IET Generation, Transmission & Distribution
Volume 9, Issue 16, 03 December 2015
Volumes & issues:
Volume 9, Issue 16
03 December 2015
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- Author(s): Haitian Wang ; Guangfu Tang ; Zhiyuan He ; Junzheng Cao ; Xiaoping Zhang
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2455 –2465
- DOI: 10.1049/iet-gtd.2015.0228
- Type: Article
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The voltages of the upper and lower arms per phase unit in a modular multilevel converter (MMC) are analysed. In addition, the enabled probabilities of each submodule (SM) in the upper and lower arms are proposed on the basis of the relationship between the arm voltage and the number of enabled SMs. Analytical models of the currents in the switches can be obtained from the current path and sign. Then, the average or root mean square (RMS) current can be obtained from the corresponding model. Therefore, the conduction and essential switching losses can be expressed by analytical formulas. In the inverter and rectifier modes, the two losses of the corresponding upper and lower switches of the SM are compared, and the sums of the two losses of the upper and lower switches are compared with the analytical method. Simulation studies are performed on a 1000 MW 320 kV MMC-high-voltage direct current system under typical operating conditions. The magnitudes of the compared losses are validated by the simulation results. Both the relative errors of the total conduction and essential switching losses are within ±2.5 and ±7%, respectively, and the comparison results demonstrate the effectiveness of the analytical method.
- Author(s): Xin Jiang ; Hongkun Chen ; Tieyuan Xiang
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2466 –2473
- DOI: 10.1049/iet-gtd.2015.0483
- Type: Article
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A probabilistic approach with considering the peaking characteristics of wind power is proposed to determine the maximum wind power penetration level (WPPL). To evaluate the effect wind peaking characteristics brought to the hosting capacity of systems, a detailed simulation of wind speed/load distributions over a long period is required. Thus, taking an hour as the time scale, the time-sharing peaking characteristics of wind power are discussed by describing the hourly distribution of wind output and load. Based on the chance constrained programming, a WPPL model is established in this study. The optimisation process is achieved using the improved particle swarm optimisation algorithm based on Monte–Carlo simulation. This proposed approach has been applied to an actual power system in central China. Simulation results show that the WPPL would be too optimistic without considering the anti-peaking characteristics of wind power. Besides various sensitivity analyses are performed to assess the effect of other parameters on the maximum penetration level.
- Author(s): Chunxia Dou ; Mengfei Lv ; Tianyu Zhao ; Yeping Ji ; Heng Li
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2474 –2484
- DOI: 10.1049/iet-gtd.2015.0397
- Type: Article
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In this study, a two-hierarchical decentralised coordinated control scheme based on the multi-agent system (MAS) is proposed to improve the security and the stability of the microgrid. The coordinated switching control strategies are constructed in upper level agent to ensure the microgrid security. The making process of the coordinated switching control strategies is regarded as searching the optimal switching operation mode by means of designing constraint violation function and colour Petri-net, so that the operation mode of the microgrid can be switched during larger power unbalance. The decentralised continuous control is designed by integrating the outer loop droop controller with the inner loop prescribed performance controller in the lower level unit agents to guarantee its unit system stability. Finally, the simulation results demonstrate the effectiveness of the decentralised coordination control based on MAS.
- Author(s): Xin Zhou ; Haishun Sun ; Bing Zhao ; Jinyu Wen ; Asad Waqar
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2485 –2492
- DOI: 10.1049/iet-gtd.2015.0798
- Type: Article
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The Central China Power Grid (CCPG) and North China Power Grid (NCPG) are connected together by a single AC ultra-high-voltage (UHV) transmission link. When suffering power disturbances, power oscillation with high magnitude and long period would happen on the UHV tie-line, which may affect the synchronous and stable operation of the interconnected two power grids. This study proposes a novel emergency control scheme for high-voltage direct current (HVDC) in CCPG to suppress the high peak value of the power oscillation. Based on a two-machine equivalent model, the maximum rising slope of power oscillat`ion is used to predict the peak value of power oscillation and power disturbance which is used as the reference of emergency power modulation. Simulation verification is carried out based on the full model of the CCPG and NCPG, using Power System Analysis Software Package. Moreover, field test has also been carried out in CCPG. Both simulation results and recorded wave curve show that the proposed HVDC emergency control scheme can effectively suppress the peak value under different power disturbances. This significantly improves the transient performance of the interconnected power system and the power transfer capacity of the UHV tie-line.
- Author(s): Fuping Zeng ; Yulin Dong ; Ju Tang
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2493 –2500
- DOI: 10.1049/iet-gtd.2015.0403
- Type: Article
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Partial discharge (PD) is an early manifestation of insulation fault that occurs in electrical equipment, which holds rich feature information used to insulation assessment. In this study, step voltage method was applied to investigate the PD development process of typical protrusion defects in gas-insulated switchgear. Nine features were extracted to represent the deterioration degree of internal insulation. Fuzzy C means clustering was applied to solve the state centres. PD severity was divided into four states based on the PD developing process, and the harmfulness of each state was illustrated. Finally, adaptive objective weight technology based on the theory of maximising deviation was adopted, and two-level fuzzy comprehensive evaluation (TL-FCE) model was established to address the problem of the weight allocation of different features on the evaluation result. The experimental test has been conducted to test the validity and effectiveness of the model. It is proved that TL-FCE owns good performance to assess PD severity, and it is more suitable to handle fuzzy boundary problems than support vector machine.
- Author(s): Masume Khodsuz and Mohammad Mirzaie
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2501 –2508
- DOI: 10.1049/iet-gtd.2015.0640
- Type: Article
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Metal–oxide surge arresters (MOSAs) are essential equipments for power system protection and devices from lightning and switching transient overvoltages. Therefore, their operating condition and diagnosis are very important. In this study, a multi-layer support vector machine (SVM) classifier has been used for MOSA conditions monitoring based on experimental tests. Three features are extracted based on the test results for determining surge arresters operating conditions including clean virgin, ultraviolet (UV) aged clean surface, surface contaminations after and before UV housing ageing, and degraded varistors along active column. Then, the multi-layer SVM classifier is trained with the training samples, which are extracted by the above data processing. Finally, the five fault types of surge arresters are identified by this classifier. The test results show that the classifier has an excellent performance on training speed and reliability which confirm the high applicability of introduced features for correct diagnostic of surge arresters conditions.
- Author(s): José Ramírez-Niño ; Alberth Pascacio ; Rito Mijarez ; Joaquín Rodríguez– Rodríguez
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2509 –2516
- DOI: 10.1049/iet-gtd.2014.1136
- Type: Article
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An on-line fault monitoring diagnostic system for hydroelectric generators based on spectrum analysis of neutral current is presented. Hydroelectric generators are fundamental elements in the power train at hydroelectric power plants and require an adequate diagnostic analysis. Unexpected generator failures can lead to a significant financial effect owing to the elevated costs of emergency repairs and lost revenues caused by forced outage extended periods. Determining the actual operating conditions of a generator is a crucial phase in assessing the risk of failures. The on-line instrumentation fault monitoring diagnostic system uses a simplified electrical model of fault simulation in order to help interpret the harmonic sources in the neutral current. Field measurement results proved that the spectrum analysis model for detecting mechanical faults is effective.
- Author(s): Zoran Radakovic ; Nikola Paunovic ; Vladimir Milosevic ; Milos Jovanovic
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2517 –2525
- DOI: 10.1049/iet-gtd.2014.0853
- Type: Article
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This study presents the procedure of generating simple-to-apply engineering recommendation for earthing systems and boundaries for setting of earth faults relay protection in power systems with solidly earthed neutral. The simple rules are based on ‘the worst case analyses’. Motivation for this work was simplification of the engineering process with acceptable deviation from economic optimum. Another reason is addressing the specific problems occurring in studied arid desert terrains conditions, which are described in this study. The analyses are based on calculation of earth fault current, its distribution over multiple earthing systems along the power line connected via protective conductor, tripping time dependent on relay curve, and allowed step and touch voltages depending on tripping time and characteristics of soil and optional additional surface material. For these calculations, the Excel/VBA software tool is developed and used. Different topologies of earthing systems (with grounding contours, rods, with/without backfill materials, etc.) considering layout of equipment in substation are studied using finite-elements software in order to determine the ratio of touch and step voltages to ground potential rise – GPR. The methodology is explained through a prominent case study of overhead line with overhead ground wire and metallic poles in the rural area.
- Author(s): Yizhong Hu ; Wenchuan Wu ; Boming Zhang
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2526 –2533
- DOI: 10.1049/iet-gtd.2015.0368
- Type: Article
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Rational models of frequency-dependent network equivalents (FDNEs) have been used in real-time digital simulator (RTDS) for power-system simulation. However, this can lead to a computational burden issue; the application of FDNEs may result in a loss of real-time simulation features because the computational cost of the FDNE component exceeds the limits of RTDS. The authors describe a solution that combines compacting and partitioning of the FDNEs, whereby the former reduces the redundancy in the mathematical model and the latter allows us to exploit parallel computer architectures. Then they describe the results of numerical simulations that demonstrate the effectiveness of the approach. Moreover, the proposed simulation solution is not limited to the applications of FDNEs in RTDS, it solves a set of subsistent computational issues when apply rational models in real-time electromagnetic transients programs tools.
- Author(s): Manuel Barragán-Villarejo ; Alejandro Marano-Marcolini ; Jose Maria Maza-Ortega ; Antonio Gómez-Expósito
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2534 –2543
- DOI: 10.1049/iet-gtd.2015.0068
- Type: Article
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Shunt-series ac links constitute a class of so-called vector switching converters, capable of controlling power flows by synthesising an adjustable series voltage. A novel steady-state model for the recently introduced three-leg shunt-series ac link, suitable for power flow studies, is developed in this study. The new model is then applied in two optimal power flow problems arising in distribution systems, namely, power loss reduction and integration of distributed generation, where the performance of the three-leg topology is compared with that of the conventional four-leg scheme. The CIGRE Task Force C06.04.02 benchmark network is used as case study.
- Author(s): Rehana Perveen ; Nand Kishor ; Soumya R. Mohanty
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2544 –2554
- DOI: 10.1049/iet-gtd.2015.0247
- Type: Article
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The fault study in offshore wind farm connected to onshore grid is carried out using empirical mode decomposition (EMD) which is a powerful technique for analysing linear, non-linear, stationary and non-stationary signals. The efficacy of the proposed approach is carried out by virtue of comparative assessment with other well-established signal processing techniques: wavelet transform, Stockwell transform, hyperbolic Stockwell transform in the literature. The intrinsic mode functions (IMFs) are obtained using EMD for signals (normal and fault) retrieved at different sections. Hilbert transform is applied to each IMF in order to evaluate the magnitude and phase angle information used for analysing the signal. Both qualitative and quantitative analyses are carried out to demonstrate the effective detection of fault occurrence. The adopted approach accurately discriminates the occurrence of fault in AC/DC network section. The validation of the detection algorithm has been demonstrated through real-time digital simulator studies. In addition, faulty sections are characterised adopting classification strategy using support vector machines.
- Author(s): Salah Bahramara ; Mohsen Parsa Moghaddam ; Mahmoud Reza Haghifam
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2555 –2564
- DOI: 10.1049/iet-gtd.2015.0327
- Type: Article
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In this study, a hierarchical decision making framework for operation of active distribution grids (ADGs) in which distribution company (Disco) and microgrids (MGs) cooperate with each other is modelled. Since there are several MGs, which may have independent decision makers, in ADGs, two levels of decision makers are considered in this framework. The mentioned framework is modelled as a bi-level optimisation problem in which Disco and MGs are considered as the leader and the followers, respectively. The resulting model is a non-linear bi-level problem which is transformed into a linear single-level problem through Karush–Kuhn–Tucker conditions and dual theory. To evaluate the effectiveness of the model, a hypothetical distribution grid is considered as the case study.
- Author(s): Bruno Canizes ; João Soares ; Zita Vale ; Cristina Lobo
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2565 –2574
- DOI: 10.1049/iet-gtd.2014.1196
- Type: Article
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This study proposes a new methodology to increase the power delivered to any load point in a radial distribution network, through the identification of new investments in order to improve the repair time. This research work is innovative and consists in proposing a full optimisation model based on mixed-integer non-linear programming considering the Pareto front technique. The goal is to achieve a reduction in repair times of the distribution networks components, while minimising the costs of that reduction as well as non-supplied energy costs. The optimisation model considers the distribution network technical constraints, the substation transformer taps, and it is able to choose the capacitor banks size. A case study based on a 33-bus distribution network is presented in order to illustrate in detail the application of the proposed methodology.
- Author(s): Nand Kishor ; Janne M. Seppänen ; Jukka Turunen ; Antti-Juhani Nikkilä ; Liisa C. Haarla ; Shubhi Purwar
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2575 –2585
- DOI: 10.1049/iet-gtd.2015.0268
- Type: Article
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This study discusses the use of time-delayed remote signals available through phasor measuring units (PMUs) for low-order controller design in order to stabilise the power oscillations in the range of 0.3–0.42 Hz between two areas. In the proposed approach, first synchronisation measures are determined among the group of generators located in two areas. Then, an index that characterises the joint observability and controllability property in terms of Hankel singular values is defined as a criterion to preselect the remote feedback signal. Following this, a low-order controller design based on minimisation of H ∞ norm is considered. The measurement redundancy is taken into account in controller design using rotor angle, power flow or speed deviation as feedback signal from one of the generators. Additionally, if some specific PMU fails to provide measurements from a chosen generator, then controller effectiveness is guaranteed using signal from other generator in the same area. The performance of controller is verified considering single-step and multi-step disturbances applied to the reference voltage of exciter system. The comparison with design functions such as H 2 norm, complex stability radius and spectral abscissa are also presented. The analytical results confirm using H ∞ design algorithm provides better dynamic performance.
- Author(s): Mahdi Zarif ; Sadegh Khaleghi ; Mohammad Hossein Javidi
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2586 –2592
- DOI: 10.1049/iet-gtd.2015.0837
- Type: Article
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Today, there are serious trends to use all potentials of the available energy carriers through the concept of energy hubs. However, different types of inherent uncertainties in these systems are the main challenge for utilisation of energy hubs. Furthermore, a framework is presented to analyse the multi-carrier energy systems under five zones of uncertainty in order to achieve the maximum electricity profits. For example, it is shown that the profit of the system is <8.5% despite the 50% of uncertainty in the state without combined heat and power (CHP) while system earns a profit of at least 12.8 in the state with CHP. The Monte Carlo simulation method has used to generate different scenarios. The proposed design methodology decides on which model is suitable for hub. It includes detailed models for transducer performance and hub using the mean and variance of profits and assess of their impact individually. The model also considers information on energy products used as per-unit form. Price and electricity markets have intended as in the day-ahead and real-time pricing with three types of tariffs during the day.
- Author(s): José Rubens Macedo ; José Wilson Resende ; Carlos Augusto Bissochi Jr ; Daniel Carvalho ; Fernando C. Castro
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2593 –2601
- DOI: 10.1049/iet-gtd.2015.0407
- Type: Article
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This study presents the preliminary results of a new methodology for detecting high-impedance faults in distribution systems based on interharmonic signatures. The methodology involves incorporation of an interharmonic current analysis system into a conventional protection system, such as automatic reclosers and sectionalisers. To check the functionality of the proposed methodology, the authors carried out field tests on different types of soil, involving instantaneous current waveform measurements during the occurrence of faults. The results suggest that the methodology, based on interharmonic currents produced by variations in electric arc length during the occurrence of high-impedance faults, shows great promise when it comes to detection of the disturbance.
- Author(s): Shuaihu Li ; Yong Li ; Yijia Cao ; Yi Tan ; Björn Keune
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2602 –2610
- DOI: 10.1049/iet-gtd.2014.1047
- Type: Article
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Unlike the traditional methods that only take static voltage stability or minimum network loss into consideration when optimising capacity of distribution static synchronous compensator (D-STATCOM), a new approach is proposed with considering the risk of voltage sag as well as the network loss and the investment cost of D-STATCOM. This approach can balance the investment cost and technical performance. Monte Carlo method is used for the random setting of fault types and locations to obtain the original probability of voltage sag under some given configuration schemes. Moreover, through revealing the hidden relationship between the original probability and the real-time load, the converted probability is presented to fit the expression for calculating the original probability of voltage sag with respect to the size of additional D-STATCOM. Finally, a single-objective capacity optimisation model is established to obtain the optimum size of additional D-STATCOM, which is based on the economic assessment method of risk. The proposed method is validated in Chinese Dongguang Distribution Networks. The result confirms this method can not only reduce the loss of voltage sag, but also significantly improve the efficiency of D-STATCOM.
- Author(s): Hany M. Hasanien and S.M. Muyeen
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2611 –2616
- DOI: 10.1049/iet-gtd.2014.1146
- Type: Article
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This study presents a novel adaptive control scheme for variable-speed wind turbine (VSWT) driven permanent magnet synchronous generator (PMSG) to ensure its operation under different operating conditions. The adaptive control scheme is based on the affine projection algorithm (APA) which provides a faster convergence and less computational complexity than the least-mean-square algorithm. The proposed adaptive controller is used to control both the generator-side converter and the grid-side inverter without giving additional tuning efforts. Each vector control scheme for the converter/inverter has four APA-based adaptive proportional-integral (PI) controllers. Detailed modelling and the control strategies of the system under study are demonstrated. Real wind speed data extracted from Hokkaido island, Japan is used in this study. The dynamic characteristics of a grid-connected VSWT-PMSG are investigated in details to ensure the proposed controller operation under different operating conditions. The effectiveness of the proposed adaptive controller is compared with that obtained using optimised PI controllers by Taguchi method. The validity of the adaptive vector control scheme is verified by the simulation results which are performed using PSCAD/EMTDC environment.
- Author(s): Eduardo Coelho M. Costa and Sérgio Kurokawa
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2617 –2624
- DOI: 10.1049/iet-gtd.2014.0746
- Type: Article
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An estimation procedure for transmission line parameters is developed that combines a new method of determining line parameters with others available in the technical literature. Each estimation method has certain advantages and restrictions that depend on the operating conditions of the transmission system (e.g. the load profile), the physical characteristics of the line (e.g. the length and the geometry) and electromagnetic phenomena (e.g. single- or multiphase faults). The proposed estimation procedure exploits the major attributes of both the new determination method developed in this study and other well-established methods previously presented in the technical literature. Based on current and voltage measurements obtained from synchronised fault records from both line terminals, a combination of multiple methods can be used to accurately estimate most line parameters, a task that is typically impossible using a single method.
- Author(s): Jerneja Bogovic ; Urban Rudez ; Rafael Mihalic
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2625 –2632
- DOI: 10.1049/iet-gtd.2015.0533
- Type: Article
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Underfrequency load shedding (UFLS) is one of the measures performed when an emergency situation occurs in the power system in order to prevent system collapse. Owing to its importance, a lot of effort is dedicated to research and development of the optimal UFLS. Therefore, several different approaches are available to improve the so-called traditional UFLS schemes into more sophisticated adaptive schemes. On the other hand, the literature lacks a systematic analysis of traditional UFLS schemes, which still present the majority within all UFLS schemes actually used in real power systems. For that reason, the probabilistic power flow is used to quantify the level of performance of many different configurations of traditional UFLS schemes (varied both in the number of shedding steps as well as their size) in the whole variety of operating conditions. With the use of probability power flow the probability density function of active-power imbalance is calculated. The obtained results enable to extract those configurations that yield the best results in most probable events and at the same time avoid giving too much attention on poor performance during less probable system conditions. The results were obtained by performing dynamic simulations on the north-western part of a Slovenian power system.
- Author(s): Jian Liu ; Nengling Tai ; Chunju Fan ; Wentao Huang
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2633 –2643
- DOI: 10.1049/iet-gtd.2015.0792
- Type: Article
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This study presents a new protection scheme for high-voltage direct-current (HVDC) transmission lines which only uses a specific frequency AC current (SFAC) at one of the line terminals during fault transients. The fluctuation characteristic of the root mean square (RMS) of SFAC is analysed under different fault conditions. The fluctuation in the RMS of SFAC during the transient period of internal and external faults is quite different. A fluctuation coefficient (FC) is proposed to measure the fluctuation. Fault types and the faulted line can be distinguished by calculating FC. A HVDC test system modelled in PSCAD/EMTDC is used to validate the proposed scheme considering different fault types, operation modes, sampling frequency and interference. Comprehensive test studies show that the performance of the proposed protection scheme is inspiring, and it is simpler and is of higher reliability compared with some traditional protections based on harmonic currents.
- Author(s): Jiashen Teh and Ian Cotton
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2644 –2652
- DOI: 10.1049/iet-gtd.2015.0601
- Type: Article
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Dynamic thermal rating (DTR) system is one of the efficient ways to increase transmission lines utilisation. Ideally, its application requires the deployment of sensors on each span of the transmission line. This is because a transmission line normally traverses a large geographical area and is affected by various weather conditions. Consequently, each span elongates differently and has different thermal ratings from one another. However, due to the large number of spans, it is uneconomical to place sensors on each span. Whilst doing that, it is also vital to ensure that the DTRs do not cause overrating in any spans to the point of causing ground clearance infringement. Among these spans, some appear to have lower thermal capacity due to its undesirable surrounding weather conditions and may also have smaller ground clearances. In this study, these spans are known as the “critical span”. This study proposed that by monitoring only these critical spans, the DTRs obtained can be safely applied to all other spans without the risk of ground clearance infringement. To do that, a novel critical span identification technique for the optimum placement of DTR sensors is presented in this paper.
- Author(s): Akram Elmitwally ; Abdelfattah Eladl ; Sobhy Mohamed Abdelkader
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2653 –2663
- DOI: 10.1049/iet-gtd.2015.0597
- Type: Article
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This study proposes a new analytical method for transmission power loss allocation in hybrid market power systems. It is based on circuit laws and the orthogonal projection. In this method, the current flow in each branch is divided into two components. The first one is due to the power transfer from generators to loads. The second component is due to the voltage differences between generator buses. The later currents are called no-load or circulating currents. These current components are computed by using the superposition principle. The responsibility of each load and generator to power losses in each branch of the network is derived analytically. Hence, the share of each load or generator in the overall transmission network losses is estimated. Furthermore, the impact of bilateral/multilateral contracts is included in the transmission network power loss allocation algorithm. The method is extended to consider the time variation of loads and wind generation. The proposed method is applied to four test systems and compared with other methods.
- Author(s): Sen Ouyang ; Ping Liu ; Liyuan Liu ; Xiang Li
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2664 –2671
- DOI: 10.1049/iet-gtd.2015.0547
- Type: Article
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This study discusses the sensitivity (i.e. ride-through performance) of low-voltage releases to voltage sags on the basis of extensive tests, and presents two sensitivity models to assess the tripping characteristics of low-voltage releases, which have not been studied before. First, working principle of low-voltage release and existing standards are reviewed. Second, a detailed test scheme is proposed and ten kinds of low-voltage releases have been tested. Test results show that magnitude, duration and point-on-wave angle of voltage sag jointly determine the sensitivity of low-voltage releases. After extremely processing test results and applying the curve fitting theory, the functions representing the relationship between magnitude and duration at different point-on-wave angles are formed, which symbolise a detailed sensitivity model of low-voltage release. Moreover, the other simpler and more practical sensitivity model is proposed by introducing rectangular envelope lines of voltage tolerance curves at different point-on-wave angle.
- Author(s): Le Zheng ; Wei Hu ; Qiuyu Lu ; Yong Min
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2672 –2678
- DOI: 10.1049/iet-gtd.2014.1168
- Type: Article
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In recent years, the energy storage system (ESS) has been demonstrated to be involved in many aspects of the integration of wind power. For ESS application, ESS allocation of the installation location, power rating, and energy rating is the first concern. Different from previous studies, this study emphasises the significance of the ESS operation in the study of ESS allocation. A bi-level-programming-based model is proposed to take the interaction of allocation and operation into consideration at the same time, with the external level optimising allocation and the internal level optimising operation. The complexity assessment and solution algorithm of the model is also discussed. Next, a genetic numerical algorithm is proposed to solve the bi-level model. The authors’ results were tested on a modified IEEE 39 bus system and a provincial regional power system to verify both the flexibility and applicability of the proposed model and algorithm. This model is useful for various types of ESS and provides a foundation for ESS application.
- Author(s): Andrew J. Urquhart and Murray Thomson
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2679 –2685
- DOI: 10.1049/iet-gtd.2015.0546
- Type: Article
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Models of power distribution networks require accurate cable impedance data. For unbalanced networks, both the self-impedances and the mutual impedances are needed. However, published studies use differing approaches to determine cable impedances, leaving uncertainty over the level of detail required. This study compares impedances provided by the manufacturer with those from several analytical methods, showing the impact of modelling the non-circular geometry and of including corrections allowing for the AC resistance. The analysis is compared to results from a freely available finite element (FE) solver where the current distribution is modelled in detail, taking account of eddy currents and the rotation of the cores relative to the neutral due to the cable lay. At 50 Hz, the analytical methods provide a good approximation, but the FE results show that eddy currents affect the impedance at harmonic frequencies. The results also show the impact of including the ground path in the impedance calculation. The current distribution in the ground has a wide cross-sectional area, suggesting that the assumption of a perfect multi-grounded neutral is inappropriate for low voltage networks with short cable lengths.
- Author(s): Ghader Isazadeh ; Amin Khodabakhshian ; Eskandar Gholipour
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2686 –2696
- DOI: 10.1049/iet-gtd.2015.0576
- Type: Article
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This study presents a new intelligent controlled islanding scheme based on wide area measurement systems data to avoid the wide area blackout. Three offline, online and real-time parts are applied to solve three problems including where and when to implement islanding and what to do after separation. New security-based criteria are used to determine the initial stable coherent groups. The boundaries of islands are obtained adaptively considering different operating points by using the weighted time varying graph structure of the network. To reach more stable islands, reactive power is considered by using a self-tuned online fuzzy factor in graph weights. The number of necessary islands with their locations is determined in online part by monitoring the dominant inter-area oscillations between the initial groups (IGs). Then, the network is split into islands with the objective of minimum power flow disruption. To detect the unavoidable islanding cases correctly, a new parallel adaptive neuro-fuzzy inference system (ANFIS) structure is designed. In a parallel structure, for each of two adjacent IGs a distinct ANFIS is also applied to consider variable stability margins between groups. Simulation results confirm that the blackout can be avoided in a large power grid by using the proposed method.
- Author(s): Jiashen Teh and Ian Cotton
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2697 –2704
- DOI: 10.1049/iet-gtd.2015.0351
- Type: Article
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Future grids will be operated much closer to their security limits due to the ever increasing power demands and the restrictions on land and space to build more transmission corridors. As one of the many smart grid technologies, the dynamic thermal rating (DTR) system of transmission lines offers the solution to increase line current capacity without infringing the conductor's maximum operating temperature. Hence, it has emerged as a popular solution for the aforementioned challenges. Owing to that, there is a strong need to assess the integrity of this technology. For this reason, this study presents a systematic framework for assessing the reliability and the risk of a DTR system. The research was carried out in two parts and is able to optimise the risk and the reliability (cost) of the DTR system. In addition, a weather estimation model is proposed to estimate the weather data when the DTR sensors are not functional. This is contrary to the existing literature which suggests that conservative assumptions be made. The results show that the proposed weather estimation model avoids overestimation of the DTR system risk.
- Author(s): Ahmed M.A. Haidar ; Kashem M. Muttaqi ; Mohammed H. Haque
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2705 –2716
- DOI: 10.1049/iet-gtd.2014.1019
- Type: Article
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p.
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Accurate electric vehicle (EV) load modelling is a daunting task because the proportion and characteristics of these extra electrical loads in the grids are continuously changing. In many recent EV studies, EV load is assumed to be a constant power load to analyse the effect of EV charging on electric network. However, such an assumption would not be effective in real-time application and can give misleading results. This study proposes a multistage time-variant EV load modelling technique based on the characteristics of EV load demand due to EV battery charging. To capture the transitions between different stages of battery charging, the EV loads are modelled with a multistage scheme and implemented ZIP model. A comparative study of energy losses and voltage profile is carried out on the IEEE 69-bus test system for the use of a traditional constant load model, conventional ZIP load model and the proposed multistage time-variant EV load model. Results show that the load models can significantly affect the energy losses and terminal voltages, and provide misrepresentation if EV load is not accurately modelled. Therefore, for proper analysis of EV loads during unidirectional charging, it is essential to have accurate models for predicting true EV behaviour.
- Author(s): Ziyi Huang ; James A Pilgrim ; Paul Lewin ; Steve Swingler ; Gregory Tzemis
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2717 –2723
- DOI: 10.1049/iet-gtd.2015.0551
- Type: Article
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2717
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With an increasing number of offshore high-voltage direct current wind farm projects planned, submarine cable crossings become inevitable. It is important to accurately rate these circuits, because if high temperatures occur at crossing points, the cable may age prematurely. At present, the IEC60287-3-3 crossing rating method is inapplicable to such crossings due to a failure of the ‘Image’ theory, and it is challenging to carry out other analytical studies due to the difficulties in modelling the subsea thermal environment. As a solution, this study presents a new finite element analysis approach to study the thermal performance of submarine crossings under various continuous rating combinations and rock protection layer conditions, to provide guidelines for crossing operation. With focus on the free thermal convection mechanism within the rock layer, the significance of this mechanism is highlighted in a quantitative manner. It shows that when the free convection is preserved, the upper circuit can operate safely with its stand-alone rating regardless of the crossing; while the lower circuit may require a de-rating if its stand-alone rating is thermally limited.
- Author(s): Amir Fazeli ; Mark Sumner ; Mark Christopher Johnson ; Edward Christopher
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2724 –2735
- DOI: 10.1049/iet-gtd.2015.0182
- Type: Article
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Integration of intermittent renewable resources and mass electrification of heat and transport into the existing electricity network, with limited network asset reinforcement requires incorporation of intelligence in the form of active management of flexible resources within different sections of the distribution network. A hierarchical multi-level control framework is proposed for this purpose which incorporates the appropriate optimisation and control strategies at different levels. In particular, a novel deterministic control algorithm for controlling power flows at the community cell level has been developed and presented in this study. This algorithm incorporates robustness to communication and device failure and is easily expandable to an arbitrary number of devices. The simulation results presented in this study show that the effectiveness of the proposed control technique depends on distributed energy resources flexibility and storage capacity.
- Author(s): Marek Florkowski ; Jakub Furgał ; Maciej Kuniewski
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2736 –2742
- DOI: 10.1049/iet-gtd.2015.0395
- Type: Article
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In modern power grids more and more switching and reconfiguration operations are performed, leading to harmful overvoltages. In addition, external factors causing overvoltages may also be dangerous to insulation systems, especially those which occur during lightning strikes. Overvoltages propagate in power transformers along the windings and between them, influencing the insulation systems of the windings as well as those of other electrical devices. An interesting phenomena which takes place in the networks relates to the transferred overvoltages propagating through distribution transformers. The internal and transferred overvoltages for transformers with a conventional steel core and for those with an amorphous core are analysed in this study. The frequency response of overvoltages which occur when the transformer is exposed to a voltage impulse of rectangular shape form the basis of the analysis. Surges of rectangular shapes simulate transient voltages occurring at surge arresters. The frequency response of overvoltages reveals the transformer response to oscillating transient components of overvoltages generated in the power systems. The coincidence of frequency responses of overvoltages and admittances for transformers is also presented.
- Author(s): Alexander C. Melhorn and Aleksandar Dimitrovski
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2743 –2750
- DOI: 10.1049/iet-gtd.2015.0521
- Type: Article
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2743
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With the introduction of higher levels of renewables and demand response programs, traditional deterministic power system tools fall short of expectations. Probabilistic load flow (PLF) takes into account the inconsistency or the unknown loads, and generation in the fundamental load flow analysis. This study proposes a PLF solution for both balanced and unbalanced, radial and weakly meshed networks without explicitly using the Y -bus matrix. It allows for discrete probability density functions as input variables without having to assume a predefined distribution. The nodal voltages and the power flows can be calculated independently from one another. The proposed method is applied to the IEEE 123 Node Test Feeder and the IEEE 13 Node Test Feeder in both its original radial configuration and a modified mesh configuration, including a load replaced with a wind turbine. The results are validated by comparison of the proposed method's solutions to those obtained using cumulants and Monte Carlo simulation. The proposed PLF method provides an accurate and practical way for finding the solution to stochastic problems occurring in power distribution systems allowing for real-system data to be analysed.
- Author(s): Liang Wang ; Xiaorong Xie ; Qirong Jiang ; Xiangdong Liu
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2751 –2759
- DOI: 10.1049/iet-gtd.2015.0720
- Type: Article
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2751
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Practical subsynchronous instability events have been observed in doubly fed induction generator-based wind farms, which are radially connected to fixed series compensated transmission lines. As a special type of subsynchronous resonance, this phenomenon is described here as subsynchronous control interaction (SSCI). This study proposes a centralised SSCI mitigation scheme named as subsynchronous damper (SSD). In this scheme, an additional high-power electronic voltage-sourced converter is added to the collection bus of wind farms. It is designed to dissipate the electrical resonance power of SSCI. Thus, SSD provides positive damping for SSCI. Its basic principle is explained with equivalent electric circuit and the sufficient conditions for stabilisation are obtained mathematically. Controller design guidelines are given and have been verified first by eigenvalue analysis. Then a method to choose the capacity of power electronic converter is proposed. The effectiveness of SSD is finally demonstrated by extensive time-domain simulations on a target system.
- Author(s): Yang Weng ; Marija D. Ilić ; Qiao Li ; Rohit Negi
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2760 –2767
- DOI: 10.1049/iet-gtd.2015.0191
- Type: Article
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This study is motivated by major needs for accurate bad data detection and topology identification in the emerging electric energy systems. Due to the non-convex problem formulation, past methods usually reach a local optimum. This deficiency may lead to wrong bus/branch modelling and inappropriate noise assumption, causing significantly biased state estimate, incorrect system operation, and user cutoff. To overcome the local optimum issue, the authors propose in this study how to convexify bad data detection and topology identification problems to efficiently locate a global optimum result. To reduce relaxation error in the convexification procedure, a nuclear norm penalty is added to better approximate the original problems. Finally, they propose a new metric to evaluate the detection and identification results, which enables system operator to know how confidence one is for further system operations. Simulation results performed for several IEEE test systems show promising results for the future smart grid in improved accuracy.
- Author(s): Mamdouh Abdel-Akher ; Ali Selim ; Mohamed M. Aly
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2768 –2774
- DOI: 10.1049/iet-gtd.2015.0866
- Type: Article
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This study presents a developed formulation for solving the quasi-static time-series simulation in unbalanced power distribution systems. This simulation is very important for analysing a set of given daily load curves under various operating conditions. The Lagrange polynomial approximation is implemented to predict an initial guess of both voltage magnitude and phase angle at time instants in vicinity of the given power-flow solutions. The developed methods are categorised based on the required number of power-flow solutions to predict the initial guess. The linear approximation of the Lagrange polynomial requires the knowledge of two power-flow solutions, whereas the non-linear approximation requires three power-flow solutions. The predicted values of both voltage magnitudes and angles are corrected using power-flow engine. The adopted power-flow solver uses the forward/backward sweep. The developed methods were tested using the unbalanced IEEE 123-node and 33-node test feeders with a set of daily load curves and intermittent distributed energy resources. The developed methods are compared with the method which utilises the previous power-flow solution as an initial guess. The results show that the number of iterations and computation time of quasi-static time-series simulations are greatly reduced.
- Author(s): Her-Terng Yau ; Cheng-Chi Wang ; Chin-Tsung Hsieh ; Shang-Yi Wu
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2775 –2781
- DOI: 10.1049/iet-gtd.2015.0500
- Type: Article
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It is known that real-time power quality monitoring is usually rather difficult to achieve due to the requirement of expensive equipments and necessary of more signals to be captured. To solve this problem, this study combines fractional order Sprott chaos synchronisation system with extension theory to detect power signal disturbance including voltage swell, sag, interruption, and harmonics for real-time power quality monitoring. The use of fractional order chaotic systems can significantly improve the situations of misjudgement due to the dynamic error is too large by using general integer order chaotic systems. Otherwise, the three-dimensional (3D) Sprott error dynamics can be reduced to 2D error system. It will become easier and cheaper to implement this scheme in the portable device. The results of numerical simulation show that the detection accuracy rate is 100% and it is better than the methods in previous studies. It should be able to get a very high diagnostic accuracy if this method can be applied to the actual power system.
- Author(s): Asghar Ali ; Abdul Qayyum Khan ; Babar Hussain ; Muhammad Taskeen Raza ; Muhammad Arif
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2782 –2791
- DOI: 10.1049/iet-gtd.2014.1023
- Type: Article
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The study discusses a model-based fault diagnosis scheme for detection of faults in power systems. The fault models in power generating units (PGUs) and transmission and distribution networks (T&DN) have been derived in state space form. An observer-based fault detection filter (FDF) has been used to detect these faults. Observer-based FDF is used because of its simplicity, reliability and ease of implementation. A single machine infinite bus power system is considered wherein a synchronous generator is connected to a T&DN through a bus system. Actuator and sensor faults in PGU, and symmetric faults in T&DN have been modelled and simulated in Matlab/Simulink. The simulation results show that a fault, whenever occurs in the aforementioned parts of power systems, is detected using the knowledge of the faults models proposed in this work.
- Author(s): Chao Duan ; Wanliang Fang ; Lin Jiang ; Jun Liu
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2792 –2798
- DOI: 10.1049/iet-gtd.2015.0623
- Type: Article
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Three measures, namely, the adaptive barrier update strategy, the filter-line-search method and the feasibility restore phase, are simultaneously introduced in the conventional primal–dual interior point method (IPM) framework to enhance the robustness of existing optimal power flow algorithms when applied to systems with considerable number of flexible AC transmission system (FACTS) devices. First, an adaptive barrier parameter strategy is employed to update the barrier parameter after the current μ-barrier problem solved to certain accuracy. Second, a filter-line-search procedure is introduced to generate the next iterate. Third, the algorithm initiates a feasibility restore phase as a remedy in case of getting stuck at a non-optimal point. Comparative case studies with previous algorithms on both standard test systems and large-scale real-world systems demonstrate the novel algorithm outperforms conventional IPMs in robustness and efficiency.
- Author(s): Jianqiang Hu ; Jinde Cao ; Taiyou Yong
- Source: IET Generation, Transmission & Distribution, Volume 9, Issue 16, p. 2799 –2810
- DOI: 10.1049/iet-gtd.2015.0232
- Type: Article
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Demand-side resources have considerable potential, which can provide efficient load shedding operations so as to maintain the supply–demand balance together with generating units. This study is concerned with active power dispatch and control problems by considering both generating units and demand-side resources, where some controllable loads in demand-side are aggregated under each bus load agent. A multi-level dispatch control architecture is proposed, which can handle the optimisation and control problems in different time scales. Specifically, an upper layer performs calculation of system's look-ahead dispatch for generating units and bus load agents, while a middle level computes control actions for multiple load clusters in each bus load agent via a distributed consensus estimation algorithm, and multiple energy management units in the lower layer respond the control instruction issued from the load cluster based on a distributed pinning control algorithm. For the middle and lower layers, participants can communicate with its neighbours via sparse communication networks for the sake of distributed calculation or distributed control, which is more robust than the centralised strategies in terms of dealing with massive amounts of participation units. The simulation results on a modified IEEE 9 bus system show the applicability of the proposed architecture.
Analytical approximate calculation of losses for modular multilevel converters
Assessing the effect of wind power peaking characteristics on the maximum penetration level of wind power
Decentralised coordinated control of microgrid based on multi-agent system
Applying high-voltage direct current emergency control to suppress the peak value of ultra-high-voltage tie-line power oscillation
Feature extraction and severity assessment of partial discharge under protrusion defect based on fuzzy comprehensive evaluation
Monitoring and identification of metal–oxide surge arrester conditions using multi-layer support vector machine
On-line fault monitoring system for hydroelectric generators based on spectrum analysis of the neutral current
Generating simple-to-apply comprehensive engineering recommendation for earthing safety in systems with solidly earthed neutral
Compacting and partitioning-based simulation solution for frequency-dependent network equivalents in real-time digital simulator
Steady-state model for the three-leg shunt-series ac-link power flow controller
Fault detection for offshore wind farm connected to onshore grid via voltage source converter-high voltage direct current
Modelling hierarchical decision making framework for operation of active distribution grids
Multi-criteria optimisation approach to increase the delivered power in radial distribution networks
Low-order controller design using remotely measured time delayed signals for stabilisation of equivalent power grid
Assessment of electricity price uncertainty impact on the operation of multi-carrier energy systems
Proposition of an interharmonic-based methodology for high-impedance fault detection in distribution systems
Capacity optimisation method of distribution static synchronous compensator considering the risk of voltage sag in high-voltage distribution networks
Affine projection algorithm based adaptive control scheme for operation of variable-speed wind generator
Estimation of transmission line parameters using multiple methods
Probability-based approach for parametrisation of traditional underfrequency load-shedding schemes
Protection scheme for high-voltage direct-current transmission lines based on transient AC current
Critical span identification model for dynamic thermal rating system placement
Efficient algorithm for transmission system energy loss allocation considering multilateral contracts and load variation
Test and analysis on sensitivity of low-voltage releases to voltage sags
Optimal energy storage system allocation and operation for improving wind power penetration
Series impedance of distribution cables with sector-shaped conductors
New intelligent controlled islanding scheme in large interconnected power systems
Risk informed design modification of dynamic thermal rating system
Multistage time-variant electric vehicle load modelling for capturing accurate electric vehicle behaviour and electric vehicle impact on electricity distribution grids
Thermal modelling and analysis for offshore submarine high-voltage direct current cable crossings
Real-time deterministic power flow control through dispatch of distributed energy resources
Propagation of overvoltages in distribution transformers with silicon steel and amorphous cores
Three-phase probabilistic load flow in radial and meshed distribution networks
Centralised solution for subsynchronous control interaction of doubly fed induction generators using voltage-sourced converter
Convexification of bad data and topology error detection and identification problems in AC electric power systems
Initialised load-flow analysis based on Lagrange polynomial approximation for efficient quasi-static time-series simulation
Fractional order Sprott chaos synchronisation-based real-time extension power quality detection method
Fault modelling and detection in power generation, transmission and distribution systems
Adaptive barrier filter-line-search interior point method for optimal power flow with FACTS devices
Multi-level dispatch control architecture for power systems with demand-side resources
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