Nonlinear control of single stage grid-tied photovoltaic systems based on a 3L-NPC topology

Abstract

In this paper, the problem of controlling the single-phase grid connected to the photovoltaic system based on a 3-level half-bridge neutral point inverter with an L-filter is presented. The proposed controller is designed to meet three main control objectives: (i) regulating the capacitor voltages at the inverter input to a reference provided by the MPPT block to achieve maximum power, (ii) satisfying the power factor correction (PFC) requirement, (iii) balanced power exchange by regulating the two capacitor voltages at the inverter input to the same voltage value. The controller includes three control loops, namely, the inner current tracking loop designed with the integral sliding mode approach, the outer voltage regulation loop designed with the filtered PI controller, and the voltage balance loop designed with the PI controller. The performance, efficiency, and robustness of the proposed control strategies with respect to climate change are demonstrated through simulation in the Matlab/Simulink environment.