[Show abstract][Hide abstract] ABSTRACT: In this paper a high level functional architecture for frequency and voltage control for the future (2030+) power system is presented. The proposal suggests a decomposition of the present organization of power system operation into a “web of cells”. Each cell in this web is managed by a single system operator who assumes responsibility for real-time balance and voltage control of the cell, minimizing the dependency on inter-cell communication for secure system operation. The web-of-cells architecture ensures overall system stability by a combination of decentralized and distributed control patterns for frequency and voltage control. In each control cell, the operator maintains an accurate view on the overall cell state, based on adequate monitoring capabilities, and ensures secure operation by allocating and dispatching reserves located in the cell. Intercell coordination provides for efficient system-wide management and economic optimization.
[Show abstract][Hide abstract] ABSTRACT: This paper summarizes the control mechanisms for operation of the future network (2030 and beyond)
proposed by the ongoing EU-funded ELECTRA Integrated Research Programme (IRP) on Smart Grids
. After describing a future grid scenario in compliancewith the European Energy Strategy, the new ELECTRA control scheme is introduced to outline a high-level functional architecture for frequency and voltage control. The future role of resources connected to the distribution network for the provision of ancillary services is formulated and the requirements necessary for the integration of all stakeholders drafted.
[Show abstract][Hide abstract] 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.
No preview · Article · May 2015 · IEEE Transactions on Smart Grid
[Show abstract][Hide abstract] 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.
No preview · Article · May 2015 · IEEE Transactions on Power Systems
[Show abstract][Hide abstract] ABSTRACT: In this paper, a locational marginal pricing algorithm is proposed to control the voltage in unbalanced distribution grids. The increasing amount of photovoltaic (PV) generation installed in the grid may cause the voltage to rise to unacceptable levels during periods of low consumption. With locational prices, the distribution system operator can steer the reactive power consumption and active power curtailment of PV panels to guarantee a safe network operation. Flexible loads also respond to these prices. A distributed gradient algorithm automatically defines the locational prices that avoid voltage problems. Using these locational prices results in a minimum cost for the distribution operator to control the voltage. Locational prices can differ between the three phases in unbalanced grids. This is caused by a higher consumption or production in one of the phases compared to the other phases and provides the opportunity for arbitrage, where power is transferred from a phase with a low price to a phase with a high price. The effect of arbitrage is analyzed. The proposed algorithm is applied to an existing three-phase four-wire radial grid. Several simulations with realistic data are performed.
[Show abstract][Hide abstract] ABSTRACT: Experimental test results of a voltage control mechanism for LV distribution networks are presented in this work. The main goal of the voltage control system is to mitigate over- and under voltages. The control mechanism uses the readily available flexibility of residential smart appliances. The main advantage of the control system is that it does not require a communication network between the different households within the LV network. The control system merely requires communication between the smart appliances within one household, and uses locally available measurements, such as the household supply voltage, e.g. provided by a smart meter. The control system is rolled out in the LINEAR residential demand response pilot for approximately 100 families, from December 2013.
[Show abstract][Hide abstract] 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.
No preview · Article · Nov 2014 · IEEE Transactions on Smart Grid
[Show abstract][Hide abstract] ABSTRACT: The aim of this paper is to investigate the impact of the current ripple, originating from the dc-dc converter of e.g. a PHEV powertrain, on the ageing of Li-ion batteries. Most research concerning batteries focuses on very low (fxHz) to low (Hz) frequencies and low current ripples to create very accurate battery models which can determine e.g. the State of Charge of the battery. On the other hand the design of dc-dc converters tries to reduce the current ripple by using multiple phases with interleaving technique and capacitors in parallel with the battery. The interaction between the current ripple of the dc-dc converter and the battery has received little attention so far. A test set-up is build with two identical 304 V, 12 kWh Li-ion batteries and two 100 A dc-dc converters. The dc-dc converter can be connected to an LCL-filter or solely to the primary inductor of this filter, such that the battery current contains a small or large current ripple respectively. The batteries are discharged and charged to simulate the circumstances in which a plug-in hybrid electric vehicle is used. After each month, during which the battery either experiences a small or large current ripple, characterization tests are performed to establisch the ageing of the batteries. Based on the test results, the current ripple does not appear to have a measurable impact on the battery resistance and the Discharge and Regen Power. There is an increase of the resistance and a decrease of the Discharge and Regen Power, but this is to be expected as the battery packs are submitted to 3 months of Combined Cycle Life Testing. The temperature of the battery turns out to be far more important for the resistance and attained power levels of the batteries. The absent effect of the current ripple on the ageing of the batteries may be due to the intrinsic double-layer capacitor. This capacitor at the surface of the electrodes carries part of the current ripple and reduces the current ripple as experienced by the actual charge transfer reaction which carries the dc-part of the current.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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%.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 %.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
Preview · Article · Dec 2012 · Journal of Communications and Networks
[Show abstract][Hide abstract] 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.
No preview · Article · Dec 2012 · IEEE Transactions on Smart Grid
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
Full-text · Article · Jan 2011 · IEEE Transactions on Industrial Electronics
[Show abstract][Hide abstract] 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.