Direct drive concept for heavy-duty traction applications with the brushless doubly-fed induction machine

In this paper, the brushless doubly-fed induction machine (BDFM) is presented as a direct drive system for heavy-duty traction applications (near-wheel or wheel-hub drive). In conventional direct drive traction systems, every motor needs its own inverter, which has to be dimensioned to at least the motor's full power. Because of the natural operating characteristics of the BDFM, in the new proposed system the motors can be supplied mainly from a large, shared inverter, whereas the wheel's speed differences and torque regulation can be controlled from small, auxiliary inverters for each motor. On the one hand, this can lead to cost savings on system level, and on the other hand the BDFM offers advantages like simple materials and production as well as increased functional safety because of the lack of magnets and brushes. As the power density of the BDFM is smaller in comparison to conventional machines, this concept may be mainly interesting for heavy-duty vehicles, where the motor's weight is less important.