Research On Analysis Method For Performance Of Permanent Magnet Electrical Machine Based On The Electromagnetic Field Numerical Calculation

Design and application of Permanent Magnet (PM) motors have been a forward research topic in the study of electrical machines. From the basic electromagnetic field theory, the performance and parameters of PM motors are investigated using Finite Element Method (FEM). A series of computation methods and analysis models that are more complete and more accurate are presented. The research work is important step in the design and optimization of PM motors. This thesis contains six chapters.The purpose and meaning of this topic are introduced in chapter 1. It mainly describes the present state and perspective of PM motors and PM material. Various methods used in analyzing PM motors are summarized. It is pointed that FEM posses the advantage in accurate performance analysis. Key problems and research status in PM motor area are summed up. The main research contents of this thesis are presented here.Mathematical model of PM in electromagnetic field computation in PM motors is investigated in chapter 2. Various models adopted in analysis method and numerical method calculation are summed up. An improved discrete method of boarder equivalent surface current model is presented in this thesis; which is suitable to arbitrarily complex shapes, and can conveniently solve different magnetizing direction problem, such as parallel, radial and circumferential direction. It is important to utilize the PM motor FEM program.The performance of PMDC motors is analyzed in chapter 3. A precise moving FEM analysis model is presented, in which the cogging effect and commutation are included in performance calculation. For the first time the performance of odd number slots of small size motors is precisely calculated. A convenient method is presented to calculate the cogging torque in skew slot and skew pole structure motors. The reasons of torque fluctuation are researched and the methods to decrease fluctuation are discussed.Asynchronous start permanent magnet synchronous motors (PMSM) are investigated in chapter 4. When using universal finite element software to analyze PMSM, the relative position of stator and rotor axis is unknown, which is the precondition for load field calculation. From the basic relationship of electromagnetic variables in PMSM, a simple and efficient searching strategy is presented. Through solving inverse electromagnetic field problem, an iteration method is used to acquire the relative position. Load method is used to calculate the parameters of PMSM, in which the material characteristics reflect the magnetic saturation under actual operation. An improved calculation method of reactance of armature reaction is put forward, which need less computation time and have higher accuracy degree.inSteady state performance of PMSM is analyzed using circuit-field coupled FEM time-stepping method in chapter 5. For the first time, a complete field-circuit FEM time stepping model including both rotor and stator circuits is presented, which is more accurate and cover the shortage of lacking rotor circuit in past model. The Newton-Laphson method is taken to solve circuit-field coupled FEM time-stepping nonlinear problem. Jacobi matrix and the residue vector are derived in element analysis. The model used in this thesis not only improves the steady state analysis in PMSM, but also is helpful in transient state performance analysis.Steady and transient state performance of brushless DC (BLDC) motors are calculated in chapter 6. For the first time segment circuits and field coupled FEM model is put forward, which is very suitable to analyze the BLDC motors. Through analyzing the performance characteristics of BLDC motors, the circuits at each operating interval and operating mode are obtained. The element analysis of segment circuits and field coupled FEM is studied. It is significant to accurately analyzing BLDC motors.