Byung-Il Kwon

Interior permanent magnet synchronous motors (IPMSMs) offer high torque density. However, they are expensive owing to the rising prices of rare earth elements used in permanent magnets (PMs). This study proposes a double-layer flared-shaped IPMSM (DF-IPMSM) that achieves equivalent output torque and reduced torque ripple, while minimizing PM usage. It achieves flux concentration using C-type ferrite PMs arranged in a flared configuration and enhances reluctance torque by increasing the difference between L_d and L_q using a double-layer PM arrangement. Finite element analysis (FEA) under rated load and drive conditions demonstrates that the DF-IPMSM achieves output torque and efficiency equivalent to those of a single-layer flared-shaped IPMSM (SF-IPMSM) despite the reduced PM usage. To verify the structural advantages of the DF-IPMSM, it was compared with three alternatives, namely, SF-IPMSM, double-bar type IPMSM (DB-IPMSM), and double-spoke type IPMSM (DS-IPMSM), under rated load conditions. The FEA results indicated that the DF-IPMSM achieves the highest reluctance torque at equivalent output torque and efficiency. Although DF-IPMSM utilizes the reluctance torque more effectively than SF-IPMSM, it has the disadvantage of increasing torque ripple due to magnetic saturation and harmonic distortion. We performed an optimization rotor geometry design to improve this drawback. Sample points were generated using Latin Hypercube Sampling (LHS) and constructed a Kriging-based surrogate model. Subsequently, a genetic algorithm (GA) was employed to determine the optimal values for minimizing torque ripple. Finally, the FEA results of the optimized model were compared with the prototype measurements to verify the validity of the proposed DF-IPMSM. The proposed DF-IPMSM design offers a cost-effective alternative to conventional IPMSMs by significantly reducing reliance on rare earth PMs while maintaining high torque performance and efficiency.

In this paper, the surface-mounted permanent magnet motor (SPMM) which uses multi-level magnet combination to improve air gap magnetic field distribution is modeled and optimized based on analytical method. The multi-level magnets adopt the specific combination of NdFeB and ferrite with different remanences to reduce the harmonics of the air gap magnetic field and the torque ripple. Firstly, the analytical modeling method of SPMM with multi-level NdFeB and ferrite magnets is presented, and the results are compared with finite element method (FEM) results. To further improve the performance, the manta ray foraging optimization (MRFO) algorithm is used to optimize the average torque, torque ripple, and magnet cost, taking the angles of different magnets as variables. The effectiveness of the optimization approach is verified by comparing the fitness and computation with the particle swarm optimization (PSO) algorithm. Finally, a prototype is manufactured based on the optimization results, and the tested electromagnetic performance is compared with the FEM and analytical results.

As the applications and production demands for high-speed axial flux permanent magnet (AFPM) motors continue to expand, conventional motor designs are increasingly challenged to achieve high-quality torque while adhering to shorter design cycles. To address this issue, this paper proposes an analytical method for slotless AFPM motor with specific magnets to make back electromotive force (EMF) sinusoidal for low torque ripple. Initially, the design principle of the sinusoidal magnet is introduced, and the air gap magnetic field of the AFPM motor is modeled based on the sinusoidal magnet shape, with a comparison of the ring magnet. Subsequently, the back EMF of the AFPM motor with toroidal and bunched winding is deduced and compared by winding function. The torque performance is further calculated to verify the effectiveness of the low torque ripple design. Finally, the prototype with sinusoidal magnets and bunched winding is manufactured, and the analytical results are consistent with experimental tests.

An analytical and optimisation method is presented to improve the air‐gap magnetic field of the surface‐mounted permanent magnet machine with multi‐level array magnets, which can reduce air‐gap magnetic field harmonics and torque ripple. Different from the conventional analytical method (AM) around the entire single‐magnet pole, the modelling method of multi‐level equal‐thickness ferrite magnets with different remanences for improving the air‐gap flux density is investigated. Considering the influence of air‐gap relative permeability by stator slots and multi‐level magnet remanences on the air‐gap flux density, the proposed AM for improving air‐gap flux density is derived by analysing the slotless air‐gap flux density and slotted air‐gap relative permeability. The cogging torque is predicted with energy method by analysing the tangential magnetic field distribution at stator slots. Then, the back electromotive force is predicted by analysing the winding distribution and radial air‐gap flux density. Based on the proposed AM, the simulated annealing particle swarm optimisation algorithm is used by optimising the widths and thicknesses of the multi‐level array magnets to further reduce torque ripple and increase output torque. Finally, the accuracy of the proposed AM is verified by comparing with the finite element method.

In this study, a torque enhancement principle for a stator permanent-magnet (PM) Vernier machine with a consequent pole structure is proposed. The novelty of the manuscript is the explanation of how stator PM Vernier machines benefit from consequent pole structure. Although a similar concept of stator PM Vernier machines with a consequent pole structure has been investigated in previous studies, a clear torque enhancement principle was absent. The keys to torque enhancement are the decrement of nonworking harmonics and increment of working harmonics. To demonstrate these phenomena, the torque contributions from the harmonics were calculated. Subsequently, the performances of the conventional machine and consequent pole machine were compared to verify the enhancement principle. The electromagnetic performances, including the back electromotive force and torque, were compared. The results show that the stator PM Vernier machine benefits significantly from torque enhancement using the consequent pole structure, and the torque enhancement principle was verified.

This paper proposes a dual-mode brushless wound rotor synchronous machine (DBL-WRSM) for high starting torque. The proposed DBL-WRSM consists of two modes: induction and brushless (BL)-synchronous modes. First, the induction mode operates as a wound rotor induction machine (WRIM) to achieve a high starting torque. Second, the BL-synchronous mode operates as a brushless wound rotor synchronous machine (BL-WRSM) using the subharmonic of the stator magnetomotive force (MMF) in the steady state. To realize the dual-mode topology of the proposed machine, the stator is composed of two divided armature windings and two inverters that can produce subharmonics. The rotor has five switches that convert the rotor winding configuration between the two modes. To verify the proposed topology of DBL-WRSM, finite element analysis (FEA) was performed. Through the FEA results of the transient electromagnetic torque for the voltage source, it was confirmed that the proposed DBL-WRSM not only operates as a BL-WRSM in a steady state but also has a sufficiently high starting torque even under a full-load condition.

This study proposes an analytical method (AM) for V-type consequent-pole permanent magnet (V-CPM) machines to quickly determine the suitable permanent magnet (PM) volume while reducing the PM volume compared to that of the V-type interior PM (V-IPM) machine. Special air-gap magnetic flux density modeling is adopted in the AM, which consists of 4 asymmetric regions under one PM and the iron pole of the V-CPM. This specific modeling is utilized for the V-CPM topology, which has a different magnetic saturation trend from the conventional surface-mounted CPM (S-CPM). Hence, additional consideration of rotor saturation by novel method has been done compared to the previous works. To achieve average torque similar to that of the V-IPM machine, a V-CPM machine is designed by the proposed AM to have the same fundamental harmonic value of air-gap flux density. Furthermore, two conditions are considered for the V-CPM machine design to prevent unnecessary saturation and to minimize torque ripple. All the performance metrics of the designed V-CPM machine are compared with those of the other machines to demonstrate its superiority.

This paper proposes a rotary-linear surface-mounted permanent magnet (PM) voice coil motor (RL-SVCM) with PM flux bridges in place of the iron flux bridges in a traditional RL-SVCM for enhancing average torque and force ripple but slight damage of torque ripple and average linear force. The iron flux bridges in a basic RL-SVCM cannot participate in the generation of rotary torque. In contrast, the PM flux bridges in the proposed RL-SVCM can participate in the generation of rotary torque. The magnetic equivalent circuit (MEC) is used to analyze the magnetic circuits of the basic and proposed models. The results explain the reasons for the performance improvements achieved by the proposed motor. The finite element method (FEM) is used to derive the precise output performance of the basic and proposed motors. Additionally, a prototype of the proposed RL-SVCM with PM flux bridges was manufactured for experimental verification. Close agreement between the experimental results and FEM results validates the feasibility of the proposed RL-SVCM.