Research On The Dynamic Process Of Line Start Permanent Magnet Motor With Finite Element Method And Experiment

Dynamic process of line-start rare-earth permanent magnet motors were researched in this dissertation with nonlinear characteristics of ferromagnetic material and complex structure of permanent magnetic circuit precisely considered.Firstly,the common problems such as local electromagnetic force,electromagnetic torque computation,and field-circuit-motion directly coupled solution problems were studied.And then dynamic process including starting,losing step,reclosing and open-phase operations were analyzed with tine-stepping finite element method(FEM) and field experiments.The main innovations are summarized as follows:1.In the study on common problems of synchronous motors' dynamic analysis,an equivalent nodal force formula considering saturation of ferromagnetic material is derived,and thus a model is founded for electromagnetic force density calculation in analyzing local magnetic force of permanent magnet motor;a field-circuit coupled stationary finite element method,suitable for electrical excitation and permanent magnet motors,is proposed,and a novel time-stepping FEM model with field-circuit-motion direct coupled is established for the analysis of dynamic process.2.Based on a great deal of computations and experiments,the reasons for asymmetry of locked-rotor currents and for locked torque's fluctuation due to the change of locking position are revealed,as well as the impacts of the initial starting condition and line impedance on starting performance.3.Through the time-stepping FEM research of abnormal transient processes such as losing step,reclosing and open-phase operation,a new efficient and accurate calculation method for pull-out torque and a practical reclosing criterion to reduce inrush current and torque are proposed;the relationship between load and the amplitude change of rotor current,the loss and torque in open-phase operation is revealed as well.4.An economical and practical program for real-time measurement of transient speed and torque is proposed,and synchronous acquisition of mechanical and electric quantities is thus achieved.Moreover,an integrated test platform for dynamic performance of permanent magnet motor is designed and developed.