A simple active auxiliary commutation circuit for three-level inverters

This paper presents the analysis and design of a new low loss auxiliary circuit for three level PWM single-phase inverters which achieve soft-switching at all semiconductor devices. The active auxiliary commutation circuit is composed of a LC circuit and two bi-directional switches which operate at ZCS and ZVS. The proposed active auxiliary commutation circuit (AACC) dispenses the use of auxiliary voltage sources. Low reactive energy is added to the converter resulting in low RMS current stresses at main switches and consequently higher efficiency is achieved. The design and experimental results are presented to prove the operation principle. A full description of the circuit operation is given.