Cycles of the second kind for uncertain pendulum-like systems with several nonlinearities

The existence of cycles of the second kind was considered for uncertain pendulum-like systems with several nonlinearities. On the basis of the Kalman–Yakubovich–Popov (KYP) lemma, linear matrix inequality (LMI) conditions guaranteeing the existence of cycles of the second kind for such nonlinear systems under parameter uncertainties are established. By virtue of these results, an interesting conclusion is reached: that the synthesis problem ensuring the existence of cycles of the second kind for such an uncertain nonlinear system can be converted into a synthesis problem for a system without uncertainties. A concrete application to a synchronous machine demonstrates the validity of the proposed approach.