There are a lot of examples in the Simscape (and add-on products) documentation.
If you want to do a more idealized system-level model with piecewise linear semiconductor characteristics, I'd advise looking into Simscape Power Systems Specialized Technology: https://www.mathworks.com/help/physmod/sps/examples/buck-boost-converter.html
Else, look into Simscape Electronics for more detailed models of devices, such as in https://www.mathworks.com/help/physmod/elec/examples/buck-converter.html.
With Simscape Electronics you can go as far as doing thermal modeling of your devices: https://www.mathworks.com/help/physmod/elec/examples/buck-converter-with-thermal-dynamics.html
- Sebastian
