Minimisation of power losses in source-R-C circuit with any (possibly nonlinear) capacitor

In power electronics circuits, the capacitor, whose charging and discharging provides the energy transfer from a source to the load is, usually, a linear one. It is interesting to consider also a nonlinear capacitor having a smooth voltage-current characteristic, as, e.g. a ferroelectric capacitor, or a piecewise linear characteristic, as a switched unit in which linear capacitors are switched. This can give a designer an additional degree of freedom for optimisation of such a circuit, first of all for minimisation of the power losses in it. The proof of the reasonability to use a current (and not a voltage) source is provided in terms of the variation principle that is widely used in classical mechanics. The use of the variational principle not just for optimisation of some parameters (which is usual), but also for the qualitative conclusion regarding the circuit structure - the use of the current source - is another methodological point not to be missed.