Control Strategy Design of PV Grid-Connected System Based on Equivalent Input Disturbance

Abstract

The output power quality of three-phase two-stage photovoltaic (PV) grid-connected system is directly determined by the controlled performance of LCL-type inverter. However, the disturbance caused by dead time effect reduces the output power quality, even leads to system instability. In addition, the strong coupling terms and inherent resonance of LCL-filter also pose the system performance. In this paper, an equivalent input disturbance (EID)-based two degrees of freedom current control strategy is proposed to damp dead time effect and inherent resonance for PV grid-connected system. Firstly, the modified model by taking the coupling terms and the disturbance caused by the dead time effect as a lumped disturbance. Then an EID-based current controller is designed, and its stability analysis and implementation method are given. The proposed current controller realizes the model decoupling, active damping and comprehensive disturbance rejection. Without dead time, the THD value is 0.54%. With the increase of the dead time, the THD value is always lower than 2%.