Cogging torque FFT results and theoretical content are different.

    • Byeongchul Lee


      I have a question about MOTORCAD.

      The model is 8 poles and 12 slots, and the cogging torque cycle is 24 cycles, which is the least common multiple of 8 and 12. (360 Mdeg)

      If the waveform is analyzed by FFT, it is predicted that the proportion of the 24th order component will be large.

      I confirmed that the prediction was correct using Maxwell's program.

      However, as shown in the attached picture, the result of Motor CAD is different.
      (An unidentified 23rd order appears.)

      This confuses me quite a bit.

      Please help me.


    • HDLI
      Ansys Employee

      Hello Byeongchu Lee,

             Could you enter 24 in “points per cycle” of cogging torque calculations of input data -> settings -> calculation?

              This default value may not be good to present 24 cycles. As we know, the cogging torque frequency is the LCM (least Common Multiplier) of rotor pole and stator pole number, so we may need a good number for the points per cycle.


    • HDLI
      Ansys Employee

      Hello Byeongchu,

           Could you show your machine with 12 slot and 8 pole? and points per cycle and results again?

            Do you have a skew?

            I could not download anything by this forum guideline.

            I believe we should find 24th order when teeth are straight.


      • Byeongchul Lee


        1. model 8P12S (simple model)


        2. Setting

        3. Setting



        4. Setting

        (No Skewing)

        5. Result

        Cogging torque data has 23 period too

        I don't know why that has 23 too.




Viewing 2 reply threads
  • You must be logged in to reply to this topic.