Belmans, Ronnie

D'Hulster, Frederik

Desmet, Jan

Stockman, Kurt

Verhaege, Kevin

English

Ghent University Academic Bibliography

Voltage dip immunity test set-up for induction motor drives

WK,17(51$7,21$/6<0326,80RQ32:(5(/(&7521,&6(H;,0H XQDURGQLVLPSR]LMXP(QHUJHWVNDHOHNWURQLND±(H129,6$'<8*26/$9,$2&7±1291$EVWUDFW $ JURZLQJ QXPEHU RI LQGXVWULDO IDFLOLWLHV LVXVLQJDGMXVWDEOHVSHHGLQGXFWLRQPRWRUGULYHVLQRUGHUWRLQFUHDVH WKHTXDOLW\RI WKHLUSURGXFWVDQG WKH IOH[LELOLW\LQ WKH SURGXFWLRQ SURFHVV 7KH UHOLDELOLW\ RI WKHSURGXFWLRQSODQWGHFUHDVHVZLWK WKHQXPEHURI LQVWDOOHGGULYHVGXHWRWKHLUVHQVLWLYLW\WRZDUGVYROWDJHGLSV7KLVSDSHUSUHVHQWVDWHVWVHWXSWRGHWHUPLQHWKHLPPXQLW\RIVWDQGDUG LQGXFWLRQPRWRU GULYHV DJDLQVW VXSSO\ YROWDJHGLSV XQGHU YDULRXV ORDG FRQGLWLRQV  )XUWKHUPRUH WKHPHDVXUHPHQWVDUHFRPSDUHGWRVLPXODWLRQUHVXOWV.H\:RUGV$GMXVWDEOH VSHHGGULYHV YROWDJHGLSV GLSLPPXQLW\ULGHWKURXJK,1752'8&7,21A voltage dip is a momentary reduction of the rmsvoltage at a customer position. Bollen [1] characterises avoltage dip by a magnitude and a duration (0.5 – 30cycles).   The voltage dips are caused by faults in theutility distribution system and transported to all facilitieson the same distribution network.Voltage dips are widely recognised as the main causeof disturbances in production plants, equipped withadjustable speed drives (ASD).  McGranaghan et al. [2]show that the economic impact of the possible loss ofproduction due to voltage dips can be very high.   Inorder to prevent tripping of an ASD during a dip,  theimmunity of drives should be taken into account duringthe design stage of production plants.   This paper givesthe design engineers a helpful insight in the possibleride-through ability of standard drives for inductionmachines under typical load conditions.(1(5*<&216,'(5$7,216Fig. 1 shows the topology of an AC adjustable speeddrive.  It consists of three major parts: a diode rectifier, aDC buffer link and a controlled inverter.The behaviour of the ASD, during a supply voltagedip, can be represented by an energy balance .    ((( =+ (1a)( ) ( )( ) ( ) ( )( )∫=−+−21..22 12221222GW7WW-W8W8&ωωω (1b)Note that, if the symmetrical voltage dip is below theDC-link voltage 8  , no energy is fed from the AC-supply into the DC-link because of the reverse biaseddiodes in the rectifier.When analysing the energy balance, we candetermine three main parameters influencing thebehaviour of an ASD during a supply voltage dip ofduration W 	 ±W  :• The DC-link capacitor &: determines the electricenergy (   stored in the DC-link;• The load inertia - : determines the mechanicalenergy (   stored in the rotating parts;• The motor load profile 7ω: the energy consumer.In low-inertia systems, the discharge-rate of thecapacitor determines the survival-duration of the loadeddrive.  Typical values for the DC-link capacitor arebetween 75 and 360 µF/kW [1].  Fig.2 shows the decayof the DC-link voltage with such capacitor size underconstant power demand 3 as expressed inW&38W8 .2)( 20 −= (2)The energy-amount in a loaded capacitor is notenough to drive the load longer than 1.5 periods, with aDC-link undervoltage protection of 65% 8    8  .If the DC-link voltage drops below the minimum voltageprotection level 8    , the inverter is inhibited and thecharging resistor 5 (Fig. 1) is activated, limiting thecharging current at return of the supply voltage.  If thevoltage is restored, before reaching the DC-link9ROWDJHGLSLPPXQLW\WHVWVHWXSIRULQGXFWLRQPRWRUGULYHV.XUW6WRFNPDQ)UHGHULN'¶KXOVWHU.HYLQ9HUKDHJH-DQ'HVPHW5RQQLH%HOPDQV* Hogeschool West-Vlaanderen, dept. P.I.H., Graaf Karel de Goedelaan 5, B-8500 Kortrijk, Belgium** K.U.Leuven, dept. ESAT/ELEN, Kasteelpark Arenberg 10, B-3001 Leuven, BelgiumWVUDIODE RECTIFIERCL+INVERTER(CONTROLLED)ACSUPPLY DC-LINKL1L2L33Ph-motorωTLRUFig. 1 7\SLFDO$&DGMXVWDEOHVSHHGGULYHWRSRORJ\20 0.01 0.02 0.03 0.04 0.05 0.060102030405060708090100time [s]DC-link voltage [% U 0]75 µF/kW     360 µF/kW    UDC minundervoltage protection, the transient behaviour ismainly determined by the R-L-C combination in thesupply and DC-link.  Poor damping of this electricalsecond order system results in a DC-overvoltage and apeak supply current, at the re-entry of the supply voltageafter a dip.  This peak current  can cause severe stress onthe drive rectifier unit.6,08/$7,2102'(/Fig.3 represents a Matlab / Simulink discretemodel of an ASD with PWM-pulse control. Thedipgenerator feeds the rectifier with a three-phasecontrollable power source.  A PWM-pulse generatorcontrols the switching pattern of the IGBT’s in theinverter. The slip-speed controller generates the requiredfrequency and amplitude for the sine reference generator.The U/f-ratio is kept constant over the overal speedrange. In order to simulate the behaviour of standardinduction motor drives under various load conditions,one can select whether the load is function of time orspeed. Different voltage dip ride-through techniques, e.g.kinetic buffering can be implemented in the model. Fig.4 shows the RMS supply line voltage, the DC-linkvoltage, the rotor speed, the load torque, the motor0 0.5 1 1.5 2 2.50200400600800Motor 4kW  --  JL = 0.166 kg.m²  --  C = 660 µFtime [s]Voltage [V]ulrmsUDC    0 0.5 1 1.5 2 2.5050100150200time [s]Rotor speed [rad/s] ; Motor load [Nm]Rotor speed referenceActual rotor speed   Motor load           0 0.5 1 1.5 2 2.5-20-1001020time [s]Motor current [A]0 0.5 1 1.5 2 2.5-4000-20000200040006000time [s]Electro-mechanical power [W]current and the electromechanical power delivered by themotor. This model is used to analyse the behaviour of astandard induction motor drive under different voltagedips and load conditions.7(676(783An experimental test set-up is build to measure theimmunity of variable speed drives towards voltage dipsunder different load profiles. Fig. 5 shows theexperimental set-up. It consists of four major parts: aFig. 2 ,QIOXHQFHRIFDSDFLWRUVL]HRQ'&OLQNYROWDJHFig. 4 6LPXODWLRQ UHVXOWV RI WKH EHKDYLRXU RI D3:0SXOVHFRQWUROOHGN:LQGXFWLRQPRWRUOut1Out2Out3dipgeneratorSwitchSpeedstep (Hz)f refwmf rVSlip-Speedcontrollerf rVOut1Sine referencegeneratorm wmMeas.DemuxTm=a+b*wm+c*wm^2Load profile f(wm)Load f(t)VDCdelta_fKinetic_bufferingA B C Tmm_SIInduction machine4 kW - 400 V50 Hz - 1440 rpm+-pulsesABCIGBT InverterSignal(s) PulsesDiscretePWM Generator6 pulsesKAV+VDC1V-DC-linkABCK A 6 - pulse diode  rectifierFig.3 6LPXODWLRQPRGHORIDQ$6'ZLWK3:0SXOVHFRQWURO3programmable power source, the adjustable speed drive,the load machine and the load controller. Aprogrammable power source (3x5kVA) is used togenerate both balanced and unbalanced voltage dipsaccording to the IEC 61000-4-11 standard [3].  The EUT,consisting of an adjustable speed drive with inductionmotor (up to 11kW) is loaded by a torque controlled DC-machine. Using a dSpace DS1103 PPC controller-board, a Matlab / Simulink program is run to controlthe test set-up in real-time. Speed and load torque aremeasured to generate the necessary corrections,according to the selected loading profile. With the real-time user-interface ControlDesk, different load profilescan be programmed in the controller. All signals areisolated in order to protect the controller-card againstEMC, ground loops and overvoltages.0($685(0(175(68/76Several standard induction motor drives have beensubjected to balanced and unbalanced voltage dips.  Themeasurement results are compared to the simulationresults in order to prove the validity of the model.  Fig. 6shows a voltage dip measurement of the transientbehaviour of a 4kW ASD under full load condition.0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5-1000100200300400500600700800time (s)[Speed = 100%Nom, Torque = 100%Nom]Torque x 10 (Nm) Speed x 1/2 (rpm) Uline (Vrms) UDC (V)The transition in slew rate of the DC-link voltage marksthe drive tripping point.To represent the behaviour of drives under dipconditions, voltage tolerance curves are used.  A voltagetolerance curve divides the dip magnitude - durationplane in a ride-through (pass) and a trip (fail) area.  Theonly standard that currently describes how to measurethe voltage tolerance of three-phase equipment is IEC61000-4-11. However, this standard does not mentionanything about voltage tolerance curves. Only somediscrete dips (depth and duration) should be measured todefine the voltage tolerance. Using these predefinedmeasurements, the voltage tolerance curve cannot beconstructed as not all measurements are pass-failtransition points. On the test set-up, the depth andduration of voltage dips were continuously changed inorder to define the limits of ride-through (voltagetolerance).Fig. 7 compares the simulated and measured voltagetolerance curve for a 4kW ASD at full load (T = 25Nm).If the remaining voltage during the dip is below theundervoltage limit of the ASD, the drive will always trip.The rectifier stops conducting and all energy has to betaken from the capacitors.  As seen from Fig. 7, the drivetrips after 17 ms.0 20 40 60 80 100 120 140 160 180 2000102030405060708090100Voltage Tolerance Curve     [T = 100%Nom, n = 100%Nom]Dip duration (ms)U (%Nom)T=100%Nom, n=100%Nom (SIMULATION)T=100%Nom, n=100%Nom (MEASURED)  UDC MIN=74.5% Nom           PASS FAIL Fig. 7 9ROWDJHWROHUDQFHFXUYHN:7      Q      Fig. 6 9ROWDJHWROHUDQFHPHDVXUHPHQWN:7      Q      Fig. 5 ([SHULPHQWDOVHWXSMω ﬀ ﬁ ﬂ ﬃTωDC-DRIVEFREQ. OMVORMER M3LEM MODULESIU-LEMIV-LEMIW-LEM Tref3 x 400VACωφ3 x 400VACDS1103 PPC Controller Board ! " # $ %& ' ( ) *SCHAFFNERSCHAFFNERSCHAFFNERSCHAFFNERSCHAFFNER+ , -/. 01, 2 0 3 .(DIP GENERATIE)enableenableT,ω4By reducing the depth of the dip, one can find asupply line voltage for which the drive does no longertrip. Depending on the torque and speed conditions of themachine, this value differs from the undervoltagetreshold level due to the ripple on the DC-bus voltage.Fig. 8 represents the influence of the motor load on thevoltage tolerance curve.0 20 40 60 80 100 120 140 160 180 2000102030405060708090100Dip duration (ms)Voltage Tolerance Curve     [speed = 100%Nom]U (%Nom)T=125%Nom,n=100%Nom T=100%Nom,n=100%Nom T=75%Nom,n=100%Nom  T=50%Nom,n=100%Nom  UDCMin=74.5%NomPASS FAIL Considering a constant torque and reducing the speedof the machine results in a decreasing power demand.The ripple on the DC-bus voltage thus becomes smaller.Fig. 9 shows that the operation at reduced speedimproves the immunity against voltage dips.0 20 40 60 80 100 120 140 160 180 2000102030405060708090100Voltage tolerance Curve     [Torque = 100%]Dip duration (ms)U (%Nom)T=100%Nom, n=100%Nom T=100%Nom, n=50%Nom  UDC MIN=74.5%NomPASS FAIL The point on wave at which the voltage dip occurs,also has an influence on the possible ride-through time.Fig. 10 shows the influence of the dip start-time for athree-phase balanced dip. For the same dip-duration, thedash-dotted voltage curve trips and the solid curvesurvives, due to a higher energy level in the DC-link atdip-initiation.Up to now, only balanced dips have been discussed.In practice, however, unbalanced dips occur morefrequently.  Single-phase-to-ground (SPTG) faults do notstrongly affect the behaviour of an ASD (Fig. 11). Thethree-phase rectifier acts as a single-phase rectifier. Inthis case the DC-link can recharge every 10 ms from thetwo remaining supply lines. Fig. 5 shows a simulation ofthe DC-link with a SLTG fault (40ms) in the power0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1350400450500550600650700Motor 4kW  --  JL = 0.166 kg.m²  --  C = 660 µFtime [s]DC-link voltage [V]supply. At full motor load (4 kW), the DC-link voltagenever reaches the undervoltage protection level (UDC min= 74.5%).For a two-phase-to-ground (TPTG) fault, theremaining line voltage at the rectifier equals the systemphase voltage. The maximum available DC-link voltageis:3088 = (3)If the undervoltage limit cannot be reduced under thisvoltage level, the behaviour can be compared to abalanced voltage dip. Fig. 11 shows a simulation of aSPTG fault versus a TPTG fault.0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1200250300350400450500550600Motor 4kW  --  JL = 0.166 kg.m²  --  C = 660 µFtime [s]Voltage [V] Single-phase-to-ground faultTwo-phase-to-ground fault   &21&/86,216This paper introduces a test setup to obtain voltagetolerance curves for ASD under different loadconditions.  Furthermore the measurement results areverified with the simulation model.  Standard ASD arevery sensitive to voltage dips.  The main restriction is theDC-link undervoltage protection level, defined by themanufacturer.  It can be seen from Fig. 2 that increasingthe capacitor value is not a very effective way to improvethe ride-through time.Fig. 8 ,QIOXHQFH RI PRWRU ORDG RQ YROWDJH WROHUDQFHFXUYHPHDVXUHPHQWFig. 9 ,QIOXHQFH RI PRWRU VSHHG RQ YROWDJH WROHUDQFHFXUYHPHDVXUHPHQWFig. 10 ,QIOXHQFH RI WKH YROWDJH GLSLQLWLDWLRQ WLPHVLPXODWLRQFig. 11 637*YHUVXV737*IDXOWIXOOORDGVLPXODWLRQ5Further research and measurements will concentrateon the improvement of the immunity of the ASD.  Newtolerance curves for ASD with kinetic buffering,  boostmodules and other ride-through equipment will help thedesign engineer to choose the correct mitigationequipment to reach the desired level of ride-through.$&.12:/('*(0(17The authors wish to thank the Flemish Governmentfor granting the project ’Invloed van spanningsdips bijsnelheidsgeregelde aandrijvingen’  (IWT-HOBU).5()(5(1&(6 [1] Math H.J. Bollen, 8QGHUVWDQGLQJ 3RZHU 4XDOLW\3UREOHPV  9ROWDJH 6DJV DQG ,QWHUUXSWLRQV, IEEEPress Series on Power Engineering, 2000.[2] M.F. McGranaghan, D.R. Mueller, M.J. Samotuj,"Voltage Sags in Industrial Systems", IEEETransactions on Industry Applications, Vol 29, No.2,March/April 1993, pp. 397-403.[3] “Voltage dips, short interruptions and voltagevariations immunity tests”,  IEC Std.  61000-4-11.

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Voltage dip immunity test set-up for induction motor drives

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Ghent University Academic Bibliography

Ghent University Academic Bibliography