In an aircraft electric power system (EPS), a supervisory control unit must actuate a set of switches to distribute power from generators to loads, while satisfying safety, reliability and real-time performance requirements. To reduce expensive re-design steps in current design methodologies, such a control problem is generally addressed based on minor incremental changes on top of consolidated solutions, since it is difficult to estimate the impact of earlier design decisions on the final implementation. In this paper, we introduce a methodology for the design space exploration and virtual prototyping of EPS supervisory control protocols, following the platform-based design (PBD) paradigm. Moreover, we describe the modeling infrastructure that supports the methodology. In PBD, design space exploration is carried out as a sequence of refinement steps from the initial specification towards a final implementation, by mapping higher-level behavioral models into a set of library components at a lower level of abstraction. In our flow, the system specification is captured using SysML requirement and structure diagrams. State-machine diagrams enable verification of the control protocol at a high level of abstraction, while lowerlevel hybrid models, implemented in Simulink, are used to verify properties related to physical quantities, such as time, voltage and current values. The effectiveness of our approach is illustrated on a prototype EPS control protocol design.