Control and Capacity Design of Station-Hybrid HVDC System with DRU and MMC in Parallel for Offshore Wind Power Integration

The station-hybrid HVDC system combining diode rectifier unit (DRU) and modular multilevel converter (MMC) in parallel has garnered significant attention within the field of light-duty HVDC systems. This paper presents a comprehensive investigation into the control and capacity design of this station-hybrid scheme. Firstly, a coordinated power control strategy is presented to provide grid-forming capability and mitigate transmission losses. In addition, a software-based harmonic suppression strategy is introduced. This innovative approach eliminates the need for additional hardware filters in the DRU, streamlining the system while effectively suppressing unwanted harmonics. Moreover, the capacity of the station is meticulously designed to optimize overall system performance. An economic evaluation is conducted to compare the proposed station-hybrid scheme with the conventional compact MMC scheme, shedding light on the economic feasibility and competitiveness of the proposed configuration. Finally, the paper validates the proposed coordinated power control and harmonic suppression strategy through simulations using the PSCAD platform. The results confirm the practicality and effectiveness of these control strategies in real-world applications.