Frequency-domain harmonic modeling and analysis for 12-pulse series-connected rectifier under unbalanced supply voltage

The paper proposes a frequency-domain harmonic model for 12-pulse series-connected thyristor-controlled rectifier under unbalanced supply voltage, considering the firing angle offset and commutation overlap angle caused by unbalanced voltage. The harmonic coupled admittance matrix of 12-pulse rectifier is derived based on positive-sequence and negative-sequence voltages for the frequency-domain harmonic model. The simplified model of 12-pulse rectifier that only considers the primary matrix elements is proposed by comparing the values and distribution of admittance matrix elements under positive-sequence and negative-sequence voltages and analyzing the harmonic production process of the AC current of rectifier. The application condition of different simplified models is investigated by analyzing the calculation errors changing with the firing angle or commutation overlap angle. The accuracy and efficiency of the proposed models is verified by simulation and experimentation.