Research On The Application Of Electrical Dissection Theory In The Low Frequency Oscillation Of Wind Power Networks

Low Frequency Oscillation(LFO)is an important problem which threatens the safe and stable operation of power grids.In particular,with the continuous development of wind power generation,LFO problems of the power system connected to the large scale wind turbine have become more and more complicated.For wind power networks with LFO problems,on the one hand,we need to quickly identify LFO modal information.On the other hand,we need to accurately locate the oscillation source,in order to take measures to isolate and restrain its adverse impact.From mathematical model aspect and signal analysis aspect,this paper researched the identification modal information and the oscillation source locating of LFO problems on the power system connected to direct-drive permanent magnet synchronous generator wind turbines(PMSG),which have significant advantages on service life and production efficiency.In order to identify the wind power networks LFO modes of information quickly and effectively,the electrical dissection method was innovatively introduced to the research of the PMSG small signal model from a mathematical perspective based on the physical order reduction method.First of all,the paper established a PMSG mathematical model,which is suitable for the LFO research.And then,the relationship between electrical dissection path chain and PMSG dynamic mathematical model was analyzed,and PMSG electrical dissection subsystem structure model was established.Finally,the mathematical model was linearized under electrical dissection condition,and a PMSG electrical dissection small signal model was established.This model can derive an electrical dissection subsystem,which is only related to the PMSG,and analyze its modal information.From theoretical height,the modal analysis was conducted in PMSG electrical dissection subsystem,and two conclusions were derived.Namely,the modes of PMSG electrical dissection subsystem are derived from the all modes of the wind power networks,are only related to PMSG,and are independent of other modes of the wind power networks.The applicability of the small signal model was proved conducting on an example,and two important conclusions were derived.Namely,the dominant oscillation modes from PMSG electrical dissection subsystem inherit from the modes of the original system,and PMSG connecting the power system often perform as a forced oscillation source.These two conclusions have a certain guiding role for wind power networks LFO source locating.In order to quickly find oscillation source in wind power networks with LFO,two technical routes were put forward from the perspectives of the mathematical model and the signal analysis based on the physical order reduction and energy flow respectively.Thus,a wind power networks LFO source locating method was developed.First of all,this method applied electrical dissection method to set model of the power grid and filter electrical dissection subsystem and the suspected units associated with oscillation points.And then,the oscillations source was locked in a unit or a few units using wind turbines electrical dissection small signal model,equivalent damping coefficient calculation and oscillation energy flow calculation sequentially.In order to reach the goal of engineering application,this paper analyzed the concrete applicable conditions of the above research results,and put forward a wind power networks LFO source locating method integrated application strategy.An example confirmed that this locating method can be quickly applied to the accurate identification and oscillation source locating of the wind power networks LFO problems,and this strategy can realize online application.