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

Contents

Feedback conversionIn some applications, it is useful to convert the feedbacksignal. One example is using a pressure signal to provideflow feedback. Since the square root of pressure is propor-tional to flow, the square root of the pressure signal yieldsa value proportional to the flow. This is shown inIllustration 2.17.+- PIDPPP130BA358.11Ref.signalDesiredflow P 20-07FB conversionRef.FBFlowFBsignalFlowP 20-04P 20-01Illustration 2.17 Feedback Conversion2.5 Automated Operational FunctionsAutomated operational features are active as soon as thefrequency converter is operating. Most of them require noprogramming or set-up. Understanding that these featuresare present can optimise a system design and possiblyavoid introducing redundant components or functionality.For details of any set-up required, in particular motorparameters, refer to the Programming Guide.The frequency converter has a range of built-in protectionfunctions to protect itself and the motor it is running.2.5.1 Short Circuit ProtectionMotor (phase-phase)The frequency converter is protected against short circuitson the motor side by current measurement in each of the3 motor phases or in the DC link. A short circuit between 2output phases causes an overcurrent in the inverter. Theinverter is turned off when the short-circuit currentexceeds the permitted value (Alarm 16 Trip Lock).Mains sideA frequency converter that works correctly limits thecurrent it can draw from the supply. Still, it isrecommended to use fuses and/or circuit breakers on thesupply side as protection in case of component break-down inside the frequency converter (first fault). Seechapter 7.7 Fuses and Circuit Breakers for more information.NOTICETo ensure compliance with IEC 60364 for CE or NEC 2009for UL, it is mandatory to use fuses and/or circuitbreakers.Brake resistorThe frequency converter is protected from a short-circuit inthe brake resistor.Load sharingTo protect the DC bus against short-circuits and thefrequency converters from overload, install DC fuses inseries with the load sharing terminals of all connectedunits. See chapter 2.3.5 Load Sharing for more information.2.5.2 Overvoltage ProtectionMotor-generated overvoltageThe voltage in the intermediate circuit is increased whenthe motor acts as a generator. This occurs in followingcases:• The load drives the motor (at constant outputfrequency from the frequency converter), forexample, the load generates energy.• During deceleration (ramp-down) if the momentof inertia is high, the friction is low and the ramp-down time is too short for the energy to bedissipated as a loss in the frequency converter,the motor, and the installation.• Incorrect slip compensation setting may causehigher DC-link voltage.• Back EMF from PM motor operation. If coasted athigh RPM, the PM motor back EMF maypotentially exceed the maximum voltagetolerance of the frequency converter and causedamage. To help prevent this, the value of4-19 Max Output Frequency is automaticallylimited via an internal calculation based on thevalue of 1-40 Back EMF at 1000 RPM, 1-25 MotorNominal Speed, and 1-39 Motor Poles.NOTICETo avoid motor overspeeding (for example, due toexcessive windmilling effects or uncontrolled water flow),equip the frequency converter with a brake resistor.The overvoltage can handled by either using a brakefunction (2-10 Brake Function) or using overvoltage control(2-17 Over-voltage Control).Overvoltage control (OVC)OVC reduces the risk of the frequency converter trippingdue to an overvoltage on the DC-link. This is managed byautomatically extending the ramp-down time.Product Overview Design Guide26 Danfoss A/S © 09/2014 All rights reserved. MG20N60222