A fast and robust closed-loop photovoltaic MPPT approach based on sliding mode techniques

This article presents a closed-loop Maximum Power Point Tracking (MPPT) method for a photovoltaic (PV) system that includes a PV array, a DC-DC converter and a DC bus. The proposal consists of a controller and two observers developed into the sliding mode (SM) theoretical framework. The converter switching signal is driven by an Integral First-Order Sliding Mode (IFOSM) controller whose input corresponds to the PV power gradient estimation. This estimation is obtained through a pair of Second Order Sliding Mode Observers (SOSM). The first one corresponds to a Levant's differentiator which estimates the first-time derivative of the PV voltage and feds a specific SOSM which delivers the PV power gradient estimation. These kinds of observers converge in finite time even in the presence of unmodeled dynamics and external perturbations. The proposed structure permits to synthesise a whole MPPT closed-loop system with a fast-tracking dynamics, a moderate computational burden and a reduced hardware cost, requiring only two variable measurements. This approach, simplifies the controller design and the system start-up, which does not need any specific initial conditions to be started from. The system performance is evaluated using representative computer simulations with standardised radiation and temperature profiles and corroborated through experimental tests. Finally, the proposal capabilities to work under partial shading conditions are also evaluated.