Thyristor Controlled Reactors (TCR) and Harmonic Suppression by Discontinuous Phase Controlled (DPC) Switching

Thyristor controlled reactors (TCR) are extensively used in power system to control the voltage and stability but the conventional TCR introduce high-order harmonics in the line current. Earlier, two-reactor based half-wave control scheme was used but this scheme is good for upper-half control range only. In this work, discontinuous phase control (DPC) is used and several circuit topologies are proposed to control reactive (inductive) power. Both double winding and three-inductor configurations are found good for reactors of high-density magnetic flux. A configuration of multistage reactor of different magnitudes is proposed which offers very low THD over almost the whole control range. In this case, the switching of a particular reactor pair is done such that the control lies in the upper-half control range only to maintain THD less than 10%. Fourth configuration is also proposed where reactors of equal magnitude are used. Like integral cycle control, on-off control is used for coarse control and fine control is achieved by phase control like a conventional TCR. The analysis is done with MATLAB/Simulink software and the results verify the proposed schemes.