This manuscript was submitted to IEEE Power Engineering Letters.
We propose an extension of the Dissipating Energy Flow (DEF) method for
locating sources of forced oscillations (FOs), based on an energy
function constructed by the complex integral approach, which we call
Complex DEF (CDEF). To trace sources of FO, we study the scalar
projection of CDEF in a specific direction on the complex plane. We show
by simulated cases that this alternative has a good performance in cases
where the original DEF fails.