Design And Optimization Of A Low-Speed Outer-Rotor Permanent Magnet Synchronous Generator

The world demand for clean and sustainable energy has been increasing in the last years and with it,the demand for low-cost small-scale wind power generation systems is increased,as small-scale wind turbines are considered as an economic and flexible solution for power generation.The advantage of small-scale wind turbines is that they generate power near the load centers,thereby eliminating the need to run high-voltage transmission lines,which is very suitable for remote areas with 'abundant wind resources.Permanent magnet synchronous generator(PMSG)has the advantages of high torque,no requirement for an external excitation current and variable speed operation ability.Therefore it is an ideal choice for small-scale wind turbine.Moreover,outer-rotor PMSGs are directly driven,which eliminates the gearbox from the system,thus reducing the costs and noise and improving the total power generation efficiency of the system.This paper presents the design and optimization of a small-scale direct-drive outer-rotor surface-inset PMSG wind turbine.The paper first introduces commonly-used wind power systems,which include types and structures of PSMG,configurations of permanent magnet and arrangements of the stator winding.Analytical models are developed to determine the basic electromagnetic properties of the permanent magnet,main dimensions,slot parameters,slot numbers,pole numbers and winding structure of small-scale PMSG.Using the analytical models an optimizing routine is developed in Matlab to find optimal generator geometries according to a given set of design criteria.The structure of the PMSG is designed based on the optimization results.The derived models are validated with the use of finite element method(FEM)analysis.The finite element method is applied using Maxwell2D to analyze the detailed characteristics of the PMSG,which include the magnetic flux density distribution,magnetic flux lines,no-load back-EMF waveform and torque.After that,the influence of stator slot parameters and permanent magnet size on the performance of the PMSG are analyzed,mainly on the air gap flux density,no-load back EMF waveform and cogging torque of the PMSG.A joint simulation between the FEM model and Maxwell Simplorer is conducted to verify the performance of the generator.According to the FEM model parameters,a physical generator is manufactured and tested.The no-load back EMF waveform is obtained and the voltage-speed curve is drawn.Experimental test results show a good agreement with theoretical work.In summary,the rationality of the PMSG designed is verified.