Active Distribution Network Management Research Articles

Development of an optimization algorithm for the energy management of an industrial Smart User

The growth of world energy demand combined with global warming and climate change is one of the most urgent global challenges and induced policy measures to foster the use of renewable energy sources. In order to cope with the intrinsic variability of solar and wind, active management of distribution networks and customers is required, if the creation of the so called Smart Grid is desired.This paper focuses on the strategies to enable prosumers (i.e. customers able to self-generate all or part of their energy needs) to optimally manage their generation and loads in order to minimize their energy bill and, at the same time, support the distribution grid stability by responding flexibly to its requirements in terms of active load management. In this study an industrial prosumer equipped with solar and wind generation as well as with a co-generation unit with absorption chiller and heat/cold storage was considered. The work presents an optimization algorithm that was developed and applied to this Smart User to manage operations of the CHP in order to optimize the power generation and the usage depending on internal and external inputs as loads, weather forecast and price from the electricity and natural gas market. The proposed algorithm was tested with real experimental inputs of different typical days and its performance was compared with three common scenarios, i.e. traditional supply, electric load following and thermal load following operation of the CHP. Results compare the different control strategies of the CHP (i.e. thermal and electric load following) and shows economic advantages allowed by means of the optimization algorithm, which appears to be an effective instrument to prepare prosumers to the smart grid of the future.

An efficient linear model for optimal day ahead scheduling of CHP units in active distribution networks considering load commitment programs

The Optimal day-ahead Scheduling of Combined Heat and Power (OSCHP) units is a crucial problem in the energy management of Active Distribution Networks (ADNs), especially in the presence of Electrical and Thermal Energy Storages considering Load Commitment (LC) programs. The ADN operator may use Combined Heat and Power (CHP) units to supply its Industrial Customers (ICs) and can transact electricity with the upstream wholesale electricity market. The OSCHP problem is a Mixed Integer Non Linear Programming (MINLP) problem with many variables and constraints. However, the optimal operation of CHP units, Electrical and Thermal Energy Storages considering LC programs and contingency scenarios, may highly complicate this problem. In this paper, linearization techniques are adopted to linearize equations and a two-stage Stochastic Mixed-Integer Linear Programming (SMILP) model is utilized to solve the problem. The first stage models the behavior of operation parameters and minimizes the operation costs, verifies the feasibility of the ICs' requested power exchanges and the second stage considers LC programs and the system's stochastic contingency scenarios. The effectiveness of the proposed algorithm has been demonstrated considering 18-bus, 33-bus and 123-bus IEEE test systems.

On Distributed PV Hosting Capacity Estimation, Sensitivity Study, and Improvement

This paper first studies the estimated distributed photovoltaic (PV) hosting capacities of 17 utility distribution feeders using the Monte Carlo simulation based stochastic analysis, and then analyzes the sensitivity of PV hosting capacity to both feeder and PV system characteristics. Furthermore, an active distribution network management approach is proposed to maximize PV hosting capacity by optimally switching capacitors, adjusting voltage regulator taps, managing controllable branch switches, and controlling smart PV inverters. The approach is formulated as a mixed-integer nonlinear optimization problem and a genetic algorithm is developed to obtain the solution. Multiple simulation cases are studied and the effectiveness of the proposed approach on increasing PV hosting capacity is demonstrated.

Regulatory and market barriers to the realization of demand response in electricity distribution networks: A European perspective

Improving electricity demand response (DR) to support the operation and planning of distribution networks is an essential component of the European Commission strategy to increase economic efficiency in electric power systems across Europe. Due to the lack of the appropriate infrastructure, end consumers have traditionally been blind to wholesale market conditions as well as from the real costs they cause on the network and the power system operation. With the recent deployment of smart metering and communication technologies, provided an appropriate regulatory environment exists, new forms of local DR involving distribution system operators and small consumers could be developed. In a context where many EU Member States are still in the process of opening their retail sectors up to competition and being any active distribution management procedures still to be defined, DR is materializing at a very slow rate. It is the role of regulators to provide a suitable regulatory framework to allow DR to become effective at distribution level. This paper revises the main regulatory barriers that slow down the successful development of demand response mechanisms addressed to small consumers and an active distribution network management across Europe. In order to illustrate this discussion, an overview of six particular national examples is provided: France, Germany, Italy, Spain, Great Britain and Sweden. Finally, recommendations for policy makers and regulators are given.

Unlocking distribution network capacity through real-time thermal rating for high penetration of DGs

Highly stochastic loading in the emerging active distribution networks means that electric utilities need to use their assets to the fullest by deploying intelligent network management tools. Real-time thermal rating (RTTR) provides possibility for short term and even real-time active distribution network management enabling the network to run closer to an overload state without damage. In this study, a RTTR based active distribution network management framework is formulated giving hour-by-hour network capacity limits. Relationships of stochasticities in customer loads and DG output with thermal responses of underground cables, overhead lines and distribution transformers are explained. RTTR is applied on all distribution network components with simulated scenarios involving various levels of DG penetration. This study quantifies the potential for an increased DG utilization and an increased potential for new DG installations when RTTR is integrated with distribution management systems.

A Review of Active Management for Distribution Networks: Current Status and Future Development Trends

Driven by smart distribution technologies, by the widespread use of distributed generation sources, and by the injection of new loads, such as electric vehicles, distribution networks are evolving from passive to active. The integration of distributed generation, including renewable distributed generation changes the power flow of a distribution network from unidirectional to bi-directional. The adoption of electric vehicles makes the management of distribution networks even more challenging. As such, an active network management has to be fulfilled by taking advantage of the emerging techniques of control, monitoring, protection, and communication to assist distribution network operators in an optimal manner. This article presents a short review of recent advancements and identifies emerging technologies and future development trends to support active management of distribution networks.

Chance-Constrained Optimization-Based Unbalanced Optimal Power Flow for Radial Distribution Networks

Optimal power flow (OPF) is an important tool for active management of distribution networks with renewable energy generation (REG). It is better to treat REG as stochastic variables in the distribution network OPF. In addition, distribution networks are unbalanced in nature. Thus, in this paper, a chance constrained optimization-based multiobjective OPF model is formulated to consider the forecast errors of REG in the short-term operation of radial unbalanced distribution networks. In the model, expected total active power losses of distribution lines, expected overload risk and voltage violation risk with respect to N-1 contingencies are minimized, and inequality constraints in the normal state are satisfied with a predefined probability level. Thus, the profitability and security can be balanced in the presence of stochastic REG. The proposed multiobjective OPF problem is solved by the multiobjective group search optimization and the two-point estimate method. Simulation results show that distribution network economy and postcontingency performance deteriorate with increased penetration level of REG, and the penetration level has a greater impact than the forecast errors of REG.

Two-stage approach for optimal dispatch of distributed energy resources in distribution networks considering virtual power plant concept

SUMMARY With increasing levels of distributed generation (DG) penetration, especially variable output ones, new challenges have appeared in electric power systems. The outputs of these generators are variable and determined largely by nature of the power sources such as wind, wave, and sunlight. One solution to decrease problems caused by the variable output of these resources is to aggregate them into a virtual power plant (VPP). The VPP is an energy management system tasked to aggregate the capacity of some DGs, storage facilities, and dispatchable loads (DL) for the purpose of energy trading and/or providing system support services. The economically optimal control of distributed energy resources (DERs) included in the VPP is complicated by uncertainties, nonlinearities, and inter-temporal constraints. Therefore, a novel two-stage dispatch framework is presented here for the integration of the stochastic and the controllable DERs in the distribution network through the VPP concept. The first stage deals with the VPP optimal bidding model (VOBM). A probabilistic price-based unit commitment using point estimate method (PEM) is used in the VOBM to allow the VPP to decide on the unit commitment of its DERs and the optimal bids to the day-ahead market. The second stage deals with active distribution network management. The distribution system operator uses input from the VOBM to manage any local network constraints and to determine the characteristics of the entire local network at the grid supply points, while seeking to minimize the hourly operation cost. The proposed optimization algorithm is applied to an 18-bus system. Copyright © 2012 John Wiley & Sons, Ltd.

Cost-Benefit Analyses of Active Distribution Network Management, Part II: Investment Reduction Analysis

Based on the traditional network expansion planning formulation, a new formulation is built by taking into consideration the curtailment of renewable energy generation (REG), e.g., wind farm generation. The objective is to minimize the total cost of building new circuits and to curtail the output of REG generation. Loss in REG generation curtailment is computed according to its annual output duration curve. In the proposed formulation, operational conditions under peak and trough load levels, the different outputs of REG, and the N-1 security criterion are altogether considered. The whole formulation is solved by Benders' decomposition method. The proposed method is tested on a practical network. Network expansion schemes obtained from the classical and the proposed methods are compared and analyzed. Test results show that network investment can be reduced or deferred by deploying the autonomous regional active network management system (AuRA-NMS). Although some of the wind farm generation is curtailed, the loss is smaller than the reduction of network investment cost. The present work shows the potential of installing an active control system as an alternative of network reinforcement to accommodate increasing REG connections.

Cost-Benefit Analyses of Active Distribution Network Management, Part I: Annual Benefit Analysis

With more and more renewable energy generation (REG) connections, busbar voltage violation and line overloading problems may occur for some parts of a distribution network. However, building new circuits to accommodate REG may have high monetary and environmental costs. This paper considers distribution automation as a supplementary scheme to traditional primary asset investments and analyzes the operational benefits from introducing an autonomous regional active network management system (AuRA-NMS) to a practical distribution system with rich renewable sources. The benefits are quantified in terms of optimal power flow control and investment deferral, and the resulting quantification will inform distribution network operators of the trade-offs between investment in the automation system and in the primary assets, thus helping them to make cost-effective investment decisions. Time-series-based simulation for over an entire year is implemented to calculate the benefits of active power loss and curtailment reductions for AuRA-NMS over the current practice. Part I of this paper illustrates the current schemes for voltage control and constraint management, advanced voltage control and constraint management enabled by the distribution automation, and the annual benefit by introducing the AuRA-NMS to the system with different considerable new DG integrations. Part II analyzes the investment deferral benefit by deploying AuRA-NMS.

A Sequence Frame-Based Distributed Slack Bus Model for Energy Management of Active Distribution Networks

This paper proposes and develops a new distributed slack bus (DSB) model , in the sequence-components frame, for power-flow analysis of an islanded active distribution network (ADN) dominated by electronically coupled distributed energy resource (DER) units. The power-flow analysis distributes the system slack among several participating sources since, unlike the grid-connected systems, the reference bus DER unit is anticipated to have a limited power capacity. The main application of the DSB model is for a fast power-flow analysis of an islanded ADN to enable its real-time energy management and prevent DER capacity violation in between two consecutive optimal power-flow runs. Unlike the existing DSB models, the proposed model incorporates i) the participation of DER units with different control strategies (PQ and PV) in the system real and reactive slack compensation and ii) the DER power capacity limits. Based on a new definition of the “participating sources,” the power-flow equations are augmented to incorporate the system real and reactive power slack as state variables. The proposed DSB formulation is incorporated in a sequence-frame power-flow solver (SFPS). Case studies are conducted to evaluate the impacts of adopting the proposed DSB model in the SFPS tool.

Evaluating maximum wind energy exploitation in active distribution networks

The increased spreading of distributed and renewable generation requires moving towards active management of distribution networks. In order to evaluate maximum wind energy exploitation in active distribution networks, a method based on a multi-period optimal power flow analysis is proposed. Active network management schemes such as coordinated voltage control, energy curtailment and power factor control are integrated in the method in order to investigate their impacts on the maximisation of wind energy exploitation. Some case studies, using real data from a Danish distribution system, confirmed the effectiveness of the proposed method in evaluating the optimal applications of active management schemes to increase wind energy harvesting without costly network reinforcement for the connection of wind generation.

Future development of the electricity systems with distributed generation

Electrical power systems have been traditionally designed taking energy from high-voltage levels, and distributing it to lower voltage level networks. There are large generation units connected to transmission networks. But in the future there will be a large number of small generators connected to the distribution networks. Efficient integration of this distributed generation requires network innovations. A development of active distribution network management, from centralised to more distributed system management, is needed. Information, communication, and control infrastructures will be needed with increasing complexity of system management. Some innovative concepts such as microgrids and virtual utilities will be presented.

Assessment of Switched Communication Network Availability for State Estimation of Distribution Networks With Generation

Active management of complex distribution networks with distributed generation requires state estimation. As complete supervisory control and data acquisition systems are seldom available on 11-kV or lower voltage distribution networks, real-time measurements at remote points on 11-kV distribution networks are expensive. Therefore, the economical selection of a communication system for active management of distribution networks with distributed generation becomes an important issue. This paper presents the investigations into a leased communication system made of public-switched communication network channels for a distribution network state estimation application. It analyzes the effects of a different number of primary channels for real-time measurements on the distribution network state estimation accuracy. The leased communication system availability performance has also been analyzed and used to identify a number of reserve channels required to improve the leased system availability. The overall cost for improving the leased communication system availability has been calculated and compared with both a fiber-optic communication system and a power-line carrier communication system. The results show that the leased communication system is able to provide the lowest overall cost performance for the distribution network state estimation application.

Integrating distributed generation into electric power systems: A review of drivers, challenges and opportunities

It is now more than a decade since distributed generation (DG) began to excite major interest amongst electric power system planners and operators, energy policy makers and regulators as well as developers. This paper presents an overview of the key issues concerning the integration of distributed generation into electric power systems that are of most interest today. The main drivers behind the focus on DG integration, especially of the renewable type, in many countries around the world are discussed. A synopsis of the main challenges that must be overcome in the process is presented. Particular emphasis is placed on the need to move away from the fit and forget approach of connecting DG to electric power systems to a policy of integrating DG into power system planning and operation through active management of distribution networks and application of other novel concepts. The paper also analyses the repercussions in transmission system operation and expansion that result from the connection of large amounts of DG of different energy conversion systems focusing on issues related with impacts in steady state operation, contingency analysis, protection coordination as well as dynamic behaviour analysis. A discussion on the possibility of provision of ancillary services by DG is also included. Some results from studies performed in the interconnected Portuguese transmission system are presented and discussed. Some of the opportunities that could be exploited in support of the integration and hence greater penetration of DG into electric power systems are also explored.