Comparison of control approaches for permanent magnet motors

Examensarbete för masterexamen

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Type: Examensarbete för masterexamen
Master Thesis
Title: Comparison of control approaches for permanent magnet motors
Authors: Klintberg, Emil
Abstract: This thesis deals with comparing control techniques for two existing permanent magnet motors with harmonics in their back emfs. To do so, ideal models of a Brushless DC (BLDC) motor and a Permanent Magnet Synchronous Motor (PMSM) have been modified to describe the behavior of two existing permanent magnet motors. Comparisons of the motor constant and the relative torque ripple are performed when the motors are controlled with Field Oriented Control (FOC) as well as with traditional BLDC control. A novel control scheme aiming at controlling the currents to have the same shape as the back emfs are presented. Simulations are performed to show how this method affects the motor constant and relative torque ripple. Torque ripple due to phase commutation in BLDC motors is discussed and a version of lead angle adjustment is implemented to reduce this problem. Even though an ideal BLDC motor has a higher motor constant than an ideal PMSM, simulations showed that a higher motor constant (almost 5% and about 2% for the two motors respectively) can be obtained by utilizing FOC compared to traditional BLDC control. A lower relative torque ripple (almost 86% and almost 44% for the two motors respectively) was also obtained for FOC compared to traditional BLDC control. A higher average torque per peak current was, however, obtained with traditional BLDC control. These results are valid for both motors. Simulations showed that it is possible to achieve a higher motor constant, compared to FOC and traditional BLDC control, by controlling the currents to have the same shape as the back emfs. The relative torque ripple was however increased by using this method. It is also shown, by an example, that the motor constant can be increased by implementing lead angle adjustment.
Keywords: Elkraftteknik;Electric power engineering
Issue Date: 2013
Publisher: Chalmers tekniska högskola / Institutionen för energi och miljö
Chalmers University of Technology / Department of Energy and Environment
Collection:Examensarbeten för masterexamen // Master Theses

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