In recent years, power demand has considerably increased, and there is the need to improve the quality of electric power, such as voltage change and three phase voltage unbalance. Static var compensators have been used for suppressing the disturbance of power distribution lines in mainly industrial fields and now the application is going to be expanded to rail way systems and power transmission systems(1)_??_(3). A conventional static var compensator is a naturally commutated one consisting of thyristor controlled reactors. Recently, self-commutated static var compensators have started to be used in practical applications, and the largest capacity of the self-commutated static var compensators reaches to 100 MVA(4)(5). They have the ability of quick and flexible control to compensate reactive power.
This paper describes the control system for self-commutated static var compensators to suppress three phase voltage unbalance as well as line voltage change. The features of the SVC control system are as follows.
(1) Independent current control of positive-phase and negative-phase sequence components.
(2) P-Q decoupling control
The authors have examined the SVC control system by an experimental model and verified the satisfied characteristics.
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