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

Abstract

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° 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.