Comparative Study of Induction and Wound Rotor Synchronous Motors for the Traction Drive of a Mining Dump Truck Operating in Wide Constant Power Speed Range

Motors with rare earth permanent magnets are the most compact and energy efficient in most applications. However, their use as traction motors for off-highway vehicles, such as mining dump trucks, is challenging not only because of the high cost of the magnets, but also because of the difficulty of providing a wide range of constant power speed control due to the unregulated permanent magnet flux. For this reason, induction motors remain the most popular type of motor for hybrid and all-electric mining dump trucks. However, the use of an induction motor results in increased power loss, increased current, and high temperature ripple of the power switches of the solid-state inverter when stopping on a slope with an electric brake. In this article, a theoretical comparison between an induction motor (IM) and a magnet-free wound rotor synchronous motor (WRSM) with a rotor DC-excitation in a mining dump truck drive is presented. Both motors have an identical stator outer diameter, and their geometry is optimized using the Nelder-Mead method. 2D finite element analysis in the time domain is used to calculate the IM characteristics. Steady-state characteristics of the motors such as efficiency, losses, torque ripple, required inverter power, dimensions, weight and cost of active materials are compared. In addition, losses and temperature ripples in the power modules of the semiconductor inverter, which affect the reliability of the drive, are compared when using the considered motors. The study demonstrates that the WRSM offers significant benefits such as reduced power loss, inverter power requirement, cost and mass of active materials, making it promising for use in mining trucks.