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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "F: Electrical Engineering".

Deadline for manuscript submissions: closed (30 April 2021) | Viewed by 43632

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Prof. Ilhan Kocar

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Electrical Engineering, Ecole Polytechnique de Montreal, 5596 Montreal, Quebec PQ H3T 1J4, Canada

Special Issue Information

Dear Colleague,

We are inviting submissions to a Special Issue of Energies on the subject of "Electric distribution system modeling and analysis".

Electric distribution systems have been central to recent efforts in the modernization and decarbonization of electric grids. There are unprecedented challenges in the modeling and analysis of distribution grids due to large-scale integration of advanced equipment including smart grid assets and inverter-based distributed energy resources (IBDERs). To assess the potential impacts of increasing IDBERs and advanced distribution system equipment in a more comprehensive manner, there is a need for the establishment of highly accurate, efficient, and unified simulation environments. Simulation tools depend on component models and numerical analysis techniques. Component modeling and system analysis are also the key elements in the design, optimization and real-time management of electric distribution systems.

Historically, distribution system planning and protection studies have been performed in steady-state with simplified source models. State estimation, an essential element of distribution management system, has been simplified to a load allocation problem given the challenges associated with the lack of available measurements (and consequently of observability), and the large size of distribution networks and their unbalanced nature. The radial topology of conventional networks has shaped the architectures of analysis methods to favor the simplicity of algorithms and to deal with the computational limitations of the past. Today, active distribution networks with increasing IDBERs, availability of measurement data including smart meter data, and the integration of dc/ac microgrids challenge existing analysis paradigms and engineering practices. A wide range of studies from steady-state to time-series and fast transients is deliberated within the context of distribution system analysis. Large-scale system capable methods are proposed to address the need for detailed analysis of secondary grid systems found in dense urban areas and the modeling of distribution networks including sub-transmission level. Researchers try to discover generalization paths to arbitrary network topologies and include arbitrary device connections.

Topics of interest for publication include, but are not limited to the following:

Numerical techniques and models to conduct a wide range of studies in distribution grids
Modeling of inverter-based distributed energy resources (IBDERs)
Modeling of advanced distribution system equipment and smart grid assets
Simulation of new distribution-level grid technologies
Simulation of active distribution networks
Integrated analysis of distribution grids, initialization of time-domain analysis from multi-phase load flow
Quasi-static time-series models, dynamic and EMT type models
Application of real-time simulation and hardware-in-the-loop methodologies in the analysis of distribution systems
Multiphase and unbalanced analysis of distribution systems: load flow, steady-state short circuit, state estimation, dynamic and transient analysis
Analysis of hybrid ac/dc microgrids
Analysis of inverter-based grids

Prof. Ilhan Kocar
Guest Editor

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Published Papers (13 papers)

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Research

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17 pages, 5801 KiB

Open AccessArticle

A Simulation Model for Providing Analysis of Wind Farms Frequency and Voltage Regulation Services in an Electrical Power System

by Hubert Bialas, Ryszard Pawelek and Irena Wasiak

Energies 2021, 14(8), 2250; https://doi.org/10.3390/en14082250 - 16 Apr 2021

Cited by 4 | Viewed by 2367

Abstract

The article presents an original simulation model of a wind farm (WF) consisting of 30 wind turbine-generator units connected to the electrical power system (EPS) through power converters. The model is dedicated to the evaluation of the WF capabilities to participate in frequency and voltage regulation services in the power system. A system that allows for frequency and voltage control is proposed and implemented in the presented model. The system includes primary frequency regulation with synthetic inertia and secondary regulation available on request from the system operator. The concept of a reference power generation unit was introduced, according to which only one wind generator unit was modeled in detail, and the other units were replaced with simple current sources. Such a solution allowed for the reduction of size and complexity of the model as well as shortened the simulation time. Simulation tests were conducted in the PSCAD/EMTDC environment for an electrical power system composed of the wind farm, a synchronous generator, and a dummy load. The performance of the wind farm control system was analyzed in different operation conditions, and the control capabilities of the farm were assessed. Selected simulation results are presented and discussed in the paper. They illustrate the regulatory properties of the WF and confirm the correctness of the developed model. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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21 pages, 8935 KiB

Open AccessArticle

Laplacian Matrix-Based Power Flow Formulation for LVDC Grids with Radial and Meshed Configurations

by Zahid Javid, Ulas Karaagac, Ilhan Kocar and Ka Wing Chan

Energies 2021, 14(7), 1866; https://doi.org/10.3390/en14071866 - 27 Mar 2021

Cited by 10 | Viewed by 2599

Abstract

There is an increasing interest in low voltage direct current (LVDC) distribution grids due to advancements in power electronics enabling efficient and economical electrical networks in the DC paradigm. Power flow equations in LVDC grids are non-linear and non-convex due to the presence of constant power nodes. Depending on the implementation, power flow equations may lead to more than one solution and unrealistic solutions; therefore, the uniqueness of the solution should not be taken for granted. This paper proposes a new power flow solver based on a graph theory for LVDC grids having radial or meshed configurations. The solver provides a unique solution. Two test feeders composed of 33 nodes and 69 nodes are considered to validate the effectiveness of the proposed method. The proposed method is compared with a fixed-point methodology called direct load flow (DLF) having a mathematical formulation equivalent to a backward forward sweep (BFS) class of solvers in the case of radial distribution networks but that can handle meshed networks more easily thanks to the use of connectivity matrices. In addition, the convergence and uniqueness of the solution is demonstrated using a Banach fixed-point theorem. The performance of the proposed method is tested for different loading conditions. The results show that the proposed method is robust and has fast convergence characteristics even with high loading conditions. All simulations are carried out in MATLAB 2020b software. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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34 pages, 2476 KiB

Open AccessArticle

Modeling of German Low Voltage Cables with Ground Return Path

by Johanna Geis-Schroer, Sebastian Hubschneider, Lukas Held, Frederik Gielnik, Michael Armbruster, Michael Suriyah and Thomas Leibfried

Energies 2021, 14(5), 1265; https://doi.org/10.3390/en14051265 - 25 Feb 2021

Cited by 12 | Viewed by 5937

Abstract

In this contribution, measurement data of phase, neutral, and ground currents from real low voltage (LV) feeders in Germany is presented and analyzed. The data obtained is used to review and evaluate common modeling approaches for LV systems. An alternative modeling approach for detailed cable and ground modeling, which allows for the consideration of typical German LV earthing conditions and asymmetrical cable design, is proposed. Further, analytical calculation methods for model parameters are described and compared to laboratory measurement results of real LV cables. The models are then evaluated in terms of parameter sensitivity and parameter relevance, focusing on the influence of conventionally performed simplifications, such as neglecting house junction cables, shunt admittances, or temperature dependencies. By comparing measurement data from a real LV feeder to simulation results, the proposed modeling approach is validated. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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20 pages, 1008 KiB

Open AccessArticle

Power Hardware-in-the-Loop: Response of Power Components in Real-Time Grid Simulation Environment

by Moiz Muhammad, Holger Behrends, Stefan Geißendörfer, Karsten von Maydell and Carsten Agert

Energies 2021, 14(3), 593; https://doi.org/10.3390/en14030593 - 25 Jan 2021

Cited by 13 | Viewed by 3411

Abstract

With increasing changes in the contemporary energy system, it becomes essential to test the autonomous control strategies for distributed energy resources in a controlled environment to investigate power grid stability. Power hardware-in-the-loop (PHIL) concept is an efficient approach for such evaluations in which a virtually simulated power grid is interfaced to a real hardware device. This strongly coupled software-hardware system introduces obstacles that need attention for smooth operation of the laboratory setup to validate robust control algorithms for decentralized grids. This paper presents a novel methodology and its implementation to develop a test-bench for a real-time PHIL simulation of a typical power distribution grid to study the dynamic behavior of the real power components in connection with the simulated grid. The application of hybrid simulation in a single software environment is realized to model the power grid which obviates the need to simulate the complete grid with a lower discretized sample-time. As an outcome, an environment is established interconnecting the virtual model to the real-world devices. The inaccuracies linked to the power components are examined at length and consequently a suitable compensation strategy is devised to improve the performance of the hardware under test (HUT). Finally, the compensation strategy is also validated through a simulation scenario. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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14 pages, 1789 KiB

Open AccessArticle

Assessment of the Risk of Damage to 110 kV Overhead Lines Due to Wind

by Andrew Lukas Chojnacki

Energies 2021, 14(3), 556; https://doi.org/10.3390/en14030556 - 22 Jan 2021

Cited by 11 | Viewed by 2499

Abstract

The article presents an assessment of the risk of damage to 110 kV overhead power lines as a result of the impact of wind of variable speeds on that equipment. A statistical method for the assessment of the reliability of power structures in conditions of variable strength of the structure and at variable exposure values is presented. This method is based on the analysis of the shape and mutual location of the distributions of the probability density of the momentary resistance (strength) of the tested structure and the exposures of variable values occurring in its surroundings. The risk of wind damage to 110 kV lines has been determined on the basis of many years of observations of wind speed and failure rate of the lines. Wind has been shown to be the fault factor or co-factor responsible for damage in one in five failures of such equipment. The final part of the article includes an analysis of the obtained results and their interpretation. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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19 pages, 13272 KiB

Open AccessArticle

Incomplete Cross-Bonding in the MV Line. Experience from the Operation of MV Single Cable Lines

by Krzysztof Dobrzynski, Zbigniew Lubosny, Jacek Klucznik, Janusz Grala and Dominik Falkowski

Energies 2020, 13(20), 5292; https://doi.org/10.3390/en13205292 - 12 Oct 2020

Cited by 1 | Viewed by 1979

Abstract

Cable lines are one of the basic components of power systems. Medium and high voltage cables mainly comprise a metallic sheath, which is concentric to the main core conductor. There are several operating schemes of such cable lines, which differ in the place of earthing of sheaths and the possible use of the sheaths and/or conductors crossing. The sheaths cross-bonding is typically done in two places of one cable line section, and it allows to reduce power losses. Nevertheless, the use of incomplete sheaths crossing—only in one place on cable route may have economic justification. The paper presents an incomplete sheaths cross-bonding analysis of an existing medium voltage cable line. The results obtained by the mathematical model are validated by measurements taken on 30 October 2019 on an existing cable line. Measurements recorded on a real object for various systems of crossing sheaths are presented. The influence of incorrect sheaths crossing on the measured quantities was shown. In addition, the risk of excess voltage on the sheaths during short-circuits has been verified using a mathematical model. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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30 pages, 10253 KiB

Open AccessArticle

Evaluation of Grid Capacities for Integrating Future E-Mobility and Heat Pumps into Low-Voltage Grids

by Bernd Thormann and Thomas Kienberger

Energies 2020, 13(19), 5083; https://doi.org/10.3390/en13195083 - 29 Sep 2020

Cited by 28 | Viewed by 3179

Abstract

While an area-wide implementation of electric vehicles (EVs) and electric heat pumps (HPs) will contribute to a decarbonization of the energy system, they represent new challenges for existing low-voltage (LV) power grids. Hence, this study investigates potential grid congestions on the basis of three contrasting load approaches applied to four different grid regions. Within the three load approaches, temporal characteristics of various grid customer classes (EVs, HPs, households etc.) are derived from highly resolved realistic load profiles. In accordance with classic grid planning, firstly a static load approach is analyzed by applying the modeled coincidence for each consumer class individually. Secondly, this static approach is modified by including combined coincidence factors, taking temporal consumer class interactions into account. Finally, both static load approaches are compared with detailed annual time series analyses by means of load flow simulations using real-life LV grid data. The evaluation of inadmissible voltage characteristics and thermal congestions identifies future grid extension needs depending on the considered grid region. In addition, the variation of the applied load approach highlights the need to consider consumer-specific temporal behavior. In fact, by neglecting temporal interactions between conventional and future grid customers, the classic grid planning approach overestimates future grid extension needs. To counteract an oversizing of future grid structures, this paper presents a combined consideration of EVs’ and HPs’ coincidence as well as resulting grid consequences on the LV level. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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23 pages, 3469 KiB

Open AccessArticle

Voltage and Reactive Power Optimization Using a Simplified Linear Equations at Distribution Networks with DG

by Seok-Il Go, Sang-Yun Yun, Seon-Ju Ahn and Joon-Ho Choi

Energies 2020, 13(13), 3334; https://doi.org/10.3390/en13133334 - 30 Jun 2020

Cited by 12 | Viewed by 2828

Abstract

In this paper, the VVO (Volt/Var optimization) is proposed using simplified linear equations. For fast computation, the characteristics of voltage control devices in a distribution system are expressed as a simplified linear equation. The voltage control devices are classified according to the characteristics of voltage control and represented as the simplified linear equation. The estimated voltage of distribution networks is represented by the sum of the simplified linear equations for the voltage control devices using the superposition principle. The voltage variation by the reactive power of distributed generations (DGs) can be expressed as the matrix of reactance. The voltage variation of tap changing devices can be linearized into the control area factor. The voltage variation by capacitor banks can also be expressed as the matrix of reactance. The voltage equations expressed as simplified linear equations are formulated by quadratic programming (QP). The variables of voltage control devices are defined, and the objective function is formulated as the QP form. The constraints are set using operating voltage range of distribution networks and the control ranges of each voltage control device. In order to derive the optimal solution, mixed-integer quadratic programming (MIQP), which is a type of mixed-integer nonlinear programming (MINLP), is used. The optimal results and proposed method results are compared by using MATLAB simulation and are confirmed to be close to the optimal solution. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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22 pages, 6392 KiB

Open AccessArticle

Heuristic Coordinated Voltage Control Schemes in Distribution Network with Distributed Generations

by Seok-Il Go, Sang-Yun Yun, Seon-Ju Ahn, Hyun-Woo Kim and Joon-Ho Choi

Energies 2020, 13(11), 2849; https://doi.org/10.3390/en13112849 - 3 Jun 2020

Cited by 5 | Viewed by 1922

Abstract

The voltage and reactive power control (Volt/VAR Control, VVC) in distribution networks has become a challenging issue with the increasing utilization of distributed generations (DGs). In this paper, a heuristic-based coordinated voltage control scheme that considers distribution voltage control devices, i.e., on-load tap changers (OLTC) and step voltage regulators (SVR), as well as reactive power control devices, i.e., DGs, are proposed. Conventional voltage control methods using non-linear node voltage equations require complex computation. In this paper, the formulation of simplified node voltage equations accounting for changes in tap position of distribution voltage control devices and reactive power changes of reactive power control devices are presented. A heuristic coordinated voltage control scheme using the proposed simplified node voltage equations is proposed. A coordinated voltage control scheme to achieve voltage control for nominal voltage and conservative voltage reduction (CVR) is presented. The results of the proposed schemes are compared with the results from the quadratic optimization method to confirm that the proposed schemes yields suitably similar results. Furthermore, a tap scheduling method is proposed to reduce the number of tap changes while controlling network voltage. The tap position is readjusted using a voltage control performance index (PI). Simulation results confirm that when using this method the number of tap changes is reduced. The proposed scheme not only produces reasonable performance in terms of control voltage of networks but also reduces the number of tap changes made by OLTC. The proposed control method is an alternative candidate for a system to be applied to practical distribution networks due to its simplified calculations and robust performance. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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20 pages, 6468 KiB

Open AccessArticle

Analysis of Internal Overvoltages in Transformer Windings during Transients in Electrical Networks

by Jakub Furgał, Maciej Kuniewski and Piotr Pająk

Energies 2020, 13(10), 2644; https://doi.org/10.3390/en13102644 - 22 May 2020

Cited by 7 | Viewed by 5600

Abstract

Due to the increasing requirements for the reliability of electrical power supply and associated apparatus, it is necessary to provide a detailed analysis of the overvoltage risk of power transformer insulation systems and equipment connected to their terminals. Exposure of transformer windings to overvoltages is the result of the propagation condition of electromagnetic waves in electrical networks and transformer windings. An analysis of transformer winding responses to transients in power systems is of particular importance, especially when protection against surges by typical overvoltage protection systems is applied. The analysis of internal overvoltages in transformers during a typical transient related to switching operations and selected failures is of great importance, particularly to assess the overvoltage exposure of insulation systems in operating conditions. The random nature of overvoltage phenomena in electrical networks implies the usage of computer simulations for the analysis of overvoltage exposures of electrical devices in operation. This article presents the analysis of the impact of transient phenomena in a model of a medium-voltage electrical network during switching operations and ground faults on overvoltages in the internal insulation systems of transformer windings. The basis of the analysis is simulations of overvoltages in the windings, made in the Electromagnetic Transients Program/Alternative Transients Program (EMTP/ATP) using a model with lumped parameters of transformer windings. The analysis covers the impact of the cable line length and the ground fault resistance value on internal overvoltage distributions. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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23 pages, 2904 KiB

Open AccessArticle

Low-Capacity Exploitation of Distribution Networks and Its Effect on the Planning of Distribution Networks

by Jorge A. Alarcon, Francisco Santamaria, Ameena S. Al-Sumaiti and Sergio Rivera

Energies 2020, 13(8), 1920; https://doi.org/10.3390/en13081920 - 14 Apr 2020

Cited by 4 | Viewed by 1863

Abstract

The continuous variation and dispersion of the load demand during a 24-h day are uncontrolled aspects that affect the efficiency, operational conditions, and total cost of the power distribution network. The cost of the network is strongly related to the peak of demand, but the available capacity of the network is not used efficiently during the day because feeders and branches usually work under 70% of their full capacity. In this way, it is necessary to measure how efficiently the distribution network capacity is used and to identify the aspects that can be modified to improve it. This article proposes a new exploitation capacity index to measure the efficiency of a/the whole distribution network throughout the day in relation to the total available capacity of the branches that compose the network. The paper presents the mathematical formulation and the validation process of the index, and then it provides a planning case study in which the index and the total cost of the planning problem are calculated and compared in four different scenarios in which the peak of the load demand changes. The results show a direct relation between the exploitation capacity and the peak of demand, so lower exploitation capacities are strongly related to higher peaks of demand. As for the capital investments for the network planning, it is found that higher peaks of demand involve more upgrade necessities and higher capital investments compared to the other cases. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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15 pages, 1660 KiB

Open AccessArticle

A Reliability-Based Network Reconfiguration Model in Distribution System with DGs and ESSs Using Mixed-Integer Programming

by Shanghua Guo, Jian Lin, Yuming Zhao, Longjun Wang, Gang Wang and Guowei Liu

Energies 2020, 13(5), 1219; https://doi.org/10.3390/en13051219 - 6 Mar 2020

Cited by 17 | Viewed by 2619

Abstract

Widely used distribution generations (DGs) and energy storage systems (ESSs) enable a distribution system to have a more flexible fault reconfiguration capability. In order to enhance the service reliability and the benefit of distribution networks with DGs and ESSs, this paper proposes a novel distribution system reconfiguration (DSR) model including DGs and ESSs. Meanwhile, the impact of sectionalizing switches and tie switches on reliability is considered. The concept of “boundary switch” is introduced for quantifying the customer interruption duration. The DSR model is presented to minimize the sum of the customer interruption cost, the operation cost of switches, and the depreciation cost of DGs and ESSs. Furthermore, the proposed model is converted into a mixed-integer linear programming, which can be efficiently solved by commercial solvers. Finally, the validity and efficiency of the proposed DSR model are verified by a modified IEEE 33-bus system and a modified PG&E69-bus network. The obtained results indicate the advantages of DGs and ESSs in reducing outage time, and suggest that the types and locations of SSs have great effects on the resulting benefit of DGs and ESSs. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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Review

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17 pages, 975 KiB

Open AccessReview

Review of Steady-State Electric Power Distribution System Datasets

by Steffen Meinecke, Leon Thurner and Martin Braun

Energies 2020, 13(18), 4826; https://doi.org/10.3390/en13184826 - 15 Sep 2020

Cited by 16 | Viewed by 3989

Abstract

Publicly available grid datasets with electric steady-state equivalent circuit models are crucial for the development and comparison of a variety of power system simulation tools and algorithms. Such algorithms are essential to analyze and improve the integration of distributed energy resources (DERs) in electrical power systems. Increased penetration of DERs, new technologies, and changing regulatory frameworks require the continuous development of the grid infrastructure. As a result, the number and versatility of grid datasets, which are required in power system research, increases. Furthermore, the used grids are created by different methods and intentions. This paper gives orientation within these developments: First, a concise overview of well-known, publicly available grid datasets is provided. Second, background information on the compilation of the grid datasets, including different methods, intentions and data origins, is reviewed and characterized. Third, common terms to describe electric steady-state distribution grids, such as representative grid or benchmark grid, are assembled and reviewed. Recommendations for the use of these grid terms are made. Full article

(This article belongs to the Special Issue Electric Distribution System Modeling and Analysis)

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