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Publications (7 of 7) Show all publications
Andreasson, M., Sjödin, E., Sandberg, H. & Johansson, K. H. (2017). Coherence in Synchronizing Power Networks with Distributed Integral Control. In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017: . Paper presented at IEEE 56th Annual Conference on Decision and Control (CDC), DEC 12-15, 2017, Melbourne, Australia (pp. 6683-6688). IEEE
Open this publication in new window or tab >>Coherence in Synchronizing Power Networks with Distributed Integral Control
2017 (English)In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, IEEE , 2017, p. 6683-6688Conference paper, Published paper (Refereed)
Abstract [en]

We consider frequency control of synchronous generator networks and study transient performance under both primary and secondary frequency control. We model random step changes in power loads and evaluate performance in terms of expected deviations from a synchronous frequency over the synchronization transient; what can be thought of as lack of frequency coherence. We compare a standard droop control strategy to two secondary proportional integral (PI) controllers: centralized averaging PI control (CAPI) and distributed averaging PI control (DAPI). We show that the performance of a power system with DAPI control is always superior to that of a CAPI controlled system, which in turn has the same transient performance as standard droop control. Furthermore, for a large class of network graphs, performance scales unfavorably with network size with CAPI and droop control, which is not the case with DAPI control. We discuss optimal tuning of the DAPI controller and describe how internodal alignment of the integral states affects performance. Our results are demonstrated through simulations of the Nordic power grid.

Place, publisher, year, edition, pages
IEEE, 2017
Series
IEEE Conference on Decision and Control, ISSN 0743-1546
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-223842 (URN)10.1109/CDC.2017.8264666 (DOI)000424696906009 ()2-s2.0-85046117509 (Scopus ID)978-1-5090-2873-3 (ISBN)
Conference
IEEE 56th Annual Conference on Decision and Control (CDC), DEC 12-15, 2017, Melbourne, Australia
Funder
Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research Swedish Research Council, 2014-6282; 2013-5523
Note

QC 20180306

Available from: 2018-03-06 Created: 2018-03-06 Last updated: 2018-06-04Bibliographically approved
Tegling, E., Andreasson, M., Simpson-Porco, J. W. & Sandberg, H. (2016). Improving performance of droop-controlled microgrids through distributed PI-control. In: 2016 AMERICAN CONTROL CONFERENCE (ACC): . Paper presented at American Control Conference (ACC), JUL 06-08, 2016, Boston, MA (pp. 2321-2327). IEEE conference proceedings
Open this publication in new window or tab >>Improving performance of droop-controlled microgrids through distributed PI-control
2016 (English)In: 2016 AMERICAN CONTROL CONFERENCE (ACC), IEEE conference proceedings, 2016, p. 2321-2327Conference paper, Published paper (Refereed)
Abstract [en]

This paper investigates transient performance of inverter-based microgrids in terms of the resistive power losses incurred in regulating frequency under persistent stochastic disturbances. We model the inverters as second-order oscillators and compare two algorithms for frequency regulation: the standard frequency droop controller and a distributed proportional-integral (PI) controller. The transient power losses can be quantified using an input-output H-2 norm. We show that the distributed PI-controller, which has previously been proposed for secondary frequency control (the elimination of static errors), also has the potential to significantly improve performance by reducing transient power losses. This loss reduction is shown to be larger in a loosely interconnected network than in a highly interconnected one, whereas losses do not depend on connectivity if standard droop control is employed. Moreover, our results indicate that there is an optimal tuning of the distributed PI-controller for loss reduction. Overall, our results provide an additional argument in favor of distributed algorithms for secondary frequency control in microgrids.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2016
Series
Proceedings of the American Control Conference, ISSN 0743-1619
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-204147 (URN)10.1109/ACC.2016.7525264 (DOI)000388376102062 ()2-s2.0-8499212861 (Scopus ID)978-1-4673-8682-1 (ISBN)
Conference
American Control Conference (ACC), JUL 06-08, 2016, Boston, MA
Note

QC 20170327

Available from: 2017-03-27 Created: 2017-03-27 Last updated: 2017-03-27Bibliographically approved
Tegling, E. (2016). On performance limitations of large-scale networks with distributed feedback control. (Licentiate dissertation). Stockholm, Sweden: KTH Royal Institute of Technology
Open this publication in new window or tab >>On performance limitations of large-scale networks with distributed feedback control
2016 (English)Licentiate thesis, monograph (Other academic)
Abstract [en]

We address the question of performance of large-scale networks with distributed feedback control. We consider networked dynamical systems with single and double integrator dynamics, subject to distributed disturbances. We focus on two types of problems. First, we consider problems modeled over regular lattice structures. Here, we treat consensus and vehicular formation problems and evaluate performance in terms of measures of “global order”, which capture the notion of network coherence. Second, we consider electric power networks, which we treat as dynamical systems modeled over general graphs. Here, we evaluate performance in terms of the resistive power losses that are incurred in maintaining network synchrony. These losses are associated with transient power flows that are a consequence of “local disorder” caused by lack of synchrony. In both cases, we characterize fundamental limitations to performance as networks become large. Previous studies have shown that such limitations hold for coherence in networks with regular lattice structures. These imply that connections in 3 spatial dimensions are necessary to achieve full coherence, when the controller uses static feedback from relative measurements in a local neighborhood. We show that these limitations remain valid also with dynamic feedback, where each controller has an internal memory state. However, if the controller can access certain absolute state information, dynamic feedback can improve performance compared to static feedback, allowing also 1-dimensional formations to be fully coherent. For electric power networks, we show that the transient power losses grow unboundedly with network size. However, in contrast to previous results, performance does not improve with increased network connectivity. We also show that a certain type of distributed dynamic feedback controller can improve performance by reducing losses, but that their scaling with network size remains an important limitation. 

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2016. p. viii, 156
Series
TRITA-EE, ISSN 1653-5146
Keywords
Networked control systems, microgrids, platooning, vehicular formation, multi-agent systems, H2 norms, fundamental limitations, consensus, Distributed control, large-scale networks, oscillator networks, power networks, power system dynamics, system performance, spatially invariant systems
National Category
Control Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-186180 (URN)978-91-7729-001-8 (ISBN)
Presentation
2016-05-27, Q2, Osquldas väg 10, KTH Campus, Stockholm, 13:00 (English)
Supervisors
Note

QC 20160504

Available from: 2016-05-04 Created: 2016-05-03 Last updated: 2016-05-06Bibliographically approved
Tegling, E., Gayme, D. F. & Sandberg, H. (2015). Performance metrics for droop-controlled microgrids with variable voltage dynamics. In: Decision and Control (CDC), 2015 IEEE 54th Annual Conference on: . Paper presented at Decision and Control (CDC), 2015 IEEE 54th Annual Conference on (pp. 7502-7509). IEEE
Open this publication in new window or tab >>Performance metrics for droop-controlled microgrids with variable voltage dynamics
2015 (English)In: Decision and Control (CDC), 2015 IEEE 54th Annual Conference on, IEEE , 2015, p. 7502-7509Conference paper, Published paper (Refereed)
Abstract [en]

This paper investigates the performance of a microgrid with droop-controlled inverters in terms of the total power losses incurred in maintaining synchrony under persistent small disturbances. The inverters are modeled with variable frequencies and voltages under droop control. For small fluctuations from a steady state, these transient power losses can be quantified by an input-output H2 norm of a linear system subject to distributed disturbances. We evaluate this H2 norm under the assumption of a dominantly inductive network with identical inverters. The results indicate that while phase synchronization, in accordance with previous findings, produces losses that scale with a network's size but only weakly depend on its connectivity, the losses associated with the voltage control will be larger in a highly connected network than in a loosely connected one. The typically higher rate of convergence in a highly interconnected network thus comes at a cost of higher losses associated with the power flows used to reach the steady state.

Place, publisher, year, edition, pages
IEEE, 2015
National Category
Control Engineering
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-182039 (URN)10.1109/CDC.2015.7403404 (DOI)000381554507114 ()2-s2.0-84962016580 (Scopus ID)978-1-4799-7884-7 (ISBN)
Conference
Decision and Control (CDC), 2015 IEEE 54th Annual Conference on
Note

QC 20160317

Available from: 2016-02-12 Created: 2016-02-12 Last updated: 2016-12-15Bibliographically approved
Tegling, E., Bamieh, B. & Gayme, D. F. (2015). The Price of Synchrony: Evaluating the Resistive Losses in Synchronizing Power Networks. IEEE TRANSACTIONS ON CONTROL OF NETWORK SYSTEMS, 2(3), 254-266
Open this publication in new window or tab >>The Price of Synchrony: Evaluating the Resistive Losses in Synchronizing Power Networks
2015 (English)In: IEEE TRANSACTIONS ON CONTROL OF NETWORK SYSTEMS, ISSN 2325-5870, Vol. 2, no 3, p. 254-266Article in journal (Refereed) Published
Abstract [en]

This paper investigates the resistive power losses that are incurred in keeping a network of synchronous generators in a synchronous state. These losses arise due to the transient power-flow fluctuations that occur when the system is perturbed from a synchronous state by a small transient event or in the face of persistent stochastic disturbances. We call these losses the "price of synchrony," as they reflect the real power-flow costs incurred in resynchronizing the system. In the case of small fluctuations at each generator node, we show how the total network's resistive losses can be quantified using an H-2 norm of a linear system of coupled swing equations subject to distributed disturbances. This norm is shown to be a function of transmission-line and generator properties, to scale unboundedly with network size, and to be weakly dependent on the network topology. This conclusion differentiates the price of synchrony from typical power systems stability notions, which show highly connected networks to be more coherent and, thus, easier to synchronize. In particular, the price of synchrony is more dependent on a network's size than its topology. We discuss possible implications of these results in terms of the design of future power grids, which are expected to have highly distributed generation resources leading to larger networks with the potential for greater transient losses.

Place, publisher, year, edition, pages
IEEE Press, 2015
Keywords
Distributed control, large-scale networks, oscillator networks, power networks, power system dynamics system performance
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-179181 (URN)10.1109/TCNS.2015.2399193 (DOI)000365086400004 ()2-s2.0-84959305136 (Scopus ID)
Note

QC 20151211

Available from: 2015-12-11 Created: 2015-12-11 Last updated: 2015-12-15Bibliographically approved
Sjödin, E. & Gayme, D. F. (2014). Transient losses in synchronizing renewable energy integrated power networks. In: American Control Conference (ACC), 2014: . Paper presented at 2014 American Control Conference, ACC 2014, Portland, OR, United States, 4 June 2014 through 6 June 2014. (pp. 5217-5223). IEEE
Open this publication in new window or tab >>Transient losses in synchronizing renewable energy integrated power networks
2014 (English)In: American Control Conference (ACC), 2014, IEEE , 2014, p. 5217-5223Conference paper, Published paper (Refereed)
Abstract [en]

This paper quantifies the transient power losses incurred in re-synchronizing a network of generators and loads. The power system is represented using a network preserving model with loads and asynchronous generators modeled as frequency dependent power injections, which we refer to as ‘first-order oscillators’. Coupling these models with the swing equations of traditional generators leads to a mixed-oscillator system. The power flows used to maintain network synchronization induce resistive (real power) losses in the system, which we quantify through an H2 norm that is shown to scale with network size. Our results also show that given a fixed network size, this H2 norm is the same for first-order, second-order and mixed-oscillator systems, provided that the damping coefficients are all equal. Therefore, if the renewable power generators being added to a power network can be controlled so that their effective dampings match those of the existing generators, they will not increase transient power losses in the system.

Place, publisher, year, edition, pages
IEEE, 2014
Series
American Control Conference. Proceedings, ISSN 0743-1619
Keywords
Control of networks, Linear systems, Power systems
National Category
Control Engineering
Identifiers
urn:nbn:se:kth:diva-154062 (URN)10.1109/ACC.2014.6858992 (DOI)2-s2.0-84905715108 (Scopus ID)978-147993272-6 (ISBN)
Conference
2014 American Control Conference, ACC 2014, Portland, OR, United States, 4 June 2014 through 6 June 2014.
Note

QC 20150216

Available from: 2014-10-13 Created: 2014-10-13 Last updated: 2015-02-16Bibliographically approved
Sjödin, E., Gayme, D. F. & Topcu, U. (2012). Risk-mitigated optimal power flow for wind powered grids. In: 2012 American Control Conference (ACC). Paper presented at 2012 American Control Conference, ACC 2012, 27 June 2012 through 29 June 2012, Montreal, QC (pp. 4431-4437). IEEE Computer Society
Open this publication in new window or tab >>Risk-mitigated optimal power flow for wind powered grids
2012 (English)In: 2012 American Control Conference (ACC), IEEE Computer Society, 2012, p. 4431-4437Conference paper, Published paper (Refereed)
Abstract [en]

Increased penetration of renewable energy sources poses new challenges to the power grid. Grid integrated energy storage combined with fast-ramping conventional generation can help to address challenges associated with power output variability. This paper proposes a risk mitigating optimal power flow (OPF) framework to study the dispatch and placement of energy storage units in a power system with wind generators that are supplemented by fast-ramping conventional back-up generators. This OPF with storage charge/discharge dynamics is solved as a finite-horizon optimal control problem. Chance constraints are used to implement the risk mitigation strategy. The model is applied to case studies based on the IEEE 14 bus benchmark system. First, we study the scheduling of spinning reserves and storage when generation and loads are subject to uncertainties. The framework is then extended to investigate the optimal placement of storage across different network topologies. The results of the case studies quantify the need for storage and reserves as well as suggest a strategy for their scheduling and placement.

Place, publisher, year, edition, pages
IEEE Computer Society, 2012
Series
Proceedings of the American Control Conference, ISSN 0743-1619
Keywords
Back-up generators, Benchmark system, Chance constraint, Conventional generation, Energy storage unit, Fast-ramping, Network topology, Optimal control problem, Optimal placements, Optimal power flows, Power grids, Power out put, Renewable energy source, Risk mitigating, Risk mitigation strategy, Spinning reserves, Storage charges, Wind generator systems, Acoustic generators, Electric network topology, Energy storage, Optimal control systems, Renewable energy resources, Scheduling, Electric load flow
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-108018 (URN)000310776204119 ()2-s2.0-84869442174 (Scopus ID)978-145771095-7 (ISBN)
Conference
2012 American Control Conference, ACC 2012, 27 June 2012 through 29 June 2012, Montreal, QC
Note

QC 20121221

Available from: 2012-12-21 Created: 2012-12-19 Last updated: 2013-01-14Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-8975-1801

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