Research On Design And Grid Connection Of PMSG Used In Wind Power Systems

Growing awareness of green energy and desire to reduce the dependence on fossil fuel are bringing the wind energy to the forefront. Distributed small wind power systems, which can make full use of wind energy resources, realize the goal of power generation, usage and grid-connection locally. Under the background, this thesis makes a deep study of the small permanent magnet wind power system. In order to reduce the starting wind speed and improve the wind power energy conversion efficiency, the overall design scheme of small permanent magnet wind power generation system has been studied with emphasis on the design of high efficiency permanent synchronous wind generator(PMSG) and the grid-connection control strategy.Firstly, according to the shortcomings of big starting resistance moment and low efficiency in permanent magnet wind power system, this thesis put forwards the necessity of reducing the cogging torque. Based on the general expression of cogging torque, four ways of reducing the cogging torque: magnet pole-shifting, optimal pole-arc to pole-pitch ratio, tooth shaping and stepped skewing are given. The results of finite-element analysis verified the validity of the methods which could weaken the cogging torque effectively.Secondly, the research is mainly focused on the PMSG with fractional slot concentrated winding(FSCW), analyzing the characteristics and constraints of the winding. The method of eccentric magnet pole is used to reduce the cogging torque and lower the voltage total harmonic distortion(THD). And the validity is verified by the results of finite element models by Maxwell2 D. By the testing of two prototypes under no load condition, the prototype with FSCW can improve the induced voltage waveform.Then the combination of RMxprt and Maxwell2 D is used to optimize the parameters of the PMSG, designing a 1.0 k W small permanent magnet wind generator with small cogging torque and good induced voltage waveform. The performance of the PMSG in no-load, rated load and short circuit faults is analyzed using finite element method, Meanwhile, the demagnetization phenomenon under short-circuit faults is mainly studied and a guideline is given for optimal design.At last, the PMSG mathematical model is established under the dq coordinate system. Control strategies of the back-to-back PWM converter including generator-side and grid-side PWM converter are researched. The designed PMSG parameters are used in small grid-connection wind power system which is built in MATLAB/Simulink. And the dynamic response ability and grid- connection performance are verified.