Harmonic modelling and analysis in the context of energy islands

Details

Supervisors

De Jaeger, Emmanuel

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil électricien, à finalité spécialisée

Abstract

enThe increasing integration of offshore wind energy into power systems poses significant challenges related to harmonic distortion, particularly within the emerging concept of energy islands. This thesis investigates harmonic behaviour in the Modular Offshore Grid II project developed by the Belgian transmission system operator Elia. The study focuses on constructing a detailed harmonic model of the first phase of the MOG II infrastructure, which includes multiple voltage levels linked by numerous transformers, a High Voltage Alternating Current export system comprised of extensive AC cable networks and shunt reactors, and finally a 700 MW Wind Farm composed of numerous Wind Turbines and a High Voltage collection grid. These key components harmonic model is derived and validated using both frequency-domain and time-domain methods using MATLAB Simulink software. A harmonic simulation of the complete system was then performed to capture the resonance and harmonic propagation phenomena occurring across the system. Simulation results reveal strong low order harmonic emissions from individual Wind Turbines, particularly the 5th and 7th, whose magnitude and phase depend on operating conditions. When aggregated in the collection grid, these injections interact with cable impedances and transformer connections, leading to constructive or destructive interference. The topology and block configuration of the grid play a decisive role in either mitigating or amplifying this distortion propagation. Beyond the farm, the long HVAC export system introduces parallel resonances in the same frequency range as the turbine emissions, causing significant amplification of these low order harmonics at the onshore connection and, in some cases, standards exceedance. The findings underline the importance of accurate harmonic modelling in mitigating power quality issues in offshore renewable integration and lay a foundation for future improvements in energy island design and operation.