A modified DEP and AHP for load shedding scheme of islanded distribution system incorporating stability index

Abstract

Islanding of distribution network can severely affect the system frequency and voltage due to imbalance power between generation and load demand. In a standard practice, distributed generations (DGs) are required to be disconnected when islanding occurs because of the technical concerns. However, the practice is not an ideal approach as the DGs can be used to energize some of the loads in the system. However, DGs can be allowed to continuously operate by addressing the power imbalance between generation and load demand by means of load shedding scheme (LSS). Therefore, this paper proposes an improved LSS based on modified Discrete Evolutionary Programming (MDEP) and analytic hierarchy process (AHP). Two factors, which are the minimum power imbalance and minimum stability index are considered to attain a stable frequency and voltage of the system. The MDEP starts by short-listing the bus candidates to be shed while AHP method decides on the rank of the load to be shed considering both the power imbalance and stability index. The performance of the proposed LSS is evaluated based on the frequency responses. The effectiveness of the proposed scheme is tested on an 11 kV Malaysian distribution network, energized by the grid and two mini-hydros. Simulation results show a significant improvement in the consistency (73.3%) of the proposed MDEP and converged at lower iteration number. Comparative study reveals the effectiveness of the proposed LSS in stabilizing the system frequency without frequency overshoot, a reduction of 68.4% and 17.7% of operating time during islanding and overloading events. Voltage profile of the system is also improved for all buses.