Pedro M S Carvalho

University of Lisbon | UL · Department of Electrical and Computer Engineering

The transition towards the smart grid requires better information on the electrical networks at the distribution system level. Information about electrical line parameters is a critical part of such information. An algorithm for estimating electric line parameters of medium‐voltage distribution networks is proposed. The algorithm relies upon active...

Demand Response (DR) has been proposed and implemented in recent years to enable the participation of active consumers in energy management. However, existing programs do not consider the characteristics and opportunities introduced by electric vehicles (EVs). EVs have more flexibility than traditional loads and can be used as battery energy storag...

This paper presents an application of a novel quadratic unconstrained binary optimization (QUBO) formulation to the minimum loss problem in distribution networks. The proposed QUBO formulation was conceived to be employed in quantum annealing—a quantum computing paradigm useful for solving combinatorial optimization problems. Quantum annealing is e...

Structured Abstract Purpose This study is a targeted review of some of the major changes in European regulation that guided energy policy decisions in the Iberian Peninsula and how they may have aggravated the problem of lack of flexibility. This study aims to assess some of the proposed short-term solutions to address this issue considering the u...

Due to the intermittent and variable nature of wind, Wind Power Generation Forecast (WPGF) has become an essential task for power system operators who are looking for reliable wind penetration into the electric grid. Since there is a need to forecast wind power generation accurately, the main contribution of this paper is the development, implement...

Smart grid operations require accurate information on network topology and electrical equipment parameters. This paper proposes estimating such information with data from the smart grid. Assuming that the availability of bus voltage data is restricted to their magnitude, a linear model of the relationship between these data and the parameters of th...

This paper first reviews today’s hierarchical control and highlights modelling and control assumptions which may no longer hold in the changing electric energy systems. To overcome this fundamental problem, we conceptualise electric energy systems as complex dynamical systems using physically intuitive multi-layered energy modelling as the basis fo...

With more and more micro-generation being connected to the low-voltage network, it becomes increasingly difficult for operators to anticipate the loading condition of their networks. Several facts concur with such difficulty, one being the frequent lack of knowledge about the generation component of the measured net load. The generation component i...

New electronic devices such as soft open points (SOPs) are posing new challenges to distribution system operators, imposing serious difficulties to the state estimation (SE) process of weakly monitored grids. This paper proposes to overcome such difficulties with a new SOP modeling approach, where the device operational principles are encapsulated...

Energy transition, leading to the electrification of energy consumption, results in new challenges for DSOs, often requiring upgrading existing networks and improving the management of existing assets. To improve asset management capabilities, E-REDES developed a risk assessment methodology aiming at obtaining a quantitative risk assessment of the...

In this paper, particle-hopping cellular automaton (CA) models of elastic demand are used to investigate the value added to plug-in electric vehicles (PEV) aggregators by adopting vehicle-to-grid (V2G) responsive services. CA models used earlier to study load-sifting responses are modified to capture discharge/ recharge capabilities of V2G. Results...

We introduce a novel quadratic unconstrained binary optimization (QUBO) formulation for a classical problem in electrical engineering – the optimal reconfiguration of distribution grids. For a given graph representing the grid infrastructure and known nodal loads, the problem consists in finding the spanning tree that minimizes the total link ohmic...

We propose to conceptualise electric energy systems as complex dynamical systems using physically intuitive multilayered energy modelling as the basis for systematic diverse technology integration, and control in on-line operations. It is shown that such modelling exhibits unique structure which comes from the conservation of instantaneous power (P...

We introduce a novel quadratic unconstrained binary optimization (QUBO) formulation for a classical problem in electrical engineering -- the optimal reconfiguration of distribution grids. For a given graph representing the grid infrastructure and known nodal loads, the problem consists in finding the spanning tree that minimizes the total link ohmi...

The role of the private sector is essential in providing energy access to all by 2030. However, private investors often face the decision problem of deciding where to implement off-grid projects. This selection process can be considered a multifactorial task because it requires accounting not only for local conditions, technical constraints, and ec...

Investment decision making in the energy sector is a complex process due to the inherent long-term uncertainty. This work investigates the importance of representing a wide range of economic and physical sources of uncertainty in the modelling of the electricity market, both for investment decision making and descriptive market modelling. The resul...

The dissemination of low-carbon technologies, such as urban photovoltaic distributed generation, imposes new challenges to the operation of distribution grids. Distributed generation may introduce significant net-load asymmetries between feeders in the course of the day, resulting in higher losses. The dynamic reconfiguration of the grid could miti...

Driven by environmental policy making, electro-mobility has become a crucial tool to mitigate the transport induced CO2 emissions and is being subsidized by Governments, creating more incentives for end users to adapt it. This article addresses the extensive e-mobility transition’s influence on the wholesale electricity market in Lithuania. The ana...

The Government of Bolivia (GoB) aims to provide electricity coverage for all citizens by 2025. This implies reaching remote areas, where electricity access rates are currently below 90% (as of 2018). To achieve this objective, the country has implemented several initiatives, such as the “Living with Dignity” program (PEVD) launched in 2008 to promo...

Demand flexibility and its responsiveness under price-based control is a major research field. Much attention has been paid to model demand elasticity as synonymous with demand flexibility. But demand flexibility comes mostly as load shifting, and load shifting dynamics have been neglected when modelling demand response. In this paper, we model loa...

This paper presents a mixed integer linear programming (MILP) approach to deal with the volatility associated with loads and distributed energy resources (DER) in low observability distribution networks. Distribution networks, characterized by having many buses and few meters, have recently faced massive integration of DER, whose injection increase...

Policy makers are tasked with selecting, designing, and implementing policies to support the transition to a sustainable power system. As part of the task, they often turn to models to quantify and compare the options available to them. In this work, we investigate the importance of the approach to representing long-term uncertainty in the modellin...

In this paper, previous theory and results regarding Low-Voltage (LV) distribution losses are validated through power-flow simulation using real load data with standard metering resolution. The validated results are then used to build a generalized loss prediction model for arbitrary grid topologies and metering resolutions. The paper provides the...

Wind power production is uncertain. The imbalance between committed and delivered energy in pool markets leads to the increase of system costs, which must be incurred by defaulting producers, thereby decreasing their revenues. To avoid this situation, wind producers can submit their bids together with hydro resources. Then the mismatches between th...

Decision makers rely on models to make important regulatory, policy, and investment decisions. For power systems, these models must capture (i) the future challenges introduced by the integration of large quantities of variable renewable energy sources and (ii) the role that energy storage technologies should play. In this paper, we explore several...

Future smart grid operations must rely upon accurate state estimation (SE). Estimation at the distribution level is very challenging since the customary monitoring infrastructure inhibits access to real-time widespread information, precluding redundancy. To overcome the lack of redundancy, we propose to use Markov information on load dynamics inste...

The hosting capacity approach is presented as a planning, improving, and communication tool for electrical distribution systems operating under specific uncertainties, such as power quality issues, power stabilities, and reliability, among others. In other words, it is an important technique, when renewable sources are present, to answer the amount...

This paper analyses the impact of substantial changes in energy production driven by self-supply associated with photovoltaic (PV) adoption, regarding the tariff rates payed by adopters and non-adopters and the revenues yielded by regulated tariffs. Three different regulatory design options are analysed with a model developed to estimate the evolut...

EDP Distribuição is developing initiatives aimed at adapting to new realities and technologies, taking advantage of the continued technological investments being made in AMI. In this context, specific data analytics methodologies were developed to characterize the stochasticity of real data from measured load profiles and to adapt planning tools to...

In this paper, end-use storage loads with elasticity constrained by a time window are modelled by a particle hopping cellular automaton. The automaton model is introduced and parameterized to obtain results on ideal load-shifting response. Simulation is used to analyse the intrinsic limitations of load-shifting ramping capabilities. New concepts ar...

This paper investigates the impact of the combined effects of load variability and phase imbalance onto simulated low-voltage grid losses. The paper proposes new indices for relative load time-variability and phase-imbalance. With those indices, linear mappings are derived for the relative losses caused by a single three-phase load when modeled as...

This chapter presents a hybrid methodology based on a local search algorithm and a genetic algorithm, used to address the multi-objective and multistage optimal distribution expansion planning problem. The methodology is conceived to solve optimal network investment problems under the new possibilities enabled by the smart grid, namely the new obse...

Wind generation in Portugal and Spain has grown due to a decrease in technology cost and the availability of renewables electricity generation incentives. There is a strong interconnection between Spain's and Portugal's transmission systems, resulting in common prices in both countries. However, Portuguese and Spanish producers receive the incentiv...

This paper introduces a brief analysis on hosting capacity and related concepts as applied to distribution network systems. Furthermore, it addresses the applicability of hosting capacity study methodologies to harmonic voltage distortion caused by photovoltaic panels (PV) connected at a low-voltage (LV) side of a university campus grid. The analys...

This paper introduces a brief analysis on hosting capacity and related concepts as applied to distribution network systems. Furthermore, it addresses the applicability of hosting capacity study methodologies to harmonic voltage distortion caused by photovoltaic panels (PV) connected at a low-voltage (LV) side of a university campus grid. The analys...

In this paper optimal grid design problems are revisited in view of the ongoing transformations in distribution systems. The transformations are those caused by distributed generation, changes in load use, and smart grid operation. These transformations have an expressive impact on the way planning must be carried out. Trends on grid design are adv...

Electricity grids are facing significant challenges with new energy sources starting to be integrated into grids on a large scale. Distributed generation, changes in load use, and smart grid operation have each caused transformations in grid design. This monograph revisits optimal grid design problems in view of these ongoing transformations in dis...

This research analyses the impacts of substantial changes in energy production driven by self-supply through Photovoltaic (PV) adoption. Three different regulatory design options are analysed with a model developed to estimate the evolution of self-supply deployment as a function of price by: (i) starting with the actual tariff structure and parame...

In this paper we detail the method used to build a set of LV typical grids, which are able to capture the variability of assets and operating conditions in order to assess the non-linear impact of distributed generation on losses. Based on simulations carried out over such typical networks, the impact of PV distributed generation on LV grid losses...

Renewable energy support policies of renewable generation have driven a substantial growth of wind generation in Portugal and Spain. Renewable energy support policies in Portugal include a guarantee for the energy produced to be sold above the market price – a feed-in tariff –, which is supported by end-user customers. Portuguese and Spanish elect...

This paper proposes a new method to generate synthetic load and generation profiles that can be customized to simulate different groups of consumers or energy production technologies. The method relies upon generic individual profiles and specific aggregate profiles to set up a discrete-time non-stationary Markov process that realistically reproduc...

As low-voltage distribution grids and microgrids emerge, their decentralized control design is a major issue and needs rethinking, as several recent examples of oscillatory behavior in voltage and reactive power have been reported. This paper analyzes a few possible reasons for these oscillations. Oscillations can occur as a result of connecting di...

This document describes the implementation details and the results of the four test beds proposed by the DSOs in the previous deliverables of WP5. After reporting the results obtained from the field tests and simulations, a critical analysis is carried out in order to determine the advantages and disadvantages of each operational method as well as...

This paper proposes a risk analysis methodology to complement the traditional economical evaluation of investment projects in electrical grids. The methodology is meant to quantify the risk of projects at a given confidence level with minimum additional effort from the planning engineer. This requires a specific scenario generation approach to repr...

This paper proposes a risk analysis methodology to complement the traditional economical evaluation of investment projects in distribution networks, and proposes a method to assess the overall investment projects portfolio risk. The first methodology is meant to quantify the risk of projects at a given confidence level with minimum additional evalu...

The paper addresses the problem of determining the maximum distributed energy resource (DER) capacity that can be connected to low-voltage (LV) networks without creating voltage-rise problems. That maximum capacity depends on the network characteristics and on the candidate sites for DER connection. When sites are multiple and LV networks are poorl...

This paper aims to bring new insight into the topic of congestion management, make its solution more efficient and reliable and change it into a more grid-like management approach in the context of smart grids. A novel approach is proposed to manage higher-level grid congestions by demand side management (DSM) together with lower-level grid reconfi...

Deliverable (D) No: 4.2 Report on new methods to maximize integration of EV and DER in distribution grids (methods for optimization under uncertainty, for storage modelling and for statistical behaviour of EV and DER)

Wind forecasts are an important tool for electric system operators. Proper use of wind power forecasts to make operating decisions must account for the uncertainty associated with the forecast. Data from different regions in the USA with forecasts made by different vendors show the forecast error distribution is strongly dependent on the forecast l...

During the past two decades, utilities have saved tremendous capital investments in new transformers by improving utilization of existing transformers in distribution systems. Meanwhile, in these highly-utilized systems, deteriorated reliability has been observed at the end-user level. This is mainly because utilities determine transformer utilizat...

Day-ahead load and wind power forecasts provide useful information for operational decision making, but they are imperfect and forecast errors must be offset with operational reserves and balancing of (real time) energy. Procurement of these reserves is of great operational and financial importance in integrating large-scale wind power. We present...

This paper concerns transforming today's operations and asset management in large-scale distribution grids into efficient and reliable grid management. Particular emphasis is on dynamic monitoring and decision systems (DYMONDS) embedded into system users, distribution network and operators of distribution, sub-transmission and transmission systems,...

In this chapter, we study the impact of different-sized wind parks on Flores and São Miguel power systems and estimate the ideal number of wind turbines for both islands. If the number of wind turbines is over the ideal, the energy produced might not be injected into the grid, with all the costs associated with that. To estimate the wind energy ava...

Due to the increasing environmental concerns, recently there has been much interest in integrating Distributed Generation (DG) into distribution systems. Despite providing extra sources of both power and voltage support, DG in distribution systems, which conventionally are not designed for the connection of generators, may lead to problematic volta...

Due to the recent increase in environmental concerns, there has been interest in integrating Distributed Generation (DG) into distribution systems. Keeping the voltage of a DG-integrated system within the range of pre-defined standards has been a major challenge. For this reason, interaction of DG and feeders' steady state voltage has been widely s...

The integration of distributed energy resources (DER) in low-voltage networks is expected to increase significantly in the next few years. It is known that the large-scale integration of DER in conventional low-voltage (LV) networks poses many challenges such as voltage rise. To mitigate voltage rise caused by DER, utilities are defining simple vol...

During the past two decades, utilities have increased transformer's utilization by about 30% in North American power distribution systems. High utilization levels, for transformers in particular, make utility companies more financially efficient, and this is potentially beneficial to both stockholders and customers. However, reduced customer servic...

A reconfigurable network can change its topology by opening and closing switches on power lines. We use real wind, solar, load, and cost data and a model of a reconfigurable distribution grid to show that reconfiguration allows a grid operator to reduce operational losses as well as to accept more intermittent renewable generation than a static con...

We investigate the economic viability of coupling a wind farm with compressed air energy storage (CAES) to participate in the day-ahead electricity market at a time when renewable portfolio standards are not binding and wind competes freely in the marketplace. In our model, the CAES is used to reduce the risk of committing uncertain quantities of w...

The number of electric vehicles (EV) and microgeneration units connected to LV grids are expected to increase significantly during the present decade. Both EV and microgeneration units have an impact on the operational conditions of LV grids – namely concerning power flows and voltage profile – that, in some cases, will force the DNO (Distribution...

Emergency reconfiguration can improve distribution systems' reliability by enabling load transfer among substations. Previous studies, although present its operation strategies, seldom explore emergency reconfiguration's effects on distribution system planning. This paper explores how reconfiguration affects planning decisions and what benefits rec...

In this paper we illustrate PV single inverter response to voltage rise in LV networks and simulate multiple PV cascading that may result from inverter's response. We then address potential solutions to mitigate the drawbacks of simplistic control approaches, such as reinforcing the network, shifting supply phases, and implementing enhanced control...

This paper addresses the problem of large scale low voltage distribution network planning. The focus is on the interaction between probabilistic approach and the recently available metering hourly profile data, and how such interaction enables a better planning. This is especially important to be able to plan for large-scale integration of distribu...

In the framework of the so-called microgeneration, small photovoltaic units are being installed in the roofs of the buildings and connected to the low-voltage distribution networks. This is posing some new challenges to the distribution network operators. On one hand, the off-service regulation of the transformer taps must comply with a hard twofol...

The present paper discusses a Methodology and Practice developed to tackle the problem of Voltage Harmonic Distortion in MV Bus Bars of HV/MV Substations. In the last few years, EDP Distribuição (EDPD) has been developing harmonic analysis models for simulation of voltage distortion for different network topologies in different load and reactive co...

This paper surveys major technical challenges for power system operations in support of large-scale wind energy integration. The fundamental difficulties of integrating wind power arise from its high inter-temporal variation and limited predictability. The impact of wind power integration is manifested in, but not limited to, scheduling, frequency...

The concept of self-healing has been recently introduced in power systems. The general self-healing framework is complex and includes several aspects of networks’ operation. This paper deals with automated switching in the context of autonomous operation of distribution networks. The paper presents a new network data model that allows effective rec...

Electric power distribution networks are large-scale infrastructures that need to be planned regularly and operated continuously. The planning and operation tasks involve difficult decision-making processes that can be formulated as optimization problems: large-scale combinatorial optimization problems. These problems have been addressed successful...

This paper addresses the subject matter of harmonic analysis in MV and HV distribution networks. EDP has been developing harmonic analysis models for simulation of voltage distortion for different topologies in different load and reactive compensation conditions. The corresponding tools will help planners and operators guarantee voltage quality to...

This paper addresses the problem of probabilistic assessment of large scale low voltage distribution networks. The focus is on network safety, security and efficiency. The paper shows that probabilistic assessment of large scale networks is necessary and possible. Necessary, because of the leading role of LV networks in electrical energy distributi...