Unified Model Framework for Electrified Propulsion Systems Based on Equivalent Circuit Models

This paper introduces a unified and physically grounded modeling framework for electric propulsion systems, formulated using active Equivalent Circuit Models (ECMs). The proposed framework integrates the coupled dynamics of the propulsion system, hierarchical control architecture, and hull surge motion within a single circuit-theoretic structure, enabling a consistent representation of electrical, mechanical, and hydrodynamic interactions. Key dynamic phenomena including torque generation, inertial responses, and hydrodynamic loads are represented through electrical equivalents, enabling a computationally efficient yet physically interpretable simulation environment. The control system, from ship speed regulation to motor-drive control, is modeled as a hierarchical set of circuit-level submodels that retain domain-specific dynamics and their interdependencies. Model validation is performed via two complementary approaches. First, a switching-based simulation model is developed to verify dynamic motor behavior under no-load conditions, demonstrating consistency in predicted q-axis current, motor speed, and electromagnetic torque. Second, experimental validation focuses on steady-state propulsion characteristics, including thrust, propeller torque, effective power, and self-propulsion point. All ECM parameters are derived from scaled experimental measurements, including towing tank resistance and propeller open-water tests. The proposed model offers structural scalability and extensibility, positioning it as a foundation for real-time simulation, system-level co-design, and digital twin development in next-generation electric and hybrid-electric marine vessels.