Research on Zero-Sequence Transfer Suppression in Non-isolated Medium Voltage Flexible DC Interconnected System

In order to realize the fault ride-through of non-isolated medium-voltage flexible-direct interconnected system under single-phase-to-ground fault, the fault characteristics and the generation and transmission mechanism of zero-sequence component are analyzed: the zero-sequence component generated by the fault side will be transmitted to the non-fault network through the DC side, resulting in voltage imbalance in the non-fault network. Aiming at the shortcomings of other suppression strategies, such as low economy and complex control, this paper proposes a method to suppress the fluctuation of DC bus voltage by configuring a series compensation circuit on the DC side. The corresponding control algorithm is designed to suppress the transmission of zero-sequence components and ensure the voltage balance of non-fault network. Finally, the simulation model is established in Matlab/Simulink to verify the theoretical analysis and the proposed fault control.