Novel Controllable-Line-Commutated Converter for Eliminating Commutation Failures of LCC-HVDC System

To entirely eliminate commutation failure (CF) in conventional line-commutated converter based high-voltage direct current (LCC-HVDC) transmission system, a novel controllable line-commutated converter (CLCC) based on the combination of partially and fully controllable semiconductor devices is presented in this paper. The operating principle of CLCC and its control strategy are proposed. In addition, the voltage and current stress are analyzed. To verify correction and application of presented CLCC solution to the project, a CLCC-HVDC system model, adopting LCC at the rectifier side and CLCC at the inverter side, is developed in PSCAD/EMTDC software. Based on the model, the transient responses of the CLCC-HVDC system under various AC faults are simulated and compared with the pure LCC-HVDC. Simulation results show that the presented CLCC topology and its control strategy can not only eliminate CFs in various types of AC faults, but also improve the transient performance of the system after faults, while inheriting the attributes of traditional LCC such as large capacity, low cost and almost the same system control strategy. This is quite positive and meaningful for application of the CLCC-HVDC to multi-DC infeed system particularly.