Transmission System Operators Research Articles

Opening of Ancillary Service Markets to Distributed Energy Resources: A Review

Electric power systems are moving toward more decentralized models, where energy generation is performed by small and distributed power plants, often from renewables. With the gradual phase out from fossil fuels, however, Distribution Energy Resources (DERs) are expected to take over in the provision of all regulation services required to operate the grid. To this purpose, the opening of national Ancillary Service Markets (ASMs) to DERs is considered an essential passage. In order to allow this transition to happen, current opportunities and barriers to market participation of DERs must be clearly identified. In this work, a comprehensive review is provided of the state-of-the-art of research on DER integration into ASMs. The topic at hand is analyzed from different perspectives. First, the current situation and main trends regarding the reformation processes of national ASMs are analyzed to get a clear picture of the evolutions expected and adjustment required in the future, according to the scientific community. Then, the focus is moved to the strategies to be adopted by aggregators for the effective control and coordination of DERs, exploring the challenges posed by the uncertainties affecting the problem. Coordination schemes between transmission and distribution system operators, and the implications on the grid infrastructure operation and planning, are also investigated. Finally, the review deepens the control capabilities required for DER technologies to perform the needed control actions.

Energy Hub Gas: A Modular Setup for the Evaluation of Local Flexibility and Renewable Energy Carriers Provision

The ambitious targets for the reduction of Greenhouse Gas (GHG) emissions force the enhanced integration and installation of Renewable Energy Sources (RESs). Furthermore, the increased reliance of multiple sectors on electrical energy additionally challenges the electricity grid with high volatility from the demand side. In order to keep the transmission system operation stable and secure, the present approach adds local flexibility into the distribution system using the modular Energy Hub Gas (EHG) concept. For this concept, two different test cases are configured and evaluated. The two configured EHGs demonstrate the ability to provide flexibility and adaptability by reducing the difference between maximal and minimal load in the surrounding grid infrastructure by 30% in certain time periods. Furthermore, the average energy exchange is reduced by 8%. Therefore, by relieving the grid infrastructure in the local surroundings, the additional potential of RES is enabled and the curtailment of existing ones can be reduced.

CURRENT STATE AND WAYS OF RECOVERY OF UKRAINE'S ECONOMY

The article reviews the main consequences of a full-scale military invasion and the impact on the main results of Ukrainian industry in the short and long term. It has been established that the industries that provide the basic needs of the population (produce food, clothing, or shoes) are best preserved and/or restored. It has been proven that the full-scale military aggression emphasized the weak points of the Ukrainian economy. It was established that the first few months of the full-scale invasion of Ukraine were accompanied by a fuel crisis, which set the government and business leaders the task of setting up fuel logistics from scratch. This circumstance also reduced the pace of recovery of the country's economy. Based on the processing of statistical data, it is proven that military actions led to a 32% drop in Ukraine's GDP in 2022, caused the devaluation of the hryvnia, and caused a decline in industrial production and consumer sentiment. The deterioration of the situation in the economy was also contributed by the shortage of electricity. The national electricity transmission operator was forced to apply restrictions on electricity consumption in the country. After each successive strike, the situation worsened, and after the missile strikes in November, there was a short but total blackout. It was the power outages that worsened business sentiment and led to revisions in macroeconomic forecasts. It was established that in several industries (production of building materials, metallurgy and metalworking, chemical industry and mechanical engineering) a critical drop in production is recorded. Even in the woodworking industry, which is mainly concentrated in the west and north of the country, only 35% of enterprises are operating at almost full capacity. The data confirm that entire industries have quickly become hostages of war, with supply chains disrupted, seaborne export routes blocked, and demand reduced. It has been proven that to successfully restore the country's economy, restore export opportunities and withstand competition on world markets, to stand up in the struggle for sales markets for its products, Ukraine needs to: increase the efficiency of the economy, which is based on the development of market relations; comprehensively increase the export orientation of foreign economic activity; ensure the transition to settlements with foreign partners in freely convertible currency; to improve the concept of development of export-import operations.

Development and Validation of a Load Flow Based Scheme for Optimum Placing and Quantifying of Distributed Generation for Alleviation of Congestion in Interconnected Power Systems

The energy supply entities widely adopt distributed generators (DG) to meet the additional power requirement due to scheduled or unscheduled interruptions. The expansion of transmission and distribution systems via the inclusion of loads and generators and the occurrence of line interruptions are significant causes of congestion of transmission lines in interconnected systems. The management and alleviation of congested lines is a primary requirement for a power system network’s reliable and efficient operation. The researchers investigated the potential scope of distributed generation (DG) to alleviate the congested branches in interconnected transmission systems. The development of a reliable scheme to arrive at the best location and size of local generators for alleviating congestion deserves considerable importance. This paper attempted to develop a simple and reliable strategy for the optimum placement and sizing of DGs to be integrated with a transmission line system of DGs for congestion relief in transmission lines by analyzing power flow solutions. This research work considered the 14-bus system of IEEE for the preliminary analysis to identify the parameters employed for assessing the severity of line congestion and the best placement and sizing of DGs for congestion relief. This work analyzed power flows by load flow algorithms using ETAP software in the 14-bus IEEE system for different line outage cases. The analysis of power flow solutions of the 14-bus system of IEEE revealed that the percentage violation of the system can be regarded as an essential parameter to assess the extent of congestion in an interconnected system. A detailed power flow analysis of the system with various capacities of DG integration at several buses in the system revealed the application of two indices, namely the index of severity (SI) and sensitivity factor (SF), for optimum placement with the best capacity of DGs for congestion alleviation in the system. This work proposed a reliable algorithm for the best siting and sizing of DGs for congestion relief by using the identified indices. The proposed methodology is system indices allied load flow-based algorithm. This work produced a fast simulation solution without any mismatch through this developed scheme. The approximations linked with the algorithm were very minute, resulting in comprehensive bests instead of inexact limited bests with less simulation time and more convergence probability and availing the benefits of the mathematical approach. The work investigated the feasibility of the proposed methodology for optimum placing and quantifying DGs for congestion solutions for a practical interconnected bus system in the supply entity of the Kerala grid with many buses. Any transmission system operator can adopt this method in similar connected systems anywhere. The proposed algorithm determined the most severe cases of congestion and the optimum site and size of DGs for managing congested feeders in the grid system. The analysis of the losses in the system for different cases of DG penetration by load flow analysis validated the suitability of the obtained results.

A novel vibration-based prognostic scheme for gear health management in surface wear progression of the intelligent manufacturing system

Gearbox has a compact structure, a stable transmission capability, and high transmission efficiency. Thus, it is widely applied and used as a critical transmission system in intelligent manufacturing systems, such as machine tools and robotics. The gearbox usually operates in harsh and non-stationary working environments, making the gear surface prone to wear. The progression of gear surface wear may lead to severe gear failures, such as gear tooth breakage and root crack, potentially damaging the whole gear transmission system. Therefore, it is essential to assess the gear surface wear progression and predict its remaining useful life (RUL) in order to ensure the reliable operation of the gear transmission system. To this end, this paper developed a novel gear wear prognostic scheme based on vibration analysis for gear health management. More specifically, a novel health indicator (HI) is first developed for gear wear monitoring in the proposed prognostic scheme. The novel HI, inferred from the cyclic correntropy and Wasserstein distance (WD), can accurately reflect the wear-induced cyclic correntropy spectra distribution change over time. Therefore, the novel HI can robustly evaluate the gear wear severity with high accuracy. With the developed HI, a network, namely the optimized gated recurrent unit (GRU), is applied for predicting the gear transmission system RUL during surface wear progression. As for the optimized GRU network, the genetic algorithm (GA) is applied to find the optimal hyperparameters adaptively, which can significantly improve the practicality of the developed prognostic scheme. To conclude, the developed prognostic scheme can effectively reveal the gear wear propagation characteristics and predict the RUL accurately. A series of endurance tests are conducted to verify the effectiveness of the developed prognostic scheme for gear health management in surface wear progression.

Spillovers of underground gas storage facilities and their role in the sustainable energy markets: assessment and policy recommendations

PurposeThe purpose of this study is to investigate the impact of the construction and operation of underground gas storage (UGS) facilities, under the prism of the recent rise in energy prices. The focus is on developing energy markets interconnected with gas producers through pipelines and has access to liquefied natural gas (LNG) facilities in parallel.Design/methodology/approachThrough a focal market in Europe, the authors estimate the economic value for both stakeholders and consumers by introducing a methodology, appropriately adjusted to the specificities of the domestic energy market. The Transmission System Operator, the Energy Market Regulator, the Energy Exchange and Eurostat are the main data sources for our calculations and conclusions.FindingsThe authors investigate the perspectives of UGS facilities, identifying financial challenges considering specific energy market conditions which are barriers to new storage facilities. Nevertheless, the energy price rocketing coupled with the security of gas supply issues, which arose in autumn 2021 and were continuing in 2022 due to the Russia–Ukraine crisis, highlight that gas storage remains, at least for the midterm, at the core of European priorities.Originality/valueThe paper emphasizes on developing markets toward green transition, proposing tangible policy recommendations regarding gas storage. A new methodological approach is proposed, appropriate to quantify the economic value of UGSs in such markets. Last, a mix of energy policy options is suggested which include regulatory reforms, support schemes and new energy infrastructures that could make the gas storage investments economically viable.

Electrical energy systems resilience: A comprehensive review on definitions, challenges, enhancements and future proceedings

AbstractSecure energy providing is a critical feature of sustainable societies, where this subject requires reliable operation of generation, transmission and distribution infrastructures. In order to achieve the mentioned goal, the influence of uncertainties should be analyzed using appropriate methods, criteria and tools. The high‐impact low‐probability (HILP) events are special uncertainties that can affect the safe operation and lead to irreparable damages. This paper presents a comprehensive review of resilience in electrical energy systems consisting of fundamental concepts and definitions, challenges, enhancements and future proceedings. In this regard, a resilience evaluation framework is designed first in which all the necessary actions for a resilience study are defined. In the next step, various HILP events are introduced and then the resilience concept is defined accurately and related curves are investigated. Afterwards, the resilience assessment indices and quantitative measures are described and their details and applications are precisely explained. As well, the resilience enhancement strategies are discussed from short‐term and long‐term perspectives and eventually, resilience‐based objective functions and optimization approaches are classified in the last part. It is noteworthy that the main research gaps are also clarified according to the reviewed papers and further suggestions are expressed to cope with the declared problems.

Effective RNN-Based Forecasting Methodology Design for Improving Short-Term Power Load Forecasts: Application to Large-Scale Power-Grid Time Series

This article introduces a carefully-engineered forecasting methodology for day-ahead electric power load forecasts evaluated using the European Network of Transmission System Operators for Electricity (ENTSO-E). Two steps were employed to configure the desired forecasting methodology: First, a straightforward processing pipeline is proposed to enable systematic preprocessing of raw multivariate time-discrete power data extracted from the ENTSO-E repository, including a stride-based sliding window approach to generate time series-based batches ready for the supervised learning procedure. Second, the lightweight type of recurrent neural network method, namely gated recurrent units (GRU), is selected and carefully calibrated to yield accurate multi-step forecasts, which was trained using the preprocessed multivariate time series data to render day-ahead power load forecasts. The forecasting estimates generated by the proposed GRU model are evaluated using a set of regression-based metrics to assess the models’ precisions. The empirical results show that the proposed forecasting methodology yields outstanding day-ahead power load forecasting performance regarding the enterprise-class measured data compared to a statistical model, namely autoregressive integrated moving average with exogenous variables (ARIMAX), as well as the actual day-ahead forecasts generated by the ENTSO-E platform.

Four Speed Auto Transmission DC-DC Converter Control for E-Vehicle and Regenerative Braking Based on Simulation and Model Investigation

A novel single input multioutput (SIMO) output DC-DC converter with circular capacitors is intended to function with a single independent source to create numerous transmissions to regulate the speed at the same switching intervals. A novel single input multi output (SIMO) output DC-DC converter employing circular capacitors is designed to work with a single independent source to create numerous transmissions. The proposed converter generates 7 outputs in total, with 4 outputs generated simultaneously for forward operation (speed transmission) using the preferred source (fuel cell/battery) and 3 other different outputs used for regenerative transmissions, with the battery being the preferred storage device. This converter can control the speed of an electric vehicle (EV) by using the SIMO is output voltage to regulate the vehicle is speed, allowing for higher accelerations and decelerations with minimal energy loss and degradation of the main battery pack. It can also be used to power electronic components such as LED lights, audio systems, and mobile charging etc. The energy recovered during regenerative braking is used to charge the battery via a buck/boost operation for varied speed transmission. In addition, simulation, modelling, and analysis are used to validate the proposed system. It is intended for a fixed voltage of 12 V and output voltages ranging from 12 to 48 V. The PSIM simulation tool is used to validate the system. The validation demonstrates the suggested converter is good evidence in both braking and regenerative braking operations.

Guest Editorial Special Section on Real-World Challenges of TSO-DSO Coordination

The papers in this special section focus on the coordination of transmission system operators (TSO)-distributed system operators (DSO). Policy directives and technological innovations have fostered the emergence of a hierarchical market structure, which consists of centralized and decentralized markets. It is envisioned that energy resources will be free to participate in all market structures at the same time to extract the maximum value to the grid and monetize their services. Under this market architecture, grid operators can procure energy services from assets connected both at transmission and at distribution level in a coordinated way. This structure requires an efficient network management and optimization, also for the benefit of Distributed Energy Resources (DERs) in the transition to a decarbonized economy. The same pool of resources may be used by TSOs and DSOs, so actions by both can mutually affect each other.

On the Coordination of Transmission-Distribution Grids: A Dynamic Feasible Region Method

Recently, the turnover of energy services between transmission-distribution grids has continued to increase, arousing widespread attention to the efficient coordination between transmission system operator (TSO) and distribution system operator (DSO). The existing literature has characterized the feasible region of distribution networks via equivalent projection methods, which is conducive to the participation of DSO in TSO scheduling. However, the redundant constraints of DSO and the processing of temporal-coupled constraints remain challenging in realistic cases. To achieve an effective interaction between TSO and DSO with least information, we develop a TSO-DSO coordination framework with temporal-coupled constraints embedded, i.e., the concept of dynamic feasible region (DFR). We theoretically derive the polyhedral form of a DFR, which can be characterized as a constraint set formed by the extreme points of the dual space of the DSO optimization program. A novel outer progressive approximation (OPA)-based algorithm is designed to effectively add feasibility cuts until convergence is achieved. To reduce the redundant constraints in the DSO operation model, the enhanced umbrella constraint identification (E-UCI) method is employed. Case studies based on i) a real-world distribution grid in China and IEEE 30-bus system, ii) a Caracas 141-bus distribution network and IEEE 118-bus transmission grid are adopted to validate the effectiveness and computational efficiency of our proposed method.

MILP Model for Optimal Day-Ahead PDS Scheduling Considering TSO-DSO Interconnection Power Flow Commitment Under Uncertainty

We propose a comprehensive framework for the optimal day-ahead scheduling of power distribution systems (PDS), based on a mixed-integer linear programming (MILP) model. The interaction between transmission system operator (TSO) and distribution system operator (DSO) is considered, where TSO informs DSO of the day-ahead forecast concerning the expected power flow (PF) commitment at the TSO-DSO interconnection points and the violation costs. We propose a MILP model to determine the optimal voltage and power settings of distributed energy resources (DERs), such as dispatchable distributed generators and energy storage units and optimal adjustments of capacitor banks controlled by current. The objective function includes the minimization of energy losses, voltage violations, power curtailment of DERs using volt-watt strategy, and violation of TSO-DSO interconnection PF commitment. Furthermore, we propose a method to estimate the degree of uncertainty in the PF commitment. Therefore, the proposed method can help achieve an optimal operation of the distribution system; in addition, the TSO can best model uncertainty at TSO-DSO interface points and thereby procure reduced amounts of resources to address these uncertainties. Numerical results obtained for a system based on real data highlight the several potential applications of the proposed framework.

Transactive Energy Market Operation Through Coordinated TSO-DSOs-DERs Interactions

This paper proposes a new decentralized transactive energy (TE) market strategy integrating wholesale and local energy markets through coordinated interactions between transmission system operator (TSO), distribution system operators (DSOs), and distributed energy resource (DER) owners. The overall market-clearing problem is formulated as an optimization problem with coupling variables between different market levels, decomposed into three sub-problems for each of them to solve for locational marginal prices (LMPs), distribution LMPs, and local dispatch commands, respectively, based on the optimal output of upper level utilizing the Alternating Direction Method of Multipliers (ADMM) algorithms in a decentralized manner. The effectiveness of the proposed approach is validated through software simulations by realizing it in interconnected transmission and distribution networks.

Exploiting DERs’ Flexibility Provision in Distribution and Transmission Systems Interface

This paper presents a new market-based framework to exploit distributed energy resources’ (DERs) flexibility in distribution and transmission systems. This framework targets intra-hourly flexibility requirements of energy systems. In this regard, a local market is operated in distribution network to exploit DERs’ capabilities. Local market is cleared in coordination with wholesale market to optimize DERs’ flexibility procurement for meeting intra-hourly variability and uncertainty in distribution and transmission systems. In the proposed framework, a technical virtual power plant (TVPP) operates day-ahead (DA) local energy and flexibility markets in which DER aggregators take part. Furthermore, the TVPP participates in DA wholesale energy and flexibility markets which are cleared by the market operator and the transmission system operator, respectively. In this framework, all agents’ preferences and their transactions are addressed using a bilevel model with multiple lower levels. The proposed model is reformulated into a mixed integer linear programming problem by utilizing strong duality theory, Karush-Kuhn-Tucker optimality conditions and primal-dual counterpart. The model is implemented on an IEEE standard test system. The results demonstrate effectiveness of the framework in utilizing DERs’ capabilities to meet flexibility requirements as well as satisfying agents’ preferences.

A fuzzy logic control of a smart home with energy storage providing active and reactive power flexibility services

There is a need for enhanced flexibility to allow the high penetration of intermittent renewable power into the power system. In this way, transmission system operators (TSO) need more flexible energy resources that help to control the power system frequency by using balancing services. Distribution system operators (DSO) also seek new flexible energy resources that can counteract stochasticity, control voltage level, and manage congestions in distribution networks. Smart homes located in distribution networks are potential resources. Hence, this paper considers a smart home with flexible appliances and devices, including a battery energy storage system (BESS) interfaced with an inverter, an air conditioner (AC), and an electric vehicle (EV). The smart home aims to provide the system operators with coordinated frequency and DSO-level services while respecting the thermal comfort and schedules of the household residence. The inverter-interfaced BESS not only provides active power support for TSO and DSO, but it also injects and consumes reactive power if the DSO needs local flexibility. Fuzzy logic control system is deployed to obtain this goal. In the simulation section, a smart home with flexible appliances is scheduled. Different operations and the economic outcomes are discussed for the smart home considering real-world data.

Real-Time Estimation of Support Provision Capability for Poor-Observable Distribution Networks

An indispensable step towards coordinating the actions of distribution and transmission system operators ( <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dso</small> s- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tso</small> ) is to estimate the range of flexibility that can be offered to the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tso</small> by <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dso</small> s. Within this context, a data-driven probabilistic approach is proposed to evaluate the capability of a distribution network in providing active and reactive power support in real-time. To this end, in an offline phase, a linear discriminant analysis model, together with a piecewise linear model of the distribution network are trained to delineate the boundary of a region representing the adherence to distribution network operational constraints. In the implementation phase, this region comprises the feasible set of a series of optimization problems, formulated to determine the support provision capability. These optimization problems are of iterative linear programming type, which allows for real-time applicability. The evaluated support capability can be deemed as the available reserve in real-time transmission operation, which enables providing a coordinated response towards unexpected events, and facilitates the participation of distributed resources in the balancing market by granting an up-to-date estimation of available supports. This approach is tested on the IEEE 123-node system and verified through comparison with an AC optimal power flow technique.

ICT Architectures for TSO-DSO Coordination and Data Exchange: A European Perspective

The coordination between system operators is a key element for the decarbonization of the power system. Over the past few years, many EU-funded research projects have addressed the challenges of Transmission System Operators (TSO) and Distribution System Operators (DSO) coordination by implementing different data exchange architectures. This paper presents a review of the ICT architectures implemented for the main coordination schemes demonstrated in such projects. The main used technologies are analyzed, considering the type of data exchanged and the communication link. Finally, the paper presents the different gaps and challenges on TSO-DSO coordination related to ICT architectures that must still be faced, paying especial attention to the expected contribution of the EU-funded OneNet project on this topic.

Pricing for TSO-DSO Coordination: A Decentralized Incentive Compatible Approach

High-penetration of distributed energy resources (DERs) requires the coordinated operation of transmission and distribution systems. Different from most conventional studies, this work regards the distribution system operators (DSOs) as rational individuals, whose profit-seeking behaviors may be in conflict with the dispatch decisions of the transmission system operator (TSO). To bridge this gap, this paper proposes a market-based TSO-DSO coordination approach. Firstly, the structure and clearing process of the proposed pricing mechanism is proposed. Then, based on the individual rationality analysis, the incentive incompatibility of wholesale electricity market with the participation of DSOs is proved. Thus, uplift payments are required to incentivize the DSOs to follow the dispatch decisions of TSO. To minimize the total uplift payments in the electricity market, a transmission-and-distribution incentive compatible pricing (T&D-ICP) mechanism is proposed. Further, to preserve the individual privacy, a decentralized T&D-ICP model is reformulated and iteratively solved based on the relaxed based bi-level reformulation and decomposition (RBRD) algorithm. In the iterative process, strict privacy preservation is achieved. Comparisons of T&D-ICP with locational marginal pricing (LMP) and convex hull pricing (CHP) are conducted on T30D0, T30D2, T30D9 and T118D30 test systems. The simulation results validate the high computation efficiency, strict privacy preservation, and limited burden on the communication of the proposed T&D-ICP mechanism.

Research on digital twin technology of large-scale offshore wind power flexible direct transmission system

With the rapid development of wind power technology, offshore wind power transmission technology has gradually matured. Combined with the first large-scale offshore wind power flexible DC transmission system in China, this paper builds a digital twin system that is close to the actual system. The article first introduces the origin and definition of digital win technology and gives the five-dimensional model of the digital twin. Then, it focuses on the technical realization of the offshore wind power digital twin system, including the five-dimensional model of the offshore wind power digital twin system. The key technologies in the advanced application of the twin system - real-time simulation technology and 3D holographic visual display technology are introduced, and their effects are shown. The realization of the digital twin technology of the large-scale offshore wind power flexible DC transmission system provides more valuable information for the operation, management, scheduling, and decision-making of the offshore wind power flexible direct transmission system.

Study on the correction method of the influence of temperature factor in the simulation calculation of transformer bias current

For analyzing the mechanism of single-polar earth operation of the HVDC transmission system arousing the DC bias of the transformer and correcting the influence of temperature factors on simulation, abstract grids were built. Based on the disciplinarian of ambient temperature affecting the DC resistivity of conductors and shallow soil, the mechanism of the ambient temperature taking effect on the DC bias current of the transformer was discussed. Applying the practical field measurement results, conclusions from the simulation and calculation were proved, and the method of classification correction was present. It was indicated that the modified calculation results of the transformer DC bias current would be closer to the actual measurement values.