JP2000152504A - Reactive power compensating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reactive power compensating device which achieves low-distorted waveform and leveling voltage fluctuation without causing errors in the amount of compensation, even if system impedance and the like fluctuates on the power supply side. SOLUTION: This reactive power compensating device connecting a saturable reactor Lb and a capacitor C connected in parallel with each other between a system power supply Vs and a load 1, generating leading or lagging reactive power based on a power fluctuation in the load, canceling or suppressing the power fluctuation in the load for suppression or improvement of a receiving point voltage Vp fluctuation, is provided with a voltage-type converter 5 whose output side is serially-connected to a saturable reactor Lb for applying the desired voltage Vt to the saturable reactor Lb, a detection circuit 6 detecting power fluctuation in the load, and a compensation-amount computing circuit 7 determining the amount of compensation from the output of the detecting circuit 6, correcting an error between the outputted compensation current Ia and the amount of the determined compensation for the output control of a converter 5, and variably controls the voltage Vt for causing saturable reactor current It to vary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactive power compensator for compensating power fluctuation of a load in a power system to stabilize the system and suppress voltage fluctuation.

[0002]

2. Description of the Related Art In a power system or the like in which power is supplied from a system power source such as a substation to a load through a system bus, a variable load such as a large-capacity arc furnace, a train load, or a steel rolling load that causes system voltage fluctuation due to reactive power fluctuation. On the other hand, a reactive power compensator is provided between the system power supply and the variable load to compensate for the reactive power caused by the variable load. An example of the reactive power compensator is shown below with reference to the main circuit configuration shown in FIG.

In the figure, (Vs) is a system power supply, (Xs)
Is a system impedance, (1) is a variable load, (2) is a system bus, and (3) is a reactive power compensator. The load (1) generates reactive power of an arc furnace or the like, and is connected to a system power supply (Vs) via a system bus (2).

[0004] The reactive power compensator (3) comprises a system bus (2).
The reactor (La) is inserted in series at the load connection point of, and the power factor improving phase-advancing capacitor (Cb) and the saturable reactor (Lb) are connected in parallel to connect the connection point to the reactor (L).
a).

In the above configuration, the phase advance capacitor (C
b) and the saturable reactor (Lb) are shown in FIG.
Voltage-reactive power characteristics (VQ characteristics) indicated by the dotted line in (b)
(Xa) and (Xb), and the phase advance reactive power (Qa) changes linearly with the voltage (V) in the phase advance capacitor (Cb). In the saturable reactor (Lb), the lagging reactive power (Qb) changes linearly with the voltage (V), while the current sharply increases when reaching a predetermined voltage (Va). The reactive power (Qb) sharply increases.

Accordingly, the combined VQ characteristic is shown in FIG.
As shown by the solid line in (b), the leading reactive power (Qa) is generated together with the voltage (V) up to the predetermined voltage (Va), and when it reaches the vicinity of the predetermined voltage (Va), it is shaped like a letter. And the reactive power becomes zero once. Then, after the reactive power (Q) becomes 0, the delayed reactive power (Qb) is generated and increases as it is with the voltage (V).

Therefore, for example, the voltage at which the reactive power (Q) becomes 0 is set as the rated voltage (Vo), and the node voltage (Vq) generated when the load current flows through the reactor (La) is the rated voltage (Vo). If it becomes higher, the lagging reactive power (Qb)
Is generated, and when the connection point voltage (Vq) becomes lower than the rated voltage (Vo), a phase leading reactive power (Qa) is generated.
Then, the advanced phase reactive power (Qa) raises the voltage,
Since the delayed reactive power (Qb) lowers the voltage, it cancels or suppresses the voltage fluctuation due to the load (1), thereby canceling or improving the fluctuation of the voltage (Vp) at the receiving point (P).

[0008]

According to the reactive power compensator shown in FIG. 2A, the saturable reactor (Lb) has a large thermal loss and noise, and a voltage fluctuation occurs on the power supply side. When the system impedance (Xs) fluctuates, the operating point greatly shifts and the compensation performance fluctuates. Therefore, for example, even if the power fluctuation of the load is small, the connection point voltage (Vq) apparently fluctuates greatly and an error occurs in the compensation amount, and it becomes difficult to suppress the voltage fluctuation, and the power receiving point voltage (Vp) becomes constant. The problem that it does not occur.

Further, since the saturable reactor current rapidly increases from the saturation point and is partially distorted from the sine wave, the distorted waveform contains harmonics, and when injected into the system bus (2), A large amount of harmonic current flows, distorting the bus voltage.
Therefore, it is necessary to take measures against harmonics such as adding a filter function to the capacitor (Cb), and it is very difficult to remove all the harmonics even if such measures are taken.

Further, when the power receiving point voltage fluctuation is determined not only by the reactive power of the load (1) and the reactance of the system, but also by the active power of the load (1) and the resistance of the system,
The compensating device based on the reactive power component cannot compensate for the voltage fluctuation due to the active power component, and has a problem that the voltage variation remains as a compensation error.

An object of the present invention is to provide a reactive power compensating apparatus which does not generate an error in the amount of compensation even if the system impedance or the like fluctuates on the power supply side, realizes a low distortion waveform, and levels out the voltage fluctuation. It is.

[0012]

According to the present invention, a saturable reactor and a capacitor are connected in parallel between a system power supply and a load, and a leading or lagging reactive power is supplied in accordance with a power fluctuation of the load. In a reactive power compensator that generates and cancels or suppresses a power fluctuation of a load and cancels or improves a power receiving point voltage fluctuation, a voltage that applies a desired voltage to the saturable reactor with an output side connected in series to the saturable reactor. A type converter, a detection circuit for detecting a load current or a connection point voltage to detect a power fluctuation of the load, a compensation amount determined from the output of the detection circuit, and a compensation current output to the system and the determined compensation amount. And a compensation amount calculating circuit for controlling the output of the converter by correcting the error and variably controlling the voltage applied to the saturable reactor to vary the saturable reactor current. And butterflies.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a reactive power compensator according to the present invention will be described below with reference to FIG. In the figure, (Vs) is a system power supply, (Xs) is a system impedance, (1) is a load, (4) is a reactive power compensator according to the present invention, and a reactive power compensator (4) is a saturable reactor (Lb). And a current transformer (CTa) for detecting output current, a phase-advancing capacitor (Cb) for improving power factor, a series transformer (T), a voltage-type converter (5), a detection circuit (6), and a compensation amount calculation circuit (7). )
And

A saturable reactor (Lb) is connected in series to the primary side of a series transformer (T), and is connected to a phase advance capacitor (C).
b), and the parallel connection point is connected to the power receiving point (P) of the system bus (2) via the current transformer (CTa).

The voltage type converter (5) has a DC capacitor (Ca) connected to the input side, an output side connected to the secondary side of the series transformer (T), and saturable through the series transformer (T). A desired voltage (Vt) is applied to the saturable reactor (Lb) by an inverter connected in series to the reactor (Lb).

The detection circuit (6) detects a load current (IL) or a connection point voltage (Vq) via a current transformer (CTb) or a voltage detection transformer (PT) inserted in the system bus (2). , The active power component and the reactive power component of the power fluctuation of the load (1).

The compensation amount calculation circuit (7) outputs the detection circuit output (I
b) is input to determine the amount of compensation and at the same time
According to a), the actual compensation current (Ia) to the system side is input, and the error between the compensation current (Ia) and the determined compensation amount is corrected to control the output of the converter (5). The voltage (Vt) applied to the saturable reactor (Lb) is variably controlled by the converter (5) to control the saturable reactor current (It).
Variable.

The operation of the present invention based on the above configuration will now be described. First, it is known from the reactor saturation characteristic curve shown in FIG. 2B that the reactive power (Q) greatly changes in the horizontal direction even if the voltage (V) slightly shifts in the vertical direction. Therefore, a small capacity (for example, 10 times of the apparatus capacity) with respect to the compensation capacity is used.
%) Of the converter (5) and applying a slight desired voltage (Vt) from the converter (5) to the saturable reactor (Lb) via the transformer (T). Q),
Therefore, the saturable reactor current (It) can be largely changed.

Therefore, first, the load current (IL) is detected by the detection circuit (6) via the current transformer (CTb) or the transformer (PT).
) Or the connection point voltage (Vq) to detect the active and reactive power components of the power fluctuation of the load (1), and output (I
b) is input to the compensation amount calculation circuit (7) to determine the compensation amount. At the same time, the compensation current (Ia) output to the system side is input to the compensation amount calculation circuit (7) by the current transformer (CTa),
The output of the converter (5) is controlled by correcting an error between the compensation current (Ia) and the determined compensation amount. Then, a desired voltage (Vt) is applied to the saturable reactor (Lb) via the series transformer (T), and the saturable reactor current (It) is arbitrarily varied with a slight voltage control as described above. .

Then, even if the system impedance (Xs) or the like fluctuates on the power supply side, a desired saturable reactor current (It) is output by voltage control by the converter (5) to change the operating point, and the receiving point voltage ( Vp) can be controlled to a constant rated voltage.

Further, by adjusting the output voltage waveform of the converter (5), distorting it in advance, and adding it to the saturable reactor current (It), the bus voltage can be improved to a low distortion waveform as much as possible.

Further, since the effective and reactive components of the power fluctuation of the load (1) can be directly detected and the compensation amount can be determined, the voltage fluctuation due to the effective component can be apparently compensated by taking in and out the reactive power. Further, the power factor can be improved by flowing a leading-phase reactive current that cancels a current corresponding to the delayed-phase reactive current of the load (1).

[0023]

According to the present invention, a saturable reactor and a capacitor are connected in parallel to each other and connected between a system power supply and a load to generate a leading or lagging reactive power in accordance with a power fluctuation of the load. In a reactive power compensator that cancels or suppresses the power fluctuation of the load and cancels or improves the power point voltage fluctuation, a voltage-type converter that applies a desired voltage to the saturable reactor is added, and the detected power of the load is The compensation amount is determined by the compensation amount calculation circuit from the fluctuation, and at the same time, the error between the compensation current output to the system side and the determined compensation amount is corrected, the output of the converter is controlled, and the voltage applied to the saturable reactor Variably controls the saturable reactor current, so even if the system impedance fluctuates on the power supply side, the voltage applied to the saturable reactor is variably controlled by the voltage control of the converter to compensate for the compensation error. It can be eliminated.

Further, even if the saturable reactor current is distorted, the bus voltage distortion can be reduced as much as possible by adjusting the output voltage waveform of the converter, and the amount of compensation can be determined by detecting the power fluctuation of the load. Therefore, the voltage fluctuation due to the effective component can be suppressed, and the power factor can be improved only by looking at the reactive power.

Also, the added converter has a small capacity relative to the compensation capacity, so that additional cost and size can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a reactive power compensator according to the present invention.

FIG. 2A is a circuit diagram illustrating an example of a conventional reactive power compensator. 2 (b) shows V- of the reactive power compensator of FIG. 2 (a).
Q characteristic diagram.

[Explanation of symbols]

 Reference Signs List 1 load 2 system bus 4 reactive power compensator 5 voltage type converter 6 detection circuit 7 compensation amount calculation circuit Lb saturable reactor C capacitor T series transformer Vs system power supply

Claims (1)

[Claims] A saturable reactor and a capacitor are connected in parallel between a system power supply and a load to generate a leading or lagging reactive power in accordance with the power fluctuation of the load, thereby canceling the power fluctuation of the load. Or a suppressor, a reactive power compensator for canceling or improving the receiving point voltage fluctuation, a voltage type converter having an output side connected in series to the saturable reactor and applying a desired voltage to the saturable reactor, and a load current or connection. A detection circuit that detects a point voltage to detect a power fluctuation of a load, and determines a compensation amount from an output of the detection circuit, and corrects an error between a compensation current output to a system and the determined compensation amount to correct the error. A compensation operation circuit for controlling the output of the converter and variably controlling the voltage applied to the saturable reactor to vary the saturable reactor current. Location.