Fine inductive VAR control with high power quality using thyristor controlled reactors and discontinuous phase control switching in power systems

The thyristor-controlled reactors (TCR) are widely employed to regulate the power system voltage and improve stability. However, TCR injects higher-order harmonics in the line current. For instance, in conventional TCR configurations, the total harmonic distortion (THD) is 78.5% at 10% of the fundamental current, and even it is 10% at 80% of the fundamental current. A previously reported control approach uses two reactors with a half-wave control design, which was only effective for the upper half of the control range. This paper proposes four new circuit configurations for reactive power regulation using discontinuous phase control (DPC). The new reactor design is also proposed for high-density magnetic flux perform well with double windings and three-inductor setups under the proposed approach. The proposed configuration of a multistage reactor with varying magnitudes provides extremely low total harmonic distortion (THD) across a near-complete control range. Even, the proposed design has achieved virtually zero THD for the reactor current. For THD to be less than 10%, a specific reactor pair is switched such that the control is only in the top half of the control range. The following configuration is based on reactors with the same magnitude. Like integral cycle control, the on-off control is employed for coarse action, whereas phase control is applied for fine control. All the proposed configurations are practically realized, and the performance is experimentally verified satisfactorily.