Voltage and Frequency control of the AC grid at offshore wind farms During Disturbances in the HVDC Link to Onshore Grid

In a conventional offshore wind farm (OWF), medium voltage ac cables carry the power from individual wind turbine towers to the offshore platform, thus forming an offshore ac network/grid (OACG). A control strategy is presented in this work where the dc current reference of the line commutated converter (LCC) on the platform is used for holding the OACG voltage constant in the face of changes in voltage of the HVDC link due to onshore disturbances. Reactive powers from the grid side converters (GSC) at the wind turbines are used in droop control mode to maintain the OACG frequency. A provision is also established for maintaining the OACG voltage during islanding of the OWF due to breakdown of the HVDC link. The control is verified through simulation and experiment.