Design of a robust modulation controller over a wide range of load characteristics for AC/DC systems

A method is presented for designing a robust modulation controller to improve the dynamic performance of AC/DC systems. Static load is modeled as a nonlinear function of load bus voltage and motor. Reactive power and DC power are considered for the modulation control. A static VAr compensator (SVC) is used for the reactive power modulation. The rotor speed and angle deviations of the synchronous generator are used as a stabilizing signal to the SVC. The controller gains are selected on the basis of the eigenvalue sensitivity of the electromechanical mode of the closed-loop system with respect to the load characteristics. Eigenvalue analysis and simulation results show that the proposed reactive power modulation control improves the system response over a wide range of voltage-dependent load characteristics as compared with the control using only rotor speed deviation. However, DC power modulation based on rotor speed deviation provides effective damping for static as well as dynamic load models