Parameter Sensitivity Studies on Loss Minimization of Traction Drive Systems for Electric Vehicles

Traction motors typically operate at their best efficiency around rated conditions. Nevertheless, a significant decrease in efficiency occurs when considerable imbalances arise between copper and iron losses at light loads and low speeds. By running the motor at appropriate flux levels, according to load and speed, operating efficiency can be improved. Various loss minimization techniques exist to determine the appropriate flux magnitude to maximize the motor's efficiency. However, the machine's efficiency can be potentially impacted by variations in temperature and magnetic saturation, which can alter the optimal flux value, requiring further investigation. In this study, the effects of variation of each of the circuit parameters, namely the resistances in the stator and rotor, and magnetizing inductance on loss minimization are evaluated. It is observed that the optimization algorithm tuned for nominal magnetizing inductance can maintain near-optimality in all regions even in the presence of saturation, without significantly impacting efficiency. However, the optimal flux point shows greater sensitivity to variations in stator and rotor resistances due to temperature increase. Therefore, online estimation of these resistances is crucial to ensure the effective performance of the loss minimization algorithm. The simulation study observations are verified under dynamic operating conditions using a standard drive cycle.