The increasing complexity of modern spacecraft requires advanced tools to model, analyze, and validate their on-board subsystems before deployment. This thesis presents the design and implementation of a Digital Twin of a satellite’s Electrical Power System (EPS), with particular emphasis on the Power Control and Distribution Unit (PCDU). The Digital Twin is conceived as a high-fidelity software replica that mirrors the functional behavior of the physical system, enabling real-time monitoring, prediction, and testing in both nominal and off-nominal scenarios. The developed simulator, implemented within the SIMULUS framework, reproduces the interactions between solar arrays, batteries, and electrical loads, incorporating Constant Current/Constant Voltage (CC/CV) charging logic and realistic power flow constraints.