Multi-phase Motor Controller?

[John Jacobs]

A new large-diameter, permanent magnet motor line is currently under design
for very low speed (2 rad/sec), high-precision (10 urad) applications. For a
3-phase motor, torque ripple is ~7%, with ripple inversely proportional to
the number of phases.

An attractive alternative to the standard 3-phase controller is an FPGA
multi-phase controller where each stator coil is individually controlled.
For the preliminary design, somewhere in the range of 30 stator coils will
be utilized.

Has anyone had any experience in using an FPGA for this type of application?
Commercial drivers are primarily based on either trapezoidal or sinusoidal
commutation schemes, and it would seem that since each coil could be
individually controlled, either scheme could be readily implemented.
Commercial and open cores all seem to be based on the standard 3-phase
windings.

If any individuals with experience in this area would be interested in
working on a project such as this on a consultant basis, kindly send a brief
description of relevant experience and a contact number or email address to
jjacob @ acm-nevada . com (without spaces).

Jon Jacob
ACM Nevada

 

[Jim Granville]

John Jacobs wrote:

A new large-diameter, permanent magnet motor line is currently under design
for very low speed (2 rad/sec), high-precision (10 urad) applications. For a
3-phase motor, torque ripple is ~7%, with ripple inversely proportional to
the number of phases.

That's true for a fixed voltage/sine drive : with electronics it does
not have to be either.

An attractive alternative to the standard 3-phase controller is an FPGA
multi-phase controller where each stator coil is individually controlled.
For the preliminary design, somewhere in the range of 30 stator coils will
be utilized.

Has anyone had any experience in using an FPGA for this type of application?
Commercial drivers are primarily based on either trapezoidal or sinusoidal
commutation schemes, and it would seem that since each coil could be
individually controlled, either scheme could be readily implemented.
Commercial and open cores all seem to be based on the standard 3-phase
windings.

FPGA would be well suited to this, as would higher end DSPs, and some
DSP vendors have specific motor development kits.
At the extremes of precision, the problems are not just electrical -
the best motor-optimise designs I have seen, include a Motor-Cal-ROM,
that is the calibrations of that particular motor.
High precision absolute Rotary encoder feedback is another method to
check/calibrate the motor behaviour. Also remember copper wire has a
significant temperature coefficent.

-jg

 

[Kelvin]

it seems most likely your FPGA will be very underutilized...Go for CPLD...

Kelvin





"Jim Granville" <no.spam@designtools.co.nz> wrote in message
news:FWGFc.6084$NA1.570776@news02.tsnz.net...

John Jacobs wrote:
A new large-diameter, permanent magnet motor line is currently under
design
for very low speed (2 rad/sec), high-precision (10 urad) applications.
For a
3-phase motor, torque ripple is ~7%, with ripple inversely proportional
to
the number of phases.

That's true for a fixed voltage/sine drive : with electronics it does
not have to be either.


An attractive alternative to the standard 3-phase controller is an FPGA
multi-phase controller where each stator coil is individually
controlled.
For the preliminary design, somewhere in the range of 30 stator coils
will
be utilized.

Has anyone had any experience in using an FPGA for this type of
application?
Commercial drivers are primarily based on either trapezoidal or
sinusoidal
commutation schemes, and it would seem that since each coil could be
individually controlled, either scheme could be readily implemented.
Commercial and open cores all seem to be based on the standard 3-phase
windings.

FPGA would be well suited to this, as would higher end DSPs, and some
DSP vendors have specific motor development kits.
At the extremes of precision, the problems are not just electrical -
the best motor-optimise designs I have seen, include a Motor-Cal-ROM,
that is the calibrations of that particular motor.
High precision absolute Rotary encoder feedback is another method to
check/calibrate the motor behaviour. Also remember copper wire has a
significant temperature coefficent.

-jg

 

[Ray Andraka]

That depends on the sophistication of the motor controller. If you are
producing sinusoids for each winding, along with non-linear
acceleration/deceleration and precise positioning, the controller can pretty
quickly exceed the resources of a CPLD. I did some motor controls several
years ago for a photo printer application that included DPLLs on the motor
feedback, and very precise control of position, velocity, acceleration as well
as corrections for web tension and movement. Got to be a rather interesting
DSP app.

Kelvin wrote:

it seems most likely your FPGA will be very underutilized...Go for CPLD...

Kelvin

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email ray@andraka.com
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759