Wide-Area Adaptive Load Shedding Control to Counteract Voltage Instability

Abstract

Abstract:A two-level adaptive load shedding scheme against voltage instability is proposed, adjusting its actions to the severity of the situation. The lower level includes a set of distributed controllers which curtail loads once the voltages at monitored transmission buses fall and stay for some time below threshold values. The adaptive nature of the proposed scheme comes from the upper level adjusting those thresholds in real-time. At the time instant the upper level detects that the system enters an emergency condition, it sends a signal to the lower-level controllers requesting them to take their currently measured voltages as threshold values. The upper-level emergency detection can be based on various criteria, the key-point being that it takes advantage of a wide-area monitoring of the system. In particular, the paper illustrates the use of a voltage instability detection scheme based on sensitivity computation. In case the upper level fails sending its signal, the lower-level controllers act in purely distributed mode, each using its pre-set threshold voltage. The capabilities of the proposed scheme are illustrated on a small but realistic test system.

Toward Adaptive Load Shedding Remedial Action Schemes in Modern Electrical Power Systems

“…Ways have also been sought to give flexibility to this threshold. For example, in [71] a two-level UVLS is designed; the first level is based on rules with fixed thresholds and of the second level has a wide area monitor the state of the system, this level performs an online sensitivity study and, when detecting a sign change, identifies a system evolution to voltage instability, selecting as a threshold the value of the voltage being measured at that moment, preventing the system from further degrading to the initial threshold. An adaptive voltage threshold has been incorporated into the UVLS technique proposed by the authors of [72].…”