Improvement of the Frequency Response Indicators by Optimal UFLS Scheme Settings

Abstract

This research investigates the positive changes in the system frequency response indicators caused by the implementation of a set of optimal settings of an under-frequency load shedding (UFLS) scheme. The optimal under-frequency load shedding (UFLS) scheme is optimised by minimising the total amount of load shedding and taking into account the recovery process of the system frequency into its operational values after several losses of generation and satisfies the requirements of the under-frequency load shedding standard (PRC-006-SERC-02). The idea of implementing the optimal UFLS scheme is to identify how changes the minimum frequency, minimum time, rate of change of frequency and steady-state frequency when the amount of load shedding change. The optimal UFLS scheme formulation starts with identifying the variables to control with the optimisation and its respective bounds. Then, the objective function is formulated in terms of the total load shedding, and finally, the restrictions and requirements of the systems are written as inequality constraints. The optimal UFLS is evaluated in the IEEE 39-bus system. The simulations results demonstrate the suitability of the optimal UFLS to improve the frequency response indicators.

Optimal Under-Frequency Load Shedding Setting at Altai-Uliastai Regional Power System, Mongolia

“…The implementation of the traditional UFLS scheme is based on setting the values of the parameters of all UFRs installed in the power system. The UFRs are mainly characterised by four parameters (see Figure 3) [4]: (i) the number of stages (Ns) or steps in which the UFR will disconnect the locally connected load, (ii) the block size of LS (∆P) that will be disconnected at each stage (this value is based on the total load that is locally connected), (iii) the frequency threshold (fT) at which the load must be shed in each stage and (iv) the time delay (td) between activating the consecutive stages. Assuming that the power system has NUFR UFRs installed, the settings of the i-th UFR (i = 1, 2, …, NUFR) are mathematically described as follows:…”

“…The classical load shedding (LS) is performed at the same location where the frequency is sensed, and it can be done over one or multiple steps. The implementation of the 2 of 18 classical UFLS scheme implies identifying the most severe possible power imbalance and estimating the total amount of load disconnection, ensuring the frequency recovers above a minimum permissible value [4]. Once the total amount of LS is calculated, the parameters of the UFRs (number of load shedding stages, block size of load to be shed, frequency threshold and the time delay for each stage) must be set [5].…”

Detection and Identification of Generator Disconnection Using Multi-layer Perceptron Neural Network Considering Low Inertia Scenario

“…This phenomenon brings new challenges, essentially because now most of the power system generator units are not synchronous machines (SM) but power electronics converters-based generation [3]. The main difference between them is the lack of inertia of the last ones [4], [5]. For this reason, energy storage systems are also being integrated to achieve the capability to provide inertia, among other ancillary services [6].…”