Electrical Engineering-Systems Dept.

*** SEMINAR ***

Yoni Mandel

(M.Sc. student under the supervision of Prof. George Weiss)

on the subject:

Adaptive internal model based suppression of torque ripple in brushless DC motor drives

    Permanent magnet synchronous motors (PMSMs) are widely used as high-performance variable-speed drives. Ripple in the electric torque of such motors is often a source of vibration and tracking errors, especially at low speeds.

    In this thesis we study the torque characteristics of PMSMs and propose a method to minimize the torque ripple. First, we establish a model for the motor to cover all dynamics without any assumptions on the signals. Next, we present a Fourier analysis of the torque ripple, caused by non-sinusoidal EMF and cogging torque, where the main conclusion is that the frequencies present in the torque disturbance are integer multiples of six times the electric frequency. Some terms are proportional to the q axis current (the mutual torque), while others (the cogging torque) depend only on the rotor angle. The resulting model is highly nonlinear. We propose an adaptive controller based on the internal model principle, where the resonant frequencies of the controller and the associated gains change according to the motor speed. This is achieved by replacing the time variable by the motor angle, which simplifies the nonlinear model. Finally, simulation and experimental results are given to verify the new controller. We compare the performance of our adaptive algorithm with the well-known one from de Wit and Praly.