The paper investigates the effects of stator slot skewing in a permanent magnet brushless DC motor. A simple analytic formula for calculation of the best angle of stack skew, which leads to nearly total reduction of the cogging torque, is developed. The skew angle obtained from this formula is different to that used by the designers of PM brushless motors. The analysis is carried out for a fractional horsepower brushless permanent magnet motor with the surface-mounted magnets using a time-stepping, multi mesh-slice finite element model, to assess the impact of this change. The steady-state characteristics and core losses are analyzed quantitatively using the elaborated numerical model. It is shown that smaller skew angles obtained from the formula lead to noticeable rise in motor overall efficiency and decrease of the core loss. The possibility of accomplishment of the desired effect of skew in a real machine is also a subject of discussion.
A variety of clean-energy systems, such as electric and hybrid vehicles or wind-power sources, can appreciably benefit from motors or generators directly connected to the mechanical part of the system. This paper describes the development and experimental investigation of two radically different low-speed permanent-magnet ac machines: a multilayer-winding synchronous machine and a switched-flux machine. The study allows an in-depth comparison of these divergent concepts from the viewpoint of practical applications in the clean-energy infrastructure.
Abstract1 --A quick, simplified method is proposed to compare the axial-flux and radial-flux twin-rotor PM brushless (TRPMBL) motors, with slot-less stators, for the application of in-wheel motor for the gearless drive of an electric vehicle. This method allows answering which of these two motors with the same magnetic and current loading properties and with the same radius and axial length, when built into the wheel gives greater torque. An expression is derived for the ratio of torques of such motors. To check the validity of this method, the axial-flux and radial-flux TRPMBL motors of the same volume are modeled using FEM and their torques are compared.
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