Phase locked loop-free sliding-mode-based power control for grid-connected voltage-sourced inverters under unbalanced network conditions

Abstract

In this paper, a phase locked loop-free power control method is presented for grid-connected voltage-sourced inverters under unbalanced network conditions. The main advantages of the proposed technique are low implementation cost and simplicity of the control strategy. These advantages are achieved through elimination of phase locked loop (PLL) function by the proposed compensation strategy. Phase locked loop functions are considered as an expensive part of a system. Hence, PLL elimination leads to simpler implementation of the power control as well as reduction of the system cost. The proposed power control method is based on modification of normal sliding mode power control using compensation feedbacks for active and reactive powers. Two scenarios including unbalanced angles for three phase voltages and nonidentical voltage amplitudes are considered for unbalanced network conditions. The performance of the modified sliding mode control (SMC) in the mentioned unbalanced conditions is evaluated using simulations in MATLAB/Simulink. The results confirm that the proposed technique reduces the pulsations of active and reactive powers considerably in comparison with the normal SMC strategy.