Excitation control system for use with synchronous generators

An optimal excitation control strategy for a synchronous generator is derived using Lyapunov´s direct method and the nonlinear system equations. The control strategy requires neither phase compensation nor wash-out circuits characteristic of standard power system stabilisers (PSS). By using a nonlinear system model, the control strategy is optimal over a wide range of rotor angle and swing frequency changes. The excitation control system required to implement the control strategy is hierarchical and has a different structure to the traditional excitation control system with PSS. In the proposed structure, a primary controller damps quickly any power swings using the synchronous EMF as the feedback signal. A secondary controller maintains constant generator voltage by adjusting the reference value of the synchronous EMF fed to the primary controller to that required by the actual operating conditions. The proposed excitation control system has been tested on a single generator-infinite busbar power system with the simulation results showing excellent damping of power swings over a wide range of operating conditions whilst retaining good voltage control