Kaikai Guo

Irreversible Demagnetization Analysis of Permanent Magnet Materials in a Novel Flux Reversal Linear-Rotary Permanent Magnet Actuator

This paper proposes a novel flux reversal linear-rotary permanent magnet actuator (FR-LRPMA) with permanent magnets (PMs) mounted on the stator surface. The proposed FR-LRPMA uses only 50% of the PM materials when compared with that of the topology with four-PM poles in a conventional stator pole actuator. The FR-LRPMA provides a pathway for the magnetic field, which is generated by currents in the armature winding, resulting in substantial reduction in the possibility of irreversible demagnetization of the PMs to increase its torque density. According to the physics of PM demagnetization, a simplified fitting analytical expression, which considers the angular velocity, current, temperature, and PM thickness, is derived to determine the least work point of the PM. The torque prediction using the proposed algorithm at different currents agrees well with the values calculated using a finite-element method. It also confirms that the novel topology has a larger torque density.

A Novel Linear-Rotary Permanent-Magnet Actuator Using Interlaced Poles

This paper proposes a novel linear-rotary permanent-magnet actuator (LRPMA) with interlaced poles, which has the merit of using only 50% of the neodymium-iron-boron permanent magnets when compared with those used in traditional Halbach structure. By assuming the stator is slotless, the magnetic field distribution of the LRPMA is initially analyzed using the magnetic scalar potential in the Cartesian coordinate system. A method for calculating the relative permeance by Schwarz-Christoffel transformation (SCT) is subsequently deduced to analyze the magnetic field in detail and predict the cogging force/torque of LRPMA very accurately. The analytical linear cogging force and rotary cogging torque are derived and verified for the design optimization of the actuator. The 3-D finite-element method is used to verify the correctness and effectiveness of the proposed SCT.

Design and investigation of a fractional-slot pole-changing memory machine

This paper proposes a new pole-changing memory machine (PCMM), which tactfully incorporates fractional pole-slot combination and pole-changing with memory machine. By doubling the slot number and coil span of fractional slot concentrated winding (FSCW), the machine having 9 slots 8/4 pole (9s-8/4p) combination can be changed into the one having 18 slots 8/4 pole (18s-8/4p) with 2 pitches. The electromagnetic characteristics of the two fractional-slot PCMMs (FS-PCMM), both of which can switch between 8 pole mode (8P mode) and 4 pole mode (4P mode), are analysed and compared. It demonstrates that the 18s-8/4p machine is superior to the 9s-8/4p one in aspects of unbalanced magnetic pull (UMP) and torque ripples. This study shows that the proposed 18s-8/4p FS-PCMM features satisfying variable speed characteristic so that it can be operated in wide speed range as required in electric vehicles.

A Linear-Rotary Permanent Magnet Actuator With Independent Magnetic Circuit Structure

The paper proposes a novel linear-rotary permanent magnet actuator with an independent magnetic circuit structure, which decreases the coupling relationship between the fluxes of adjacent phases. The amplitude of cogging force is reduced by choosing proper distance between adjacent stator segments in the axial direction, while the thrust force can be increased. A 3-D model is built for analyzing the air gap magnetic flux density and a simplified model of one section is built for calculating thrust force. The expression of cogging force, end force, normal force are derived by analytic method and Maxwell stress tensor method. The analytic results verified by finite element method show that the detent force can be minimized when the distance between two adjacent stators in axial direction approaches 2τ/3.

3-D Analytical Analysis of Magnetic Field of Flux Reversal Linear-Rotary Permanent-Magnet Actuator

This paper develops a 3-D analytical model to compute the no-load magnetic-field distribution in a flux reversal linear-rotary permanent-magnet actuator (FR-LRPMA) with two permanent-magnet (PM) poles (PM_pole) and two ferromagnetic poles (Fe_pole) on each stator tooth. Laplace’s and Poisson’s equations are built assuming that the stator and the rotor are slotless and both the permeances of Fe_pole and PM_pole are the same. The tubular mover is transferred into a planar one using a curvature factor. Then a 2-D model and 3-D model for calculating the air-gap relative permeances are proposed considering the effect of slot and the permeance difference of Fe_pole and PM_pole, respectively. The expressions of 3-D magnetic flux density, cogging force, and cogging torque of the FR-LRPMA are subsequently derived and verified using the finite-element method.

Flux-Concentrated External-Rotor Switched Flux Memory Machines for Direct-Drive Applications

In this paper, an external-rotor switched flux hybrid magnet memory machine with a flux-concentration design is developed. Due to the external-rotor configuration, the stator design space is enlarged to alleviate the stator geometric conflictions existed in the internal rotor machine. Meanwhile, the spoke-type permanent magnet (PM) structure is designed to cope with the reduced armature slot area in its original “U”-shaped PM counterpart. In addition, the high-efficiency operation within a wide range of speeds and loads can be achieved. The topology, flux-adjusting principle and distinct features are introduced. Thereafter, the key design parameters including the stator/rotor pole combination, PM hybridizing ratio, and LCF PM thickness are optimized. Finally, the electromagnetic characteristics of the proposed machine are investigated and quantitatively compared with that of its“U”-shaped PM counterpart, which confirms the advantages of the proposed design.

Analysis of On-Load Magnetization Characteristics in a Novel Partitioned Stator Hybrid Magnet Memory Machine

The on-load magnetization characteristics of a newly developed partitioned stator switched flux hybrid magnet memory machine are comprehensively analyzed in this paper. First, the open-circuit and on-load permanent magnet magnetization performances are evaluated and compared. The mismatch of the required demagnetizing currents between open-circuit and on-load cases is identified. Then, the on-load demagnetization behavior of low coercive force (LCF) magnet is disclosed by the frozen permeability method. Besides, a numerical solution for the refinement of LCF magnet sizing is presented by a proposed virtual linear hysteresis model so as to effectively prevent the undesired on-load demagnetization. Finally, an optimized prototype is tested to verify the theoretical analyses.

Electromagnetic analysis of a novel axial-field switched flux hybrid magnet memory machine

This paper proposes an axial field switched flux hybrid magnet memory machine (AF-SF-HMMM). Compared with conventional axial field permanent magnet (PM) machines having PMs in rotor side, the AF-SF-HMMM benefits from good heat dissipation and high rotor robustness power density. Meanwhile, because both high-energy-product neodymium-iron-boron (NdFeB) PM and low coercive force (LCF) PM materials are used simultaneously, the proposed machine can flexibly regulate air-gap flux without much sacrificing its high torque capability, which is particular suitable for electric vehicular applications. Based on 3-dimensional (3-D) finite element analysis (FEA), the electromagnetic performance of the machine is numerically investigated. It shows that the proposed machine features high torque density and well sinusoidal flux linkages and back electromotive force (EMF).

3-D analytical cogging force and cogging torque analysis of a novel linear-rotary permanent magnet actuator

A novel linear-rotary permanent magnet actuator (LRPMA) is proposed in this paper, in which ferromagnetic poles and PM poles are mounted on the mover surface. A 3D analytical model without considering the stator slotting effect is presented for calculating no-load air-gap magnetic field, which transfers the tubular mover of the proposed LRPMA into a planar one. A permeance model is then built to consider the stator slotting effect in the circumferential and axial directions. The equations of cogging force and cogging torque are derived by the Maxwell stress tensor method and 3D finite element method (FEM). The analytical results of cogging force and cogging torque are consistent with those by 3D FEM.

Novel design of a variable reluctance permanent magnet machine with bipolar coil flux-linkage

This paper proposes a novel design concept for variable reluctance permanent magnet machines (VRPMMs) by introducing heteropolar dual stators and shifted rotors in axial direction. The machine is geometrically similar to switched reluctance machines, but with homopolar PMs alternately mounted on stator poles. With this design concept, the bipolar and sinusoidal coil flux-linkage can be obtained due to the elimination of even harmonics between two axially parallel sub-machines. In addition, this design can offer another merit of torque density improvement. The machine topology features and harmonic cancellation theory are addressed. Then the electromagnetic characteristics of the 6/4-pole machine with the proposed design concept are investigated and compared with those of the original VRPMM. The detailed analysis results and experimental validation will be presented in the full paper.