Seite - 255 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2017,10, 616 (b) Electromagnetic torque of motor in contrast model (c) Rotary speed of motor Figure6.Curvesofexpectedmotor torque,electromagnetic torque,andmotorspeed. WeunderstandfromFigure6 that themotorrotaryspeedcouldsmoothlyandswiftly followthe presetvalueandonlyhadaslightfluctuationat0.05swhenthe loadedtorque jumped. Switchingof modeshadnoimpactonrotaryspeed. Electromagnetic torqueTe couldalso followexpectedtorqueT∗e well. In thepresentcurrent followingaccuracy(h=3A), theamplitudeofelectromagnetic torque’s fluctuationwas limitedwithin 5N·mor so, but after switching to lower voltage power source 2 asmajor power source, the fluctuationwasmore drastic, which indicated that setting the higher voltagepowersourceas themajorpowersource ispreferable.Wealso foundthat themotorunder the proposedmulti-level currenthysteresismodulationhadabout30%less torquefluctuationthanthe motorunder traditional two-levelcurrenthysteresismodulation. Windingmode, torquesaturation judgmental threshold Ith, andactual integration I curvesare displayedinFigure7a,b. InFigure7a, themodesignalsaredemonstrated: 1 is starmode,2stands for trianglemode,3and 4are the lowswitchingfrequencyandhighpowerdifferencemethods, respectively, in independent mode, and 3.5 and 4.5 represented the flux-weakening region of the twomethods, respectively, in independentmode. InFigure6a,b, twopeaksofexpectedtorquecurveat0.12sand0.17s indicate thatwith increasing speed, voltage is almost saturated and electromagnetic torque cannot follow expected torque, leading to the speed controller further increasing the expected torque; from the electromagnetic torquecurve, it isevident that theactualelectromagnetic torquewillgraduallydecline becauseofvoltagesaturationbefore theexpectedtorquepeak;whentorqueerroraccumulatesenough tosatisfy torquesaturationconditions,upswitching is triggeredandelectromagnetic torquerapidly follows the expected torque after switching; Fromelectromagnetic torque beingunable to follow to the upswitching point, it only took 0.02 s. FromFigure 7b, we understand that 0.02 s before upswitching,with thevoltagealmost saturated, theswitching integrationof torqueerror rosesharply to the thresholdandupswitchingwas triggered.Afterwindingmodeswitching to trianglemodefrom 255