Active Compensation of Unbalanced Load Currents in Grid Connected Voltage Source Converters

For a 2-level 3-phase voltage source converter connected to the grid, it should be capable of supporting the grid with maximum possible active and reactive power during balanced and unbalanced load condition. This paper discusses about the unbalanced current injection algorithm from a VSC to keep the grid currents balanced and sinusoidal in case of asymmetrical loading conditions. Positive and negative sequence synchronous reference frame control have been used to filter the unbalanced component in the grid currents and to compensate it from the converter. A case study with unbalanced reactive load has been simulated to verify the algorithm and the effect of compensation. The compensation reduces the asymmetry in PCC voltage and grid currents, and makes it close to sinusoidal shape to keep it within a standard limit of unbalance in grid power quality.