Sensorless nonlinear control of flying capacitor multilevel inverter based grid-tied Photovoltaic system with an LCL filter

Abstract

This paper presents a control strategy for a single stage grid-connected photovoltaic (PV) system based on a flying capacitor multicellular inverter (FCMI) and an LCL filter. The proposed controller is designed to deal with two main objectives: (i) ensure power factor correction (PFC) and guarantee a balanced input DC voltage distribution; (ii) ensure maximum power extraction from PV panels despite climate changes and control the DC bus voltage. The proposed sensorless nonlinear controller consists of two cascaded loops: (i) an outer loop is based on a filtered proportional integral regulator for the PV panels voltage regulation, and (ii) an inner loop is developed using the Lyapunov and integral backstepping approaches for the PFC and flying capacitors voltage regulation. Additionally, a state observer is combined with the regulator to achieve the grid voltage estimation. The performances of the advanced power system and control approach are validated through numerical simulations, using MATLAB/Simulink environment under varying climatic conditions.