A Hybrid HVDC Transmission System Based on Diode Rectifier Units for Enhanced AC Grid Support

To address the critical challenge of long-distance transmission from renewable energy bases, this paper proposes a novel hybrid high-voltage direct current (HVDC) architecture. The sending end utilizes diode rectifier units (DRUs) for low-cost power rectification, while the receiving end employs a modular multilevel converter (MMC) with virtual synchronous generator (VSG) control to provide system-level inertia support. A steady-state mathematical model of the DRU is developed to quantify its external characteristics. Additionally, an analytical expression for system frequency-power sensitivity under receiving-end frequency disturbances is derived to reveal the power coupling mechanism between the DRU and MMC. Simulation results confirms the effectiveness of this architecture in enhancing frequency stability through addition active power contribution from the send-end DRU station.