This model simulates, following an external reference, a constant-power load.
It uses a simple integral controller.
There is no need to state precisely the value of vNom: it only determines the dynamic of the controller. In case the actual DC voltage is exatly equal to vNom, the controller has a dynamics exactly equal to that of a system having as transfer funcrtion G(s)=1 fed by a pure integral controller with time constant equal to Ti.