A good starting point is the following example in Simscape Electrical:
In this example a bidirectional DC-DC converter is used to charge and discharge a battery. This is using PI control but the control algorithm can be replaced with MPC. To design the MPC controller, you will need to obtain the plant equations. The MPC algorithm will depend of what exactly you plan to do, can be a simple Generalized Predictive controller or a state-space MPC with or without constraints.
