The MTAB project set out to halve the mass of the traction drive of a rail vehicle while raising its efficiency by at least thirty percent. The key to the weight reduction was the use of a higher‑speed traction motor, which allows a smaller motor and gearbox for the same power. To support the higher motor speed, Fraunhofer IISB designed a new inverter that could deliver the required higher switching frequencies and power density. The inverter was built around commercially available silicon carbide (SiC) modules from Wolfspeed, specifically the CAB450M12XM3. Two modules were paralleled in each phase to meet the power level, and the design had to synchronise the switching of the parallel SiC devices while keeping the commutation inductance low to minimise voltage overshoot.

The project compared three topologies: a two‑level hybrid B6, a two‑level SiC B6, and a three‑level silicon NPC. Switching‑time measurements showed the SiC topology achieved a 226‑nanosecond switching time, compared with 1050 ns for the hybrid and 611 ns for the silicon design. The SiC inverter operated at 20 kHz, a ten‑fold increase over the 2 kHz reference inverter, and required water cooling to dissipate the higher losses. The resulting inverter mass was 17 kg, exactly half the 34 kg of the reference system, meeting the fifty‑percent weight‑reduction target. The DC link voltage was 750 V, with an effective current of 220 A and a peak of 480 A for short bursts. The inverter’s efficiency was projected to exceed the reference by thirty percent, enabling higher power density for the rail vehicle.

The development followed a structured milestone schedule. Milestone 1 defined the reference system and target values. Milestone 2 covered conceptual design, while Milestone 3 moved to detailed design and prototype construction. After pre‑testing, the prototypes entered system testing at Alstom’s laboratory (Milestone 5). The final evaluation (Milestone 6) confirmed the performance and weight goals. Delays caused by the COVID‑19 pandemic and the delivery of the test rig extended the project to September 2022 without additional cost.

Collaboration was central to the project. Fraunhofer IISB led the inverter design and integration. Alstom coordinated the system test and provided the traction motor and gearbox, ensuring that the inverter met the real‑world operating conditions. STAMA supplied the hardware interface between the control board and the inverter, while KIT contributed loss data for system‑level simulation. The university partner usb supplied mass predictions for the overall drive train. The project was funded by the German Federal Ministry of Education and Research (BMBF) and the European Union, and all partners worked in a tightly integrated consortium, sharing data and aligning interfaces throughout the development cycle. The combined effort produced a lightweight, efficient inverter that satisfies the stringent requirements of modern rail traction systems.