Elimination of torque dips due to back EMF non-ideality in brushless AC motors with surface-mounted magnets

摘要

Permanent magnet synchronous motor may have back electromotive forces with flattened peaks, hence its torque undergoes considerable dips with pure sinusoidal excitation. The approach used for eliminating torque dips in brushless DC motor by the author in a previous paper is extended here to brushless AC motor. Establishing a normalised current reference to eliminate the dips is a centre piece in this approach. Some light is shed on what is called a brushless motor continuum. At the low end of this continuum, there exists the ideal brushless DC motor and at the high end there exists the ideal brushless AC motor. Despite being hypothetical, the brushless motor continuum brings some interesting insights into how these machines are differentiated when they are ideal and how they converge as they lose ideality. A unified approach for fixing the consequences of non-ideality seems worthy in light of the severe difficulty of building a perfect brushless motor.