Multi-loop power system stabilizers using wide-area synchronous phasor measurements

A new distributed-measurement technology using the global positioning system and accurate phasor measurements units has developed steadily in recent years to become the most powerful source of wide-area dynamic information in a foreseeable future. This paper explores new ways of putting this extended realtime knowledge of the power system behavior into use, by means of supplementary feedback loops which improve dynamic and transient system stability and, ultimately, increase the existing transmission capacity. The design of such advanced controllers is based on a two-stage methodology of which first step is built on a powerful pulse-response-based, numerical sub-space state-space identification algorithm to identify a reduced-order, small-signal MIMO model of the open-loop system. The second step is to select an appropriate control structure and then tune the stabilizer parameters accordingly. To tackle the most difficult situations, the architecture selected comprises several dynamic feedback loops, each consisting of a high-order differential filter. Controller tuning is then performed by minimizing a selective modal performance index in the parameter space. Adding stability and robustness constraints greatly improves the engineering significance of the resulting design. For illustration, we provide a full design of a three-loop stabilizer for a major synchronous-condenser station an actual power system which simultaneously uses two global and one local input signals. Both linear and nonlinear simulation results clearly demonstrate the added value of wide-area information when properly included in power system stabilizer design.