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

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

Conventional flux-reversal permanent-magnet (FRPM) machines suffer from large pole leakage flux, which leads to the poor utilization of PMs and reduction of main flux. This paper proposes a consequent-pole FRPM machine, whose magnet usage is halved compared with that of a conventional FRPM machine. Nevertheless, due to the reduction of the pole leakage flux, the proposed machine exhibits larger back EMF and torque than that of the conventional one. In this paper, the operation principles and mechanism of reduced pole leakage flux of the proposed machine are introduced. Moreover, with the employment of finite-element analysis, the electromagnetic performances of the proposed machine are evaluated and quantitatively compared with a conventional FRPM machine in terms of airgap flux density, flux linkage, back EMF, pulsating torque, rated torque, losses, and flux-weakening and overload capabilities.

Consequent-Pole Flux-Reversal Permanent-Magnet Machine for Electric Vehicle Propulsion

In this paper, one new machine family, i.e. named as flux-modulation machines which produce steady torque based on flux-modulation effect is proposed. The typical model including three components-one flux modulator, one armature and one excitation field exciters of flux-modulation machines is built. The torque relationships among the three components are developed based on the principle of electromechanical energy conversion. Then, some structure and performance features of flux-modulation machines are summarized, through which the flux-modulation topology distinguish criterion is proposed for the first time. Flux-modulation topologies can be further classified into stationary flux modulator, stationary excitation field, stationary armature field and dual-mechanical port flux-modulation machines. Many existed topologies, such as vernier, switched flux, flux reversal and transverse machines, are demonstrated that they can be classified into the flux-modulation family based on the criterion, and the processes how to convert typical models of flux-modulation machines to these machines are also given in this paper. Furthermore, in this new machine family, developed and developing theories on the vernier, switched flux, flux reversal and transverse machines can be shared with each other as well as some novel topologies in such a machine category. Based on the flux modulation principle, the nature and general theory, such as torque, power factor expressions and so on, of the flux-modulation machines are investigated. In additions, flux-modulation induction and electromagnetic transmission topologies are predicted and analyzed to enrich the flux-modulation electromagnetic topology family and the prospective applications are highlighted. Finally, one vernier permanent magnet prototype has been built and tested to verify the analysis results.

Topologies and analysis of flux-modulation machines

This paper proposes a concept of fictitious “Electrical Gear” to analyze the flux pattern in the three-phase flux-reversal machine (FRM). The rotating-flux pattern of FRM has either two or four poles depending on the number of stator poles. FRM can be analyzed on similar lines as permanent magnet synchronous machine with the concept of this gear. The flux-density distribution in FRM is analyzed with Fourier analysis. The magnitude of various space harmonics and their contribution to the winding-flux linkages are determined. The procedure for finding the rms value of air-gap flux density from machine dimensions is described. In order to verify the aforementioned analysis, a 6/14 pole FRM with distributed and concentrated windings is designed and fabricated. The experimental results are compared with those obtained from finite-element method simulation studies and analytical results.

Analysis of Flux-Reversal Machine Based on Fictitious Electrical Gear

The three phase flux reversal machine (FRM) is a doubly salient permanent magnet machine with concentrated windings. This study proposes the distributed winding for this machine. This winding (i.e. full pitch winding) offers high-power density and improves the efficiency. The permanent magnet (PM) flux linking the stator winding has effectively two or four pole flux pattern, which depends on the number of stator poles and independent of number of rotor poles. Finite element method (FEM) analysis is performed on the concentrated stator pole winding FRM (CSPFRM) and proposed full pitch winding FRM (FPFRM) to obtain induced EMF, flux linkages and inductance of the winding. The inductance of both machines is also obtained using winding function approach and compared with FEM results. The effect of armature reaction is compensated by capacitive series compensation to improve the voltage regulation. FEM analysis is also carried out on both the compensated generators to evaluate the power density. Speed of the flux pattern and that of the rotor is different in FRM. The ratio of these two speeds is termed as fictitious ‘electrical gear’. FRM and permanent magnet synchronous machine (PMSM) have sinusoidal terminal voltage and surface mounted PMs. The power density of both machines is compared using the concept of fictitious ‘electrical gear’. To verify the above analysis, a 6/14 pole FRM with distributed and concentrated winding is designed and fabricated. The experimental results are in close agreement with simulated results.

Power density improvement of three phase flux reversal machine with distributed winding

In this paper outer rotor flux reversal machine (FRM) topology is proposed for rooftop wind generator application. The prototype design of 3-phase, 2.4 kW, 214 rpm, 50 Hz, 6/14 pole outer rotor FRM is presented. Finite element analysis is carried out to evaluate the self and mutual inductance, regulation and efficiency of the machine. Outer rotor and inner rotor configurations of FRM with same outer dimensions are compared. The results show that outer rotor FRM has 1.25 times higher power density than inner rotor FRM.

Outer Rotor Flux Reversal Machine for Rooftop Wind Generator

A three-phase flux reversal machine (FRM) is modelled using the d–q theory. A fictitious ‘electrical gear’ concept is used to simplify modelling and analysis of this machine. The d–q equivalent circuits are proposed based on this gear ratio. A power density of the machine is improved with full pitch winding. The torque obtained with full pitch winding is twice that of concentrated stator pole winding for same input current. FRM with full pitch winding (FPFRM) is compared with the conventional concentrated stator pole winding FRM (CSPFRM). The results obtained using the proposed d–q circuits are compared with those obtained from FEM analysis. A steady-state performance of FPFRM and CSPFRM is evaluated with proposed d–q circuits. To validate the modelling based on d–q equivalent circuits, a 6/14 pole FRM is fabricated with the conventional concentrated stator pole winding and full pitch winding for wind power application. The analytical results are compared with finite element method (FEM) analysis results and experimental results.

Modelling and performance of three-phase 6/14 pole flux reversal machine

In this paper a d-q equivalent circuit for flux reversal machine (FRM) is proposed. In order to improve the power density, full pitch winding is proposed. FRM with this winding winding (FPFRM) is compared with conventional concentrated stator pole winding FRM (CSPFRM). The output power of FPFRM is twice that of CSPFRM for the same machine dimensions, electrical and magnetic loadings. The results obtained using proposed d-q circuits are compared with those obtained from FEM analysis. Steady state and dynamic performance of FPFRM and CSPFRM is evaluated with proposed d-q circuits.

D. S. More

Papers

Analysis of Flux-Reversal Machine Based on Fictitious Electrical Gear

Power density improvement of three phase flux reversal machine with distributed winding

Outer Rotor Flux Reversal Machine for Rooftop Wind Generator

Modelling and performance of three-phase 6/14 pole flux reversal machine

d-q equivalent circuit representation of three-phase flux reversal machine with full pitch winding