How to run a skew optimization study?

Objectives

This article shows how to use MANATEE software dedicated to the electromagnetic and vibro-acoustic simulation of electric motors to carry a fast multiobjective optimization of the skew pattern or sensitivity study on the total skew angle. Skewing can indeed help reducing both acoustic noise due to magnetic forces and torque ripple, but the objectives might be contradictory so a multi-objective optimization is required.

Principle

Skewing is an important technique to reduce electromagnetically-excited noise and vibrations in electrical powertrains. However, it reduces the average torque, it may increase radial force harmonic at some specific operating points, and more importantly it may not minimize acoustic noise and torque ripple at the same time. It is therefore necessary to quickly estimate the effect of skewing on these quantities. This can be carried in MANATEE software using a sensitivity study or a user-defined optimization project but a built-in skew study environment exists after the calculation of flux lookup tables. Two skew study environment exist, one for to run a sensitivity study on the effect of the total skew angle, one to carry a multiobjective optimization of the skew shape (e.g. angles of stepped-skew rotor magnets). In this case the following quantities are minimized:

  • max noise level during run-up
  • average noise level during run-up
  • max torque ripple during run-up
  • max average counter torque during run-up (to maximize the traction torque and avoid to much torque reduction when skewing)

Scripting implementation

To automatically run the skew angle parameter sweep at the end of the calculation, the simulation project should include Input.Simu.is_skewoptim = 1;

The maximum rotor skew angle (in stator slot pitch) is specified with Input.Simu.skew_rater_max = 2;

The total number of skewing values to be investigated is given by Input.Simu.Nb_skew = 20;

The skew angle sweep environment can also be launched after a basic simulation of MANATEE by calling the following command line: >>run_skew_sentivity_study The study results in the following graphical output:

Example of skew optimization study carried on a PMSM in MANATEE
Example of skew optimization study carried on a PMSM in MANATEE

To automatically run the skew pattern optimization at the end of the calculation, the simulation project should include Input.Simu.is_skewoptim = 2;

The maximum rotor skew angle (in stator slot pitch) is specified with Input.Simu.skew_rater_max = 2;

The skew pattern multiobjective optimization environment can also be launched after a basic simulation of MANATEE by calling the following command line: >>run_skew_optim

GUI implementation

TBC

See also

Skew optimization is illustrated in validation projects ALG_034 and ALG_035.

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