Study On Analysis And Design Method Of MW-class Brushless Doubly-fed Wind Generator With Hybrid Rotor

With the rapid development of the world economy,the development and utilization of renewable clean energy has become a hotspot in various countries in the world,and the wind power generation has been also rapidly developed.In order to meet the requirements of wind power generation,the wind turbines are developing toward high power,high reliability and low costs.Brushless doubly-fed generator(BDFG)is expected to be the next generation of wind generators because of its advantages such as no brush or slip rings,robust structure,adjustable power factor,low operation and maintenance costs as well as small rated power electronics converter.In this paper,the MW-class BDFG with hybrid rotor is researched under the support of the EU International Cooperation Project and the National Natural Science Foundation of China(NSFC).The structural characteristics,operating mechanism,design principles and methods,mathematical model,parameter calculation method and loss calculation method of the BDFG are studied in detail.The research work laies the foundation for the application and promotion of BDFGs.The main research work of the paper mainly includes the following aspects:(1)The hybrid rotor structure which is combined with radial magnetic barrier and assisted cage is used for the studied novel BDFG.The structure and operating principle of the studied BDFG are quite different from the conventional generators.In order to present and summarize the design principle of the proposed BDFG,the structural characteristics are analyzed in detail and the magnetic field modulation mechanism is revealed based on the basic electromagnetic relationship.The equivalent circuit and electromagnetic torque expression of BDFG are deduced.In addition,the energy conversion and circulation relationship of the BDFG under different operating modes are qualitatively analyzed.(2)Aiming at the particularity of the structure and the certainty of the magnetic field circuit of the BDFG with hybrid rotor,the inductance calculation method of the BDFG is proposed based on the improved winding function theory.On this basis,the mathematical model of BDFG is deduced in detail taking into account the winding conversion and frequency conversion,which laies the foundation for the control strategy of this kind of generator.The copper loss calculation model of the hybrid rotor considering the skin effect is established.In addition,based on the study and analysis of the magnetization characteristics of stator and rotor core,the accurate improved E&S core loss calculation model which taking into account the influence of harmonic magnetic field,alternating magnetization and rotating magnetization is proposed and the core losses under differnet calculation models are compared.(3)The traditional machine design methods are no longer suitable for the BDFG with multi-ports and multi-harmonics.Aiming at the speciality and complexity of the design principle and method of the BDFG,the design principles and methods of BDFG are analyzed and proposed based on the theory of magnetic field modulation.A high power BDFG with hybrid rotor is designed based on the proposed methods.The coupled factor which can be used to indicate the relationship between useful harmonic magnetic flux density and exciting magnetomotive force is proposed and the effect of design parameters such as slot number of rotor and assisted cage on the magnetic field modulation ability are analyzed and compared.In addition,the magnetic field characteristics of BDFG are deeply studied and the fact that the assisted cage can improve the magnetic field modulation capability of the rotor is proved through the theoretical analysis and calculation.(4)In order to verify the correctness,effectiveness and feasibility of the theoretical analysis and the research methods,an 8+4 pole BDFG with hybrid rotor prototype is designed and manufactured,and the experimental platform is developed.The inductance parameters of the prototype are measured,and the correctness and effectiveness of the proposed inductance calculation method is verified by the contrastive analysis.The no-load characteristics,the power distribution of windings and the voltage variation of the windings are experimentally studied to verify the correctness of the theoretical analysis and design method presented in this paper.The efficiencies of BDFG under different speed conditions are tested to indirectly verify the correctness and feasibility of the proposed copper and core loss calculation methods.