Reactive optimal power flow incorporating margin enhancement constraints with nonlinear interior point method

A reactive optimal power flow incorporating margin enhancement constraints is described. Margin sensitivity at a steady-state voltage instability point is calculated using invariant space parametric sensitivity, and can provide valuable information for selection of effective control parameters. However, weakest buses in neighbouring regions have high margin sensitivities in a certain range, so control determination using only the sensitivity information might cause violation of operational limits of the base operating point, at which the control is applied to enhance voltage stability margin in the direction of parameter increase. A nonlinear interior point method (NIPM) is applied to solve the optimal power flow formulation with margin enhancement constraints, and shunt capacitances are mainly considered as control variables. In the case study, an example applying the proposed method to the IEEE 118-bus test system is shown, and experiences with margin enhancement constraints are also included.