Study On The Fault Transient Equivalence Method Based On The DFIG Wind Farm

With the increase of wind power installed capacity,the influence on the safety and stable operation of the power system is becoming gradually prominent.Transient characteristics of fault and short-circuit current simulation analysis of wind farm is crucial.However,the model of large-scale wind farm is a large workload and low efficiency,so it is often used to simulate the dynamic characteristics of the wind farm by equivalent model.For the double-fed induction generator wind farms,the fault characteristics of the unit is complex.So the conventional wind farm equivalent method is no longer applicable to the equivalence of the transient fault.In this paper,taking the symmetrical fault as an example.Firstly,the paper analyzes the effects of crowbar protection on short circuit current of DFIG in detail.Then,considering the random factors of voltage drop and input wind of each unit which influence the crowbar action state,this paper presents a kind of wind farm fault transient equivalence method of on rotor current peak cloud model based on the theory of uncertainty mathematics.The cloud droplet sample of rotor current peak value can be obtained under random wind speed and terminal voltage drop.Then,calculate the numerical characteristics of cloud droplet sample,expectations,entropy and hyper entropy through the improved backward cloud generator.The wind turbine generators can be clustered by the feature indices through the k-means cluster algorithm,and the equivalent model parameters can be calculated based on capacity-weighted method establishing multi-machine equivalent model.In this paper,the equivalent method of the collector network is more in-depth study.Based on power loss method and weighted voltage difference method,the network transformation method is proposed,which can be realized the transform of wind farm topology from series structural to equivalent parallel structure,and is suitable for the aggregation of unit at any position of wind farm.Finally,the simulation analysis is carried out in the DIgSILENT software,comparing the equivalent method of cluster classification and collector network.The result shows that the proposed wind farm equivalent method of rotor current cloud model and collector network transformation method can accurately reflect the transient fault characteristics of the detailed wind farm model,which have high equivalent accuracy and verify the correctness.The equivalent method can also provide the support for analyzing and calculating the short-circuit current and relay protection of wind farm.