Higher Strength Low Loss Electrical Steels for Improved Design and Performance of Interior Permanent Magnet Traction Motors

The influence of high mechanical yield strength, low loss electrical steel (ES) grades on the design degree of freedom of interior permanent magnet (IPM) traction motors for electric vehicles is presented. Several ES grades with different electromagnetic and mechanical properties are compared in this investigation. Firstly, the optimal bridge thickness of the V -shaped IPM rotor is obtained by evaluating the von Mises stress at the maximum operating speed using a structural finite element (FE) analysis. Then, the optimal axial length is estimated by means of electromagnetic FE analysis using the mechanically optimized rotor design in order to achieve an equal output mechanical power of the traction motor for all evaluated ES grades. The results show that the ES grades with high mechanical yield strength and low loss adds a degree of freedom in the IPM design. It results in a higher torque density as well as lower magnetic losses in the stator and rotor cores. Hence, it leads to a more compact and lighter motor design that has a significant effect on the motor power losses and consequently on the vehicle drivetrain efficiency.