Microgrid Fundamentals and Control. Jian Sun, Professor and Director New York State Center for Future Energy Systems (518)

Transcription

1 Mcrogrd Fundamentals and Control Jan Sun, Professor and Drector New York State Center for Future Energy Systems (58)

2 Mcrogrd s not New Early Power Systems Developed by Thomas Edson and Nkola Tesla were all Mcrogrds Large Power Grds Emerged Because of Improved Relablty, Better Generaton-Load Balance, and More Stable Voltage & Frequency AC Took Over DC due to Easy Converson

3 New Drvers Why Mcrogrds Agan Utlzaton of Dstrbuted Generaton Renewable Energy, CHP, Energy Storage Reduce Transmsson and Dstrbuton Cost & Losses Improve Grd Reslency and Power Qualty Expanson of Electrfcaton New Enablng Technologes Power Electroncs, Communcaton, Control Cost-Effectve and Effcent Energy Storage 3

4 Mcrogrd Technology Many Conferences, Workshops & Semnars about Mcrogrd Deployment, Benefts & Market Techncal Materals have been Lmted to Specfc Technques for Specalsts Lack of Basc Understandng Often Leads to Hypes, False Clams/Expectatons, and Mysteres Functonalty s Easy; Performance s the Key Promse Performance, Delver Functonalty 4

5 Ths Webnar Covers the Fundamentals of Mcrogrd Technology, wth a Focus on Control Performance, wth a Focus on Power Qualty Targets Audence wth General EE Background Goals Users: Ask the Rght Questons Desgn Engneers: Know Where to Start Research Engneers: Understand Techncal Challenges and Opportuntes for Innovaton 5

6 Power Sharng Mcrogrd Control s about Sharng Power Among Multple Sources Whle Mantanng Stablty? 6

7 Control Herarches Mcrogrd Tertary Control (Grd Interface) 7 Prmary Control Inner Control Prmary Control Inner Control Loads Secondary Control (EMS) Prmary Control Inner Control Secondary & Tertary Control Power Grd Communcaton Prmary Control Inner Control 5/6 Hz

8 General Consderatons Inner and Prmary Control are Local Secondary and Tertary Control are Central Requre Communcatons Add Complexty and Cost Lmt Flexblty Plug-and-Play s Desrable for Mcrogrd Autonomous Inner and Prmary Control No/Mnmal Secondary and Tertary Control 8

9 Outlne DC Mcrogrd Control AC Mcrogrd Control Stablty, Power Qualty, and Control Development 9

10 Interconnectng DC Sources Voltage Sources can be Connected n Seres but not Drectly n Parallel Current Sources can be Paralleled but not n Seres Resstors Requred to Lmt Crculatng Currents Mnmal Resstance Requred to Avod Back Feedng Power Losses; not Feasble n Practce R R I I + V + V I + V R V v I I If If V V V R R V V V V R R V

11 Droop Control Current-Dependent Voltage Sources Vrtual Seres Resstors Avod Power Losses Open-Crcut Voltages can be Matched Select Droop Coeffcents Based on Current Sharng Goals Made Possble by Power Electroncs Applcable to Multple Voltage Sources V V I I I + + V + V V V v I I V I I V R R R I R Effects of Parastc Resstance Ignored (Output, Lne) I

12 Master-Slave Control One Source Sets the Voltage (Master) Other Sources Inject Currents (Slaves) Power Sharng not Drectly Controlled Master and Slave Unts are Pre-desgnated Whole System s Down when the Master s Down Smlar to Resdental Solar Integraton nto the Grd I I + + V I V V v R R I V R I

13 Other Varatons Master May Enter Current Lmtng Mode Master May Relnqush Voltage Regulaton Responsblty by Reducng the Voltage Slave Enters Voltage Regulaton Mode When Voltage Drops to Certan Level (Voltage Margn Control) HVDC System Control Provdes Good Source of Reference v v v I max I max 3

14 Other Varatons Cont d Renewable Sources can be Treated as Constant-P Sources Wth Max Voltage and Current Lmt Battery or Other Controllable Unts May be Used as Master Parallel wth Supercapactors to Lower Impedance Automatc Swtchng between Chargng and Dschargng Mode by Introducng a Voltage Droop v V max v v Dschargng Chargng v*=p I max 4

15 Outlne DC Mcrogrd Control AC Mcrogrd Control Stablty, Power Qualty, and Control Development 5

16 Master-Slave Control Smlar to Use n DC Mcrogrd Slaves May Inject Both Actve and Reactve Currents Synchronzaton to Grd Voltage Angle s Requred Reactve Current Causes Small Actve Power Loss Also Lmted by Total Capacty of Interface (Inverter) Reactve Power Control can be Central or Dstrbuted Q P 6

17 Droop Control Easy to Implement Voltage Magntude Droop Based on Current Magntude Unable to Control Actve/Reactve Power Sharng Matchng/Coordnatng Phase Angles Requres Central Control v 7

18 Droop Control Operaton Power s Shared Based by Droop f No Lne Impedance s Present Both Open-Crcut Voltages and Phases are Matched Complex Droop Coeffcents can be Used to Provde Dfferent Sharng of Actve and Reactve Power + R I I R E ~ E ~ I / R I R / I I E V R E V R E E cosδ R cosδ R V V j j E E sn δ R sn δ R 8

19 Effects of Lne Impedance Lne Impedance Affects Current Sharng Impossble to Cancel ths Effect Through Droop Desgn More Complcated n Large Network wth Multple Sources Also Remember the Dffculty of Matchng the Voltages Possble to Reduce the Effects by Usng Large Droop, but wll Result n Very Soft (Weak Grd) Behavor Z R I + I R E E ~ ~ I I E R V Z E V R E E cosδ V R Z cosδ V R Z j j E sn δ R Z E R sn δ Z 9

20 ~ jx E Pure Inductve Network + Load I I EV sn δ, X Wth a Small Phase Angle : P E cos δ V jx E sn δ jx Actve Power can be Controlled by Varyng the Phase () Reactve Power can be Controlled by Varyng Voltage (E) Phase Angle Relatve to the Load cannot be Measured j V ( V Q P EV X E sn δ X E X cos δ) j E cos δ V X V δ, Q ( V E) X Frequency can be Measured Locally and δ t ω(τ) dτ

21 Frequency and Voltage Droop Frequency Droop to Control Actve Power Sharng Voltage Droop to Control Reactve Power Sharng Droop Characterstc Emulates a Reactance Should be Hgh Compared to Actual Lne Reactance Cross Couplng Affects Transent Responses Integraton Introduces Dynamcs Stablty Consderatons δ t ω(τ) dτ ω ω m ( P P ) E E n ( E Q Q ) ~ jx E I + Load P P Q

22 Frequency Devaton Large P Droop Improves Actve Power Sharng Control But Results n Large f Undesrable for Certan Loads Also Increases Couplng wth Reactve Power Control Secondary Control can be Used to Restore Nomnal Frequency after Transent by Adjustng ω ω m ( P P ) P EV sn δ X, Q V ( V E X cos δ) P δ t ω(τ) dτ

23 Effects of Lne Impedance Actual Lne Impedance Depends on Dstance More Sgnfcant for Large Mcrogrds Reactance of the Lne Consumes Reactve Power Q n Q-E Droop Curve s Meant for System Reactve Power Sharng but s Measured at the Termnal of Each Unt R/X Rato, Hghly Resstve for Dstrbuton Lnes All of These May Reduce Effectveness of Droop Control ~ I jx E Z + Load I E cos δ V E sn δ j jx Z jx Z Z: Lne Impedance X: Emulated Reactance Varous Methods can be Used to Mtgate These Problems but are Usually Senstve to Actual Lne Parameters. 3

24 Droop wth Dynamcs Integral Relatonshp from to Introduces Dynamcs Addtonal Dynamcs due to Power Control Loops These May Lead to Poor Transents, Oscllatory Responses Possble Improvement by Introducng Dynamcs nto Droop Characterstcs Emulate PID Control Need Proper System Models for Desgn Nonlnear Effects of Angle and Voltage; Lnearzaton Requred δ m p P m d dp dt m Pd ω ω m P m p dp dt m d d P dt E E n p Q n d dq dt 4

25 Vrtual Impedance Method Instead of P & Q Droop, Each Unt can be Controlled to have Fxed Output Impedance Output P and Q are Controlled by Varyng E System Frequency can be Kept Constant Lmts Current at Intal Connecton, Hot Swap Capablty Resstve Output Impedance May Improve System Dampng No Drect Control of System P & Q Balance ~ E ~ E ~ E 3 ~ E n ~ E n Z Z Z 3 Z n- Z n 5

26 Droop vs. Master-Slave Control Droop Control Works Well wth Defned Power Sharng Objectves Generators, Power Supples, Parallel Modules Master-Slave Control Works for Renewable Sources Slaves Work to Maxmze Ther Power Output Master has to have Enough Capacty and Speed n Addton to Beng Relable/Controllable Varous Combnatons are Possble Droop Control of Multple Maters Democratc Mater-Slave Control 6

27 Outlne DC Mcrogrd Control AC Mcrogrd Control Stablty, Power Qualty, and Control Development 7

28 Mcrogrd Stablty Mcrogrd s a Weak Grd by Defnton Much Easer to Become Unstable than the Large Grd May Actually Degrade Relablty and Power Qualty Inner Control Desgned to be Stable for Assumed (Often Ideal) External Condtons May Become Unstable n an Actual System Droop and Master/Slave Control are Meant for Steady-State Power Sharng and Don t Guarantee Transent Stablty 8

29 Control and Stablty Tradtonal Generator Prme Mover Control Exctaton Control Prmary Control Inner Control Large Wnd Generator Turbne Speed Control DC-Lnk Control Grd Q & V Control Grd Synchronzaton Current Semconductor Control Swtchng.. Frequency (Hertz) 9

30 Weak-Grd Problem 3

31 Solar Farm 3

32 Impedance-Based Analyss Each Devce s Modeled by an Impedance Element for Small-Sgnal Analyss Dynamc, Over Entre Frequency Range of Interest System Stablty s Determned Based on the an Impedance Network State-Space Analyss Overall System Analyss Input-Output Analyss Indvdual Unt Stablty under the Influence of the System 3

33 Master-Slave Control Stablty Small-Sgnal Model Master/Grd Slave + Z g V g I g I Z Master s Modeled by an Ideal Voltage Source Behnd Impedance Each Slave s Modeled by an Ideal Current Source n Parallel wth an Output Impedance; Indvdual or Combned I (s) _ Z g Z s s I g (s) I I g ( s) ( s) Z Z ( s) ( s) Z g ( s) Z Z g ( s) ( s) 33

34 Droop Control Stablty Lumped nto a Sngle Source-Load Model Overall System Stablty and Source-Load Interactons Effects of Changes n Sources or Loads on Stablty System Impedance Network Matrx Descrpton Extenson to Other Prmary Control Methods ~ E ~ E ~ E n ~ E n ~ E s Z Z Z n- Z n Z s Z l 34

35 Smulaton Lmtatons of Small-Sgnal Analyss Startup; Shutdown; Operaton Mode Transton Abnormal Operaton; Interacton wth Protectons Nonlnear and Tme-Varyng Behavor Detaled Crcut and Control Smulaton Complements Small-Sgnal Analyss Possble due to Relatvely Small System Sze 35

36 Real-Tme (RT) Smulaton Control Hardware-n-the-Loop (CHIL) Smulaton Power Hardware-n-the-Loop (PHIL) Smulaton 36

37 HIL Smulaton of Mcrogrds Testng of Indvdual Generaton Unts Rest of System Smulated n Real-Tme Power or Control Interface wth Smulator System Control Development and Testng Secondary and Tertary Control Physcal System Smulated Along wth Local Controls RT Smulator Control 37

38 RT Smulaton Platforms Smulaton Tme Steps, PWM Control Accuracy; System (Physcal) Sze and Complexty Power Electroncs Power Systems Typhoon HIL 38

39 Grd Smulator Utlty Grd ~ = ~ = ~ = = ~ Smulated Grd wth Programmable Volt/Freq/Impedance Inverters () Central Inverters (3) ~ = PV Smulators = G M ~ 4 th Gen Wnd Turbne Smulator Electronc Loads 39

40 Summary Control s to Share Power Among Multple Sources Functonalty s Easy, Performance s the Key A Mcrogrd s a Weak Grd by Defnton Network Dynamcs Affect Inner Control Stablty Prmary Control Stablty s not Guaranteed Use of Secondary and Tertary Control Should be Mnmzed to Reduce Complexty and Cost, Improve Relablty and Flexblty Analyss and Control Desgn Tools are Avalable 4