We propose a new decentralized control scheme for DC Islanded microGrids (ImGs) composed by several Distributed Generation Units (DGUs) with a general interconnection topology. Each local controller regulates to a reference value the voltage of the Point of Common Coupling (PCC) of the corresponding DGU. Notably, off-line control design is conducted in a Plug-and-Play (PnP) fashion meaning that (i) the possibility of adding/removing a DGU without spoiling stability of the overall ImG is checked through an optimization problem; (ii) when a DGU is plugged in or out at most neighbouring DGUs have to update their controllers and (iii) the synthesis of a local controller uses only information on the corresponding DGU and lines connected to it. This guarantee total scalability of control synthesis as the ImG size grows or DGU gets replaced. Yes, under mild approximations of line dynamics, we formally guarantee stability of the overall closed-loop ImG. The performance of the proposed controllers is analyzed simulating different scenarios in PSCAD.
We consider the application of passivity theory to the problem of voltage stabilization in DC microgrids, which are composed of distributed generation units, dynamic RLC lines, and nonlinear ZIP (constant impedance, constant current, and constant power) loads. To this aim, we first study the stable interconnections of constrained passive systems and later consider its applications to microgrids. More specifically, we consider the decentralized multivariable PI controllers proposed in [29], and show that they passivate the generation units and the associated loads under certain conditions. To prove voltage stability in the closed-loop microgrid, we exploit properties of interconnection, passivity of individual components, and the LaSalle's invariance theorem. Moreover, we provide explicit inequalities on control gains to design stabilizing controllers. Control synthesis requires only the knowledge of local parameters and is always feasible allowing removal and addition of DGUs in a plug-n-play fashion. Theoretical results are backed up by simulations in PSCAD.
In this paper, we propose a new hierarchical control scheme for Microgrid (MG) clusters, given by the interconnection of atomic dc MGs with ZIP loads, each composed by both gridforming and grid-feeding converters. In the primary level, we develop a new Plug-and-Play (PnP) voltage/current controller in order to achieve simultaneous voltage support and current feeding function with local references. The coefficients of each stabilizing controller are characterized by explicit inequalities, which are related only to local electrical parameters of the MG. Moreover, we provide a sufficient condition on the ZIP loads to guarantee passivity and asymptotic stability of electric system. The robustness of performance to system uncertainties is also demonstrated. In the secondary level, a leader-based voltage/current controller is proposed to achieve both voltage and current regulation for the MG cluster without specifying the individual setpoints for each MG. The proposed distributed controller requires a communication network where each regulator exchanges information with its communication neighbors only. With the proposed scheme, each MG can plug-in/out seamlessly, irrespectively of the power line parameters and models of other MGs. Closed-loop stability proof of MG clusters is formally proved independently of the cluster topology. Moreover, theoretical results are validated by extensive hardware-in-loop (HiL) tests showing robustness of the closed-loop cluster against perturbations in the loads, PnP operations and noises/delays in the communication network.
We propose a decentralized control synthesis procedure for stabilizing voltage and frequency in AC Islanded microGrids (ImGs) composed of Distributed Generation Units (DGUs) and loads interconnected through power lines. The presented approach enables Plug-and-Play (PnP) operations, meaning that DGUs can be added or removed without compromising the overall ImG stability. The main feature of our approach is that the proposed design algorithm is line-independent. This implies that (i) the synthesis of each local controller requires only the parameters of the corresponding DGU and not the model of power lines connecting neighboring DGUs, and (ii) whenever a new DGU is plugged in, DGUs physically coupled with it do not have to retune their regulators because of the new power line connected to them. Moreover, we formally prove that stabilizing local controllers can be always computed, independently of the electrical parameters. Theoretical results are validated by simulating in PSCAD the behavior of a 10-DGUs ImG.
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