An adaptive sliding mode control technique applied in grid-connected PV system with reduced chattering effect

This work proposes an improved ac-side control for a three phase, three level neutral point clamp (NPC) inverter for grid-connected photovoltaic (PV) system using the adaptive sliding mode controllers (ASMC). The aim is to reduce the chattering effect that arises when utilizing conventional sliding mode controllers (SMC). This is achieved by introducing the adaptation laws that allow the controllers gains to be self-tuned towards their optimum values. Furthermore, the discontinuous signum function is replaced by continuous functions in the controller structure. To verify the proposed control scheme, a grid-connected PV system which comprises of a 4.6 kW PV generator, a dc/dc boost converter, a three-level NPC voltage source inverter (VSI) and an R-L filter is considered for simulation using Matlab/Simulink. The ac-side control unit includes: an outer dc bus voltage controller, an inner grid current controller and a phase angle estimator. The simulation results shows that total harmonic distortion (THD) of the grid current is reduced by 28%, while the steady state error using the ASMC-based phase angle estimator is practically brought down to zero.