Voltage Stabilization in Microgrids via Quadratic Droop Control

We consider the problem of voltage stability and reactive power balancing in islanded small-scale electrical networks outfitted with DC/AC inverters ("microgrids"). A droop-like voltage feedback controller is proposed which is quadratic in the local voltage magnitude, allowing for the application of circuit-theoretic analysis techniques to the closed-loop system. The operating points of the closed-loop microgrid are in exact correspondence with the solutions of a reduced power flow equation, and we provide explicit solutions and small-signal stability analyses under several static and dynamic load models. Controller optimality is characterized as follows: we show a one-to-one correspondence between the high-voltage equilibrium of the microgrid under quadratic droop control, and the solution of an optimization problem which minimizes a trade-off between reactive power dissipation and voltage deviations. Power sharing performance of the controller is characterized as a function of the controller gains, network topology, and parameters. Perhaps surprisingly, proportional sharing of the total load between inverters is achieved in the low-gain limit, independent of the circuit topology or reactances. All results hold for arbitrary grid topologies, with arbitrary numbers of inverters and loads. Numerical results confirm the robustness of the controller to unmodeled dynamics.Comment: 14 pages, 8 figure

Structural monitoring using fiber optic sensors of a pre-stressed concrete viaduct during construction phases

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Secondary Frequency and Voltage Control of Islanded Microgrids via Distributed Averaging

In this work we present new distributed controllers for secondary frequency and voltage control in islanded microgrids. Inspired by techniques from cooperative control, the proposed controllers use localized information and nearest-neighbor communication to collectively perform secondary control actions. The frequency controller rapidly regulates the microgrid frequency to its nominal value while maintaining active power sharing among the distributed generators. Tuning of the voltage controller provides a simple and intuitive trade-off between the conflicting goals of voltage regulation and reactive power sharing. Our designs require no knowledge of the microgrid topology, impedances or loads. The distributed architecture allows for flexibility and redundancy, and eliminates the need for a central microgrid controller. We provide a voltage stability analysis and present extensive experimental results validating our designs, verifying robust performance under communication failure and during plug-and-play operation.Comment: Accepted for publication in IEEE Transactions on Industrial Electronic

Antiplatelet therapy in elderly patients with acute coronary syndrome: Between scientific evidence and future perspectives.

Dual antiplatelet therapy (DAPT) is an important strategy for reducing cardiovascular events (CV) after an acute coronary syndrome (ACS). Elderly patients undergoing DAPT have a higher risk of bleeding than younger patients for a variety of reasons. Stratification of thrombotic/hemorrhagic risk is mandatory in order to decide on the type and duration of DAPT. The percentage of patients ≥ 75 years represented in clinical trials is not large, so very often elderly people are prescribed treatment protocols only experimented on younger patients with a lower hemorrhagic risk. However, even in patients aged ≥ 75 treated with invasive or conservative therapy, after an ACS, a DAPT with aspirin 80-100 mg/day plus a P2Y12 receptor inhibitor for 12 months is recommended. In elderly patients, DAPT should be considered a dynamic process that can be modified over time based on the patient's clinical conditions, or any other necessities (non-procrastinating surgical interventions, comorbid-like effects that can increase hemorrhagic risk). In patients with moderate-high or very high hemorrhagic risk, DAPT treatment should last less than 12 months. A prolongation of DAPT beyond 12 months in this setting is limited to a very low percentage of patients, after careful assessment of ischemic/hemorrhagic profile