On Mon, 17 Jun 2013, propcoder wrote:
> Date: Mon, 17 Jun 2013 12:33:47 +0300
> From: propcoder <[email protected]>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <[email protected]>
> To: [email protected]
> Subject: [Emc-users] BLDC - not smooth rotation with hostmot2 and 3-phase
> bridge
>
> I started to test IRAM module with MESA 5i23. I use TPEN6_6 firmware and bldc
> module in "n" mode.
>
> I am rotating it slowly (setp bldc.0.frequency 0.2). PWM outputs are true
> sinusoidal (checked on scope), but motion has some smooth (non-linear) parts
> and stop parts.
>
> BTW, I can't use bldc "n6" mode, because I don't have where to connect
> A-high-value, A-low-value, .. because bldc component has A-value, .. pins
> only. When I use "n" mode, the motion is not smooth and it does not depend on
> strength (bldc.0.value).
>
> Shouldn't PWM curve look not like sine, but with "kinks" in the center, smth.
> like this:
> http://www.postech.ac.kr/ee/cmd/102_BLDC_pedal.htm
> ?
>
> My config hal file attached. Look at X axis.
>
I would not expect very smooth operation in 'D' or step motor mode (no encoder
feedback/PID), especially with IGBTs and their long switching times that
neccessitate a large dead zone. Do you have the dead zone time set properly? I
think the default is 5 Usec which is (deliberately) huge. (note: too small
a dead time will be fatal to your IRAM)
I would get feedback running before worrying a lot about smoothness.
You definately do not want kinks in the top of the voltage waveform.
if anything you may want a voltage step at the sine zero crossing to
compensate for the dead zone (if the required dead zone is a significant
portion of the total PWM period).
Peter Wallace
Mesa Electronics
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