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

Authors: Osama Mohamed Arafa

Addresses: Department of Power Electronics and Energy Conversion, Electronics Research Institute (ERI), El-Bohous St., previously El-Tahrir St., El-Dokki, Giza, National Research Centre Buildings, ZIP Code: 12622, Egypt

Abstract: In this paper, a technique for eliminating torque dips in brushless DC motors (BLDCM) with surface-mounted magnets is introduced. The root causes of dips are the non-ideality of the back EMF waveform and the unequal rates of growth and decay of the commutating currents. The back EMF non-ideality addressed by this paper is limited to having flat intervals shorter than 120 deg. Such non-ideal BLDCM can be modelled using a set of piecewise continuous equations with the shortening angle delta as a characteristic parameter. The relation between such parameter and the magnitude of the torque dip is derived analytically. A current control strategy which proactively shapes the current reference for maintaining dip-free electromagnetic torque is explained. The proposed control strategy turns the back EMF non-ideality into an opportunity to establish a smooth commutation process during which incoming and outgoing currents have better chance to replace one another at same rate within a period of two deltas.

Keywords: brushless DC motors; BLDCM; non-ideal back EMF; brushless DC drives; torque dips; surface-mounted magnets; current control; electromagnetic torque.

DOI: 10.1504/IJIED.2015.068767

International Journal of Industrial Electronics and Drives, 2015 Vol.2 No.1, pp.20 - 34

Received: 19 Jun 2014
Accepted: 30 Jul 2014
Published online: 12 Apr 2015 *

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