A Space Vector based PWM scheme for a four level inverter using open end winding induction motor

A simple algorithm for 4-level inverter based on Space Vector PWM scheme is proposed. 4-level inversion is achieved by connecting a 3-level inverter and a 2-level inverter in open-end winding configuration. 3-level inverter is realized by cascaded connection of two 2-level inverters. The 3-level inverter is used to realize the sub hexagon center vector and 2-level inverter is used to realize the PWM signal. The individual inverters are fed with symmetric DC link voltages. The proposed scheme does not use sector identification method to find the sub hexagon, which encloses the tip of the reference space vector. When the inverter is in 3-level operation, the sub hexagon centers are directly identified from the instantaneous amplitude of the 3-phase reference sinusoid. The generated sub hexagon centers for 3-level operation are used to find the sub hexagon centers for 4-level operation. The scheme is implemented and tested with a 2-HP induction motor drive. Experimental results are presented, including operation in over modulation region.