Design and Optimization of a Brushless Direct Current Motor for Light Electric Vehicle

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This dissertation provided a multidisciplinary insight such as electromagnetic and thermal analysis, which are applied in the design and optimize the brushless direct current motor. This thesis has presented topology design of the brushless direct current motor for light electric vehicle. In the first part of this thesis, proposed a configuration design of the brushless direct current motor for light electric vehicle applications. The initial design of the proposed machine was calculated by utilizing an analytical method. The sizing methodology is used to design a BLDCM to meet a specific performance for light electric vehicle application. Furthermore, the electromagnetic performances of prototype configurations of the initial BLDCM were investigated. In the second part of the thesis, the brushless direct current motor was optimized based on the surrogate model. The optimization model of a design problem with a single objective, 2 constraints, and 7 design variables are presented. The goals of optimization is the maximum efficiency. Meanwhile,the stator and rotor yoke thickness, the stator outer diameter, the stator slot width, magnet thickness, the stator slot depth, and air-gap length are selected as design variables. The surrogate model of the machine performance was constructed using Latin hypercube sampling and Kriging modeling. The particle swarm optimization based surrogate model techniques is adopted to optimize the brushless direct current motor. A sensitivity analysis was carried out to identify the important independent design variables. The number of significant independent design variables were reduced from 9 to 7 based on a sensitivity analysis. The optimization results were successfully validated using the finite element analysis. The computational cost of the proposed technique of optimizations based on the surrogate model was lower than the conventional optimal design techniques based on a finite element analysis. In the third part of the thesis, in the process of electric motor design, it is essential to predict and provide an accurate thermal model. An improvement on the thermal performance, which was implemented into the proposed design of the brushless direct current motor, is one of the aims of this thesis. A thermal analysis of the BLDCM requires a deep understanding on the coolant behavior and the thermal mechanism in the motor. The thermal analysis is achieved based on a precise knowledge of the test motor geometry, materials, and heat sources (losses). A 2D finite element model for the BLDCM was developed to obtain the losses. The ANSYSMaxwell package was utilised to develop a power loss model for predicting power losses in different components of the BLDCM. Two thermal models (lumped parameter thermal network(LPTN) and finite element (FE)) were applied to determine the temperature distribution through the machine, using motorCAD. The models were solved at a speed of 501 rpm and average winding phase current 145.82 A , at this operating point the maximum end-winding temperature was found to be 80oC and magnet temperature found to be 65oC. Finally, the proposed machine could increase the torque up to 190.04 N·m with high efficiency of 95.25%. The simulation results have confirmed that the BLDCM can be used for light electric vehicle applications.