Mattia Marinelli

The aim of this work is twofold: on one hand it proposes a centralized approach to primary frequency control by using electric vehicles as controllable units; on the other hand, it experimentally validates whether series-produced EVs, adhering to contemporary standards, can be an effective resource for providing primary frequency control. The validation process is realized in an islanded system with renewable sources and it relies on verifying that the frequency values are within the desired… Vis mere

The aim of this work is twofold: on one hand it proposes a centralized approach to primary frequency control by using electric vehicles as controllable units; on the other hand, it experimentally validates whether series-produced EVs, adhering to contemporary standards, can be an effective resource for providing primary frequency control. The validation process is realized in an islanded system with renewable sources and it relies on verifying that the frequency values are within the desired limits following severe load steps or wind power fluctuations.

In order to reflect today’s situation, the used EVs, three Nissan Leaf, are not taking advantage of any V2G capability, but rely solely on the possibility of limiting the charge between 6 A and 16 A. The centralized approach implies that the frequency is not measured locally as it is a common practice today, but is routed via the Internet in order to include potential communication delays that would take into account the presence of different entities for controlling the vehicles, such as aggregators and utilities.

The centralised approach is pursued to support aggregators in participating in current ancillary service markets. Ultimately, this paper aims to strengthen the applied research within EV integration through the practical validation of smart grid concepts on original manufactured equipment. Vis mindre

This paper studies the provision of secondary frequency control in electric power systems based on demand response (DR) activation on thermostatically controlled loads (TCLs) and quantifies the computation resource constraints for the control of large TCL population. Since TCLs are fast responsive loads, they represent a suitable alternative to conventional sources for providing such control. An experimental investigation with domestic fridges representing the TCLs was conducted in an islanded… Vis mere

This paper studies the provision of secondary frequency control in electric power systems based on demand response (DR) activation on thermostatically controlled loads (TCLs) and quantifies the computation resource constraints for the control of large TCL population. Since TCLs are fast responsive loads, they represent a suitable alternative to conventional sources for providing such control. An experimental investigation with domestic fridges representing the TCLs was conducted in an islanded power system to evaluate the secondary frequency control. The investigation quantifies the flexibility of household fridge performance in terms of response time and ramp-up rate, as well as the impact on fridge temperature and behaviour after the control period. The experimental results show that TCLs are fast responsive loads for DR activation, with the average control signal response time of 24 s and an equivalent ramping rate of 63% per minute, which could also comply with the requirements for primary frequency control. Vis mindre

High deployment of electric vehicles (EVs) imposes great challenges for the distribution grids, especially in unbalanced systems with notable voltage variations which detrimentally affect security of supply. On the other hand, with development of Vehicle-to-Grid technology, EVs may be able to provide numerous services for grid support, e.g., voltage control. Implemented electronic equipment will allow them to exchange reactive power for autonomous voltage support without communicating with the… Vis mere

High deployment of electric vehicles (EVs) imposes great challenges for the distribution grids, especially in unbalanced systems with notable voltage variations which detrimentally affect security of supply. On the other hand, with development of Vehicle-to-Grid technology, EVs may be able to provide numerous services for grid support, e.g., voltage control. Implemented electronic equipment will allow them to exchange reactive power for autonomous voltage support without communicating with the distribution system operator or influencing the available active power for primary transportation function. This paper proposes a voltage dependent EV reactive power control and quantifies its impact on a real Danish low-voltage grid. The observed network is a heavily unbalanced three-phase four-wire grid modeled in Matlab SimPowerSystems based on real hourly measurement data. Simulations are performed in order to evaluate phase-to-neutral voltage support benefits as well as to address neutral-to-ground values, active power losses and the unbalances at the same time. The analysis shows that reactive power support both raises minimum phase-to-neutral voltage magnitudes and improves voltage dispersion while the energy losses are not notably increased. Further on, since the control is voltage dependent, provided reactive power is unequal among the phases leading to greater support on heavily loaded phases and decreased unbalances caused by residential consumption. Hence, implementation of such a phase-wise enhanced voltage support could defer the need for grid reinforcement in case of large EV penetration rates, especially in highly unbalanced networks. Vis mindre

This paper describes the application of stochastic grey-box modelling to identify electrical power consumption-to-temperature models of a domestic freezer using experimental measurements. The models are formulated using stochastic differential equations (SDEs), estimated by maximum likelihood estimation (MLE), validated through the model residuals analysis and cross-validated to detect model over-fitting. A nonlinear model based on the reversed Carnot cycle is also presented and included in the… Vis mere

This paper describes the application of stochastic grey-box modelling to identify electrical power consumption-to-temperature models of a domestic freezer using experimental measurements. The models are formulated using stochastic differential equations (SDEs), estimated by maximum likelihood estimation (MLE), validated through the model residuals analysis and cross-validated to detect model over-fitting. A nonlinear model based on the reversed Carnot cycle is also presented and included in the modelling performance analysis. As an application of the models, we apply model predictive control (MPC) to shift the electricity consumption of a freezer in demand response experiments, thereby addressing the model selection problem also from the application point of view and showing in an experimental context the ability of MPC to exploit the freezer as a demand side resource (DSR). Vis mindre

The increasing penetration of fluctuating photovoltaic (PV) generation brings operational challenges for distribution system operators, such as introducing the voltage rise problem. The situation is made worse in the presence of single-phase generation being unevenly connected to the different phases. To address this problem, distribution transformers with single-phase tapping capability, together with reactive power provision of PV systems, are under investigation. This paper presents modeling… Vis mere

The increasing penetration of fluctuating photovoltaic (PV) generation brings operational challenges for distribution system operators, such as introducing the voltage rise problem. The situation is made worse in the presence of single-phase generation being unevenly connected to the different phases. To address this problem, distribution transformers with single-phase tapping capability, together with reactive power provision of PV systems, are under investigation. This paper presents modeling and analysis of the benefits of coordinated voltage control of a decoupled three-phase on-load tap changer (OLTC) and photovoltaic inverters in a distribution system, for accommodating a greater number of photovoltaic generators in the grid. A 24 h root-mean-square simulation study is performed in the DigSilent PowerFactory with a 1 s time step using 10 min resolution consumption and production profiles on a real Danish distribution grid, as well as the developed dynamic photovoltaic generation and load models. The simulations show that the joint action of the power distribution transformer with OLTC control on each phase, and the reactive power provision of photovoltaic inverters, significantly improves the PV hosting capacity in the analyzed unbalanced scenarios without side effects, such as additional power losses, or significant neutral voltage rises. Vis mindre

This paper describes the impacts of different types of DR (demand response) activation on TCLs' (thermostatically controlled loads) aggregated power. The different parties: power system operators, DR service providers (or aggregators) and consumers, have different objectives in relation to DR activation. The outcome of this experimental study quantifies the actual flexibility of household TCLs and the consequence for the different parties with respect to power behaviour. Each DR activation… Vis mere

This paper describes the impacts of different types of DR (demand response) activation on TCLs' (thermostatically controlled loads) aggregated power. The different parties: power system operators, DR service providers (or aggregators) and consumers, have different objectives in relation to DR activation. The outcome of this experimental study quantifies the actual flexibility of household TCLs and the consequence for the different parties with respect to power behaviour. Each DR activation method adopts different scenarios to meet the power reduction, and has different impacts on the parameters. The experiments are conducted with real domestic refrigerators representing TCL. Activating refrigerators for DR with a delay reduces the ISE (integral square error) in power limitation by 28.46%, overshoot by 7.69%. The delay in refrigerator activation causes reduction in power ramp down rate by 39.90%, ramp up rate by 21.30% and the instantaneous average temperature increases by 0.13% in comparison with the scenario without activation delay. Vis mindre

In Denmark, household consumers are supplied with three phase with neutral cable. In addition, the distribution service operator cannot decide to which phase electrical appliance are connected. The technician who realizes the installation connects the loads according to his technical expertise. This may results in heavy imbalances. This paper uses a real Danish distribution system with household consumers, photovoltaic installation and electrical vehicles (EV). In this paper the possibility to… Vis mere

In Denmark, household consumers are supplied with three phase with neutral cable. In addition, the distribution service operator cannot decide to which phase electrical appliance are connected. The technician who realizes the installation connects the loads according to his technical expertise. This may results in heavy imbalances. This paper uses a real Danish distribution system with household consumers, photovoltaic installation and electrical vehicles (EV). In this paper the possibility to use EVs’ charging spots in order to reduce grid’s imbalances will be investigated. Usually, charging stations are equipped with single-phase converters. According to the designed control strategy, the charging spot can select the phase to be used for the charge. The selection is done according to a phase voltage measurement.
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This paper presents the design of a control strategy for the energy management of a grid-connected microgrid with local distributed energy resources as: 10-kW photovoltaic plant, 11-kW wind turbine, and 15-kW–190-kWh vanadium-based electric storage system. According to future regulations, the renewable energy producers will also have to provide a day-ahead hourly production plan. The overall idea is, by knowing the meteorological forecasts for the next 24 h, to dispatch the microgrid in order… Vis mere

This paper presents the design of a control strategy for the energy management of a grid-connected microgrid with local distributed energy resources as: 10-kW photovoltaic plant, 11-kW wind turbine, and 15-kW–190-kWh vanadium-based electric storage system. According to future regulations, the renewable energy producers will also have to provide a day-ahead hourly production plan. The overall idea is, by knowing the meteorological forecasts for the next 24 h, to dispatch the microgrid in order to be able to grant the scheduled hourly production by means of proper management of the storage system. The usage of the storage system is, however, minimized by the energy management strategy. The system design is validated by experimental testing carried out in SYSLAB, a distributed power system test facility at Risø Campus, Technical University of Denmark. Vis mindre

The paper aims at characterizing the electrochemical and thermal parameters of a 15 kW/320 kWh vanadium redox flow battery (VRB) installed in the SYSLAB test facility of the DTU Risø Campus and experimentally validating the proposed dynamic model realized in Matlab-Simulink. The adopted testing procedure consists of analyzing the voltage and current values during a power reference step-response and evaluating the relevant electrochemical parameters such as the internal resistance. The results… Vis mere

The paper aims at characterizing the electrochemical and thermal parameters of a 15 kW/320 kWh vanadium redox flow battery (VRB) installed in the SYSLAB test facility of the DTU Risø Campus and experimentally validating the proposed dynamic model realized in Matlab-Simulink. The adopted testing procedure consists of analyzing the voltage and current values during a power reference step-response and evaluating the relevant electrochemical parameters such as the internal resistance. The results of different tests are presented and used to define the electrical characteristics and the overall efficiency of the battery system. The test procedure has general validity and could also be used for other storage technologies.
The storage model proposed and described is suitable for electrical studies and can represent a general model in terms of validity. Finally, the model simulation outputs are compared with experimental measurements during a discharge–charge sequence. Vis mindre

This paper presents the grey-box modeling of a vapor-compression refrigeration system for residential applications based on maximum likelihood estimation of parameters in stochastic differential equations. Models obtained are useful in the view of controlling refrigerators as flexible consumption units, which operation can be shifted within temperature and operational constraints. Even if the refrigerators are not intended to be used as smart loads, validated models are useful in predicting… Vis mere

This paper presents the grey-box modeling of a vapor-compression refrigeration system for residential applications based on maximum likelihood estimation of parameters in stochastic differential equations. Models obtained are useful in the view of controlling refrigerators as flexible consumption units, which operation can be shifted within temperature and operational constraints. Even if the refrigerators are not intended to be used as smart loads, validated models are useful in predicting units consumption. This information can increase the optimality of the management of other flexible units, such as heat pumps for space heating, in order to smooth the load factor during peak hours, enhance reliability and efficiency in power networks and reduce operational costs. Vis mindre

The paper proposes the modeling and the optimal management of a hot-temperature (sodium nickel chloride) battery system coupled with wind generators connected to a medium voltage grid. A discrete-time model of the storage device reproducing the battery main dynamics (i.e., state of charge,
temperature, current, protection, and limitation systems) has been developed. The model has been validated through some experimental tests. An optimal management strategy has been implemented based on a… Vis mere

The paper proposes the modeling and the optimal management of a hot-temperature (sodium nickel chloride) battery system coupled with wind generators connected to a medium voltage grid. A discrete-time model of the storage device reproducing the battery main dynamics (i.e., state of charge,
temperature, current, protection, and limitation systems) has been developed. The model has been validated through some experimental tests. An optimal management strategy has been implemented based on a forward dynamic programming algorithm, specifically developed to exploit the energy price arbitrage along the optimization time horizon (“generation shifting”). Taking advantage of this strategy wind generation performances can be enhanced and adapted to load demand, obtaining an increased economic gain measured by the difference between the economic revenue obtained with and without the proposed generation shifting policy. Vis mindre

The aim of this thesis is to study and to describe the main dynamics that characterizes a wind farm composed by five full converter wind turbines and two different electrochemical storage technologies and to develop models, in the Matlab-Simulink simulation environment, for implementing integrated control strategies of the whole resulting system in order to evaluate the benefits that storage can provide.

Lo sviluppo del sistema di distribuzione dell’energia elettrica con il forte aumento dei livelli di penetrazione delle sorgenti distribuite di tipo rinnovabile
porta necessariamente ad esaminare e provare nuove strategie di controllo, che opportunamente integrate con sistemi di accumulo, dovrebbero
permettere di gestire al meglio la risorsa energetica complessiva. L’articolo descrive i modelli di sistemi di generazione e di accumulo per la
gestione integrata e il controllo di un parco… Vis mere

Lo sviluppo del sistema di distribuzione dell’energia elettrica con il forte aumento dei livelli di penetrazione delle sorgenti distribuite di tipo rinnovabile
porta necessariamente ad esaminare e provare nuove strategie di controllo, che opportunamente integrate con sistemi di accumulo, dovrebbero
permettere di gestire al meglio la risorsa energetica complessiva. L’articolo descrive i modelli di sistemi di generazione e di accumulo per la
gestione integrata e il controllo di un parco di generazione rinnovabile accoppiato con batterie. Il sistema di accumulo è descritto e caratterizzato sia
dal punto di vista elettrochimico che termico, mentre il parco di generazione da rinnovabile, composto da turbine eoliche, è descritto tramite una
caratterizzazione dinamica. Il sistema di accumulo, accoppiato al sistema di generazione eolica, permette di ridurre o compensare le fluttuazioni della
potenza in uscita dalla generazione eolica e realizzare scambio nullo al nodo di interfaccia. Vis mindre

Questo articolo illustra le caratteristiche di un generatore eolico a velocità variabile equipaggiato con generatore asincrono a doppia alimentazione (DFIG Doubly Fed Induction Generator) e riporta i risultati di simulazioni condotte con il programma di simulazione di sistemi elettrici, DigSilent, su un
aerogeneratore da 850 kW. Nella prima parte si analizzano brevemente le peculiarità del generatore asincrono a doppia alimentazione e le principali equazioni di coppia del sistema… Vis mere

Questo articolo illustra le caratteristiche di un generatore eolico a velocità variabile equipaggiato con generatore asincrono a doppia alimentazione (DFIG Doubly Fed Induction Generator) e riporta i risultati di simulazioni condotte con il programma di simulazione di sistemi elettrici, DigSilent, su un
aerogeneratore da 850 kW. Nella prima parte si analizzano brevemente le peculiarità del generatore asincrono a doppia alimentazione e le principali equazioni di coppia del sistema turbina-generatore. Successivamente si illustra uno dei principali requisiti che i generatori elettrici devono rispettare affinché non creino perturbazioni in rete: l’insensibilità agli abbassamenti di tensione. Lo schema a blocchi che descrive il sistema di controllo della turbina viene approfondito
nel terzo paragrafo (“Schema turbina...“). Il quarto paragrafo (“Risultati delle simulazioni...”) riporta la risposta del sistema di controllo a fronte di variazioni nella velocità del vento e il comportamento della macchina in caso di corto circuito trifase franco ai morsetti del trasformatore di macchina. Vis mindre

The paper is aimed at presenting the dynamic behaviour of a wind turbine equipped with a doubly fed induction generator (DFIG) in case of disturbances in the interconnected grid. A model of a DFIG is presented and adapted for analyzing the response of the wind generator to voltage control, frequency control, voltage sags and wind variations. Simulations, performed by a widely used power system analysis code, are reported and commented.

The massive introduction of plug-in electric vehicles (PEVs) into low voltage (LV) distribution networks will lead to several problems, such as: increase of energy losses, decrease of distribution transformer lifetime, lines and transformer overload issues, voltage drops and unbalances. In this context, this paper proposes a new multi-objective optimization algorithm in order to reduce the mentioned problems. At the same time, users’ interests in terms of charging cost and privacy have been… Vis mere

The massive introduction of plug-in electric vehicles (PEVs) into low voltage (LV) distribution networks will lead to several problems, such as: increase of energy losses, decrease of distribution transformer lifetime, lines and transformer overload issues, voltage drops and unbalances. In this context, this paper proposes a new multi-objective optimization algorithm in order to reduce the mentioned problems. At the same time, users’ interests in terms of charging cost and privacy have been taken into account. The proposed multi-objective optimization is based on minimizing the load variance and charging costs by using the weighted sum method and fuzzy control. The use of vehicle to grid (V2G) concept and load forecast uncertainties have been also considered. Furthermore, an innovative method for mitigating voltage unbalances has been developed. The effectiveness of this methodology has been tested using real data of a LV distribution network, located in Borup (Denmark). Simulation results show that this approach can reduce both energy losses and charging costs as well as it allows a high PEV penetration rates (PEV-PR). Vis mindre