Enhanced Extinction Angle Control for Subsequent Commutation Failure Mitigation Considering Harmonic Voltages Variation

Improving the extinction angle control is an effective method to mitigate subsequent commutation failure (CF) that mainly comes from the voltage harmonics. However, the potential variations of commutation voltage and dc current after the valve has been fired are neglected by the existing methods, which consequently weakens the control accuracy and may lead to failed CF mitigation. Therefore, an enhanced extinction angle control method is proposed in this paper. Firstly, the subsequent commutation voltage with harmonics in the current cycle is approximately predicted by curve fitting method based on the transient response of ac voltages measured during the previous cycles. Then the extinction angles of upcoming commutations are predicted considering subsequent variations of both ac voltage and dc current. Finally, the predicted extinction angles are introduced into the original inverter control to develop the enhanced extinction angle control. Simulation results obtained in the PSCAD/EMTDC validates the effectiveness and advancement of proposed method on subsequent CF mitigation compared with the existing strategy.