Underfrequency Load Shedding Using Locally Estimated RoCoF of the Center of Inertia

Abstract

The conventional Under Frequency Load Shedding (UFLS) scheme could result in unacceptably low frequency nadirs or overshedding in power systems with volatile inertia. This paper proposes a novel UFLS scheme for modern power systems whose inertia may vary in a wide range due to high penetration of renewable energy sources (RESs). The proposed scheme estimates the rate of change of frequency (RoCoF) of the center of inertia (CoI), and consequently, the loss of generation (LoG) size, using local frequency measurements only. An innovative inflection point detector technique is presented to remove the effect of local frequency oscillations. This enables fast and accurate LoG size calculation, thereby more effective load shedding. The proposed UFLS scheme also accounts for the effect of the inertia change resulting from LoG events. The performance of the proposed scheme is validated by conducting extensive dynamic simulations on the IEEE 39-bus test system using Real Time Digital Simulator (RTDS). Simulation results confirm that the proposed UFLS scheme outperforms the conventional UFLS scheme in terms of both arresting frequency deviations and the amount of load shed. Index Terms--Center of inertia (CoI), Underfrequency load shedding (UFLS), Rate of change of frequency (RoCoF).

Size/Location Estimation for Loss of Generation Events in Power Systems with High Penetration of Renewables

“…(i) All non-monitored RESs are first excluded from the superimposed circuit. This gives rise to (10), eliminating the concerns over the solvability of ( 4). (ii) The solution of (10) using (11) provides a starting point for the estimation of the superimposed nodal current at the candidate location, i.e., ΔI c .…”

“…The index q denotes the number of monitored RESs. The system of equations (10) can easily be solved using the OLS method as follows:…”

“…For instance, a high rate of change of frequency (RoCoF) does not necessarily indicate a large LoG size. As a result, these methods might fail to prevent extremely low nadirs or may lead to over-shedding [10].…”

A multi‐area design of under frequency load shedding schemes considering energy storage system

“…Using the phasor measurement units (PMU), this information is available at the system control center (SCC) and area operating center (AOC). Some types of adaptive UFLS plans can be realized using wide area measurement system (WAMS) [13] In the proposed adaptive scheme in [14], the RoCoF value at the center of inertia (CoI), and consequently, the loss of generation size is estimated using local frequency measurements. Another load shedding scheme for low inertia grid has been presented in [15] considering Distributed Generation (DG) capabilities.…”

Underfrequency Load Shedding Strategy With an Adaptive Variation Capability for Multi-Microgrids

“…However, the above research has not considered the problem of ensuring a continuous power supply for critical loads when dealing with power shortages. In [13], a local UFLS scheme without real-time communication was proposed. This scheme uses local frequency measurements to estimate the frequency change rate of the inertial center, which is superior to the traditional centralized UFLS scheme in terms of frequency deviation.…”