Comparison of three analytical methods for the precise calculation of cogging torque and torque ripple in axial flux PM machines

A comparison between different analytical and finite-element (FE) tools for the computation of cogging torque and torque ripple in axial flux permanent-magnet synchronous machines is made. 2D and 3D FE models are the most accurate for the computation of cogging torque and torque ripple. However, they are too time consuming to be used for optimization studies. Therefore, analytical tools are also used to obtain the cogging torque and torque ripple. In this paper, three types of analytical models are considered. They are all based on dividing the machine into many slices in the radial direction. One model computes the lateral force based on the magnetic field distribution in the air gap area. Another model is based on conformal mapping and uses complex Schwarz Christoffel (SC) transformations. The last model is based on the subdomain technique, which divides the studied geometry into a number of separate domains. The different types of models are compared for different slot openings and permanent-magnet widths. One of the main conclusions is that the subdomain model is best suited to compute the cogging torque and torque ripple with a much higher accuracy than the SC model

Coupled electromagnetic and thermal analysis of an axial flux PM machine

The rotor discs in axial flux permanent magnet (PM) machines have similar properties as a radial fan, and therefore, the convective cooling may have a significant influence on the thermal design of these machines. To research the impact of convective cooling on the thermal properties of axial flux PM machines, a coupled electromagnetic and thermal model is introduced in this paper. This technique models a segment of the stator and the rotor only and links them together by analytical equations of the convective heat transfer at different boundaries of the machine model. This results in an accurate and time efficient multiphysics model. The coupled electromagnetic and thermal modeling technique is validated with measurements on a 4 kW axial flux PM machine having the yokeless and segmented armature topology

High speed operation design considerations for fractional slot axial flux PMSM

This paper discusses intensively the design considerations for the fractional slot axial flux permanent magnet synchronous (AFPMSMs) in order to work efficiently in the constant power speed range, also known as the field weakening (FW) region. The dominant parameter in the constant power speed region is called the characteristic current which equals the ratio of the magnet flux linkage over the synchronous inductance (− ψm/Ls). Several machine parameters is affecting the characteristic current including the machine geometry and the winding configurations. In this paper, the effect of many of these parameters on the FW has been discussed; including the outer diameter, inner to outer diameter ratio, magnet size, slot opening width, slots per poles combinations,and the multi phase configurations for the Axial flux permanent magnet synchronous machine (PMSM). Two main governors are considered to evaluate the parameters’ impact on the machine overall performance; the rated machine efficiency and the torque to weight ratio at the highest values. Selection of these governors is application driven where these governors are the most influencing factors on the axial flux PMSM design. The results of the present analysis show that the fine tuning of the discussed machine parameters would derive the motor to work in the required Constant Power Speed Region (CPSR) keeping the required high efficiency and torque to weight ratio. A previously proved analytical model has been used in this study to overcome the highly time consumption in the finite element model (FEM)

Multilevel Thresholding for Image Segmentation Using an Improved Electromagnetism Optimization Algorithm

Image segmentation is considered one of the most important tasks in image processing, which has several applications in different areas such as; industry agriculture, medicine, etc. In this paper, we develop the electromagnetic optimization (EMO) algorithm based on levy function, EMO-levy, to enhance the EMO performance for determining the optimal multi-level thresholding of image segmentation. In general, EMO simulates the mechanism of attraction and repulsion between charges to develop the individuals of a population. EMO takes random samples from search space within the histogram of image, where, each sample represents each particle in EMO. The quality of each particle is assessed based on Otsu’s or Kapur objective function value. The solutions are updated using EMO operators until determine the optimal objective functions. Finally, this approach produces segmented images with optimal values for the threshold and a few number of iterations. The proposed technique is validated using different standard test images. Experimental results prove the effectiveness and superiority of the proposed algorithm for image segmentation compared with well-known optimization methods

Wide bandgap based modular driving techniques for switched reluctance motor drives

In switched reluctance motors, the stator can be seen as comprising a stator yoke and a modular tooth-coil construction. Each module consists of a concentrated winding wound around a steel pole. In the conventional driving technique, depending on the number of the stator poles, a number of coils are connected together and driven from one asymmetric H-bridge. Another possible driving technique is the modular one in which each stator coil is driven by a separate asymmetric H-bridge. In this way, the fault tolerance of the drive is highly enhanced. In this paper, three modular driving techniques are proposed, simulated and compared to the conventional one. The difference between the three modular techniques is in the number of turns per stator coil and the DC-link voltage compared to the conventional one. The first technique maintains both the number of turns per coil and the DC-link voltage, the second one maintains the number of turns per coil while halving the DC- link voltage and the last one maintains the DC-link voltage and doubles the number of turns per coil. All the techniques are applied on a 6/4 SRM machine. The technique that maintains the DC-link voltage and doubles the number of turns shows superior performance in terms of the drive efficiency and the converter power density but results in the highest torque ripple. The technique that halves the DC-link voltage achieves a low torque ripple and an efficiency equal to the conventional technique. The converter is designed using SiC technology to enable higher switching frequency capability so that, a smaller DC-link capacitance can be obtained and a high drive efficiency as well

Analytical modeling of axial flux PM machines with eccentricities

© 2017 IOS Press and the authors. All rights reserved. In this paper, an analytical quasi three-dimensional method is used to model an axial flux permanent magnet (AFPM) machine with various eccentricities. AFPM machines (AFPMMs) have various advantages but they are sensitive to geometrical imperfections for manufacturing aspect. The main aim of this paper is to propose a general analytical model to analyze the AFPMMs with various types of eccentricities. The radial and tangential magnetic flux densities in the air gap under healthy condition are obtained via combination of Maxwell's equations and Schwarz-Christoffel (SC) mapping firstly. Next, in order to investigate the eccentricities, equations for air gap length and radii are deduced. The back electromotive force (EMF) is calculated and compared with those from healthy condition and finite element (FE) analysis, respectively. The results show that the analytical predictions agree well with the FE results. Moreover, using this method has a significantly less time consuming than the 3D FM simulation process, which is a great advantage of this method. Finally, the analytical model is verified via experimental results