Revealing the mechanism of subsynchronous torsional interaction caused by LCC-HVDC from the perspective of vector synchronization

Abstract

Line-commutated converter-based high voltage direct current transmission (LCC-HVDC) has been widely applied worldwide due to its great advantages in realizing long-distance and large-capacity power transmission. However, it may also lead to instability problems, including subsynchronous torsional interaction (SSTI). This destructive phenomenon greatly threatens the safe and stable operation of power systems and has been widely concerned since the 1970 s. Existing literature has found that SSTI is caused by DC current control of rectifier station. However, the physical mechanism of this phenomenon has not been clarified clearly, which hampers further understanding of how negative damping is generated and whether it is evitable. To fill this gap, the physical process of SSTI caused by LCC-HVDC is clarified through the perspective of vector synchronization. Based on this, the negative damping mechanism is revealed. The influence of control on damping is also studied with the contribution of different control loops quantified. All results are verified through time-domain simulations and damping torque analysis.

Keywords

• LCC-HVDC
• Synchronous generator (SG)
• SSTI
• Vector
• Synchronization
• Mechanism