Multi-Dimensional Space Vector Pulse Width Modulation Scheme for Five-Phase Series-Connected Two-Motor Drives

A space vector PWM (SVPWM) technique for multiphase voltage source inverters (VSI), based on a multidimensional space approach, is considered in this paper. The additional degrees of freedom, which appear as the number of phases increases, make the SVPWM more complex because VSI space vectors are not in a single two-dimensional space any more. Existing approaches are predominantly based on n- dimensional space decomposition into (n-l)/2 two-dimensional sub-spaces and this is adequate when the output is required to be sinusoidal or sinusoidal with higher harmonic injection. However, in the case considered here (five-phase series- connected two-motor drive) there are two independent reference voltage vectors in the two sub-spaces and the problem of active voltage vector selection arises. The methodology outlined here is capable of overcoming this problem, since the voltage space vectors are selected on the basis of criteria that are formulated for the multi-dimensional space, so that all the two-dimensional sub-spaces are simultaneously considered. The paper at first summarises the mathematical analysis that establishes the necessary conditions for appropriate selection of the voltage space vectors in the multi-dimensional case. Different criteria for the general n-phase case are presented for the selection of the VSI space vectors and the validity of the SVPWM scheme is verified by simulation of a five-phase VSI supplying two series-connected five-phase motors.