A Novel Split Phase Induction Motor Drive without Harmonic Filters and with Linear Voltage Control for the Full Modulation Range

Abstract

A modulation scheme for a split phase (six phase) induction motor is presented in this paper. For a six phase induction motor drive harmonics of the order 6n ± 1 (n = 1, 3, 5 etc.,) will not contribute to the air gap flux and hence these harmonic currents are limited by the stator impedance only. So harmonic filters are needed for the suppression of these (6n ±1( n = 1, 3, 5 etc.,) high amplitude harmonic currents, when a six phase induction motor is used for variable speed application. In the proposed scheme, a modulation technique to eliminate the 6n ± 1 (n = 1, 3, 5 etc.,) harmonic currents, without the need for harmonic filters, from the stator phases of a six phase induction motor drive is explained. An openend winding drive configuration with appropriate DC-link voltages, is chosen in such away that a 12-sided polygonal voltage space phasor combinations are achieved for each 3-phase group, independently. A modulation scheme based on 12-sided polygonal voltage space phasors cancel the 6n ± 1 (n = 1, 3, 5 etc.,) harmonic voltages from all the motor phases and hence currents due to these harmonics can not flow in the motor phases of the six phase machine. For the same flux level of operation, nearly 11.5 % increase in modulation range is possible from this proposed drive (while still being in the linear PWM range), which is more than that of a six-step over modulation region in a conventional 3-phase induction motor drive. The proposed drive scheme is experimentally verified, for variable speed application, using a 1.5 kW six-phase induction motor drive.