Anomalous phenomenon of conduction angle in TCR-SVC and its control

Static VAr compensator (SVC) with thyristor controlled reactor (TCR) is widely used as a continuously variable reactive power compensator in electric power systems. Recently, unexpected sudden jumps of conduction angle were reported depending on the change of firing angle in TCR. This anomalous phenomenon named the switching time bifurcation is due to the nonlinearity caused by switching operation. Authors have studied the switching time bifurcations in a TCR-SVC circuit experimentally, numerically and theoretically, and clarified that the occurrence of bifurcations depends on the resonant frequencies and damping parameters of the circuit. In addition, they showed the possibility of subharmonic oscillations accompanied with the switching time bifurcation in experiments and simulations. The detailed analysis leads the onset of subharmonic oscillation subject to the initial conditions of state values at the instant of firing. This implies uncoordinated firing angle control might happen to generate subharmonic oscillations, and the coordinated firing angle operation is necessary to avoid subharmonic oscillations. Then, this paper proposes the firing angle regulation scheme so as to keep the initial conditions out from the domain of subharmonic oscillation.