Five-Level NPC Inverter Fed by Dual 18-Pulse Rectifier for High-Power Drives

This thesis focus on the topology of multi-pulse rectifiers and the modulation technique of multilevel inverters for high-powermedium voltage drives. A dual 18 pulse rectifier topology is proposed. The topology achieves harmonic performance of 36-pulse rectifiers by using relatively simple 18-pulse transformers. It can also neutralize the 5th and 7th harmonics caused by unbalanced secondary windings. Moreover, a novel space vector modulation (SVM) alogrithm with flexilble three-segment switchinhg sequence is proposed for multilever inverters. It features: 1) minimized device switching frequency, 2) lower weighted total harmonic distortion due to the increase of the inverter sampling frequency, and 3) easy implementation thanks to the simplified sequence design. The algorithm is applicable to various multilevel inverter topologies. Theoretical analyses and computer simulations are carried out for the proposed topology and algorithm. The harmonic performance is verified by experiments on a 10k VA 5-level NPC/H-bridge inverter fed by a dual 18-pulse rectifier.