Cogging Torque Components Research Articles

A Cogging Torque Minimization Procedure for Interior Permanent Magnet Synchronous Motors Based on a Progressive Modification of the Rotor Lamination Geometry

This article describes a simple cogging torque minimization procedure for interior permanent magnet synchronous machines (IPMSMs), consisting of a progressive modification of the rotor lamination geometry. This procedure can be generalized for the main topologies of PMSM, independently of the number of stator slots or the location of the permanent magnets. For this purpose, a basic IPMSM structure is analyzed by means of the FEM (finite element method) approach, and then, several other IPMSM geometries, obtained by adequately modifying the rotor lamination geometry of the basic IPMSM model without changing its stator configuration, are proposed and discussed. The trends of the cogging torque generated by each model are computed and compared. From this comparison, it is demonstrated that, by simply acting on the shape of the rotor lamination and by choosing the optimized pattern, the cogging torque components can be theoretically canceled.

Применение сосредоточенных обмоток для мощных синхронных ветрогенераторов

Low-power machines were commonly considered as the main application field of concentrated windings. However, a lot of paper have recently been published, which address both the theory of these windings and specific cases of their application for large synchronous machines. The article presents an analysis of the parameters of concentrated windings having various configurations intended for use in high-power gear and gearless wind generators. In assessing the winding, not only the high winding factor value was taken into account, but also the star of slot EMFs, harmonic spectra of the MMFs and EMFs, the cogging torque component and torque pulsation under load, as well as emerging losses. It is shown that the well-known advantages of concentrated windings over distributed windings can be fully realized by choosing the appropriated numbers of slots and poles.

Modified concept of axial-flux permanent magnet machine with field weakening capability

Abstract This paper presents the concept of an innovative field-controlled axial-flux permanent-magnet (FCAFPM) machine. In order to show the working principle and features of the proposed dual-rotor with surface-mounted PM’s and iron poles, a toroidally- wounded slotted single-stator FCAFPM machine is investigated and analyzed in detail, using 3-D FEAnalysis. The control range, back electromotive force (back-EMF), output and cogging torque components have been evaluated.

Magnet asymmetry in reduction of cogging torque for integer slot axial flux permanent magnet motors

Cogging torque component is one of the key issues in the design of radial and axial gap permanent magnet motors and the geometry and the position of the magnets plays a critical role in this process. This study presents the influence of magnet asymmetry in minimisation of the cogging torque for axial flux permanent magnet (AFPM) disc motors. Cogging torque minimisation techniques, such as magnet skewing and magnet shifting or groping are examined in detail by using three-dimensional finite element analysis with various types of magnet skewing alternatives since the shaping and the positioning magnets are low cost approaches to minimise or eliminate the cogging component. A prototype AFPM disc motor is built with shifted magnets based on the models which are the results validated with the experimental results for the minimum cogging component and the sinusoidal back-EMF waveform. It is shown in this study that the cogging component in AFPM motors can be practically eliminated by using magnet asymmetry and perfectly sinusoidal back-EMF can also be obtained even for integer slot/pole/phase motors.

Additional cogging torque components due to asymmetry in stator back iron of PM synchronous motors

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 pr...

Torque ripple minimization in a BLDC motor using an improved voltage control method

This paper proposes a method to reduce the torque ripple of a square wave voltage-driven BLDC motor. First of all, this paper reviews a previous voltage control method to reduce torque ripple, and shows that cogging torque component still remains. Then this paper proposes an improved voltage control method to offset cogging torque. To verify the proposed method, FE-analysis is performed for a test BLDC motor and it is shown that torque ripple is considerably reduced comparing with a previous control.

Native and Additional Cogging Torque Components of PM Synchronous Motors—Evaluation and Reduction

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.

Phenomena of additional cogging torque components influenced by stator lamination stacking methods in PM motors

PurposeThe 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/approachThe 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.FindingsOn 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 implicationsBy 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/valueThe 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.

Additional Cogging Torque Components in Permanent-Magnet Motors Due to Manufacturing Imperfections

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.

Prediction of cogging torque level in PM motors due to assembly tolerances in mass‐production

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 t...

H∞ model matching two-degree-of-freedom control with adaptive torque ripple cancellation for high performance direct drive systems

This study presents a novel adaptive robust control scheme to achieve a fast and accurate tracking performance in direct-drive (DD) systems under parameter and load uncertainties. The control combines an outer loop based on H∞ model matching (MM) in a two-degree-of-freedom (2-DOF) control structure, with an adaptive cancellation loop to increase torque ripple suppression further for improved tracking performance. A modified H∞ MM 2-DOF approach is taken by designing both the feedback loop and reference controller to achieve an improved tracking performance in the sense of H∞ MM criterion with integral action, while the robustness of the system is naturally satisfied by the 2-DOF control structure. Experimental results taken on a permanent magnet synchronous motor (PMSM) driven direct-drive system demonstrate a good tracking performance under a variety of reference trajectories. The results also demonstrate the robustness of the method against payload uncertainties and torque pulsations, except for the cogging torque components around the corner frequency. To improve attenuation of cogging torque terms further, the H∞ based outer loop is combined with an adaptive cancellation scheme derived based on the Lyapunov criteria. The developed adaptive robust control scheme demonstrates an improved robustness and tracking performance over a large frequency range.