Comparison of PM and Hybrid Excited Machines for Marine Vessel Hybrid-Electric Propulsion

This paper evaluates the maximum torque capability of a hybrid excited synchronous machine in comparison with a conventional PM synchronous motor. The main focus of the paper is on the study of the effect of DC excitation magnetic flux on the saturation of the stator teeth, which limits the torque production capability of the hybrid machine. Magnetostatic and transient analyses are carried out for both motors. As expected the hybrid motor air gap flux controllability comes at the expense of reducing its torque density. The torque density reduction penalty is quantified and some hidden limitations and challenges of designing such a hybrid motor are revealed based on an in-depth analysis of the flux distribution within the machine.