An Improved Extinction Angle Control Strategy to Mitigate Continuous Commutation Failure for HVDC system with hierarchical connection

摘要

When the hierarchical connection mode is adopted, the high-end and low-end inverters of HVDC system may occur commutation failure at the same time, which will interrupt the transmission power of the system instantaneously, weaken advantages of hierarchical connection system, and affect the stability of system. This paper proposed an improved extinction angle control strategy based on DC current variation. The dynamic fluctuation characteristics of DC current during fault and recovery process is fully utilized. Based on the DC current variation, improved extinction angle controller quickly increases the extinction angle, reduces the commutation failure and facilitates the recovery of system. This control method does not need to detect receiving end AC faults to mitigate commutation failure, so there is no detection delay. Moreover, no additional investment such as reactive power compensation device is required.