Am Dienstag 25 Januar 2011, um 14:44:05 schrieb jros: > I can see you've be seriously dealing with the internals of PMSM, and I > would like to discuss a little bit about the subject,as I'm facing some > problems related to torque rippling issue.
First, my own experience is low. Casually I have seen people fighting with this problems. Reading some pdf's from web I get some understanding. First is the change in magnetic flux if you turn the rotor by hand (without current). You feel the cogging. Second you get torque ripple if the rotating magnetic field induced by the current does not move smooth. Read some papers about magnetic design of motors. Even a 3ph ac motor - he has no cogging because no permanent magnets - may have torque ripple, if stator design is bad. Personally I have done some investigations with small motors in the range of 10- 500W. To drive a motor I bought the RDK-BLDC and RDK-ACIM kit from Luminary Mirco (now TI). You get the full source code. Plan is to measure the cogging if you switch off motor current of a spinning rotor and see what an attached 2ph encoder delivers. In the past I have done this to see the stepper motor vibrations. If you know the effect of cogging (at some speed) operate the motor at this speed and look again to the encoder signals. If minimum and maximum values of encoder signal period during one revolution inscrease, the induced rotating magnetic field is not smooth. Unfortunately servo motors operate in the frequency range of some natural vibrations of mechanics (I look at the picture of your webpage). Steel constuctions suffers from lack of damping (steel!). BTW can emc emit motor signals without special frequencies, which stimulate machancal resonances? If you use a toothed belt this can reduce the vibrations from motor, but now you have additional oscillation possibilities. To implement a feedforward method I see 3 positions: emc, a microprocessor and a fpga. Assume emc delivers some signal. Than a additional module inside emc must put in the predistortion knowing the rotor positon with high resolution. If a micro (see Kirk's AVR page) can calculate a sine modulation he can do some other function, because usualy a table with sine values are used. And this table can be modified. For very fast drives maybe a fpga solution is the way to go. (I am working on my Raggedstone1 project.) I do not have personal experience with linear motors. Lacking reduction you see magnetic problems better. Joachim ------------------------------------------------------------------------------ Special Offer-- Download ArcSight Logger for FREE (a $49 USD value)! Finally, a world-class log management solution at an even better price-free! Download using promo code Free_Logger_4_Dev2Dev. Offer expires February 28th, so secure your free ArcSight Logger TODAY! http://p.sf.net/sfu/arcsight-sfd2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
