Searching for Optimal Solutions for Motor Performance Design

This paper relates a method for seeking Pareto solutions for strength, torque-rotational speed characteristics, losses, and exciting force in the preliminary design of interior permanent magnet synchronous motors (IPMSM) and carrying out optimal design in an integrated manner. As to the constraint on strength, it was determined that the von Mises stress on the rotor core with respect to the load of the centrifugal force at 1.2 times the maximum rotational speed should not exceed the breaking strength of common electrical steel sheet material. As to the torque-rotational speed characteristic, this was determined to be the maximum torque for each rotational speed, taking into account the maximum voltage and current input when maximum torque per ampere control and field weakening control are applied. The maximum torque at low rotational speed and the maximum power at maximum rotational speed were taken as evaluation parameters. Losses were defined as the total value of DC copper loss occurring in the coil and iron loss occurring in the stator and rotor core. As to the exciting force, the 6th and 12th order components with respect to the electrical angle of the torque ripple and the radial force were taken as the objects of evaluation. Maximization of maximum torque and minimization of the weighted weight and losses were configured as the objective functions. The size of the motor, magnet layout, and magnetic flux path were defined so that they could be changed parametrically. Then the above analysis was performed automatically so that the trade-off relationships could be visualized quantitatively. As a result, it became possible to simultaneously analyze performance tendencies relating to major design changes and performance tendencies relating to detailed changes.