Nonlinear decentralized coordinated control for multimachine power systems

In this paper, a coordinated controller for multimachine power system transient stability enhancement is proposed. The controller consists of a nonlinear excitation controller and a fast valving controller for each generator. By employing the direct feedback linearization (DFL) technique, a decentralized nonlinear controller is found for multimachine power system excitation control. The excitation controller design problem for an n-machine system is converted to designing n controllers for n linearized and decoupled plants. Then, an optimal fast valving controller is designed to reduce the mechanical power input when a severe fault occurs. In order to reduce the control cost, the fast valving loop is switched on for only a certain period after a fault occurs. By the coordinated action of the two control inputs, transient stability of the system can be greatly enhanced. The proposed scheme is applied to a three-machine system. Simulation results show that power angle oscillations after large disturbance can be damped out rapidly. Simulation results also indicate that the performance of the proposed controller is robust against fault location, network variation and power transfer conditions.