Danfoss VLT 380-500 V Design Manual

Contents

Danfoss VLT 380-500 V Design Manual Manual pdf 130 page image

14 Controls14.1 Overview of Speed and Torque ControlThe frequency converter can control either the speed or the torque on the motor shaft. Setting parameter 1-00 ConfigurationMode determines the type of control.Speed controlThere are 2 types of speed control:• Open loop does not require any feedback from motor (sensorless).• Closed loop PID requires a speed feedback to an input. A properly optimized speed closed-loop control has higheraccuracy than a speed open-loop control. The speed control selects which input to use as speed PID feedback inparameter 7-00 Speed PID Feedback Source.Torque controlThe torque control function is used in applications where the torque on the motor output shaft is controlling theapplication as tension control. Torque control is selected in parameter 1-00 Configuration Mode, either in [4] VVC+ open loopor [2] Flux control closed loop with motor speed feedback. Torque setting is done by setting an analog, digital, or buscontrolled reference. The maximum speed limit factor is set in parameter 4-21 Speed Limit Factor Source. When runningtorque control, Danfoss recommends to make a full AMA procedure since the correct motor data is essential for optimalperformance.• Closed loop in flux mode with encoder feedback offers superior performance in all 4 quadrants and at all motorspeeds.• Open loop in VVC+ mode. The function is used in mechanically robust applications, but its accuracy is limited.Open-loop torque function works only in 1 speed direction. The torque is calculated from the currentmeasurement within the frequency converter. See chapter 17 Application Examples.Speed/torque referenceThe reference to these controls can either be a single reference or be the sum of various references including relativelyscaled references. For more information on handling of reference, see chapter 15 Handling of References.14.2 Control PrincipleA frequency converter rectifies AC voltage from mains into DC voltage, after which this DC voltage is converted into ACpower with a variable amplitude and frequency.The motor is supplied with variable voltage/current and frequency, which enables infinitely variable speed control of 3-phase, standard AC motors and permanent magnet synchronous motors.The control terminals provide for wiring feedback, reference, and other input signals to the following:• Frequency converter• Output of frequency converter status and fault conditions• Relays to operate auxiliary equipment• Serial communication interfaceControl terminals are programmable for various functions by selecting parameter options described in the main or quickmenus. Most control wiring is customer supplied unless factory ordered. A 24 V DC supply is also provided for use with thefrequency converter control inputs and outputs.Table 14.1 describes the functions of the control terminals. Many of these terminals have multiple functions determined byparameter settings. Some options provide more terminals. See chapter 10.5 Motor Terminal Connections for terminal locations.Controls VLT® Parallel Drive Modules128 Danfoss A/S © 6/2016 All rights reserved. MG37N1021414