Studies On The Influence Of Rotor Converter Of Double-fed Induction Wind Turbine On Short Circuit Characteristics

As one of the most scale and prospect new energy power generation, wind powergeneration is the key to guarantee future power supply and solve the global environment.Since new power grid operation standards required that WTG should maintain certaintime parallel operation during system fault, the short circuit current supplied by it wouldaffect normal safe operation of power grid equipments.Especially doubly-fed inductiongenerator has been widely used at present. Because it is sensitive to the machine voltagefall, operating characteristics depend highly on power grid, the short circuit currentsupplied by it would be influenced by the operation condition of distribution networkand short-circuit current characteristics of distribution network will become complicated.Based on these situations, this thesis has studied the transient characteristics of DFIG,and has finished the following results:Firstly, this thesis has introduced the characteristics of DFIG and its advantages invariable speed constant frequency wind power system, analyzed the basic structure andfunctions of main components, introduced the mathematical model and control strategyof DFIG, constructed a real-time simulation platform of DFIG on the basis of PSCAD,and proved the effectiveness of model by DFIG operating characteristic simulation.Secondly, in this paper, the transient processes of DFIG under grid fault wereanalyzed. The influences caused by stator dynamic and output of converter on statorcurrent were researched. The expressions of the rotor current under symmetric andasymmetric fault were proposed. Symmetrical and unsymmetrical short-circuit currentexpressions of DFIG were found with the effect of the control parameters of the rotorside converter on short-circuit current considered. Then, PSCAD/EMTDC was used forthe simulation analysis.and the simulation results show the influence of DFIG convertercontrol system on grid fault characteristics.In the end, based on the analysis of rotor crowbar protection circuit principle, theshort circuit of doubly fed induction wind turbine before and after the action of the rotorcrowbar protection circuit was simulated and compared. The simulation results showthat the short circuit current rush and the short circuit current steady-state amplitude ofDFIG after the action of crowbar circuit is less than that without crowbar circuit, andthe transient current attenuation time is shorten after the action of crowbar circuit. Sincethe relay protection setting value is according to the largest short circuit rush amplitude, the protection setting calculation without considering the influence of the action of thecrowbar circuit will cause reduce of the scope of protection. Thus the influence of thecrowbar circuit should be considered in the relay protection setting calculation.