Optimal VAR expansion considering capability curve of DFIG wind farm

This paper develops an optimal planning tool for VAR devices in the presence of a doubly fed induction generator (DFIG) based wind farm. The probabilistic wind power output associated with the capability curve of DFIG wind generator has been incorporated in the proposed formulation in order to examine its effect on the new VAR devices investment cost and compare the results with the current practice of the regulated power factor range of 0.95 leading and 0.95 lagging. The proposed method is stated as an optimization problem so that the objective function is to simultaneously minimize the sum of the annual investment cost of the new VAR devices as well as the annual expected energy loss cost. The objective function is achieved while simultaneously satisfying the investment constraints of the new VAR devices and several operating constraints including the effect of the wind park active power output and its associated VAR capability limits as well as the voltage security limits to enhance power system voltage stability.