Droop-controlled inverter-based microgrids are robust to clock drifts

Schiffer, Johannes; Ortega, Roméo; Hans, Christian A.; Raisch, Jörg

doi:10.1109/acc.2015.7171082

Cited by 35 publications

(48 citation statements)

References 19 publications

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“…As a consequence of these observations, we derive an improved model of a grid-forming inverter with unknown constant clock drift. Thereby, we also extend the previous work [21] by providing an extensive experimental motivation and validation of the derived inverter model with inaccurate clock. As discussed above, the provision of practically feasible control concepts for inverters is essential for the operation of future power systems and, hence, a very active area of research [20], [22].…”

Section: B About the Papersupporting

confidence: 53%

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Modeling, Analysis, and Experimental Validation of Clock Drift Effects in Low-Inertia Power Systems

Schiffer

Hans

Kral³

et al. 2017

IEEE Trans. Ind. Electron.

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Abstract-Clock drift in digital controllers is of great relevance in many applications. Since almost all real clocks exhibit drifts, this applies in particular to networks composed of several individual units, each of which being operated with its individual clock. In the present work, we demonstrate via extensive experiments on a microgrid in the megawatt-range that clock drifts may impair frequency synchronisation in low-inertia power systems. The experiments also show that-in the absence of a common clockthe standard model of an inverter as an ideal voltage source does not capture this phenomenon. As a consequence, we derive a suitably modified model of an inverter-interfaced unit that incorporates the phenomenon of clock drifts. By using the derived model, we investigate the effects of clock drifts on the performance of droop-controlled grid-forming inverters with regard to frequency synchronisation and active power sharing. The modelling and analysis is validated via extensive experiments on a microgrid in the megawattrange.Index Terms-Smart grid applications, low-inertia power systems, microgrids, grid-forming inverters, droop control, power sharing.

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Section: B About the Papersupporting

confidence: 53%

“…See [21] for a proof that stability of lossless (i.e. G ik = 0 for all pairs (i, k) for i, k ∈ N and i = k) droopcontrolled inverter-based MGs is robust to constant unknown clock drifts.…”

Section: Remark 42mentioning

confidence: 99%

Modeling, Analysis, and Experimental Validation of Clock Drift Effects in Low-Inertia Power Systems

Schiffer

Hans

Kral³

et al. 2017

IEEE Trans. Ind. Electron.

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“…To realize this low level control, each unit is typically equipped with its own digital controller with individual processor clock. The time signal of all controllers slightly vary from each other because of the so called clock drifts [15]. As has been shown in [15], clock drifts can be incorporated in the model of a grid-forming inverter by introducing a (constant) unknown scaling factor in the model.…”

Section: Droop Controlled Unitsmentioning

confidence: 99%

“…The time signal of all controllers slightly vary from each other because of the so called clock drifts [15]. As has been shown in [15], clock drifts can be incorporated in the model of a grid-forming inverter by introducing a (constant) unknown scaling factor in the model. Then, the dynamics of the ith unit equipped with frequency droop control is given by…”

Section: Droop Controlled Unitsmentioning

confidence: 99%

“…Most of the distributed control approaches, as they make use of the internal frequencies that are calculated by the controls of the inverters, are influenced by clock drifts. In practice, even if the units are synchronized to a global frequency, the internal frequencies of the inverters are slightly different [15]. As external synchronization units that could hamper this problem are expensive, they are not used in most of the applications.…”

Section: Introductionmentioning

confidence: 99%

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Steady state evaluation of distributed secondary frequency control strategies for microgrids in the presence of clock drifts

Krishna

Hans

Schiffer

et al. 2017

2017 25th Mediterranean Conference on Control and Automation (MED)

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©2017 IEEE. This is an author produced version of a paper published in Proceedings of 25th Mediterranean Conference on Control and Automation. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works. Uploaded in accordance with the publisher's self-archiving policy.eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request.Steady state evaluation of distributed secondary frequency control strategies for microgrids in the presence of clock drifts* Abstract-Secondary frequency control, i.e., the task of restoring the network frequency to its nominal value following a disturbance, is an important control objective in microgrids. In the present paper, we compare distributed secondary control strategies with regard to their behaviour under the explicit consideration of clock drifts. In particular we show that, if not considered in the tuning procedure, the presence of clock drifts may impair an accurate frequency restoration and power sharing. As a consequence, we derive tuning criteria such that zero steady state frequency deviation and power sharing is achieved even in the presence of clock drifts. Furthermore, the effects of clock drifts of the individual inverters on the different control strategies are discussed analytically and in a numerical case study.

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Consensus in Multi‐agent Systems

Wen

Chen

et al. 2016

Distributed Cooperative Control of Multi‐agent Systems

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A Carlos Elías y a Marina. AbstractDuring the last decade, the problem of consensus in multiagents systems has been studied with special emphasis on graph theoretical methods. Consensus can be regarded as a control objective in which is sought that all systems, or agents, in a network have an equivalent output value. This is achieved through a given control strategy usually referred to as consensus algorithm. The motivation to study such an objective comes from different areas, such as engineering, and social and natural sciences. In the control engineering field, important application examples are formation control of swarms of mobile robots and distributed electric generation. Most of the work in this area is done for agents with single or double integrator dynamics and algorithms derived as the Laplacian matrix of undirected graphs. That is, consensus is often studied as a property of particular networks and particular algorithms.In this thesis, we tackle the problem from a Control Theory perspective in an attempt to augment the class of systems that can be studied. For that we translate the consensus problem from its classical formulation for integrator systems into a general continuous time stability problem. From here, different algorithmic strategies under several dynamical assumptions of the agents can be studied through well known control theoretical tools -as Lyapunov's theory, linear matrix inequalities (LMI), or robust control -along with graph theoretical concepts. In particular, in this work we study consensus of agents with arbitrary linear dynamics under the influence of linear algorithms not necessarily derived from graphs. Furthermore, we include the possibility that the agents are disturbed by several factors as external signals, parameter uncertainties, switching dynamics, or communication failure. The theoretical analysis is also applied to the problem of power sharing in electric grids and to the analysis of distributed formation control.

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Droop-controlled inverter-based microgrids are robust to clock drifts

Cited by 35 publications

References 19 publications

Modeling, Analysis, and Experimental Validation of Clock Drift Effects in Low-Inertia Power Systems

Modeling, Analysis, and Experimental Validation of Clock Drift Effects in Low-Inertia Power Systems

Steady state evaluation of distributed secondary frequency control strategies for microgrids in the presence of clock drifts

Consensus in Multi‐agent Systems

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