Analysis And Calculation Of Circulating Current Losses In Stator Bar Of AC Machine Based On Scaled Boundary Finite Element Method

Generally,the stator bars of AC machine are composed of several parallel strands.Due to the existence of leakage magnetic field in the slot,the induction electromotive force is generated in the strands of stator bar,and the circulating current between the strands will cause a series of problems,such as uneven temperature rise of the strands.It is a serious threat to the insulation of stator bars and the service life of motors.Therefore,it is very important for the design of large AC machine to accurately calculate the circulating current and the circulating current losses of the stator bar.Scaled boundary finite element method(SBFEM)is a novel method for solving partial differential equations,which combines the advantages of the finite element method and the boundary element method with its own unique characteristics.According to the given boundary conditions and governing equation,based on the weighted residual method,the process of establishing and solving the discretized scheme of 2D curl magnetic field scaled boundary finite element method and the process of establishing and solving the discretized scheme of 3D curl magnetic field scaled boundary finite element method are described respectively.When using SBFEM to calculate,according to whether there is a current-carrying conductor in the domain and the complexity of the computational domain,the active domain and the passive domain and the subdomains of various complicated domains are divided.The combination method of various sub-domains and active-passive sub-domains is given.The established equations are used in the calculation of a typical example of a motor magnetic field,and the calculated results are compared with the results of finite element method.The correctness of the established SBFEM equations is proved,which provides a new calculation method for the analysis and calculation of motor magnetic field.The SBFEM of the two-dimensional curl magnetic field and the three-dimensional curl magnetic field is used for the calculation of the stator bar circulating current and the circulating current losses,the method of calculating the circulating current and the circulating current losses is given.The circulating current and the circulating current losses of two-dimensional non-transposition strands and the circulating current and the circulating current losses of three-dimensional non-transposition strands and transposition strands are solved respectively.According to the type of solution,the corresponding mathematical models are respectively established,and the appropriate cell grids are discretized to solve the corresponding strand circulating current and the circulating current losses.Comparing the calculation results with the numerical simulation results of FEM,it is proved that the SBFEM has the characteristics of high efficiency and high precision.The SBFEM is coupled with the FEM to calculate the circulating current and the circulating current losses of the stator bar strands.Division of the active region and the passive region,get the finite element region and the scaled boundary finite element region,which can obtained two equations respectively,the two equations are solved by the combination of interface condition.The simulation results are compared with numerical results obtained with FEM and the SBFEM,prove the correctness of this method,and the method has high accuracy and efficiency advantages,which provided another new method for calculating the magnetic field of the electric machine.