Patent ID: 11863112
Assignee: VESTAS WIND SYSTEMS A/S
Field: Electrical machinery, apparatus, energy (Electrical engineering)
Classification: CPC H  Y | IPC H

Claim 13:
14. A control system for controlling a power generating unit, the power generating unit comprises a power source, a machine side converter, a line side converter, a DC link electrically connected to an output of the machine side converter and an input of the line side converter, the control system is arranged to:
obtain a current magnitude of current supplied by the line side converter to a power grid based on a grid current;
determine a virtual impedance value based on a current difference between the current magnitude and an overcurrent threshold value, where the virtual impedance value comprises a virtual resistance value;
determine a virtual voltage over the virtual impedance value based on the virtual impedance value and the grid current;
determine a virtual grid power based on the virtual resistance value and the grid current, or based on a voltage magnitude reference and the grid current, or transformations thereof;
determine a virtual synchronous machine rotational speed and/or a synchronous machine angle, where a derivative of the virtual synchronous machine rotational speed is indicative of a deviation between a power reference for a desired power output of the power generating unit and the virtual grid power combined with a damping power;
provide a voltage magnitude reference for a desired reactive power to be generated by the line side converter; and
determine a voltage reference for controlling the line side converter to generate the desired reactive power based on the virtual synchronous machine rotational speed or angle, the virtual voltage and the voltage magnitude reference; and
wherein the virtual resistance value is determined based on a control algorithm, where the control algorithm comprises a proportional part which determines a value which is proportional with the current difference and an integral part which determines a value which is proportional with a time integral of the current difference.