Control of Power Converters in Low-Inertia Power Systems Florian D - PowerPoint PPT Presentation

Control of Power Converters in Low-Inertia Power Systems Florian D¨ orfler Automatic Control Laboratory, ETH Z¨ urich

Acknowledgements ! ! ! ! Marcello Colombino Ali Tayyebi-Khameneh Dominic Groß Irina Subotic Further: Gab-Su Seo, Brian Johnson, Mohit Sinha, & Sairaj Dhople 1

Replacing the power system foundation fuel & synchronous machines renewables & power electronics – not sustainable + sustainable + central & dispatchable generation – distributed & variable generation + large rotational inertia as buffer – almost no energy storage + self-synchronize through the grid – no inherent self-synchronization + resilient voltage / frequency control – fragile voltage / frequency control – slow actuation & control + fast / flexible / modular control 2

What do we see here ? Hz BEWAG UCTE *10 sec 3

Frequency of West Berlin re-connecting to Europe December 7, 1994 Hz BEWAG UCTE *10 sec before re-connection: islanded operation based on batteries & single boiler afterwards connected to European grid based on synchronous generation 4

The concerns are not hypothetical issues broadly recognized by TSOs, device manufacturers, academia, agencies, etc. MIGRATE project: UPDATE REPORT ! M assive I nte GRAT ion of power E lectronic devices BLACK SYSTEM EVENT IN SOUTH AUSTRALIA ON ! !"#$%% 28 SEPTEMBER 2016 "&'()*%")+,-.)'%/),-)0% 1"2%/).3**)456(-34' % AN UPDATE TO THE PRELIMINARY OPERATING INCIDENT REPORT FOR THE NATIONAL ELECTRICITY MARKET. DATA ANALYSIS AS AT 5.00 PM TUESDAY 11 OCTOBER 2016. !"#$%& ! &$ ! &'" ! ()* ! +$,,-&&"" ! Impact of Low Rotational Inertia on Power System Stability and Operation lack of robust control: Andreas Ulbig, Theodor S. Borsche, Göran Andersson ETH Zurich, Power Systems Laboratory “Nine of the 13 wind farms Physikstrasse 3, 8092 Zurich, Switzerland ulbig | borsche | andersson @ eeh.ee.ethz.ch ERCOT CONCEPT PAPER PUBLIC online did not ride through the Future Ancillary Services in ERCOT six voltage disturbances Frequency Stability Evaluation Criteria for the Synchronous Zone ERCOT is recommending the transition to the following five AS products plus one additional AS experienced during the event.” that would be used during some transition period: of Continental Europe 1. Synchronous Inertial Response Service (SIR), 2. Fast Frequency Response Service (FFR), 3. Primary Frequency Response Service (PFR), – Requirements and impacting factors – 4. Up and Down Regulating Reserve Service (RR), and Renewable and Sustainable Energy Reviews 55 (2016) 999 – 1009 5. Contingency Reserve Service (CR). RG-CE System Protection & Dynamics Sub Group between the lines: 6. Supplemental Reserve Service (SR) (during transition period) Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser However, as these sources are fully controllable, a regulation can be conventional system would added to the inverter to provide “synthetic inertia”. This can also be seen as a short term frequency support. On the other hand, these The relevance of inertia in power systems sources might be quite restricted with respect to the available capacity and possible activation time. The inverters have a very low Pieter Tielens n , Dirk Van Hertem have been more resilient (?) overload capability compared to synchronous machines. ELECTA, Department of Electrical Engineering (ESAT), University of Leuven (KU Leuven), Leuven, Belgium and EnergyVille, Genk, Belgium !"#$"% &'()*)+,-.+'%-,#"$"/)%'-0)'(+"1',%',' obstacle to sustainability: %2*30+.*.4%'3.*1)*%)+' power electronics integration 5

Critically re-visit modeling/analysis/control Foundations and Challenges of Low-Inertia Systems (Invited Paper) David J. Hill ∗ and Gregor Verbiˇ Federico Milano Florian D¨ orfler and Gabriela Hug c University College Dublin, Ireland ETH Z¨ urich, Switzerland University of Sydney, Australia ∗ also University of Hong Kong email: federico.milano@ucd.ie emails: dorfler@ethz.ch, ghug@ethz.ch emails: dhill@eee.hku.hk, gregor.verbic@sydney.edu.au The later sections contain many suggestions for further New control methodologies, e.g. new controller to work, which can be summarized as follows: • mitigate the high rate of change of frequency in low New models are needed which balance the need to • inertia systems; include key features without burdening the model A power converter is a fully actuated, modular, and (whether for analytical or computational work) with • very fast control system, which are nearly antipodal uneven and excessive detail; characteristics to those of a synchronous machine. New stability theory which properly reflects the new • Thus, one should critically reflect the control of a devices and time-scales associated with CIG, new converter as a virtual synchronous machine; and loads and use of storage; The lack of inertia in a power system does not need to • Further computational work to achieve sensitivity • (and cannot) be fixed by simply “adding inertia back” guidelines including data-based approaches; in the systems. a key unresolved challenge: control of power converters in low-inertia grids → industry & power community willing to explore green-field approach (see MIGRATE) with advanced control methods & theoretical certificates 6

Our research agenda system-level device-level (today) • low-inertia power system models, • decentralized nonlinear power stability, & performance metrics converter control strategies • optimal allocation of virtual inertia • experimental implementation , & fast-frequency response services cross-validation, & comparison P ∗ Relay 1 g Relay 2 Q ∗ Z s 1 Z s 2 406 u ∗ i dc 1 i x 1 i s 1 g i s 2 i x 2 f restoration time 404 i dc 2 dc K P I ( s ) VI nominal frequency VI 407 405 403 G dc 1 e x 1 G f e x 2 G dc 2 u dc 1 v f u dc 2 secondary control 402 408 409 VI                        inertial 401 410 411 m αβ 1 m αβ 2 primary control Y f 413 response inter-area 412 η frequency nadir η oscillations 414 θ 1 � − sin θ 1 � � − sin θ 2 � θ 2 1 1 + µ ∗ + + ˆ K s � i s 2 − ˆ i s 2 ( θ 2 ) � + 415 Σ µ f Σ 2 Σ + s cos θ 1 cos θ 2 s + P -droop 416 416 steady-behavior compensation ROCOF (max rate of change of frequency) − κ 1 ∇ W ( θ 1 ) matching control i s 2 matching control 205 201 201 203 203 v f 207 PQ -control � P ∗ VI  ���  Q ∗ � − κ 2 sin ( θ 2 − θ ∗ 2 ) 1 � � ⊤ � ⊤ � 2 i s 2 ( θ ∗ ˆ 1 g g − sin θ 1 − sin θ 1 − � Z s 1 i s 2 � 2 + � Z s 1 Y f + I � 2 v ∗ 2 2 ) = v f sync-torque 206 208 µ f = ˆ Z s 1 i s 2 + z Z s 1 i s 2 � v f � 2 − Q ∗ P ∗ u ∗  cos θ 1 cos θ 1 f  g g dc G dc 2 u ∗ dc + ˆ + 501 209 211 µ ∗ 2 = 1 � v f − Z s 2 ˆ � i s 2 ( θ ∗ 2 ) � i x 2 ( θ 2 ) u ∗ � Σ VI VI 204 204 voltage control dc + 504 502 � − sin θ ∗ � 202 210 2 1 � v f − Z s 2 ˆ i s 2 ( θ ∗ � i P V VI = 2 ) − K dc ( u dc 2 − u ∗ dc ) L g 212 cos θ ∗ µ ∗ 2 u ∗ L g 505 2 dc 215 215 213 dc -control VI 507 214 i αβ τ e VI τ m ( a ) ( b ) 10 ms/ d iv 506 VI 216 508 L g L g ω 503 509 509 217 217 VI VI 102 P ∗ P g 200 W/ div i f 315 309 g 101 0 311 310 VI 308 307 305 VI 301 304 303 306 VI VI 313 314 312 302 2 A/ d i v i s 1 ,a i s 2 ,a 7

Exciting research domain bridging communities power power electronics systems control systems 8

Outline Introduction: Low-Inertia Power Systems Problem Setup: Modeling and Specifications State of the Art: Comparison & Critical Evaluation Dispatchable Virtual Oscillator Control Experimental Validation Conclusions

Modeling: signal space in 3-phase AC circuits three-phase AC balanced (nearly true) synchronous (desired) � x a ( t ) � � x a ( t + T ) � � � � � sin( δ ( t )) sin( δ 0 + ω 0 t ) = sin( δ ( t ) − 2 π sin( δ 0 + ω 0 t − 2 π x b ( t ) x b ( t + T ) = A ( t ) 3 ) 3 ) = A x c ( t ) x c ( t + T ) sin( δ ( t ) + 2 π sin( δ 0 + ω 0 t + 2 π 3 ) 3 ) periodic with 0 average so that const. freq & amp � T 1 0 x i ( t ) dt = 0 x a ( t ) + x b ( t ) + x c ( t )=0 ⇒ const. in rot. frame T 1 1 1 x abc x abc 0 x abc 0 0 − 1 − 1 − 1 - π π -2 π 0 2 π - π π -2 π 0 2 π - π π -2 π 0 2 π δ δ δ assumption : balanced ⇒ 2d-coordinates x ( t ) = [ x α ( t ) x β ( t )] or x ( t ) = A ( t )e i δ ( t ) 9

Modeling: the network interconnecting lines via Π -models & ODEs ◮ quasi-steady state algebraic model       . . . ... ... i 1 v 1 . . . . . .       . � n . = − y k 1 · · · · · · − y kn . j =1 y kj .       . .       . . . ... ... . . . i n v n . . . � �� � � �� � � �� � nodal injections nodal potentials Laplacian matrix with y kj = 1 / complex impedance ◮ salient feature: local measurement reveal global information � i k = j y kj ( v k − v j ) ���� � �� � local variable global information 10