Lyapunov Stability Analysis of Load Frequency Control Systems with Communication Network Induced Time-Delays and EV Aggregator

Abstract

In this paper, an improved stability analysis is presented to compute the stable delay margin of a class of networked load frequency control systems involving communication channels and electric vehicle aggregator. In networked control systems with a centralized control framework, the use of communication links for information exchange among various sub-systems introduces inevitable time-delays in the feedback loop. These communication delays invariably exert a negative influence on the dynamic performance and stability of the system. If the network-induced time-delay escalates beyond a critical delay margin, called stable delay margin, the stability of the closed-loop system is lost. In recent times, for improved frequency compensation, a fleet of plug-in-electric vehicle units called aggregators are integrated as a distributed generation source in the load frequency control system. In such systems, in addition to improved frequency compensation, the integration of electric vehicles also paves way to enhancement in stability margin of the time-delayed system. In this paper, using Lyapunov-Krasovskii functional approach coupled with Wirtinger inequality, a new stability analysis is presented for determining delay-dependent stability of networked load frequency control systems integrated with electric vehicle aggregator. Furthermore, to impart a realistic operating condition, time-delays in the networked centralized control loop and electric vehicle aggregator loops are considered to be non-identical, and appropriate participation factors for effective load sharing are incorporated in the system framework. In the sequel, the analytical delay bounds are corroborated through extensive simulation studies.