Line current balancing with a unified power flow controller

This paper presents a new approach for the dynamic control of FACTS apparatus, such as the STATCOM and UPFC. The proposed approach allows for fast and independent control of real and reactive power while decoupling unbalanced disturbances from one bus to another. The control concept is based on a linearization of the dq inverter model. Traditional feedforward techniques are used to decouple the d and q-axis control. To ensure only balanced line currents flow, an asymptotic tracking control strategy is used which suppresses second harmonic in the dq-quantities. Experimental validation of the approach is carried out on a laboratory UPFC setup. The results demonstrate the fast and independent power flow control as well as the balanced line current control ability. They also show that the effects of AC system parameter variations are neglectable over a wide range and have practically no impact on the dynamic behaviour or the stability of the system