Seite - 348 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2016,9, 240 Thissystemwastestedbyvaryingthecompressorspeed. Theconclusionsshowedthatboth the heatingandthecoolingcapacitiesof thesystemincreasedwith theriseofcompressorspeed,whereas theCOPs inbothcasesdecreased. Jabardo et al. [37]alsoreportedanautomotiveACsystemequipped withavariablecapacitycompressor runbyanelectricmotorcontrolledbyafrequencyconverter. The impactonsystemperformanceofoperationalparameterssuchascompressorspeed, returnair in the evaporatorandcondensingair temperatures,wasexperimentallyevaluatedandsimulatedbymeans of thedevelopedmodel. Tobetterdevelop the inverterACsystem, all factorswhich influence the performanceof thevariable frequencyACsystemhavebeendiscussed in[38]. Effectsofcompressor frequencyontheperformanceandparametersareshowninFigure2.Atafixedambient temperature andheat transferareaofheatexchangers, thecoolingcapacityandpowerconsumption increasedas thecompressor frequency increased. Incontract, theenergyefficiencyratio (EER) initially increased butsubsequentlydecreased, so thecompressor frequencyshouldbe increased inorder to improve the coolingcapacity,while it shouldbedecreasedinorder toreducepowerconsumption. Theseresults areveryuseful foroptimizing thedesign,andautomaticallycontrollinganddiagnosingexceptions in theoperationofvariable frequencyACsystems. ȱ Figure2.Effectsofcompressor frequencyontheperformanceandparameters [38]. Inadditiontovariable-speedcompressors,adjustingthefanspeedcanleadtofurtherperformance andefficiency improvements. Lee et al. [39] focusedon the effect of outdoor coil fan speedon the performancevariationof theheatpumpsystemadoptingthehotgasbypassmethod. The integrated heating capacitywith hot gas bypasswas highest at 60% (780 rpm) fan speed. This valuewas 4.4%higher than thatof the constant speed fan. On theotherhand, theaveragedCOPof theheat pump in this casewas higher by 2.8% than the constant speed fan. Asmentioned in [40], three frequency converterswere equipped to control the speedsof the compressor, the evaporator fans and thecondenser fans, respectively. Theanalysis showedthat the three speedscouldbeadjusted simultaneouslyaccordingtobothactualworkingconditionsandoperationmodesothattheACsystem couldoperate inanoptimumstate,but inpracticalapplicationsonlyonefanspeedandcompressor speedneedtobemodulated inreal-time,consideringhardwarecostsandsystemcomplexity. Advancedcontrolalgorithmshavealsobeenstudiedbymanyauthors. Yeh et al. [41]proposed twocontrolalgorithms. Thefirstalgorithm,whichmodulatedtheoutdoor fanspeed,couldenhance thesteady-statepowerefficiency. Thesecondalgorithm,whichaddedonemoredegreeof freedomto controlbymodulating the indoor fanspeed,could improvethe transient response. Theperformance of theACsystemcouldbe improvedifbothalgorithmsweresimultaneously implemented in theway that thesecondalgorithmwasresponsible for thecontrolactionduringthestartup/transientphase ofoperation, andthefirstalgorithmtookoverat steadystate. Shi et al. [42]described threecontrol algorithms for the inverterACsystem: thematrix control, the system-relative commands control and the fuzzy control. Moreover, to realize comfort and systemenergy efficiency, they explained themechanismtoregulate the runningspeedof thecompressor, indoorandoutdoor fans, and the openingof theexpansionvalve.AsshowninFigure3,anartificialneuralnetwork-basedcontroller 348