Virtual impedance current limiting control for grid forming inverter-based resources

A method for controlling an inverter-based resource connected to a power grid during a grid event, the method comprising:

• operating, via a controller, the inverter-based resource based on a virtual impedance reference during the grid event, the virtual impedance reference being used by the controller for determining a virtual impedance of the inverter-based resource defining a virtual reactance and a virtual resistance;
• ensuring that a magnitude of the virtual impedance is maintained at or above a magnitude of the virtual impedance reference so as to reduce current oscillations in the power grid for a duration of the grid event;
• receiving, via the controller, a signal indicating that the virtual impedance can be deactivated due to the grid event being over;
• in response to receiving the signal, activating, via the controller, a soft deactivation module, wherein activating the soft deactivation module further comprises:
• determining a voltage drop across the virtual impedance;
• and
• superimposing the voltage drop upon a voltage reference of the inverter-based resource simultaneously with deactivating the virtual impedance, wherein ensuring that the magnitude of the virtual impedance is maintained at or above the magnitude of the virtual impedance reference further comprises receiving an activation signal and determining whether or not to subtract a voltage drop from a voltage reference of the inverter-based resource.

A system for controlling an inverter-based resource connected to a power grid during a grid event, the system comprising:

• a controller comprising at least one processor, the at least one processor configured to perform a plurality of operations, the plurality of operations comprising:
• operating the inverter-based resource based on a first virtual impedance reference prior to the grid event, the first virtual impedance reference being used by the controller for determining a first virtual impedance of the inverter-based resource defining a first virtual reactance and first virtual resistance;
• receiving an indication of a start of the grid event that causes a change in the first virtual impedance reference to a second virtual impedance reference that is larger than the first virtual impedance reference;
• immediately after the change in the first virtual impedance reference, activating a soft activation module for outputting a second virtual impedance defining a second virtual reactance and a second virtual resistance that maintains a magnitude of the second virtual impedance at or above a magnitude of the second virtual impedance reference so as to reduce current in the inverter-based resource;
• and
• at a certain time period after activating the soft activation module, transitioning, via the controller, the second virtual reactance and the second virtual resistance to a virtual reactance and a virtual resistance defined by the change;
• and
• ensuring that once the soft activation module is activated, the magnitude of the second virtual impedance is maintained at or above the magnitude of the second virtual impedance reference so as to reduce current oscillations in the power grid for a duration of the grid event, wherein ensuring that once the soft activation module is activated, the magnitude of the second virtual impedance is maintained at or above the magnitude of the second virtual impedance reference further comprises:
• receiving, via the controller, an activation signal;
• and
• determining whether or not to subtract a voltage drop from a voltage reference of the inverter-based resource.