Studies On The Stability Issues About Large Scale Wind Farm Grid Integration

With the increasing share of the wind power in the power system, the impact of its integration is becoming more widespread. Currently, there are some noticeable characteristics of the wind power integration behaving as following: (1) each single wind farm with larger size; (2) wind farm coupled with higher voltage level. In the power grid with higher wind power penetration, the voltage stability, transient stability and frequency stability are all influenced by the wind power integration not only because the injection of wind power will change the load flow distribution, transferred power of each transmission line and the total inertia of the whole power system, but also because the wind turbine generators perform differently in either steady-state or transient-state compared with the conventional synchronous machine. The stability issues about large scale wind farm integration are investigated in this paper; the main content of study covers the foliowings:(1) The paper derives the dynamic model and steady-state model of the normal asynchronous generator and doubly fed induction generator expressed in the reference frame rotating in synchronous speed; the aerodynamic model, shaft system model and pitch control model of the wind turbines model are presented; finally the overall model configuration of induction machine based constant speed wind turbine model and DFIG based variable speed wind turbine model are presented.(2) The control model of DFIG based variable speed wind turbine is studied; the decoupled control principle of rotor side converter and grid side converter of DFIG are derived; the rotor side converter controller, grid side converter controller, wind turbine control system and DFIG based variable speed wind turbine overall control system model are presented.(3) The mechanism of voltage stability deterioration of the power grid with the wind farm integration is analyzed and illustrated by a simplified equivalent system. The active power and reactive power characteristics of IG and DFIG is analyzed and the load flow model of different types of wind turbines are presented.(4) The P-V curve and V-Q curve methods are generally applied to analyze the steady-state voltage stability. The power grid steady-state voltage stability in the DFIG based wind farm case is better than that in the IG based wind farm case. The results of voltage stability simulated in dynamic and steady-state are compared.(5) The transient voltage stability of IG based wind turbine is studied; the shaft relaxation during the fault and its impact on transient voltage stability are analyzed. The SVC and STATCOM models are established in PowerFactory; the integrated control combined dynamic reactive power compensation with pitch control used for transient stability control is implemented to improve the transient voltage stability of IG based wind turbine.(6) The transient voltage control of rotor side converter and pitch control to enhance transient voltage stability of DFIG based wind turbines are presented to implement the low voltage ride through (LVRT) characteristic. The rotor side converter controller with transient voltage support capability provides dynamic...