Analysis And Optimization Of Multiphase Permanent Magnet Machine With Harmonic Current Injection

Multiphase permanent magnet machines (MPMM) combine advantages of both multiphase machine and permanent magnet (PM) machine. Among them, MPMM with harmonic current injection(MMHCI), whose torque density can be improved via harmonic current injection, has broad prospects for applications, which are sensitive to machine volume and mass, such as ship propulsion, electric vehicle and wind generator. To make use of the harmonic currents, intergral-slot concentrated winding could be adopted in MMHCI. However, this winding overlapped in the end and strong coupling between phase windings exists, which limit the fault tolerance of the machine. Meanwhile, fractional-slot concentrated windings (FSCW) could also be adopted, which are non-overlapping winding and the phase windings are weakly coupled, to improve the fault tolerance. However, FSCW are always short-pitched and the harmonic winding factors are low, making itself be not suitable for MMHCI. As a result, this thesis proposes one kind of new fault-tolerant MMHCI and conducts researches of this machine.Multiphase fractional-slot concentrated full-pitch winding (MFFW) is proposed considering the requirement of the fault-tolerant MMHCI. The winding factors of MFFW are equal to1and the mechanical and thermal isolation among double-layer phase windings are realized. Compared to the conventional multiphase fractional-slot concentrated winding permanent magnet machine, MFFW PM machine (MFPM) features smaller mutual inductances, higher average torques both in normal or faulty operations.The amplitude determination of the injected harmonic current is performed before further studies of MFPM because the amplitude of the injected harmonic current decides directly the machine performance. The formula of torque with harmonic currents are derived and it is pointed out that, the harmonic current amplitude ratio should be equal to that of corresponding electromotive force (EMF) harmonics to produce the maximum average torque, and the determination of the harmonic current ratios could be simplified using analytical method. MFPM is exemplified to investigate the impact of harmonic current on the torque, magneto-motive force (MMF), PM eddy current loss and the radial force density and the key design and optimization points are concluded.Investigation of implementation of phase shift and magnetic barriers methods to reduce MMF sub-harmonics for MFFW, which features rich MMF harmonics, is performed. Methods for MMF sub-harmonics reduction are analyzed and phase shift and magnetic barriers methods are adopted. MFPM with tooth and slot offset is proposed to limit the overall width of isolation teeth in phase-shifted multiphase PM machine (PSMM). With optimization of phase-shift angle, the slot-harmonic in the MMF sub-harmonics is largely reduced and PSMM is formed. Further, flux barriers are used in stator yoke of PSMM to limit the lowest-order MMF harmonic. The effectiveness of the two methods are veified using finite element analysis (FEA) simulation.Quasi-trapezoidal PM (QuPM) rotor is proposed improve the torque performance of MFPM, and it is comared to saddle PM (SaPM) rotor. The concept of equivalent PM is put forward to aviod the processing of complicated boundary conditions between PMs and air-gap when optimizing the PM shapes using2-D magnetic field analytical method. The geometric optimization of SaPM and QuPM are performed using the respective equivalent PMs and the amplitude coefficients of SsPM and QuPM variable thicknesses are drawn for maximum average torque with the edge thickness specified. Edge thickness is then determined to minimize the cogging torque using complex permeability model and segmented PM methods, and the optimized QuPM is determinzed at last. The torque performance improvement of MFPM with QuPM and the feasibility of optimization methods are verified by FEA and experimental results.The implementation of harmonic current injection is studied. The influencing factors of harmonic current control in the multiple-dimension vector control system, including inverter dead-time effect, high-order PM flux harmonics, current sample error and the variation of inductance, are summarized, and the corresponding solutions are pointed out. The control system,which is based on phase variable model of MFPM, is simulated using MATLAB/SIMULINK, and the effectiveness of the current control strategy is verified.Prototypes of five-phase MFPM with optimal QuPM and five-phase inverter are designed and manufactured, and the experimental system is built. The cogging torque, EMF, phase inductances, output torques of prototype machine excited with different harmonic currents are measured, and the theoretical analysis is validated.