Michele Tucci

A Decentralized Scalable Approach to Voltage Control of DC Islanded Microgrids

We propose a new decentralized control scheme for DC Islanded microGrids (ImGs) composed of several Distributed Generation Units (DGUs) with a general interconnection topology. Each local controller regulates the voltage of the point of common coupling of the corresponding DGU to a reference value. Notably, offline control design is conducted in a plug-and-play fashion, meaning that: 1) the possibility of adding/removing a DGU without spoiling the stability of the overall ImG is checked through an optimization problem; 2) when a DGU is plugged in or out, at most its neighboring DGUs have to update their controllers; and 3) the synthesis of a local controller uses only information on the corresponding DGU and lines connected to it. This guarantees the total scalability of control synthesis as the ImG size grows or DGUs get replaced. Yet, under mild approximations of line dynamics, we formally guarantee the stability of the overall closed-loop ImG. The performance of the proposed controllers is analyzed simulating different scenarios in PSCAD.

Voltage control of DC islanded microgrids: A decentralized scalable approach

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 DGUs gets replaced. Yet, 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.

Plug-and-play control of AC islanded microgrids with general topology

In this paper, we provide an extension of the scalable algorithm proposed in the work of Riverso et al. (2015) for the design of Plug-and-Play (PnP) controllers for AC Islanded microGrids (ImGs). The method in the work of Riverso et al. (2015) assumes Distributed Generation Units (DGUs) are arranged in a load-connected topology, i.e. loads can appear only at the output terminals of inverters. For handling totally general interconnections of DGUs and loads, we describe an approach based on Kron Reduction (KR), a network reduction method giving an equivalent load-connected model of the original ImG. However, existing KR approaches can fail in preserving the structure of transfer functions representing transmission lines. To avoid this drawback, we introduce an approximate KR algorithm, still capable to represent exactly the asymptotic periodic behavior of electric signals in balanced RL line networks with balanced and unbalanced loads. Our results are backed up with simulations illustrating features of the new KR approach as well as its use for designing PnP controllers in a 21-bus ImG derived from an IEEE test feeder.

Line-Independent Plug-and-Play Controllers for Voltage Stabilization in DC Microgrids

We consider the problem of stabilizing voltages in Direct Current (DC) microgrids given by the interconnection of Distributed Generation Units (DGUs), power lines, and loads. We propose a decentralized control architecture where the primary controller of each DGU can be designed in a plug-and-play fashion, allowing the seamless addition of new DGUs. Differently from several other approaches to primary control, local design is independent of the parameters of power lines and the only global quantity used in the synthesis algorithm is a scalar parameter. Moreover, differently from the plug-and-play control scheme in [1], the plug-in of a DGU does not require to update the controllers of neighboring DGUs. Local control design is cast into a linear matrix inequality problem that, if infeasible, allows one to deny plug-in requests that might be dangerous for microgrid stability. The proof of closed-loop stability of voltages exploits structured Lyapunov functions, the LaSalle invariance theorem and the properties of graph Laplacians. Theoretical results are backed up by simulations in PSCAD.

Voltage stabilization in DC microGrids through coupling-independent Plug-and-Play controllers

This paper addresses the problem of stabilizing voltages in DC microgrids given by the interconnection of Distributed Generation Units (DGUs), power lines and loads. As in [1], we propose a decentralized control architecture where the controller of each DGU can be designed in a Plug-and-Play (PnP) fashion by solving a local Linear Matrix Inequality (LMI) problem. However, differently from [1], when a new DGU issues a plug-in request, we no longer require that neighboring units update their local controllers in order to account for new electrical couplings. Indeed, a key feature of the novel approach is that the design of a local controller requires only the knowledge of the dynamics of the corresponding DGU. The proof of closed-loop asymptotic stability combines properties of graph Laplacians, structured Lyapunov functions and LaSalle invariance theorem. Theoretical results are backed up by simulations in PSCAD.

Plug-and-Play Voltage/Current Stabilization DC Microgrid Clusters with Grid-Forming/Feeding Converters

In this paper, we propose a new decentralized control scheme for Microgrid (MG) clusters, given by the interconnection of atomic dc MGs, each composed by grid-forming and grid-feeding converters. In particular, we develop a new Plug-and-Play (PnP) voltage/current controller for each MG 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. With the proposed controller, each MG can plug-in/out of the clusters seamlessly irrespectively of the power line parameters and models of other MGs. A profound proof of closed-loop stability of MG clusters is provided. Moreover, theoretical results are validated by hardware-in-loop (HiL.) tests.

Stable current sharing and voltage balancing in DC microgrids: A consensus-based secondary control layer

Abstract In this paper, we propose a secondary consensus-based control layer for current sharing and voltage balancing in DC microGrids (mGs). To this purpose, we assume that Distributed Generation Units (DGUs) are equipped with decentralized primary controllers guaranteeing voltage stability. This goal can be achieved using, for instance, Plug-and-Play (PnP) regulators, which allow one to analyze the behavior of the closed-loop mG by approximating local primary control loops with either unitary gains or first-order transfer functions. Besides proving exponential stability, current sharing, and voltage balancing, we describe how to design secondary controllers in a PnP fashion when DGUs are added or removed. Theoretical results are complemented by simulations, using a 7-DGUs mG implemented in Simulink/PLECS, and experiments on a 3-DGUs mG.

Plug-and-play design of current controllers for grid-feeding converters in DC microgrids

In this paper, we address the problem of synthesizing decentralized current controllers for grid-feeding converters of current-controlled distributed generation units (CDGUs) in dc microgrids (MGs). Notably, a plug-and-play (PnP) design procedure is proposed to achieve grid-feeding current tracking while preserving the collective MG stability. Through the presented control scheme, seamless addition/removal of each CDGU to/from the MG is ensured, with no need to update controllers of neighboring CDGUs and to know the information of the MG. At the mathematical level, the set of control coefficients guaranteeing the aforementioned features is explicitly characterized in terms of simple inequalities. The inequality set only depends on the local parameters. Moreover, the proof of the MG closed-loop stability exploits structured Lyapunov functions, the LaSalle invariance theorem and properties of graph Laplacians. Finally, theoretical results are validated by hardware-in-loop simulation tests.