Danfoss VLT AQUA Drive FC 202 Design Manual

Also see for VLT AQUA Drive FC 202: Service guide Installation guide Installation guide Operating guide Installation guide

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Danfoss VLT AQUA Drive FC 202 Design Manual Manual pdf 24 page image

2.4.2 Control Structure Closed-loopIn closed-loop mode, an internal PID controller allows theadjustable frequency drive to process system reference andfeedback signals to act as an independent control unit. Thedrive can provide status and alarm messages, along withmany other programmable options, for external systemmonitoring while operating independently in closed-loop.Figure 2.12 Block Diagram of Closed-loop ControllerFor example, consider a pump application in which thespeed of a pump is controlled so that the static pressure ina pipe is constant (see Figure 2.12). The adjustablefrequency drive receives a feedback signal from a sensor inthe system. It compares this feedback to a setpointreference value and determines the error, if any, betweenthese two signals. It then adjusts the speed of the motorto correct this error.The desired static pressure setpoint is the reference signalto the adjustable frequency drive. A static pressure sensormeasures the actual static pressure in the pipe andprovides this information to the adjustable frequency driveas a feedback signal. If the feedback signal is greater thanthe setpoint reference, the adjustable frequency driveramps downs to reduce the pressure. Similarly, if the pipepressure is lower than the setpoint reference, theadjustable frequency drive ramps up to increase the pumppressure.While the default values for the adjustable frequency drivein closed-loop often provide satisfactory performance,system control can often be optimized by tuning the PIDparameters. Auto tuning is provided for this optimization.Other programmable features include:• Inverse regulation - motor speed increases whena feedback signal is high.• Start-up frequency - lets the system quickly reachan operating status before the PID controllertakes over.• Built-in low-pass filter - reduces feedback signalnoise.2.4.3 Local (Hand On) and Remote (AutoOn) ControlThe adjustable frequency drive can be operated manuallyvia the LCP, or remotely via analog and digital inputs andserial bus.Active reference and configuration modeThe active reference is either a local reference or a remotereference. Remote reference is the default setting.• To use the local reference, configure in Handmode. To enable Hand mode, adapt parametersettings in parameter group 0-4* LCP Keypad. Formore information, refer to the programmingguide.• To use the remote reference, configure in Automode, which is the default mode. In Auto mode,it is possible to control the adjustable frequencydrive via the digital inputs and various serialinterfaces (RS485, USB, or an optional serialcommunication bus).• Figure 2.13 illustrates the configuration moderesulting from active reference selection, eitherlocal or remote.• Figure 2.14 illustrates manual configuration modefor local reference.Product Overview VLT® AQUA Drive FC 20222 Danfoss A/S © 09/2014 All rights reserved. MG20N62222