An Evolutional Line-Commutated Converter Integrated With Thyristor-Based Full-Bridge Module to Mitigate the Commutation Failure

With thyristor-based full-bridge module (TFBM) embedded in the converter valve, an evolutional line-commutated converter (ELCC) is proposed to enhance the commutation failure (CF) immunity. The operating principle of the TFBM and the coordinated control strategy between the TFBM and series-connected valve are presented. The voltage-current stress of the TFBM is analyzed, and the method to select the capacitor parameter is also presented. Then, the ELCC high-voltage direct current (HVDC) under the presented control strategy is developed in PSCAD/EMTDC, and its dynamic responses under ac fault condition are compared with that of capacitor-commutated converter-based HVDC (CCC-HVDC) and conventional line-commutated converter (LCC) HVDC. A dual-infeed HVDC system with TFBM embedded in one HVDC link is also developed to further investigate the merits of TFBM. Finally, the increased capital cost and power loss of the ELCC-HVDC are discussed. The results show that the presented ELCC-HVDC has the ability to reduce the CF risk effectively and also exhibits favorable steady-state and dynamic performances.