Compact Realisation of PWM-VSl Current Controller For

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Compact Realisation of PWM-VSl Current Controller for PMSMDriveApplication using low cost standard microcontrollerLars Norum, Wala'emar Sulkowski,h s rne Aga

Department of Electrical Engineering and Computer ScienceThe N orwegian Institute of Techn ology, N-7034 Trondheim. NorwayPhone: +47 7 594241 T ek fa x: 4 7 59 42 79Abs;ract:This paper presen ts a com pletely digital realisation of PWM-VSI current controller for PUSU drive application. l%ccurrent controll algorithm, including &coupling andcompensationfor mrrschinc parameters variation, ispresented.Thc controller is implemented in a single-board controlcomputer which is based on a new 16 bit microcontroller.Experimental results are included

IntroductionThe high efficiency, combined with compact design,make permanent magnet excited AC motors auractive in highperformance electric drives. In tool machine servo and mobileapplications, the torque requirement is usually high for lowspeeds, but allowing for decreased to qu e at higher speeds, i.e.requirements which typically are met by field weakening intraditional motor drives. As explained in [1,2,9], the salientpole permanent magnet synchronous motor (PMSM) is analternative for drives where toque characteristic with fluxDigital current controller and voltage modulation canonly give high bandwith cutrent control when the executiontime is short. n neported digital current controllers, either fast

signal processors with additional hardware devices or ASKS[8] have been used to obtain satisfactory calculation speed.These solutions give additional complexity in controllerhardware and qu ite a bit of sof tware challenges. However, theperfomance of sin& chip microcontrollers mproves rapidly.'Ihispaper p-ts a PMSM drive with a fully digital regulatorimplemented in a microcontroller with on-chip peripheralswithout additionalprocessing circuits.To use the onchip embedded microcontroller peripheralsto realize the PWM output it was necessary to use a simplean d' fast modulation algorithm, suitable for digitalimplementation. For accurate dynamic curren t control thecoomller structure should take into account existing PMSMnonlinear prope rties i.e. cur rant dependentreactances.The piesented control algorithm have been tested on anexperimental 2.8 kW PMSM drive. The applied control strategy

is presented, but the paper mostly focuses on the realization ofthe digital controller and the performance obtained. The driveis schematically drawn in figure 1.

weakening isqmted.

Gw&&mmh'Ihe d-q transformed PMSM model in per unit valueswith basic assumption that reference frame d-axe is fmed with

rotor permanent magnet flux Ymcan be described as a set ofnonlinear differential equations with current and temperahuedependent parameters [6.7].

(3 )(4)

where: ud. uq, b.q.Yd, Yq are the complex space-vectord-q comp onents for voltage.cum?nt and fluxrespectively;q nd % are d-q axis synchronousreactances.

0-7803-0695-3192$3.00' 992 IEEE

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e+tI IFig.2. The tructure of PMSM mathematical model.

The Em f of ro tation in electrical part and torque equationin mechanical part are sources of nonlinearity. The corenonlinear property (saturation) affects in form of Xd and x4changing with stator current. Assuming that current controlstrategy keeps id current compone nt on zero level theinfluence of the xd parameter variations can be neglected. Thedyna mic chang es of IYmI af fects as disturbance on id as Emfof transform ation represented as dLy, derivative block.

Due to requirement for good dynamic and staticperformance in different operation regimes (as acceleration,breaking, field weakening) the current controller needs toguarantee d-q stator current components decoupled control.This implies controller structure inherently based onmachines mathematical model shown in fig.2. To keep statorcurrent components separated the nonlinear regulators withdecoupling compensation terms were applied.As a result of controller fixed constant reactancesvalues Xbef and Xqref, the cross disturban ces and steady state

errors occurs. Figure 8a shows family of the + currentresponces to the +ref step changes.

The current regulators amplification factor Kqcalculated for the constant reactances values[6,7] is inadequa tefor the whole used currents range. The proposed decouplingis based on knowlege of & stator current dependent m achineparameters.Tomake fast responce and avoid overshooting theamplification of current regulator Kq , reactances Xdref andxqRf were stored as $ stator current dependent nonlinearfunctions values in look-up tables.Calculated stator voltage vector d-q components Vdref andVqref and rotor position 8 were used as a input values forPWM voltage vector averaging method algorithm [16,171.

\ \5IUf

Fig 3. The algorithmfor current controllerfor salient-polePMSM

COMPACTREALISATION-n experimental PMSM drive with a commercial 2.8kWsalient pole motor and fully digital current controller has beenbuilt. The m otor data listed in the appendix is given by themanufacturer [18]. The motor is supplied from a three phaseinverter with IGBTwitches.

The current controller algorithm is implemented in aSiemens SAB80C166 [20] microcontroller. Themicrocontroller is sited to a evaluation board from ertec Gmbh[21] supporting RAM, ROM, addressing logic and clockingcrystal. It is a high performance single-chip microcontrollerwith ten 10 bit A/D converter channels, sixteen capture andcompare channels based on two 16-bit time bases. Thecapturdcompare units have a resolution of 400ns. There is agod priority scheme for the interrupt system, with 40Onsinterrupt response. Interrupts for data transfer can be servicedby cycle stealing direct memory accessby the pheriperal eventcontroller (PEC). The 32kB RAM and 32kB ROM give suffi-cient space for the programs, look-up tables and also forlogging of control variables and measurements. Usercom mun ication and presentation of mon itored data isperformed on a PC connected through the RS232 port. Figure4 gives an overv iew of the measurement and calculation hard-ware. For simplicity, only functions which are necessary fo rthis drive are shown.

A resolver on the shaft provides rotor position. Resolverto digital (WD) onversion is performed by an AD2S80KD[22]. The maximum speed limits the resolution of position to12 bit.

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41 4

12- 121-

4% i i i i i o i 2 i 4 i 6 ia AN

~ I ~ -

b)1 I 1

Fig.7. Responses in q-axis current to diflerent changes in q-axiscurrent reference iqreffora) constantcontroller parameters b) iq dependent controller parameters

At the end of the current loop routine the time instant forthe next software interrupt is loaded. Logging of measured andcalculated values can also be performed. Finaly currentsreferences are generated.The method for currents reference generation can bechosen from terminal PC. The references can be read from atables or calculated by the speed controller. The speedcontroller reference is generated in about the same fashion asthe current co nm ller references.

EXPERIMENTALRESULTS

The speed and current controller implemented in by theSimens micro contro ller SAB8OC166 was tested on 2.8kWPMSM rive (seemotor data [18]) with IGBT voltage sourceinverter. The samp ling time for speed and current control wasThe performance of the current controller can bedescribed in classical way by the response to a reference stepchange. The rise time and the oversho ot of the curren tresponse are trade offs when tuning the drive parameters.Fig.7b. shows the iq stator current response family to referencestep change for proposed iq dependent nonlinear parametertuned current controller. This allows for no overshootoperation and c m n t rising time less then lms. Stator currentswere measured by LEM elements transformed and stored atmicro contro ller memory by part of control algorithm. Loggeddata was analysed and presented by using Matlab routines inhostPC. he more detailed test is shown in figure 8. where thecurrent controller response for one per unit step change is

shown. The proper &coupling and Emf compensation isprove d by the no transien ts behaviour in d-axis and zero steadystate exror in both d and q axis current regulators outputs.The current loop dynamic performance, to sinusoidalperturbations of + c m n t eferen ce, is shown in figure 9 as aamplitude and phase diagram.

loop.

Fig.8. The current controller response or iqrefone pe r unit step changea ) iq current resppnse b) idcurrent response c) output of dcurrent

regulator d) output of iq current regulator.

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l ooc0 3

-100120i iw140 10802Fig.9.. Thc dynamicallyp e r j o r m ~ c cf he iq cyrrQIl ontroller

The dynamically performance of the whole drive withspeed and current control at no load condition is shown on fig10. By applying a constant reference signal with a smallsinusoidal component added, the mechanical speed bandwithwas m e a s a d . The mult shows god performance up tolOOHz with the filter in speed measucement limiting thebandwith.

$Fig.10. The dyMmic.CdlypCrfonC oflhewhole drive with speed andbcurrent controlatno load conditwn

CONCLUSIONTh e realisation of a high performance fully digitalPMSM drive requks a current controller with &c oupling andcompensations for nonlinearities. By using a low costmicrocontroller this can be realized in a compact form. Fastexecution time, and though high speed and current bandwith.can be achived by effecient programing. With this solution,10- m, mg frequency for the current control loop wasobtained. The current rise time to nominal value, withoutovershoot in the quadrature axis, and speed bandwith up tolOOHz was obtained.

REFERENCES[ l ] Jahns, T.M.,Wan, G.B., Neumann, T.W.,"Interiorpermanent-magnet synchronous motors for adjustable-121 Bose, B.K., "A high performance inverter-fed drivesystem of an interior permanent magnet sylrchronousmotor" GM. o c . IEEE IAS annual meeting, pp.269-76, 1987.Pfdf, G.,Weschta, A., Wick, A., "Design and experi-mental d t a f a brushless ec servo-drive" GM. ec.[4] Xu, L., Xu, X.. Lipo, T.A., Novo tay, D.W., "Vectorcontrol of a synchronous reluctance motor includingsaturationand Iron loss", IEEE , pp359-64,1990[51 Matsui,N .,Ohashi, H., "DSP-based adaptive control of abrushless motor". EEE, pp375-80,1988161 Balda, J.C., Pillay, P:; "Speed controlled design for avectorcontrolled permanent magnet synchronous motordrive with parameter variations". IEEE, pp163-68,1990[71 Pill ay, P.. Krishnan, R., "Application characteristics ofpermanent magnet synchronous and brushless dc m otorsfo r servo drives",IEEE. p 380-90,1987Nielsen. P.E., Thomsen, E.C.. Nielsen, M.T., "Dig italvoltage vector control with adaptive parameter tuning"

Adnanes, AK., "High efficiency, high performancepermanent magnet synchronous motor drives".thesis,The University of Trondheim, The NorwegianInstitute of Technology, Department of elec trica l PowerEngineering, Division of Electrical Power Engineering,1991[lo] N M ~ ,., Reuss, H.C., "Synchronous servodrive: Avery compact solution of control problems by means of asingle-chipmicrocomputer",IEEE,p266-7 1,198 8U11 Naunin. D., Hetzel, D., Reuss, H.C., Sechehann. C.,"Completely digital position feedback control forsynchronous servodrives"JEEE, pp452-59.19891121 Krishnan, R., Bharadw aj. A.S., "Single chipmicrocontroller implementation of an incontrolledinduction motor drive system",IEEE, pp 265-71.1989[131 Holtz, J.. Lammert, Pbtzkat, W., "High-speed DriveSystem with Ultrasonic MOSFET PWM Inverter andSingle-Chip M icroprocessor Control", IEEE Trans. nd.

1141 Rowan, T.M.. Kerkman. R.J.. "A new SynchronousCurren t Regulator and Analysis of Current-R egulatedPWM Inverters" IEEE Trans. Ind, Appl., vol. -22. no. 4,JulyIAug. 1986.(151 Lessmeier, R.. Schumacher, W., Lehonard, W.,"MicroprocessorControlled AC-Servo Drives withSynchronous Induction Motors: Which is Wferable?",JEEE Trans. nd. Appl., vol IA-22. pp812-819.1986[16] Pollmann, A.J. "Software Pulsewidth modulation for c(PControl of AC Drives" IEEE Trans. n d . Appl., vol. -22,no. 4, 1986.

Speed drives" IEEE T-IA,V O ~A-22, pp.738-47,1986.

131IEEE U Sd &lg, pp.692-97,1982.

[81G M ~o c .EPE, pp.313-318,1989191

App l., ~~ 10 11 -1 5 ,987

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[17] Norum, L.. Adnanes. A.K.. Sulkowski, W., Aga, L.A.,"The Realization of a Permanent Magnet SynchrounousMotor Drive with Digital Voltage Vector SelectionCurrent Controller". IECON91, Kobe, Japan, Oct 1991,proceedings pp 182- 187[18] Industrial Drives, "B-206 Technical Data Publication"Industrial Drives, 201 Rock Road, Radford Virginia24141, Phone +17 03 639-2495Fax +1703 731-0847.[19] Norum, L., "Microprocessor applications in powerelectronics" dissertation, The Norwegian Institute ofTechnology, 1985[20] S IEMEN S "M icrocomputer Comp onents SAB80C16616-bit CMOS Single-Chip Microcontrollers forEmbed ded Control ApplicationsUser's Manual 6.90"[21] Evaluation board EVA166 Manual, ertec GmbH,January 1991[221 Ana log Devices, "Analog-digital conversion handbook"Prentice Hall, ISBN 0-13-032848-0. 1986.

Motor dataM.nuf.cturer ModelIndustrial Drlves [*+I B-206.c

Ratedcumnt (m) Irated 10ARated voltage (rms,1-1) h l ? d 250 v

Ratedmue TPIICA 6.83NmW s p c e d %ted 4900rpm

D m t axis inductance 4 5.33mHQuadratlirepxlripdll- Lq 1 3 . W

31.1VkrpmBack cqf(rms 1-1) KEMomentof inertia I 2.512 . IO4 knm2

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Compact Realisation of PWM-VSl Current Controller For

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