ANALYSIS AND DEVELOPMENT OF SINGLE STAGE SOLAR PV INVERTER SYSTEM

Abstract

T HEgrowingelectricitydemandisrisingduetotherisingpopulationanddepletionof non-renewableenergysources,rapidclimatechangeandglobalwarmingareamongthe major threats to today’sworld. Renewable energy sources (RESs) such as solar photovoltaic(PV)havebecomeanalternativeoptionforrisingenergydemands.Solarenergy iscountedamongsteasily availableRESs.One ofthemajoradvantages ofsolarPVis thatitis independentofend-userlocation.Inthecaseofnon-electrifiedremote areas,itbecomesmore economical to use solar photovoltaic (PV) based power generation compared to the conventional grid-connectedsystem.Critical loadapplications suchashealthcarefacilities, informationtechnology-enabledservices, telecommunicationnetworkingandelectronicloads likecomputersrequireanuninterruptedpowersupply.ThePVelectricityisnotaccessibleat night or during rainyweather.Grid-tied solar energyconversion system(SECS) delivers electricitytoessentialloads.However,gridoutagesarerelativelyfrequentinIndia,loweringthe dependabilityofgrid-tiedSECS.Thebatteryenergystorage(BES)systemcanbeinterfaced with/withoutabidirectionalDC/DCconverterattheDClinktoimprovegrid-tiedSEC system reliability.TheSECsystemcanbeclassifiedintotwomaincategories: two-stageandsingle stage. GridoutagesisfrequentandverycommoninIndia.Therefore, theutilitymainsmustbe isolatedseamlesslysoasnot toaffect critical loads and theoccurrenceof voltage/current sag/swellshouldnotaffectsystemperformance.Unintentionalgrid-outagemayoccurdueto theutilitymainsfailure,circuitbreakeropening,orhumanmistake.Henceforth,anislanding detection(ID)/re-synchronizationcontroller is requiredtobemadeoperational. Ingrid-tied mode, theACmainsmaintain the amplitude and frequencyof gridvoltage.However, in islandedmode, it isessential tomaintainloadvoltageamplitude, frequencyandTHDwithin thelimits inlinewithIEEE-519.Non-linearloadsconnectedatthepointofcommoncoupling pollute theutilitymainsby injectingharmonics.Harmonics in thegridcurrentmaycause overheating, short lifespans, andmalfunctioningof appliances.Thepower qualityofgrid currentistobesustainedwithinalimitinaccordancewithIEEE-519.Therefore,acontrolled single-phaseVSCalsooperatesasaDSTATCOMtocatertotheload'sreactivepowerdemand. Inthisthesiswork,dual-modetwo-stageandsingle-stagemultifunctional self-reliantgrid interactive single-phase SEC-BES systems are designed, controlled, simulated and implemented.Theprimegoalof thisworkis tosupplycontinuouspower tothecritical load i regardlessof theavailabilityof theACmains. Insurpluspowermode(SPM), thegenerated power fromthePVishigher thanthedemandpower fromthecritical loads.Therefore, the surpluspowerofthePVisusedtochargetheBESsystemandtheremainingactivepoweris injectedintotheACmains. Indeficitpowermode(DPM), thegeneratedpowerof thePVis lesserthanthedemandpowerofthe criticalloads.Insuchacase,thebalancepowerissupplied either fromtheACmainsor theBESsystem,whichdependsontheavailabilityof theAC mains. Thisworkmainlyclassifies the grid-tiedSEC-BES systemcontrol scheme into three categories.Inthefirstcategory,aPI-Leadcompensator-baseddual-loopandmodelpredictive controlschemesfor abidirectional DC/DCconverteraredesigned,simulatedandimplemented tocontrol theDCbusvoltageandBESsystemcharging/dischargingcurrentundervarious operatingmodes.Inaddition,thepresentedDC/DCconvertercontrolschemealsoensuresthe extractofmaximumpowerfromthePVarray.Moreover,astate-of-chargecontrollerwitha bidirectionalDC/DCconverterprotectstheBESsystemfromdeep-discharging/overcharging. ThestabilityanalysisofabidirectionalDC/DCconverterhasbeenpresentedthoroughlyboth for the PI-lead compensator and model predictive controller. Designing the PI-Lead compensator parametersbasedon systemstabilityconstrained tooperate thebidirectional DC/DCconverter inastableregionundervariousoperatingconditionsbecomes important. Therefore, thedual-loopPI-Leadcontroller parametersaredesignedbasedon the stability constraintsinthefrequency domain. Thestabilityanalysis ofabidirectionalDC/DCconverter for amodel predictive controller is analysed in the Z-domain. The Jacobianmatrix is constructedusingthestatevariableequationsofabidirectionalDC/DCconverter.TheJacobian matrixeigenvaluesdeterminethestabilityofabidirectionalDC/DCconverter. Ifeigenvalues liesinsidetheunitecirclethentheDC/DC converteroperates inastableregion.Otherwise,the systemisunstable. ThebidirectionalDC/DCconverterparameters (DCbus capacitor and converter inductance)andtheweightingfactorforamodelpredictivecontrolleraredesigned basedonbidirectional DC/DCconverteroperation ina stability region.