Re: [oc] VHDL PID Motor Controller

[Jean Masson <Jean.Masson@lium.univ-lemans.fr>]

Hello Josh,

I have not implemented a PID system in FPGA, but the system is basicaly an ALU, with a multiplier
(MAC of DSPs).
You can use elements for arithmetic treatments : adder, shifter, multiplier (Brown or Boothe
cellular structure) :
P, is a multiplier by a constant. I, is an adder (integration) with multiply and D, is a
substractor (time derivative) with
perhaps multiply.

A good source is the site of Federal Institute of Technology in Zürich (CH), Dr. Zimmermann has
done implementation
of a great number of arithmetic subsystems, in VHDL. His tutorial on binary arithmetic is also
excellent.

If you have enough room on your Virtex, a pipe-line architecture, with a one PID evaluation by
clock cycle, is feasible.
This is an excellent student project thema, that I keep in mind !

It remains one question, is Virtex cheaper, better, or faster than, says, 3 pipe-lined DSPs SHARC
for the same performance ?
Did you think that a 100 MHz PID evaluations for a motor speed control is realy necessary ? No over
killing...
I perform motor speed control with a simple Cygnal system, and 8051 code (12 bits of ADC and DAC)
with a pulse
tachymeter.

Best regards,

Jean MASSON


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