Analytical Switching Modelling Method of Grid-Connected Converters for Transient Stability Analysis

In recent years, grid-connected power electronic converters have had a continuously increasing influence on dynamics of bulk power systems. Consequently, modelling of power electronic converters has become critical to modern power system stability studies. However, few existing studies can systematically model switching control characteristics or handle discontinuous state variables of power electronic converters. To address these limitations, this article proposes a general four-step analytical switching modelling method of grid-connected converters, which involves formulating holonomic differential-algebraic equations of the converter including all switching actions, transforming all state-dependent switching conditions into time-dependent ones, deriving differential equations of the system for all time periods, and analyzing the continuity of each state variable at all switching moments. An example model is established and then evaluated through detailed simulations to verify the effectiveness of the proposed modelling method. The revealed switching-induced transient instability mechanism and corresponding stability enhancement method based on the example model demonstrate the practicality of the proposed method and emphasize the importance of considering switching characteristics in analytical modelling of power electronic converters.