Electric motors for vehicles are evolving rapidly, driven by the need for compact designs, high power density, energy efficiency, and affordability. As a result, permanent magnet synchronous machines (PMSMs) with NdFeB magnets are still commonly used for electric traction applications due to their unmatched efficiency, power density, and torque density. However, as the back electromotive force (EMF) of PMSMs is proportional to their speed, the available DC bus voltage limits their speed.

The HighScape project explored various strategies to address this limitation, including field weakening, the use of mechanical gearboxes, and buck-boost DC-DC converters. While these solutions can extend the motor’s speed range, they often introduce compromises in efficiency, increase system complexity, or add significant costs, making them less than ideal for practical applications.

The project identified one promising alternative in winding changeover techniques, specifically e-gears with mechanical switches (e.g., relays, and contactors). The switches — which are implemented by means of mechanical relays — allow to change the winding connection of the electric machine from a series to a parallel connection and hence double its efficient speed range.

Download the paper by Hendrik Vansompel, et al. to understand how the HighScape project tested the concept through simulations. The experimental results on a 4-kW axial-flux PMSM confirm the concept’s feasibility and prove that the reconfiguration can be conducted in less than 35 ms.