Six-phase space vector PWM under stator one-phase open-circuit fault condition

Abstract

The torque pulsation and speed pulsation of a six-phase induction machine with double Y-connected windings displaced by 30° increase after one phase of the stator winding is open-circuited. To reduce the pulsations, a method of six-phase space vector pulse width modulation (PWM) with fault-tolerance is proposed. The star point of the open-circuit winding group is connected to the centre point of the converter DC voltage. The 32 column matrices, which represent 32 stator winding voltages, are mapped to the d-q and z1-z2 planes using a new five-dimensional orthogonal matrix; then, 32 basic vectors are obtained. By using an optimal model, six auxiliary vectors and an equivalent null vector are constructed, the magnitudes of which are all zero in the z1-z2 plane. By using the auxiliary vectors and equivalent null vector, the reference vector is synthesized, the zero magnitude of which in the z1-z2 plane can suppress the harmonic voltages, and the circular trajectory of which in the d-q plane can make the torque smooth. The simulation and experimental results show that the torque pulsation range and speed pulsation range of the proposed method with fault-tolerance are 30% and 25% of those of the classical method without fault-tolerance, respectively. Thus, the phase-deficient operation performance of the system is improved.