amplitude. SinceadifferenttypeofPWMpoweramplifierwasusedininboard(airturbineside)and outboard bearing, againadjustment blockwasaddedtocompensate thedifferent gainused.Asafegain featurewillbetriggered toprotectthebearingsystemathigherspeedwhentherotororbitexceeds the predefined orbitsize.Also,awhirling featurewasimplemented toinvestigate thedynamic behavior of themagnetically suspended rotorsystemaswellastocheckbackup bearings. Whirling orbitsize, startingangle,andthecenterpointoforbitarealluserdefinedtoinvestigate bounce modeandtilting mode.Alltheabove-mentioned features cancontrolinboardandoutboard bearings separately. Coilsor/andamplifiers failingsituations aresimulated bymanually shutting downtheircontrolcurrent commands fromthecontroller cockpit.Thiseliminated abunchofmechanical switches showninFigure 2.Asimpledataacquisition systemwindow wasaddedtothenexttothecontrolcockpitwindow to monitorthesystemperformance. Experimental Results Figure6showsthatcurrentinputstocompensate thepole1(oneoftoptwopoles)failedoperation at0 rpm.Theadjacent pole2(theothertoppole)neededamorecontrolforceandtwobottompoles5and6 hadreduced controlforcestocompensate thelessattracted forcecausedbypole1failure,whilefour horizontal poles3,4,7,and8hadlittleimpacts. Figure7showsthatcurrentinputstocompensate theconsecutive 1-4-6thpolesfailedoperation at0rpm. Whenpole4failed,theadjacent pole3needed alittlemorecontrolforceandtheotheropposing horizontal poles7and8hadlittleimpacts because horizontal polesdidn'ttakeaccount ofrotorweight. Whenpole6failed,atoppole2hadreduced controlforcetocompensate thelessattracted forcecaused bypole6failure,whiletwohorizontal poles7and8hadlittleimpacts. Nowweincreased therotorspeeduptothemaximum allowable speedof20,000rpmwithoutchanging gainsetdoneinexperiments at0rpmdescribed inFigures6and7.Figure8showsthatcurrentinputsto compensate theconsecutive 2-3-5-7thpolesfailedoperation at20,000rpm.Whenpole2failed,the adjacent pole1needed alittlemorecontrolforce(sameasinFigure6)andtwobottompoles5and6 hadreduced controlforcestocompensate thelessattracted forcecausedbypole2failure,whilefour horizontal poles3,4,7,and8hadlittleimpacts. Whenpole3failed,theadjacent pole4needed alittle morecontrolforceandtheotheropposing horizontal poles7and8hadlittleimpacts because horizontal polesdidn'ttakeaccount ofrotorweight.Whenpole5failed,atoppole1hadreduced controlforceto compensate thelessattracted forcecausedbypole5failure,whiletwohorizontal poles7and8hadlittle impacts. Evenfailedpole7didn'taffecttheremaining activepoles1,4,6,and8. Wecontinuously killedpoles6and8toseeifonlytwoactivepoles1and4canhandletheworst scenario ofmultiple coilandamplifier failures. Figure9showsthatcurrentinputstocompensate the consecutive 6thand8thpolesfailures withpoles2,3,5,and7pre-killed. Whenpole6failed,only remained toppole1neededalittlemorecontrolforcetohandletherotorweight,whilehorizontal poles4 and8neededslightlyreduced controlforces.Finally,pole8failureaffected alittleimpactonpole4. Avarietyoffailedsituations wasinvestigated andalltheresultsagreedwiththoseshowninFigures6 through9.Figure10showsanother caseofusingonlytwoactivepoles.Itshowsthatcurrentinputsto compensate theconsecutive 2_dand4thpolesfailureswithpoles5,6,7,and8pre-killed. Whenpole2 failed,onlyremained toppole1neededarelatively largecontrolforcetohandletherotorweight,while horizontal poles3and4neededslightlyincreased controlforces.Finally,pole4failureaffected alarge impactonpole3,whilepole1wasbarelyaffected. Also,itwasdemonstrated thatforanyfailedsituations, thepredefined desired rotorposition was maintained because anintegrator successfully generated acorrective forcetocompensate thesteady stateposition error.Figure11showsthatatransient sensorsignalplotofthefailedsituation ofthecase ofFigure10.Whenpole2failed,therotorwasmoving down,butanintegrator wastriggered immediately togenerate acorrective force,whichenabled therotortomovebacktotheoriginalposition inlessthan0.3second. Whenpole4failed,therotorwasmovingtorightbecause ofstrongattractive forcecausedbypole3.However, therotorrecovered itsdesiredpositionwithinlessthan0.5second. 129