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

Nowadays, emerging modernized microgrids (MMGs) have significantly employed the voltage-source inverters (VSIs). VSIs are enabling technologies to form multiinfeed 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 voltagesource inverters (GC-VSIs), particularly when integrated into a weak network. In order to address this challenging problem, the full integration of the phase-locked loop (PLL) dynamics with those of GC-VSIs is accomplished in this paper 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. Also, 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, so from the standpoint of control theories, mismatched disturbances and uncertainties should be overcome. Satisfying them is a challenging task in control of nonlinear systems. Therefore, one of the main contributions of this research 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 paper presents a novel 2-degree-of-freedom (2DoF) methodology with an enhanced modular design. It combines the sliding-mode control with e “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 mathematical analyses (including stability assessments via various theorems using Lyapunov stability criterion), simulation results, and experiments provided, this article demonstrates the effectiveness of the proposed control methodology. The industrially accepted GC-VSI equipped with an LCL-filter is used here.