Analysis and design of voltage control of static condenser

The static condenser (STATCON) is a shunt connected voltage source converter using self commutating devices like GTOs. The principle of operation is similar to that of a synchronous condenser. This paper is concerned with the application of the STATCON for the reactive power compensation of a long transmission line by regulating the voltage at its midpoint. The design of the voltage controller and the analysis of its dynamic behaviour using eigenvalue analysis and digital simulation is presented. An important observation is that the plant transfer function is generally of the nonminimum phase type. This precludes the use of large gains in a PI controller as there is a risk of instability of an oscillatory mode of frequency between 200-300 rad/s. Eigenvalue analysis using a linearized model was carried out to design a compensator in a cascade with an integral controller to overcome this problem