This study introduces a modified dynamic multiphysics modeling framework to characterize the electromagnetic-electrothermal (EET) coupled behavior of a power conversion system during a long load operation. The modeling framework extends the prior model with more comprehensive analysis and enhanced computational efficiency and modeling simplicity. This framework incorporates a fully integrated electromagnetic circuit (FIEC) model for extracting parasitics, including self and mutual inductances and also exploring their effect on the switching characteristics and power losses, and a dynamic power loss-temperature thermal (PTT) model for describing the temperature-dependent instantaneous electrical behavior and power loss. Moreover, a simple resistance-capacitance (RC) snubber circuit design is applied to prevent overvoltage and diminish voltage oscillations and spike value during the operation, and their power losses are also assessed and considered in the dynamic EET coupled modeling. Furthermore, the proposed PTT model employs an equivalent thermal RC network to calculate the chip junction temperature with a given power. Additionally, a simple power-temperature relationship derived from the FIEC cosimulation is applied for modeling simplicity and computational efficiency. This framework is tested on a three-phase inverter operating with a 180-deg conduction mode. The proposed FIEC cosimulation and computational fluid dynamics thermal models are validated by double pulse (DPT) and infrared thermography experiments, respectively. Moreover, the PTT model is validated compared with the conventional dynamic coupled electrothermal model. Finally, a design guideline for enhanced thermal performance of the tested power conversion system is sought through parametric analysis.