Thyristor controlled susceptances for balancing compensators operated under nonsinusoidal conditions

The RMS value of the unbalanced and reactive currents in three-phase unbalanced power systems can be reduced with a balancing compensator that has an adaptive property. Circuits that provide a controllable susceptance are the main components of these compensators. They can be built from thyristors, switched inductors and reactive elements. The susceptance of such circuits is referred to as `thyristor controlled susceptance´ (TCS) in the paper. The harmonic currents generated by switched thyristors and injected into the supply cause a waveform distortion, however. They have to be often operated, moreover, at distorted supply voltage, and a resonance with the system inductance may occur for harmonic frequencies. As a consequence, the load balancing and power factor improvement are obtained at the expense of an increase in waveform distortion. This distortion can be reduced if the structure of the circuit that provides the TCS is properly selected. In this paper, various circuits that can provide the TCS are analysed and compared with respect to generated harmonic currents and frequency properties