Optimal Space Vector Sequence Investigation Based on Natural Sampling SVM for Medium-Voltage Current-Source Converter

The device switching frequency of current-source converters (CSCs) in high-power medium-voltage (MV) drive applications is normally around 500 Hz. Conventional space vector modulation (SVM) features fast dynamic response but its output contains low-order harmonics with high magnitudes. Recently, a natural-sampling-based SVM (NS-SVM) with superior low-order harmonics performance has been proposed for MV CSCs. This study further investigates the low-order harmonics performance of different space vector sequences for MV CSCs based on NS-SVM. Dwell times equations based on NS-SVM for each space vector sequence with minimized switching frequency are analyzed and derived; comparisons of different vector sequences in terms of low-order harmonics and load/grid-side total demand distortion performance are thoroughly conducted. Among all the investigated sequences, sequence 2 (SQ2) is the best one; its linear two-step dwell times equations are provided for online implementation. Simulations and experiments are provided to verify its performance.