Stabilizing a DG-fed islanded system through load shedding on the basis of the rate of change of frequency and frequency decline

Abstract

Whenever a distribution network is about to become unstable, protection relays will start to work, thus creating unintentional islanding. In order to keep balance between generated and consumed power in an islanded system, it is necessary to shed loads. This paper proposes a new method for load shedding based on the rate of change of frequency (RoCoF) at the first step and on frequency decline at subsequent steps. For this purpose, three lookup tables were created in order to prioritize loads to be shed according to the willingness of subscribers to pay (WSP) and the RoCoF. The strength of the proposed method was verified by considering four cases. Consumption load was considered as voltage- and frequency-dependent in three of the cases, and as constant-power in the fourth case. The results indicate that the proposed method is flexible and, in comparison with previous research, results in a slighter frequency decline and stabilizes the islanded system in a shorter time.