Enabling transmission of state variables and controller command signals between physics-based model and physical or emulated PLC requires developing fast and synchronous communication interface. This research investigates four methods of interface communication: (a) reading/writing to text files, (b) serial communication, (c) TCP communication, and (d) shared memory. The shared memory interfacing method provides the best performance, reliability, and fidelity. It is validated by linking a representative PLC controller to a Simulink dynamic simulation model of a fully integrated space reactor power system with multiple closed Brayton cycle loops for energy conversion (DynMo-CBC). Transient performance results of the PLC controlled dynamic simulation model are identical to those obtained using the Simulink model with internal control.