Research On Harmonic Resonance Of Mountain Wind Farm Considering Collected Network System

Wind power is well-known for its mature technology and widely applied in the field of power generation.Given that there are abundant wind resources with low wind energy density in China,the construction of distributed power generation mountain wind farms has become an inevitable trend.Mountain wind farms have the following characteristics: 1)Wind turbines are scattered and have different operating modes;2)the collection cables are dense;3)the collection network is complicated.These characteristics lead to some severe problem.One is that the collection network and dense collection cables will complicate the role of the inductive and capacitive devices in the system,and generate a wide frequency range and wide coverage resonance frequency,resulting in the resonance analysis of the mountain wind farm grid-connected system.Another is that the dispersed wind turbines interact through the current collection network,and the injected harmonics are coupled with each other.Those problems make system different types of coupling resonances and bring complicate harmonic amplification problems,which will give the mountain construction and selection of wind farms poses no small challenges.To tackle with this situation,this paper takes mountain wind farms as the research object,and studies the resonance point changes caused by the changes in the structure of the collection system and the possible coupling resonance,harmonic amplification,and harmonic transmission mechanisms in the field.The specific research content is as follows:(1)The modeling methods of mountain wind farm systems under different current collection structures are studied.The harmonic equivalent model of "double-fed wind turbine-box transformer-collection cable-transmission system-external power grid" under different current collection system structures is established.Based on this,the node matrix of the system and the multiple-input multiple-output(MIMO)matrix of the system are further constructed.(2)The change law of the resonance point of mountain wind farms under different current collection structures is studied.According to the established system model and node impedance matrix,the harmonic frequency scanning method is used to analyze the resonance influence law of the grid-connected system of mountain wind farms under the changing conditions of power collection system structure and power collection cable length.(3)The coupling resonance characteristics of mountain wind farms and the harmonic transmission amplification mechanism are studied.Using the s-domain function method and applying the principle of two-port network equivalence,the output current expressions of mountain wind farms under different collection system structures are derived.Based on the formed multi-input multi-output matrix,the harmonic conduction coefficient and shunt conductance are defined.Nano index is used to explore the mechanism of harmonic transmission amplification,so as to further study the coupling resonance characteristics and its influence law.(4)In view of the coupling resonance characteristics of mountain wind farms and the harmonic transmission amplification law,combined with the harmonic spectrum characteristics of the measured data of the wind farms in the two places,the pre-evaluation software of the wind power grid-connected system is developed,and the key module of the software simulation analysis is constructed.On this ground,the implementation process of software simulation is described,and verified by software simulation.Finally,the research content of the full text is summarized overall,and the next research plan is prospected.