Wind power as a green and low-carbon renewable energy could effectively mitigate the energy crisis and reduce environmental pollution, including the rapid developing offshore wind power with its rich reserves, wind stability, high wind speed, less interference, noise and other advantages. The trend for development of offshore wind farms is towards a growing size of installed power. This together with higher distances from the shore leads in many cases to HVDC connection as a preferred choice for power export. Thus, the wind turbines are connected through a collection grid to an offshore platform. As the offshore wind farm contains a large number of power electronic devices and submarine cables, it will inevitably lead to the occurrence of harmonic resonance. Offshore wind farm harmonic and resonance will affect the power quality, while poses a huge challenge to the power grid and wind power.
In this thesis work, a comprehensive harmonic analysis in offshore wind farm was studied. Firstly, a detail configuration of the wind energy conversion system and harmonic analysis basics are described and interpreted. Next, a suitable model of one offshore wind farm is built and validated in Matlab/Simulink. The equivalent circuit is calculated for the components in the aggregated wind farm based on their harmonic model. And potential resonance problems are analyzed by frequency scan method to calculate the resonance impedance and frequency. Afterwards, based on the self-built system model, potential harmonic issues that arise in the system are investigated in time domain to interpret the THD at PCC between the collection grid and the onshore grid. As well, a few effective strategy for suppressing harmonics are simulated to evaluate the various influence on the harmonic issue. Both the designed C-type filter and active power filter performed a satisfying results on harmonics suppression.