Electric power networks are being modified fast, mainly due to the changes introduced in generation systems and load features. Research studies indicate that this process is going to continue in the near future. In this context, several control strategies and devices are used to increase the stability and performance of the new power systems. An optimization with constraints for the excitation control in synchronous generators is presented in this work, in order to damp oscillations in the grid. Generator states move away from their operating points in presence of disturbances in the electric network such as sudden load variations, transmission line losses and short circuits. Then, the generator states must be brought back to its equilibrium point by the excitation control. As the generator model is nonlinear, the controller tuning in order to perform this function is not easy, being necessary to apply nonlinear techniques to obtain a high performance. Moreover, optimal control schemes are currently required owing to a demanding market which rewards power units that deal with energy in an optimal way and keep the generator stable even under network faults. (C) 2011 Elsevier Ltd. All rights reserved.