Equivalent Power System Research Articles

АНАЛІЗ НАЛАШТУВАННЯ ПРИСТРОЇВ АВТОМАТИЧНОГО ЧАСТОТНОГО РОЗВАНТАЖЕННЯ З УРАХУВАННЯМ ЄВРОПЕЙСЬКИХ ВИМОГ

The paper deals with the structure of under-frequency load shedding (UFLS) relays in the interconnected power system (IPS) of Ukraine. The equivalent power system model to study the UFLS operation is developed, and UFLS configuration scenarios considering the requirements of ENTSO-E, are configured. The frequency stability for different scenarios of UFLS settings considering planned and emergency active power imbalances are studied. The plots illustrating the frequency change in the power system under these conditions are presented. References 4, table 1, figures 5.

Analysis of Hybrid Ship Machinery System with Proton Exchange Membrane Fuel Cells and Battery Pack

As marine traffic is contributing to pollution, and most vessels have predictable routes with repetitive load profiles, to reduce their impact on environment, hybrid systems with proton exchange membrane fuel cells (PEMFC-s) and battery pack are a promising replacement. For this purpose, the new approach takes into consideration an alternative to diesel propulsion with the additional benefit of carbon neutrality and increase of system efficiency. Additionally, in the developed numerical model, control of the PEMFC–battery hybrid energy system with balance of plant is incorporated with repowering existing vessels that have two diesel engines with 300 kWe. The goal of this paper is to develop a numerical model that analyzes and determines an equivalent hybrid ship propulsion system for a known traveling route. The developed numerical model consists of an interconnected system with the PEMFC stack and a battery pack as power sources. The numerical model was developed and optimized to meet the minimal required power demand for a successful route, which has variable loads and sees ships sail daily six times along the same route—in total 54 nautical miles. The results showed that the equivalent hybrid power system consists of a 300 kWe PEMFC stack and battery pack with 424 kWh battery and state of charge varying between 20 and 87%. To power this new hybrid power system, a hydrogen tank of 7200 L holding 284.7 kg at pressure of 700 bar is required, compared to previous system that consumed 1524 kg of diesel and generated 4886 kg of CO2.

Development of the equivalent Great Britain 36-zone power system for frequency control studies

This paper presents a dynamic model of the equivalent Great Britain (GB) 36-zone power system, which can be used for reliable and realistic assessment of emerging load frequency control mechanisms. Flexible architecture of the presented dynamic test system permits a broad range of security of supply and small-signal stability studies for design of future power grids. It can be particularly useful for academic research, but also for undertaking feasibility studies in power industries. The proposed dynamic test system, which is obtained through network reduction of the original full-scale GB transmission power system developed by National Grid Electricity System Operator (NGESO) Company, provides detailed information about the GB power system. In this regard, the required data and modelling approaches to develop the 36-zone system are provided in detail. The presented dynamic test system represents the system topology, impedance characteristics and electromechanical oscillations of the original GB power system however, it is not an exact equivalent of the master GB system. Illustrative dynamic models of the key system components, including synchronous generators, automatic voltage regulators, power system stabilizers, hydro and steam turbines models along with speed governing systems are presented. Dynamic behavior of 36-zone test system in response to infeed loss contingencies is investigated. Particularly, the impact of changes in the system inertia on the system electromechanical modes is examined using the modal analysis approach. In this context, the mode shape concept is employed to determine dominant generators and contribution of different zones in the low frequency oscillations. Moreover, time-domain simulations are undertaken to validate the modal analysis results. Additionally, the condition of different zones from the viewpoint of frequency nadir and maximum rate of change of frequency for various contingencies and extreme cases are examined.

The Influence of Renewable Energy Sources and Electric Energy Storages on Grid Power Balances

In recent decades, increasingly more attention has been paid in our country and abroad to the use of renewable energy sources (RES). However, such factors as nonuniform distribution of RESs over the country territory and stochastic nature of their availability in time impede their wide-scale application. For RESs to be used on a wider scale, relevant regulatory and technical documents stipulating the electric power system designing should be developed, and a number of technical problems should be solved, e.g., those relating to the need of smoothing the electricity generation nonuniformity. In this study, distribution power grids containing RESs (wind and solar power plants) and electric energy storages are considered. The aim of the study is to develop proposals for a procedure of integrating RESs and energy storages into grids. The study results are supposed to be used in developing software and hardware solutions for control of an energy storage and predict the electricity consumption and electricity generation by RESs in power grids. In the study, mathematical modeling (computation experiment) methods were used for development of energy storage and RES models that take into account climatic factors (wind velocity, solar irradiance, and temperature) in certain geographical locations received from open data bases. For studying the grid power balance reliability, the operation of RESs within a generalized distribution grid is considered. The grid contains an equivalent centralized power system source, a distribution network, consumer loads, various types of RESs (wind and solar power plants), and a centralized electric energy storage. The power outputs produced by wind and solar power plants for a day (based on hourly averaged meteorological conditions) and month are analyzed for a number of regions in Russia; the annual amount of electricity generated by them is estimated, and the effect of smoothing the generation schedules due to combination of various types of RES and use of electric energy storages is evaluated. Universal models of RESs and electric energy storages for electric grid load flow analysis are suggested; the application of the developed models for power balance analysis of grids containing RESs and energy storages is illustrated; the key stages of introducing RESs and energy storage devices are identified and described, and tasks for which electrical operation modes have to be numerically analyzed are formulated.

Comparison of Machine Learning Algorithms for the Prediction of Mechanical Stress in Three-Phase Power Transformer Winding Conductors

This research compares four machine learning techniques: linear regression, support vector regression, random forests, and artificial neural networks, with regard to the determination of mechanical stress in power transformer winding conductors due to three-phase electrical faults. The accuracy compared with finite element results was evaluated for each model. The input data were the transient electrical fault currents of power system equivalents with impedances from low to high values. The output data were the mechanical stress in the conductors located in the middle of the winding. To simplify the design, only one hyperparameter was varied on each machine learning technique. The random forests technique had the most accurate results. The highest errors were found for low-stress values, mainly due to the high difference between maximum and minimum stresses, which made the training of the machine learning models difficult. In the end, an accurate model that could be used in the continuous monitoring of mechanical stress was obtained.

A Recursive Least-Squares Approach with Memorizing Factor for Deriving Dynamic Equivalents of Power Systems

In this research, a two-stage identification-based approach is proposed to obtain a two-machine equivalent (TME) system of an interconnected power system for transient stability studies. To estimate the parameters of the equivalent system, a three-phase fault is applied near and/or at the bus of a local machine in the original multimachine system. The electrical parameters of the equivalent system are calculated in the first stage by equating the active and reactive powers of the local machine in both the original and the predefined equivalent systems. The mechanical parameters are estimated in the second stage by using a recursive least-squares estimation (RLSE) technique with a factor called “memorizing factor”. The approach is demonstrated on New England 10-machine 39-bus system, and its accuracy and efficiency are verified by computer simulation in MATLAB software. The results obtained from the TME system agree well with those obtained from the original multimachine system.

Power System Impedance Estimation Using a Fast Voltage and Current Changes Measurements

Equivalent power system impedance is an important electrical quantity from many points of view. Areas in which this parameter plays an important role include, in particular: Voltage stability analysis, power quality, or fault condition analysis. Power system impedance estimation in real operation conditions can be performed by one of the non-invasive methods described by different authors. This paper aims to investigate and compare seven different methods for power system impedance estimation based on voltage and current variations measurement. After a brief description of selected methods, these methods were applied for power system impedance estimation in the case of two simple simulation tests and then in the case of three real measured data. Voltage and current changes used for power system impedance estimation in real conditions were measured in high voltage (HV) and medium voltage (MV) substations feeding steel mill with the electric arc furnace (EAF) operation. As the results presented in this paper have shown, not all of the methods analyzed are suitable for determining the power system impedance based on the fast step changes of voltage and current that occur, for example, during an EAF operation. Indeed, some of the tested methods were originally designed to determine the power system impedance from changes in voltages and currents recorded at steady state.

Harmonic analysis of thyristor controlled series capacitor in polluted Algerian network

This paper presents the study of the impact of harmonic distortion generated by the thyristors controlled series capacitor (TCSC) in Algerian electric power system. By applying Fourier transform of terminal voltage and switching function, the TCSC model is used as a harmonic admittance matrix, in the frequency domain, and then integrated into a balanced harmonic load flow algorithm based on the Newton-Raphson method. The study has been carried out with the equivalent Algerian power system 114 bus. The total harmonics and RMS voltages are evaluated under different operating regions of the TCSC.

Frequency Response Model and Its Closed-Form Solution of Two-Machine Equivalent Power System

For the purpose of considering the spatial-temporal characteristics (STC) of large-scale interconnected power system in the modeling, calculation, and analysis of dynamic frequency response (FR), this paper establishes a two-machine equivalent frequency response (TEFR) model and gets its closed-form solution (CFS), which can be used to analytically analysis and fast calculation. In the modeling, the network structure is idealized through simplified matrix of DC power flow and the system is reduced to a typical two-degree-of-freedom vibration system with viscous damping and excitation forces through breaking closed-loop and variable approximation. After that, modal analysis method is managed to obtain TEFR-CFS which represent the dynamic FR of TEFR model as the superposition of system FR and frequency oscillation. And the influence of parameters on frequency oscillation, such as electrical distance, inertial distribution, initial disturbance power distribution coefficient, etc., are analyzed. Furthermore, the analytical expressions of the key characteristics of dynamic FR, such as the initial decline slope, the nadir and the arrival time of nadir, etc., are derived. Numerical simulation proves that STC has significant influence on FR and can be described by TEFR model, TEFR-CFS and the expressions of its key characteristics with accuracy and efficiency.

A hybrid bacterial foraging-particle swarm optimization technique for solving optimal reactive power dispatch problem

<div data-canvas-width="397.27351844386203">This paper presents a hybrid evolutionary computation algorithm termed as hybrid bacterial foraging-particle swarm optimization (HBFPSO) algorithm, to optimal reactive power dispatch (ORPD) problem. HBFPSO algorithm merges velocity and position updating strategy of particle swarm optimization (PSO) algorithm and reproduction and elimination dispersal of bacterial foraging algorithm (BFA). The ORPD is solved for minimization of two objective functions; system real power loss and voltage stability L-index. The objective is minimized by optimally choosing the control variables; generator excitations, tap positions of on-load tap changing transformers and switched var compensators while satisfying their constraints and also the constraints of dependent variabl</div><div data-canvas-width="98.30049385204596">es; voltages of all load buses and reactive power generation of all generators. The proposed approach has been evaluated on a standard IEEE 30 bus test system and 24 bus EHV southern region equivalent Indian power system. The results offered by the proposed algorithm are compared with those offered by other evolutionary computation algorithms reported in the recent state of the art literature and the superiority of the proposed algorithm is demonstrated.</div>

Hybrid Bacteria Foraging Particle Swarm Optimization based Optimal Reactive Power Dispatch for the Alleviation of Voltage Deviations

This paper presents a hybrid algorithm for optimal reactive power dispatch by combining two popular evolutionary computation algorithms; Bacterial Foraging algorithm and Particle Swarm Optimization. The Hybrid algorithm combines velocity and position updating strategy of Particle swarm optimization algorithm and reproduction and elimination dispersal of Bacterial foraging algorithm. The proposed algorithm is applied to solve optimal power flow with the objective of minimization of Sum of squares of voltage deviations of all load buses. The proposed approach has been evaluated on a standard IEEE 30 bus test system and 24 bus EHV southern region equivalent Indian power system. The results obtained by the proposed Hybrid algorithm are compared with their basic counter parts and superiority of the proposed hybrid algorithm is demonstrated.

A novel measurement-based procedure for dynamic equivalents of electric power systems for stability studies using improved sine cosine algorithm

Abstract Dynamic equivalent (DE) is an important process of multi-area interconnected power systems. It allows to perform stability assessment of a specific area (area of interest) at minimum cost. This study is intended to investigate the dynamic equivalent of two relatively large power systems. The fourth-order model of synchronous generators with a simplified excitation system is used as equivalent to the group of generators in the external system. To improve the accuracy of the estimated model, the identification is carried in two stages. First, using the global search Sine Cosine Algorithm (SCA) to find a starting set values, then this set is used as starting point for the fine-tuning made through the Pattern Search (PS) algorithm. To increase the reliability of the model’s parameters, two disturbances are used to avoid the identification based on a specific event. The developed program is applied on two standard power systems, namely, the New England (NE) system and the Northeast Power Coordinating Council (NPCC) system. Simulation results confirm the ability of the optimized model to preserve the main dynamic properties of the original system with accuracy.

Online dynamic voltage stability assessment method of AC/DC power systems

The reactive power absorption of conventional line commutated converter–high-voltage direct current transmission systems challenges on the voltage stability of AC/DC power systems. Many online dynamic voltage stability assessment approaches have been put forward to AC power systems, but the impact of DC transmissions is seldom taken into account for AC/DC power systems. In this study, an online dynamic voltage stability assessment method of AC/DC power systems is proposed. The proposed method models the converter as an equivalent AC voltage source in series with the internal impedance by utilising the control mode model of DC transmission systems and the measured data of the converter bus. The equivalent AC voltage source can identify the dynamic of DC transmissions. Then the AC/DC power system can be modelled by the equivalent AC power system. Based on the nodal equivalent method, the proposed method establishes a voltage stability index of the equivalent AC power systems for the dynamic voltage stability assessment of AC/DC power systems. The simulation demonstrated the effectiveness of the proposed method.

Performance Evaluation of BESS for Korean Power System Using Equivalent Power System Circuit Model

Abstract This paper describes a method of modeling power system elements involved in frequency-active power control using frequency data of south Korea power system. A particle swarm optimization method is used for estimating the parameters of the transfer function which illustrates the relationship between frequency and active power deviation. To obtain the optimal parameter estimation, we use the mean absolute percentage error (MAPE) index for evaluating the accuracy of estimation compared to real data. Real frequency and power data from KPX were used for comparison studies. From the proposed equivalent power system circuit model, we achieved 0.0052% MAPE compared to real data. To evaluate the BESS frequency regulation performance, we considered the BESS control algorithm which is based on the data of Korea electric power corporation (KEPCO). From this case study, we confirmed that the BESS which is operated in south Korea can improve frequency regulation in case of frequency event by increasing nadir frequency up to 0.0335Hz.

A procedure to design wide-area damping controllers for power system oscillations considering promising input–output pairs

The expansion of the wide-area measurement system has provided some control strategies to improve the low-frequency oscillation modes in electric power systems. One of these strategies is to use remote signals for a wide-area damping controller (WADC) to enhance the small-signal stability of the power system. However, the expansion of the Electric Power System increased the generator number connected to the grid, and then some challenges to the WADC design surged such as which input–output pairs of the WADC should be designed to improve the closed loop system damping. Typically, the WADC is a centralized controller and may have many design elements. The interactions among the elements may compromise the central controller design and its purpose. This paper proposes a procedure based on genetic algorithms in order to design a robust central controller. This procedure automatically chooses the input–output pairs of the central controller that will contribute to damping the low-frequency oscillation modes. The design procedure considers topological changes and time delay variations. Small-signal analysis and time-domain nonlinear simulations are carried out in the multi-machine Australian Equivalent Power System, an IEEE benchmark model for small-signal stability analysis.

Advanced Active Power Filter Performance for Grid Integrated Hybrid Renewable Power Generation Systems

An active power filter implemented with a four leg voltage-source inverter using a predictive control scheme is presented. The use of a four leg voltage-source inverter allows the compensation of current harmonic components, as well as unbalanced current generated by single-phase nonlinear loads. A detailed yet simple mathematical model of the active power filter, including the effect of the equivalent power system impedance, is derived and used to design the predictive control algorithm. The compensation performance of the proposed active power filter and the associated control scheme under steady state and transient operating conditions is demonstrated through simulations and experimental results.

Single‐port and multi‐port frequency‐dependent network equivalents with numerically stable branches

This study proposes new methods for finding frequency-dependent network equivalents of power systems. Since stability of the time-domain solution is a major concern, additional constraints are added to ensure the stability in both single-port and multi-port network equivalents. For single-port problem, an equivalent circuit consisting of only passive elements is estimated to ensure passivity and, consequently, stability of the time-domain solution. For multi-port case, additional stable branches are added to fit the frequency response data with high accuracy while maintaining stability of the equivalent. Several case studies are considered to evaluate the performance of the proposed approaches. The simulation results prove the efficacy of the proposed methods for finding stable equivalent circuits with high accuracy.

A method of Modelling and Simulating the Back-to-Back Modular Multilevel Converter HVDC Transmission System

This paper proposes a method to simulate a back-to-back modular multilevel converter (MMC) HVDC transmission system. In this paper we utilize an equivalent networks to simulate the dynamic power system. Moreover, to account for the performance of converter station, core components of model of the converter station gives a basic model of simulation. The proposed method is applied to an equivalent real power system.

A methodology for computing robust dynamic equivalents of large power systems

This paper presents a simple and computationally efficient methodology for computing robust dynamic equivalents. While simple to implement, the methodology involves many factors, and these are discussed, explained and justified throughout the paper. It classifies clusters of generators to be equivalenced by their electrical distances, and identifies second order reduced models for them. It maps them into classical synchronous machine models and aggregates them. Reduction of the network is based on the Ward PV method. The quality of the dynamic equivalent, in terms of flexibility and reduced dependence on disturbances, is automatically verified by performance indices. The methodology can easily be embedded in time domain simulation packages. Two large real power system networks are used for testing the performance of the approach.

Application of Balanced Realizations for Model-Order Reduction of Dynamic Power System Equivalents

This paper reviews and applies the balanced realization (BR) theory to obtain reduced-order models from dynamic system equivalents of electric power networks. BR allows obtaining reduced-order models via a process in which the original asymptotic stable system is internally balanced. The balanced system is truncated according to its dominant dynamics. It can be proven that the truncated, that is, reduced-order, system is also stable. This paper applies the BR method to dynamic system equivalents represented as frequency-dependent network equivalents (FDNEs). Furthermore, it shows that an assumed reduced-order FDNE can be further reduced via the BR process. Four case studies, involving one transmission network and three wind power plants, are presented.