Analysis of electromagnetic torque for induction motors with a novel non-skewed rotor structure

Abstract

Purpose Pulsating torques cause a number of problems in electrical machines, including mechanical vibrations, acoustic noise and the depreciation of mechanical equipment. In induction motors, the slot skewing method is an effective way to solve these issues; however, it has some drawbacks such as output torque drop, stray loss intensification due to inter-bar currents and iron loss increment. Besides, slot skewing may not be practical in higher-rated induction motors. In this regard, this paper introduces a modified non-skewed rotor (MNSR) structure as a possible alternative to the skewed designs. Design/methodology/approach The proposed structure includes a two-segmented rotor with an intermediate ring between the rotor parts that are mounted on the shaft with a relative shift angle. Detailed information about the idea and structure of the MNSR as well as its manufacturing aspects will be presented in the second section of the paper. First, the working principle of the proposed design is described via analytical equations to provide an insight into the concept. The shifting angle will then be calculated by analyzing the harmonic contents of the electromagnetic torque. Finally, the validity of the analytical method will be verified by developing three-dimensional finite element models. Findings It is demonstrated that by using the proposed rotor structure, the torque ripple has been reduced to a satisfactory level without significantly affecting the mean torque, unlike the skewing method. Furthermore, the new method could avoid the disadvantages of the skewing method while enhancing other motor characteristics such as iron loss. Also, the total volume of the MNSR is equal to the initial design, and the mass and material differences are also negligible. Originality/value In this paper, a MNSR is introduced as a possible alternative to the skewed patterns. The study mainly focused on electromagnetic torque profile characteristics, i.e. the mean torque enhancement and the ripple reduction. The MNSR structure can be used for general purposes and high-performance applications, especially where excellent torque characteristics are required.

Improved air gap permeance modelling for single-slice magnetic equivalent circuits of skewed induction motors

“…The proposed skew method Improved air gap permeance modelling exhibits the desired torque ripple reduction (Kawase et al, 2009). As rotor skew increases, the length and the resistance of the rotor bars increase, which reduces the average torque at the rated slip to a minor extent as observed (Darjazini et al, 2021;Asad et al, 2021). In contrast, Kawase et al (2009) observed an optimum of the average torque for a skew of one rotor slot pitch.…”

Design Optimization of Induction Motors with Different Stator Slot Rotor Bar Combinations Considering Drive Cycle

“…Regarding the optimal selection of stator slot rotor bar (SSRB) combination, various articles for other industry applications can be found. The investigations have covered different combinations of SSRB from the point of view of noise [23], vibration, crawling, steady-state performance [24,25], rotor bar current waveform [26], etc.…”