What is passivity-based control and how is it used?

Passivity-based control exploits energy concepts for stability - a passive system cannot generate energy (output power <= stored energy change). Interconnection of passive systems is passive and stable. Design shapes energy function (storage function) so the closed-loop has minimum at desired equilibrium. Port-Hamiltonian framework provides systematic design method. Benefits include: inherent stability robustness, physical interpretation, handles nonlinearities naturally, and applies to networked systems. Used in robotics, power electronics, and mechanical systems where energy structure is clear.