A fault handling current control strategy for offshore wind turbines in interconnected offshore wind farms with different types of HVDC transmission

Offshore wind turbines built at a long distance from public ac-grid are connected via HVDC-transmission. Future HVDC-systems may connect offshore wind farms via uncontrolled diode rectifiers instead of VSC-HVDC converters. Due to this wind turbine inverters must own a grid forming capability. This Paper describes a fault handling strategy for offshore the wind turbines during faults in the ac-offshore island grid. The control strategy is based on a fixed reference frame current source operation of all line side converters in the wind farm.