Danfoss AHF005 Design Manual

Also see for VLT AHF 005: Instruction manual Operating instructions Operating instructions Design guide

Contents

Danfoss AHF005 Design Manual Manual pdf 15 page image

5 Selection of Advanced Harmon-ic 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 (I M,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 (U L ), the calculated current must be corrected with theratio 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 (I AHF,N ) equal toor larger than the calculated frequency converter mains inputcurrent (IFC,L ).NOTEDo not oversize the AHF. The best harmonic perform-ance is obtained at nominal filter load. Using anoversized filter will most likely result in reduced THiDperformance.If several frequency converters are to be connected to thesame filter, the AHF must be sized according to the sum of thecalculated 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): 380 VMotor name plate power(PM): 55 kWMotor 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 96 A filter must be chosen.Selection of Advanced Harmo... AHF005/010 Design GuideMG.80.C3.02 - VLT® is a registered Danfoss trademark 155 5