Robust STATCOM voltage controller design using loop-shaping technique

Static synchronous compensator (STATCOM) is a shunt-connected converter, which can affect rapid control of reactive flow in the transmission line by controlling the generated a.c. voltage. This article presents a robust STATCOM voltage controller design for power system damping. The method of multiplicative uncertainty has been employed to model the variations of the operating points. The design is carried out applying robustness criteria for stability and performance. A loop-shaping technique has been employed to select a suitable open-loop transfer function, from which the robust controller function is constructed. The controller was tested for a number of disturbances including three-phase fault. The damping provided by the robust controller was compared with a fixed-parameter PID controller, whose gains were calculated through a pole-placement technique. It has been observed that the PID control is ineffective at operating points other than nominal. The robust design has been demonstrated to provide extremely good damping characteristics over a range of operating conditions.