A multi-agent NI approach to the secondary voltage synchronisation problem of AC microgrid with controller performance comparison

This research study devises a new dynamic output feedback cooperative control scheme relying on the Negative Imaginary (NI) toolkit to address the secondary voltage synchronisation issue of the inverter-based Distributed Generating Units (DGUs) that constitute an AC microgrid. Each DGU can be modelled by a nonlinear descriptor system, which, upon being feedback-linearised, gives a double integrator map from the auxiliary input (q<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</inf>) to the d-component of the output voltage $\left( {{v_{o{d_i}}}} \right)$. As a double integrator dynamics intrinsically exhibits the NI property, the feedback-linearised DGUs connected via a network manifest the multi-agent NI property. Therefore, a distributed Strictly NI (SNI) control law can achieve the desired voltage synchronisation among the DGUs of a microgrid. The proof of consensus invokes the Eigenvalue Loci technique, for which a complicated Lyapunov theory-based derivation is not necessary. The scheme is resilient to bounded disturbances and variation in the interaction topology and can handle plug-and-play operations. The paper also examines the performance of various first-order and second-order distributed SNI controllers in achieving the desired voltage consensus.