JPH0612930B2 - Control device for reactive power compensation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention compensates for a variable load connected to a power system, such as reactive power generated from an arc furnace, a welder, a steel rolling facility, etc. The present invention relates to a control device for controlling a thyristor phase control reactor type reactive power compensator (hereinafter, also simply abbreviated as TCR) that suppresses fluctuations (flicker).

[Conventional technology]

FIG. 4 is a block diagram showing a compensation system of this type. In the figure, 1 is a TCR control device, 2 is a TCR, 3 is a filter capacitor, and 4 is a load. In Such systems, system load, TCR and the reactive power of the filter capacitor (var), respectively Q _S, Q _L, Q _TCR and Q
When the _{C, Q S = Q L +} Q TCR + Q by controlling the TCR to satisfy the _C 0 becomes a function to compensate the reactive power, to suppress a voltage drop due to system impedance X _S. At this time, particularly for a load such as an arc furnace that changes abruptly, it is necessary to predict the reactive power of the load every half cycle and control the TCR at high speed.

FIG. 5 is a block diagram showing a conventional example of a reactive power compensation control device, and FIG. 6 is an operation explanatory diagram thereof.

Reference numeral 11a in FIG. 5 is a sample hold circuit, which samples the system voltage e ₀ at the zero point of the load current i _L as shown in FIG. 6 (a). This value is E as shown in FIG. 6 (b).
_sin (E: system voltage effective value ,: power factor angle). 1
Reference numeral 2 denotes an integrator, which performs integration from the load current zero point during the integration period θ _i as shown in FIG. This integral When the load current i _L is close to a sine wave, it is proportional to its effective value.
Therefore, when these values are multiplied by the multiplier 13, Then (see FIG. 6 (d)), by sampling this value at the time of θ ⁱ by the sample hold circuit 11b as shown in FIG. 6 (e), the predicted reactive power of the load can be obtained. 14 is a compensation characteristic adjusting circuit, a circuit for determining the compensation characteristics such compensation sensitivity to the predicted value of the resultant reactive power Q _L, sub connexion pulse generator 1 at its output
Ignition signal g of desired control phase at 5 (see FIG. 6 (f))
Is configured to obtain.

[Problems to be solved by the invention]

However, according to such a control device, although the prediction accuracy is high when the load current is close to a sine waveform, the prediction error is large when the load current contains many harmonics such as in an arc furnace. There are drawbacks. FIG. 7 is for explaining this, and if the waveform distortion near the current zero (the period of θ ⁱ ) is large, the prediction error becomes large, and in this example, the current integrated value is detected to be large. It shows a case where the I _L predicted value becomes larger than the fundamental wave effective value of i _L. Needless to say, the opposite case may occur due to the distortion of the waveform.

Therefore, it is an object of the present invention to provide a control device with high prediction accuracy by reducing the prediction error of load reactive power due to such waveform distortion.

[Means for solving problems]

Multipliers for multiplying the load current and the system voltage to obtain the reactive power instantaneous value and the active power instantaneous value, respectively, and a double of the integrated value obtained by integrating the reactive power instantaneous value from the zero point of the load current twice. A calculation circuit for calculating a first function obtained by adding the integral value of the instantaneous value of the active power and a second function related to the phase control angle for determining the reactive power generated by the reactive power compensator. A function generator for generating is provided, and the first function is a function θ ² proportional to the square of the time from the load current zero point.
The second function is compared with the function obtained by dividing by, and when both are equal, a firing signal for firing the thyristor of the reactive power compensator is emitted.

[Action]

Instantaneous value p of active power obtained by multiplying load current i _L and system voltage e _0, and voltage e ₉₀ 90 ° behind load current i _L and system voltage
And a reactive power instantaneous value q obtained by multiplying a, (the θ angle from the load current zero point) the first function = 2∫∫qdθdθ + ∫pdθ calculates the reactive power Q _L of the load is The control angle phase of the TCR is determined on the basis of the relational expression expressed as follows. By performing control by the integrated value of the reactive power instantaneous value q until immediately before the control of the thyristor,
The harmonic components contained in the load current are averaged to improve the prediction accuracy of the reactive power. As a method of obtaining the ignition signal,
The second function f (β) related to the phase control angle β that determines the reactive power generated by the compensator, A method for obtaining a pulse with the proviso that bets are equal, theta ²
There is a method of obtaining a pulse under the condition that × f (β) and (2∫∫qdθdθ + ∫pdθ) are equal.

Example of Invention

The control relational expression of the TCR for compensating the reactive power of the load is expressed by the following expression.

K _F (Q _L −Q _L0 ) + Q _TCR = K (constant) (1) where K _F is the compensation sensitivity, Q _L is the reactive power of the load, and Q _L0 is the non-variable component of Q _L (base component). ), Q _TCR is the reactive power generated by the TCR. Since K = Q _TCR (rated reactive power of TCR) is usually selected, the above equation (1) is Becomes Here, when Q _TCR is represented by a control angle β starting from the phase of 90 ° from the system voltage zero point, It becomes like. Here, βmin is the minimum control phase angle at which the TCR produces the rated reactive power Q _TCRR .

Substituting Eq. (3) into Eq. (2), K _F (Q _L −Q _L0 ) = f (β) (4) However, Is.

On the other hand, considering the fundamental wave component of the load current i _L , (Θ is an electrical angle from the load current zero point), the active power instantaneous value p and the reactive power instantaneous value q
Are respectively expressed by the following equations. However, E ₀ is a system voltage effective value, and is a power factor angle.

The integral value from the current zero point of p is Becomes

Also, the integral value of q from the current zero point is And integrating again, Becomes

From 2 × (10) formula + (8) formula, Is obtained. Load reactive power Q _L, so it is _{Q L = E 0 I L sin} , 2∫∫qdθdθ + ∫pdθ = Q L × θ 2 relational expression is satisfied. Therefore, Then, substituting equation (4) above equation (12), Becomes Therefore, if the two functions of the left side and the right side are created and their intersections are obtained, the control phase of the TCR satisfying the equation (13) is obtained.

FIG. 1 is a block diagram showing an embodiment of the present invention, which is for concretely realizing the above-mentioned calculation. Also, the second
The figure is a waveform chart of each part for explaining the operation.

In FIG. 1, multipliers 13a and 13b are shown in FIG.
From the load current i _L , the voltage e ₀ in phase with the system voltage, and the voltage e ₉₀ with a 90 ° phase delay from that shown in Fig. 2, the reactive power instantaneous value q and the active power instantaneous value p as shown in Fig. 2 (b) are shown. Is calculated. The output q of the multiplier 13a is converted to the integrator 12
After integrating twice by a and 12b, the proportional amplifier 16
The gain is adjusted by a to obtain the output h = 2∫∫qdθdθ (see FIG. 2C), and the output p of the multiplier 13b is integrated by the integrator 12c to output i = ∫pdθ (Fig. 2 ( C)) is obtained, the two are added by the adder 17a to output j =
2∫∫qdθdθ + ∫pdθ (see FIG. 2C) is calculated. Further, the signal j is input to the divider 18 and divided by the function θ ² generated by the function generator 19 And subtracting the value of Q _L0 set in the voltage setter 20 in the subtractor 17b, multiplying it by K _{F in the} proportional amplifier 16b, and inputting it to the comparator 22. The function f (β) created by the function generator 21 is input to the other input of the comparator 22, and a firing signal is obtained at a point where both inputs are equal as shown in FIG. With such a configuration, it is possible to obtain the ignition signal q (see FIG. 2 (e)) of the control phase that satisfies the relational expression (13).

FIG. 3 is a block diagram showing another embodiment of the present invention.

This is obtained by multiplying both sides of the equation (13) by θ ² and transforming it into K _F (2∫∫qdθdθ + ∫pdθ−θ ² QL ₀ ) = θ ² f (β) (14) The ignition signal is obtained by creating two functions on both sides and comparing the two. The basic idea is the same as that shown in FIG. 1, and since the calculation of equation (14) is simply replaced with a specific circuit, detailed description will be omitted.

〔The invention's effect〕

According to the present invention, the prediction is stopped based on the integral value of the load current i _{L for} a certain period of time, the reactive power q and the active power p are continuously integrated, and the integral value up to immediately before the control of the thyristor is used. Since the ignition signal satisfying the TCR control condition is obtained, the influence of the harmonics contained in the load current is reduced, and the advantage of significantly improving the prediction accuracy of the load reactive power is brought about.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform chart of respective parts for explaining the operation, FIG. 3 is a block diagram showing another embodiment of the present invention, and FIG. FIG. 5 is a block diagram showing a general example of a power compensation system, FIG. 5 is a block diagram showing a conventional example of a reactive power compensation control device, FIG. 6 is a waveform diagram of each part for explaining the operation, and FIG. It is explanatory drawing for demonstrating the prediction error of the reactive power by waveform distortion. Reference numeral 1 ... Reactive power compensation control device, 2 ... Reactive power compensation device (TCR), 3 ... Filter capacitor, 4 ... Load, 11a, 11b ... Sample and hold circuit, 12,
12a, 12b, 12c ... integrator, 13, 13a, 1
3b, 13c, 13d ... Multiplier, 14 ... Compensation characteristic adjusting circuit, 15 ... Pulse generator, 16a, 16b ... Proportional amplifier, 17a, 17b ... Adder / subtractor, 18 ... Divider, 19, 21 ... Function generator, 22 ... Comparator.

Claims (4)

[Claims] 1. A control device for controlling a thyristor phase control type reactive power compensator provided for compensating reactive power generated by a fluctuating load connected to a power system and suppressing a voltage fluctuation, comprising a load current. And a system voltage to obtain a reactive power instantaneous value and an active power instantaneous value, respectively, and a value that is twice the integrated value obtained by integrating the reactive power instantaneous value from the zero point of the load current twice. An arithmetic circuit that calculates a first function obtained by adding the integrated value of the active power instantaneous value, and a second function that is related to the phase control angle that determines the reactive power generated by the reactive power compensator. And a function generator obtained by dividing the first function by a function θ ² proportional to the square of the time from the load current zero point, and comparing the second function with the second function. Ignite the thyristor when it is fired Reactive power compensation control apparatus characterized by issuing a firing signal for. 2. A reactive power compensation controller according to claim 1, wherein the first function and the second function are compared with a function obtained by multiplying the function by a function θ ^2. A reactive power compensating control device, which emits an ignition signal when struck. 3. The reactive power compensating control device according to claim 1, wherein a function to be compared with the second function is obtained by dividing the first function by the function θ ^2. A reactive power compensating control device, wherein a predetermined value corresponding to a non-variable component (base component) of load reactive power is subtracted. 4. The reactive power compensating controller according to claim 2, wherein a function to be compared with a function obtained by multiplying the ^second function by θ ² is loaded from the first function. A reactive power compensating control device, wherein a predetermined value corresponding to a non-variable component (base component) of reactive power is multiplied by a function θ ² and subtracted.