R. D'hulst

KU Leuven, Leuven, VLG, Belgium

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Publications (18)6.5 Total impact

  • 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 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
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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
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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
  • 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: 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 01/2012; 3(4):2121-2127.
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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; · 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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    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: 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
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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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    ABSTRACT: Battery systems have a much lower energy density than fuels. The use of fuel based micro power generation units instead of batteries can therefore become interesting in certain applications. This paper describes the problems that occur when designing such a power generation unit. It is shown that operational conditions and geometrical restrictions impose tough requirements on the design of different components. The solutions as found in traditional fuel based generation systems cannot simply be downscaled, but several concepts have to be fundamentally rethought
    Electric Machines and Drives, 2005 IEEE International Conference on; 06/2005
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    ABSTRACT: This contribution describes a power extraction circuit designed to interface to a vibrational energy harvester. Vibrational energy harvesters produce an AC voltage and therefore a power processing circuit is needed to convert the AC voltage into a DC voltage of an appropriate level for supplying a low power load. The power conversion circuitry must also present the correct electrical impedance to the generator to maximize its power output. The buck-boost topology is chosen for the extraction circuit, its operating point in to discontinuous mode. A reservoir capacitor is present to store the extracted energy. An implementation of the design was simulated using a standard 80 V CMOS process, and eciencies of over 60% are demonstrated. With suitable control, the input impedance of the circuit is indeed resistive as well as variable and thus well suited as a load for powerMEMS generators.
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    ABSTRACT: The aim of the proposed stochastic methodology is to study and analyze the response of the Belgian HV-grid to the injection of a high wind power input. Factors such as the season of the year, the time of day, the installed power or the geographical spread of wind turbines are studied as well as the way they influence the power output and how to handle this behaviour for the benefit of the grid. The power flows in every line, the possible overloads, the most critical cases were reflected, and corresponding conclusions are drawn.
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    ABSTRACT: The output of a vibration-based energy harvester generally is an AC-voltage, whereas the input to an electronic load should be a certain DC-voltage. A voltage regulator circuit is therefore needed to provide the correct voltage. In this contribution, the main requirements for such a voltage regulator are given. Different design options are discussed: linear voltage regulators, classical switching techniques and switched-capacitor regulators. Pros and conts of each configuration are discussed, thereby concluding that the best design option is highly dependent on the output characteristics of the energy harvester.
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    R. D'hulst, J. Driesen
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    ABSTRACT: In this contribution, the power output of a vibration-driven energy scavenger is optimized when connected to a resistive, linear load and a nonlinear load, an AC-DC converter. The optimization of the power output is constrained by the limited generator size. The optimal loading is calculated for both load cases in various operating conditions, and the optimal generated power is compared. It is shown that the difference in power output for both load cases is very small. This conclusion is important for the design of the power management circuit, required to transform the scavenger output voltages to a suitable form. The current advances in performance and functionality of micro- and nano-systems have stimulated the development of intelligent networks of autonomous systems. The demand for a small, mobile and reliable energy supply for each autonomous network node has led to the development of a new type of generators, as the use of conventional electrochemical batteries is not always an option because of their limited lifespan, the need for replacement, and the volume-dependency of the amount of stored energy. Motion energy or vibrations are an attractive source for powering miniature energy harvesting generators (1). In this paper, the optimal power output of a vibration-based energy scavenger is calculated for a resistive, linear load, and for a nonlinear load, an AC-DC converter. The vibration-driven generator is considered as being of the inertial type: a proof mass m is suspended within a frame, and energy is extracted by a transducer that damps the motion of the mass. A schematic overview of the generator is shown in Figure 1: the mass m is modeled as being suspended by a spring with spring constant k, while its motion is damped by a parasitic damping d due to friction and air. The mass is also damped by the generator, exerting a reaction force Fg. The displacement of the mass z(t) is restricted to zMAX, the size of the device. The amplitude of the motion of the package y(t) is Y0. An electric circuit equivalent of the same generator is shown in Figure 2, this circuit equivalent is valid for electrostatic, electromagnetic and piezo-electric devices (2)(3). In this electric circuit, the voltages represent forces, and charges represent displacements. The electrical model is further used to analyze the behavior of the scavenger with different loads.