Robust Multi-Objective Control of VSC-Based DC-Voltage Power Port in Hybrid AC/DC Multi-Terminal Micro-Grids

Abstract

Hybrid ac/dc multi-terminal micro-grids are gaining high momentum under the smart grid paradigm to integrate renewable and clean energy resources either in the transmission or distribution systems. This paper presents a robust multi-objective controller for the voltage-source-converter (VSC)-based dc-voltage power-port in hybrid ac/dc networks. The proposed controller ensures excellent tracking performance, robust disturbance rejection, and robust stability against operating point and parameter variation with a simple fixed-parameter low-order controller. A two-degree-of-freedom control structure is proposed, where feed-forward tracking and base-line robust disturbance rejection controllers are employed to decouple disturbance rejection and tracking objectives. A disturbance rejection controller is designed, based on the singular-values (μ) synthesis approach, to achieve robustness against variation in converter operation point. Further, the effect of parametric uncertainty in the effective dc-link capacitance is mitigated by modifying the robust disturbance rejection controller, via the polynomial method, to ensure that the closed-loop poles are allocated in the pre-defined region in the complex plane even under parameter variation. A theoretical analysis and comparative simulation and experimental results are presented to show the effectiveness of the proposed control structure.