A novel controller for harmonics reduction of grid-tied converters in unbalanced networks

This paper proposes a novel controller for a grid-tied converter interfaced to a network with unbalanced voltage conditions. Due to the influence of negative sequence voltage and current components created by unbalanced voltages, conventional PI controller alone cannot adequately deal with the fluctuations in active and reactive powers generated from converters. In order to overcome this inadequacy, a systematic and comprehensive controller, namely Linear Parameter Varying (LPV) controller is designed and presented in this work. The proposed LPV controller is implemented using the well-known voltage oriented control (VOC) approach. The unbalanced network voltages are first decomposed using a signal delay technique with the support of Clarke's transformation in order to filter out the negative sequence components. An enhanced phase-locked loop (ePLL) is then developed to reduce the higher-order harmonics. The feasibility of the proposed controller and the effectiveness of ePLL are verified by experimental studies.