Stability Analysis of Islanded Microgrid with EVs

Renewable energy resources (RESs) and electric vehicles (EVs) have emerged as powerful concepts which can replace the conventional energy and transportation systems with more flexibility and efficiency. Due to low inertia of microgrid and intermittent nature of RESs, the rapid increase in the penetration level of RESs and EVs in smart grids may lead to frequency stability issue. However, EVs, as the mobile energy storage system, can contribute to the improvement of the frequency fluctuation and stability. This paper proposes a method to control the EVs integrated in an islanded microgrid so that they participate in load frequency control (LFC). On the contrary to the approaches proposed in the literature, the proposed control method enables the investigation of time delay effect on LFC and considers the communication latency on the LFC stability. The delay-dependent stability criterion of the proposed method is derived based on Lyapunov theory in the form of linear matrix inequality (LMI). The LMI is solved to find the parameters impacting the maximum allowable delay (MAD) and to obtain the MAD by which the stability of the LFC system is guaranteed. The effectiveness of the proposed method is validated through numerical simulation of a case study.