A Generalized Single-Carrier PWM Scheme for Multilevel Converters

This article proposes a novel and generalized single-carrier (SC) pulsewidth modulation (PWM) scheme suitable for multilevel converters. Compared with the existing SC-PWM schemes, the proposed one presents a simpler approach to replicate the behavior of the phase disposition PWM method at any operating point. Besides having an easier digital implementation, the proposed SC-PWM scheme results in great control flexibility to optimize the operation of multilevel converters. Based on the rationales of the proposed SC-PWM scheme, an optimized switching strategy for a cascaded H-bridge (CHB) multilevel inverter architecture is developed. The proposed optimized switching strategy imposes appropriate switching sequences with a minimum number of power device commutations per cycle, leading to both half-wave and quarter-wave symmetries at the individual H-bridge cell level, which subsequently improves the converter harmonic performances and reduces the overall switching losses. The validity and effectiveness of both proposed modulation and switching strategies are demonstrated through the intensive simulation and experimental test results provided both in time and frequency domains. The experimental results are obtained on a three-phase seven-level CHB inverter for an 18-kW laboratory prototype.