Ziegler Nichols method based Robust reactive current controller for STATCOM

The STATIC Synchronous Compensator is a shunt connected Voltage Source Converter (VSC) using self-commutating devices such as GTOs utilized for reactive power control. The purpose of employing STATCOM at somewhere in the middle of long transmission line by regulating the voltage at the point of connection for the intensification of power transfer capability or reactive power control at the load centre. The reactive current control, makes use of PI controller without and with nonlinear feedback controller. The step response of the reactive current and Eigen value analysis is carried out using 3phase model and D-Q models of STATCOM. It is observed that, fast acting conventional PI controller causes reactive current oscillations in inductive mode of operation of STATCOM which leads to instability.. The problem of instability can be overcome by using nonlinear feedback controller and by controller parameter optimization for good transient response. The present work is mainly focused on elimination of the requirement of nonlinear feedback controller while ensuring good transient response. This paper presents a approach of tuning the parameters of PI controller using Ziegler Nichols method for reactive current control of STATCOM. The assessment of effectiveness of the designed controller is carried out by transient simulation. It is observed that the proposed controller exhibits good transient response while ensuring robust performance under varying operating conditions.