You could either (1) build your own model in simulink by means of existing blocks or (2) model the circuit by means of differential equations (ODE's).
(1) This would be typically done in the Laplace domain. However, if the power circuit contains many electrical components, this modelling approach becomes tedious.
(2) In this case the circuit is described as a system of linear equations. The equations depend on the states of the switches and diodes in your model, so the ODE's dynamically change during operation. Again the complexity depends on the number of components in the power circuit. Some commercial tools are available (e.g. SimPowerSystems, Sentrix,...) that apply this approach.