Power Decoupling of an AC-Side Voltage Sensorless Three-Phase Converter Under Unbalanced Grid Conditions

In order to support the grid, it is desirable for distributed generation systems to remain operational during grid faults. However, under such scenarios, existing methods for grid current injection do not guarantee the absence of power pulsations on the dc-bus. To address this issue, this work proposes a power decoupling strategy for an ac-side, LCL-filtered, grid-tied dc-ac three-phase converter under unbalanced grid conditions. The strategy suppresses second harmonic power ripple on the dc-bus during grid fault conditions, regardless of the grid power injection method employed, thereby expanding the operating capabilities of the converter. The nonlinear zero-sequence model of the system is linearized using the exact feedback-linearization technique. Experimental and simulation corroborates the validity and effectiveness of the proposal.