Study on Single Valve Turn-off Test Method of Controllable Line-commutated Converter

The controllable line-commutated converter (CLCC) not only inherits the advantages of large capacity, low loss, and high overload capacity of traditional line commutated converter (LCC), but also has the ability to shut off the bridge arm actively, which can fundamentally prevent commutation failure. In June 2023, the CLCC valves were successfully applied in the ±500 kV/1 200 A Genan DC renovation project, and since operation the operating characteristics have been good. The ability of turning off high current for the CLCC valve determines whether it can successfully withstand commutation failure in the event of AC faults. Therefore, it is necessary to carry out a single valve large current turn-off test to verify the synchronous turn-on and turn-off consistency and the transient electrical stress tolerance level of more than 100 controllable devices in the CLCC valves under AC failure. Based on the principle of forced commutation process in the case of AC failure of CLCC valves, this paper firstly analyzes the key stress of IGBT sub-valve during the main-auxiliary branch transfer and bridge arm forced shutdown process, and extracts the key stress parameters in each stage. Secondly, using hundred-millisecond back-off and isolation control method of the hundred-kV supplementary AC voltage source and LC resonant current source, a high current turn-off test device for single CLCC valve is developed, the analytical relationship between key stress parameters and test circuit parameters is established, and the parameters of the test device are designed. A large current turn-off test platform for a single ±500 kV/1 200 A CLCC valve was built to evaluate the working capability of the CLCC valves, and the equivalence and correctness of this method were verified through comparison between experiments and simulation. The method can also provide theoretical guidance for the subsequent single valve turn-off test of CLCC valves with different voltage levels. © 2024 Chin.Soc.for Elec.Eng.