A DRU-MMC Hybrid HVDC Transmission System Based on Flexible Transformer

This paper proposes a hybrid HVDC transmission system using the diode rectifier unit (DRU) at the sending end and the voltage source converter (VSC) at the receiving end. To solve the problem of the lack of regulation capability in the converter station at the sending end, a scheme is proposed to replace traditional converter transformers with flexible transformers at the sending end based on the operating characteristics of diodes. Then, this paper designs the basic control strategy of the system, including flexible transformers and MMC at the receiving end. Subsequently, an equivalent simulation model of ±10kV/10MW is built in the electromagnetic transient simulation software, and typical scenarios such as power step and AC faults at the sending end are simulated to verify the effectiveness of the proposed hybrid HVDC transmission system and its control strategy.