spurious z event

info51 · ‎2003-08-04

Posted on August 04, 2003 at 15:12

spurious z event

info51 · ‎2011-05-17

Posted on May 17, 2011 at 10:16

In my application , 230 V ( 115 and 100V too ) 4 poles motor pump voltage mode close loop,1000/1500/2000/2500/3000/3500 rpm selectable i have no problems when i' am using 6,25khz pwm frequency.

When otherwise i'am using 12,5 khz pwm frequency or more ( and for noise reason i must use 13,5 or 15,4khz ) i get same spurious z event , that give a next commutation too early with bad motor behaviour .

I tryed to change the threshold and to mask and the z interupt and /or cancel the pending z interupt during the d event without results.

Is strange that shapes on the oscilloscope of d_ event + z_event of a good event and a bad one seem really similar (for time and voltage level ).

I tryed to use only the softdemag in both side as samebody said to me but i get a not flexible motor to reach the target speed.

Now i' am using a pwm only in the same side during d and z event.

The Reo bit can be use for retard the z event as it seems from page 51/132 72141 datasheet ?

The z filter could be incremented more then 20usec ?

Could help me to change the OS2.0 bit in MCRB?

The SA3.0 bit in MPRSR with different frequency then my pwm frequency ( i'am in voltage mode) could cause my problem?

Have you some suggestion ?

Thanks in advance

bye

maxime2399 · ‎2011-05-17

Posted on May 17, 2011 at 10:16

May be your problem comes from the demagnetization. The demagnetization exists to mask the BEMF zero crossing event until the end of the winding demagnetization in order to avoid false BEMF reading.

If, for whatever reason the demagnetization event D comes to early, the ST72141 wil take the end of demagnetisation for the BEMF zerocrossing event.

As the BEMF is sampled at the PWM frequency it does not seem wrong that your problem disapear when you change the frequence.

If you use only the hardware demagnetization, the system will probably miss one once in a while and stop the system, therefore I recommend to use the software demagnetization as a back-up.