Detailed Equivalent Model for an MMC-HVDC Connected Offshore Wind Farm under Normal and Fault Dynamic Performance Analysis

The increasing integration of renewable energy sources into electrical grids necessitates efficient transmission solutions, particularly for offshore wind farms requiring connection to distant onshore networks. Modular Multilevel Converters (MMCs) present significant computational challenges in HVDC system simulations due to their complex structure involving hundreds of submodules and nodes. This study presents a novel detailed equivalent modeling approach using Thevenin equivalent circuits to efficiently simulate MMC behavior while maintaining accuracy for system-wide studies and DC fault analysis.

The research develops comprehensive Thevenin equivalent models that dramatically reduce computational complexity by representing hundreds of individual submodule nodes through three equivalent nodes per arm. The proposed modeling approach connects islanded offshore wind farms to onshore AC grids through MMC-based VSC HVDC symmetrical monopole systems, where the onshore converter controls DC voltage while the offshore converter maintains AC voltage magnitude and frequency as a slack bus.

The developed Thevenin equivalent models demonstrate excellent performance under both normal operating conditions and fault scenarios. During normal operation, the models accurately capture steady-state power transmission characteristics, dynamic response to wind variations, and control system interactions. Under fault conditions, the models successfully represent transient phenomena, fault current contributions, and system recovery dynamics for various fault scenarios including DC line faults and AC grid disturbances. The developed modeling technique provides a computationally efficient yet accurate representation of offshore wind farm integration via MMC-HVDC systems, enabling comprehensive analysis of both normal and fault dynamic performance for renewable energy integration studies.