The Pole Controls are the heart of the HVDC control system. The DC power flow is controlled to the operator’s set point. Steady-state and dynamic performance of the AC systems is also enhanced by the Pole Controls. Features such as power swing stabilization, frequency limit control and sub synchronous resonance damping are some of the available features. The primary function of the Pole Control System is to maintain the transmitted power at the operator selected value. This is achieved with an optimal response during system disturbances and is robust and stable for all system configurations. During normal undisturbed operation, DC current control is active at the Rectifier and DC voltage control at the Inverter. A backup extinction angle control provides a safety margin to minimize commutation failures at the Inverter following disturbances in its AC system. An Inverter current control function becomes active should the Rectifier station be unable to provide the ordered DC current during AC System disturbances. Converter control coordinates the conversion of current order to a firing angle order or PWM duty cycle, tap changer control and other protection sequences.