Nonlinear state-variable-feedback excitation-and governor-control design using decoupling theory

Modern microprocessor capabilities permit the control designer to consider using relatively complicated nonlinear control algorithms, which would have been considered impractical in the past. The paper presents the results of a study of the potential usefulness of nonlinear decoupling algorithms for the design of excitation and governor controllers for a power system using state-variable feedback. A control law for decoupling rotor angle and field flux is derived. For the rejection of load disturbance, the design of a servocompensator consisting of strings of integrators in the outer ioop around the decoupled inner loop is proposed. The closed-loop system is shown to be asymptotically stable. The system can be transferred to a new operating condition corresponding to any desired terminal voltage Vt and tie-line power Ptie The simulation results using a first-order compensator show that system asymptotically tracks the desired Vt and Ptie under unknown piecewise constant disturbances. Results show good transient and steady-state responses in rotor angle, field flux and frequency. Steady-state errors in Vt and Ptie owing to parameter uncertainty are reduced to zero by changing the command inputs using an external loop. The effect of stochastic load on the response is small.