This paper presents issues for reducing cogging torque of permanent-magnet motors. When proper methods are employed, it is theoretically possible to minimize its level or even to eliminate it. FFT ...analyses of cogging torque in mass-produced motors have shown additional harmonic components, which are in tight correlation with assembly tolerances and/or permanent-magnet imperfections. Finite element method has been used to study the sensitivity of different motor models relative to manufacturing tolerances and to determine rules for detecting imperfections in mass-production.
High performance motor drive applications require permanent-magnet synchronous motors that produce smooth torque with very low components of cogging torque. To fulfil such demands a variety of design ...techniques can be used to reduce or even eliminate cogging torque components. Rotor design techniques are in comparison to the stator ones much more effective, but their effectiveness depend considerably on the motor design parameters. Calculations have shown that the cogging torque can be significantly reduced while maintaining the output torque at the same level by the appropriate use of two or more presented techniques. However, the detailed analysis of cogging torque components has revealed that besides well-know native cogging torque components also additional cogging torque components exist which are provoked by assembly tolerances in mass-production. Since these two groups of cogging torque components are concerning design techniques mostly in contradiction, a minimization of the total cogging torque becomes a challenging task. A finite element method and Fast Fourier transformation were used to study the sensitivity of several motor simulation models with regard to manufacturing tolerances and assembly imperfections. On the bases of numerous simulations and analyses, it follows that manufacturing assembly tolerances and material imperfections cause the phenomena of additional cogging torque harmonic components, which are not present in the case of a perfect motor. The ascertainment that some permanent-magnet motor designs are more sensitive to the phenomenon of additional harmonic components in cogging torque than the others is an important fact for the producers of such motors, which must be seriously considered in the process of motor design optimization.
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.
Purpose - The purpose of this paper is to estimate and evaluate how cogging torque in permanent magnet (PM) motor designs is sensitive to the number of applied interlocks in stator back-iron, which ...is a standard method for stator lamination stacking.Design methodology approach - The 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 sensitivity of the cogging torque to the applied interlocks. A procedure that would predict and evaluate cogging torque components relative to chosen number and positions of interlocks was proposed.Findings - On the basis of theoretical considerations, which were verified by numerous performed simulations using different FEM models, it was found out and proved that interlocks in the stator back-iron cause the phenomenon of additional cogging torque harmonic components (AHC). Taking into account presented theoretical aspects motor designers can predict, which AHC will comprise the cogging torque. Each motor design has its own optimal value of interlocks, therefore a precise study should be performed during the design process.Practical implications - By utilizing presented method and considering recommendations, advanced designers of PM motors will have a reliable tool for predicting the order and the level of AHC in total cogging torque due to the stator lamination stacking methods.Originality value - The paper presents theoretical aspects and analytical equations of AHC of PM motors. So far, the authors dealing with the cogging torque of the PM motors did not take into account the influence of the stator lamination stacking method on the level of torque oscillations. The new contribution is also the study of the sensitivity of different motor designs to the number and position of interlocks, which enables the minimization of the AHC in order to fulfil stringent market demands for low-cogging torque level.
In this article, we present an investigation into the sound radiation from a permanent-magnet DC electric motor using the finite-element (FE) and boundary-element (BE) models. A three-times-coupled ...electromagnetic-mechanical-acoustic numerical model was set-up to predict the acoustic field. The first stage was to calculate the magnetic forces that excite the structure of the motor by using the FEM. In the second stage, the exciting magnetic forces were applied to the structural model, where the harmonic analysis was carried out using the FEM. The last stage was to model the acoustics by using the BEM. In order to evaluate the numerical model, the computational results were compared with the vibration and acoustic measurements and a reasonable agreement was found.
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.
Za sinkrone motore s permanentnim magnetima koji se primjenjuju u elektromotornim pogonima s visokim zahtjevima na radne karakteristike, mora se osigurati niska razina komponenata pulsirajućeg ...momenta nastalog zbog ozubljenja statora. Za ispunjenje toga zahtjeva koriste se razne. Tehnike izvedbe rotora u usporedbi s tehnikama izvedbe statora mnogo su efikasnije, međutim efikasnost u značajnoj mjeri ovisi o izvedbenim parametrima rotora. Proračuni su pokazali da se uz zadržavanje iznosa izlaznog momenta stroja, pulsirajući moment može značajno smanjiti primjenom dviju ili više tehnika prezentiranih u radu. Međutim, detaljna je analiza komponenata pulsirajućeg toka pokazala da se pored komponenata tzv. prirodnog pulsirajućeg momenta zbog ozubljenja, pojavljuju i dodatne komponente koje su rezultat slaganja dijelova stroja u masovnoj industrijskoj proizvodnji. Budući da eliminacija tih dviju grupa pulsirajućeg momenta zbog ozubljenja rezultira kontradiktornim zahtjevima na tehnološku izvedbu stroja, eliminacija ukupnog pulsirajućeg momenta zbog ozubljenja predstavlja zahtjevan i izazovan zadatak za projektanta. U radu se koriste metoda konačnih elemenata i brza Fourierova transformacija za analizu osjetljivosti izabranih simulacijskih modela s obzirom na tolerancije u proizvodnji i na nesavršenosti pri sklapanju dijelova stroja. Na osnovi brojnih simulacija i analiza pokazano je da tolerancije u proizvodnji i tolerancije u samim dijelovima stroja rezultiraju dodatnim harmoničkim komponentama pulsirajućeg toka, koje nisu prisutne u idealnom stroju. Činjenica da su neke izvedbe motora osjetljivije od drugih s obzirom na fenomen dodatnog pulsirajućeg momenta, proizvođačima je važna činjenica koja se mora uzeti u obzir u fazi projektiranja motora.
In this article, we present an investigation into the sound radiation from a permanentmagnet DC electric motor using the finiteelement FE and boundaryelement BE models. A threetimescoupled ...electromagneticmechanicalacoustic numerical model was setup to predict the acoustic field. The first stage was to calculate the magnetic forces that excite the structure of the motor by using the FEM. In the second stage, the exciting magnetic forces were applied to the structural model, where the harmonic analysis was carried out using the FEM. The last stage was to model the acoustics by using the BEM. In order to evaluate the numerical model, the computational results were compared with the vibration and acoustic measurements and a reasonable agreement was found.
In this paper we present the basic approaches to building a sequentially coupled model of an alternator to evaluate the vibro-acoustic response resulting from different excitations, such as engine ...vibration, rotor unbalance and magnetic forces. Special emphasis is given to the set-up and verification of the three-dimensional (3D) structural finite-element (FE) model for the whole alternator and for the alternator components. The verification of the structural model was carried out using experimental modal analysis (EMA), which was also applied for the estimation of the modal damping and for the structural FE model updating. Special emphasis is given to the evaluation of magnetic noise, generated due to the magnetic force excitation in the alternator To estimate the magnetic forces and their harmonic components a 3D magnetic FE model of the alternator was prepared. Finally, the exciting magnetic forces, calculated for the specific operation conditions of the alternator, were transferred into a structural FE model, where the structural and acoustic responses were calculated and analysed.
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