I . INTRODUCTIONSurface-mounted permanent magnet (SPM) motors have been increasingly favored due to smaller volume, higher power density, higher efficiency, and higher positioning accuracy, widely applied in many applications such as textile machinery, robot,and packaging machinery . The interaction between permanent magnet (PM) and the slotted iron produces the cogging torque . For SPM motor with high-performance sintered Nd-Fe-B, cogging torque is more serious, which causes torque ripple, vibration, and noise of PM motor . For PM motor design, one of the most significant tasks is to make the cogging torque as small as possible [1] . Up to now, there have been a few researches about the conventional tooth notching only involved in its shape and number, which are uniform both in the axial and circumferential directions [2]- [3] . Due to this structural characteristic, the effect of the conventional notching on reducing the cogging torque is not very effective . In addition, we are not able to find any study in the literatures which were related to notching position and the nonuniform structure . The purpose of this paper is to present a practical method to reduce cogging torque and minimize torque ripple using tooth notching pairing . The results illustrate that the cogging torque is reduced greatly and the torque ripple is suppressed effectively with this method .
II . QUALITATIVE ANALYSIS OF NOTCHING PAIRING MECHANISM AND NUMERICAL CALCULATIONThe gap permeance function and gap flux density have a key influence on the cogging torque . In this paper, the focus is mainly on a reduction of the gap permeance function . The cogging torque is changed with width and position of tooth notching, including its amplitude and phase . When the cogging torque waveforms with the different phases add up, they can cancel each other and the cogging torque sum is reduced significantly . This characteristic is made full of, and tooth notching pairing is proposed . α 1 and α 2 represent notching position and width . Two waveforms are selected form the numerical calculations of the cogging torque, one waveform T 1 when α 1 =3 .2mm and α 2 =2 .7mm, another waveform T 2 when α 1 =3 .4mm and α 2 =1 .2mm . These two waveforms are practically in opposite phase . These two waveforms are practically in opposite phase . With Fast Fourier Transformation (FFT), the amplitudes and phases of n order harmonics of T 1 and T 2 are obtained . A novel stator stack is presented in Fig . 1, which is composed of two different stator stacks with notching . The length of each stack length is designed being K 1 =14mm and K 2 =21mm . Fig . 2 illustrates the comparison of the cogging torque . After notching pairing is employed in stator, the resultant amplitude of the fundamental harmonic is reduced significantly . The peak value of the cogging torque of notching-pairing model is only 0 .091Nm, which is reduced by 79 .3%, 74 .7%, 61 .4%, as compared to no-notching, T 1 and T 2 , respectively . The cogging torques produced in two stacks will then cancel each ...
