Control challenges of an externally excited synchronous machine in an automotive traction drive application

Externally excited synchronous machines exceptionally suit the needs of axle drives in automotive applications due to their high efficiency over the whole operation range and the advantages for the realization of the functional safety. With the rotor current giving an additional degree of freedom new possibilities and necessities come up, bearing special challenges regarding the control. A loss minimum operation of the machine is needed, to achieve the requested vehicle autonomy at limited battery capacity, and is realized by a loss optimized reference current processing. With both costs and system weight needing maximum thermal utilization of the components, special attention is paid to a compatible derating concept. Since a quick torque response is important for the vehicle stability control and the driving performance, it is shown, that even with the comparatively high rotor time constant a highly dynamic torque control is realizable by a suitable system design and control structure. Fulfilling safety requirements forced by high ASIL classifications of vehicle drives is shown at the determination of the rotor temperature. Finally the handling in case of a system malfunction to realize a proper shutoff behavior is described.