A Simulation-Aided LCL Filter Design for Grid-Interactive Three-Phase Photovoltaic Inverters

Abstract

Photovoltaic (PV) inverters, as the key technology for integrating PVs into the grid, are increasingly gaining importance. They are manufactured from a few kW for a single inverter to tens of kW for a number of inverters operating in parallel. The two-level three-phase topology is the basic topology for such inverters. It produces lots of harmonics which necessitates significant suppressions prior to be connected to the grid. The LCL filter is known as an effective topology in significantly attenuating harmonics with small filter components. In this paper, we propose a simulation-aided design for the LCL filter to be employed in grid-interactive PV inverters. Starting from some initial values for the filter parameters, the proposed approach imposes analytical as well as simulation constraints. Simulations, performed in Matlab/Simulink, are repeated as long as the Total Harmonics Distortions (THD) in the injected current to grid reaches its limit, i.e. THD =5%. As a design goal, attempts are made to reduce inductors' sizes, since they are voluminous and sources for Electromagnetic Interferences (EMI).Simulations are provided both for the inverter mode in which some active power is injected to the grid and for the active rectifier mode in which some active power is absorbed from the grid.