Improvement of power quality using self-commutated converters

This paper describes the system to control reactive power and harmonics flowing into a power system using a self commutated converter. Active filters and the reactive power controls which use voltage source inverters are put to practical use with many applications. A SVG (static VAr generator) has been used in order to restrain power oscillation against fluctuation of the power system. SVG has been applied in order to control the voltage of an electric train substation. Passive filters compensate for harmonics and reactive power of the power system. When parallel resonance occurs between the passive filter and reactance of the power system, harmonics of the power system spread. A self commutated converter compensates for harmonic load current and restrains parallel resonance between the system and the passive filters. Power converters are used for a power supply of superconducting coils such as SMES. Because the volume of these power supplies is more than dozens of MVA, many converters work in parallel. As a power supply for the superconducting coil, a parallel system of thyristor converters and self commutated converters has been examined. The passive filter is connected for reactive power compensation and harmonics absorption of the thyristor converter. A self commutated converter controls reactive power of all thyristor converters and the passive filter. It restrains harmonics further while damping parallel resonance of the passive filter and power system.