Future Distribution Grids Research Articles

Concepts, Configurations, and Challenges of Solid-State Transformer: A Review

Abstract: Rapid and suddenly increasing use of small distributed renewable energy resources (DRER) and distributed energy storage (DES), reduced compact dynamic electrical power consumer-like electrical vehicle loads, the requirement of bidirectional power flow communication network to exchange critical information, other ancillary services, etc. has to be envisaged and fulfilled by a future smart distribution grid system. A solid-state transformer (SST) has more potential solutions to provide stable and efficient distribution system operation to overcome the above problem.From various designs of converter control schemes, the solid-state transformer concept has been evaluated and summarised. The benefits and downsides of converters in the AC/DC, DC/DC, and DC/AC stages are studied for the best configuration. The High Frequency Transformer(HFT) is a main part of SST.The design and optimization of a HFT is approached on the objective of minimising the weight and size of the SST.Researchers also face several challanges in the prototype design and implementation of SST before operating effectively in the distribution system which is presented . Some of expected solutions and future recommendations for the establishment of the solid state transformer for future smart electrical distribution systems are discussed.

Providing Distributed Flexibility for Curative Transmission System Operation Using a Scalable Robust Optimization Approach

Managing flexibility across transmission and distribution system boundaries unlocks degrees of freedom for efficient system operation. It is attractive to use this freedom for curative transmission system operation, i.e., an operation that reliably reestablishes safe states after contingencies while enabling higher grid utilization in the normal state. However, the computational complexity of coordinating the fast-growing number of renewables becomes challenging. For this reason, we develop a fast and robust optimization approach to calculate flexibility potentials of individual assets and aggregated flexibility potentials across the grid interconnections. The proposed method guarantees that the flexibility-providing grid always remains in a safe state while providing maximum flexibility. The method is successfully tested on a real European sub-transmission system. As part of a future distribution grid control function, the method can be used to provide flexibility to transmission system operation and provide the necessary aggregation methods to handle thousands of distributed assets.

Operationally-Safe Peer-to-Peer Energy Trading in Distribution Grids: A Game-Theoretic Market-Clearing Mechanism

In future distribution grids, prosumers (i.e., energy consumers with storage and/or production capabilities) will trade energy with each other and with the main grid. To ensure an efficient and safe operation of energy trading, in this paper, we formulate a peer-to-peer energy market of prosumers as a generalized aggregative game, in which a network operator is only responsible for the operational constraints of the system. We design a distributed market-clearing mechanism with convergence guarantee to an economically-efficient and operationally-safe configuration (i.e., a variational generalized Nash equilibrium). Numerical studies on the IEEE 37-bus testcase show the scalability of the proposed approach and suggest that active participation in the market is beneficial for both prosumers and the network operator.

Editorial for the Special Issue on Active Control and Protection of Future Renewables-dominated Distribution Grid

Editorial for the Special Issue on Active Control and Protection of Future Renewables-dominated Distribution Grid

Editorial: Advanced Technologies for Modeling, Optimization and Control of the Future Distribution Grid

Editorial: Advanced Technologies for Modeling, Optimization and Control of the Future Distribution Grid

Guest editorial: Future distribution grids and integrated energy systems (IES)

Guest editorial: Future distribution grids and integrated energy systems (IES)

Implementation and Test of an IEC 61850-Based Automation Framework for the Automated Data Model Integration of DES (ADMID) into DSO SCADA

As a result of the energy transition, an increasing number of Decentralized Energy Systems (DES) will be installed in the distribution grid in the future. Accordingly, new methods to systematically integrate the growing DES in distribution power systems must be developed utilizing the constantly evolving Information and Communication Technologies (ICT). This paper proposes the Automated Data Model Integration of DES (ADMID) approach for the integration of DES into the ICT environment of the Distribution System Operator (DSO). The proposed ADMID utilizes the data model structure defined by the standard-series IEC 61850 and has been implemented as a Python package. The presented two Use Cases focus on the Supervisory Control and Data Acquisition (SCADA) on the DSO operational level following a four-stage test procedure, while this approach has enormous potential for advanced DSO applications. The test results obtained during simulation or real-time communication to field devices indicate that the utilization of IEC 61850-compliant data models is eligible for the proposed automation approach, and the implemented framework can be a considerable solution for the system integration in future distribution grids with a high share of DES. As a proof-of-concept study, the proposed ADMID approach requires additional development with a focus on the harmonization with the Common Information Model (CIM), which could significantly improve its functional interoperability and help it reach a higher Technology Readiness Level (TRL).

Characterization of Supraharmonic Emission from Three Different Electric Vehicle Charging Infrastructures in Time and Frequency Domain

With the recent proliferation of electric vehicles (EVs), maintaining power quality within acceptable limits in future distribution grids will become a challenging task. A specific concern is the spread of Supraharmonics in the range from 2 to 150 kHz, generated by modern power electronic devices. In this paper, the long term Supraharmonic distortion from three differently sized electric vehicle charging infrastructures is analyzed in frequency and time domain. At the monitored sites several interruptions of EV charging processes were observed due to poor power quality. It was found that vehicles disconnect when exposed to high levels of harmonic distortion. Moreover, the impact of the charging EVs on the Supraharmonic distortion and the interaction with the background distortion for the individual sites is discussed. Results show that a general increase in Supraharmonics emission can be expected due to the rising number of EVs. However, measurements also indicate that damping effects can occur for certain load configurations.

Reactive Power Markets: A Review

Liberalization of the energy system sets the way towards market-based solutions for ancillary service provision. Local reactive power markets are envisioned to achieve more economically and technically efficient reactive power provision to solve voltage control problems in future distribution and transmission grids. However, market-based reactive power procurement is a difficult and yet unsolved problem. This survey provides a comprehensive overview of the characteristics and hardships of reactive power markets. That is followed by a literature overview of reactive power market design, including local markets and markets on system operator level. Further, methods how to analyse reactive power markets are discussed, focusing on market power, game theoretical approaches, Reinforcement Learning, and manipulation of reactive power markets. From this overview, trends and current research gaps are derived and some general research recommendations are given to serve as a guideline for future research in the field of reactive power markets.

Operational concerns and solutions in smart electricity distribution systems

Interfacing high penetration of Renewable Energy Sources (RES) with energy storage and microgrid control systems is an essential feature of future distribution grids for optimal utilization and management of Distributed Energy Resources (DERs). This feature allows distributed system operators to follow the right path to transform their traditional grids into smart grids. With the continued expansion of DERs, the current distribution grid is moving toward a carbon-free electricity system and greener energy-transportation applications. However, there are some practical concerns as well as technical and operational challenges in an interconnected power network. Therefore, this paper reviews the most prominent issues associated with smart grid, such as large-scale distributed generation integration, energy storage, energy trading, operational planning, service reliability, and cyber resiliency, in light of recent technological advancements. Through reviewing several emerging technologies, this study shows the necessary methodologies for establishing smart energy distribution. Finally, this study highlights future research prospects for a fully functional smart grid system.

Fault-Ride-Through Approach for Grid-Tied Smart Transformers without Local Energy Storage

The Smart Transformer (ST) is being envisioned as the possible backbone of future distribution grids given the enhanced controllability it provides. Moreover, the ST offers DC-link connectivity, making it an attractive solution for the deployment of hybrid AC/DC distribution grids which offer important advantages for the deployment of Renewable Energy Sources, Energy Storage Systems (ESSs) and Electric Vehicles. However, compared to traditional low-frequency magnetic transformers, the ST is inherently more vulnerable to fault disturbances which may force the ST to disconnect in order to protect its power electronic converters, posing important challenges to the hybrid AC/DC grid connected to it. This paper proposes a Fault-Ride-Through (FRT) strategy suited for grid-tied ST with no locally available ESS, which exploits a dump-load and the sensitivity of the hybrid AC/DC distribution grid’s power to voltage and frequency to provide enhanced control to the ST in order to handle AC-side voltage sags. The proposed FRT strategy can exploit all the hybrid AC/DC distribution grid (including the MV DC sub-network) and existing controllable DER resources, providing FRT against balanced and unbalanced faults in the upstream AC grid. The proposed strategy is demonstrated in this paper through computational simulation.

Experimental Validation and Deployment of Observability Applications for Monitoring of Low-Voltage Distribution Grids.

Future distribution grids will be subjected to fluctuations in voltages and power flows due to the presence of renewable sources with intermittent power generation. The advanced smart metering infrastructure (AMI) enables the distribution system operators (DSOs) to measure and analyze electrical quantities such as voltages, currents and power at each customer connection point. Various smart grid applications can make use of the AMI data either in offline or close to real-time mode to assess the grid voltage conditions and estimate losses in the lines/cables. The outputs of these applications can enable DSOs to take corrective action and make a proper plan for grid upgrades. In this paper, the process of development and deployment of applications for improving the observability of distributions grids is described, which consists of the novel deployment framework that encompasses the proposition of data collection, communication to the servers, data storage, and data visualization. This paper discussed the development of two observability applications for grid monitoring and loss calculation, their validation in a laboratory setup, and their field deployment. A representative distribution grid in Denmark is chosen for the study using an OPAL-RT real-time simulator. The results of the experimental studies show that the proposed applications have high accuracy in estimating grid voltage magnitudes and active energy losses. Further, the field deployment of the applications prove that DSOs can gain insightful information about their grids and use them for planning purposes.

Formal specification and verification of fault location, isolation and service restoration of local topology model based on distributed processing for active distribution network

Active distribution network (ADN) technology, as an important trend of the future smart distribution grid, is able to effectively absorb distributed energy resource (DER), to reasonably optimise grid-load operation characteristics, and to safely support the reliability of power supply. Through enhancing energy utilisation efficiency and friendly interaction with user access, ADN technology is also able to comprehensively improve the power supply reliability of the distribution network. However, distributed feeder automation (FA), as an important part of ADN technology, will also meet new problems and challenges with the access of DER in the distribution network. The formal method can analyse the correctness and effectiveness of a distributed fault processing algorithm from mathematical logic, which provides an important theoretical basis for distributed fault processing. The focus herein is on the formal description and verification of topology modelling in fault location, isolation, and service restoration (FLISR) based on distributed processing. By abstracting and simplifying the complex power system features, the adaptability of the formal method is solved. The logical correctness of the topology model in FLISR based on distributed processing is verified. Finally, the distributed local topology model and algorithm is verified through a formal method using an actual ADN example.

Optimal Sizing and Energy Management of Microgrids with Vehicle-to-Grid Technology: A Critical Review and Future Trends

The topic of microgrids (MGs) is a fast-growing and very promising field of research in terms of energy production quality, pollution reduction and sustainable development. Moreover, MGs are, above all, designed to considerably improve the autonomy, sustainability, and reliability of future electrical distribution grid. At the same time, aspects of MGs energy management, taking into consideration distribution generation systems, energy storage devices, electric vehicles, and consumption components have been widely investigated. Besides, grid architectures including DC, AC, or hybrid power generation systems, energy dispatching problems modelling, operating modes (islanded or grid connected), MGs sizing, simulations and problems solving optimization approaches, and other aspects, have been raised as topics of great interest for both electrical and computer sciences research communities. Furthermore, the United Nations Framework Convention on Climate Change and government policies and incentives have paved the way to massive electric vehicle (EV) deployment. Hence, several research studies have been conducted to investigate the integration of EVs in national power grid and future MGs. Specifically, EV charging stations’ bi-directional power flow control and energy management have been considerably explored. These issues index challenging research topics, which are in most cases still under progress. This paper gives an overview of MGs technology advancement in recent decades, taking into consideration distributed energy generation (DER), energy storage systems (ESS), EVs, and loads. It reviews the main MGs architecture, operating modes, sizing and energy management systems (EMS) and EVs integration.

Comprehensive Benefit/Cost Analysis of Utilizing PEV Parking Lots as Virtual Energy Storage for the Energy Supply Sustainability of Future Distribution Systems

The proliferation of plug-in electric vehicles has led to increased public charging infrastructure in cities worldwide. Grid-connected parking lot spaces are the most common charging option due to their technological readiness and convenience of adoption. Since the batteries aggregated by parking lots can be regarded as virtual energy storage, grid-connected parking lots are expected to provide many benefits to the urban distribution grid. This paper proposes a comprehensive methodological framework to evaluate the potential benefits and costs of utilizing grid-connected parking lot infrastructures to promote energy supply sustainability in future power distribution grids. Capacity-value-based and cost-effectiveness indexes are developed, which quantify the potential contribution of parking lots to power supply reliability and the associated economic implications. To realistically describe the available generation capacity of parking lot resources, a comprehensive model is presented, which explicitly considers the impact of external stimuli (incentive rates) on the behavioral patterns of lot users. Vehicle user responsiveness to incentive grades is derived from social field surveys. To conduct the evaluation, a hybrid algorithm based on Monte Carlo simulations is employed. The proposed methodology is illustrated on a real distribution grid in Beijing. The results confirm the effectiveness of our proposed approach and support practical policy suggestions.

Short-Term Electric Load Forecasting With Sparse Coding Methods

Short-term load forecasting is a key task for planning and stability of the current and future distribution grid, as it can significantly contribute to the management of energy market for ancillary services. In this paper we introduce the beneficial properties of applications of sparse representation and corresponding dictionary learning to the net load forecasting problem on a substation level. In this context, sparse representation theory can provide parsimonial predictive models, which become attractive mainly due to their ability to successfully model the input space in a self-learning manner, by interacting between theory, algorithms, and applications. Several techniques are implemented, incorporating numerous dictionary learning and sparse decomposition algorithms, and a hierarchical structured model is proposed. The concept of sparsity in each case is embedded throughout the utilization of different regularization forms which include the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tree</sup> norms. The observed superiority of the proposed theory, especially the one which embeds the atoms and corresponding coefficients in a tree structure, stems from the construction of the dictionary so as to represent efficiently the ambient electricity signal space and the consequent extraction of sparse basis-vectors. The performance of each model is evaluated using real hourly load measurements from a high voltage/medium voltage (HV/MV) substation and compared with that of widely used machine learning methods. The provided analytical results, verify the effectiveness of hierarchical sparse representation in short-term load forecasting applications, in terms of common accuracy indices.

Modelling End-User Behavior and Behavioral Change in Smart Grids. An Application of the Model of Frame Selection

This paper presents an agent-based model (ABM) for residential end-users, which is part of a larger, interdisciplinary co-simulation framework that helps to investigate the performance of future power distribution grids (i.e., smart grid scenarios). Different modes of governance (strong, soft and self-organization) as well as end-users’ heterogeneous behavior represent key influential factors. Feedback was implemented as a measure to foster grid-beneficial behavior, which encompasses a range of monetary and non-monetary incentives (e.g., via social comparison). The model of frame selection (MFS) serves as theoretical background for modelling end-users’ decision-making. Additionally, we conducted an online survey to ground the end-user sub-model on empirical data. Despite these empirical and theoretical foundations, the model presented should be viewed as a conceptual framework, which requires further data collection. Using an example scenario, representing a lowly populated residential area (167 households) with a high share of photovoltaic systems (30%), different modes of governance were compared with regard to their suitability for improving system stability (measured in cumulated load). Both soft and strong control were able to decrease overall fluctuations as well as the mean cumulated load (by approx. 10%, based on weekly observation). However, we argue that soft control could be sufficient and more societally desirable.

Flexible scheduling of reconfigurable microgrid-based distribution networks considering demand response program

In future smart distribution grids, the number of microgrids can be increased within the network. In this paper, the optimal reconfiguration of microgrid-based distribution networks is modeled by considering demand response program to enhance the network scheduling flexibility. According to the proposed method, the optimal configuration of distribution network is determined to meet the best scheduling goals. Furthermore, the optimal state of interconnecting switches between microgrids and the main grid is determined as well. The optimal topology of microgrid-based distribution networks is given for each hour of operation, using optimal power flow. The results are obtained with and without demand response program that are applied to each microgrid. Different load profiles such as residential, industrial, commercial and official are considered and manipulated with suitable demand response programs. For better observation, various cases are investigated separately to meet the different goals considered by the distribution network operator. In the presented paper, the optimization aims to minimize total system operation cost and losses with optimal networked-microgrid reconfiguration. The effects of demand response programs are shown in the results of optimal topology of microgrids. To show the effectiveness of the presented approach, IEEE 85-bus modified test system is employed.

Activating current and future flexibility potential in the distribution grid through local energy markets

Increasing shares of volatile generation and additional peak demand through electric vehicles and heat–pumps challenge the stable operation of current and especially future distribution grids. In order to cope with these challenges, several approaches to reduce peak feed-in and demand are possible. For example, the curtailment of renewable generation or peak loads or the activation of demand-side flexibility through, e.g., time of use tariffs. Local energy markets (LEMs) are a promising alternative concept to combine various of these measures and activate untapped flexibility potential of the demand- and generation-side as well as storages. In this study, the authors propose a linear optimisation-based market mechanism that can explicitly consider demand, generation and storage flexibility in the form of flexibility orders. Through the simulation of a LEM in a rural region of Germany with a high share of renewable feed-in, they demonstrate the effects of the proposed LEM for the current situation and a future scenario with additional load through electric vehicles and heat pumps. The results show that, compared to a business as usual case, the LEM can provide both peak-shaving of PV feed-in during midday and a significant reduction of evening demand peaks of up to 23%.

Guest Editorial Theory and Application of PMUs in Power Distribution Systems

Operational practices of power distribution systems are impacted by the increasing connection of renewable energy resources, electric vehicles, energy storage systems and deployment of demand-response mechanisms. The synchronized, low-latency, and high-resolution measurements that are provided by distribution-level phasor measurement units (D-PMUs) can enable the better operation of power distribution systems. However, data availability is only a necessary step to build an enhanced operational intelligence that is required by the future distribution grid. Data must be furnished with useful analytics to translate said data into actionable information.