Future Distribution Systems Research Articles

Power Scalable Bi-Directional DC-DC Conversion Solutions for Future Aircraft Applications

With the introduction of the more electric aircraft, there is growing emphasis on improving overall efficiency and thus gravimetric and volumetric power density, as well as smart functionalities and safety of an aircraft. In future on-board power distribution networks, so-called high voltage DC (HVDC, typically +/−270VDC) supplies will be introduced to facilitate distribution and reduce the associated mass and volume, including harness. Future aircraft power distribution systems will also very likely include energy storage devices (probably, batteries) for emergency back up and engine starting. Correspondingly, novel DC-DC conversion solutions are required, which can interface the traditional low voltage (28 V) DC bus with the new 270 V one. Such solutions presently need to cater for a significant degree of flexibility in their power ratings, power transfer capability and number of inputs/outputs. Specifically, multi-port power-scalable bi-directional converters are required. This paper presents the design and testing of such a solution, addressing the use of leading edge wide-band-gap (WBG) solid state technology, especially silicon carbide (SiC), for use as high-frequency switches within the bi-directional converter on the high-voltage side.

Designing a Transactive Framework for Future Distribution Systems

This article introduces a novel transactive energy management mechanism for future distribution systems with private microgrids. A third-party agent based on a transactive energy trading mechanism is designed which provides secure information sharing between participants. The proposed third-part agent acts as an independent economic entity (IEE) and clears the local energy market between the microgrid and distribution system. IEE determines the transactions corresponding to the maximum social welfare based on participants' submitted economic values. The economic values of entities are bids for buying and offers for selling the power. Two different pricing strategies for the approved transactions are presented. Distributed optimization for the self-scheduling based on an alternating direction method of multipliers has been implemented. Distributed optimization in a rolling fashion satisfies equality of complicated voltage magnitude, and voltage angles constraints at the connection buses. Furthermore, the participation of the distribution system in the day-ahead and real-time markets besides the transactive market is studied. The proposed structure is evaluated on a test distribution system with three microgrids in terms of energy trading analysis, and operation scheduling. COMP: Please remove colon appearing after table number in all the table captions.

Impact of battery energy storage, controllable load and network reconfiguration on contemporary distribution network under uncertain environment

The design of future distribution systems involves the application of flexible technologies such as renewable-based distributed generations (DGs), battery energy storage systems (BESSs), demand response for controllable load management and distribution network reconfiguration for achieving assets optimisation and for improving the efficiency of the distribution systems. The renewable-based DGs are the source of uncertainty that can be overcome by the proper modelling of renewable resources and application of energy storage devices. However, the coordination of these flexible technologies is essential to avoid counterproductive results and to extract maximum possible benefits from these technologies. This work, therefore, aims to study the coordinated impact of controllable load with renewable-based DGs, BESSs and network reconfiguration for improving the performance of distribution systems. The coordination of these technologies is a very complex optimisation problem due to various constraints associated with charging and discharging of BESSs, complex nature of controllable load management and feeder current limits of distribution network. In this study, an improved water evaporation optimisation algorithm is developed to solve this multi-constraint complex optimisation problem to minimise the network loss and voltage profile improvement for distribution system. The results show that this coordinated operational problem significantly improves the performance of distribution systems.

Networked Microgrids for Grid Resilience, Robustness, and Efficiency: A Review

Networked microgrids (NMGs) are clusters of microgrids that are physically connected and functionally interoperable. The massive and unprecedented deployment of smart grid technologies, new business models, and involvement of new stakeholders enable NMGs to be a conceptual operation paradigm for future distribution systems. Much work needs to be done, however, to enable NMGs to achieve seamless coordination, including physical, communication, and functional integration. In this paper, we review and summarize the state-of-the-art methodologies for operation and control of NMGs. We also specifically discuss the notion of dynamic boundaries for advanced microgrid applications. In addition, we introduce the opportunities, challenges, and possible solutions regarding NMGs for improving grid resilience, robustness, and efficiency.

Real-Time Control of Plug-in Electric Vehicles for Congestion Management of Radial LV Networks: A Comparison of Implementations

The global proliferation of plug-in electric vehicles (PEVs) poses a major challenge for current and future distribution systems. If uncoordinated, their charging process may cause congestion on both network transformers and feeders, resulting in overheating, deterioration, protection triggering and eventual risk of failure, seriously compromising the stability and reliability of the grid. To mitigate such impacts and increase their hosting capacity in radial distribution systems, the present study compares the levels of effectiveness and performances of three alternative centralized thermal management formulations for a real-time agent-based charge control algorithm that aims to minimize the total impact upon car owners. A linear formulation and a convex formulation of the optimization problem are presented and solved respectively by means of integer linear programming and a genetic algorithm. The obtained results are then compared, in terms of their total impact on the end-users and overall performance, with those of the current heuristic implementation of the algorithm. All implementations were tested using a simulation environment considering multiple vehicle penetration and base load levels, and equipment modeled after commercially available charging stations and vehicles. Results show how faster resolution times are achieved by the heuristic implementation, but no significant differences between formulations exist in terms of network management and end-user impact. Every vehicle reached its maximum charge level while all thermal impacts were mitigated for all considered scenarios. The most demanding scenario showcased over a 30% reduction in the peak load for all thermal variants.

Rethinking buildings. Should buildings simply be enclosures that house different functions?

This document presents BasES, which is a tool kit disseminated as an open educational resource. BasES is focused on the topic of buildings-as-energy services, promoting the knowledge integration to envisage buildings as components of future distributed renewable and interactive energy systems (DRIs). BasES will allow users of exploring and analysing DRIs' emergent properties at the local level, developing, and implementing the tool kit proposed. The specific objective concerns the use of the tool kit in the organisation of a technology support net (TSN) for buildings-as-a-service. TSN is composed of a multitude of actors, who often have different perspectives and scopes, but they are called to work collaboratively in order to establish work rules, requisite skills, work contents, standards and measures, culture and organisational patterns with regard to the emergent systems. Buildings-as-a-service is a completely new topic, and thus, an appropriate TSN is needed urgently. Our tool kit (i.e. Buildings-as-Energy-Services; BasES) will be a ground-breaking cognitive apparatus for involving stakeholders in knowledge transfer and integration processes. Thus, a new generation of product-service systems will be promoted. BasES is expected to configure a multi-stakeholder co-designed UK roadmap on socio-technical innovation in DRIs transition.

Performance Assessment of an Energy Management System for a Home Microgrid with PV Generation

Home energy management systems (HEMS) are a key technology for managing future electricity distribution systems as they can shift household electricity usage away from peak consumption times and can reduce the amount of local generation penetrating into the wider distribution system. In doing this they can also provide significant cost savings to domestic electricity users. This paper studies a HEMS which minimizes the daily energy costs, reduces energy lost to the utility, and improves photovoltaic (PV) self-consumption by controlling a home battery storage system (HBSS). The study assesses factors such as the overnight charging level, forecasting uncertainty, control sample time and tariff policy. Two management strategies have been used to control the HBSS; (1) a HEMS based on a real-time controller (RTC) and (2) a HEMS based on a model predictive controller (MPC). Several methods have been developed for home demand energy forecasting and PV generation forecasting and their impact on the HEMS is assessed. The influence of changing the battery’s capacity and the PV system size on the energy costs and the lost energy are also evaluated. A significant reduction in energy costs and energy lost to the utility can be achieved by combining a suitable overnight charging level, an appropriate sample time, and an accurate forecasting tool. The HEMS has been implemented on an experimental house emulation system to demonstrate it can operate in real-time.

Optimal planning of multi-micro grids based-on networks reliability

Traditional electrical grid as the largest and most complex industry in the world is currently under fundamental development. According to the IEEE Std1547.4, large distribution systems can be clustered into a number of micro-grids (MGs) to facilitate the control and operation infrastructure in future distribution systems. A distribution network with distributed energy resources serving a group of loads, can be operated as a MG, in grid-connected or isolated grid modes. Most recently, the concept of MGs has become an important subject in smart grid area, demanding a systematic method for their optimal planning. The prosperous development of the micro-grid concept implies the definition of an appropriate regulation for its integration on distribution systems. The MG operators are responsible for a reliable energy supply to their consumers. MG formation represents a suitable solution for uninterrupted supplying of critical loads, in the absence of network.In this study, a systematic approach is presented for optimal construction of micro-grid. The problem is solved in two stages. In the first stage, the network is designed as an integrated and active distribution network considering the importance of reliability by using Backward–forward load flow. Next, the distribution network is designed to be divided in to several MGs in order to minimize the cost of electricity generation, improve reliability and voltage profile. In the presented study, stochastic models are considered for representing generation availability related to wind energy and solar energy. The generated power of distributed generation resources such as wind turbines and photovoltaic, have been modeled per hours of the day and the amount of important network parameters are obtained from the results of probabilistic load flow. Practical and important factors such as problem solving space reduction, load controllability, load priority, bus voltage limitation, line capacity limitation and the possibility of forming larger micro-grids by connecting switches between the obtained initial MGs from the first stage are considered in the proposed method.The proposed methodology is implemented for a standard 69-bus distribution system by applying the Imperialist Competitive Algorithm (ICA) in MATLAB software. Results verify the usefulness of the proposed approach in transforming an existing radial distribution network into several autonomous MG.

Load modeling techniques in distribution networks: a review

Power system operation and control required models of generators, lines and loads to be accurately estimated, this is to enable operators make a reliable decision on the system. Generators and lines models are so far considered accurate, while load models are considered perplexing due to invention of new types of loads, distribution system are transforming from passive to active. Future distribution systems are desired to be smart and for a network to be smart the system as to be fully and accurately represented. Penetration of renewable energy and application of power electronic devices as well as participation of active customers in distribution systems make traditional methods of load modeling absolute. Accurate load modeling is required to address the new challenges evolving in the task of power system operation, control and stability studies. It is also an interest of power system researchers globally to realize Smart Networks (SNs), in which accurate load models are required. This work described a review of techniques and approaches for load modeling from traditional methods to the state of art in the area. In addition, gaps in the literature as well as research directions are also pointed out.

Design for independent and self‐adequate microgrids in distribution systems considering optimal allocation of DG units

Introducing the concept of distributed generations (DGs) and local demand supply have led to significant changes in distribution networks. The idea of aggregating loads and DGs in an appropriate way have resulted in microgrids' (MGs) appearance. Considering the economic and environmental concerns, MGs will play important roles in future distribution systems. However, it is necessary to implement an efficient procedure for the optimal design of MGs. This study proposes optimised methods in order to construct a set of independent, self-sufficient MGs in distribution networks. Increasing self-adequacy of constructed MGs is obtained by minimising the power imbalance within them or minimising transferred power between them. The stochastic nature of DGs and consumed loads are also considered. In this regard, optimal allocating and sizing of distributed resources are also studied. In this study, the optimal DG placement is considered with the aim of improving system load factor and decreasing system losses. The presented strategy facilitates controlling strategies of smart distribution systems, such as self-healing, by using virtual MGs in the future distribution systems. The related formulation and solution algorithms are presented in this study. Moreover, the proposed strategy is studied in the PG&E 69-bus distribution system.

Study of the European regulatory framework for smart grid solutions in future distribution systems

Electric distribution systems in Europe are facing significant challenges due to climate change goals, changing market frameworks and technological innovations, which will significantly impact the role of the distribution system operators. The nature and scale of these challenges are strongly driven by the European vision and strategies on climate and energy. This study identifies which policies can become barriers for distribution grid innovation and the implementation of advanced smart grid solutions developed within the UNITED-GRID project. After an extensive review of new policy priority areas within the energy and climate framework and electricity market design, and subsequent discussions with three partner distribution system operators, five priority barriers are identified. The results show that ambitious decarbonisation targets and changing expectations on the distribution system operators’ role in the energy system would require more flexible and efficient network management. However, binding income frameworks, lacking incentives for innovation and regulatory uncertainties hinder modernisation in distribution systems. It can be concluded that these concerns increase the risks for distribution system operators and have to be considered by research projects and developers of smart grid solutions in order to implement and achieve market uptake of the developed solutions within the next 5–10 years.

Multi-agent-based Rolling Optimization Method for Restoration Scheduling of Distribution Systems with Distributed Generation

Resilience against major disasters is the most essential characteristic of future electrical distribution systems (EDSs). A multi-agent-based rolling optimization method for EDS restoration scheduling is proposed in this paper. When a blackout occurs, considering the risk of losing the centralized authority due to the failure of the common core communication network, the available agents after disasters or cyber-attacks identify the communication-connected parts (CCPs) in the EDS with distributed communication. A multi-time interval optimization model is formulated and solved by the agents for the restoration scheduling of a CCP. A rolling optimization process for the entire EDS restoration is proposed. During the scheduling/rescheduling in the rolling process, CCPs in EDS are re-identified and the restoration schedules for CCPs are updated. Through decentralized decision-making and rolling optimization, EDS restoration scheduling can automatically start and periodically update itself, providing an effective solution for EDS restoration scheduling in a blackout event. A modified IEEE 123-bus EDS is utilized to demonstrate the effectiveness of the proposed method.

Advanced FLISR With Intentional Islanding Operations in an ADMS Environment Using GridAPPS-D

An advanced distribution management system (ADMS) is a software platform that supports grid management and decision support applications to address the growing operational challenges faced by power distribution systems to ensure reliable, resilient, and economic operations. In this paper, a fault location, isolation, and restoration (FLISR) application is developed and integrated with an open-source standards-based platform for ADMS application development viz. GridAPPS-D, developed by Pacific Northwest National Laboratory (PNNL). Also, a new distribution system restoration (DSR) algorithm, an integral part of the FLISR application, is proposed that utilizes backup feeders and distributed generators (along with intentional islanding features) to restore critical loads. The proposed application is developed in python and is tested on a modified IEEE 8500-node test system using the GridAPPS-D platform. The successful deployment of the FLISR application on the GridAPPS-D platform provides a proof-of-concept for the adoption of new and advanced ADMS applications to support future power distribution systems.

Multi-layered simulation platform for future worlds distribution system scenarios

With the current distribution system operator (DSO) transition, DSOs are looking for novel cost-effective solutions to manage distribution networks. To avoid operational failures these solutions must be evaluated in a realistic end to end test environment prior to deployment. To meet this requirement Power Network Demonstration Centre (PNDC) is presently developing a platform that integrates solutions for power system analysis, market modelling and real-time simulation. This multi-layered simulation platform will be used to investigate the impact of different DSO operational scenarios (e.g. flexibility procurement, communication interfaces, and vendor-provided solutions). To develop the case study presented in this study aspects of the open networks ‘Future Worlds’ were utilised. The ‘Future Worlds’ were developed by the UK Energy Networks Association and represent potential scenarios for the UK future electricity industry structure. This study presents a case study using the PNDC platform. This case study reflects ‘Future World A’ and simulates an enforced power exchange profile at a grid supply point. In the case study, a controllable demand is simulated in real-time and interfaces with power flow analysis and an optimal flexibility procurement algorithm. The case study demonstrates the capability of the multi-layered platform to manage network limitations by procuring flexibility services within a simulated distribution network.

Towards Plug-and-Play Protection for Meshed Distribution Systems With DG

Future distribution systems are expected to display increased complexity, mainly due to looped/meshed operation, switch between grid-connected and islanded mode and considerable integration of distributed generation. This paper investigates a plug-and-play protection solution for overhead distribution systems with such variable operation conditions, employing existing numerical relay capabilities. This solution is applied by designing plug-and-play, communication-assisted, multifunctional relays with integrated protection element settings, which apply universally to all distribution system conditions, rendering the protection scheme independent of a specific system. Hence, the need for user-defined settings or future revisions due to system changes is eliminated. The scheme ensures coordination between main line relays and backup protection of laterals, without a coordination study. There is no need to replace or modify existing lateral protection means for this purpose; only their known time-overcurrent curves are uploaded to the relays by the user. The scheme is described and evaluated through simulations in two test systems. Meaningful conclusions are finally derived.

Microgrid Optimal Power Flow Using the Generalized Benders Decomposition Approach

The future distribution system is envisioned to be a network of distributed energy resources (DER), being able to operate in both the grid connected and islanded modes. This paper presents an optimal power flow algorithm based on the generalized benders decomposition (GBD) method for scheduling DER and voltage regulation device operations to meet economic and network security objectives. Among the key model features, the proposed algorithm performs multi-interval scheduling studies on the unbalanced distribution system network model with conservation voltage reduction. It is also able to support the microgrid operation in the grid-connected and islanded modes. The GBD-based OPF algorithm has been successfully tested on the IEEE 123-node test feeder model and demonstrated potential for large-scale system applications.

Distribution System Reliability Assessment for Improved Feeder Configurations

This Paper enlightens the significance of the reliability evaluation for an electrical power distribution network using the analytical technique FMEA. The power distribution system is subject to interruptions frequently as a lot of devices are responsible for its effective operation. All the possible failures of each component are considered and the reliability is evaluated in terms of system reliability indices like SAIFI, SAIDI, ENS, and ASAI. FMEA method observes the failure modes of a procedure and reduces it by ranking over its impacts. In this paper, RBTS bus2 distribution network is used for the analysis. The influences of various feeder reconfigurations are considered and the system reliability indices are obtained. The obtained results show that the reliability of the distribution system is enriched with various feeder reconfigurations. Reliability Evaluation helps to design the future Distribution system and its expansion.

Innovative Volt/VAr Control Philosophy for Future Distribution Systems Embedded With Voltage-Regulating Devices and Distributed Renewable Energy Resources

Conventional voltage-regulating devices such as load tap changers, voltage regulators, and local capacitor banks are commonly used for voltage-regulation purposes in medium-voltage distribution systems. Although such devices exhibit excellent capability for Volt/VAr control (VVC) support, fine-tuning of their controller parameters and enactment of Volt/VAr support by renewable distributed generation (DG) units is essential for effective and efficient operation of future distribution systems embedded with wind and solar-Photo-voltaic (PV) units. In this paper, an innovative algorithm is conceptualized for control set-point re-adjustment of different VVC devices for coordinated voltage control in distribution systems. The intended VVC strategy is able to minimize the voltage variations including voltage drop and rise cases mainly caused by power output of renewable DG units that cannot be solved by voltage regulating devices due to their time-delayed operation. Moreover, the control algorithm is proposed to be implemented online using advanced distribution management system for effective voltage control. The simulation studies are carried out using the test distribution system derived from an electricity network in New South Wales, Australia. The simulation results show that voltage regulation can effectively be achieved in renewable rich future distribution systems by applying the proposed tuning algorithm, which has been designed based on a new VVC philosophy.

A Transactive Energy Framework for Coordinated Energy Management of Networked Microgrids With Distributionally Robust Optimization

Networked microgrids (MGs) are considered as an emerging grid design for the future distribution system (DS). The coordination of the networked MGs is critical in order to further enhance the operation efficiency and reliability of the system. In this paper, a transactive energy (TE) framework is proposed for the coordinated energy management of networked MGs in DS. Instead of direct coordination signals and fixed pricing schemes, the distribution network operator (DNO) organizes a transactive market with the MGs to coordinate the energy management in the operation. Further, a distributionally robust optimization (DRO)-based algorithm is developed to provide a robust solution of the detailed scheduling decisions in the proposed TE framework under uncertainty without being too conservative. Case studies with the proposed framework were conducted with the IEEE 33-bus system with three MGs and the IEEE 123-bus system with nine MGs. The results of the case studies show that the proposed TE-based framework can effectively coordinate the energy scheduling of the MGs. The operational cost of the DS is reduced significantly. Meanwhile, the proposed DRO-based algorithm provides a robust but not over-conservative solution for the operation decisions of the DNO and MGs in the proposed framework.

Finite-Element Analysis Modeling of High-Frequency Single-Phase Transformers Enabled by Metal Amorphous Nanocomposites and Calculation of Leakage Inductance for Different Winding Topologies

The solid-state transformer (SST) is an emerging technology which is gaining increasing importance for future power distribution systems. Here, we present 2-D finite-element analysis (FEA) of single-phase SSTs for operating frequencies of 50 kHz. We consider designs to benchmark materials aimed at controlling high-frequency losses to achieve higher power densities. The FEA model is solved in the time domain for frequencies of 50 kHz, at a fixed 800 V input voltage and 10 kW output power for the first four cycles. This paper analyzes the influence of leakage inductance on the waveform with an increasing number of turns and discusses how to calculate the leakage inductance of the different winding topologies by FEA. In addition, transformer topologies are coupled to a power analysis using a Steinmetz parameterization of magnetic losses capturing induction and field scaling for transformer losses for FeNi-based metal amorphous nanocomposites (MANCs) for SST applications and their benchmarking with amorphous and other MANCs and ferrites. Recently, discovered FeNi-based MANCs allow smaller transformers at equivalent power as compared to Si steels, Metglas, and Co-based MANCs. These Fe-rich and non-Co containing MANCs also offer economies based on lower raw materials costs as compared with Co-based MANCs and significantly improved mechanical properties with respect to commercially available Fe-based MANCs.