Adaptive observer-based nonlinear control of grid-tied PV-fed multicell inverter with harmonic mitigation capability

This work addresses the adaptive nonlinear control of a single-stage grid-connected photovoltaic (PV) system, focusing on harmonic current mitigation in highly distorted electrical grids. The proposed interfacing system employs a multilevel inverter topology, which improves power quality compared to its conventional two-level counterpart, particularly in single-stage PV applications. The control scheme employs a dual-loop structure to achieve the following three key objectives: (i) maximum power extraction from the PV arrays, (ii) reduced voltage stress on the switching devices, and (iii) power factor correction (PFC). To enhance performance under realistic grid conditions, the controller incorporates an adaptive observer for real-time estimation of grid voltage and impedance, which are often assumed to be known or directly measurable. The controller's design and analysis are carried out using Lyapunov stability theory. The theoretically predicted performances of the controller are confirmed by numerical simulations performed in Matlab/SimPowerSystems environment and in a Processor-In-the-Loop (PIL) implementation.