Design And Study On Mechanical Structure And Cooling System Of Double-stator Brushless Doubly-fed Wind Generator

Taking the project supported by National Natural Science Foundation of China(NSFC)as background,in order to solve the problems of weak rotor coupling capacity,large harmonic magnetic field and low power density of brushless doubly-fed generator,a MW class semi-direct drive double-stator brushless doubly-fed generator(DSBDFG)with cage-barrier rotor for wind power generation is proposed,which has novel mechanical structure,transmission form and cooling system.The main contents of this thesis include the following aspects:(1)The operating system of MW class semi-direct drive DSBDFG with cage-barrier rotor is introduced.Considering the existing structural design methods of wind turbine,after comparison of the advantages and disadvantages between the current topological structures of double-stator motor,two novel topological structures for double-stator motor are proposed.On this basis,mechanical structure is designed for the MW class semi-direct drive DSBDFG in this thesis.The selection principle of interference amount between housing case and outer stator is determined by analytical derivation and FEM.Then the stress,deformation and modal of housing case are analyzed and the improvement scheme of its structure is put forward.FEM is used to determine the assembly form between hollow stationary shaft and inner stator.The effects of inner and outer diameters of hollow stationary shaft on the stress and deformation quantity are studied.Through comparing different rotor cage-barrier structure schemes,the structure forms are determined.The influences of different parameters of rotor cage-barrier dovetail structure on the stress and deformation quantity are compared and analyzed.(2)The MW class semi-direct drive DSBDFG is taken as the research object.The influence of electric current in rotor cage bars on air gap magnetic field is analyzed.The analytical expression of air gap magnetic field considering the influence of control winding variable frequency electric current and rotor cage bar electric current is deduced.On this basis,Maxwell’s rule is used to deduce the analytical expressions of normal direction electromagnetic excitation force wave.The frequencies of them which have the main influence on electromagnetic vibration are analyzed and identified.The influence of electromagnetic force wave frequency on the housing case vibration is analyzed by FEM.(3)Due to the complex mechanical structure of MW class semi-direct drive DSBDFG,it is different to calculate the temperature accurately.Therefore,a novel thermal network model considering the whole machine structure is set up and the thermal resistance mathematical models of special structural parts are deduced.MTATLAB software is used to write the temperature calculation program and the FEM is used to calculate the steady-state temperature of each structure under natural cooling condition.By comparing the temperature results of two methods,the rationality and validity of the proposed thermal network model for MW class semi-direct drive DSBDFG is verified.(4)In order to solve the problem of high temperature of MW class semi-direct drive DSBDFG,the double-water cooling structure and air-water mixed cooling structure are both proposed for this novel generator.By means of analytical derivation and FEM simulation,the influence of waterway number,cross-sectional area,water velocity and size on cooling effect of external unit machine are analyzed.The influences of “U” type pipe number and size on cooling effect of internal unit machine are compared by FEM.The air rheological characteristics is studied by finite volume method and the improved scheme for original wind path structure is designed.The temperature of MW class semi-direct drive DSBDFG with double-water cooling structure and air-water mixed cooling structure are simulated respectively by FEM.The final cooling structure suited for MW class semi-direct drive DSBDFG is confirmed.(5)In order to verify the rationality and validity of MW class semi-direct drive DSBDFG design methods,a 50 kW prototype machine with the same mechanical structure,transmission mode and cooling structure but small volume are processed and manufactured.The vibration and noise testing platform are set up and the results of vibration and noise of DSBDFG under rated speed and power are tested.The temperature testing platform is set up and the winding temperature curves with time are tested under different conditions such as: loads,rate of flow and the situation of exchanging excitation winding.The rationality and validity of design methods of mechanical mechanism,transmission type and cooling structure for this MW class semi-direct drive DSBDFG is verified.