The digital twin of an AC active power cycling laboratory setup using the quasi-threshold voltage as temperature-sensitive electrical parameter for junction temperature estimation is developed. It represents a system-level converter system which consists of power electronics based on 1.2 kV/120 A SiC MOSFETs with temperature-dependent parameters including parasitic components in the gate loop, a control system, and a quasi-threshold voltage acquisition circuit. A comparison of the TSEP acquisition from the digital twin with actual measurements at different temperatures achieves a deviation of less than 3%. The digital twin opens the way to reduce development time, test hypotheses in the control strategies and the gate and power loop design, and to obtain synthesized data for machine learning.