Smart Transformer (ST)-based Meshed Hybrid Microgrids (MHM) present advantages concerning the performance of conventional AC-DC microgrids (MG). Integrating the ST in MHM and Optimal Power Flow (OPF) algorithms is a suitable alternative for managing microgrids with high penetration of distributed energy resources. Thus, equivalent models of converters associated with the MG and ST are required to facilitate the formulation and solution of the optimization problem. This paper proposes an equivalent power flow model in ST-based MHM to formulate an optimal power management algorithm for day-ahead operation. The management algorithm delivers the optimal operating points of each of the MG converters to allow power control on both the AC and DC sides. The feasible solution of the OPF is verified in a simulation model in Matlab® Simulink® and its implementation in Real-time on the OPAL-RT platform to compare the results and validate the accuracy of the static models of the OPF. According to the tests performed, the accuracy of the ST equivalent model for Optimal Power Flow for day-ahead operation problems of MHM was verified based on Software-In-the-Loop (SIL) approach.