Analysis Of Electromagnetism In DDPMG And Research On Eddy-current Loss Of Permanent Magnet

With the development of offshore wind turbine, the installed capacity has beenlarger and larger. Directly driven permanent magnet synchronous wind turbine canreduce the weight of wind turbine as it omits variable speed gear box. Directly drivenpermanent magnet synchronous wind turbine featured large volume and heavy weighthas many pole-pairs, so magnetic circuit structure and mechanical supportingstructure should be designed rationally.To reduce cogging torque of DDPMG and higher harmonic’s back EMF introducefractional-slot concentrated winding to DDPMG. The tooth profile and grooveselection of stator mainly considers windings installation and stator heat dissipation.Employ surface-mounted radial magnetizing to rotor. Electromagnetic parameters arecalculated for verifying rationality of the DDPMG, including unloaded leakagemagnetic coefficient, air gap magnetic field, back EMF in the winding, inductance ofair gap armature coil, groove and cogging torque and so forth.This paper studies on the reasons of PM heating, at the same time analyzes therelationship between eddy current loss and motor parameters. Air gap magnetic fieldgenerated by magnetomotive force consists of high air gap flux density harmonic. ThePM flux change is caused by relative motion between rotor and high air gap fluxdensity harmonic. Then the induced magnetomotive force will generate eddy currentloss. Air gap magnetic field generated by armature magnetomotive force consists ofboth high and low air gap flux density harmonic. The PM flux change is caused byrelative motion between rotor and air gap flux density harmonic. Then the inducedelectromotive force will generate eddy current loss.Starting with the generation principle of eddy current loss, PM eddy current loss iscalculated. First space time equation describing how air gap magnetic field changes instator space should be analyzed. Then space time equation describing how air gapmagnetic field changes in rotor space should be analyzed. Calculate the electromotiveforce induced from variable magnetic field. Eddy current density can be presentedbased on Ohms Law. Furthermore, eddy current loss can be obtained. The PM eddy current loss is also calculated by finite element method(FEM). Theproposed method is confirmed. It is very important for reducing PM eddy current lossto analyze the relationship between eddy current loss and motor parameters.