Comparative Evaluation of Harmonic Performance, Loss, and DC-Link Balancing Characteristics of Continuous and Discontinuous PWM for Phase-Leg Stacked Inverters

The phase-leg stacked PWM inverter generates multiphase voltages from a single stacked leg using a segmented dc link and ac-side dc-blocking capacitors. This paper compares six two-level PWM methods: SPWM, SVPWM, 60°&30° DPWM, +30°&−30° DPWM, DPWMMAX, and DPWMMIN. They are classified as continuous, asymmetric-clamping, and symmetric-clamping PWM and evaluated for current harmonics, switching frequency, semiconductor loss, dc-link ripple, and balancing dynamics. Results from a 450-V three-stack three-phase prototype show that continuous PWM gives lower current distortion and better balancing at low modulation indices. DPWM reduces the average switching frequency by about one-third and improves light- and medium-load efficiency. DPWMMAX and DPWMMIN offer the best compromise between loss reduction and stable dc-link regulation without clamp-type alternation. PWM selection guidelines are presented according to modulation index, load power factor, and operating objective.