A Modular Adaptive Robust Nonlinear Control for Resilient Integration of VSIs Into Emerging Modernized Microgrids

Abstract

Nowadays, emerging modernized microgrids (MMGs) have significantly employed the voltage-source inverters (VSIs). VSIs are enabling technologies to form multi-infeed ac/dc (MIACDC) power systems integrating a variety of generation units and different loads into one coherent grid. In emerging MMGs, the frequency-dependent dynamics of multiple components affect the PQ-controlled, grid-connected VSIs (GC-VSIs), particularly when integrated into a weak network. In order to address this challenging problem, the full integration of the dynamics of the phase-locked loop (PLL) into those of GC-VSIs is accomplished in this research via an innovative modular structure to improve the VSI’s performance. This action is expected to significantly reduce the effect of the ac-side dynamics on the control of GC-VSIs. In addition, there are uncertainties associated with the parameters in the system. Accordingly, mismatched disturbances and uncertainties (both matched and mismatched ones) will appear in a nonlinear dynamic problem, and therefore, from the standpoint of control theories, mismatched disturbances and uncertainties should be overcome. Satisfying them is a difficult task in control of nonlinear systems. Therefore, one of the main contributions of this work is finding an appropriate mathematical model of GC-VSIs in the $dq$ -frame for the problem under study. Afterward, in order to control both active and reactive power independently, this article presents a novel two-degree-of-freedom (2DoF) methodology with an enhanced modular design. It combines the sliding-mode control with a “new sliding manifold” and a disturbance observer with a “new adaptation rule” taking care of uncertainties and mismatched disturbances. Those disturbance signals may be generated by the PLL dynamics or voltage signals affecting the GC-VSI’s dynamics. Through providing mathe- matical analyses (including stability assessments via various theorems using Lyapunov stability criterion), simulation results, and experiments, this article demonstrates the effectiveness of the proposed control methodology. The industrially accepted GC-VSI equipped with an $LCL$ -filter is used here.