Event-Based Under-Frequency Load Shedding Scheme in a Standalone Power System

Abstract

Under-frequency load shedding (UFLS) prevents a power grid from a blackout when a severe contingency occurs. UFLS schemes can be classified into two categories—event-based and response-driven. A response-driven scheme utilizes 81L relays with pre-determined settings while an event-based scheme develops a pre-specified look-up table. In this work, an event-based UFLS scheme is presented for use in an offshore standalone power grid with renewables to avoid cascading outages due to low frequency protection of wind power generators and photovoltaic arrays. Possible “N-1” and “N-2” forced outages for peak and off-peak load scenarios in summer and winter are investigated. For each forced outage event, the total shed load is minimized and the frequency nadir is maximized using particle swarm optimization (PSO). In order to reduce the computation time, initialization and parallel computing are implemented using MATLAB/Simulink because all forced outage events and all particles in PSO are mutually independent. A standalone 38-bus power grid with two wind turbines of 2 × 2 MW and photovoltaics of 7.563 MW was studied. For each event, the proposed method generally obtains a result with a smaller shed load and a smaller overshoot frequency than the utility and existing methods. These simulation results verify that the proposed method is practically applicable in a standalone power system with penetration of renewables.

UFLS and Smart Load for Frequency Regulation in Electrical Power System: A Review

“…Adaptive UFLS schemes are based on events or responses, frequency prediction, and RoCoF [43]. Below are the characteristics of the different adaptive schemes found in the literature, explained in more depth.…”

“…The objective of the proposed UFLS is to provide stability after the system is forced to operate on two independent islands when considering the output of the mentioned lines. In [43], an event-based UFLS is presented to be employed in an isolated offshore power system that includes renewable generation and aims to avoid service interruption due to cascading trips caused by low-frequency protections of wind and photovoltaic generators. Additionally, the algorithm's operation is studied under N-1 and N-2 contingencies in scenarios of maximum and minimum demand, minimizing the load shed and maximizing the frequency nadir through Particle Swarm Optimization (PSO).…”

A Case Study on National Electricity Blackout of Turkey

“…For the creation of an event-based under-frequency load shedding scheme, a particle swarm optimization (PSO) approach utilizing the least-upper bound method was proposed [33]. PSO was utilized to minimize the amount of load shed while maximizing the frequency nadir without the need for power deficiency estimation.…”

“…Otherwise, many frequency-related protection devices may be triggered and then result in severe consequences. Thus, it can be inferred that the frequency dynamics play an important role in the process of cascading failure [22,[32][33][34]. The blackout that occurred in Europe on 4 November 2006 can be given as a first important example.…”

Coordination of Multiple Flexible Resources Considering Virtual Power Plants and Emergency Frequency Control

“…To prevent large frequency deviations caused by large power losses, emergency frequency control (EFC) is adopted to prevent the frequency from falling below the underfrequency load-shedding threshold [8]. For a HVDC blocking disturbance, the event-driven EFC can act immediately after disturbance to quickly reduce the active power imbalance and ensure system frequency stability [9]. For the receiving-end power grid with multiinfeed HVDC, EFC measures include HVDC emergency power support, cutting out any pumped-storage pump, and emergency load shedding (ELS) [10].…”