Acknowledgements Control of Low-Inertia Power Systems: Naive & Foundational Approaches ! ! ! ! (extended set of slides) Florian D¨ orfler B.K. Poolla C. Arghir T. Jouini P. L¨ utolf D. Groß S. Bolognani S. Curi M. Colombino 2 / 54 What do we see here? Frequency of West Berlin when re-connecting to Europe Source: Energie-Museum Berlin December 7, 1994 Hz Hz BEWAG UCTE *10 sec BEWAG UCTE *10 sec before re-connection: islanded operation based on batteries & single boiler afterwards connected to European grid based on synchronous generation 3 / 54 4 / 54
Essentially, the pre/post West Berlin curves date back to. . . Operation centered around bulk synchronous generation 50.02 50.02 f [Hz] f [Hz] Primary Control Tertiary Control 50.01 50.01 50.00 50.00 f - Setpoint 49.99 49.99 49.98 49.98 Secondary Control 49.97 49.97 49.96 49.96 PP - Outage Oscillation/Control 49.95 49.95 PS Oscillation 49.94 49.94 49.93 49.93 Fact: all of AC power systems built around synchronous machines ! Mechanical Inertia 49.92 49.92 49.91 49.91 θ , ω At the heart of it is the generator swing equation : 49.90 49.90 τ m 49.89 49.89 generation demand M d dt ω ( t ) = P generation ( t ) − P demand ( t ) τ 49.88 49.88 16:45:00 16:45:00 16:50:00 16:50:00 16:55:00 16:55:00 17:00:00 17:00:00 17:05:00 17:05:00 17:10:00 17:10:00 17:15:00 17:15:00 8. Dezember 2004 8. Dezember 2004 Frequency Mettlen, Switzerland Frequency Athens change of kinetic energy = instantaneous power balance M Source: W. Sattinger, Swissgrid 5 / 54 6 / 54 Renewable/distributed/non-rotational generation on the rise The foundation of today’s power system synchronous generator new workhorse scaling Synchronous machines with rotational inertia M d dt ω ≈ P generation − P demand new primary sources location & distributed implementation Today’s grid operation heavily relies on 1 robust stabilization of frequency and voltage by generator controls 2 self-synchronization of machines through the grid 2 M ω 2 as safeguard against disturbances 3 kinetic energy 1 focus today on non-rotational generation We are replacing this solid foundation with . . . 7 / 54 8 / 54
Tomorrow’s clean and sustainable power system Black System Event in South Australia (Sep 2016) Key events 1 1 intermittent voltage disturbances due to line faults Non-synchronous generation connected via power electronics 2 loss of synchronism between SA and remainder of the grid As of today, power electronic converters 3 SA islanded: frequency collapse in a quarter of a second 1 lack robust control for voltage and frequency 2 do not inherently synchronize through the grid “ Nine of the 13 wind farms online did not ride through the 3 provide almost no energy storage six voltage disturbances experienced during the event.” What could possibly go wrong ? 1 AEMO: Update Report - Black System Event in South Australia on 28 September 2016 9 / 54 10 / 54 Low inertia issues have been broadly recognized Low-inertia issues close to home by TSOs, device manufacturers, academia, funding agencies, etc. 2001 2002 2003 2004 2005 2006 2007 2008 2009 30000 2010 MIGRATE project: 25000 M assive I nte GRAT ion of power E lectronic devices 20000 Frequency Stability Evaluation Duration [s] 15000 Events [-] Criteria for the Synchronous Zone 10000 of Continental Europe 5000 – Requirements and impacting factors – 0 RG-CE System Protection & Dynamics Sub Group Number * 10 Months of the year However, as these sources are fully controllable, a regulation can be added to the inverter to provide “synthetic inertia”. This can also be # frequency violations in Nordic grid Number * 10 Duration seen as a short term frequency support. On the other hand, these sources might be quite restricted with respect to the available (source: ENTSO-E) same in Switzerland (source: Swissgrid) capacity and possible activation time. The inverters have a very low overload capability compared to synchronous machines. Renewable and Sustainable Energy Reviews 55 (2016) 999 – 1009 Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser PUBLIC The relevance of inertia in power systems ERCOT CONCEPT PAPER Pieter Tielens n , Dirk Van Hertem Future Ancillary Services in ERCOT Impact of Low Rotational Inertia on ELECTA, Department of Electrical Engineering (ESAT), University of Leuven (KU Leuven), Leuven, Belgium and EnergyVille, Genk, Belgium Power System Stability and Operation ERCOT is recommending the transition to the following five AS products plus one additional AS Andreas Ulbig, Theodor S. Borsche, Göran Andersson that would be used during some transition period: t eal 1. Synchronous Inertial Response Service (SIR), ETH Zurich, Power Systems Laboratory 2. Fast Frequency Response Service (FFR), Physikstrasse 3, 8092 Zurich, Switzerland ulbig | borsche | andersson @ eeh.ee.ethz.ch 3. Primary Frequency Response Service (PFR), 4. Up and Down Regulating Reserve Service (RR), and 5. Contingency Reserve Service (CR). 6. Supplemental Reserve Service (SR) (during transition period) a day in Ireland (source: F. Emiliano) a year in France (source: RTE) 11 / 54 12 / 54 15
Obvious insight: loss of inertia & frequency stability Berlin curves before and after re-connecting to Europe Source: Energie-Museum Berlin We loose our giant electromechanical low-pass filter: θ , ω τ m generation M d demand dt ω ( t ) = P generation ( t ) − P demand ( t ) τ loss of 1200 MW change of kinetic energy = instantaneous power balance M loss of 2500 MW Berlin re-connected to Europe 50 49.8 M J f [Hz] 49.6 49.4 islanded Berlin grid loss of 146 MW 49.2 49 0 5 10 15 20 25 30 35 Time t [s] 13 / 54 14 / 54 Baseline solution: virtual inertia emulation !""" #$%&'%(#!)&' )& *)+"$ ','#"-'. /)01 23. &)1 2. -%, 2456 5676 !"#$%&'"'() %* +$,(-.'() /'-#%(-' !89:;8;<=><? />@=AB: !<;@=>B >< CD!EFGBH;I .( 0.1$%2$.3- 4-.(2 5.$)6,7 !('$)., +><I *JK;@ E;<;@B=>J< 8.".-9 :%(. ! "#$%&'# (&)*&+! ,--- ; :6$<,(,$,<,(, =%%77, ! (&)*&+! ,--- ; ,(3 06>67 ?@ ?9,(3%$>,$ ! (&)*&+! ,--- -JLB88BI@;MB DBNLB@> -J?LBIIB8 %@B<> ! "#$%&'# (&)*&+! ,--- . B<I "LBO D1 ":F'BBIB<P ! "&'./+ (&)*&+! ,--- !"#$%&'()*+,-+#'"(./#0*/1(2-33/*04($(5&*0-$1(( Virtual synchronous generators: A survey and new perspectives 6#+*0&$(7*/8&9+9(:"(!&;0*&:-0+9(<#+*="(20/*$=+( Hassan Bevrani a,b, ⇑ , Toshifumi Ise b , Yushi Miura b a Dept. of Electrical and Computer Eng., University of Kurdistan, PO Box 416, Sanandaj, Iran 0/(6;/1$0+9(7/>+*(2";0+%;(( b Dept. of Electrical, Electronic and Information Eng., Osaka University, Osaka, Japan !""" #$%&'%(#!)&' )& *)+"$ ','#"-'. /)01 23. &)1 2. -%, 2456 ?$-0@&+*(!+1&11+A( !"#$"%&'())) A(B*-#/()*$#C/&;A( *"+,-%'!"#$"%&'())) A($#9(?&11+;(D$1$*$#=+( obvious insights lead to !789:;< "=>?<:;@7 (@7:9@? ':9<:8AB C@9 !"#$%&#'$%()*+'",'"%-#,.%/#",012%3#*',#4% /'(DE/F( #9<7G=;GG;@7 'BG:8=G 5,)"16'% H;8I8; JK>. (<=LI8?? F1 M@@:K. N9<;7 *1 %O<=. %7O98P H1 $@GQ@8. <7O (K9;G N1 M9;AK: 7898:%+1*%;'<'*=''4> ? %@%58;8A8%$'%A11* ? @% !"#$%&'("()"&*'+,,, @%98%/1"'21 B %1*$%38%/#<<4.'" C @% !"#$%&'("()"&'+,,, % obvious (naive) answers M d dt ω ( t ) = P generation ( t ) − P demand ( t ) ≈ derivative control on ω ( t ) ⇒ focus today: where to do it? how to implement it properly? . . . we are not just loosing inertia . . . what else to do ? 15 / 54
Outline Virtual inertia is becoming a technology and a product so let’s see how we can make use of it Introduction System Level: Optimal Placement of Virtual Inertia network, disturbances, & performance metrics matter Device Level: Proper Virtual Inertia Emulation Strategy maybe we should not think about frequency and inertia A Foundational Control Approach restart from scratch for low-inertia systems Conclusions 16 / 54 General power system & inertia emulation model power system model (detailed & linearized) disturbance inputs performance outputs synchronous machines, governors, loads, transmission, batteries, PLL, … (e.g., generator frequencies) (e.g., loss of load/generation) i P V L g L g τ e i αβ τ m controlled injections measured frequencies ω L g optimal placement L g i f (e.g., at PV, (e.g., at AC batteries, etc.) voltage bus via a PLL) of virtual inertia virtual inertia & damping (implemented as causal PD) . . . M i s + ˜ ˜ ω u D i T i s + 1 . . . 17 / 54
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