The SMES-FCL Control Strategy And Capacity Optimization For Improving LVRT Capability Of Wind Farm Integrated System

The doubly fed induction generator(DFIG)system is the most widely used grid-connected wind power system,which existing problems of weak low voltage ride through(LVRT)performance and unstable output power.The superconducting magnetic energy storage-fault current limiter system(SMES-FCL)has dual functions of energy storage and fault current limiting,the fastly energy storage function of SMES can be used to suppress the fluctuation of output power in steady state,in the case of system failure,the function of current limiting can be combined to reduce the required capacity of conventional SMES for improving LVRT capability,increasing utilization ratio of superconducting magnet,providing a new idea for improving stability of wind farm integrated system.This paper focuses on studing related problems of SMES-FCL for improving LVRT capability of wind farm integrated system.Aiming at the problem of weak LVRT performance of DFIG,the electromagnetic transient models suitable for studing DFIG low voltage characteristics are established,analysising dynamic characteristics of DFIG in different fault conditions.Carring out comparative analysis of LVRT technologies in terms of applicability and economical efficiency,the control strategy and capacity optimization of SMES-FCL are proposed.Firstly,studing integrated configuration and working characteristics of SMES-FCL used in DFIG integrated system,aiming at the time-varying characteristics of DFIG and the nonlinear characteristics of SMES-FCL,fuzzy-PI control strategy is introduced into converter control system of SMES-FCL,realizing coordinated control with chopper.Simulation model of DFIG with SMES-FCL is established by MATLAB/Simulink,simulation experiments are carried out under multi-conditions,such as normal operation and short circuit fault,results show that the proposed method can not only improve the output power stability of DFIG,but also enhance the LVRTcapability.For the initial energy storage capacity optimization of SMES-FCL,the evaluation index of DFIG's LVRT capability is presented,based on the stability of wind farm integrated system and economical efficiency,establishing the optimization model of magnetic initial energy storage capacity and using NSGA-?algorithm to obtain optimal magnet capacity of conform to research target.