With the development of high power gate tun-off (GTO) thyristors, large capacity self-commutated power converters have been applied to electric power systems. The self-commutated static var compensator (SVC) contributes to power system stabilization since it dose not fail in commutation due to any power system fault. Pulse width modulation (PWM) control keeps harmonics low. Active and reactive power can be controlled separately and continuously.
On the other hand, there are two problems, a large loss at the high switching frequency of the GTOs, and excessive current due to DC excitation of the multiple transformer needed for large capacity.
A 50MVA self-commutated SVC has been installed in the Shin-shinano Substation of Tokyo Electric Power Company where it has been undergoing a field test since March 1992. Recently, we developed a high performance control method, which uses low harmonics PWM control and high response inhibition of DC excitation of the multiple transformer, under the condition of 2-pulse PWM control (GTO switching frequency is 100Hz). The control method has been applied to the 50MVA self-commutated SVC since June 1995.
In this paper, the control method and the field test results are described.