Attenuation of voltage distortion effects on a Three-Phase Grid-Connected converter

The paper reports the power quality improvement of a grid-connected three-phase voltage source converter (VSC) aimed at interfacing electrochemical energy storage to the power system. Two control algorithms have been synthesized and experimentally validated, considering an LCL-filter VSC that implements a current feedback control on a synchronous reference frame. The comparison between a proportional-integral (PI) controller with a hybrid one, characterised by the joining of PI and resonant (R) controllers, specifically designed for reducing the effects of fifth and seventh voltage harmonics, has been performed. The PI-R controller outcomes show a significant improvement concerning PI one regarding the total harmonic distortion of the injected converter current for output power values lower than the 30% of rated one. This solution permits the extension of the lower power limit for which the current total harmonic distortion is lower than 5%, till to 18%. Therefore, the hybrid PI-R controller results are suitable for those applications, such as the energy storage system, requiring power quality in an ample range of working operative conditions.