This thesis is performed to analyze harmonics in HVDC-connected offshore windfarms and investigates different approaches to damp grid resonances so that the resulting harmonics are within standardized levels. This is done using Hitachi Energy’s inhouse developed MATLAB-tools. 

This thesis comprises background and theory on modelling of offshore windfarms equipment such as cables, wind turbines, transformers, and converters. Harmonics and amplification of harmonics have been calculated in the windfarm for numerous system configurations, and with different mitigation approaches such as active control damping and passive damping using filters. 

This thesis presents three different passive mitigation options; Platform filters which will be implemented to each PCC, String filters connected to each string and Wind Turbine filters placed in all wind turbines. 

The results have shown that without any mitigation the system is inherently undamped resulting in extreme amplification of harmonics. Using only active control damping does not help to damp the amplification of harmonics and passive damping is required. When utilizing Passive filters such as Platform filters, String filters or WTG filters the damping has been successfully implied to the system and the THD complies with the design limits.