Optimization of the effective reactive power adjustable capacity of DFIG wind farms considering the small signal stability restraints

In allusion to the coupling relationship between power grid and wind farms, the reactive power regulation characteristics of doubly fed inductive generators (DFIGs) are studied. First of all, taking the wind power integration as a clue, the model of DFIG wind farms for small signal stability analysis is established based on Thevenin equivalence and wind farm equivalence, then an explicit expression for static stability region under specific active-power mode is derivated considering grid-side operation state. On the basis of this expression and taking other steady-state operation constraints into consideration, the mathematical model for reactive power capacity of DFIG wind farms is proposed and interior point method is used to solve the problem. Examples show that the restraints of the small-signal stability must be taken into consideration when determining the adjustable reactive power capability of the DFIG wind farms, and the voltage support ability of the power grid should be also considered because it has direct impact on the static stability and the reactive power regulation ability of wind farms.