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Purpose - The purpose of this paper is to present the dependence of the level and harmonic structure of the cogging torque in permanent magnet synchronous motors (PMSM) to interlocks and notches in a stator back iron, which are standard methods for stator lamination stacking in mass-production. Design/methodology/approach - Methods of stacking up the lamination like welding or interlocking are introducing magnetic asymmetries in stator back iron which causes additional harmonic components (AHC). A finite element method and Fast Fourier transform were used to calculate cogging torque harmonic components (HC) with regard to the applied number and positions of interlocks and notches. All simulation results were verified by laboratory tests. Findings - It has been established and proved that technologies for stacking lamination packs cause local saturation peaks in back iron which give rise to additional cogging torque AHC and consequently increase the total cogging torque. It is also shown that the magnetic properties of interlocks cannot be simply considered as air regions but adequate relative permeability of such affected soft magnetic material must be determined to improve the accuracy of FEM calculations. Practical implications - Considering presented results, it is possible to foresee which AHC will include the cogging torque of mass-produced PMSMs due to the stator lamination stacking methods. In this way, the optimal stacking method can be selected in order to minimize the effect of AHC. Originality/value - So far, authors dealing with the cogging torque have not taken into account the influence of the stator lamination stacking method on the level of torque oscillations. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this study is to estimate the sensitivity of cogging torque in permanent magnet (PM) motor designs due to PM assembly tolerance and/or PM imperfections and to evaluate how such faults can be reliably detected in simulated and measured cogging torque signals. Design/methodology/approach - PM motors exhibit inherent cogging torque, which creates torque ripple and prevents smooth rotation of the rotor, resulting in undesirable vibration and noise. While cogging torque minimization is necessary to improve PM motor performance, several FEM models have been developed to study and present data demonstrating the sensitivity of cogging torque to PM assemblies and/or PM imperfections. Some procedures that would predict and evaluate cogging torque components relative to measured PM positions on assembled PM motors were proposed. Findings - On the basis of numerous performed simulations using different FEM models and experimental results on rotors from mass-production, it was found and proved that PM assembly tolerance and/or PM imperfections cause the phenomenon of additional cogging torque harmonic components. Considering the presented theoretical aspects motor designers can predict which additional harmonic components will comprise the cogging torque, as a result of which the appropriate technique for minimizing native and additional harmonic components can be applied. Research limitations/implications - The presented research of cogging torque sensitivity in different PM motor designs to assembly tolerance and/or PM imperfections should in future also consider stator irregularities and different methods of lamination stacking such as notches, welding, and interlocking. Practical implications - By utilizing the presented method and considering recommendations, advanced motor designers have a reliable tool for predicting the order and level of additional harmonic components in total cogging torque. Thus, adequate critical manufacturing tolerances can be defined in order to achieve minimal waste in produced PM motors. Originality/value - The originality of the paper is explained by the theoretical aspects and analytical equations of additional harmonic components in cogging torque of PM motors. Also original are the expressions for amplitude calculation of additional harmonic components influenced by manufacturing tolerances. [ABSTRACT FROM AUTHOR]