Re: Do you think NI can fix my PLL?

"Chris Carlen" <crcarleRemoveThis@xxxxxxxxxxxxxxx> wrote in message
news:e5pogq0hav@xxxxxxxxxxxxxxxxxxxx
Hi:


I'm attempting to build another motor PLL system and running into some
difficulties stabilizing the loop. Since there is a lot of work to do,
I have considered contracting out the PLL design to a well known control
expert outside of my company, so I can focus on building other
subsystems of the project.

Basically, the PLL is to lock a 136mmx2.54mm Al wheel to a 400Hz
reference (24kRPM, 1 pulse/rev position sensor). Must be 2nd order PLL
yielding zero phase error with constant frequency input. Wheel to be
driven directly by a Maxon 200W brushless DC motor with an Advanced
Motion Controls B15A8 PWM servo driver running in open loop mode. I
have found that the open-loop mode of the motor drive results in not
very linear DC transfer of ref. voltage in to motor phase voltage out,
as well as not yielding a very linear dynamic response as well (rise
time != fall time, but only by about 10-20%).


~~ snip ~~

I have no idea about what NI can do for you, but I notice you have 2 lots of
90' phase shift within the PLL loop so the maths is not like an ordinary
electronic PLL, the conversion of rpm to phase difference unavoidably shifts
90', the mass of the flywheel also provides 90' phase shift - above a
certain frequency determined by mass of the flywheel and the series
resistance of the motor etc. this makes for a second order loop already but
with no polo/zero compensation providing loop stability. I dont know what
you have put in your model or if you have a loop filter as well, but it
should be able to model it quite well even in a circuit simulator converting
the mass of the flywheel to an electronice equivalent.

To get it to work you would need to make sure the open loop PLL gain is 90'
at and around unity gain, this could well mean a very much lower loop gain.

Idealy the motor would have speed feedback to remove the phase shift from
the flywheel, isnt the servo loop capable of doing this or is there a reason
why it cant be used ?

Another option is to use a negative impedance motor driver wich compensates
for the voltage drop acros the motor resistance thereby minimising the lag
cuased by the flywheel (will then be slew rate limited).

I have done washing machine motor speed feedback controllers and many vco
type PLL, but not motor phase control, what your doing sounds far more
interesting than washing machines .... zzzzz

Colin =^.^=


.

Relevant Pages

  • Re: Do you think NI can fix my PLL?
    ... 90' phase shift within the PLL loop so the maths is not like an ordinary ... electronic PLL, the conversion of rpm to phase difference unavoidably shifts ... certain frequency determined by mass of the flywheel and the series ... Yes, I have modeled the motor as an electronic equivalent circuit, and set up loop compensation to provide>45 deg phase margin at unity, also -6dB/oct slope through unity. ...
    (sci.electronics.design)
  • Re: Do you think NI can fix my PLL?
    ... Since there is a lot of work to do, I have considered contracting out the PLL design to a well known control expert outside of my company, so I can focus on building other subsystems of the project. ... Wheel to be driven directly by a Maxon 200W brushless DC motor with an Advanced Motion Controls B15A8 PWM servo driver running in open loop mode. ...
    (sci.electronics.design)
  • Re: Do you think NI can fix my PLL?
    ... I'm attempting to build another motor PLL system and running into some difficulties stabilizing the loop. ... Since there is a lot of work to do, I have considered contracting out the PLL design to a well known control expert outside of my company, so I can focus on building other subsystems of the project. ... Wheel to be driven directly by a Maxon 200W brushless DC motor with an Advanced Motion Controls B15A8 PWM servo driver running in open loop mode. ...
    (sci.electronics.design)
  • Do you think NI can fix my PLL?
    ... Since there is a lot of work to do, I have considered contracting out the PLL design to a well known control expert outside of my company, so I can focus on building other subsystems of the project. ... Wheel to be driven directly by a Maxon 200W brushless DC motor with an Advanced Motion Controls B15A8 PWM servo driver running in open loop mode. ... My assertion has been that PLL stabilization is not something that can be done the way most controls are handled around here where you can use heuristic algorithms to getting it to work). ...
    (sci.electronics.design)
  • Re: Do you think NI can fix my PLL?
    ... It seems like you may need a much higher bandwidth than the typical servo amp provides. ... I am assuming there is some digital circuitry in the servo amp (has to be at least a PWM ... The PM motor was driven with a linear amp, a transistor boosted power op-amp, like you speak of below. ... The PLL loop compensation filter took care of the rest. ...
    (sci.electronics.design)
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