Abstract
In this paper we consider the problem of restoring the voltage for stand-alone inverter-based Microgrids despite the effects of the time-delays arising with the information exchange among the electrical busses. To guarantee that all Distributed Generators (DGs) reach in a finite-time and maintain the voltage set-point, as imposed by a virtual DG acting as a leader, we suggest a novel robust networked-based control protocol that is also able to counteract both the time-varying communication delays and natural fluctuations caused by the primary controllers. The finite-time stability of the whole Microgrid is analytically proven by exploiting Lyapunov-Krasovskii theory and finite-time stability mathematical tools. In so doing, delay-dependent stability conditions are derived as a set of Linear Matrix Inequalities (LMIs), whose solution allows the proper tuning of the control gains such that the control objective is achieved with required transient and steady-state performances. A thorough numerical analysis is carried out on the IEEE 14-bus test system. Simulation results corroborate the analytical derivation and reveal both the effectiveness and the robustness of the suggested controller in ensuring the voltage restoration in finite-time in spite of the effects of time-varying communication delays.
Highlights
Over the past few years, Microgrids (MGs) have received considerable attention due to their potential role in mitigating consequences of sudden grid interruption, guaranteeing an uninterrupted energy supply for the electrical loads, and reliable grid operation [1]
The most common approach is to deploy a three-layer hierarchical control architecture [8], which is based on the following interactive modules: i) a Primary Control (PC) level, commonly called zero-level, involving the local hardware control of each Distributed Generators (DGs) unit and designed to stabilize the power network, as well as to share active and reactive power among different distributed energy sources, without any communication links; ii) a Secondary Control (SC), properly designed in order to compensate inevitable voltage and frequency fluctuations caused by the operation of PC layer; iii) a Tertiary Control (TC) aimed at optimizing the power flows exchanged by the MG components [9]
From [22], [35], by exploiting LyapunovKrasovskii theory and Finite-Time stability tools, we provide a delay-dependent control gain tuning procedure, expressed as set of Linear Matrix Inequalities (LMIs), whose solution allows finding the voltage controller gain and state trajectories bound as function of the upper bound for the communication time-delay; this guarantees a certain stability margin w.r.t. sudden packet losses, which can be modeled as hard delays;
Summary
Over the past few years, Microgrids (MGs) have received considerable attention due to their potential role in mitigating consequences of sudden grid interruption, guaranteeing an uninterrupted energy supply for the electrical loads, and reliable grid operation [1]. The more challenging problem of designing a distributed control strategy, ensuring prescribed transient behaviour for the MG while coping with communication time-varying delays has sparsely been addressed Along this line, the very recent work in [33] suggests a distributed finite-time control protocol, for frequency and voltage restoration, that leverages the Artstein model reduction method for counteracting the unique constant delay affecting the communication network.
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