A New Perspective for Frequency and DC Voltage Stability Comprehension in Two-Terminal VSC-HVDC Systems With Virtual Inertia Control

—This letter proposes a new perspective for the interactive stability mechanism between frequency and dc voltage in a voltage-source converter-based high-voltage direct current (VSC-HVDC) system with virtual inertia control. The system model is first established, providing a new physical insight into dc voltage and frequency stability. It is found that the frequency instability may be caused by the control loop of virtual inertia or the oscillation transfer of dc voltage. Similarly, the dc voltage oscillation can be induced by the inappropriate design of dc voltage control loop or the transfer of the frequency. The complex oscillation coupling mechanism as well as the oscillation transfer essence is clarified physically. Finally, the correctness as well as the feasibility of the theoretical analysis is verified by the hardware-in-loop experiment.