Comparative study of small-signal stability under weak AC system integration for different VSCs

Voltage source converters (VSCs) with self-commutation ability are suitable to interconnect weak AC systems. This paper conducts a comparative study of the small-signal stability characteristics for three typical VSCs, namely, the two-level VSCs (TL-VSCs), the half-bridge modular multilevel converters (HB-MMCs) and the hybrid MMCs (HY-MMCs),underweak AC system integration with special consideration on both inverter and rectifier operation. The frequency responses based on impedance models are compared using the frequency-domain analysis. The oscillation frequencies and mainly participated state variables of the unstable modes are compared using root locus and participation factor analysis in time-domain. Proper parameter retuning approaches for stability enhancement are proposed. The above analysis is adequately validated by electromagnetic simulations