Sliding mode excitation control of synchronous generator for power systems stability

When power systems are affected by disturbances, oscillations occur in rotor angles and terminal voltages of generators in the system. In order to maintain the stability of power systems, the oscillations should be properly damped. It is convenient approach that excitation control of synchronous generators is used for suppressing low amplitude and low frequency (0.2 ? 3 Hz) oscillations.There are two approaches for improving power system stability via excitation control. The first approach is to add supplementary control signal to excitation control loop by using power system stabilizer (PSS). The other approach is to use an excitation controller regarding both voltage and power system stability.In this study, both the approaches are investigated. For designing the controllers, simplified 4. and 3. order linear state-space models of single machine infinite bus system are obtained. The state-space models are built on measurable variables. Sliding mode control method is used to establish robust control against operation point variations, parameter uncertainty and disturbances, which are frequently seen in power systems. In this study, three methods have proposed for improving power systems stability via excitation control. They are a sliding mode PSS and two sliding mode excitation controllers based on fourth order and third order state space models. The switching surface giving the optimal performance is optimized by using Genetic Algorithm (GA).Performances of the proposed controllers are tested against disturbances in wide uncertainty range. It is shown that the proposed methods provide better rotor angle and voltage stability performance than conventional PSS as regarding simulation results.