The thesis addresses pros and cons of the ISG (integrated starter generator) and highlights the permanent magnet synchronous motor as one of the leading candidates for applications in the ISG field. It shows the potentially dangerous hazards that unwanted short-circuits and related braking torques pose in ISG applications and aims to determine them as close as possible. It develops a two-axis model of the permanent magnet synchronous motor and explains the necessary mathematical and physical background. It offers an in-depth explanation of the problems that nonlinear ferromagnetic materials pose. The basic two-axis model is improved with data obtained from the finite element method, which aims to create more realistic simulations and takes into account the nonlinearity of ferromagnetic materials, temperature dependence and iron losses. Problems that arise during this process are highlighted. An exact calculation of all the needed inductances proves to be an especially tenacious obstacle, as it turns out that even small discrepancies have a sizeable impact on the simulation. Simulation results of the basic and improved model are shown and compared to measured values. Finally, possible explanations for remaining discrepancies are shown, and other, possibly better approaches to the problem, are proposed.