A Suppression Method of Commutation Failure in LCC-UHVDC Systems Based on the Dynamic Tracking of the Turn-Off Angle Setting Value

Commutation failure is still one of the most common faults in LCC-UHVDC (line commutated converter-based, ultra-high voltage direct current) systems, and if the inverter side, extinction angle, and rectification value remain constant during the fault, it may lead to commutation failure or even continuous commutation failure. Therefore, this paper first analyzes the structure of the LCC-UHVDC system and the mechanism of commutation failure and, on this basis, proposes a commutation failure suppression method based on dynamic tracking of the extinction angle rectification value. The desired DC voltage of the system under fault conditions is calculated based on key state quantities such as the AC voltage RMS value, the extinction angle, and the leading angle during the fault process. The compensation amount is obtained by comparing the desired DC voltage with the actual DC voltage and superimposition on the extinction angle rectification value in the inverter extinction angle control. When there is a risk of commutation failure, dynamically adjusting the extinction angle setting value according to the compensation value is beneficial for the rapid and stable recovery of the extinction angle, reducing the probability of commutation failure. A bipolar neutral ground LCC-UHVDC testing model system is established in PSCAD/EMTDC for simulation verification to show that the proposed improved control strategy effectively reduces the probability of commutation failure and significantly improves the stable operation characteristics of the LCC-UHVDC system.