Turning Off Control Strategy for IGCT-LCC Based on Valve Current Changing Rate Detection

Thyristors play a crucial role in ultra high voltage direct current (UHVDC) transmission projects by being used to build converter valves. However, due to their semi-controlled nature, thyristors can only control conduction and lack the ability to control shutdown, resulting in inherent issues such as commutation failure that can pose risks to the safe and stable operation of the power system. Addressing this challenge, the paper proposes a turn off control strategy for the LCC converter valve based on a controllable shut-off device called the reverse blocking integrated gate commutated thyristor (RB-IGCT). This strategy takes into account factors such as device shut-off capability, maximum commutation angle, valve current changing rate, upcoming commutation valve conduction state, and bypass valve conduction state, fully leveraging the control dimension of IGCT device controllable shut-off. The strategy offers reasonable control instructions for the operating status of the converter valve. The simulation is carried out in PSCAD/EMTDC and the results validate the feasibility and effectiveness of the proposed turning off control strategy.