A novel five-level SPWM Inverter system for dual-fed induction motor drive

In this paper, a new five-level inverter system for dual-fed induction motor drive is described. The dual-fed structure is realized by opening the neutral-point of the conventional squirrel cage induction motor. The five-level inversion is obtained by feeding the dual-fed induction motor with four-level inverter from one end and two-level inverter from the other end. The four-level inverter used in this proposed topology is obtained by connecting three 2-level inverters with equal DC link voltage in cascade. This inverter scheme does not experience neutral point fluctuations and uses a lesser number of DC sources compared to the series H-bridge topology. A multilevel carrier based Sinusoidal Pulse Width Modulation is implemented for the proposed drive where a progressive discrete DC bias depending upon the speed range is given to the reference wave to reduce the inverter switchings.