REAL AND REACTIVE POWER CONTROL OF A THREE-PHASESINGLE-STAGE PV SYSTEM AND PV VOLTAGE STABILITYSUDHEER KUMAR.DARISICONTENTS:Introduction PV array characteristics Control of real and reactive power output of single stage PV systema. Fixed real power and voltage/Var controlb.MPP controlc.!witching between fixed real power mode and MPP control mode.PV voltage stability in MPP control. conclusionsINTRODUCTION"For grid#connected PV systems$ %C power from the PV array is converted to&C power at the appropriate voltage level and in'ected into the grid by power electronic converters PV systems trac( the maximum power point )MPP* of the PV array to extract maximum available solar energyhe most common PV interface configurations are +.two stage converters ,. single#stage invertershetwo#stageconvertersconsistofa%C#to#%Cboost converterforthefirststage$whichbooststhePV arrayoutput %C voltage up for the second stage and performs MPP second stage is an inverter which generates -rid compactable &C voltage and provides voltage/var control!ingle#stage inverters only consist of an inverter which controls the real and reactive power output as well as generates a grid compatible voltage. single#stage inverter has # higher power conversion efficiency$ # lower cost#higherreliabilitysincethechanceofcomponentfailureislowerwith respect to the two#stage converter.Main problem with single stage inverter is it re.uires high %C voltageMany control algorithms have been developed for the MPP control of PV systems.the control algorithm of grid#interfaced PV system needs to achieve these functions" )+* generate a grid compatible sinusoidal waveform/ ),* perform maximumpower point trac(ing )MPP*)0* provide voltage regulation or follow a reactive power output reference)1* ensure PV %C voltage stability.PV &22&3 C4&2&C52I!IC! & PV array is composed of PV cells connected in series and in parallel to achieve the desired %C power and %C voltage input for an inverter system.Isc is the short circuit current/ Voc is the open circuit voltage; Vmaxp and Imaxp are voltage and current at the MPP, respectively.hree characteristic operation points for the PV system"open circuit$ MPP and short circuitIn the current source region small current increase results %C voltage collapsePv array current is more sensitive to solar irradation changethan the voltage and it generates more power at high solar irradations.Pv array output power increases with temperature drops.he pv array output voltage is more sensitive to thetemperature changes than the curentCONTROL OF REAL AND REACTIVE POWER OUTPUT OF SINGLE-STAGE PV SYSTEMWhere Vt and Vc are the RMS values of thePCC terminal voltage and inverter terminal voltage is the phase angle between Vc and Vt and Xl is is the equivalent reactance of the transformer.real power fow is controlled by regulating the phase angle of Vc and the reactive power is controlled by regulating the amplitude of Vc.FIXED REAL POWER AND VOLTAGE/ VAR CONTROLControl goal is maintaining the fxed amount of real power and reactive power/voltage.MPPT CONTROLControl objective is keeping dppv/dvpv=0 or near to zero. SWITCHING BETWEEN FIXED REAL POWER MODE AND MPPT CONTROL MODE:hePV system needs to beable toseamlesslyswitch between fixed real power control mode and MPP control modePVsysteminitiallyoperatedinthefixedrealpowercontrol mode.Ifacloudbloc(sthesunandcausesthePVarray6s maximum power to drop below the fixed real power setting)or*%uringalightloadlevel$thePVarrayneedstoreducethe realpoweroutputtopreventthePCCvoltageincrease$!oPV systemneedstoswitchtooperatingatthefixedrealpower control modeSeamless switching between fxed real power and MPPT control is necessary for PV systems to operate smoothly during dynamic atmospheric and power grid conditions7hen ppv/vpv is equalto or slightly larger than 8$ it means that the PV inverter output power is on the edge of maximum power limit and MPP control needs to be switched on.7hen the PV output power is well below the fixed real power reference$ regardless of the value of ppv/vpv, the MPPT control is engaged.If the PV inverter real power is approaching Pre and alls into a tolerance range$ !, the ixed po"er control "ill #e activated.PV V9:&-5 !&;I:I3 I< MPP C9