Advanced simulation concept for the power train of an AC locomotive and its verification

Recent AC railway traction vehicles contain two main power electronic components in the power train, the four-quadrant converter and the three-phase machine-side inverter. They are joined by a common DC-link capacitor and - often - a resonant circuit tuned to twice the supply frequency. Converter and inverter are mainly controlled separately. The overall performance of the traction vehicle can be improved considerably by an integrated control of converter and inverter, explicitly taking into account the dynamics of the DC-link filter. This requires, however, enhanced control and simulation effort. The simulation has to deal with a hybrid system, described on the one hand by continuous differential equations and on the other hand by converter switching functions. The continuous part of the system is described by state-space equations solved by the Bulirsch-Stoer implementation of the Richardson extrapolation, the switchings are modeled using Petri Nets. This combination allows high-speed simulations of the complete system at suitable precision. For verification the simulation results are compared to measurements made at a 50-kW laboratory test set-up of the complete power train. At this early stage of the project, simple control schemes are used for first tests of simulation and test set-up. Measured and simulated quantities are in very good agreement, allowing to proceed to more sophisticated control schemes.