Controller freeze

Last modified: 17 Mar 2025

About controller freeze

During overvoltage or undervoltage events, inverters enter Fault Ride Through (FRT) mode and ignore external control commands. This can cause the controller's correction values to increase. Once the event ends and inverters resume following commands, this mismatch can cause power oscillations. The Controller freeze function prevents such issues by “freezing” correction values (holding them constant) during the event. This ensures a smoother transition back to normal operation and enhances overall grid stability.

When activated, controller freeze works in 3 phases:

Event detection: The controller automatically detects an overvoltage or undervoltage event
Behaviour during event: The controller freezes the last correction values for active and reactive power
Return to normal operation: Once the freezing time has expired, the controller resumes calculating new correction values

Configure controller freeze

Steps

Navigate to Power Control > Reactive power > Extended settings
In the Behaviour in event of error tab, activate the Controller freeze toggle.
Set the parameters as per the table below. The default values are already pre-configured.
The function is active. Controller freeze will be triggered the next time the voltage thresholds are “violated”/reached.

Parameter	Description
Voltage threshold undervoltage	Should match the voltage level at which the inverters enter FRT mode.
Voltage threshold overvoltage	Should match the voltage level at which the inverters enter FRT mode.
Voltage criterion	Select how the event is detected: Mean: The average value of the three phase voltages Phase-related: For overvoltage, the greatest voltage of the three phase-to-phase voltages is used. For undervoltage, the lowest voltage of the three phase-to-phase voltages is used.
Freezing time	Ideally, the freezing time should match how long the inverters ignore the controller values.