Mixed integer linear formulation for undervoltage load shedding to provide voltage stability

Undervoltage load shedding (UVLS) is the last resort against voltage instability in critical situations. Here, the UVLS scheme is formulated as a mixed integer programming (MIP) model. The aim of the proposed UVLS model is to provide a predetermined value of loading margin with minimum amount of load shed. The full non-linear AC power flow equations are linearised using a piecewise linear technique. The proposed linear AC power flow is then integrated into the UVLS problem. A ZIP load model is utilised to demonstrate the fulfilment of the MIP-based UVLS model under non-linear static loads. The efficacy of the developed linear AC power flow is verified under different operational conditions and contingencies. The results of the proposed MIP-based UVLS model are compared with the original non-linear programming UVLS formulation. To verify the performance of the developed load shedding strategy, the proposed MIP-based UVLS model is implemented in IEEE 14-bus and IEEE 118-bus test systems.