Research and Design on Hybrid Excitation Generator Driven by Wind Turbine

With the consumption of traditional fossil energy and the enhancement of public’s consciousness of environmental protection, the wind energy has been paid more attention to as a kind of vast and clean renewable energy by world. At present, in wind power system, because of the existence of brush and collector ring, electrically excited synchronous generator does not be applied in harsh environments. And the air-gap magnetic field of permanent magnet generator is determined by permanent magnet (PM) and the permeance of magnetic circuit, so it is very difficult to control the fixed excitation provided by the PM. In order to make up for the shortcomings, hybrid excitation generator is introduced into wind power system in the paper. Combining with the characteristic of variable-speed constant-voltage, the main research contents are as follows:Firstly, combining with the characteristic of direct-drive and multibrid low-speed wind generators, the several typical structures of hybrid excitation machine are filtrated. Modular structure is introduced, and then the selected structure is improved.Secondly, magnetic field distribution of the selected hybrid excitation generator is obtained by using three-dimensional finite element method. According to results of the analysis, original equivalent magnetic circuit model is modified. In original equivalent magnetic circuit model, the traffic diversion effect of permanent magnet is not considered, and there is large deviation for maximum adjustable speed range of the generator. So in this paper, the guarantee for accurate design of the selected hybrid excitation generator is offered by modifying original equivalent magnetic circuit model.Thirdly, the structure and characteristics of modular generator are analyzed, and its installation gaps and the size of slot openings are mainly researched. In order to facilitate the generator assembly, modular generator usually has wider installation gaps. So the effect of installation gaps on electromagnetic performance should be researched. In addition, closed slots can be actualized in order to reduce starting resistant moment, but slot leakage reactance could be increased due to closed slots. Therefore, the determination of slot openings is also researched in this paper. Finally, test of the prototype is completed. Electromagnetic field analysis results and the validity of equivalent magnetic are verified, and improvement of the generator is proposed.