Damping techniques for grid-connected voltage source converters based on LCL filter: An overview

Distributed generation systems have been expanded considerably in recent years. These systems are generally based on power electronics converters, whose switching harmonics need to be reduced by means of passive filters. LCL filter is a solution that has been strongly employed. However, LCL filter presents a resonant frequency that needs to be damped. This work presents a detailed review on the topics involving the mathematical modeling and design of the main structures and strategies for damping in a grid-connected three-phase PV system based on LCL filter. Four techniques are analyzed: Series passive damping (SPD), capacitor current feedback based strategy (CCF), capacitor voltage feedback based strategy (CVF) and notch filter based method (NF). This study analyzes low frequency models, control design and operation in weak grid conditions. Finally, transfer functions of the harmonic rejection capability of each damping strategy are illustrated. This work finishes with a case study of a 10 kW inverter, which evaluates all issues previously approached.