Stability analysis of dual infeed VSCs integrated to weak ac system

The small signal stability of parallel connected VSCs integrated to a weak ac system is affected by main circuit and control system parameters. The small signal method is used to analyze the dual parallel integrated VSC system. First, based on the small signal model and participation factor analysis, the critical factor to the system stability is carried out. Second, three different parallel connected VSC scenarios are investigated. The relationship between system parameters and stability is analyzed. Simulations and calculations validated the following two conclusions: 1) all the small signal modes of parallel connected VSCs are interaction modes, both the main circuit and control parameters have impact on the system stability; 2) electrical distance show different effects on VSC connected to a single ac system or parallel ac systems, the phase angle difference between parallel ac systems shows a negative effect on system stability.