An MILP formulation for controlled islanding coordinated with under frequeny load shedding plan

Abstract

As both controlled islanding and under frequency load shedding (UFLS) plans, curtail a predetermined amount of load, they must be coordinated to avoid excessive and unnecessary load shedding. In this paper, firstly an MILP formulation for controlled islanding with the purpose of determining island boundaries is presented, then a two-stage plan is proposed to coordinate the controlled islanding strategy and the UFLS plan. In the first stage, the islanding boundaries are determined using a mixed integer linear programming (MILP) model. In this stage, the set of splitting lines and the required load shedding for the controlled islanding plan are determined to achieve the minimum power imbalance over all resulted islands. However, as the UFLS relays are armed in each island, the resulted islanding strategy should be modified in the presence of UFLS relays. In the second stage, the required amount of load shedding is adjusted if the UFLS plan is not enough to make power balance in that island. The system frequency response is discretized considering the governor actions, load damping and UFLS activation. To achieve a practical controlled islanding plan coordinated with UFLS relay’s settings, a variety of operational and structural constraints are included. Also, the AC power balance equations are linearized at a given operating point. The proposed coordinated controlled islanding scheme is applied over the IEEE 118-bus test system.