Analysis of a traction induction motor drive operating under maximum efficiency and maximum torque per ampere conditions

The efficiency of an induction motor drive plays an important role in energy conservation, especially for electric vehicle applications. For the most commonly referred motor drive efficiency indexes, maximum efficiency (or minimum loss) and maximum torque per Ampere, it was found that through theoretical derivation, these two indexes do not occur at the same point in most speed and torque conditions. Closed form solutions of the two indexes as a function of slip have been derived. Their corresponding currents are also derived for comparison purpose. A traction motor-inverter drive system has been designed and tested to verify the concept. The experimental results agree reasonably well with the theoretical prediction.