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VFD's and 3phase Induction motors FAQ corner / pls. Read all first

Discussion in 'Motor actuators and drivers' started by speedy, Dec 23, 2013.

  1. Martin van Hagen

    Martin van Hagen not trying brings you nothing! SimAxe Beta Tester Gold Contributor

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    @speedy I think we are, and am exploring the possibilities how to deploy such set-up. To enable the collected data to be translated into a mechanical motion there is a need for an interface between the computer and the VFD. Then reading various posts I am forming the opinion that an Arduino could function as an interface in either a analogue signal 0 - 10 Vdc (-100% to + 100%) and, as you answered my question, this would be in position mode. Correct me if I am wrong but if the Arduino send a 7,5Vdc signal tot he VFD this would mean a 75% of the total travel of the calibrated distance. So far so good. Now I am looking into what if I can add a RS485 shield onto my arduino, daisy chain the drives and remap the MODBUS configuration to communicate with my drives. That, with some experimenting, should not be that difficult. So I have requested the mapping of the Delta drives, will buy a few RS485 shields and, over then next weeks, start the task to get up to par with MODBUS and emulate the drives as a project. :D Good thing is that I travel a lot so this can be dragged around relatively easy.
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    Last edited: Oct 8, 2014
  2. speedy

    speedy Well-Known Member

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    @Martin van Hagen ...
    This is what i think i know about positional control for this application. Your Arduino that is connected to the PC will do the PID and send an analog voltage and the direction of rotation to the VFD. Practically you start to accelerate in the game, the control board compares position feedback with the new set point received from the PC, the controller then determines the changes and sends a calculated analog voltage to the drive (say 2 volts) and a direction (say FWD) ... so motor is moving with 20% of its max speed approaching the new physical position ... The closer the motor moving to the new set point / the smaller the error becomes in the controller / a continuous descending analog signal is produced in the FWR direction / sent to the VFD drive until a 0.0V / a full stop to the motor in the new set point .

    using the MODBUS through the RS485 is not what you need as DIY at all ... I'm not going that way ,Sorry .
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  3. Martin van Hagen

    Martin van Hagen not trying brings you nothing! SimAxe Beta Tester Gold Contributor

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    @speedy Thanks for that explanation! :thumbs It will be position mode as my preferred method of operation.
    On the whole MODBUS situation I am just going to experiment with it as it has my own personal interest and I would like to use the internal features that come with these VFDs to get the maximum out of them. I have seen some impressive response times and accuracies using the tweak functions integrated in these VDFs and since they are not cheap I like to squeeze them a bit and parallel to all this get some more in-depth knowledge on this.:grin
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  4. speedy

    speedy Well-Known Member

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    Easy @Martin van Hagen ... Good luck in your research .
    But first please tell me the principles of the next phrase ...
    I'm totally 0% knowledge in Arduino .
    I don't now that Adruino can do that ... please tell me How ?
    I don't think that any VFD will accept this 7.5v as motion control operation command ...
    How to represent distance with voltage ? in how much motion resolution intervals for 50cm ?
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    Last edited: Oct 10, 2014
  5. speedy

    speedy Well-Known Member

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  6. Martin van Hagen

    Martin van Hagen not trying brings you nothing! SimAxe Beta Tester Gold Contributor

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    Well @speedy, easy it will not be and I like to use the word challenging in this instance. I believe that is why we do this and share the "pain", the sweat, the frustration, joy and knowledge.

    When utilizing the VFD as a servo controller this can be done, I look at this as a positioner that will go to a calibrated position equal to the command (voltage level) put on the input. Reading up on the Servo controller you could scale the servo within the range of 0 - 10Vdc (+/-) = 0 - 64 defined steps (or even 128 steps). My understanding of this is that on the output shaft of the reduction gear box a rotation of 180 degrees would be something like this sketch:

    Rotation vs voltage.jpg
    I would personally go for the (B)setting with a 0%=0,5Vdc to ensure that all is well as 0V is difficult value with 100% = 9,5Vdc to keep it all nice and tidy. According to what I have been reading is the PID controller & all the "bells and whistles" embedded in the VFD more than capable of getting to the next position at with in a certain set time frame and controlling it all, with some tuning, to a soft stop at the set position. With 64 programmable positions or I believe double that with some playing a resolution of 1,4 degree per position is feasible.

    The 0 to 10Vdc comes from a circuit that you @speedy made me aware of:
    PWM to 10 Vdc.jpg
    For the code I should do some more reading how all is presented by motion software but surely that would be possible with some further reading on the subject and various codes presented within this forum. :)
  7. speedy

    speedy Well-Known Member

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    Servo motors comes in the DC motors classification with position feed back "Encoders" on it's axle ... So is servo controllers .
    http://en.wikipedia.org/wiki/Servomotor

    Stepper motors comes in the AC motors classification with a position control system in the stepper driver itself .
    http://en.wikipedia.org/wiki/Stepper_motor

    @Martin van Hagen ... All you can is to utilize Yobuddy's circuit to drive the Servo / Stepper driver analog input .
    Or , Do you're research on the other way of communication .
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    Last edited: Oct 10, 2014
  8. speedy

    speedy Well-Known Member

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    Last edited: Oct 15, 2014
  9. Bluestoneracing

    Bluestoneracing New Member

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    Hi, I'm new to this whole forum, but when I joined I did promise to try and contribute as much as I can. OK so I'm a control systems engineer who works for Siemens - so VFD, PID loops etc is my bread and butter - so please ask away. I started at the first post on the thread and please excuse me if this has already been covered! One point I picked up is running VFD's at 400 odd hz - very much not reccomended!! In the US should be 50 maybe 100 at the max the UK 60 upto 100- mototrs really don't like it, or the VFD - the motor gearbox etc should be sized according to the frequency not the other way around :)

    In terms of using the PID functions in VFD's - again probably to be avoided although the PID function we are talking for this are extremely simple and straight forward so probably not too much of a problem, just more fiddly and complex using the VFD for this. It would be very simple to put a pot on the motor to give a feedback of speed to the PC :)

    In terms of MODBUS - please remember MODBUS is very slow!!! I'm mean really slow - OK with the amount og data being used it'll probably be OK - in my world (I'm doing a complex MODBUS project at the moment) I'm talking 1 to 3 second update times - it's a very old protocol and in my opinion best to avoid!! VFD's will accept 1-5v 0-10v and 4-20 mA - the 0-10 v signal is normally avoided.

    You can also try SSD drives (used to be Eurotherm drives) they do a low cost single to 3 phase VFD and I've used lots of them :)

    If I can help please let me know :)
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  10. speedy

    speedy Well-Known Member

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    I hate to see professionals are pretending to be confused and driving junior members attention away from the facts ...
    So maybe we can use a pot like this :grin:grin:grin
    4377204063_e4f2341de1.jpg

    Dear @Bluestoneracing ... speed control is NOT position control .
    Can you dissolve oil in water ?
    Last edited: Oct 24, 2014
  11. Bluestoneracing

    Bluestoneracing New Member

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    OK sorry @speedy I was merely suggesting the use of a feedback pot for PID loop control - sorry what was your question again?

    Oh I see yes sorry I did make the mistake of stating speed of the motor back to the PC so apologies for this (to be fair I thought it was pretty clear that I meant position feedback) or feedback for the three term controller for calculation purposes - thank you for pointing out my error in such an imaginative way ;)

    It's certainly not speed control alone (can be if you want it to be). Three term control can be used for lots of things - even controlling the temperature of the pot you put a picture of ;) And it can be used for position control (which I hear it is on the sim tool SW :) )

    This is merely for using an external pot rather than using the three term controller built into the VFD - of course you could still wire a pot to the analogue input of the VFD and use the inbuilt three term controller in the VFD.

    And using a 5 kohm pot with a 950 ohm resistor in series will do this nicely (based on an input impedance of 250 ohm and 24 vdc)

    And in answer to your question can you dissolve oil in water - the answer is yes, certain oils will dissolve some water depending on the chemistry of the oil, each oil has its own specific water saturation point.
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  12. Bluestoneracing

    Bluestoneracing New Member

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    Oh and @speedy (before you pick me up on another omission!!) I was talking about a standard ISO 4 to 20 mA input when I refer to using a 5 kohm pot :) In industry we don't use 0 to 10 v as inputs and most VFD's will have 4 to 20 mA (or 1 to 5 v (which of course its effectively the same - which I'm sure you'll know, or do you want me to explain how that works as well!! :) )

    I'm trying to assist with my vast knowledge of three term control and industrial automation :)
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  13. speedy

    speedy Well-Known Member

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    Excuse my english @Bluestoneracing ... small missing words can lead to different meanings ... So we have to be accurate all the time 24/7 .

    Go on please if you have time and explain to all of us how that works ?
    I really want to have it from your point of view.:cheers
  14. Bluestoneracing

    Bluestoneracing New Member

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    Apologies @speedy - just seemed a bit of a dig that's all. There was a reference in an early post to using the inbuilt PID controls on a VFD - I've done this and it can be difficult - although as I say thankfully using three term control for such a fast process as position is relatively easy.

    Therefore I was suggesting using a pot (as you would normally do with a DC motor set up from what I can see) to give position feedback of the motor rather than using the VFD. One big problem with using a VFD is that the VFD just assumes where the motor is (based upon the output it's giving) of course this may not be the case, so by wiring a pot (in exactly the same way as is done here time after time with DC motor set ups) would be a better option.

    Also in my experience VFD’s with built in three term control are more expensive than ones without (in the Siemens range this is the case), so to save cost just avoid the ones with built in PID control.

    Now I don’t know yet what the input capabilities of the sim SW is or the PC in question – that’s your field. So over to you :)

    As I said I’m offering help as I work for Siemens (again I saw on a post about the big companies not caring about sim users), and I also have extensive knowledge in three term control and process control/automation – that’s all , nothing more and I’m not pretending to have any experience on sim setups – just here to help if I can. And happy to get answers on VFD’s whatever the make (they listen to me – trust me ;) )
  15. Bluestoneracing

    Bluestoneracing New Member

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    @speedy and to be fair I did start my post by saying 'sorry if this has already been covered' but yes I do need to be 100% correct as it can be misleading - so point taken and I'll make sure take care when posting next time ;)

    But you can still dissolve oil in water ;)
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  16. speedy

    speedy Well-Known Member

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    Sure we all do ... you've got yourself targeted for the next year ... :grin:grin:grin
    please , you still didn't answer my request :think.
  17. Bluestoneracing

    Bluestoneracing New Member

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    Sorry, what was your request?
  18. speedy

    speedy Well-Known Member

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    Last edited: Oct 24, 2014
  19. Bluestoneracing

    Bluestoneracing New Member

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    250 ohm resistor across the input :)

    Anyway we don't refer to the motor controllers as VFD's when using for this application so was confused.

    This is Siemens offering :)



    A lot cheaper than a VFD as well ;)
  20. speedy

    speedy Well-Known Member

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    Great work ... But these are still servo motors my dear ... very expensive compared to normal 3ph induction motor .

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    Last edited: Aug 27, 2015