Generator power peak limiting in virtual synchronous machine wind turbine

A wind turbine control system arranged for limiting generator loads in a wind turbine comprising a power converter with a line side inverter arranged to supply power to a power grid, the wind turbine control system is arranged to perform an operation for limiting generator loads in the wind turbine, the operation comprising:

• determining a maximum grid current value based on a measured generator load and a limit function which sets an upper maximum grid current value and a lower maximum grid current value so that the maximum grid current value approaches the lower maximum current value if generator load is greater than a maximum generator load and so that the maximum grid current value approaches the upper maximum current value if the generator load is smaller than the maximum generator load or is smaller than a low maximum generator load;
• determining a virtual impedance value based on a current difference between a current magnitude which relates to a grid current and the maximum grid current value, where the virtual impedance value comprises a virtual resistance value and optionally a virtual reactance value;
• determining a virtual voltage drop over the virtual impedance value based on the virtual impedance value and the grid current;
• determining a virtual grid power based on the virtual resistance value and the grid current, or based on the grid current and a voltage magnitude reference for a desired grid voltage or a desired reactive power to be generated by the line side inverter;
• determining a virtual synchronous machine angle based on a power reference for a desired power output of the power generating unit and the virtual grid power;
• and
• determining a voltage reference for controlling the line side inverter to generate power based on the virtual synchronous machine angle, the virtual voltage drop and the voltage magnitude reference.

A wind turbine, comprising:

• a tower;
• a nacelle disposed on the tower;
• a rotor extending from the nacelle and have a plurality of blades disposed at a distal end thereof;
• a control system configured to perform an operation for limiting generator loads in the wind turbine, the operation comprising:
• determining a maximum grid current value based on a measured generator load and a limit function which sets an upper maximum grid current value and a lower maximum grid current value so that the maximum grid current value approaches the lower maximum current value if generator load is greater than a maximum generator load and so that the maximum grid current value approaches the upper maximum current value if the generator load is smaller than the maximum generator load or is smaller than a low maximum generator load;
• determining a virtual impedance value based on a current difference between a current magnitude which relates to a grid current and the maximum grid current value, where the virtual impedance value comprises a virtual resistance value and optionally a virtual reactance value;
• determining a virtual voltage drop over the virtual impedance value based on the virtual impedance value and the grid current;
• determining a virtual grid power based on the virtual resistance value and the grid current, or based on the grid current and a voltage magnitude reference for a desired grid voltage or a desired reactive power to be generated by the line side inverter;
• determining a virtual synchronous machine angle based on a power reference for a desired power output of the power generating unit and the virtual grid power, and
• determining a voltage reference for controlling the line side inverter to generate power based on the virtual synchronous machine angle, the virtual voltage drop and the voltage magnitude reference.