Design Optimization of High-Performance Interior Permanent Magnet Machines Using a Fast and Accurate FE-based Technique

This thesis focuses on the design optimization of high-performance interior permanent magnet (IPM) machines. A fractional-slot concentrated-Winding (FSCW) IPM machine is considered for the study. The objectives of the design optimization are high efficiency and torque density, low torque ripple and wide constant power speed range (CPSR). The design space of the FSCW IPM machines is very large as a number of different slot and pole combinations, and different rotor topologies need to be considered. Hence, a well-defined, large-scale design optimization technique is necessary to find a global optimum design that can achieve the targeted objectives. Most of the existing finite-element (FE) model-based design optimization techniques of PM synchronous machines (PMSMs) often aim to reduce the computation time and resources required for such large-scale problems and as a consequence overlook magnetic saturation and other non-linear characteristics while predicting inductances, saliency ratio, characteristic current and maximum torque per ampere (MTPA). It is shown in the thesis that overlooking of non-linearity in the design optimization of an FSCW IPM machine can result in a wrongful design selection. As a solution to such issue, the thesis develops a fast and accurate FE-based optimization package, which systematically explores the design space of FSCW IPM machines to find the best design. A baseline FSCW IPM machine with V-type magnets was optimized and then prototyped to experimentally demonstrate the effectiveness and accuracy of the optimization package. To find a global optimum design of FSCW IPM machine, the most commonly used slot and pole combinations of FSCW stator and the well-known IPM rotor topologies are considered for a larger optimization study. A comprehensive comparison of the optimized designs has led to the proposal of a novel Y-type magnet configuration. The novel Y-type FSCW IPM machine can deliver high efficiency and low torque ripple with increased torque density while maintaining low material cost and high rotor mechanical integrity. For experimental verification, several prototypes including the novel Y-type FSCW IPM machine have been constructed and tested. Comparison of the measured results clearly indicates the superiority of the Y-type FSCW IPM machine among the other topologies investigated in this thesis