A Direct Current-Synchronization Control for Voltage Source Converter With Enhanced Fault Ride-Through Capability

For grid-forming (GFM) controlled voltage-source converters (VSCs), there is a challenge in addressing their fault ride-through (FRT) capability under large grid disturbances. Specifically, the challenge lies in achieving rapid and robust synchronization with the faulted grid while effectively limiting the fault current. To address this, this article proposes a direct current-synchronization control (DCSC) scheme in the converter synchronous reference frame, which directly regulates the VSC current for synchronization. The validity of DCSC is substantiated by analyzing the relationship between the VSC current and phase angle, where power serves as an intermediate variable. The analytical solution for the steady-state stability boundary of the DCSC-based VSC-grid system under fault conditions is derived, which demonstrates the enhanced synchronization stability of DCSC compared to the conventional power-balance-based synchronization (PBBS) after large grid disturbances. The stability boundary of DCSC under fault conditions exhibits a voltage-magnitude-independent characteristic, resulting in a wider power angle boundary. Furthermore, this stability boundary can be translated to determine the stable operating range of the power reference ratio so that a consistently stable DCSC-based VSC-grid system can be assured under fault conditions. To increase the dynamic synchronization speed after faults, a control gain self-adaptability (CGSA) approach is introduced into the DCSC scheme. The experimental results validate the theoretical findings, affirming the effectiveness of the proposed control scheme.