New sinusoidal AC servo drive development


View Poll Results: Preferred power stage type (see descriptions below)

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  • SMD discrete MOSFETs

    22 14.19%
  • IRAMS10UP60A power module

    26 16.77%
  • Discrete through-hole MOSFETs with heatsink

    78 50.32%
  • SMD discrete MOSFETS + possibility to connect own custom external power stage

    13 8.39%
  • Controller logic only without integrated power stage. An external power stage must be used.

    13 8.39%
  • Some other solution (please specify)

    3 1.94%
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Thread: New sinusoidal AC servo drive development

  1. #1
    Registered Xerxes's Avatar
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    Default New sinusoidal AC servo drive development

    Hello! As many might have noticed from Surplus motors thread I have been designing my own servo drive especially for those Sanyo P5 motors. Many of Sanyo owners seems to be interested about my drive so I must ask for some opinions to get the idea what kind of drive is most wanted.

    I already have a working "proof of concept" running and I'm starting to build a real prototype soon. First thing to decide is the type of the power stage. Some explanations of each choice:

    1) Surface mount discrete MOSFETs: Continuous output power would probably be limited to about 500 Watts. However it has the most solid contruction and the lowest total component cost.

    2) IRAMS10UP60A power module (3 phase 600V 10A max). An easy solution (speeds up design process) but the voltage rating is somewhat unoptimal for 100Vac motors. Maximum output power would be around 500-800W.

    3) Discrete through-hole MOSFETs with heatsink. Over 1kW output power possible but has most undesirable construction. Many parts to cool down and heatsink must be insulated etc.

    4) SMD discrete MOSFETS + possibility to connect own custom external power stage of any power. Enough power for most applications (<500W) but enables to drive higher loads too. Requires lots of time to get it well tested.

    5) Controller logic only without integrated power stage. An external power stage must be used. Virtually any power possible.

    A typical power stage consists a) six power transistors, b) gate drivers for transistors, c) current sensing circuity and possibly d) short circuit protection (optional).

    Those 1kW servos have peak power rating of 3kW for 10% duty cycle. Because motor efficiency is not 100% it would require about 4kW power stage to squeeze everything out of motors. That kind of power stage can be complex and expensive.

    I wonder what kind of CNC machine it takes to utilize that kind of power. It must be a massive industrial size machine weighting tons that rapids at 1000 IPM. How many of you are planning to build one? I don't think its very good idea to pay for 4kW drives if you really need "only" 400W. Anyway I'm open to suggestions.



    Xerxes

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  2. #2
    Community Moderator ger21's Avatar
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    I've got 300w motors, so #1 sounds best to me.

    What about something like a rutex, that just accepts power from a simple power supply?

    Gerry

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  3. #3
    Registered Xerxes's Avatar
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    I'm planning to use 150V or 200V rated parts. However I don't recommend powering drive directly from power lines. An isolation trasformer can save lives.



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    You might remember from another thread that I'm also working on a similar project. I am using discrete IGBTs because I want to be able to handle higher voltage motors also (like the Compumotor SM series frequently available on Ebay). That IRAMS power module you found looks pretty sweet though also. and I might steal that idea for a future more compact version :-)

    If you think the surface mount MOSFETS can handle 500W output then that option would be great for the large number of people with the 300 and 400 watt motors, and "lowest cost" will certainly have appeal!

    I'll make a thread to document my progress in a week or two. Good luck with your design! It will be good to have several open source efforts in progress.



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    Default Joint Development?

    Just a suggestion, so take it with a grain of salt, and I'm not sure if its even feasable per Rutex's current product offerings/development path. But, I'd rather see a joint development effort to assist Vlad/Tom in a sinusoidal or otherwise modified Rutex, if that is indeed necessary to correctly drive the current AC brushless servos such as the P5.

    You're obviously skilled, willing, and interested in going to production with a product. Which is great. The only additional consideration is that Rutex has an established product platform with their current offerings, which adds stablity and the "warm fuzzies" to those like me who are interested in investing in a solid platform for retrofits to ease installation and tuning issues and that will be there in a few years with a replacement when a drive finally blows.

    I deal with licensing intellectual property, trade secrets, etc., in the semiconductor industry as my profession, so am aware of the difficulties and would be willing to assist if interested.

    Again, just a suggestion, and the undertaking of a sinusoidal drive is appreciated as I have 10 of the 1KW P5s--so whatever happens, my suggestion would be Rutex-style with sinusoidal amplification and headroom for at least 100V, 12amps cont., and about 40 amps peak, all for use with an independent unregulated power supply (basically enough to push the motors hard enough for retrofits to small VMCs with about 200-300ipm rapids).



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    FWIW
    A joint venture sounds like a good idea to me as well.
    I do not profess to be an expert in these units.
    Rutex seem to have most of the front end stuff already in place,just the power/motor interface side seems lacking.
    I have 6 of the 1kw units myself.
    Intended use are a knee mill and a gantry router/plasma cutter.
    hope this assists you.
    Des



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    why not use the IRAMX16UP60A parts that have higher output power? They are $31 single quantity instead of $23.



  8. #8
    Community Moderator ger21's Avatar
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    It looks like the 300-400w guys might one one type, and the 1Kw guys might want another. How about both.

    Gerry

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    personally, the reason I like the IR devices is that there is tons of circuitry in there that would have to be replicated on a circuit board with discrete devices. To me, the prices are so low it's a no-brainer.



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    Will the drives be adjusted with software or pots?

    Darek



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    Hmm, I agree that using the module is a no brainer just to simplify the circuit design by a huge amount. It might also be possible to "piggyback" the modules to scale the power output to any level possible (I may be wrong here).

    What did you plan on using for the brains of the device? There are tons of MCU/DSP chips that would work. Which device are you using?? Oh, and the setup below looks like it may work for lower power outputs. Not sure about price though.

    http://www.irf.com/technical-info/re...ns/iradk10.pdf

    Thanks,
    David Bloomfield



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    Xerxes,

    what microcontroller are you using ?

    are you planning on optoisolating the microcontroller from the powerstage ?

    what about current feedback, measure just one phase, or two/three for vector control ?

    any chance you will publish the plans and code somewhere ?

    I was thinking dsPIC30F3011 + IRAMS 10A myself. with current measurement on at least two phases for possible vector control. control of amp would be a ttl pwm torque command and ttl direction signal

    in the PC I would have a mesa electronics (www.mesanet.com) 5i20 PCI card giving torque commands to the servos and reading the encoders. control software would be EMC.



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    Would the IRF IRAMS10UP60A provide more than 400-500watt if driving servos at 300 volts instead of 100v?
    thanks



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    Quote Originally Posted by lolailando
    Would the IRF IRAMS10UP60A provide more than 400-500watt if driving servos at 300 volts instead of 100v?
    thanks
    yes, P = U*I (P power, U voltage, I current)

    but the surpluscenter motors are rated at 100VAC so it's probably not a good idea to drive them with a higher voltage (they will run at a higher rpm than rated but with less torque I guess)

    btw. does anyone know of a good DIY way of testing motors/drives.
    would be nice to do a comparison of different commutation methods.
    I am thinking about torque vs. rpm plots.



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    The IRAMS option seems be getting better. One can use that 16 amp IRAMX module instead of IRAMS if more power is needed. They are pin to pin compatible. IRAMX data sheet says it is suitable for 0.75-2kW/85-254Vac motors. That would mean about 850W power for 100Vac.

    andy55: My current work is based on ATmega8 MCU but I'm switching to dsPIC to deal with that 8000 CPR encoder. Two phase current sensing is enough for any kind of control.

    HillBilly: My design will be "stand alone" unit. No software tuning required.

    It might be too early to think about how to share these drives. Let's see that when we have almost ready product. Maybe indutrial made PCB's and pre-programmed chips would be the most cost effective?



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    it's not trivial to test motors. At work, we have a $16000 dynamometer, and that's the cheap one. It does 5hp, but it can't put power back into the motor which is required for 4 quadrant testing.



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    unterhaus, how about putting a large inertial mass on motor shaft? Acceleratin/decelerating that with certain speed would provide any motor load power.



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    in the old days they used strap torque meters, which had a strap wrapped around a pulley. I'm sure they are still around. The tighter the strap, the more torque. You also see people lifting weights, this would be more for stall testing. The idea of using a mass would work, but in general, you'd want load to be independent of acceleration.

    A milling machine isn't a bad test stand, you can vary the weight on the table.



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    Pardon my ignorance but I have a few questions...

    I kinda jumped the gun and bought 3 of the 400w Sanyo Denki P5 motors from Surplus Center before I fully appreciated the difference between AC and DC servo motors.

    Obviously, the AC Drives are pretty $Steep$.

    What I'd really like to see is a full 3-axis or 4-axis driver that incorporates the necesary parts to use a PC-based controller. I want to use it all to convert a small mill to CNC.

    Is this what you are proposing as a driver?
    Or are you thinking of discrete, individual 1-driver-per-motor drivers that are attached to a more conventional CNC controller such as an Aerotech U11, U511, U600 etc?

    And what sort of pricing are you thinking your unit will end up being (as project, kit, or assembled unit)

    Thanks,

    Tom



  20. #20
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    Looks like IRAMS option is winning this time. I'm almost fully decided to start developing the prototype with that power module to get project started as quickly as possible. The other optios are not abandoned though, maybe some alternative versions could follow later.

    Tom, combining many axes on single PCB gives little or no cost savings compared to single axis boards. That's why I'm going to to design a single axis drive.



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