An internal model approach to (optimal) frequency regulation in power grids with time-varying voltages

This paper studies the problem of frequency regulation in power grids under unknown and possible time-varying load changes, while minimizing the generation costs. We formulate this problem as an output agreement problem for distribution networks and address it using incremental passivity and distributed internal-model-based controllers. Incremental passivity enables a systematic approach to study convergence to the steady state with zero frequency deviation and to design the controller in the presence of time-varying voltages, whereas the internal-model principle is applied to tackle the uncertain nature of the loads.Comment: 16 pages. Abridged version appeared in the Proceedings of the 21st International Symposium on Mathematical Theory of Networks and Systems, MTNS 2014, Groningen, the Netherlands. Submitted in December 201

Distributed control of power networks:Passivity, optimality and energy functions

Sociale en technologische ontwikkelingen hebben geleid tot een toename van de vraag naar elektriciteit, gegenereerd door een steeds grotere hoeveelheid hernieuwbare energiebronnen. Ondanks de potentiële voordelen hiervan, vormen deze ontwikkelingen belangrijke uitdagingen voor de planning en de werking van de bestaande elektriciteitsnetwerken. Een belangrijk operationeel aspect in elektriciteitsnetwerken, waarop dit werk zich focust, is de regulering van de frequentie.In aanwezigheid van meer en kleinere generatie eenheden is een zorgvuldige coördinatie tussen de afzonderlijke onderdelen in het elektriciteitsnet nodig om ervoor te zorgen dat het gehele netwerk juist functioneert. Wij ontwerpen en analyseren gedistribueerde regelaars, die ervoor zorgen dat de acties van lokale regelaars in overeenstemming zijn met de globale optimaliteitsdoelstellingen, zoals het minimaliseren van de generatiekosten. De totale energie van het netwerk speelt een belangrijke rol in dit proces, waardoor het mogelijk is om nuttige systeemtheoretische eigenschappen te formuleren zonder gedetailleerde kennis van alle componenten.We tonen aan dat het belangrijk is om de generatiezijde en het communicatienetwerk expliciet in de ontwerpfase van regelaars te integreren en dat het achterwege laten kan leiden tot een ongerechtvaardigd geloof dat de stabiliteit van het netwerk is gewaarborgd.Social and technological developments resulted in an increase of electricity demand, generated by an ever increasing amount of renewable energy sources. Despite its potential benefits, a continuation of these developments poses significant challenges to the planning and operation of the existing power networks. An important operational aspect in power networks is the regulation of its frequency, which is the focus of this work.In the presence of more and smaller generation units, careful coordination among the individual parts in the power network is needed, ensuring proper overall functioning. We design and analyse distributed controllers, that ensure that actions taken by local controllers are consistent with global optimality objectives, such as the minimization of generation costs. The total energy of the power network plays a major role in this process, enabling the derivation of useful system theoretic properties without detailed knowledge of all components. Particularly, this work shows that energy functions are suitable to derive passivity properties of various nonlinear power system models, that form an excellent staring point for the controller design. Proposed controllers are shown to regulate the frequency and to obtain an economic dispatch.We show that it is, although challenging, of importance to incorporate the generation side and the communication network explicitly in the design phase of controllers and that neglecting these aspects can result in an unjustified belief that stability of the network is guaranteed by suggested solutions

Broadcasting protocols for coordinating nonlinear network systems

We propose a new methodology to design broadcasting protocols for coordinating nonlinear network systems. Our design of the scheduling of information transmission is based on the introduction of clock variables, whose dynamics are regulated through a suitable storage function. Required clock dynamics, ensuring stability, follow then elegantly from Lyapunov like arguments. For illustrative purposes, we first consider an example of a consensus algorithm, whereafter we discuss a distributed integral controller in feedback interconnection to a network composed of output strictly incrementally passive subsystems. Finally, we show how the proposed method can be used to redesign a popular distributed controller in power grids, enabling a sampled-data implementation

Optimal regulation of flow networks with transient constraints

This paper investigates the control of flow networks, where the control objective is to regulate the measured output (e.g. storage levels) towards a desired value. We present a distributed controller that dynamically adjusts the inputs and flows, to achieve output regulation in the presence of unknown constant disturbances, while satisfying given input and flow constraints. Optimal coordination among the controllers minimizing a suitable cost function of the inputs at the nodes, is achieved by exchanging information over a communication network. Exploiting an incremental passivity property, the desired steady state is proven to be globally asymptotically attractive under the closed loop dynamics. Two case studies (a district heating system and a super-conducting DC network) show the effectiveness of the proposed solution. (C) 2019 Elsevier Ltd. All rights reserved

Distributed MPC for controlling mu-CHPs in a network

This paper describes a dynamic price mechanism to coordinate electricity generation from micro Combined Heat and Power (mu-CHP) systems in a network of households. The control is done on household level in a completely distributed manner. Distributed Model Predictive control is applied to the network of households with mu-CHP installed. Each house has a unique demand pattern based on realistic data. Information from a few neighbors are taken into account in the local optimal control problems. Desired behavior for the network model in the distributed MPC approach is showed by simulation