Under-excitation limiter design by variable structure control

A new technique to the design of under-excitation limiters (UEL) for synchronous generators using variable structure control is presented. Based on a linearized model of the a radial power system, the design problem has been formulated as one where the UEL gains are allowed to vary. Some useful expressions relating the gains with system parameters have been derived. The approach has been generalized to include operating conditions and parameter variations likely to occur in power systems. The VSC UEL is shown to be robust and provide much improved damping compared to that based on the conventionally designed UEL.