Commutation failure suppression strategy of hybrid DC transmission based on active current limiting

Abstract

Aiming at the problem of large inrush current when the commutation fails in the hybrid direct current (DC) transmission system,the relationship between the inrush current amplitude and the voltage source converter (VSC) is firstly derived. The number of submodule invested by VSC is a key parameter to determine the inrush current when the commutation fails. Then,the main factors affecting the commutation capability of the line commutated converter (LCC) are studied,and a commutation failure suppression strategy based on active current limiting is proposed. The DC disturbance amount and the accurate current (AC) disturbance coefficient are added to the VSC modulation wave,thereby changing the switching mode of the submodule and suppressing the peak value and rising speed of the commutation failure impulse current. Finally,the simulation model of the hybrid DC transmission system at both ends is built in Matlab/Simulink to verify the effectiveness of the proposed strategy in the event of different degrees of voltage drop faults on the AC side of the inverter station. The results show that the proposed strategy limits the inrush current and reduces the current stress of the bridge arm,thus effectively preventing continuous commutation failure.

Keywords

• hybrid direct current (dc) transmission
• commutation failure
• line commutated converter (lcc)
• modular multilevel converter (mmc)
• active current limiting
• nearest level modulation