Analytical Modeling,Analyzing And Optimal Designing Of Permanent Magnet Eddy-current Couplings

The permanent magnet eddy-current coupling has become a research hotspot in application of the permanent magnet drive technology and has been widely used in many kinds of fans and pumps and other inefficient loads which have serious vibration and may start and stop frequently due to its advantages of non-contact transmission,vibrational isolation,overload protection,no electromagnetic pollution and so on.Taking the permanent magnet eddy-current couplings as the research object,the mathematical models of the magnetic field and eddy current field are set up based on several kinds of analytical methods in this thesis.These models are analysed in order to investigate the effects of structure and design parameters on performances.On this basis,two optimization algorithms are adopted to obtain the optimized structure parameter of permanent magnet eddy-current couplings.In order to prove the accuracy of the model all the computed results are compared with those from the finite element method and experiments.Therefore,the research work of the permanent magnet eddy-current couplings is of great significance academically and practically.The main points of the study are as follows:(1)In order to analyze static magnetic field distribution in the air gap between two plate of the permanent magnet eddy-current coupling,the analysis and calculation method based on equivalent surface current is proposed in chapter two.Between the permanent magnets and moving conductor,the magnetic fields induce eddy currents in the plate which in turn interacts with the source magnetic field to create electromagnetic torque.So,study on the magnetic field distribution from PM blocks in the air gap is of great significance.When there is no slip speed between two rotors,the magnetic field only comes from the PM blocks.It makes the equivalent surface current method presented its advantage.The calculated results analytically are compared with those from finite element simulation results to verify the accuracy.(2)In order to analyze magnetic circuit of the permanent magnet eddy-current coupling and calculate the unmeasurable quantity eddy current density distribution in a simple and intuitive manner.This chapter draws on equivalent magnetic circuit which is usually used in electric machine analysis and Ampere's Law to calculate the flux density in the air gap and the eddy current density distribution at small slip speed.Then the electromagnetic torque of permanent magnet eddy-current coupling is calculated based on the analytical model in the thesis.On the basis of theoretical research,a permanent magnet eddy-current coupling is built and an experimental platform is set up.A series of tests were conducted on experimental platform and the experimental results verify the correctness of the theoretical research in this thesis.(3)To overcome the shortcomings of the equivalent magnetic circuit method,maxwell's equations in the three dimensional coordinate system which can be solved by variables separation method are established.The mathematical models of the magnetic field and eddy current field of permanent magnet eddy-current coupling(include regular type and Halbach PM array type)are set up in chapter four.The results from analytical method were compared with those of finite element method.FE results confirm the rationality and validity of the analytical model.It is meaningful for performance analysis.The effects of structure and design parameters on performances and parameter sensitivity are investigated and analyzed.(4)In order to make the indicators of the permanent magnet eddy-current coupling such as output torque,the moment of inertia,volume and so on as optimal as possible,this thesis proposes a variable population-size genetic algorithm(VPGA)which takes death and war factors into account and a multiple population genetic algorithm(MPGA)to obtain the best compromise among the optimization goals which are in conflict with each other.3D finite element analysis(3D-FEA)and experimental results prove the validity and feasibility of the proposed method.After comparing with other existing optimization algorithm,these two optimization algorithm based on analytical model have good optimal effects in optimization of structural parameters.It can provide the reference basis for the structure optimization design in the future.