General Control Scheme for Asymmetrical Machines Applied to a 15-Phase PM Machine

Asymmetrical multi-phase machines can be supplied by independent inverters thus further improving the fault tolerance referring to symmetrical windings. As the control of asymmetrical systems is more complex, this paper details a space vector modeling applicable to any phase number: it is based on the virtual equivalence between asymmetrical and symmetrical systems for which the opposite phases are connected in anti-series. The images by the connection function of the odd -order Fortescue (symmetrical) components define the modified Fortes-cue basis for the asymmetrical system. As these components are decoupling for the phase-to-phase magnetic coupling application, meaningful control strategies are derived with the possibility of implementing several rotating frames, thus facilitating the control (considering the specific harmonic mapping). A better insight of the machine behavior is obtained regarding the magnetomotive force spectrum, especially for multi star machine when some stars are switched off. These properties are illustrated with time step simulations of a 3×5-phase Surface-mounted PM machine.