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)

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

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

Investigation of six-phase surface permanent magnet machine with typical slot/pole combinations for integrated onboard chargers through methodical design optimization

This article presents an analytical magnetic equivalent circuit (MEC) modeling approach for a six-phase surface-mounted permanent magnet (SPM) machine equipped with fractional slot concentrated winding (FSCW) for integrated onboard chargers. For the sake of comparison, the selected asymmetrical six-phase slot/pole combinations with the same design specifications and constraints are first designed based on the parametric MEC model and then optimized using a multiobjective genetic algorithm (MOGA). The commercial BMW i3 design specifications are adopted in this article. The main focus of this study is to achieve optimal design of the SPM machine considering both the propulsion and charging performances. Thus, a comparative study of the optimization cost functions, including the peak-to-peak torque ripple and core losses under both motoring and charging modes and electromagnetic forces (EMFs) under charging, is conducted. In addition, the demagnetization capability in the charging mode and the overall cost of the employed machines are optimized. Since the average propulsion torque is crucial in electric vehicle (EV) applications, it is maintained through the design optimization process. Furthermore, finite element (FE) simulations have been carried out to verify the results obtained from the analytical MEC model. Eventually, the effectiveness of the proposed design optimization process is corroborated by experimental tests on a 2-kW prototype system

Magnetic Equivalent Circuit and Lagrange Interpolation Function Modeling of Induction Machines Under Broken Bar Faults

This paper introduces a mesh-based magnetic equivalent circuit (MEC) modeling technique for induction machines (IMs) in healthy and broken rotor bars conditions. The MEC model is presented as a highly accurate and computationally efficient alternative to finite element (FE) models. By incorporating modifications to the air gap coupling method, including a new Lagrange interpolation function, and utilizing a harmonic MEC model, the accuracy of the solution is improved while reducing electrical and mechanical transients. Compared to experiments and 2D FE models, this model achieves precise results for electromagnetic torque, rotational speed, and forces across various conditions. The Lagrange interpolation function forms the basis for the air gap coupling between stator and rotor flux densities. The results demonstrate the MEC model’s exceptional accuracy in predicting speed oscillations, calculating forces, and analyzing current harmonics in faulty IMs. Furthermore, the MEC model performs over 30 times faster than the 2D FE models.acceptedVersionPeer reviewe