Design and Simulation of Load Prioritization using Fuzzy Logic /

Abstract

Variations in load cause the fluctuations in system frequency when the system is running in islanding mode. To avoid blackouts load shedding schemes are implemented. Load shedding schemes being implemented in the power systems are typically based on consecutively disconnecting pre-determined amounts of loads in case of system’s frequency dropping lower than a certain level. This can result in unnecessary delays in dropping the load because of consecutive operation of switch gear and in-adequate or extra amounts of loads to be dropped. The solutions available in the existing literature for load shedding in case of islanding are either very complex or costly or not efficient enough for optimal load shedding. The proposed method in this thesis enables the simultaneous dropping of loads in cases of huge power differences to avoid major blackouts. Frequency as well as rate of change of frequency is measured and fed to the fuzzy logic controller (FLC). FLC continuously monitors the frequency and rate of change of frequency. Rules are defined for the FLC which calculate the amount of load to be dropped in case of low frequency and negative rate of change of frequency. This technique also takes care of the protection of the Distributed Generator (DG) and if the system frequency goes lower than a certain level then DG gets disconnected from the system immediately. The proposed method does not require any extra infrastructure for computing the variables and only rely on the local frequency and frequency derivative measurements thus results in negligible additional costs in the existing system. For checking the efficiency and robustness of the proposed technique, two cases are simulated which prove it as the best solution for the load shedding problem in case of islanding.