Wideband Oscillation Mechanism Analysis in VSC-HVDC Systems With Virtual Synchronous Machine in Master-Slave Mode

Virtual synchronous machine (VSM) has been applied in voltage source converter high voltage direct current (VSC-HVDC) system. This paper proposes a stability evaluation model for ‘rate of change of frequency-transient frequency excursion’ as well as ‘rate of change of voltage-transient voltage excursion’ for clarifying the physical essence of instability of the DC voltage and AC frequency in the VSC-HVDC system with virtual synchronous machines. The proposed model framework can help understanding the mechanism and physical significance of wideband oscillation in VSC-HVDC systems. In addition, a comprehensive analysis is developed for wideband oscillations and loss of synchronization in VSC-HVDC system. It is found that the grid stiffness impacts the wideband oscillation and loss of synchronization stability simultaneously, where it is also demonstrated by simulations. Finally, the theoretical analysis is validated by simulations.