Danfoss VLT AHF005 Design Manual

Contents

Danfoss VLT AHF005 Design Manual Manual pdf 16 page image

5 Selection of Advanced Harmonic FilterThis chapter will provide guidance about how to choose theright filter size and contains calculation examples, electricaldata and the general specification of the filters.5.1 How to Select the Correct AHFFor optimal performance the AHF should be sized for themains input current to the frequency converter. This is theinput current drawn based on the expected load of thefrequency converter and not the size of the frequencyconverter itself.5.1.1 Calculation of the Correct Filter SizeNeededThe mains input current of the frequency converter (IFC,L) canbe calculated using the nominal motor current (IM,N) and thedisplacement factor (Cos φ) of the motor. Both values arenormally printed on the name plate of the motor. In case thenominal motor voltage (UM,N) is unequal to the actual mainsvoltage (UL), the calculated current must be corrected withthe ratio between these voltages as shown in the followingequation:IFC .L = 1.1 ×IM ,N ×cos(ρ) ×UM ,NULThe AHF chosen must have a nominal current (IAHF,N) equal toor larger than the calculated frequency converter mainsinput current (IFC,L).NOTEDo not oversize the AHF. The best harmonic performance isobtained at nominal filter load. Using an oversized filter willmost likely result in reduced THiD performance.If several frequency converters are to be connected to thesame filter, the AHF must be sized according to the sum ofthe calculated mains input currents.NOTEIf the AHF is sized for a specific load and the motor ischanged, the current must be recalculated to avoidoverloading the AHF.5.1.2 Calculation ExampleSystem mains voltage (UL): 380VMotor name plate power(PM): 55kWMotor efficiency (ƞM): 0.96FC efficiency (ƞFC): 0.97AHF effiency (ƞAHF)(worst case estimate): 0.98Maximum line current (RMS):PM × 1000UL × ηM × ηFC × ηAHF × 3 = 55 × 1000380 × 0.96 × 0.97 × 0.98 × 3 = 91.57AIn this case a 96A filter must be chosen.5.1.3 Voltage BoostIn stand-by and under low condition, the AHFs will boost theinput voltage with up to 5%. This means that the voltage atthe frequency converter terminals is up to 5% higher thanthe voltage at the input of the filter. This should beconsidered at the design of the installation. Special careshould be taken in 690V applications, where the voltagetolerance of the frequency converter is reduced to +5%, theboost voltage can, at low load and stand-by, be limited viathe available capacitor disconnect. For more information seesection 6.2.2.Selection of Advanced Harmo... AHF005/010 Design GuideMG.80.C4.02 - VLT® is a registered Danfoss trademark 155 5