Design and analysis of innovative concentrated windings for SPM machines

The use of permanent magnet synchronous machines (PMSMs) is becoming more popular [ 1 ] thanks to their compactness, high torque density and increased flux weakening performance [ 2 ]. Other advantages can be gained by equipping PMSM with concentrated winding in the stator. In fact, using concentrated winding can be beneficial regarding easy manufacturing and consequently lower production costs, modularity [ 3 ] and fault tolerance. More Fractional-Slot Concentrated Winding (FSCW) is an increasingly attractive option for the stator winding of synchronous permanent-magnet machines. Despite of the extensive studies conducted so far, there seem to be further interesting margins for expanding and improving such technology. A well-known drawback of their adoption is the occurrence of large magneto-motive force (MMF) harmonics, which produce eddycurrent losses in rotor permanent magnets. Moreover, it is commonly assumed in the existing literature that a symmetrical three-phase FSCW is feasible only on condition that the number of slots Z is an integer multiple of 3 times the maximum common divisor between Z and the number of pole pairs p. This thesis is intended to optimize the multi-layer winding design through a new general systematic methodology having the form of a multi-objective quadratic programming problem. The use of a multilayer design, with coils of different phases wound around the same tooth, is a possible countermeasure to mitigate problems as large magneto-motive force (MMF) harmonics, which produce eddy-current losses in rotor permanent magnets. In addition, this thesis explores the possibility to synthetize a symmetrical FSCWs having unconventional slot-pole combinations, i.e., with a number of slots and a number of poles that are commonly believed incompatible. It is shown that a multi-layer FSCW with (theoretically) arbitrary slot-pole combinations can be implemented and a methodology to synthetize it optimally is given. The performance of FSCW designs with conventional and unconventional pole-slot combinations is comparatively assessed. A study case is provided to illustrate the possible practical advantage of choosing an unconventional pole-slot combination.

Fractional-Slot Concentrated Winding (FSCW) is an increasingly attractive option for the stator winding of synchronous permanent-magnet machines. Despite of the extensive studies conducted so far, there seem to be further interesting margins for expanding and improving such technology. A well-known drawback of their adoption is the occurrence of large magneto-motive force (MMF) harmonics, which produce eddycurrent losses in rotor permanent magnets. Moreover, it is commonly assumed in the existing literature that a symmetrical three-phase FSCW is feasible only on condition that the number of slots Z is an integer multiple of 3 times the maximum common divisor between Z and the number of pole pairs p. This thesis is intended to optimize the multi-layer winding design through a new general systematic methodology having the form of a multi-objective quadratic programming problem. The use of a multilayer design, with coils of different phases wound around the same tooth, is a possible countermeasure to mitigate problems as large magneto-motive force (MMF) harmonics, which produce eddy-current losses in rotor permanent magnets. In addition, this thesis explores the possibility to synthetize a symmetrical FSCWs having unconventional slot-pole combinations, i.e., with a number of slots and a number of poles that are commonly believed incompatible. It is shown that a multi-layer FSCW with (theoretically) arbitrary slot-pole combinations can be implemented and a methodology to synthetize it optimally is given. The performance of FSCW designs with conventional and unconventional pole-slot combinations is comparatively assessed. A study case is provided to illustrate the possible practical advantage of choosing an unconventional pole-slot combination.