DESIGN OF REACTIVE CURRENT AND VOLTAGE CONTROLLER OF STATIC CONDENSER

The STATic CONdenser (STATCON) is a shunt connected voltage source con verter using self-commutating devices like GTOs which can be used for reactive power control. Their principle of operation is similar to tha t of a synchronous condenser A typical application of a STATCON is for voltage regulation at the midpoint of a long transmission line. In th is paper a two stage structure for the control of voltage is investiga ted. This uses a closed loop reactive current controller whose referen ce is set by an outer voltage controller For reactive current current control, the use of a PI controller and a fuzzy logic PI controller is investigated. It is found that the fuzzy logic controller overcomes t he problem of oscillatory instability encountered when a conventional PI controller is used. Art important observation is that the plant tra nsfer function for voltage control (by reactive current injection) is generally of the nonminimum phase type. This precludes the use of larg e gains in a PI controller as there is a risk of instability of an osc illatory mode. Eigenvalue analysis using a linearized model is carried out to design a compensator in cascade with an integral controller to overcome this problem. (C) 1997 Elsevier Science Ltd.