Before revision:  The frequency-domain passivity framework provides powerful analysis tools to study the coupled stability of linear time-invariant systems. In the literature, coupled stability of one-port models of SEA has been studied for various controllers while rendering certain basic environments, and the necessary and sufficient conditions for such passive terminations have been derived. In this study, we extend the one-port passivity analyzes provided in the literature and provide the necessary and sufficient condition for two-port passivity of SEA under velocity-sourced impedance control  . Based on the newly established conditions, we derive non-conservative passivity bounds for a virtual coupler .
After revision:  In this study, we extend the one-port passivity analyzes provided in the literature and provide the necessary and sufficient condition for two-port passivity of SEA under velocity-sourced impedance control . Based on the newly established conditions, we derive non-conservative passivity bounds for a virtual coupler .