HB-MMC Converter Loss Minimization by Applying a Flexible Volt-age Security Margin using On-Load-Tap-Changers

Abstract:
HVDC systems are increasingly becoming an important component for modern sustainable and emission free energy systems because of their controllability, flexibility and their capability of transmitting bulk power with low power losses over long distances. However, because of the high power ratings of HVDC systems even small increases in efficiency can have a significant impact on the economic and ecological operation of the system. Therefore, this paper introduces an approach using the on-load-tap-changer transformer to minimize losses of the most common half-bridge MMC-con-verter technology that can also be applied to existing systems. Besides an introduction and discussion of the novel ap-proach, a proof of concept based on a numerical case study has been carried out to quantify the loss minimization potential under various grid conditions. The results show that the potential to reduce power losses using the OLTC can be signifi-cant.