Danfoss VLT 6002-6011 Installation, Operation And Maintenance Manual

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Danfoss VLT 6002-6011 Installation, Operation And Maintenance Manual Manual pdf 64 page image

64PID for Process RegulationThe built-in proportional, integral, derivative (PID) controller in thedrive maintains a constant condition (pressure, temperature, flow, etc.)in the system. It adjusts motor speed based upon a reference and/orsetpoint and the feedback signal. The PID controller is activated bysetting parameter 100, Configuration, to Closed loop.A transmitter supplies the PID controller with a feedback signal from theprocess to indicate its current state. The type of feedback signal in usedepends upon the type of process.This means that deviations that occur between the reference/setpointand the actual process state are sensed. Such deviations arecompensated for by the PID regulator by adjusting the output frequencyas required by the difference (or error) between the reference/setpointand the feedback signal.The PID controller in the drive has been designed for use in HVACapplications and to perform a number of specialized functions.Previously, it was necessary for a building management system tohandle these special functions by installing extra modules to programthe system.With the VLT 6000, there is no need for extra modules to be installed.Only the reference and/or setpoint and a selected feedback signal needto be programmed. An advanced feature of the VLT 6000 is the drive’sability to accept two feedback signals, making two-zone regulationpossible.Voltage drop in long control cables can be compensated for by usingthe scaling parameters for the analog inputs.FeedbackThe feedback signal must be connected to the drive according to thetable below, depending on the type of feedback signal and the settingsof the associated parameters listed.Feedback type Terminal ParametersPulse 33 307Voltage 53 or 54 308, 309, 310 or311, 312, 313Current 60 314, 315, 316Bus feedback 1* 68 and 69 537Bus feedback 2* 68 and 69 538* The bus feedbacks can only be set by serial communication.If two analog feedback signals are to be used, they both must bevoltage signals.The Minimum Feedback and Maximum Feedback, parameters 413and 414, must be set for the feedback signals. The type of process unitfor the signals is selected in parameter 415, Process Units.Reference (Set Point)In parameter 205, Maximum Reference, the maximum value of the sumof all reference signals is set.The Minimum Reference, set in parameter 204, indicates the smallestvalue that the resulting reference can assume.The reference range cannot exceed the feedback range.If multiple Preset References are required, use multiple setups or setthem in parameters 211 to 214 Preset Reference. See ReferenceHandling.If a current signal is used as a feedback signal, voltage can be used asan analog reference. Use the table below to decide which terminal touse and which parameters to program.Reference type Terminal ParametersPulse 17 or 29 301 or 305Voltage 53 or 54 308, 309, 310 or311, 312, 313Current 60 314, 315, 316Preset reference 211, 212, 213, 214Setpoints 418, 419Bus reference * 68 and 69* The bus reference can only be set by serial communication.Terminals that are not used should be set to No function.Inverse RegulationNormal regulation means that the motor speed increases when thereference/setpoint is higher than the feedback signal. Inverse regula-tion means that the motor speed decreases when the reference/setpointis higher than the feedback signal. If there is a need for inverseregulation, inverse must be programmed in parameter 420, PIDNormal/Inverse Control.Anti-WindupThe process controller is factory set with an active anti-windup function.This function ensures that when either a frequency limit or a current limitis reached, the integrator will be reset to zero. If the frequency limit orcurrent limit is cleared, the integrator will turn on again. This functioncan be disabled in parameter 421, PID Anti-windup.Start-up ConditionsIn some applications, the optimum setting of the process regulator takesa long time to reach. In such cases, a start-up frequency can beentered in parameter 422, PID Start-up Frequency. The drive willramp directly to this frequency before PID control begins. This avoidscontrol by deviation between the reference/setpoint and the actual stateof the process during acceleration. It also avoids overshoot of theprocess requirement during acceleration due to lag in the feedbacksignal.