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 article, feasible minimum limits for IE4 class are analyzed, taking into account the estimated efficiency limits and rated efficiency for emergent or commercially best available line-start PMSM technologies. The presented results can be useful to set up future international standard super-premium or IE4-class levels/limits. The practicability and technical limits associated with the IE4-class efficiency levels are addressed, taking into account technical and economical limitations. It is expected that advanced technologies will enable manufacturers to design motors for the IE4-class efficiency levels, with mechanical dimensions compatible with the existing IMs of lower efficiency classes (e.g., flanges, shaft heights, or frame sizes as defined in standards EN 50347 and NEMA MG1). NEMA frames sizes are larger than the IEC frame sizes, allowing the use of more active materials. In addition, 60-Hz operation enables higher power density and higher efficiency levels with the same frame sizes.

Standards for Efficiency of Electric Motors

The multilevel method has been presented for design optimization of electrical machines and drive systems for optimal system performances and efficiency in our previous work. For framework design of the multilevel optimization method, four techniques are presented in this paper, including the sizing equation, local sensitivity analysis, global sensitivity analysis, and design of experiments techniques. For each technique, a general and theoretical analysis procedure is presented before the application study. To demonstrate the effectiveness, a permanent magnet claw-pole motor with soft magnetic composite core and 3-D finite-element analysis model is investigated to minimize the material cost and maximize the output power while keeping the volume constant. The calculated motor performance based on this 3-D finite-element model has been verified by the experimental results. As shown, these techniques are simple to implement, and the resultant multilevel optimization framework can significantly improve the motor performance and reduce the required sample number of finite-element analysis.

Techniques for Multilevel Design Optimization of Permanent Magnet Motors

In safety critical aerospace applications, fault-tolerant drives can help reach the necessary system reliability levels without replicating the entire drive system and thus minimizing the overall system weight. Machine selection and design for fault tolerance has to be considered at an early stage to ensure optimal performance at a system level. This paper looks at the fault-tolerant properties of permanent-magnet flux-switching machines (PMFSMs) and proposes a new configuration able to fulfill the fault-tolerant requirements. PMFSMs have the distinct property of having a robust rotor construction with the permanent magnets embedded in the stator while having their operational characteristics similar to those of synchronous permanent-magnet machines. While these machines have numerous inherent advantages for achieving a high power density, in their basic form, they are not tolerant to short-circuit winding failures. This paper will look at a novel stator structure able to achieve a 1-p.u. winding inductance and will subsequently look at design iterations to maximize the torque density.

Design Considerations for a Fault-Tolerant Flux-Switching Permanent-Magnet Machine

This paper overviews various switched flux permanent magnet machines and their design and performance features, with particular emphasis on machine topologies with reduced magnet usage or without using magnet, as well as with variable flux capability. In addition, this paper also describes their relationships with doubly-salient permanent magnet machines and flux reversal permanent magnet machines.

Switched flux permanent magnet machines — Innovation continues

This paper proposes a novel permanent-magnet (PM) flux switching (PMFS) machine with an outer-rotor configuration for in-wheel light traction applications. The geometric topology of the outer-rotor PMFS machine is introduced, and the analytical sizing equations are derived to determine the main design parameters of the machine. Two-dimensional finite-element analysis (FEA) models are developed to investigate and optimize the machine performance. Furthermore, the flux-weakening capability of the machine is analyzed and further improved by segmental PMs with iron bridges. The machine performance predictions by 2-D FEA models are validated by experimental tests on the prototype machine. The suitability of the proposed outer-rotor PMFS machine for in-wheel light traction application is demonstrated.

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A Novel Permanent-Magnet Flux Switching Machine With an Outer-Rotor Configuration for In-Wheel Light Traction Applications

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

A novel twelve-stator-pole, twenty-two-rotor-pole (12/22) outer-rotor permanent-magnet flux-switching (PMFS) machine for electric propulsion in a lightweight electric vehicle is presented. Analytical equations are derived for the dimensioning of a 3-phase 5kW in-wheel motor. Optimisation techniques are employed to maximise the performance of the machine. The validity of the analytical equations is verified by finite element analysis (FEA). The results show that the PMFS machine combines the key advantages of the PM machines and the switched reluctance machine, and thus demonstrate the viability of the proposed machine as a suitable candidate for in-wheel electric propulsion.

A novel outer-rotor permanent-magnet flux-switching machine for urban electric vehicle propulsion

This paper investigates the cogging torque and torque ripple features of a permanent-magnet flux-switching integrated starter generator. The effects of the rotor pole arc width on the cogging torque, torque ripple, and output torque are first established using finite-element analysis (FEA). Three torque ripple reduction techniques based on the optimization of three different rotor pole configurations, namely, uniform, step skewed, and axial pairing, are then proposed. The torque characteristics of each rotor configuration at varying load currents and phase angles are studied in detail. A prototype machine with a common stator and the three optimized rotor configurations are built for experimental validation. Both the FEA results and the experimental tests show that the step skewed and axial pairing techniques can alleviate the cogging torque significantly, but the latter is less effective than the former in reducing the overall torque ripple.

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Permanent-Magnet Flux-Switching Integrated Starter Generator With Different Rotor Configurations for Cogging Torque and Torque Ripple Mitigations

This paper aims at optimal analysis and design of a three-phase line-start PMSM with simple structure, low cost and good performance. A prototype with 4 magnet poles is designed and manufactured. Simulation and experimental results are approximately the same and the prototype essentially satisfies the design request. Moreover, measures are taken to further optimize the design.

Yu Wang

Papers

A Novel Permanent-Magnet Flux Switching Machine With an Outer-Rotor Configuration for In-Wheel Light Traction Applications

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

A novel outer-rotor permanent-magnet flux-switching machine for urban electric vehicle propulsion

Permanent-Magnet Flux-Switching Integrated Starter Generator With Different Rotor Configurations for Cogging Torque and Torque Ripple Mitigations

Optimal design and experimental verification of a line-start permanent magnet synchronous motor