal is based on exceeding the upper limit set value, the pulse generator 10
If the pulse generator is based on the one that increases the current of the thyristor 5 to measure the drop of the system voltage by adding it to the input of
Since the gate of 10 is turned off and the thyristor 5 is cut off, the system voltage rises.

[Problem] By the way, in the above-described upper and lower limit voltage detection circuit of FIG. 3, when there is a voltage above the upper limit value or below the lower limit value, the pulse generator from the dead zone circuit 15 The signal to 10 is not a continuous signal but may have a sudden fluctuation, and if the thyristor 5 is suddenly controlled accordingly, it may transiently induce voltage fluctuations in the system, and voltage feedback control (correction control However, sometimes there are cases where over-compensation and under-compensation of reactive power occur.

[Means for Solving the Problem] An object of the present invention is to perform the suppression control of voltage fluctuation by preventing the transient fluctuation of the voltage of the system and the occurrence of overcompensation (undercompensation). In a reactive power compensator in which a thyristor energizes and controls a high-impedance transformer in parallel with a variable load, or a transformer and a reactor are connected, a reactive power control circuit for the thyristor responds to a drop or rise in system voltage. A voltage control circuit that includes a voltage detector and a proportional integrator with upper and lower limit setting devices is added to enable voltage feedback in the range where the input from the voltage detector exceeds the setting upper limit value or falls below the setting lower limit value. It is intended to achieve the above object by performing control.

The present invention will be described below with reference to the embodiment shown in FIG. The same parts as those in FIGS. 2 and 3 are designated by the same reference numerals. (A) is a block diagram showing an embodiment of the present invention, and (B) shows a voltage control circuit.

Similar to FIG. 3, a variable impedance 8 connected to the bus 3 connected to the infinite bus 1, for example, an arc furnace in parallel, a high impedance transformer 6 or a thyristor 5 connected in antiparallel with a transformer and a reactor. Connected in series. Although the figure shows only one phase, a similar configuration is adopted for each phase. Q detector 9 receives inputs from CT7 coupled to the conductor of variable load 8 and PT6 coupled to bus 3. The Q detector 9 is connected to the pulse generator 10 via the adder 16, and the pulse signal output of the pulse generator 10 controls the firing of the thyristor 5.

The voltage detector 11 is connected to the output side of PT6, and the voltage signal is input to the proportional integrators 17 and 18. Reference numerals 13 and 14 are an upper limit setting device and a lower limit setting device, respectively, and their output signals are input to the proportional integrators 17 and 18, respectively. The output signals of the proportional integrators 17 and 18 are input to the adder 16.

If the output from the voltage detector 11 is within the predetermined voltage value determined by the upper limit setter 13 and the lower limit setter 14 based on the bus voltage, the output signal from the adder 16 is output only from the Q detector 9. Only the VQ, the output signal VQ enters the pulse generator 10, and the thyristor 5 controls the energization of the high impedance transformer 6 in the direction of suppressing the fluctuation reactive power in response to the fluctuation of the fluctuation load 8. .

Details of the voltage control circuit configured as described above are shown in FIG. 111 is a voltage detector including a multiplier and a filter. Output signal from voltage detector 111 and upper limit setter 1
The output signal from 31 is input to the proportional integrator 171 including an adder. The + signal is cut off here. Further, the output from the voltage detector 111 and the output from the lower limit setting unit 141 are input to the proportional integrator 181 including an adder. Where-the signal is cut.

Proportional integrator when system voltage rises above the upper limit setting
171 performs PI control, outputs 0-− signal, and is added to the signal VQ in the adder 161, and this signal becomes the thyristor phase control signal in the pulse generator 10, and feedback control is performed so that the system voltage becomes the upper limit set value. To do.

Similarly, when the voltage drops and becomes less than or equal to the lower limit set value, the proportional integrator 181 performs PI control and outputs a 0 to + signal, which is added to VQ by the adder 161, and this signal controls the phase of the thyristor, and the lower limit. Feedback control is performed so that the set value is reached.

In addition, by comparing ST ₁ and ST ₂ of the proportional integrators 171, 181, with the response time ST ₀ of the Q detector 9 and setting ST ₁ = ST ₂ 20ST ₀ , in the range of the upper limit setting value V _L lower limit setting value, Only Q control is given priority, and other than this, relatively slow voltage feedback control is added, so transient fluctuations in the system are also suppressed.

[Effect] As described above, according to the present invention, not only compensation of reactive power fluctuations in a fluctuating load, but also when the system voltage becomes equal to or higher than a predetermined upper limit value and equal to or lower than a lower limit value, this voltage fluctuation Continuous feedback control is also used for suppression, and reactive power control is performed while keeping the system voltage within the upper and lower limit set voltages. Also, at this time, a proportional integrator is used, so that no transient phenomenon occurs when the upper and lower limit set values converge, in the system.

The present invention can realize from reactive power compensation to voltage fluctuation countermeasures with a simple circuit configuration.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, FIG. 1A is a block diagram showing the embodiment, and FIG. 1B is a block diagram of a voltage control circuit. FIG. 2 is a block diagram of a conventional Q detection control type reactive power compensator. FIG. 3 is a block diagram of a reactive power compensator with upper / lower limit setting device. 1 ... Infinity bus, 3 ... Bus, 4 ... High impedance transformer, 5 ... Thyristor, 6 ... PT, 7 ... CT, 8
...... Fluctuating load, 9 ... Q detector, 10 ... Pulse generator,
11 …… Voltage detector, 12 …… Upper / lower limit comparator, 13 …… Upper limit setter, 14 …… Lower limit setter, 15 …… Dead band circuit, 16 ……
Adder, 17, 18 ... Proportional integrator.

Claims (1)

[Claims] 1. A reactive power compensator in which a high-impedance transformer whose current is controlled by a thyristor or a transformer and a reactor are connected in parallel to a variable load connected to a power source, and a reactive power control circuit for the thyristor is provided with a system. A voltage detector provided to respond to a drop in voltage is added, and a proportional integrator equipped with the detector and an adder having the output signal of the upper / lower limit set as an input is added as a voltage control circuit, and the input from the voltage detector is In a region that exceeds the set upper limit value or falls below the set lower limit value, the output signal of the voltage control circuit is added to the reactive power control signal so that the system voltage is equal to or less than the system voltage determined by the upper / lower limit setting unit. Upper limit value, or
A reactive power compensator characterized by performing voltage feedback control so as to reach a lower limit and also performing system voltage fluctuation control.