Permanent magnet (PM) brushless machines having magnets and windings in stator (the so-called stator-PM machines) have attracted more and more attention in the past decade due to its definite advantages of robust structure, high power density, high efficiency, etc. In this paper, an overview of the stator-PM machine is presented, with particular emphasis on concepts, operation principles, machine topologies, electromagnetic performance, and control strategies. Both brushless ac and dc operation modes are described. The key features of the machines, including the merits and drawbacks of the machines, are summarized. Moreover, the latest development of the machines is also discussed.

Overview of Stator-Permanent Magnet Brushless Machines

This paper overviews the recent development and new topologies of flux-switching (FS) machines, with particularly emphasis on the permanent magnet (PM) type. Specific design issues, including winding configurations, combinations of stator and rotor pole numbers, rotor pole width, split ratio, etc., are investigated, while the torque capability of selected FSPM machines is also compared.

Advanced Flux-Switching Permanent Magnet Brushless Machines

In this paper, switched flux permanent magnet (SFPM) machines are analyzed from the perspective of the air-gap field harmonics. It is found that the modulation of the salient rotor to PM and armature reaction fields in SFPM machines is similar to that of the iron pieces to those fields in the magnetic gear and magnetically geared machine. The magnetic gearing effect is analyzed in SFPM machines with different stator/rotor pole combinations, winding configurations, and stator lamination segment types by a simple magnetomotive force-permeance model, and validated by finite-element (FE) analysis. Different from fractional-slot surface-mounted PM machines in which the working air-gap field harmonic generates 95% of the average electromagnetic torque, 95% of the average electromagnetic torque in SFPM machines having ps stator pole pairs and n
 r
 rotor poles are contributed by several dominating field harmonics, i.e., rotating ones with |kn
 r
 ± (2i - 1)p
 s
| pole pair (k = 1, i = 1, 2, 3) and static ones with (2i - 1)ps pole pair (i = 1, 2, 3). The FE predicted average static torques in SFPM machines are validated by measurements on prototype machines.

Analysis of Air-Gap Field Modulation and Magnetic Gearing Effects in Switched Flux Permanent Magnet Machines

The paper deals with the possibility of replacing a mechanical planetary gear system by a magnetic planetary gearbox. The magnetic planetary gearbox has many advantages such as contact-free, no gear lubrication, high-speed-reduction ratio and high durability. Firstly, the principle of operation, design equations and Willis relation for the magnetic and the mechanical planetary gears are given. A comparative study between the two systems in terms of torque transmission capabilities is presented.

Comparative Study Between Mechanical and Magnetic Planetary Gears

This paper proposes a novel linear permanent-magnet (PM) vernier machine, which offers high force density, high efficiency, simple structure, and low cost. The novelty of the proposed machine is substantiated by integrating appropriate magnetization directions of PMs in the armature core. First, the structure and the operation principle of the proposed machine are descried. The machine is subsequently designed for a given set of specifications and its electromagnetic performances are analyzed by time-stepped transient finite-element method. An analytical equation is derived for evaluation of the thrust force ripple. Finally, experiments on a prototype of the proposed machine are carried out for validation.

Design and Analysis of a Linear Permanent- Magnet Vernier Machine With Improved Force Density

High-torque and low-speed electrical drives are often employed for applications where mechanical gearing cannot be accommodated. On the other hand, permanent-magnet (PM) gear has drawn significant attention from both academies and industries due to the conspicuous merits, such as reduced acoustic noise, maintenance free, improved reliability, precise peak torque transmission capability, and inherent overload protection. In this paper, a magnetic-geared PM brushless motor is presented. It is a novel low-speed and high-torque motor which merges the advantages of conventional PM brushless motor and PM gear. Its topology and operation principle are introduced. Some techniques are employed to optimize and improve the motor performance, while the validity of the proposed techniques is verified with finite-element analysis. Moreover, an alternative operation condition, which can further reduce the motor speed and increase its output torque, is proposed and analyzed.

Development of a Magnetic-Geared Permanent-Magnet Brushless Motor

The permanent magnet (PM) flux-switching linear motor, which is developed from the PM flux-switching rotary machine, possesses similar advantages such as high power density and simple structure. Furthermore, the PM flux-switching linear motor has a potential for mass production at low cost, since the expensive coils and magnets are both set on the short mover. However, the detent force which is induced by both slot-effect and end-effect deteriorates the motor performance. Some methods to reduce detent force which are effective in PM linear synchronous motors do not work in PM flux-switching linear motors, due to their special structure. This paper describes a new method to reduce the detent force by fixing assistant teeth on the mover ends. Finite element analysis shows some interesting results which will be detailed in this paper.

A New Method for Reduction of Detent Force in Permanent Magnet Flux-Switching Linear Motors

We propose a new topology for a permanent-magnet flux-switching (PMFS) linear machine. We describe its unique structure and compare it with the conventional PMFS linear machine. Finite-element analysis (FEA) shows that the proposed machine not only inherits advantages from the conventional PMFS machines, but also possesses many new merits such as more efficient usage of magnets, high fault tolerance, and easy assembly. These positive features make the proposed machine suitable for many applications. We prototyped both the conventional and proposed machines for verification and found good agreement between FEA and the experimental results.

A Modular Permanent-Magnet Flux-Switching Linear Machine With Fault-Tolerant Capability

This paper deals with a permanent magnet (PM) brushless machine used for integrated starter generator (ISG) in an electric vehicle (EV) onboard range extender (ORX). Proper machine configuration selection is briefly introduced. Then, ISGs with both surface-mounted PM (SPM) and interior PM (IPM) rotors have been developed for comparatively analysis. Some techniques for eddy current loss reduction are discussed, while influence of the rotor protecting sleeve material and thickness, axial segmental sleeves, and short circuit rings (ShCRs) around each magnet are particularly investigated. Subsequently, experimental results as of the starter and generator are presented respectively. Moreover, cost evaluation is also presented.

A Permanent Magnet Integrated Starter Generator for Electric Vehicle Onboard Range Extender Application

A novel permanent magnet flux-switching linear motor is investigated in this paper. It is cost-effective, since the magnets and coils are both set in the mover, while the long stator is only made of laminated iron core. This simple motor structure costs much lower than other conventional types. Finite element analysis (FEA) shows that, with proper design, the performance can be rather good.

Canfei Wang

Papers

Development of a Magnetic-Geared Permanent-Magnet Brushless Motor

A New Method for Reduction of Detent Force in Permanent Magnet Flux-Switching Linear Motors

A Modular Permanent-Magnet Flux-Switching Linear Machine With Fault-Tolerant Capability

A Permanent Magnet Integrated Starter Generator for Electric Vehicle Onboard Range Extender Application

A novel permanent magnet flux-switching linear motor