Transient Stability Analysis of Grid-Forming Converters During Presynchronization Process in Islanded Mode

Power synchronization control (PSC) is usually used for power distribution and grid synchronization of grid-forming converters. Yet, the sequential startup of PSC for paralleled converters will cause an active power mismatch between converters and load, and then induce the synchronization stability issue. To address this problem, the transient model for grid-forming converter is proposed to elaborate the synchronization interaction among paralleled converters in the islanded mode, and the parameter boundary, including droop coefficients, power reference, and load power is analyzed in detail, etc. The mechanism of transient synchronization instability is revealed and the dynamic behaviors of paralleled converters are described by phase portraits. Then the controller parameters are designed for the converter which waits for pre-synchronization and the effects of power controller parameters on the transient synchronization stability is discussed. Finally, experimental results are provided to verify the correctness of the theoretical analysis.