An alternative proposal for HVDC transmission systems using 24-pulse AC/DC converters based on three-winding non-conventional transformers

摘要

In order to promote savings on installed filters in traditional HVDC transmission systems, and thus provide a less polluted power quality, this paper proposes a 24-pulse controlled converter that uses two identical three-phase three-winding special transformers, as well as four thyristor-controlled 6-pulse AC/DC converters connected in series. The configuration of the two transformers, and the necessary tap calculations are presented in order to achieve the 7.5 degrees phase lag required to obtain the 24-pulse converter system. An analysis of the performance indices (power factor and Total Harmonic Distortion - THD) of both HVDC systems (traditional 12-pulse and the proposed 24-pulse) is performed and the results show improvements in the indices when using the proposed 24-pulse system. Simulation analysis was performed using Matlab/Simulink software in order to validate the proposed 24-pulse converter for use in HVDC transmission systems, considering the operationality of the proposed system under normal and degraded operating conditions. A laboratory prototype was designed and executed based on transformers with extended delta primary windings to validate the proposed 24-pulse converter in terms of harmonic mitigation and improved power quality. The results confirm the viability and applicability of the proposed converter in HVDC transmission systems.