Designing Energy Efficient Traction Machines for Electric and Hybrid Vehicles (NAFEMS World Congress 2019)

The design of powertrain motors for electric or hybrid vehicles presents many challenges. The designer faces multiple constraints on weight, compactness, cost, efficiency and temperature rise. The efficiency of the motor impacts directly the autonomy of the vehicle. In a race to sustainability, designers need innovative methodologies and fast tools to meet the many requirements of electric mobility. Rotating machines are traditionally optimized at their rated operating point. For powertrain applications, motors operate over a wide range of speeds and torques. The efficiency of the motors must be optimized considering the full driving cycle of the vehicle. Today, such optimization can be achieved using new dedicated and fast analysis tools. These design tools deliver reliable evaluation of the motor efficiency throughout the driving cycles. These tools help the designer select the most efficient machine topology early at the predesign stage. Constraints on efficiency and temperature rise make evaluation of losses a key element of the design process. During predesign, a pure sinusoidal power supply is considered and eddy current losses in the permanent magnets are ignored. Because of the high-speed operations of the motor and the use of pulse width modulation (PWM) power supply, a full evaluation of the losses is needed. PWM power supplies introduce harmonics in the currents fed into the machine. Detailed losses in permanent magne ts, back iron, and windings must be evaluated to predict the motor efficiency in an accurate way. The impact of the losses on the temperature rise can be evaluated. An adjusted design can mitigate the losses and better meet the thermal constraints of the machine. A coupled magnetic/thermal simulation is needed. In such a computation, electromagnetic losses are the sources for the thermal problem. This full methodology is shown through the design of a powertrain motor, starting from the initial specifications of the motor. We will show how simulation and optimization tools can be used to help maximizing the overall efficiency of the motor and meet all design requirements.