Change search
Refine search result
1 - 10 of 10
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Andreasson, Martin
    et al.
    KTH, School of Industrial Engineering and Management (ITM). KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sjödin, Emma
    KTH, School of Industrial Engineering and Management (ITM). KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Sandberg, Henrik
    KTH, School of Industrial Engineering and Management (ITM). KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, School of Industrial Engineering and Management (ITM). KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Coherence in Synchronizing Power Networks with Distributed Integral Control2017In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, IEEE , 2017, p. 6683-6688Conference 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.

  • 2. Govindarajan, Nithin
    et al.
    Arbabi, Hassan
    van Blargian, Louis
    Matchen, Timothy
    Tegling, Emma
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Mezic, Igor
    An operator-theoretic viewpoint to non-smooth dynamical systems: Koopman analysis of a hybrid pendulum2016In: 2016 IEEE 55th Conference on Decision and Control, CDC 2016, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 6477-6484, article id 7799266Conference paper (Refereed)
    Abstract [en]

    We apply an operator-theoretic viewpoint to a class of non-smooth dynamical systems that are exposed to event-triggered state resets. The considered benchmark problem is that of a pendulum which receives a downward kick at certain fixed angles. The pendulum is modeled as a hybrid automaton and is analyzed from both a geometric perspective and the formalism of Koopman operator theory. A connection is drawn between these two interpretations of a dynamical system by establishing a link between the spectral properties of the Koopman operator and the geometric properties in the state-space.

  • 3.
    Sjödin, Emma
    et al.
    KTH, School of Electrical Engineering (EES).
    Gayme, D. F.
    Topcu, U.
    Risk-mitigated optimal power flow for wind powered grids2012In: 2012 American Control Conference (ACC), IEEE Computer Society, 2012, p. 4431-4437Conference 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.

  • 4.
    Sjödin, Emma
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. Johns Hopkins University, USA.
    Gayme, Dennice F.
    The Johns Hopkins University, USA.
    Transient losses in synchronizing renewable energy integrated power networks2014In: American Control Conference (ACC), 2014, IEEE , 2014, p. 5217-5223Conference 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.

  • 5.
    Tegling, Emma
    KTH, School of Electrical Engineering and Computer Science (EECS), Automatic Control.
    Fundamental Limitations of Distributed Feedback Control in Large-Scale Networks2018Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Networked systems accomplish global behaviors through local feedback interactions. The purpose of a distributed control design is to select interaction rules and control protocols that achieve desired global control objectives. In this thesis, we address the question of fundamental limitations to such control designs, in terms of the global performance that is achievable in large-scale networks. 

    We consider networked dynamical systems with single- and double- integrator dynamics controlled with linear consensus-like protocols. Such systems can be used to model, for example, vehicular formation dynamics and synchronization in electric power networks. We assume that the systems are subject to distributed disturbances and study performance in terms of H2 norm metrics that capture the notion of network coherence. In the context of power networks, we also show how such metrics can be used to quantify resistive losses caused by non-equilibrium, or transient, power flows due to a lack of synchrony. 

    Distributed static feedback control based on localized, relative state measurements is subject to known limitations that, for example, cause coherence metrics to scale unfavorably with network size in lattices of low spatial dimensions. This causes an inevitable lack of rigidity in one-dimensional formations, such as strings of vehicles. We show here that the same limitations in general apply also to dynamic feedback controllers that are locally of first order. The proof relies partly on a fundamental limitation of localized relative feedback in networks of integrators of order three or higher, which we show to cause instability if the network grows beyond a certain finite size. 

    This result holds unless the controller can access measurements of its local state with respect to an absolute reference frame, in which case dynamic feedback in the form of distributed derivative or integral control can fundamentally improve performance. This case applies, for example, to frequency control in power networks. However, if the absolute state measurements are subject to noise, the advantage of the distributed integral controller in terms of its performance scaling is lost. We show that scalable integral control of networks in principle requires centralization or all-to-all communication. 

    For electric power networks, we show that performance in terms of transient power losses scales with the number of generator nodes in a network. However, in sharp contrast to the previous results, an increased connectivity does not in general improve performance. We discuss possible implications of these results in terms of the design of future power grids with increasingly distributed electricity generation. 

  • 6.
    Tegling, Emma
    KTH, School of Electrical Engineering (EES), Automatic Control.
    On performance limitations of large-scale networks with distributed feedback control2016Licentiate 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. 

  • 7.
    Tegling, Emma
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Andreasson, Martin
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Simpson-Porco, John W.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Improving performance of droop-controlled microgrids through distributed PI-control2016In: 2016 AMERICAN CONTROL CONFERENCE (ACC), IEEE conference proceedings, 2016, p. 2321-2327Conference 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.

  • 8.
    Tegling, Emma
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Bamieh, Bassam
    Gayme, Dennice F.
    The Price of Synchrony: Evaluating the Resistive Losses in Synchronizing Power Networks2015In: IEEE TRANSACTIONS ON CONTROL OF NETWORK SYSTEMS, ISSN 2325-5870, Vol. 2, no 3, p. 254-266Article in journal (Refereed)
    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.

  • 9.
    Tegling, Emma
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gayme, D. F.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Performance metrics for droop-controlled microgrids with variable voltage dynamics2015In: Decision and Control (CDC), 2015 IEEE 54th Annual Conference on, IEEE , 2015, p. 7502-7509Conference 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.

  • 10.
    Tegling, Emma
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Sandberg, Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    On the Coherence of Large-Scale Networks With Distributed PI and PD Control2017In: IEEE Control Systems Letters, ISSN 2475-1456, Vol. 1, no 1, p. 170-175Article in journal (Refereed)
    Abstract [en]

    We consider distributed control of double-integrator networks, where agents are subject to stochastic disturbances. We study performance of such networks in terms of coherence, defined through an H2 norm metric that represents the variance of nodal state fluctuations. Specifically, we address known performance limitations of the standard consensus protocol, which cause this variance to scale unboundedly with network size for a large class of networks. We propose distributed proportional integral and proportional derivative controllers that relax these limitations and achieve bounded variance, in cases where agents can access an absolute measurement of one of their states. This case applies to, for example, frequency control of power networks and vehicular formation control with limited sensing. We discuss optimal tuning of the controllers with respect to network coherence and demonstrate our results in simulations.

1 - 10 of 10
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf