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Design, Modelling and Control of Electrical Machines With Applications to Iron-powder Machines and Acoustic Noise David Mart´ınez Munõz Doctoral DissertationinIndustrialElectricalEngineering Department of IndustrialElectricalEngineering andAutomation Departmentof IndustrialElectricalEngineeringandAutomation LundInstituteofTechnology LundUniversity P.O.Box118 SE-22100LUND SWEDEN http://www.iea.lth.se ISBN91-88934-35-7 CODEN:LUTEDX/(TEIE-1043)/1-338/(2004) (cid:1)c DavidMart´ınezMunõz,2004 PrintedinSwedenbyMedia-Tryck LundUniversity Lund2004 ii To my parents: Manuel and Josefa iii iv Abstract Thisthesisconsistsoftwoparts,thefirstdealingwiththedesignofiron-powder synchronous machines, and the second with the analysis and prediction of the acousticnoiseinelectricalmachines. In Part I, a 1.6 kW electrically magnetized claw-pole machine with magnetically conductingend-plates has beenanalyzed and aprototype tested. The machineisbuiltfromsoftmagneticcompositematerial (SMC),alsoknownas iron-powder. ThemagneticisotropyofSMCgivesenormousflexibilityinelec- trical machine design, enabling new topologies exploiting three dimensional flux paths. This is the main advantage compared to conventional machines using laminations, where the flux is constrained into two dimensions. The novelty of the machine presented lies in that the slip-rings in the rotor are no longer needed, since the field coils are removed from the rotor and placed in magnetically conducting end-plates attached to both sides of the stator. This also improves the cooling capability of the copper losses from the field wind- ing, allowing an increased electric loading. The rotor is of the claw-pole type, and the end-plates close the magnetic circuit between the stator and the rotor. The machine has been optimized using a magnetic equivalent circuit model allowing rotation, where non-linearities have been included using an iterative approach based on the linearisation of the BH curve. The traditional leakage pathsinclaw-polemachinesaremodifiedbecauseofthemagneticallyconduct- ingend-plates,andalternativesareproposedtoreducethem. Themachinehas also been compared to two alternative topologies with electrical magnetization andanotherwithpermanentmagnets. Thecomparisonhasbeencarriedoutfor a similar temperature rise in the windings, and thermal models have been developed for every machine to determine their maximum electric loading. The rotational and alternating components of the iron losses are calculated using the finite element method (FEM). The results from the measurements indi- v catethattheaveragetorqueis14%lowerthanpredicted. Thisisprobablydue to a leakage path between the end-plates through the shaft, which carries the homopolar flux, and that was not considered in the predictions. The concept of series magnetization has also been tested. This consists of feeding the field windingdirectlyfromtherectifiedthreephasearmaturecurrentsattheneutral point,thereforeeliminatingtheneedforthed.c.powersource. Electricalmachinesarefindingapplicationinnewenvironmentswherelower noise levels are demanded. The main focus of Part II is the measurement and predictionof the noise emissions frominductionmotors usingthe vectorcon- troltechniqueaswellastheanalysisofsomestructuralchangestoreducethese emissions. A digital drive system has been developed for a 2.2 kW induction motor, and its dynamic capabilities demonstrated for a wide range of the fre- quency spectrum. This tool has been used for the experimental evaluation of the noise emissions when the flux and/or the torque are modulated with high frequencynoisesignals. Theresultsshowedthatthenoiseemissionswerehigher whenthefluxwasmodulatedcomparedtothetorque,althoughthedifferences were considerably reducedwhen themachine was loaded. It was also observed that the noise emissions were decreased importantly at load. Sound pressure andsoundintensitymeasurementshavebeenconductedwiththerotorstation- ary and rotating at low speed, showing that the most proper way to quantify the noise emissions from electric machinery is to measure the sound power. A method for the prediction of the noise emissions has been proposed, based on the interactive use of commercial packages for mechanical, electromagnetic and acoustic analyses based in the finite and boundary element methods. The results show that the accuracy of the noise prediction depends on the proper calculationofthemodesofvibrationinthestructuralanalysis,aswellasasuit- able selection of the material damping. Skewing also needs to be modelled in ordertoaccountfortherotorharmonics. Astudyhasbeenconductedtoassess theeffectivenessof introducingperipheral airgaplayers around thestator core to reduce the noise emissions. It was observed that the acoustic behaviour was not improved, since the reduction of the stiffness in the outer part of the core actuallyincreaseditssensitivitytothevibrations. vi Preface This thesis constitutes the work I have carried out in my pursuit of a PhD in IndustrialElectricalEngineeringattheDepartmentofIndustrialElectricalEn- gineeringandAutomation(IEA),LundUniversity,Sweden. Duringthecourse of my PhD studies I also had the opportunity to spend almost one year as a guest research fellow at the Acoustics and Vibration Unit (AVU), University College, The University of New South Wales, at the Australian Defence Force Academy,inCanberra,Australia. Thethesisaddressestwotopicsinelectricalmachines. Thefirstisconcerned withthedesignofiron-powdermachines. Thesecondisaboutmodellingacous- ticnoiseinelectricalmachines. Thethesisisdividedintotwopartsaccordingly, both written as a monograph. For the sake of clarity, each part has been orga- nized in a series of chapters followed by the bibliography and the appendices relatedtothatpart. DuringtheyearsofPhDstudies,partofthematerialinthethesishasbeen publishedat other occasions. The research on iron-powder machines has been publishedinthefollowingarticles: • Mart´ınez-Munõz,D.andAlaku¨la,M.(2003). “Comparisonbetweenanovel claw-poleelectricallymagnetizedsynchronousmachinewithoutslip-ringsand a permanent magnet machine”. IEEE International Electrical Machines and Drives Conference, IEMDC’03 Conf. Proc., Madison, WI, USA, June 2003, pp. 1351-1356. • Mart´ınez-Munõz, D. and Alaku¨la, M. (2004a). “Alternatives for leakage reduction in a novel claw-pole electrically magnetized synchronous machine”. IEEInternationalConferenceonPowerElectronics,MachinesandDrives,PEMD 2004Conf. Proc.,Edinburgh,UK,April2004,pp. 386-391. vii • Mart´ınez-Munõz, D. and Alaku¨la, M. (2004b). “A MEC network method based on the BH curve linearisation: study of a claw-pole machine”. Inter- national Conference on Electrical Machines, ICEM’04 Conf. Proc., Cracow, Poland,Sept. 2004,6pp. • Mart´ınez-Munõz, D., Reinap, A. and Alaku¨la, M. (2004a). “Comparison betweenthreeiron-powdertopologiesofelectricallymagnetizedsynchronous machines”. International Conference on Electrical Machines, ICEM’04 Conf. Proc.,Cracow,Poland,Sept. 2004,6pp. • Mart´ınez-Munõz, D., Reinap, A. and Alaku¨la, M. (2004b). “Comparison between four topologies of synchronous machines using SMC”, invited pa- per, The UK Magnetics Society, Seminar on SMC and their use in electrical machines,Newcastle,UK,Nov. 2004,7pp. The thesis author has also co-authored the following publication in the samefield. Thecontributionmadebythethesisauthorinthispaperisminor: • Reinap,A.,Mart´ınez-Munõz,D.andAlaku¨la,M.(2004). “Ironlosscalcula- tioninaclaw-polestructure”. IEEENordicWorkshoponPowerandIndustrial Electronics, NORPIE’04 Workshop Proc., Trondheim, Norway, June 2004, 5 pp. Theresearchonacousticnoiseinelectricalmachinesisreportedinthefol- lowingarticles: • Mart´ınez-Munõz, D., Pulle, D. W. J., Alaku¨la, M. and Weibull, H. (1999). “Adrivesystemforacousticalanalysis”. IEEInternationalConferenceonElec- trical Machines and Drives, EMD’99 Conf. Proc., Canterbury, UK, Sept. 1999,pp. 147-150. • Mart´ınez-Munõz,D.andLai,J.C.S.(2003). “Acousticnoisepredictionina vectorcontrolledinductionmachine”. IEEEInternationalElectricalMachines and Drives Conference, IEMDC’03 Conf. Proc., Madison, WI, USA, June 2003,pp. 104-110. • Mart´ınez-Munõz,D.,Lai,J.C.S.andPulle,D.W.J.(2003). “Acousticnoise radiatedfromvectorcontrolledinductionmotordrives”. EuropeanConference on Power Electronics and Applications, EPE’03 Conf. Proc., Toulouse, France, Sept. 2003,10pp. viii • Mart´ınez-Munõz, D., Lai, J. C. S. and Alaku¨la, M. (2003). “A study of the acoustical properties of stators with an outer-surface layer of air gaps”. Eu- ropean Conference on Power Electronics and Applications, EPE’03 Conf. Proc., Toulouse,France,Sept. 2003,10pp. Acknowledgements Along the years of PhD studies I have had the privilege to work with different supervisors. IwouldliketoexpressmysinceregratitudetoProf.MatsAlaku¨la, who welcomed me at the department already as an exchange student and gave metheopportunitytocontinuewiththePhDstudies. Matsisveryencouraging and really enjoys exploring unconventional ideas. I am very grateful to Prof. JosephC.S.Lai (AVU)whowas my advisorforthe research on acousticnoise and invited me to work at the AVU. Joseph is very friendly and helpful and without his support the acoustic experiments and simulations would not have beenpossible. IamalsothankfultoProf.DucoW.J.Pulleforhisadviceinthe firststagesofmyPhDstudies. I would like to especially thank my colleague and friend Avo Reinap, who hasbeenanextraordinaryworkingcompanion. Avoisalwayswillingtodiscuss anytopicandtofillthewhiteboardinouroffice. A number of people earn my gratitude for their support during the experimental work. Dr Thomas Rundqvist (ProEngCo Permedyn) and Ludvig Wadsten(Motor&Bilelektra)havebeenveryhelpfulwiththeconstructionof theprototype machineinPart I.Andrew Roberts, GlennTorrand DrAndrew DombekattheAVUhelpedwithpracticalaspectsrelatedtotheacousticnoise experimentsinPartII.AttheAVUIalsowouldliketothankAnttiPappiniemi forenjoyablediscussions. The structural models of the test motor included in Part II were created by Dr Chong Wang during his PhD studies at the AVU, and their availability is acknowledged. Dr Alex Michaelides at the VectorFields support in Oxford has been a good help in the initial stages of the electromagnetic finite element modelling. I would also like to thank my former colleague Tech. Lic. Svante Anderssonforinterestingdiscussions. IwouldliketoexpressmygratitudetothestaffatIEA.Evenifallthepeople at the department are helpful and friendly there are those that I owe a special thank. GetachewDargehasprovidedveryvaluablehelpwithpracticalissuesfor ix theexperiments. DrMortenHemmingssontakescareoftheLaTeXpackagein UNIX,whichIuseformostofthewriting. DrGunnarLindstedthelpstokeep myPChealthyandalsoallowedmeto“occupy”thecomputersinthelabwith mysimulations. IamalsogratefultoProf.GustafOlsson,whoIbelieveplayed animportantroleinmyadmissionasaPhDstudentatthedepartment. Apartfrommysupervisors,anumberofpeopleearnmygratitudeforproof readingpartsofthethesis. PartIhasbeenreviewedbyProf.StureErikssonand Tech. Lic.Svante Andersson. Part II has been reviewed by Prof. Lars Gertmar, DrKelvinMaliti,andTech.Lic.AndersDanerydinaseminar. Theircomments havecertainlycontributedtoimprovethequalityofthethesis. IwouldalsoliketothankDrOlaStenla˚a˚s,DrRolfEgnellandDrOlofEr- landsson from the joined project for Part I. Together with the members of the steeringcommittee, Prof.Sture Eriksson(EME/KTH), Go¨ran Masus (Finnve- den Powertrain), Dr Go¨ran Johansson (Volvo), and Tech. Lic. Joachim Lind- stro¨m(Volvo)theyareacknowledgedforfruitfulcommentsanddiscussions. TheprojectsinPartIandPartIIhavebeenfinanciallysupportedbySTEM (The SwedishEnergy Agency), and NUTEK (The Swedish Business Develop- mentAgency),respectively. Thissupportisgratefullyacknowledged. Finally, I would like to thank my parents Manuel and Josefa, and my two brothers Manuel and Jose´ Andre´s, in Spain, for all their love, trust and sup- portovertheyears. Iwouldliketopaytributetomyparents,whoalwayshave supportedmyprojectsandhaveencouragedmetotravel. Theirwisdom,under- standingandcarehasenabledmeandmybrotherstoattaingraduateeducation. Thisthesisisdedicatedtothem. Lund,November20,2004, DavidMart´ınezMunõz