Three-Level Discontinuous PWM for Loss and Thermal Redistribution of T-NPC Inverter at Low Modulation Index

With conventional pulsewidth modulation (PWM) strategies, the switches of a three-level T-type neutral-point-clamped (T-NPC) inverter are not equally utilized at modulation indices lower than 0.5, limiting the inverter power throughput. The inner switches incur more losses than the outer switches. This article investigates a series of space-vector-based discontinuous PWM (DPWM) templates for modulation indices lower than 0.5. The templates relocate the phase current from the inner to the outer switches of a T-NPC inverter. Using them, the device losses are reduced and get redistributed more equally among the inner and outer switches, enabling a higher inverter output current or switching frequency. Confirmatory simulation and experimental results are provided to demonstrate the potential of the three-level DPWM templates in comparison to the conventional PWM templates.