A High Resolution Multilevel Voltage Space Phasor Generation for an Open-end Winding Induction Motor Drive

A topology for high resolution voltage space generation for an open-end winding induction motor drive is presented in this paper. The open-end winding induction motor is fed from both ends by two 3-level inverters with asymmetrical d.c. links. This results in voltage space phasor levels equivalent to a conventional 9-level inverter. The 3-level inverters used in the proposed drive, are realised by cascading two 2-level inverters and do not require the neutral point clamping diodes. Compared to the H-bridge topology, the proposed scheme uses a lower number of power supplies. In the multilevel carrier based Sinusoidal Pulse Width Modulation (SPWM), used for the proposed drive, a progressive discrete d.c. bias depending upon the speed range is given to the reference wave so that the drive can operate in the i-level modes (i = 2, 3, ..9) depending on the speed range. The inverter with the higher d.c.-link voltage is switching less frequently, compared to the inverter with the lower d.c.-link voltage. The drive is implemented and tested with a 1.5 kW open-end winding induction motor and the experimental results are presented.