Open channel communication is a major prerequisite for next generation power networks in which time delays are inevitable. Due to unforeseen variations in the load demand, the mismatch between power generation and demand occurs. If this situation is not properly tackled, it may induce some unintended consequences like fluctuations in the tie-line power and system frequency which are highly undesirable. To ensure grid reliability, the frequency should always stay within its stipulated range. This is accomplished by load frequency control (LFC) technique. In networked LFC systems, load frequency regulation signals are transferred via communication networks, causing time delays in the feedback paths that can destabilize the power grid. As a consequence, for ensuring stability, the stable delay margin must, therefore, be determined. In this paper, the delay-dependent stability problem of two area LFC systems combined with electric vehicle aggregator (EVA) is addressed. The conducted Lyapunov based analysis yields a stable delay margin within which the closed loop system remains asymptotically stable. Moreover, the analytical delay margin values are validated using the simulation studies. In the sequel, the effect of participating factors on the system stability is also investigated.
Key words: Load frequency control; Delay-dependent stability; Lyapunov-Krasovskii functional; Linear matrix inequality; Electric Vehicle Aggregator; Stability criterion.
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