Induction machine design for dynamic loss minimization along driving cycles for traction applications

Classical induction machine design generally focuses on achieving high steady state efficiency. In contrast, automotive applications consist of almost continuous transients, where the flux linkage is varied along the driving cycle to save energy. With conventional induction machines designed for high steady state efficiency, higher peak current and excessive machine losses can occur during the transient with varied flux linkage. Therefore, this paper focuses on the transient machine losses occurring during the highly dynamic driving cycle typically encountered by electric vehicle traction motors. The induction machine design methodologies that are most compatible to loss minimizing control are developed. The effect of magnetizing inductance and leakage inductance on rotor flux dynamics and transient and steady state losses are evaluated. The effect of changes in rotor slot dimensions on machine parameters is evaluated and losses along driving cycles are compared using the previously developed dynamic loss minimization control method. It has been found that the increased magnetizing inductance has a larger effect on loss reduction than a decreased leakage inductance. Unlike common guideline to minimize the leakage inductance, the leakage inductance can be appropriately increased for a higher magnetizing inductance to achieve a higher effective electromagnetic field coupling for lower losses along driving cycles.