Fixed Angle Difference Control for Multi-Converter Grid-Connected System to Improve Transient Stability During Grid Faults

Multi-converter grid-connected system is prone to transient instability under grid faults, due to the complex interaction between voltage source converters (VSCs). However, existing research has primarily focused on analyzing the impact of the interaction on the transient stability of multi-converter grid-connected system, without proposing methods for eliminating the interaction. To fill this gap, the mathematical model of two-converter grid-connected system under grid faults is firstly established. Then, the interaction between VSCs is analyzed, it is found that changing the output angle difference between two phase-locked loops (PLLs) will affect the interaction. Based on it, a transient stability enhancement control method is proposed to eliminate the interaction between two VSCs, by fixing the output angle difference between PLLs. Finally, simulation results validate the theoretical analysis and proposed method.