Multilevel inverter with 18-sided polygonal voltage space vector for an open-end winding induction motor drive

A simple multilevel inverter scheme with 18-sided polygonal voltage space vector structure is proposed for an induction motor drive with an open-end winding configuration. The motor is fed from one end with a conventional two-level inverter and from the other end with a three level inverter, realised by cascading two conventional two-level inverters. The inverters are fed with asymmetrical DC link voltages. A simple linear PWM control scheme up to 18-step mode is proposed, based only on the motor reference phase amplitudes. The present scheme does not require complicated signal processing and control loop, as in the case of PWM scheme with conventional hexagonal voltage space vector structure, in over modulation regions. The proposed scheme gives and increased modulation range with the elimination of 5(th) 7(th) 11(th) and 13(th) order harmonies, when compared to any conventional schemes.