engleski

A Systematic Approach to Optimized Design of Permanent Magnet Motors With Reduced Torque Pulsations

This thesis deals with optimal design of surface and interior permanent magnet motors with an emphasis on reduced torque pulsations while maximizing the motor performance in all regimes of operation and minimizing the size of the motor. The optimization for both types of motors has been formulated as a constrained multiobjective minimization problem where a population of nondominant solutions is determined from which a single solution is selected as the best compromise. This optimization scheme is based on Differential Evolution optimization algorithm. A novel approach to analytical field calculation in the air gap of a surface PM motor has been developed. The concept of complex relative air gap permeance has been derived based on conformal mapping of the slot geometry and used to accurately calculate the radial and tangential components of the flux density in the slotted air gap. This model of air gap permeance has been utilized to calculate the motor parameters, including losses and efficiency, needed for the design optimization. For an interior PM motor the finite element method has been used to calculate its parameters during the optimization process. The principle of permeance freezing has been applied to extract lumped parameters from the FE model at any steady state operating point. A combined analytical and numerical technique has also been developed to reduce the time required for cogging torque calculations which utilizes the complex relative air gap permeance to estimate the cogging torque waveform based on only two magnetostatic FE simulations. The effectiveness of the proposed design methodology has been shown on examples of a 5 kW SPM motor and a 1.65 kW IPM motor with two layers of cavities in the rotor for which a prototype has been built and tested. In addition, a comparative analysis has been carried out for the optimized 5 kW, 50 kW and 200 kW IPM motors with two and three layers of cavities in the rotor to show design trade-offs between goals to minimize the motor volume while maximizing the power output in the field weakening regime with the back emf constraint as the main limiting factor in the design.

Permanent magnet motor; pulsating torque; optimization; Differential Evolution; complex relative air gap permance

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