Danfoss VLT 2800 Manual

Also see for VLT 2800: Operating instructions Manual Instruction manual Quick guide Design guide

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Danfoss VLT 2800 Manual Manual pdf 99 page image

slow changes and an appropriate frequency contribu-tion for quick changes can be preset. This is doneusing the speed regulation in parameter 420 SpeedPID Differentiator gain limit and Process regulation inparameter 443 Process PID Differentiator gain limit.Lowpass filterIf there is a lot of noise in the feedback signal, thesecan be dampened using an integrated lowpass filter.A suitable lowpass filter time constant is preset.If the lowpass filter is preset to 0.1 s, the cut-off fre-quency will be 10 RAD/sec, corresponding to (10 / 2x ) = 1.6 Hz. This will mean that all currents/voltagesthat vary by more than 1.6 oscillations per second willbe dampened. In other words, there will only be regu-lation on the basis of a feedback signal that varies bya frequency of less than 1.6 Hz. The appropriate timeconstant is selected in Speed Regulation in parameter421 Speed PID lowpass filter time and in Process Reg-ulation in parameter 444 Process PID lowpass filtertime.Inverse regulationNormal regulation means that the motor speed is in-creased when the reference/setpoint is greater thanthe feedback signal. If it is necessary to run inverseregulation, in which the speed is reduced when thereference/setpoint is greater than the feedback signal,parameter 437 PID normal/inverted control must beprogrammed at Inverted .Anti WindupIn the factory the process regulator is preset with anactive anti windup function. This function means thatwhen either a frequency limit, a current limit or a volt-age limit is reached, the integrator is initialised at afrequency corresponding to the present output fre-quency. This is a means of avoiding the integration ofa variance between the reference and the process'sactual mode that cannot be deregulated by means ofa change of speed. This function can be deselected inparameter 438 Process PID anti windup.Starting conditionsIn some applications the optimal setting of the processregulator will mean that a relatively long period of timewill pass before the required process condition is ach-ieved. In these applications it can be a good idea todefine an output frequency to which the frequencyconverter must run the motor before the process reg-ulator is activated. This is done by programming a startfrequency in parameter 439 Process PID start frequen-cy.Handling of feedbackFeedback handling is depicted in this flowchart.The flowchart shows which parameters can affect thehandling of feedback and how. A choice can be madebetween voltage, current and pulse feedback signals.= factory setting, () = display text, [] = value for use in communication via serial communication portMG.27.E2.02 - VLT is a registered Danfoss trademark 99Programming