MICROPROCESSOR-BASED NONLINEAR EXCITATION CONTROLLER FOR SYNCHRONOUS MACHINES

The synchronous machines in power systems have the excitation systems of field winding to improve the transient stability of power systems. The synchronous machines are nonlinear systems, however, the excitatio n systems have been designed based on linearized systems, because the stability analysis of nonlinear systems is difficult and the generaliz ed control method of nonlinear systems has not been developed yet. Thi s paper proposes a nonlinear excitation controller for synchronous mac hines in power systems. For the sake of simplification of the nonlinea r state feedback control, this paper considers both the transient stab ility and the suppression of the rotor swings in transient conditions. The effect of the automatic voltage regulator (AVR) for the synchrono us generator is not discussed here. This controller is designed based on Lyapunov's direct method that can directly judge the stability of n onlinear systems. The usefulness and validity of the proposed excitati on controller are confirmed by numerical simulations and experiments. The microprocessor based generator excitation system that consists of a nonlinear controller, state variable detector, and PWM inverter, is constructed. The nonlinear excitation controller can improve the trans ient stability of synchronous machines.