A Hybrid Seven Level Inverter Topology Formed by Cascading T-Type and Active Neutral Point Clamped Inverter for Induction Motor Drives

This paper proposes a hybrid 7-level inverter scheme formed by cascading basic inverter cells. The proposed inverter is realized by cascading basic 3-level T-type converter with 5-level active neutral point clamped inverter. The proposed topology uses low voltage semiconductor devices and floating capacitors which are balanced in every PWM switching cycle using pole voltage redundancies for every pole voltage levels. The balancing of capacitors are independent of modulation index and load power factor. The topology forms two stacks at the front-end which uses individual symmetrical reduced DC sources and each stack works only for half the fundamental period. The open loop V/f control is simulated as well as experimentally verified on induction machine using proposed inverter topology. The experimental and simulation results for transient and steady state operations are included in the paper. Further, a brief comparison of proposed topology with conventional 7-level topologies have also been included.