This paper studies the application of Hilbert Huang Transform (HHT) to oscillations generated by common power system phenomena. Firstly, an investigation was performed on the kind of damped modes that can be analyzed through HHT. HHT was then applied on signals from a nonlinear model of AC grid containing two close HVDC lines and power electronic devices. Two cases were studied: identification of coupling mode and temporal tracking of coupling mode during switching events. Results were compared with those obtained in modal analysis. In both cases it was found that HHT was able to provide better depth and clarity in off-line stability analysis.