Sensorless Integral Sliding Mode Control of Single-Phase Grid-Connected PV System

This paper presents a grid-connected photovoltaic (PV) system. The conversion scheme consists of a three-level boost converter (TLBC), a half-bridge inverter (HBI), and an LCL filter to adapt the PV energy and inject it into the grid with low total harmonic distortion (THD) and unity power factor (PF). This study aims to achieve four main objectives: i) Ensure maximum available PV power with high robustness against environmental variations, ii) Guarantee PF correction (PFC) where the output current must have a sinusoidal waveform in phase with the grid voltage, iii) Regulate the DC link voltage to follow a defined reference, iv) Ensure balance between TLBC output voltages. To achieve the mentioned objectives, a nonlinear controller based on the integral sliding mode approach (ISM) is developed. In addition, a Kalman observer is designed to estimate the PV voltage and current in order to reduce the number of physical sensors and thus the cost and space of the studied system. Then, based on the PV current and voltage estimated by the designed observer, a sensorless maximum power point tracker (MPPT) based on the INC & COND algorithm is implemented to extract the maximum PV power despite changing weather conditions. Simulation results were performed in the Matlab/Simulink/SimPowerSystems environment to evaluate the proposed control strategy and observer. These results demonstrate that the proposed controller and observer achieve the set objectives under standard and changing climate conditions.