Time-delay compensation of a wide-area measurements-based hierarchical voltage and speed regulator

This paper presents a delay-insensitive version of a wide-area measurements-based two-level hierarchical controller. This hierarchical structure consists of a central controller, at the secondary level, dedicated to inter-generator interactions compensation, and conventional controllers (automatic voltage regulator, power system stabilizer, and speed governor), at the primary level, to dampen local oscillations. First, a Smith prediction approach is used to preserve performance in the presence of large remote-measurement time delays and communication time delays between central and local controllers. Second, an optimization algorithm is used to considerably reduce the complexity of the controller and thereby increase its reliability. Finally, sets of realistic tests are performed to assess the robustness of the proposed structure in the presence of uncertainties over time delays and power system parameters. Simulation results reveal that time-delay compensation is effectively required to enhance the hierarchical-structure performance in realistic situations. Furthermore, the performance of local controllers is considerably improved by the secondary-level controller action. The stability margin of the system is improved in the presence of severe contingencies.