Optimum look-up table for reduction of current harmonics in direct torque controlled dual three-phase permanent magnet brushless AC machine drives

This paper presents an investigation into application of direct torque control (DTC) methodology to a dual three-phase (DTP) permanent magnet (PM) brushless AC (BLAC) machine drive. Fundamentally, DTP topology including two sets of three-phase windings shifted by 30 electrical degrees in space together with two isolated neutrals enables cancellation of the 6th harmonic torque component and therefore results in enhancement of torque production. However, since the stator phase current harmonic components which do not participate in electromagnetic torque production are let freely circulate inside the machine and only limited by values of the stator phase resistance and leakage inductance, the stator phase current waveforms under the DTP topology are seriously non-sinusoidal. Therefore, a voltage vector selection scheme together with an optimum look-up table (LUT) for DTC technique is proposed to minimize these useless current harmonic components. Simulation results confirm validity of the proposed method.