Power Converters for Variable Speed Induction Motor Drive

This paper presents a system consisting of a 54-pulse converter and 7-level symmetric configured modified cascaded H-bridge multilevel inverter fed medium voltage induction motor drive (MVIMD) system. A multi-winding transformer based 54-pulse rectification is used to follow the IEEE power quality standard at the grid end. An inverter for the drive system with an aim of minimizing total harmonics distortion (THD) and losses, a 7-level symmetric inverter based on nearest level control switching technique is adopted. A conventional 7-level cascaded H-bridge multilevel inverter has twelve-switches per phase, however, in this paper a modified topology of a 7-level cascaded H-bridge inverter is presented, which uses 8-switches per phase, thereby reducing switching losses and number of gate-drivers required in the circuit. Performance of the drive system using an indirect field-oriented control (IFOC) under steady state and transient conditions is demonstrated in detail. Performance and effectiveness of proposed system is validated by simulation of a 29S.4kW induction motor drive.