A polyphase cartesian vector approach to control of polyphase AC machines

Abstract

The traditional approach to the three-phase space vector theory and its extension to polyphase systems (5, 7, 9 phases and more) does not give a complete insight. Due to the assumption that all phase axes lay in a single plane, the additional degrees of freedom that exist in polyphase systems are lost. By putting the phase axis into an orthonormal system, all degrees of freedom are preserved and can be utilized. As a result, it is shown in this paper that two five-phase AC machines can be independently controlled from a single five-phase inverter by utilizing all 4 degrees of freedom (one degree of freedom is always the zero axis, which cannot be used without the neutral wire). By generalizing this approach, it is possible to independently control ((N-1)/2) N-phase AC machines using a single N-phase inverter. Simulation results confirm this theory. An algorithm for the five-phase space vector calculation was developed and can be generalized to an arbitrary number of phases.