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GS4 multi-motor control modes

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  • GS4 multi-motor control modes

    A while ago I watched the video on the multi-motor control modes that the GS4 drive is capable of performing (viewable here: I have an application that I think this would work well for and am wanting to get to our plant to give it a shot. It is on our hydraulic pump system, where we have some 50hp hydraulic pumps feeding a couple dozen machines with hydraulic loads, the demand on the hydraulics varies depending how many of these machines are in operation, but nobody seems to remember to turn off any pumps when the demand is lower.

    Management has recognized the need for control, but they have it stuck in their mind that each pump would need a VFD and don't want to spend that much. The video covers it quite quickly and doesn't get into much detail, so I'm wondering if this information might be shared in a whitepaper or somewhere else on the website that I might be able to go over with them. I've tried searching the site and have only found the video and what is briefly covered in the manual. Doing a web search on "multi-motor control" gives a ton of hits, but nothing related to these control modes that I'm interested in.

    - Paul

  • #2
    If you are wanting to regulate the pressure of a pump system, then you would have a pressure sensor feeding into a PID loop as a feedback (and of course being compared to a set point), and the output of the PID would be the speed of the motor.
    A VFD can only control 1 output frequency, so how would you control more than 1 pressure loop with 1 drive?
    The multi-motor application for VFD's is for multiple motors to run at the same speed, like conveyors or circulation fans, or something like that. Not for motors needing different speeds.


    • #3
      I apologize if my question wasn't clear, the actual control loop wasn't what I was asking about, but rather the multi-motor modes shown in the video that the GS4 drives support with the goal of maintaining some system setpoint – in my case, hydraulic pressure. To clarify it is just one hydraulic loop, with multiple pumps feeding the system, and multiple, variable loads coming off of it.

      The control mode I'm particularly interested in is what they call Quantity Cycle, which according to the video, allows you to add motors as demand increases using a single drive. Starting up, the first motor is started under drive control, then as demand increases that motor is ramped up until it reaches its rated frequency, at which time it is switched over to line power and then the dive brings in and spins up the next motor. Using this method, one drive can control up to 4 motors in total (I imagine it could do more, if more I/O was available on the drive). As demand decreases, the drive will start dropping out motors, reducing power consumption and minimizing wear on the motors.

      I'm just asking for verification that my application should work, and if there are more details or written documentation that I can share and help sell it to management.


      • #4
        Never heard of such a thing with a single drive turning on and off motors as it goes. Ill have to watch that video you linked and check it out.


        • #5
          That does look very interesting, and you are right it does in fact show a single drive controlling multiple motors at variable speed and adding in or subtracting drives from the total on the fly during runtime. Unfortunately, I cannot find any information in a manual or appendix on how to set it up properly. Your best bet would be talk to automation support.

          The only thing I can see for sure is that you would use something like a pair of these motor contactors and a single mechanical interlock per motor:

          It looks like the drive uses its built in relay outputs to switch between contactors for each motor. Depending on how the drive switches relays would probably dictate whether you need the auto unlatching mechanical interlock or the typical mechanical lockout one.
          Last edited by MikeN; 03-17-2020, 12:33 PM.


          • #6
            Got it, that makes sense, and is a valid function. However I've normally found that the cost and complexity of wiring typically outweighs the slight cost savings versus separate drives. For example, lots of drives offer 2 motor setups so you can run one motor or another depending on the machine function. But, by the time you add the required contactors and interlocks, the cost is prohibitive. I see very few guys using this function.

            If I were to implement a scheme like this, I'd likely use a separate PLC to future-proof the drive application, since the next generation could drop this function from it's features.