Comparison of Three-Clamping-Level and Two-Clamping-Level Discontinuous Modulations in Cascaded H-Bridge Static Compensators

This paper formulates a three-clamping-level discontinuous pulsewidth modulation (DPWM) for three-phase cascaded H-bridge static compensators with star configuration. Analytical expressions of capacitor voltage and zero-sequence voltage under the three-clamping-level DPWM are provided considering the inherent capacitor voltage oscillations. Based on the derived expressions, the paper analyses: (i) the inductive operation limits, and (ii) the total harmonic distortion (THD) and weighted THD of the output voltages. The results are compared with the continuous modulation and the conventional two-clamping-level DPWM, showing their different performances.