Grid Integration of Photovoltaic System based on An LLC Resonant DC-DC Converter

Abstract

The paper presents a grid-connected photovoltaic array system that converts solar energy to the unity grid using two stages topology consists of an LLC resonant DC-DC converter and a voltage source converter VSC. The emphasis in this work is particularly given to the design procedure of the LLC resonant DC-DC converter and VSC parameters, which is to be more suitable for the grid connection. For maximum power point tracking MPPT,  Perturb & Observe and the Incremental Conductance algorithms are considered for the PV array system. Whereas these algorithms are individually applied to the resonant converter, and their performances are analyzed and matched under different operation conditions. The PI control in this work is achieved depending on a voltage controlled oscillator VCO method and then integrated with both of the MPPT algorithms to carry out the maximum power extraction. The VSC is utilized to connect the grid in which it can regulate the output voltage of the resonant DC-DC converter at the DC link, and also it is used to convert the solar energy to the AC grid side at the unity power factor. A simulation model of the presented topology having a 20-kW solar array is designed and built in Matlab/Simulink environment. It includes a full-bridge LLC resonant DC-DC converter and three-level VSC. The simulation results are obtained to show the validity and effectiveness of modeled topology. Also, the performance of this model based on both of the MPPT algorithms is analyzed while connected to the grid under different operating of sun irradiations.