Comparison of control strategies for grid-connected photovoltaic systems during unbalanced voltage dips

Unbalanced voltage dips are common disturbances in power systems. Therefore, grid-connected photovoltaic systems need to be able to work during these disturbances. Conventional control strategies do not consider the negative sequence current control, which is an important limitation. In this context, this paper compares through simulations four strategies of negative sequence current control: Notch filter based strategy, measured signals decoupling based strategy, reference and error signals decoupling based strategy and resonant controllers based strategy. All simulations are performed in Matlab/Simulink environment. Representation of point of common coupling voltage (PCC) uses experimental data of an unbalanced voltage sag. Comparisons during unbalanced voltage sags and the impact of voltage harmonics on techniques are analyzed. Obtained results shows resonant controllers based strategy has a superior behavior, in terms of robustness and simplicity.