JP3003552B2 - Self-excited reactive power compensator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-excited type reactive power compensator suitable for stabilizing a system and preventing flicker and voltage fluctuation of a load having a large reactive power variation such as an arc furnace.

[0002]

2. Description of the Related Art In a power system, a fluctuating load such as a large-capacity arc furnace, a train load, a steel rolling load, etc., which causes a system voltage fluctuation due to a reactive power fluctuation, fluctuates between a system power supply and the fluctuating load. A reactive power compensator for compensating for reactive power due to a load is provided, and one example thereof is a self-excited reactive power compensator (hereinafter, referred to as a self-excited SVC).
As shown in FIG. 2, the self-excited SVC includes two square-wave inverters (1a) and (1b), one high-frequency PWM inverter (2), and a control command unit (not shown). Inverters (1a), (1b), and (2) are connected in parallel to a reactive power generation load (not shown) such as an arc furnace by connecting to the system power supply (Vs) via the grid connection transformer (Tm) Is done.
(Xs) is the system impedance.

The transformer (Tm) is a transformer for a square wave inverter (Ta) (Tb) and a transformer for a PWM inverter (Tc).
The transformers (Ta) and (Tb) for a square wave inverter connect each high-voltage side (primary side) (Pa) and (Pb) in parallel and multiplex via an inter-phase reactor (L), and are connected to the reactor (L). It is connected to the system power supply (Vs) via the system impedance (Xs), and the square wave inverters (1a) (1b) are connected to each low-voltage side (secondary side) (Qa) (Qb). Also, the high voltage side (Pc) is connected in series to the parallel connection point of the square wave inverter transformers (Ta) (Tb), and the PWM inverter (2) is connected to the low voltage side (Qc). Connected.

As described above, the square wave inverters (1a) and (1b) are connected to the low voltage side (Qa) and (Qb) of the transformers (Ta) and (Tb), respectively, and are DC-charged by a converter or the like. This is a large-capacity, low-loss, slow-response inverter that generates a fixed square wave base voltage (Vp) having a fundamental frequency (50, 60 Hz) from a DC voltage of a capacitor (not shown). As described above, the PWM inverter (2) is connected to the low voltage side (Qc) of the transformer (Tc), and compensates for a reactive current from a DC voltage of a capacitor (not shown) charged by a converter or the like. This is a small-capacity, high-loss, fast-response inverter that generates a high-frequency variable square-wave voltage component (Vq) for generating a high-frequency variable square-wave voltage component (Vq).

At this time, a transformer for a square wave inverter (Ta)
By changing the output voltage phase of (Tb) and performing parallel multiplexing, harmonic components of the compensation currents (Ia) and (Ib) flowing from the transformers (Ta) and (Tb) to the power supply side are canceled and reduced.
Also, even if the two square wave inverters (1a) and (1b) or the transformers (Ta) and (Tb) have the same capacity, if each output voltage becomes unbalanced due to an error or the like, each transformer becomes (Ta)
A cross current (It) refluxing between (Tb) occurs, which does not flow to the power supply side, flows into the transformer (Ta) or (Tb), and unexpectedly occurs beyond the transformer's capability. is there. Therefore, an interphase reactor (L) between the transformer (Ta) (Tb)
And adjust the impedance value to adjust the cross current (I
t) is controlled so as to easily flow to the power supply side, and the cross current (I) flowing between the transformers (Ta) (Tb) by the reactor (L) is controlled.
t).

In general, when transformers are multiplexed in series, the series voltage sharing applied to each transformer during system interconnection (when the switch is ON) is determined by the excitation impedance ratio of the transformer. On the other hand, each inverter (1a) (1b) (2)
Since the voltage required for the power supply is predetermined, if an error occurs in each of the excitation impedance ratios, the low-voltage side of the transformer becomes improper and an undesired overvoltage is applied to the inverters (1a) (1b) (2). May be added. Therefore, conventionally, a gap is provided in the transformer core, or an exciting impedance adjusting reactor is provided on the low voltage side, and the transformer (Ta) (Tb) has a PW
When an M inverter transformer (Tc) is connected in series, the excitation impedance ratio is adjusted to an appropriate value to adjust the series voltage sharing. At this time, if the transformers (Ta) and (Tb) are connected in parallel and multiplexed to form a series multiplexed configuration with the transformer (Tc), the series configuration of the three transformers becomes two stages. Adjustment becomes easy.

According to the above configuration, when the load current is detected and the generation of the reactive power due to the load fluctuation is detected, each of the inverters (1a), (1b) and (2) generates the reactive power (Q) for compensation.
It is supplied to the system bus via a transformer (Tm) to cancel out reactive power due to load fluctuation. The reactive power (Q) is
Q = {Vs · (Vp + Vq) / Xs}, and the voltage component (Vq) by the PWM inverter (2) is variably controlled and set as appropriate.

[0008]

The problem to be solved is that if two transformers (Ta) and (Tb) for a square wave inverter are connected in parallel in a self-excited reactive power compensator, the interphase reactor (L) becomes In addition, the reactor (L) is on the high voltage side and its insulation equipment is also required, so that the overall size of the transformer (Tm) is increased and the cost is increased. Therefore, an object of the present invention is to provide a self-excited SVC in which the interphase reactor (L) is omitted and cost and space are saved.

[0009]

SUMMARY OF THE INVENTION The present invention provides a transformer for a plurality of square wave inverters having a large capacity low speed response square wave inverter for generating a base voltage equal to the system voltage connected to the low voltage side, and a reactive current canceling device. And a transformer for a PWM inverter in which a small-capacity and high-speed PWM inverter for generating a voltage component for generating a compensation current is connected to a low-voltage side, and a sum of output voltages of the respective inverters is connected to a system via a system impedance. be one that generates a compensating reactive power by the amplitude control voltage in phase, multi-series changes its output voltage phase of the high-pressure side of the plurality of square wave inverter transformer and PWM inverter transformer When you connect
In both cases, the excitation impedance of multiple transformers for square wave inverters
-The dance ratio can be increased by providing a gap in the transformer core.
Adjustable and square wave inverter transformer and PWM
The excitation impedance ratio of the transformer transformer excitation impedance
The adjustment is performed by providing a dance adjustment reactor .

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a self-excited var compensator according to the present invention will be described below with reference to FIG. The same parts as those shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. The difference is that in the configuration of the transformer (Tn), each high-voltage side (Pa) (Pb) of a plurality of square wave inverter transformers (Ta) (Tb) is multiplexed in series and each low-voltage side (Qa)
This means that square wave inverters (1a) and (1b) were connected to (Qb), respectively. And transformer for square wave inverter (T
a) The high voltage side (Pa) and (Pb) of (Tb) are further connected in series with the high voltage side (Pc) of the transformer for a PWM inverter (Tc), and the PWM inverter (2) is connected to the low voltage side (Qc).

According to the above configuration, the square wave inverter (1
a) The voltages output from (1b) and the PWM inverter (2) are converted into series multiplexed transformers (Ta) (Tb) and (Tc).
And is output to the power supply side. Then, since no reflux occurs between the transformers (Ta) (Tb), the transformer (Ta)
The occurrence of the cross current (It) due to the imbalance of the respective output voltages of (Tb) is eliminated, and the interphase reactor (L) becomes unnecessary. As in the conventional case, the harmonics are reduced by changing the phase of the output voltage of the transformer (Ta) (Tb).

[0012]

EXAMPLES Further, more specific examples of the present invention will be described below. First, three transformers (Ta), (Tb), and (Tc) are connected in series and multiplexed, so that the excitation impedance ratio is adjusted so that each series voltage distribution during system interconnection (switch ON) is appropriate. There is a need to. Therefore, in the square wave inverters (1a) and (1b) having the same performance, a gap is provided in the transformer core to adjust the excitation impedance ratio. Also, two square wave inverter transformers (Ta) (T
b) and a transformer for PWM inverter (Tc) are provided with an exciting impedance adjusting reactor to adjust the exciting impedance ratio.

[0013]

According to the present invention, since the high-voltage sides of the plurality of square-wave inverter transformers in the self-excited var compensator are connected in series and the low-voltage sides are connected to the square-wave inverter, the interphase reactor is In addition, the insulating equipment is not required, the number of parts is reduced, and low cost and space saving can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a self-excited var compensator according to the present invention.

FIG. 2 is a circuit diagram illustrating an example of a conventional self-excited var compensator.

[Explanation of symbols]

 1a, 1b Square wave inverter 2 PWM inverter Tn transformer Ta, Tb Square wave inverter transformer Tc PWM inverter transformer Vs System power supply Xs System impedance

Claims (1)

(57) [Claims] 1. A transformer for a plurality of square-wave inverters having a large-capacity low-speed-response square-wave inverter for generating a base voltage equal to a system voltage connected to a low-voltage side, and a voltage for generating a compensation current for canceling a reactive current. And a PWM inverter transformer in which a small-capacity high-speed PWM inverter for generating components is connected to the low-voltage side, and the added value of the output voltage of each inverter is amplitude-controlled in phase with the system voltage via the system impedance. Generates reactive power for compensation
A plurality of square wave inverter transformers and P
A high pressure side of the WM inverter transformer the output voltage phase
In addition to serial multiplex connection , multiple square wave
The excitation impedance ratio of the transformer for the
Adjustment by providing a gap and
Excitation of transformer for inverter and transformer for PWM inverter
The reactor for adjusting the excitation impedance
A self-excited reactive power compensator characterized in that the self-excited reactive power compensator is adjusted by applying a force.