Design And Research On Dual-Rotor Permanent-Magnet Wind Generator Based On Finite Element Analysis

With the increasing depletion of fuel resources and strengthening awareness of environmental protection, wind power generation, as the most competitive and promising renewable energy technologies, is receiving more and more attention all over the world. Dual-rotor permanent-magnet wind generator has a unique advantage due to its different rotation mode from the traditional motors, which is the armature part and the permanent-magnet rotor revolve at the opposite direction. Consequently, the capability of power generation is twice as much as that of traditional wind generators at the same wind speed. Furthermore, the lowest working wind speed can reduce to the half of that of traditional permanent-magnet generators while the highest keeps the same, thus widening the range of the working wind speed and improving the wind utilization. Meanwhile, the working speed of dual-rotor permanent-magnet wind generator is half of that of traditional permanent-magnet generators at the same poles, which means it would be more welcomed in the direct-driven wind generation.However, its structure design and electromagnetic design are more complicated and the dynamic performance is very different. So far, the research on dual-rotor permanent-magnet wind generators is still in its early stage in China,thus its design and research has an important theoretical and practical significance. A dual-rotor permanent-magnet wind generator with a low starting wind speed is designed in this paper, and the finite element method is used for a comprehensive analysis.A brief introduction about the principle, characteristics and mathematical model of the dual-rotor permanent-magnet wind generator is presented and the equivalent magnetic circuit method is applied to design and analyze the generator. In this process, some new methods for the calculation and selection of several parameters are proposed. At last, the electromagnetic design program of the dual-rotor permanent-magnet wind generator based on the field-circuit coupled method is compiled by C++ language.Then, this paper analyses and calculates the static electromagnetic field of the dual-rotor permanent-magnet wind generator at no-load and rated-load based on the finite element analysis and design process. A detailed analysis about the impact of the ratio of length to diameter, airgap length and permanent magnet length on the performance and other parameters of the dual-rotor permanent-magnet wind generator is executed, thus providing the optimization of the three parameters and improving the reliability of the dual-rotor permanent-magnet wind generator design.The greatest innovation of the dual-rotor permanent-magnet wind generator is its rotation mode and the magnetostatic field analysis does not reflect its dynamic performance adequately,so its field-circuit coupled time-stepping finite element analysis is carried out. When using finite element method to calculate the transient magnetic field, the relative motion between the outer and inner rotor needs to be considered and the traditional motion band method is no longer applicable, so a new double motion band method is developed to establish the relationship between the corresponding nodes. After that, a field-circuit coupled model is presented and solved by the Newton-Raphson method. The results under no-load and different load condition are given according to the model. Furthermore, the analytical expression of the cogging torque is obtained by energy method and Fourier transform and its calculation results under different pole embraces are shown by Maxwell tensor method.At last, the prototype test, including the no-load, rated-load and efficiency test, is finished by using two DC motors to drive the two rotors inversely at the same speed. The output voltage, power and efficiency are satisfied the design targets and a good agreement is achieved among the test, calculated and finite element results, which verifies the validity of the design and analysis of the dual-rotor permanent-magnet wind generator.