Low-Frequency Oscillation Analysis of VSM-Based VSC-HVDC Systems Based on the Five-Dimensional Impedance Stability Criterion

Virtual synchronous machine (VSM) based high voltage dc systems enhance the inertia of power system. However, dynamic interactions between VSM-based rectifier station, inverter and grid could induce system oscillation, which has been investigated in this article. At first, hybrid ac–dc impedance models VSMs considering coupling ac dynamics are established. Then, relationships impedance, dq -frame presented. It is found that station d-d channel behave as negative resistors low-frequency range. Moreover, a five-dimensional stability criterion on generalized inverse Nyquist proposed to assess stability. The analysis results show oscillation occurs when short-circuit ratio small. Finally, simulation experimental verify criterion.