Asymmetrical Fault Ride-Through and Power Oscillation Characterization for Grid-Tied Voltage Source Converters

As the number of converter-interfaced distributed energy resources connected to the power system continues to increase rapidly, recent grid codes require these grid-tied converters to maintain grid connection during faults to ensure power supply security and reliability. In this work, we analyze the oscillation in the injected real and reactive power that a grid-tied voltage source converter (VSC) introduces as it attempts to contribute to the power quality and improve the voltage at the point of common coupling (PCC) during an asymmetrical fault. We propose a new double sequence current reference generation method that can be utilized to derive a closed-form quantification of the peak value of both the real and reactive power oscillation during asymmetrical fault ride-through (AFRT) analytically. The effect of the resulting bus voltage oscillation and ripple current requirement at twice the grid frequency, corresponding to the real power oscillation, on the input DC bus capacitor and upstream converter is analyzed for facilitating system component sizing. Furthermore, the proposed current reference generation formulation helps control the negative-sequence current injection during fault to assist with fault identification. The theoretical analysis is validated through simulation in PLECS for both asymmetrical and symmetrical fault scenarios. Experimental results for a three-phase, grid-tied VSC operating under both asymmetrical and symmetrical faults are provided to evaluate the performance of the proposed current reference generation method and validate the analysis presented