This controller modulates either VSV C or BSV C by processing a signal obtained from local measurements. The objective is to damp critical low frequency inter area or local modes that can affect stability during disturbances. The control signals are selected on the basis of following criteria
1. The signal should predominantly contain the mode that needs to be damped. 2. The controller design based on a particular control signal should be simple and reject noise. 3. The controller should not destabilize modes that are otherwise stable.