Method and controller for controlling a power converter connected to a grid

A method for controlling a power converter connected to a grid, wherein the power converter is initially controlled in a grid-forming mode to output current at a nominal voltage, based on control data provided by a controller, the controller comprising a control system which determines the control data based on measured signals indicative of currents and/or voltages downstream from the power converter, and a reference signal;

• the method comprising:
• determining, by the controller, that a first parameter related to the controller and/or the power converter exceeds a first threshold;
• responsive to determining that the first parameter exceeds the first threshold:
• controlling, by the controller, the power converter in a first limiting mode, by limiting the power converter output current based on a present value and/or a reference value;
• determining, by the controller, the output current of the power converter;
• responsive to determining that the output current is at or is close to an equilibrium condition:
• determining, by the controller, a virtual impedance for the power converter based on the output current of the power converter;
• modifying, by the controller, the control system based on the virtual impedance;
• and
• controlling, by the controller, the power converter in a first constrained grid-forming mode, comprising the modified control system determining the control data based on measured signals indicative of currents and/or voltages downstream from the power converter, and a reference signal.