Research On Transient Characteristics Of Directly-driven Wind Turbine With Permanent Magnet Synchronous Generator And Impact On Distribution Protection

The direct-driven wind turbine with permanent-magnet synchronous generator(D-PMSG) has become an important research direction of the wind power generation after the doubly-fed wind turbine(DFIG),because of its high efficiency,flexible control and high reliability.While the D-PMSG has a certain scale in the actual wind farm,it is still lack of sufficient practical operating experience.and a lot of key technologies and problems of engineering practice has not yet been resolved.This paper studies the modeling and control strategy of D-PMSG,fault transient characteristics and the impact on distribution protection.The results of this paper are of great significance on the further development of wind power, security of the relay protection and stability of the power system.Firstly,this paper studies the mathematical model of D-PMSG, mainly including the mathematical model of wind turbine and generator,control strategy of generator-side and grid-side conventer,and low voltage ride-through control strategy.Secondly,build two detailed simulation model of D-PMSG with different control strategy of grid-side converter in PSCAD/EMTDC based on the mathematical model and the corresponding control strategy diagram,then analyse the operation characteristics of D-PMSG under variable speed and constant speed with the simulation model.The comparison between simulation results and the experimental results of dynamic model, verifies the correctness of the simulation model.Considering the vector control strategy of D-PMSG grid-side converter,this paper derivates short-circuit current expressionand analyses factors that affect the short-circuit current in accordance with the expression.Combined with the expression and simulation results,study on the specific transient characterstics of D-PMSG from four aspects:different fault types,control strategy of grid-side converter,operating conditions and different fault location.Finally,this paper has studied the impact on current protection,fault phase selector and traditional fault location scheme of distribution network,while D-PMSG is connected to distribution network.Then two modified scheme of distribution network fault location is proposed respectively based on directional element and relative error,solve the fault location error caused by the wrong fault current information in feeder switches due to the access of D-PMSG in the distribution network.