Full-Feedforward Schemes of Grid Voltages for a Three-Phase $LCL$-Type Grid-Connected Inverter

Abstract

This paper investigates the feedforward schemes of grid voltages for a three-phase <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -type grid-connected inverter. The full-feedforward functions of grid voltages are derived for the stationary α- β frame, synchronous <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> frame, and decoupled synchronous <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> frame-controlled three-phase <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -type grid-connected inverters. The derived full-feedforward functions mainly consist of three parts which are proportional, derivative, and second derivative parts. The use of the traditional proportional feedforward function in the three-phase <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> -type grid-connected inverter will result in the amplification of the high-frequency injected grid current harmonics. With the proposed full-feedforward schemes, the injected grid current harmonics and unbalance caused by grid voltages can be greatly reduced. The effectiveness of the proposed feedforward schemes is verified by the experimental results.