Open Access

ARTICLE

AC Fault Characteristic Analysis and Fault Ride-through of Offshore Wind Farms Based on Hybrid DRU-MMC

Haokai Xie¹, Yi Lu¹, Xiaojun Ni¹, Yilei Gu¹, Sihao Fu^2,*, Wenyao Ye³, Zheren Zhang², Zheng Xu²
1 State Grid Zhejiang Electric Power Co., Ltd., Research Institute, DC Technology Research Institute, Hangzhou, 310000, China
2 College of Electrical Engineering, Zhejiang University, Hangzhou, 310027, China
3 Polytechnic Institute, Zhejiang University, Hangzhou, 310027, China
* Corresponding Author: Sihao Fu. Email:

Energy Engineering https://doi.org/10.32604/ee.2025.070934

Received 28 July 2025; Accepted 10 September 2025; Published online 02 October 2025

Abstract

With the rapid development of large-scale offshore wind farms, efficient and reliable power transmission systems are urgently needed. Hybrid high-voltage direct current (HVDC) configurations combining a diode rectifier unit (DRU) and a modular multilevel converter (MMC) have emerged as a promising solution, offering advantages in cost-effectiveness and control capability. However, the uncontrollable nature of the DRU poses significant challenges for system stability under offshore AC fault conditions, particularly due to its inability to provide fault current or voltage support. This paper investigates the offshore AC fault characteristics and fault ride-through (FRT) strategy of a hybrid offshore wind power transmission system based on a diode rectifier unit DRU and MMC. First, the dynamic response of the hybrid system under offshore symmetrical three-phase faults is analyzed. It is demonstrated that due to the unidirectional conduction nature of the DRU, its AC current rapidly drops to zero during faults, and the fault current is solely contributed by the wind turbine generators (WTGs) and wind farm MMC (WFMMC). Based on this analysis, a coordinated FRT strategy is proposed, which combines a segmented current limiting control for the wind-turbine (WT) grid-side converters (GSCs) and a constant AC current control for the WFMMC. The strategy ensures effective voltage support during the fault and prevents MMC current saturation during fault recovery, enabling fast and stable system restoration. Electromagnetic transient simulations in PSCAD/EMTDC verify the feasibility of the proposed fault ride-through strategy.

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Keywords

Diode rectifier unit; offshore AC fault analysis; fault ride-through; coordinate control

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