Groups > comp.arch.embedded > #20098

encoders measurements in speed control loop

From	al.basili@gmail.com (alb)
Newsgroups	comp.arch.embedded
Subject	encoders measurements in speed control loop
Date	2015-02-16 09:22 +0000
Message-ID	<ckdr69F3at4U1@mid.individual.net> (permalink)

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Hi everyone,

I have to control a sinusoidal BLDC through a PWM and an H-bridge, 
following a profile written in a table.

 I have encoders reading as feedback but I have not quite well 
understood how to measure the difference between the position table and 
the encoders reading.

In general if the encoder reading is in the same turn as the table than 
everything is fine:

p = 78 deg (position)
m = 75 deg (measure)

e = p - m = 3 deg

But when I cross the 0 deg (360 deg) I have some stupid issues with signs:

p = 359 deg
m = 1   deg

e = p - m = 358 deg

while I would like to get -2 deg!
Even with modulo function I'd not be better off:

e = mod(p - m, 360) = 358 deg!

Should it be dependent on the quadrant I'm in?

I'm missing some basics here. And yes, a pointer to elementary school 
math is definitely appreciated!

Al

-- 
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encoders measurements in speed control loop al.basili@gmail.com (alb) - 2015-02-16 09:22 +0000
  Re: encoders measurements in speed control loop al.basili@gmail.com (alb) - 2015-02-16 10:06 +0000
  Re: encoders measurements in speed control loop Grant Edwards <invalid@invalid.invalid> - 2015-02-16 15:21 +0000
    Re: encoders measurements in speed control loop Tim Wescott <tim@seemywebsite.com> - 2015-02-16 10:30 -0600
      Re: encoders measurements in speed control loop Grant Edwards <invalid@invalid.invalid> - 2015-02-16 17:07 +0000
        Re: encoders measurements in speed control loop Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2015-02-16 20:09 +0200
  Re: encoders measurements in speed control loop langwadt@fonz.dk - 2015-02-16 11:52 -0800
  Re: encoders measurements in speed control loop Bruce Varley - 2015-02-17 20:14 +0800
    Re: encoders measurements in speed control loop Tim Wescott <seemywebsite@myfooter.really> - 2015-02-17 13:03 -0600
      Re: encoders measurements in speed control loop Bruce Varley - 2015-02-18 20:38 +0800
        Re: encoders measurements in speed control loop Tim Wescott <seemywebsite@myfooter.really> - 2015-02-20 12:27 -0600

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