Time-Varying Capacitors as Lossless Two-Port Devices

Inspired by recent assertions that imply incorrectness of the classical constitutive relationship of time-varying capacitance, energetic and system-theoretic perspectives are invoked that, instead of incorrectness, show incompleteness of the associated one-port device model. Based on dissipativity and passivity theory, an energetic analysis is presented that naturally leads to a complete two-port device model that is consistent with the laws of thermodynamics.