Research On Magnetic Coupling Capability Of BDFG With Series Cage Bars Combined With Magnetic Barrier Rotor

With the increasing demand for energy,the consumption rate of fossil fuels such as coal and oil has risen sharply.Finding and utilizing clean energy has become the research direction of all countries in the world.Therefore,wind power develops rapidly.Large capacity,low cost and high reliability have gradually become the development direction of offshore wind turbines at present.Brushless doubly-fed generator（BDFG）,as a new type of AC speed regulating motor,has unique advantages,eliminating brushes and slip rings and improving system reliability.Smaller inverter capacity brings lower cost.Therefore,BDFG is very suitable for large offshore variable-speed constant-frequency power generation systems,and is expected to become the mainstream model of offshore wind power generation.In this paper,a new type of brushless doubly-fed generator with series cage-bar-assisted magnetic barrier rotor is taken as the research object,focusing on its magnetic field modulation mechanism,topological structure characteristics,electromagnetic design method and other issues.The simulation study of auxiliary magnetic barrier rotor brushless doubly-fed generator verifies the correctness and feasibility of the theoretical research in this paper.The main work of this paper includes the following contents:（1）The stator and rotor structure characteristics of brushless doubly-fed generator are introduced in detail,and the advantages and disadvantages of common rotor structures are analyzed.In order to meet the development needs of offshore wind power.The working principle of the new rotor BDFG is analyzed according to the slip ratio..（2）The magnetic field of the new hybrid rotor brushless doubly-fed generator is rich.According to the particularity of its rotor structure,the modulation mechanism of magnetic barrier rotor to air gap magnetic field is analyzed,and the analytical model of magnetomotive force generated by auxiliary cage bars is deduced.The element method is used to analyze the influence of the position of the cage bar embedded in the magnetic barrier on the magnetic field modulation ability.（3）In view of the complex magnetic field distribution of BDFG,the design ideas of stator and rotor structure,electromagnetic load and main dimensions of 25 k W series cage-bar-assisted brushless doubly-fed generator are studied.Detailed analysis.The influence of the structural parameters of rotor magnetic grid,common cage bars and series cage bars on the magnetic field modulation ability is summarized.The design principle of hybrid rotor is summarized,and the final generator design scheme is determined.（4）The electromagnetic characteristics of the new hybrid rotor brushless doubly-fed generator at no-load and load under rated conditions are analyzed by finite element method,and the rationality of the motor design is verified.The magnetic field modulation of different rotor structures of brushless doubly-fed generator is compared.The results verify the improvement of the rotor magnetic field modulation ability of the proposed series cage bar auxiliary magnetic grid structure.