Comparison of Cogging Torque Reduction in Permanent Magnet Brushless Machines by Conventional and Herringbone Skewing Techniques

Abstract

Cogging torque, as one of the main parasitic demerits of permanent magnet brushless machines, is of particular importance and primary concern during the machine design stage in many high-performance applications. Hence, numerous design techniques have been proposed and employed to effectively alleviate the cogging torque in permanent magnet brushless machines. The effects of rotor step skewing techniques including both conventional and herringbone styles on the cogging torque of permanent magnet brushless machine are comprehensively investigated and compared by synthesized 2-D and 3-D finite-element analysis in this paper. The results have revealed that both the conventional and herringbone rotor step skewing techniques can reduce the cogging torque significantly, but the latter is less effective than the former especially with small skewing step numbers. Moreover, the machine with herringbone rotor step skewing technique has rather peculiar and asymmetric cogging torque profiles, while the machine with conventional rotor step skewing technique exhibits normal and symmetric ones. The validity of the obtained results and findings is underpinned by the experiments on the prototype machine.Index Terms-Axial electromagnetic force, back electromotive force, cogging torque, conventional step skewing, finite-element analysis (FEA), herringbone step skewing, permanent magnet brushless machine, three-dimensional.

Techniques for Reduction of the Cogging Torque in Claw Pole Machines with SMC Cores

“…For the stator design, it can be classified into stator slot width optimization [25], stator tooth pairing [26], stator tooth shifting [27], stator tooth notching [11], odd slot number, and stator skewing [28]. For the rotor design, it can be classified into rotor pole width optimization [3], magnet shaping [3,29], magnet pole width optimization [30,31], magnet skewing [1], magnet shifting [8], and magnet segmentation [32,33]. In this paper, the CPM is designed with three phases and six pole pairs.…”

“…As one of main parasitic parameters in permanent magnet synchronous machines (PMSMs), cogging torque is the main component of torque ripple, which has always been the handicap in the high-performance drive applications [1]. During the last two decades, various kinds of work were conducted on the cogging torque of radial-flux and axial-flux PMSMs [2,3].…”

Analytical Prediction of Torque Ripple in Surface-Mounted Permanent Magnet Motors Due to Manufacturing Variations

“…Furthermore, the skew factor in (2) modifies the torque ripple magnitude and depends upon the type of skewing is applied to the motor such as continuous, conventional step-skew or herringbone step-skew [15].…”

Optimal rotor shape design of 3-step skew spoke type BLAC motor to reducing cogging torque

“…By neglecting axial-coupling effects between the steps and the end effects, the overall cogging torque of the machine with rotor step skewing techniques can be obtained by synthesizing the cogging torque produced by FEA results as shown in expression Eq. (3) [5] …”

“…There is no exception for the BLAC motor employed as the EPS system. Therefore, the cogging torque minimization of the BLAC motor is becoming necessary since its low torque ripple is required in the EPS application.This paper presents the rotor Shape optimization of a 3-step skewing [5] spoke type BLAC motor, which is designed for an electric power steering application. The design specification of the BLAC motor for the EPS application is listed in Table 1, and proto type of the spoke type BLAC motor is illustrated in Fig.…”