Integral sliding mode-improved adaptive MPPT control scheme for suppressing grid current harmonics for PV system

摘要

This study proposes a new control scheme for grid integration of a three-phase two-stage photovoltaic (PV) system by employing an integral sliding mode current control loop and an improved adaptive maximum power point tracking (MPPT) algorithm. Integral sliding mode control (ISMC) offers fast control action and is insensitive to plant parametric uncertainties. In a grid-connected PV system, ISMC suffers from steady-state error in tracking reference grid current signal due to disturbances in the dc-link voltage caused by the MPPT. To improve the performance of the ISMC, the authors propose a direct duty ratio control-based variable step size perturb and observe (P&O) MPPT algorithm for reducing the oscillations in the dc-link voltage. The efficacy of the proposed control scheme is verified by first simulating it using MATLAB/Simulink and then through real-time implementation on a prototype PV control setup. To evaluate the performance of this ISMC-improved adaptive P&O-based controller, its performance is compared with Lagrangian interpolation-based particle swarm optimisation MPPT, sliding mode controller and proportional-integral controller. From the comparison, it is observed that the former exhibits superior performance and suppresses the harmonic content in the grid current despite the presence of low-order harmonics in the utility grid voltage.