Smart Inverter Controls and Microgrid Interoperation at DECC

Technical Innovation vs. State of the ArtORNL research is catalyzing the transformation of the electric distribution grid atthe supply and consumer level.TECHNOLOGY ORNL FOCUS EXISTING TECHNOLOGYDER CompositionHigh penetration inverter‐based for both ongridand islanding.Adaptive “on the fly” control: self‐tuningparameters for flexibility and adaptability.Multi‐layer: (1) communication‐capable localDER layer and (2) central management layer.Hybrid control: local droop control (P‐f, Q‐V)with secondary frequency and voltage controlbased on central MG‐wide management.Cost vs. performance evaluation of MG controlfor different communications.iEconomic DER dispatch (P, Q) with responsiveload and energy storage management.Low penetration inverter‐based for on‐ grid;Rotating generation for MG frequency.Non‐adaptive control parameters preset andfixed (based on studies).Single local DER layer.Smart tInverter ControlAd ti “ th fl ” t l lf t i N d ti t l t t dMicrogrid (MG)ArchitectureMG ControlHbid l l ld l (P f Q V) Local open loop droop control (P‐f, Q‐V) with ihsteady‐state frequency and voltage controlerrorMG communicationsLiterature review has not revealed similarwork.MG energyLiterature review has not revealed similarmanagement systemwork.MG protectionCurrent magnitudes and direction change withOvercurrent methods designed foron‐grid vs. islanding modes: ORNL developedadaptive methods (leveraging another project).unidirectional flow in distribution systems.Directional protection currently used intransmission systems. December 200888

Technical AccomplishmentsSmart Inverter (SI) ControlsDER Connectedto DistributionSystemSmart Inverter ControllerCurrent FY12 Developed PV inverter model andcontrol algorithms (Nov’11) Develop secondary frequency andvoltage control for microgrid inverterPrior FYsoperation (Sep’12). Developed adaptive controls for single Work with vendor inverter on controlsinverter (FY06 to FY11).(Sep’12). Extended adaptive control methodologyto support multiple inverters connected Out Yearsto distribution system/circuit (FY11). SI mode switching (i.e., P2030) SI controls for microgrid applications for Prior year accomplishmentfrequency and voltage transition and FY12 focussmooth transition from grid to microgridDecember 2008 Out Years 9

Prior FYs Established DECC for invertercontrols testing (FY06) Completed second inverter testsystem at DECC (FY11). Multiple (Two) inverters testedtogether on-grid at DECC undervoltage control (FY11). Designed and beganconstructing plug-and-play,flexible and reconfigurable lowvoltageand low-power test bed(FY11).Current FY12Technical AccomplishmentsTesting & Tech TransferDECC Lab Completed new test bed andinstalled third inverter (Mar’12) Out Years Partnered with major inverter Install MG communicationsmanufacturer (Feb’12) Install cables to form radial-loop MG. Prior year accomplishment Test inverter controls in new Test MG in islanding mode. FY12 focus Out Yearstest bed (Jun’12) Install MG transition hardware Test MG mode transitionsDecember 200811

Project Team CapabilitiesORNL Team has key domain experts from industry, academia, and otherNational Labs needed to advance the R&D of the future electric grid.TEAM CAPABILITIESORNL, UTK, and Industry Partners Smart inverter (SI) controls (>7 yrs) expertiseadvancing in self-healing microgrids (MGs). Power systems, protection, power electronicsand control expertise. Chair task force on volt/var control with highpenetration renewables. Member of IEEE PES WG in smart distributionand DER integration Support SI standards development (SCC21,1547, NIST, and EPRI). DECC Lab provides “in-the field” SI and MGtesting with actual distribution system. SPIDERS leveraging ORNL inverter controlsexpertise for military MGs. ORNL partnership with UTK’s DOE/NSFsponsored CURENT center. Industry team (TVA, EPRI, SCE, TVPPA,LCUB, …) provides technical input andguidance Inverter companies provide technical supportand materials. December 200812

Funding LeverageORNL plays a unique role in both providing innovative SI and MG development(controls, communications & protection) and a testing platform on an actualdistribution ib ti system.December 200813These figures above do not reflect the leverage value of a PV inverter, an automobile batteryassembly , and MG equipment to be provided by industry.

Contact InformationD. Tom Rizyrizydt@ornl.gov865-574.5203 office, 207.6769 cellYan Xuxuy3@ornl.gov865-574-7734 office, 929.4219 cellOak Ridge National Laboratory1 Bethel Valley Road, Oak Ridge, TN 37831Power & Energy Systems (PES) Group:http://www.ornl.gov/sci/ees/etsd/pes/Energy & Transportation Science Division (ETSD)http://www.ornl.gov/sci/ees/etsd/Electric Deliveries Technology (EDT) Programhttp://www.ornl.gov/sci/electricdelivery/December 200814

BACK‐UP SLIDESDecember 200815

Distributed EnergyCommunications & Controls(DECC) LaboratoryDecember 200816

DECC Laboratory is located onNorth ORNL CampusDECC LabDECC AnnexLoadBanksDecember 200817

NWEDECC Lab LayoutS3147EXIT6’ Door WaySG - INVERTERSG –SynchronousCondenserDoorsSG – A/C STALL& FREQ RESPLOADDECC LAB TESTINGSG – PVINVERTERRestroomFire Ext.EXITIPAC - IntelligentPower AutomationCenterGRIDEYE8’ Door WayMainPowerPanelSG – TEST BEDAED & Fire Ext.Microturbines December & 2008Associated Equipment 18

DECC Lab AssetsDecember 200819

Technical Approach –Microgrid DemonstrationLeverage DECC assets to demonstrate microgridperformance and B2G from vendor for energy storage.Distribution System Sources LoadsDecember 200820

DECC Lab’s Test SystemsDecember 200821

DECC Lab Flexible Test BedCompleted Electrical Infrastructure Lower Voltage and Power Plug and Play AC and DC Reconfigurable test rack Accelerated smart inverter testing Bridges design, development andsimulation with higher voltageand power testingDC120/208ACDecember 200822

DECC Lab PV Test System• PV Arrays & ConventionalInverterOverhead DCLine toConventionalInverter• DC Bus for Research InverterDC Bus in Room 2 forResearch hInverter50kW PV Array across Bethel ValleyRoad supply 400‐600Vdc, 135AdcLocation of DCTransfer Switch insideIsolation RoomDecember 200823

Smart Inverter (SI) ControlsDecember 200824

Smart Inverter (SI) Adaptive Control Fixed control:DE: Distributed Energy ResourceControl variable: PCC voltageReference: Desired PCC voltagevalueError: Difference between referenceand measured PCC voltage‣ PI control with fixed K p and K i‣ K p and K i determined typically bytrial & errorIncorrect gains result in underperformance,oscillation, or instability Adaptive control:K p and K i are initially conservative butadjusted in real-time to achievedesired system response timeDecember 200825

SI Controllable VariablesReactive powerrelated variablesActive powerrelated variablesActivepowerActivecurrentPowerfactorFrequencyReactive power Yes Yes Yes YesReactive current Yes Yes Yes YesPower factor Yes Yes NA YesLocal voltage Yes Yes Yes YesDecember 200826

SI Voltage Regulationwith Fixed vs. Adaptive SI Control(a) Load current (rms) during load change(b) PCC voltage (rms) without regulation(c) PCC voltage (rms) with non-adaptivevoltage regulation(d) PCC voltage (rms)with adaptive voltage regulation.December 200827

SI Active (P) & Non‐Active (Q) ControlIncrease P, Q Fixed• Complete eventon left.• Zoomed in to 10to 20 kW changeon right.• Active powerreference (P ref )P ref changed from 10 kW to 50 kWfrom 10 to 50kW.• Nonactive powerreference (Q ref )set to10 kVar.• P does not reach50 kW and Qdrops because ofthe invertercurrent limit(60A).P ref change from 10 to 20kWDecember 2008Q ref set to10kVar Q ref set to10kVar. 28

SI Active (P) & Non‐Active (Q) ControlDecrease P on Left, Decrease Q on RightP ref changed from 50 to 10kWQ ref set to 10kVar• Active power(P ref ) changewhile keepingnon-active power(Q ref ) constant onleft.• Nonactive power(Q P ref set to 20kWref ) changewhile keepingactive power(P ref) constant onright.• Plots display theindependentcontrol of P & Qthat has beenachievedQ ref changed from 50 December to 20 kVar 2008.29

PV Inverter Active and ReactivePower ControlP(W)250T=25 o C 1200 w/m 21000 w/m 2200150100800 w/m 25000 10 20 30 40V (V)Output (P vs. V) at different solar irradiationsP (W)25020015010010 o CG=1000 w/m 2 25 o C75 o CGrid-connected three-phase5000 10 20 30 40V (V)Output (P vs. V) at different temperaturessingle-stage inverter PV systemNo DC-to-DC converter for lower cost and higher efficiency.P (MPPT or fixed P) and Q (PCC voltage or fixed Q) controlled by inverter.PV array DC voltage stability maintained by inverter control - resistant toDecember 2008disturbances caused by changing weather or system. 30

PV Inverter Active and ReactivePower Control Simulation ResultsCase 1: Maximum power point tracking (MPPT) & PCC voltage control with varyingsolar irradiation (worst case)1200351100100030G(W/m2)900800P(kW)257002060010 15 20 25 30 35 40 45 50 55 60time(s)700650Solar Irradiance155 10 15 20 25 30 35 40 45 50 55time(s)275PV array active power outputtage(V)PV array DC volt600550500450400350V(V)274273272271PCC voltageVoltage reference3005 10 15 20 25 30 35 40 45 50time(s)2705 10 15 20 25 30 35 40 45 50 55time(s)PV array output DC voltage December 200831PCC voltage and reference (rms)

PV Inverter Active and ReactivePower Control Simulation ResultsCase 2: MPPT & Fixed reactive power control with varying solar irradiation(worst case) 351200110030G(W W/m2)1000900800P(kW)2520PVarray DC voltag ge(V)70060010 15 20 25 30 35 40 45 50 55 60time(s)700650600550500450400350Solar Irradiance30010 20 30 40 50 60time(s)Q(kVAr)1510 15 20 25 30 35 40 45 50 55 60time(s)252015PV array active power outputPV inverter Q injectionQ reference10 20 30 40 50time(s)December 2008PV array output DC voltage32Fixed reactive power control1

PV Inverter Active and ReactivePower Control Simulation ResultsCase 3: Automatic smooth transition between fixed active power controlto MPPT and then back120035110030G(W/m2)1000900800700P(kW)262015P referencePV inverter injection60010 15 20 25 30 35 40 45 50 55 60time(s)Solar Irradiance1015 21.5 25 30 35 40 43.5 50time(s)Switching between fixed realpower control and MPPT controlDecember 2008 33

Adaptive Multiple Inverters Voltage ControlApplicable to radial with or without meshed distribution system with multiple DERs;simulated and proved with three in this case.Multiple l inverters for coordinated d voltage control to prevent hunting.Self-adjusted control parameters to achieve fast response performance.Primarily local voltage control by invertersOnly limited communication needed: initially, for large disturbance or for network changeAdaptability to radial distribution feeder or looped distribution systemsPlug and play feature without need for network parametersDecember 200834

Adaptive Multiple Inverters Voltage ControlSimulation ResultsCase 1: Voltage responses of DER with ideal communication (No latency)282 282280280oltage(V)v278276274desired voltage responseactual voltage responsevoltage reference2720 0.1 0.2 0.3 0.4 0.5 0.6 0.7time(s)Voltage response of DER1282v oltage(V)278276274desired voltage responseactual voltage responsevoltage reference2720 0.1 0.2 0.3 0.4 0.5 0.6 0.7time(s)Voltage response of DER2280voltage(V)278276274desired voltage responseactual voltage responsevoltage reference2720 0.1 0.2 0.3 0.4 0.5 0.6 0.7time(s)December 2008Voltage response of DER3 35

Adaptive Multiple Inverters Voltage ControlSimulation ResultsCase 2: Voltage responses of DER with communication latency (worst case)282 282280280vo oltage(V)278276274desired voltage responseactual voltage responsevoltage referencevo oltage(V)278276274desired voltage responseactual voltage responsevoltage reference2722820.05 0.2 0.35 0.5 0.6 0.7time(s)Voltage response of DER12720.05 0.2 0.35 0.5 0.6 0.7time(s)Voltage response of DER3voltage(V)280278276274272desired voltage responseactual voltage responsevoltage reference0.05 0.2 0.35 0.5 0.6 0.7time(s)Voltage response of DER2A9cycle 9-cycle latency is assumed, whichis typical to wide-area-monitoringbased on paper by Anjan Bose(WSU) and should be much higherthan the latency in a distributionsystem.December 200836

Multiple Inverter Testing at DECC LabDECC Lab physicalconfiguration formultiple DERtesting. Two Inverter-based DERs (150Aeach) on same circuit.Electrically connected via theprimary conductor of circuit #2. One DER is located at building 3114. Second DER is located at building3129 which about 700ft away.December 200837

Multiple Inverter Controls DevelopmentTesting ResultsTwo inverters operated simultaneously on the same 480V circuit in ORNLdistribution ib ti system.Inverters performing voltage regulation with different reference settings.Inverter current limited to 60Arms.Current vs. TimeVoltage vs. TimeDecember 200838

Microgrid (MG) Architecture &InteroperationDecember 200839

Multi‐layer Microgrid ArchitechtureDecember 200840

Microgrid ControlReactive Power and Voltage Regulation (Q‐V)• Voltage is a local variable• Droop control is applicable• Challenges:• DER Q output sharing errors due tothe impedances and local loads• Q circulation because of impropervoltage references• Voltage Regulation Approaches• Ideally system model & monitoring• Preset local PCC voltage referenceand use droop control withoutcommunication‣ Stti Setting local lPCC voltage referencevia central dispatch or scheduleEffective Reactive Powerat PCCTotal:DER1:DER2:December 200841

Microgrid Control StrategiesExistingPP2maxP1maxP3maxQ (kVar)Q1maxQ3maxQ2max0Q2min09 0.9 1.01.11V(pu)Q3minf1 f2 fnorm f3 f4fQ1minDER P‐f Droop factorDER Q‐V Droop factor• Droop control with artificial droop curves• Different slopes to have different responses• Applicable to P‐f and Q‐V control• Steady‐state tt error• No communication or central control required42December 200842

Microgrid Control StrategiesORNL InnovationFrequency droop and secondary controlEnhanced Droop ControlVoltage droop and secondary control• Secondary control in addition to droop control for frequency and voltagecontrol to minimize steady‐state error• Optimal power dispatch• Only low‐speed and infrequent communication neededDecember 200843

Microgrid Control for RenewablesOn‐grid ModeOngrid vs. Islanding Modes• MPPT is the default• Or dispatch P based schedule• Adjust P if high or low frequency ifnot all operating at MPPTIslanding Mode• Frequency control is top priority• If multiple DE: one DE providessecondary while the others providedroop control• Frequency within normal band (f2 tof3): DEs only use droop control• Frequency outside of normal:December 2008secondary control is kicked 44

Microgrid Time Sequence andLow‐Voltage Ride‐ThroughThe German low-voltage ridethroughstandards for mediumvoltageenergy resourcesinterconnection (BDEW)recommend 7.5 cycles ridethrough time if the voltage isbelow 0.3 pu, 35 cycles if thevoltage is between 0.3 pu and0.7 pu, and 75 cycles if thevoltage is between 0.7 pu and0.9 pu.Coordination with Protection and DER LVR and Tripping• Microgrid switch is coordinated to be slower than grid relay protection•Microgrid switch is coordinated to be faster than Individual device tripping• Microgrid switch needs to be high speed to meet the individual inverterlow-voltage ride-through setting.December 200845

MicrogridLow‐Volt Ride‐Through and Multi‐Input PI ControlSmart Inverter Control for Microgrid• Decoupled PQ control• Multiple l control modes• Hierarchical control coordination to determine mode selection• Multi-mode PI controller ensures smooth transition between modesDecember 200846

Microgrid SimulationDiagram of ORNL MicrogridDecember 200847

PublicationsDecember 200848

FY12 Publications• Lakshmi Gopi Reddy, Leon M. Tolbert, Burak Ozpineci, Yan Xu, D. Tom Rizy, “Reliability of IGBTin a STATCOM for harmonic compensation and power factor correction”, presented at IEEEApplied Power Electronics Conference and Exposition, Orlando FL, February 2012.• Philip Irminger, D. Tom Rizy, Huijuan Li, Travis Smith, Keith Rice, Fangxing Li, Sarina Adhikari,“Air Conditioning Stall Phenomenon – Testing, Model Development, and Simulation”, presentedat the IEEE PES T&D Meeting & Exposition, Orlando FL, May 2012.• Huijuan Li, Yan Xu, Sarina Adhikari, D. Tom Rizy, Fangxing Li, Philip Irminger, “Real and reactivepower control of a three-phase single-stage PV system and PV voltage stability”, to be presentedat IEEE Power Engineering Society (PES) Annual Meeting 2012, San Diego CA, July 2012.• Yan Xu, Huijuan Li, Leon M. Tolbert, “Inverter-based microgrid control and stable islandingtransition”, to be presented at IEEE Energy Conversion Congress and Exposition, Raleigh NC,September 2012.• Rukun Mao, Huijuan Li, Husheng Li, Yan Xu, “Wireless communication for controlling microgrids:co-simulation and performance evaluation”, submitted to 3 rd IEEE International Conference onSmart Grid Communications, Tainan City, Taiwan, November 2012.• Huijuan Li, Fangxing Li, Yan Xu and D. Tom Rizy, “Autonomous and Adaptive Voltage Controlusing Multiple Distributed Energy Resources”. Under review, submitted to IEEE Trans. PowerSystemsDecember 200849

FY11 Publications• “Microgrids and Distributed Energy Resources (DER)” , Poster, 8th InternationalConference on Power & Electronics (ECCE Asia), Jeju, South Korea, May 30‐Jun 3, 2011.• “Impacts of Varying Penetration of Distributed Resources with & without Volt/VarControl: Case Study of Varying Load Types”, 2011 IEEE PES General Meeting, Jul.2011, pp.1‐7, 24‐29 July 2011.• “Volt/Var Control Using Inverter‐based Distributed Energy Resources”, 2011 IEEE PESGeneral Meeting, Jul. 2011, pp.1‐8, 24‐29 July 2011.• "Adaptive voltage control with distributed energy resources: Algorithm, theoreticalanalysis, simulation, and field test verification," 2011 IEEE PES General Meeting, pp.1,24‐29 July 2011.• “Impact of Power Factor Correction and Harmonic Compensation by STATCOM onConverter Temperature and Reliability”, Paper No EC‐0736, 2011 IEEE EnergyConversion Congress & Exposition, Phoenix, AZ, Sept. 2011.December 200850

FY10 Publications• "An adaptive voltage control algorithm with multiple distributed energy resources,"North thAmerican Power Symposium (NAPS), 2009 , pp.1‐6, Ot2009 Oct. 2009.• "Local Voltage Support From Distributed Energy Resources To Prevent Air ConditionerMotor Stalling," Innovative Smart Grid Technologies (ISGT), 2010 , pp.1‐6, Jan. 2010.• "Properly understanding the impacts of distributed resources on distributionsystems," 2010 IEEE Power and Energy Society General Meeting, pp.1‐5, Jul. 2010.• "Adaptive Voltage Control With Distributed Energy Resources: Algorithm, TheoreticalAnalysis, Simulation, and Field Test Verification," IEEE Trans. Power Systems, vol.25,no.3, pp.1638‐1647, Aug. 2010.• "Instantaneous active and nonactive power control of distributed energy resourceswith a current limiter," 2010 IEEE Energy Conversion Congress and Exposition (ECCE),pp. 3855‐3861, Sept. 2010.• "Voltage and current unbalance compensation using a static var compensator," IETPower Electronics, vol.3, l3 no.6, pp.977‐988, 988 Nov. 2010.December 200851

FY09 Publications• "Using Distributed Energy Resources to Supply Reactive Power for Dynamic VoltageRegulation," "International ti lReview of Electrical l Engineering, i vol. 3, no. 5, pp. 795‐802,October 2008.• "Local Dynamic Reactive Power for Correction of System Voltage Problems,"ORNL/TM‐2008/174, Oak Ridge National Laboratory, TN, November 2008.• "A Framework to Quantitatively Evaluate the Economic Benefits from Reactive PowerCompensation," International Review of Electrical Engineering, vol. 3, no. 6, pp. 989‐998, December 2008.• "Preventing delayed voltage recovery with voltage‐regulating distributed energyresources," IEEE PowerTech2009, Bucharest, pp.1‐6, June‐July 2009.December 200852

FY08 Publications• "The application of droop‐control in distributed energy resources to extend thevoltage collapse margin," "IEEE IAS Industrial and Commercial lPower Systems TechnicalConference 2008 (ICPS 2008), May 4‐8, 2008.• "Voltage regulation with multiple distributed energy resources," (invited) IEEE PESGeneral Meeting 2008, Pittsburgh, PA, July 20‐24, 24 2008.• "Interaction of multiple distributed energy resources in voltage regulation", IEEE PESGeneral Meeting 2008, Pittsburgh, PA, July 20‐24, 2008.• “Active power and nonactive power control of distributed energy resources”, The 40thNorth American Power Symposium, , Calgary Canada, September 28 – 30, 2008December 200853

FY07 Publications• "Assessment of the Economic Benefits from Reactive Power Compensation,"Proceeding of the IEEE Power Systems Conference and Exposition 2006, pp. 1767‐1773, Atlanta, GA, October 2006.• "Reactive Power from Distributed Energy," The Electricity Journal, vol. 19, no. 10, pp.27‐38, December 2006.• “Dynamic Voltage Regulation Using Distributed Energy Resources,” Proceedings ofCIRED 2007, Vienna, Austria, May 20‐24, 2007.• “Nonactive‐power‐related ancillary services provided by distributed energyresources,” IEEE Power Engineering Society General Meeting, June 24‐28, 2007,Tampa, Florida.• “Experiment and Simulation of Dynamic Voltage Regulation with Multiple DistributedEnergy Resources,” IREP Symposium 2007 ‐ Bulk Power System Dynamics and Control,Charleston, SC, August 2007.December 200854