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Electric machines with high torque density are needed in many applications, such as electric vehicles, electric robotics, electric ships, electric aircraft, etc. and they can avoid planetary gears thus reducing manufacturing costs. This paper presents a novel axial-radial flux permanent magnet (ARFPM) machine with high torque density. The proposed ARFPM machine integrates both axial-flux and radial-flux machine topologies in a compact space, which effectively improves the copper utilization of the machine. First, the radial rotor can balance the large axial forces on axial rotors and prevent them from deforming due to the forces. On the other hand, the machine adopts Halbach-array permanent magnets (PMs) on the rotors to suppress air-gap flux density harmonics. Also, the Halbach-array PMs can reduce the total attracted force on axial rotors. The operational principle of the ARFPM machine was investigated and analyzed. Then, 3D finite-element analysis (FEA) was conducted to show the merits of the ARFPM machine. Demonstration results with different parameters are compared to obtain an optimal structure. These indicated that the proposed ARFPM machine with Halbach-array PMs can achieve a more sinusoidal back electromotive force (EMF). In addition, a comparative analysis was conducted for the proposed ARFPM machine. The machine was compared with a conventional axial-flux permanent magnet (AFPM) machine and a radial-flux permanent magnet (RFPM) machine based on the same dimensions. This showed that the proposed ARFPM machine had the highest torque density and relatively small torque ripple.

Tidal energy, as a stable and predictable renewable energy source, is garnering increasing attention. However, tidal energy generation faces challenges such as low energy conversion efficiency and high mechanical losses in low-velocity environments. To address these issues, this paper proposes a novel design for a tidal energy generator based on an axial field coreless structure. This design significantly reduces mechanical losses and enhances energy conversion efficiency by employing a direct-drive structure and a coreless stator. Additionally, the introduction of a Halbach array permanent magnet and soft magnetic composite further optimizes the generator’s electromagnetic performance, thereby increasing power output. Simulation results demonstrate that the designed generator can achieve a power output of 300 W at a tidal velocity of 1.8 m/s, with an average generation efficiency of 90.6%. This design exhibits excellent performance in low-velocity tidal environments and provides valuable technical support for the design of tidal energy generators.

In order to develop an electrical continuously variable transmission (E-CVT) to replace mechanical power coupling equipment applied in series-parallel hybrid electric vehicle (HEV), this paper proposes a magnetic-field modulated brushless dual-mechanical port motor with Halbach array permanent magnets, which has a more compact structure. The operating characteristics are analyzed by the lever analogy. It is concluded that the motor can realize the speed and torque decoupling between the engine and the wheel, which meet multi-mode operation requirements for HEV. To realize the multi-objective design of torque output, torque ripple and usage amount of permanent magnets, an optimization scheme combined parameter sensitivity with response surface methodology is adopted. The trade-offs among the optimization objectives are considered, then the key structural parameters and its optimal values are efficiently determined. Based on a two-dimensional model, the electromagnetic performances are simulated and analyzed. The results show that, after the parameters optimization, the no-load back electromotive force (EMF) has better sinusoidal characteristic, and the torque ripples and cogging torque peaks of the motor have been significantly reduced. Furthermore, a prototype motor is tested. The experimental results are consistent with the simulation results, which demonstrates the validity of the proposed structure and parameter optimization method.

Purpose - The purpose of this paper is to minimize the torque pulsation in Halbach array permanent magnet synchronous machines (PMSMs).Design methodology approach - Because of its specific structure, the cogging torque influences the main part of the torque pulsation in a Halbach array PMSM. In this paper, first it is shown that the conventional magnet skewing method does not have a significant effect on the torque pulsation in this motor, and then an improved skewing method with fewer skewing steps is proposed. In this method permanent magnet segments are placed sinusoidally, with two-step skewing along the rotor. Generalization with different combinations of slots and poles is considered for a Halbach array PMSM.Findings - Using a detailed finite element method (FEM) it was found that with the proposed technique the cogging torque factor is reduced to as low as 8 percent, while the average value of the torque is maintained near the machine nominal average torque.Practical implications - Halbach array PMSMs are very good candidates for high dynamic performance applications such as aerospace applications due to their high acceleration and deceleration features. This technique also resolves the mechanical vibration and acoustic noise issues, which are caused by torque pulsation and significantly affect machine performance.Originality value - The originality of this paper lies in the FEM results. Since Halbach array PMSMs have a special structure it was shown that the conventional skewing method does not work well for this machine. The new proposed technique has a significant effect on the torque pulsation.

Purpose The purpose of the paper is to study the stability control of permanent magnet (PM) and electromagnetic hybrid Halbach array electrodynamic suspension (EDS) system because of the poor suspension stability caused by the well-known under-damped nature of PM EDS system. The adjustment control is realized by PM and electromagnetic hybrid Halbach array, which is composed by winding active normal conductor coils on PM surface. Design/methodology/approach The three-dimensional (3-D) electromagnetic force analytical expression of PM and electromagnetic hybrid Halbach array EDS system for a nonmagnetic conductive plate is derived. And the accuracy of the derived equations is verified by a 3-D finite-element model (FEM). Basing on the 3-D levitation force expression, an acceleration feedback suspension controller is designed to suppress the vibration of PM EDS system, and the suspension stability of the system under the track and load disturbance was simulated and analyzed. Findings The 3-D electromagnetic force comparison of analytical model and FEM are in good agreement, which verifies the correctness of the analytical expression. The simulation results show that the acceleration feedback suspension controller can make the system have good suspension stability under the external disturbance. So it proved that the PM and electromagnetic hybrid Halbach array EDS system can overcome the poor suspension stability caused by the under-damped nature of PM EDS system through the designed acceleration feedback suspension controller. Originality/value This paper designed an acceleration feedback suspension controller to suppress the vibration of PM and electromagnetic hybrid Halbach array EDS system under external disturbance, basing on the derived levitation force analytical expression. And the simulation results show that the acceleration feedback suspension controller can make the system have good suspension stability under the external disturbance.

Variable-speed constant-frequency generating systems are commonly employed in wind turbines to enhance efficiency and minimize losses. Additionally, the utilization of dual-rotor wind turbines enables the capture of a greater amount of wind energy, leading to a significant increase in efficiency. Traditionally, dual-rotor wind turbines are managed by a full-scale power converter, and the rotor current is transmitted through brushes, which substantially raises the system's cost. To address these challenges, this study introduces a novel configuration that enables power control with a smaller power converter. In contrast to conventional dual-rotor wind turbines that generate power using both rotors, the proposed structure designates one rotor as a system controller. Apart from these benefits, the proposed structure greatly enhances conversion performance by notably improving the power factor. A comparison with existing configurations described in literature is conducted to demonstrate the superiority of the proposed structure.

Analysis of Halbach array placed in open space by using finite element method involves substantial consumption of memory, time, and cost. To address this problem, development of a mathematical modeling and analytic analysis method for Halbach array can be a solution, but research on this topic is currently insufficient. Therefore, a novel mathematical modeling and analytic analysis method for Halbach array in open space is proposed in this study, which is termed as the Ampere model and the Biot–Savart law (AB method). The proposed AB method can analyze the Halbach array rapidly and accurately with minimal consumption of memory. The usefulness of the AB method in terms of accuracy and memory and time consumption is verified by comparing the AB method with finite element method in this paper.

A magnetic lead screw (MLS) uses the magnetic field of permanent magnets to convert between linear and rotational motions while achieving a gearing action. This mechanism converts low-speed, high-force linear motion to high-speed, low-torque rotational motion. The MLS is ideal for wave energy applications, where the low-speed oscillatory motion of waves can be converted into usable electrical energy. It harnesses the high-force, low-speed linear motion of waves and converts it into rotational motion for generators, all while maintaining contact-free power transfer, reducing maintenance and machine size compared to linear machines. In this study, two controllers are proposed for an ideal Halbach magnetic lead screw: a proportional-resonant (PR) controller and an observer-based state feedback controller (O-SFC). The proportional-integral (PI) controller is also presented as a benchmark. These controllers are developed based on the linearized model of the ideal Halbach MLS and validated through simulation studies of its non-linear model. Results show that both the PR and O-SFC controllers significantly improve system performance compared to the PI controller, with the O-SFC providing superior performance over both the PR and PI controllers.

A dual-rotor yokeless and segmented armature (YASA)-type axial-flux permanent magnet (AFPM) motor with a surface-mounted permanent magnet (SPM) array type was developed for urban air mobility (UAM) aircraft in this work. The proposed AFPM motor had rated and peak output powers of 75.5 and 104 kW, respectively, with rated and peak rotational speeds of 1800 rpm. To achieve a high torque, a cobalt–iron alloy core material was used for the stator core. The prototype AFPM motor, developed by KSEP in the Republic of Korea, was successfully manufactured and verified through experimentation. Additionally, the thermal stability of the winding and permanent magnets (PMs) was confirmed with a water-cooling system. A structure analysis of the proposed AFPM motor was conducted due to the detachment of an uneven air-gap length in the prototype AFPM motor. An output performance comparison based on core materials for the stator and rotor was carried out to explore the material cost reduction. Subsequently, the design for performance improvement by applying a Halbach permanent magnet (HPM) array type was investigated for further research.

The rim-driven device (RDD) integrates the motor and the impeller, which can achieve shaftless, modular, and integrated operation of the turbomachinery system and has broad application prospects. To reduce the axial length and radial thickness of the RDD, a motor with a thin-yoke wide-tooth fractional slot concentrated winding stator and a coreless Halbach permanent magnet array rotor is designed. Theoretical and finite element simulation analyses of its air gap magnetic field characteristics were carried out. The results show that, for the thin-yoke wide-tooth fractional slot concentrated winding permanent magnet motor, the harmonic magnetic field generated by the magnetic poles should mainly consider the magnetic field components produced by the interaction between the harmonic magnetomotive force of the magnetic poles and the constant air gap specific magnetic permeability, as well as the magnetic field components generated by the interaction between the fundamental magnetomotive force of the magnetic poles and the fundamental and second-order harmonic air gap specific magnetic permeability. The harmonic magnetic field generated by the current should mainly consider the magnetic field components produced by the interaction between the harmonic magnetomotive force with a small number of pole pairs (NOPP) and large amplitude generated by the current and the constant air gap specific magnetic permeability. Compared with radial magnetic flux density, tangential magnetic flux density has the same NOPP and frequency components, with a phase difference of 90°. The fundamental amplitude difference between them is larger, while the harmonic amplitude difference between them is smaller.