Study On Power System Voltage Stability With The Integration Of DFIG

With the annual increase of wind power generation capacity, the influence of large-scale wind power on power grid stability can't be ignored. Therefore, it is of practical significance to study the cause of the wind generator on power system voltage stability and grid fault ride-through capability. By using PS AT and PSCAD/EMTDC simulation platform, this paper works on power system static voltage stability and transient ride through capability concerned about the DFIGs. The main work focus on the following three aspects:(1)The IEEE 39-bus system containing DFIG is constructed in the PSAT. Modal analysis method is used for investigating the impacts of grid-connected DFIG on the static voltage stability of power system including different grid-connected positions and electrical distance. The simulation results show that static voltage stability can be improved when DFIG is connected to heavy load areas. Growing electrical distance between DFIG and grid will reduce static voltage stability of wind farm and its associated areas, the effects can change due to different positions of grid-connected DFIG.(2) In order to effectively evaluate the transient of DFIG, two major factors are analyzed:the stator and rotor short-circuit characteristics after crowbar switched on during a grid fault, the dynamic response under two kinds of typical crowbar control strategy. An index function is presented to evaluate the dynamic response. Then by comparing a series of simulation results, the optimal crowbar control strategies are obtained for LVRT under the different grid voltage drops.(3) The DFIG equivalent wind farm is built up in PSCAD/EMTDC. In view of the existing weak transient problems of wind farms, the optimization of control strategy to fault ride-through of DFIGs is proposed considering DFIGs, low-voltage protection circuit and reactive power compensation equipments. Two critical aspects are discussed:the steady-state and transient reactive power characteristics of wind turbines under the influence of the crowbar protection circuit, transient operating characteristics of reactive power compensation equipments. Examples are set to verify the proposed method. Simulation results validate the proposed strategy.