Overview

Inter-area oscillations in power systems are triggered by, for example, disturbances such as variation in load demand or the action of voltage regulators due to a short circuit. The primary function of the damping controllers is to minimize the impact of these disturbances on the system within the limited dynamic rating of the actuator devices (excitation systems, FACTS-devices). In H _? control term, this is equivalent to designing a controller that minimizes the infinity norm of a chosen mix of closed-loop quantities.

The concept of H _? techniques for power system damping control design is about ten years old [1] [5]. An interesting comparison between various techniques is made in [6]. There are two approaches for solving a standard H _? optimization problem: analytical and numerical. While the analytical approach seeks a positive semi definite solution to the Riccati equation [7], the numerical approach is to solve the Riccati inequality to optimize the relevant performance index. Although the Riccati inequality is non-linear, there are linearization techniques to convert it into a set of linear matrix inequalities (LMIs) [8] [7], which simplifies the computational process.

The analytical approach is relatively straightforward but generally produces a controller that suffers from pole-zero cancellations between the plant and the controller [9]. The closed-loop damping ratio, which is very important in power system control design, can not be captured in a straight forward manner in a Riccati based design [10]. The numerical approach to the solution, using the linear matrix inequality (LMI)...