Research On Equivalent Modeling Of Wind Power Plants For Electromechnical Transients In Power Systems

With the rapid development of wind power plant(WPP)and wind power base,wind power has recently become the third largest energy,after thermal power and hydropower,in China.On the contrary,there is still no consensus on how to build a rational and effective WPP model,which seriously hinders the analysis on the grid-connected characteristics of wind power.This paper takes full account of the own characteristics of different types of WPPs,and proposes the targeted clustering principle,resperctively.We solve the problem of the number of clustering group and the accuracy of equivalent WPP model,and give the calculation or acquisition method of clustering criterion index from the practical engineering point of view.The established equivalent model can accurately reflect the electromechanical transient characteristics of WPPs.The main contribitions contains four parts:(1)In this paper,the relationship between the growth of post-fault rotor current and the amplitude of the terminal voltage dip is studied by analyzing the rotor current characteristics of a doubly fed induction generator(DFIG)during the fault process.Then,a terminal voltage dip criterion which can identify crowbar conduction is proposed.Considering the different grid connection structures for single DFIG and WPP,the criterion is revised and the crowbar conduction is judged depending on the revised criterion.Finally,an aggregation model of the WPP is established based on the division principle of crowbar conduction.(2)This paper proposes an innovative clustering concept for the equivalent modeling of a permanent magnet synchronous generator(PMSG)-based WPP,in which the impacts of both the chopper protection and the coordinated control of active and reactive powers are taken into account.First,the post-fault DC link voltage is selected as a concentrated expression of unit parameters,incoming wind and electrical distance to a fault point to reflect the transient characteristics of PMSGs.Next,we provide an effective method for calculating the post-fault DC link voltage based on the pre-fault wind energy and the terminal voltage dip.Third,PMSGs are divided into groups by analyzing the calculated DC link voltages without any clustering algorithm.Finally,PMSGs of the same group are equivalent as one rescaled PMSG to realize the transient equivalent modeling of the PMSG-based WPP.(3)Based on the coherence influencing factors,a new equivalencing modeling method for squirrel-cage induction generator(SCIG)-based WPP was proposed.The rotor speed vectors of the wind turbines were sampled in different combinations of operating conditon and short-circuit faults.The two-step cluster method was utilised to divide the wind turbines into groups,and the significance between different groups was tested with the Fisher discriminant analysis.Considering annual wind resource statistics of WPP s and the rates of different system fault types,the probabilistic equivalent model for WPP was established depend on the largest probability group result.The probabilistic equivalent model is able to reflect annual external characteristics of WPP,and has a great value in engineering applications.(4)We propose an equivalent node model for mixed WPP,which is different from coherency-based equivalent method.Based on the system identification,the mixed WPP is regarded as a ?black box?.The input and output data of the WPP are trained and tested by the adaptive and self-learning ability of BP neural network,which makes the neural network model meet the accuracy requirements.In this case,the linear combination of the weights on the neurons and their excitation functions is the established mixed WPP equivalent node model.The equivalent node model of the mixed WPP breaks the barriers of the academic and engineering simulation platforms and makes it easier for the power dispatch department to use.