R. D'hulst

Flemish Institute for Technological Research, Moll, Flemish, Belgium

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Publications (26)26.01 Total impact

  • Sam Weckx · Reinhilde D'Hulst · Johan Driesen
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    ABSTRACT: New voltage control algorithms are necessary to cope with the increasing amount of distributed generation and electric vehicles in distribution networks. Many of the newly proposed voltage control algorithms are based on linearized dependencies between the voltage magnitude, and the active and reactive power consumption. These linearized dependencies are normally obtained by algorithms, which rely on accurate grid topology information. Due to the traditionally passive operation of low voltage (LV) distribution networks, this information is typically missing, incomplete, or inaccurate. Therefore, this paper introduces a method to extract these linear dependencies based on historical smart meter data only. No information about the grid topology is required. The model adapts to the changing load conditions in the network. The algorithm has a low complexity and is applied to an unbalanced LV distribution network. Data of a practical laboratory setup is used to validate the proposed method in real-life conditions. With the obtained voltage sensitivity factors a voltage management strategy was implemented for the laboratory grid.
    IEEE Transactions on Smart Grid 05/2015; 6(3):1271-1280. DOI:10.1109/TSG.2014.2380642 · 4.33 Impact Factor
  • Sam Weckx · Reinhilde D'Hulst · Johan Driesen
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    ABSTRACT: Decentralized demand control can help to ensure the balance between electricity demand and supply. In this paper, a multi-agent demand control system is proposed where residential demand is controlled to provide spinning reserves. With the proposed control framework, an aggregator of dynamic demand is able to control the consumption and the response on frequency changes of a cluster of loads. The primary frequency support by the cluster of loads can emulate the primary control of a conventional generator. The total customer welfare remains maximal during the frequency support by applying utility functions for each device.
    IEEE Transactions on Power Systems 05/2015; 30(3):1394-1404. DOI:10.1109/TPWRS.2014.2340582 · 3.53 Impact Factor
  • Sam Weckx · Reinhilde D'hulst · Johan Driesen
    Energies 05/2015; 8(5):4607-4628. DOI:10.3390/en8054607 · 1.60 Impact Factor
  • sam Weckx · Reinhilde D'Hulst · Bert Claessens · Johan Driesensam
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    ABSTRACT: In this paper, a market based multiagent control mechanism that incorporates distribution transformer and voltage constraints for the charging of a fleet of electric vehicles (EVs) is presented. The algorithm solves a utility maximization problem in a distributed way, assigning most charging power to the EVs with the highest need for energy. The algorithm does not rely on an iterative exchange of messages, but finds the optimal solution after the exchange of just one single message. A substation agent is responsible for guaranteeing a safe network operation. It uses the remaining capacity of each of the EV chargers for reactive voltage control. The performance of the algorithm is evaluated on an existing three-phase four-wire distribution grid. Simulation results show that the fleet of EVs can be charged at a minimal increase of costs, without jeopardizing the network.
    IEEE Transactions on Smart Grid 11/2014; 5(6):2857-2867. DOI:10.1109/TSG.2014.2345886 · 4.33 Impact Factor
  • Reinhilde D'hulst · Fjo De Ridder · Bert Claessens · Luk Knapen · Davy Janssens
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    ABSTRACT: SUMMARYA method to coordinate the charging of electric vehicles to avoid network congestion issues is proposed. The novelty is that the proposed method uses both the temporal as well as the locational flexibility of the electric vehicles for coordination. Based on the vehicle behavior information (trajectories, parking places and duration, etc…), the algorithm assures that all vehicles can follow their planned trajectories and that power constraints on each car park are always met. The proposed method, a price-based coordination method, is ran in a decentralized way. As a consequence the responsibility for constructing the charging schedules is put solely with the vehicle owners, and the charging location managers need only to be concerned with the network congestion issues. Simulation results for 1000 EV's and 132 parking locations are presented and discussed. Copyright © 2014 John Wiley & Sons, Ltd.
    International Transactions on Electrical Energy Systems 08/2014; DOI:10.1002/etep.1983 · 0.63 Impact Factor
  • F. De Ridder · R. D'Hulst · Luk KNAPEN · Davy JANSSENS
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    ABSTRACT: This chapter presents a coordination algorithm for charging electric vehicles that can be used for avoiding capacity problems in the power distribution grid and for decreasing imbalance costs for retailers. Since it is expected that the fraction of electric vehicles will exceed 50% in the next decades, charging these vehicles will roughly double the domestic power consumption. Not all parts of the grid are expected to be able to provide the required power. Good estimates of the vehicles’ use (routes driven, trip duration and length, when and where cars are parked) is crucial information to test the grid. The authors have chosen to use FEATHERS, an agent-based behavioral model, to provide this information. In a first case study, charging is coordinated to prevent grid capacity problems. In a second case study, charging and discharging of electric vehicles is employed by retailers to lower imbalance costs and by vehicle owners to lower charging costs. The coordination scheme can halve the imbalance cost if only charging is considered. If, on the other hand, electric vehicles can both charge and discharge, imbalance costs can completely be avoided and some revenues can be generated. The proposed coordination algorithm is a distributed algorithm, where all sensitive information that is privately owned, such as parking times, trip information, battery management, etc. is only used by the EVs. The functioning of the proposed algorithm is illustrated by simulations. It is shown that the charging can be rescheduled so that grid capacity violations are avoided. The novelty of this work is that both spatial and temporal information is used.
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    ABSTRACT: This paper describes a voltage stabilizing control mechanism using the available flexibility of smart devices within one household. The flexibility of all types of smart appliances is used, especially smart on/off devices. The main advantage of the developed control system is that it does not require a communication network between the different households, only locally available measurements, such as the household supply voltage, are taken into account. The control system will be rolled out in a real life pilot test. Simulation results point out that the amount of over and under voltage occurrences on average are lowered with 35%.
    Industrial Electronics Society, IECON 2013 - 39th Annual Conference of the IEEE; 01/2013
  • S. Weckx · J. Driesen · R. D'hulst
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    ABSTRACT: In this paper, a real-time pricing algorithm is described that allows different energy providers to share one common network, without violating the network constraints. We consider a smart grid equipped with a two-way communication system. Energy producers, system operator and end-users exchange information through the communication infrastructure in order to converge to the optimal power consumption schedules without violating network limitations. A distributed gradient algorithm automatically manages the interactions between the different agents. Customer behaviour is modelled by utility-functions, based on concepts from microeconomics. The proposed algorithm is applied to a 3-phase 4-wire radial grid.
    Power and Energy Society General Meeting (PES), 2013 IEEE; 01/2013
  • S. Weckx · J. Driesen · R. D'Hulst
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    ABSTRACT: A high penetration of renewable energy sources challenges future grid frequency control. Decentralized demand control can contribute to this frequency control. In this paper a method is proposed where residential demand is controlled to support the frequency. The total customer welfare remains maximal during this support by applying utility functions for each device. A large scale isolated power system is simulated where classic governor action is supported by frequency dependent controllers on electric vehicles and boilers, taking into account their availability. The proposed technique does not depend on a two way communication network, but if such a network is available, it can be combined with an auction based market mechanism.
    PowerTech (POWERTECH), 2013 IEEE Grenoble; 01/2013
  • S. Weckx · J. Driesen · R. D'Hulst
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    ABSTRACT: In this paper, a distributed algorithm is described to schedule binary behaving loads, such as dishwashers, washing machines or tumble dryers in a near optimal way. We consider a smart grid equipped with a two-way communication system. Energy producers and end-users exchange information through the communication infrastructure in order to converge to near optimal power consumption schedules. The near optimal scheduling is obtained by a lagrangian relaxation of the utility maximization problem. Utility functions that are decomposable in time as well as utility functions that are not decomposable in time are considered.
    PowerTech (POWERTECH), 2013 IEEE Grenoble; 01/2013
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    ABSTRACT: In this paper, we present a distributed voltage control mechanism that is being used in the large-scale field-test of the Linear project. The control system developed does not require a communication network between the different households. Only the locally measured household supply voltage is taken into account. The proposed control system is compatible with DSM infrastructure currently being developed, such as home gateways and smart meters. Moreover, the proposed control system can also be used as a fallback mechanism for other communication-based DSM control systems when communication fails or when the system has been compromised due to cyber security issues. Using Monte Carlo simulations on two accurately modeled field test grids and device models, the proposed approach and its various parameter set points are benchmarked against the optimal Dynamic Programming solution. Simulation results point out that on average the amount of over and under voltage occurrences can be lowered by more than 30 %.
    Innovative Smart Grid Technologies Europe (ISGT EUROPE), 2013 4th IEEE/PES; 01/2013
  • Koen Vanthournout · Reinhilde D'hulst · Davy Geysen · Geert Jacobs
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    ABSTRACT: Demand response is seen as a key technology to help the introduction of large volumes of intermittent renewable energy and to help mitigate the effects of the increasing load on the electricity distribution grid. A large and diverse number of control mechanisms are proposed for demand response, while multiple industrial companies are designing their own proprietary solutions. This situation demands for standardized and generalized interfaces for smart devices, i.e., interfaces based on as few indicators as possible that reflect the flexibility state, while hiding all implementation details and specifics of the device. Electric domestic hot water buffers are devices that inherently contain a lot of flexibility, i.e., the charging can be shifted without impact on the comfort of the user. This article presents four key indicators for domestic hot water buffers that meet above requirements: P, the rated power, Emax, the energy required to fully charge the buffer, SoC, the state of charge, and Emin , the energy required before the SoC increases. The correct behavior of these key indicators has been validated by means of simulations and measurements on a lab prototype. The integration of the smart buffer into a time of use demand response system is demonstrated with a test setup and measurement results.
    IEEE Transactions on Smart Grid 12/2012; 3(4):2121-2127. DOI:10.1109/TSG.2012.2205591 · 4.33 Impact Factor
  • Kevin Mets · Reinhilde D'hulst · Chris Develder
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    ABSTRACT: A potential breakthrough of the electrification of the vehicle fleet will incur a steep rise in the load on the electrical power grid. To avoid huge grid investments, coordinated charging of those vehicles is a must. In this paper, we assess algorithms to schedule charging of plug-in (hybrid) electric vehicles as to minimize the additional peak load they might cause. We first introduce two approaches, one based on a classical optimization approach using quadratic programming, and a second one, market based coordination, which is a multi-agent system that uses bidding on a virtual market to reach an equilibrium price that matches demand and supply. We benchmark these two methods against each other, as well as to a baseline scenario of uncontrolled charging. Our simulation results covering a residential area with 63 households show that controlled charging reduces peak load, load variability, and deviations from the nominal grid voltage.
    Journal of Communications and Networks 12/2012; 14(6):672-681. DOI:10.1109/JCN.2012.00033 · 0.75 Impact Factor
  • Reinhilde D'hulst · Kris Kessels · Daan Six
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    ABSTRACT: In a situation where the share of less predictable electricity production from renewable energy sources (like solar energy) in the overall electricity production-mix increases, the electricity system will be confronted with more imbalance. Balancing markets deal with these imbalances. In this context, a balancing responsible party (BRP) is responsible to maintain the balance in its portfolio on a quarter-hourly basis and is charged for any incurred imbalances. A BRP with less predictable electricity production in its portfolio, like PV production, has a higher imbalance risk and thus on average a higher imbalance cost. The case study under consideration aims at optimizing the portfolio of a BRP, which consists of a large scale PV installation and an industrial CHP unit. A software tool is used that is able to calculate to what extent the imbalance costs of the BRP can be decreased by actively controlling the available flexibility in its portfolio (in this case the CHP installation). The paper presents the results of the simulations and discusses the potential reduction in imbalance costs for the BRP if the flexibility of the CHP is used within different scenarios.
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    Reinhilde D'hulst · Tom Sterken · Robert Puers · Geert Deconinck · Johan Driesen
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    ABSTRACT: The behavior of a piezoelectric vibration-driven energy harvester with different power processing circuits is evaluated. Two load types are considered: a resistive load and an ac-dc rectifier load. An optimal resistive and optimal dc-voltage load for the harvester is analytically calculated. The difference between the optimal output power flow from the harvester to both load circuits depends on the coupling coefficient of the harvester. Two power processing circuits are designed and built, the first emulating a resistive input impedance and the second with a constant input voltage. It is shown that, in order to design an optimal harvesting system, the combination of both the ability of the circuit to harvest the optimal harvester power and the processing circuit efficiency needs to be considered and optimized. Simulations and experimental validation using a custom-made piezoelectric harvester show that the efficiency of the overall system is 64% with a buck converter as a power processing circuit, whereas an efficiency of only 40% is reached using a resistor-emulating approach.
    IEEE Transactions on Industrial Electronics 01/2011; 57(12-57):4170 - 4177. DOI:10.1109/TIE.2010.2044126 · 6.50 Impact Factor
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    R. D'hulst · J. Driesen
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    ABSTRACT: In this paper the behavior of a piezo-electric vibration-driven energy harvester is assessed with different power processing circuits. Firstly, a general model for vibration-driven harvesters is described. Using this model, an optimal linear resistive load for the harvester can be analytically calculated. As the vibration-based harvester provides varying AC power, while electronic loads need a stable DC power supply, it is useful to analyze the harvester behavior when connected to a non-linear AC-DC rectifier. Using the same general model, an optimal DC voltage load can be calculated for every frequency. The difference between the optimal output power flow from the harvester to both load circuits depends on the coupling coefficient of the harvester device. To validate previous conclusions, two power processing circuits are designed and built, the first emulating a resistive input impedance and the second with a constant input voltage. A piezo-electric bimorph is taken as energy harvesting device. A buck-boost DC-DC converter without input filter capacitor, operating in discontinuous conduction mode, is shown to have a resistive input impedance. A buck converter with input filter capacitor is used to evaluate the rectifier load-case. Simulations and experimental validation show that the efficiency of the overall system, harvester device with power processing circuit, increases if the power processing circuit has a fixed DC-voltage as input.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
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    R. D'hulst · T. Sterken · P. Fiorini · R. Puers · J. Driesen
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    ABSTRACT: This contribution describes the modeling of vibration-driven energy scavengers, either based on electrostatic, electromagnetic or piezoelectric principles. Subsequently, the behavior of the scavenger model is tested with two different types of load: a resistive load and a rectifier with a fixed voltage at the output. Optimal power output of the scavenger is calculated for both load-cases. It is shown that a resistance is not in all cases the most optimal load to maximize the power output of a scavenger. This conclusion has a big influence on the design of the power management circuit, needed to transform the scavenger output voltages to an appropriate shape for powering an electronic load.
    Industrial Electronics Society, 2007. IECON 2007. 33rd Annual Conference of the IEEE; 12/2007
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    ABSTRACT: The application of DC distribution of electrical power has been suggested as an efficient method of power delivery. This concept is inspired by the absence of reactive power, the possibility of efficient integration of small distributed generation units and the fact that, internally, many appliances operate using a DC voltage. A suitable choice of rectifier facilitates the improvement of the power quality as well as the power factor at the utility grid interface. Stand-by losses can be largely reduced. However, because of the inherent danger associated with DC voltages and currents, it is imperative that a considerable amount of design effort is allocated for risk analysis and the conception of protective devices and schemes, in order to guarantee personal and material (especially fire) safety. This paper consists of the following topics: topological design, buffering of the DC bus, interfacing distributed generators, efficiency analysis and safety measures. The conclusion of this work is that (at the moment) it is generally not efficient to implement a DC distribution system exclusively at the level of the end-user. Rather, further research should focus on the extension of DC power delivery to higher levels of the electricity grid
    IEEE Industrial Electronics, IECON 2006 - 32nd Annual Conference on; 12/2006
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    ABSTRACT: Often, in engineering education there is much emphasis on theoretical issues, especially during the first years. Still, students should be exposed to more than just theoretical knowledge. This paper describes a project-oriented approach to undergraduate teaching in the field of electrical power engineering applied in the Department of Electrical Engineering of the K.U.Leuven University, Belgium. Two projects offered to undergraduate students of the second year are presented. The first project lets the students make their own small green power plant. The second project deals with the prediction of electricity consumption in a liberalized energy market.
    Power Engineering Society General Meeting, 2005. IEEE; 07/2005
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    J. Driesen · K. De Brabandere · R. D'hulst · R. Belmans
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    ABSTRACT: Small wind turbine systems used in the built environment are an increasingly more popular renewable form of distributed generation. The three basic types and the main technical characteristics are summarized. The siting aspects are discussed, with attention for the particular difficulties of roof or building integration. The grid connection aspects for an individual turbine and for a multi-turbine installation (small wind farm) are treated. The parallel with grid connection aspects of photovoltaic systems, often complementary in power production, is discussed.
    Power Engineering Society General Meeting, 2005. IEEE; 07/2005