arXiv:2611.07276v1 Announce Type: new Abstract: The passivity of a generating station enables network stability to be established from conditions verified locally at each station. For synchronous machines, however, passivity can only be certified under conditions on the operating point, and these conditions fail under heavy loading and weak damping. This paper develops a state-feedback controller that enforces passivity using a storage battery connected at the terminal bus. A bilinear term arising from the product of the rotor-speed and stator-current deviations is treated as a bounded uncertainty, leading to robust positive-real conditions that can be enforced by a state feedback control designed using a single algebraic Riccati equation. The resulting controller guarantees passivity whenever the Riccati equation admits a positive-definite solution, with no separate condition on the operating point. Numerical examples show that existing conditions certify passivity only up to a fraction of the rated current, whereas the proposed state-feedback approach certifies it at the rated operating point of the machine.