Coordinated FRT Control for Paralleled Grid-Forming Converters with Enhanced Transient Stability and Current Control Flexibility

Grid-Forming converters (GFMs) are faced with the threat of inrush current and sever transient instability issues during grid faults, which calls for fault ride through (FRT) capability. Several FRT control strategies are proposed for single GFM connected to grid system in existing literatures while transient interaction mechanism among paralleled GFMs still remain unrevealed and corresponding FRT control are rarely discussed. To fill this gap, coordinated FRT control based on mode-switching is proposed for paralleled GFMs in this paper. The proposed FRT control would turn GFMs into current control mode during grid fault periods and return to voltage control mode after fault clearance, which enables current control flexibility during grid fault. To guarantee stable operation throughout fault period, transient interaction models in current control mode and voltage control mode are established respectively. Then, design-oriented transient stability analysis is carried out using equal area criterion (EAC) theory. Finally, detailed simulation results based on PSCAD/EMTDC and experimental results are provided to validate the effectiveness of proposed method.