Experimental evaluation of STATCOM closed loop dynamics

This paper presents a new approach for the dynamic control of FACTS apparatus, such as the STATCOM and UPFC, which utilize voltage source inverters (VSI) as the main building block. The control concept is based on a linearization of the dq inverter model. Feedforward techniques which are traditionally used for the approximate decoupling of d and q-axis control are discarded in favour of a high gain full state feedback approach which assigns both closed loop system poles and, more importantly, their associated eigenvectors. Experimental validation of the approach is carried out on a laboratory STATCOM setup. Due to the nonlinear nature of the VSI equations and the uncertainty of ac system parameters, actual closed loop system dynamics can stray quite dramatically from the desired. Root locus analysis is therefore performed to investigate the small signal system dynamic behaviour. The loci demonstrate that the effect of system nonlinearity on the closed loop poles is virtually eliminated by the proposed control. The effect of ac system parameter variations is also shown to be minimal.