A new, energy-based method is proposed for guaranteeing the stability of large classes of control systems with minimum performance losses. Based on a network presentation, the large classes of control systems are analyzed in a unified framework. In this unified network model, the concept of passivity is used to study the stability of large classes of control systems. For guaranteeing the stability condition, the time-domain passivity controller is extended to a 2-port network to make the controller 2-port passive. The developed method is tested with numerical simulation in the regulation of a single link flexible manipulator. Totally stable control is achieved under wide variety of operating condition and uncertainties without any model information.