Improved discrete current controller for grid-connected voltage source converters in distorted grids

This paper deals with improvements to the classical Proportional-Integral (PI) current controller for Voltage Source Converter (VSC) connected to a grid in the presence of harmonics. A discrete PI current controller implemented in the synchronous reference-frame has simple design procedure and robust performance in ideal grid conditions. However, low-order harmonics in the connecting grid will result in a steady state harmonic current flow between the converter and the grid. A method based on harmonic estimation to avoid the steady state harmonic injection to the grid will be discussed. The effectiveness of the described control method will be validated through simulation and experimental verification.