Research On Harmonics And Resonance For Direct-driven Wind Power System

With the guidance of domestic renewable energy development policy, China’swind power industry has achieved a rapid development, and the grid-connectedcapacity of wind power has ranked the top of the world. While,the booming of windpower has brought a lot of technical issues in power system dispatching and powerquality. A safety connection of large wind farm has become a major interest toresearchers, whereas, the harmonic and resonance problem of wind farm coulddirectly affect the power quality of grid. Therefore, this paper is mainly focusing onsolving harmonic and resonance problems of direct-driven wind power system.Firstly, a corrsponding harmonic analysis model for various components ofwind farm has been established to conduct comprehensive and deep analys is onharmonic problems of direct-driven wind farm. The main components of wind farmelectrical system consist grid connected converter, terminal step-up transformer,collector feeding system and main substation step-up transformer. Nevertheless，except grid connected converter， the harmonic analys is models of the componentswithin wind farm have been developed maturely, so this paper mainly focuses on theestablishment of the hamonic source model of grid connected converter. Theresearch is starting from the basic working principle of grid side converters, basedon the harmonic characteristics under different frequency bands, establishing highfrequency and low frequency harmonic models for grid side converters according todifferent frequency bands. And the result of compared with the simulation ofdetailed model verified the effectiveness of the proposed model.Secondly, a systemly analysis is undertaken on the harmonic and resonanceissues of wind farm. This paper makes a detailed analysis on harmonic andresonance characteristics for a simulated wind farm power system which contains25direct-drive permanent magnet wind turbines. For the wind farm resonanceproblems, this work adopts impedance scanning method to measure the effects onthe resonance point by different factors. The wind power system using the harmonicsource model proposed in this paper, taking the influence on the resonance point thatcaused by the output impedance of grid connected converter into account, and theresonant characteristics of wind farm could be reflected more exactly. Thesimulation results show that the topological structure of wind farm feeders, reactivepower compensation devices, quantity of operating wind turbines and the cablelength can affect the resonance characteristics of the wind farm, need to carefullyconsider these factors when plan and design a wind farm.Finally, based on the detailed dynamic model of wind turbine, this paper analyzes the harmonic characteristics of direct-driven wind power system, dissectsthe harmonic power flow distribution of power system containing wind farm undervarious conditions, discusses harmonic suppression measures of wind farm and theway to improve the capacity of power system consumptive wind power, designes adouble-tuned filter and install it in grid connected point. The simulation resultsshow that the effect of harmonic suppression is obvious.