Independent Speed Control of Two Six-Phase Induction Motors Using a Single Six-Phase Inverter

Abstract

Split phase (Double star, six-phase) induction motors are obtained by splitting the stator windings of three-phase induction motor into two equal halves which are spatially phase separated by 30 electrical degrees. The resulting six phases can be decomposed into three orthogonal sets of phase sequences, i.e. positive sequence components and two zero sequence components. The positive sequence component consists of all the 12n ± 1 (n = 0,1, 2, 3....etc.) order harmonics. One of the two zero sequence components consists of all the 6n ± 1 (n = 1, 3, 5....etc.) order harmonics. The triplen harmonic components 3n (n = 1, 3, 5....etc.) constitute the other zero sequence component. The zero sequence components do not contribute towards air gap flux production with the existing winding disposition. Only the positive sequence components contribute for the air gap flux and electromagnetic torque production in the motor. In this paper, a scheme is proposed where one of the zero sequence components is impressed across a second six phase motor in proper sequence so that it will become a positive sequence component for the second motor and, hence, will develop air gap flux and electromagnetic torque in the second motor. By following this method of orthogonal decomposition of the harmonic voltages of the split phase sequence, two split phase (double star, six-phase) motors can be independently controlled by a single six-phase inverter.