Method for controlling power flow within a wind park system, controller, computer program and computer program products

A computer program for controlling power flow within a wind park system for power transmission to a main power grid, the wind park system comprising two or more parallel-connected island wind park grids, each island wind park grid comprising a wind park with at least one wind turbine, the wind park being connected to an AC bus, in turn connected to a voltage source converter arranged to feed power to the main power grid by means of a respective direct current transmission line, the computer program comprising computer program code, which, when run on a controller, causes the controller to perform the steps of:

• controlling a first voltage source converter as a swing bus in frequency control, the frequency control comprising controlling frequency to a steady state reference operating point for operating points within a power dead band and by means of frequency droop control when exceeding an end point of the power dead band, and
• controlling at least a second voltage source converter in power control, the power control comprising controlling power flow to a steady state reference operating point for operating points within a frequency dead band and by means of power droop control when exceeding an end point of the frequency dead band.