Optimum Design of High-Speed Single-Phase Flux Reversal Motor with Reduced Torque Ripple

Abstract

Single-phase motors are used in low-power, cost-effective, variable-speed applications. As a replacement to traditional single-phase synchronous motors with magnets on the rotor, single-phase flux reversal motors (FRMs) with a rugged and reliable toothed rotor are considered for the high-speed applications. However, torque pulsations of single-phase motors are high. The aim of this work is to minimize the torque ripple and increase its minimum instantaneous value, as well as to reduce FRM losses. To solve this problem, an asymmetric rotor is used, and an objective function is proposed, which includes parameters characterizing the pulsations of the torque and the loss of FRM for two load conditions. To optimize the single-phase FRM and minimize the objective function, the Nelder–Mead method was applied. The optimization criterion was selected to maximize the efficiency, to reduce the torque ripple, and to the avoid the negative torque in a wide range of powers at the fan load (quadric dependence of torque on speed). Two operating loading modes are considered. After two stages of optimization, the peak-to-peak torque ripple in the FRM in the rated loading mode decreased by 1.7 times, and in the mode with reduced load by 2.7 times. In addition, in the FRM before optimization, the torque has sections with negative values, and in the FRM after optimization, the torque is positive over the entire period. Although losses in the rated mode increased by 4%, when underloaded, they decreased by 11%, which creates an additional advantage for applications that work most of the time with underload.

Optimal Design of a High-Speed Flux Reversal Motor with Bonded Rare-Earth Permanent Magnets

“…Therefore, in low-cost high-speed applications, it can be preferable to use motors with a simple and reliable toothed rotor and with magnets on the stator, such as flux switching motors (FSMs) [8,9], flux reversal motors (FRMs) [10,11], or hybrid switched reluctance motors (HSRMs) [12,13]. Applying a structurally simple toothed rotor made of a steel lamination reduces the cost of rotor manufacturing in comparison with a rotor with magnets on its surface and with a retaining ring [14] and also increases the reliability of the motor.…”

“…Applying a structurally simple toothed rotor made of a steel lamination reduces the cost of rotor manufacturing in comparison with a rotor with magnets on its surface and with a retaining ring [14] and also increases the reliability of the motor. However, to reduce eddy current loss, the sintered rare-earth magnets on the stator have to be segmented into several pieces [10,11,15]. The cost of the magnets increases with the number of magnet segmentations [16,17].…”

“…The Nelder-Mead method has previously been successfully applied to optimize various types of electrical machines using various objective functions [10,11,14,27,28]. In each of these works, a special objective function was constructed which depends on the specifics of an electrical machine and application.…”

“…Torque ripple and underload efficiency also were improved. In [11], optimization of a single-phase high-speed FRM with sintered rare-earth magnets was carried out to reduce torque oscillations and power loss when operating with a fan load profile.…”

“…However, the optimization criterion developed for an FRM with sintered rare-earth magnets [11] cannot be applied to an FRM with bonded magnets, since in this case, there is a risk of demagnetization of bonded magnets. This paper discusses various aspects of the optimal design of FRMs with bonded magnets applying the Nelder-Mead method.…”