Research On Wind Farm Fault Characteristics And Its Short Circuit Current Calculation Model

Wind power is thriving in China in recent years.However,the electromagnetic process of wind farms differs from power plants in their power generation principle and topologies.As a result,relay protection is unable to remove faults quickly and correctly.The setting and calculation of relay protection are based on a deep understanding of fault characteristics and correct calculation of short-circuit current.Therefore,in this thesis,the fault current characteristics of DFIG(Doubly Fed Induction Generator)/ PMSG(Permanent Magnet Synchronous Generator)wind farms are revealed when grid faults occur at outgoing lines.Moreover.the calculation model of fault current from wind farms are proposed.The research in this thesis lay the foundation for the settings and calculations in relay protection and ensure the safe operation of power system.To obtain a deep understanding on the fault characteristics of wind farms,short-circuit current characteristics of different types of wind farms under different scenarios,such as different fault locations/ fault types/ wind speed,are revealed,from the respective of current instantaneous value,harmonic components and sequence components,through both simulation and recorded fault data;The study provide theoretical guidance for the analysis and calculation of short-circuit current.For PMSG wind farm,its fault characteristic is seen as the response of passive network and wind generators within it;A method based on wide-band network equivalence for analyzing short-circuit current of wind farm is presented;The electromagnetic responses of passive network and converter are analyzed respectively to study the electromagnetic transient process of PMSG wind farm,followed by the proposal of its short-circuit current calculation model.For DFIG wind farm,the analyzing method proposed above is applied to study the features of passive network's current;Stator current expressions is used for studying the electromagnetic transient process of DFIG with crowbar protection;Transient response of stator and GSC(Gride-Side Converter)is revealed to study the electromagnetic transient process of DFIG with low voltage ride-through strategy;Based on analysis above,short-circuit current calculation model for DFIG wind farm is proposed.