A common problem in the simulation of electric circuits is finding a Periodic Steady State (PSS) of such a circuit.  Several approaches exist for solving this problem. For non-autonomous circuits, i.e. circuits that are driven by an input source with an a priori known period T, many methods exist. However, for autonomous circuits, the situation is less satisfactory. In the case of an autonomouscircuit, the period T becomes an additional unknown, which makes the resulting system underdetermined. In this talk, several methods will be discussed for dealing with such underdetermined systems. Several strategies for avoiding convergence towards the stationary solution will be discussed. Results of numerical experiments will be presented.