Browsing by Author "Getsh, Fikadie"

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    Modeling and Control of Half­wave Rectified Rotor Brushless Synchronous Motor
    (Addis Ababa University, 2020-08) Getsh, Fikadie; Mengesha, Mamo (PhD)
    In this thesis, modeling and control of the half­wave rectified rotor brushless synchronous motor is presented. The motor has a range of promising performance characteristics that are suitable for electric vehicle (EV) traction drive applications. Its mechanical structure is simple and robust with brushless means of field excitation capable of variable field flux control over a wide range of operating speed and torque. To use the motor for such application, accurate modeling and characterization of the motor is needed. Two different modeling paradigms were used to study the behavior of the motor. The finite element method (FEM) was used to first verify the principle of operation and next to confirm the analytical model calculations. COMSOL Multiphysics was used to perform the two dimensional (2D) FEM analysis. Besides the FEM model, a simplified analytical model and Simscape based model convenient for MATLAB/Simulink simula­ tions and control system design purposes were also built using the magnetic equivalent circuit concept. The analytical model developed in this thesis uses a closed form ana­ lytical expression for the field winding current, ifd, derived from observing FEM model behavior. This enabled a more complete description of basic motor characteristics that allowed determination of motor capabilities, limits and design of controllers which were not possible without the use of the such closed form expressions. Comparison of the re­ sponses of those models was performed. Field oriented control (FOC) based architecture was used to design and implement a velocity control system for both the FEM based and Simscape based models. The results show that the three models agree as long as effects due to the inductance variation of the FEM model because of iron cores saturation (motor load) and stator slots are taken into account. The three models showed a logarithmic relationship between the bias frequency fb and motor torque, field winding current and flux. The field winding flux was shown to be linearly dependent on the amplitude of the field excitation current component If of the stator current for a fixed bias frequency fb. The decoupled nature of field flux and torque currents allowed implementation simple PI based speed and cur­ rent controllers. In terms of field winding flux linkage variation, the analytical showed a 1.7%, Simscape a 14.8% and FEM a 18.4% of maximum deviation from the ideal con­ stant flux. As long as the basic motor characteristics such as flux, torque and efficiency are considered, the models can be used interchangeably.