Electronics, Vol. 14, Pages 2543: Black-Start Strategy for Offshore Wind Power Delivery System Based on Series-Connected DRU-MMC Hybrid Converter

Electronics doi: 10.3390/electronics14132543

Authors:
Feng Li
Danqing Chen
Honglin Chen
Shuxin Luo
Hao Yu
Tian Hou
Guoteng Wang
Ying Huang

The series-connected DRU-MMC hybrid converter, with its compact size and cost-effectiveness, presents an attractive solution for long-distance offshore wind power transmission. However, its application is limited by the DRU’s unidirectional power flow and the voltage mismatch between the auxiliary MMC and the onshore MMC during black-start operations. To overcome these challenges, a four-stage black-start strategy utilizing an auxiliary step-down transformer connected to the onshore MMC is proposed. The proposed strategy operates as follows: The onshore MMC first lowers its valve-side voltage via an auxiliary transformer, enabling reduced DC-side voltage. With the DRU bypassed, the offshore MMC draws startup power through the DC link, then switches to V/f mode with wind turbine curtailment to reduce DC current below the DRU bypass threshold. After stable, low-power operation, the DRU is integrated. The onshore MMC then restores rated DC voltage and disconnects the transformer, allowing gradual wind turbine reconnection to complete black-start. The simulation results confirm the approach’s feasibility under conditions where all wind turbines operate in grid-following mode.

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Feng Li www.mdpi.com