Magnetic Forces Analysis Of Surface-Mounted Permanent Magnet Synchronous Machines With Rotor Eccentricity

There are three kinds of vibration and noise in permanent magnet motor,which are electromagnetic vibration and noise,machinery vibration and noise,and vibration and noise caused by aerodynamics.It is meaningful to study the electromagnetic force of the permanent magnet motor because electromagnetic vibration plays a key role,and the electromagnetic force is the main reason of motor vibration and noise.Accurate calculation of electromagnetic field is required in order to analyze the electromagnetic force.An analytical model of no-load magnetic field distribution of surface-mounted permanent magnet synchronous machine(SMPMSM),considering the effects of eccentricity and cogging,is proposed,which can be used to study the SMPMSM with radially magnetized permanent magnet,parallel magnetized permanent magnet and Halbach type magnetized permanent magnet.The magnetic field domain in the SMPMSMs is divided into three simple and regular subdomains,viz.magnet,air-gap and stator slots.The analytical solution is derived by solving the magnetic field governing equations in each subdomain and applying the boundary conditions to the interfaces between these subdomains.A perturbation method is utilized to consider the effect of rotor eccentricity.Comparison between electromagnetic fields obtained by finite element method with electromagnetic fields obtained by analytical solution proposed is used to show the correctness of the analytical model.It is shown that the analytical model proposed can obtain the accurate electromagnetic field distribution of the three kinds of magnetic SMPMSMs under eccentric conditions.The Maxwell stress method is used to compute the no-load magnetic force of the three kinds of magnetic SMPMSMs under eccentric conditions.Considering the radial electro-magnetic force is the main force which causes electromagnetic vibration,the time harmonic components distribution and space harmonic components distribution of the no-load radial electromagnetic force are analyzed.Each order's amplitude of the no-load radial force is given,and the rule of time harmonic components and space harmonic components are summarized.The analytical subdomain model for the prediction of open-circuit magnetic field in surface mounted permanent magnet machines is combined with an analytical model for the prediction of armature reaction magnetic field developed by other people.The electromagnetic force distribution of loaded SMPMSMs under eccentric conditions is derived,and the time harmonic components distribution and space harmonic components distribution of load radial electromagnetic force of the SMPMSMs are also given.