Protected control method for Voltage Source Converter (VSC) in AC/DC hybrid grid under grid unbalanced faults

In AC/DC hybrid grid, the individual AC and DC grids exist. The power converters are the key power conversation interfaces between these two kinds of individual grids. Under unbalanced AC grids, the grid voltage is distorted and the harmonics is introduced. Therefore, the active and reactive power also give rise to the uncontrolled oscillations, which may damage the interface converters. In order to ensure the safety of the converters and the facilities in the grids, a proper control strategy is crucial for AC/DC hybrid grid. In this paper, the current harmonic for VSC is theoretically analyzed under unbalanced condition, furthermore methods to separate the positive- and negative- sequence components of grid voltages are summed up and analyzed. Based on the theoretical analysis, the different grid-connected converter protected control methods are analyzed and compared, and a new control method which can control the oscillations of active and reactive power by parameter k, has been proposed. Finally, the experimental results verified the validity and advantages of this proposed method.