Stability is the most important requirement for bilateral teleoperation, and time-varying delays inherent in the communication channel have a strong destabilizing effect. Time invariant passivity based approaches have been proposed to stabilize teleoperation with constant communication delays. However they dissipate energy considering the worst case scenario and result in a significant position drift between master and slave robots. A power based time domain passivity approach employing feedback passivity concept is developed to ensure passivity of bilateral teleoperation under time-varying communication delays and achieve synchronization of the master and slave robots. Passivity of the bilateral teleoperation system, and hence stability, is proved theoretically. Simulations and experiments on a custom built bilateral teleoperation system validate the efficacy of our approach.