Global phase portraits of the generalized van der Pol systems

Abstract

We consider the generalized van der Pol systems x˙=y,y˙=−x+(1−x2)f(y), where f∈R[y]. The classical van der Pol systems have f(y)=y. We first characterize when the origin of the generalized van der Pol systems is a center, and second we provide the global phase portraits in the Poincaré disc of the generalized van der Pol when f(y)=a1y+a2y2 for all a1,a2∈R.