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  • Operational flexibility of active distribution networks: Definition, quantified calculation and application
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-27
    Peng Li; Yuelong Wang; Haoran Ji; Jinli Zhao; Guanyu Song; Jianzhong Wu; Chengshan Wang

    With a high penetration of intermittent distributed generators (DGs), the uncertainties in active distribution networks (ADNs) are exacerbated and further coupled in the networks. It brings enormous challenges on system operation and puts forward a higher requirement for the operational flexibility of ADNs. However, due to the secure constraints and diverse operational requirements, the controllability of controllable resources (CRs) cannot fully facilitate the flexible operation of ADNs. Operational flexibility is seen as a link between diverse operational requirements and flexible adjustment capabilities of CRs, which also represents the ability of the network to deploy its CRs to respond to the change of operation states. Under the framework of operational flexibility, multiple types of operational optimization problems can be reinterpreted, which provides a new perspective for the operation of ADNs. In this paper, the definition and region-based mathematical formulation of operational flexibility for ADNs are proposed firstly. Then the quantified calculation method of operational flexibility is proposed to represent flexibility provision (FP) and flexibility availability (FA). The application of operational flexibility is analyzed from the perspective of diverse operation and improvement of flexibility. Finally, case studies are performed on the modified IEEE 33-node system to show the effectiveness of the proposed method.

    更新日期:2020-01-27
  • Damage analysis of CFCC wire over-sliding pulley based on finite element method
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-27
    Chao Zhou; Shijie Zhao

    A new type of stranded carbon fiber composite core (CFCC) wire has been developed to improve the properties of the bending, torsion and resistance to lateral pressure of the carbon fiber wire. The over-sliding process of CFCC wire under the coupling actions of pulling and bending loads is the key factor to determine whether the CFCC wire is damaged or not. A CFCC wire is taken as an example to study how the bottom diameter of the pulley put impact upon the strand damage and the damage mechanism. A full-size model of CFCC wire is established with the nonlinear finite element method to study the over-sliding process. The results show that the strand damage will be improved with the increasing of the bottom diameters of the pulley, whereas the equivalent plastic strain and energy loss of the strand will decrease. It is also found that the CFCC wire damage is beyond the reasonable range when the pulley is 20 times the diameter of the CFCC wire. Moreover, it is suggested that the CFCC wire strand damage is within the allowable range when the bottom diameter of the pulley is not less than 25 times the CFCC wire diameter.

    更新日期:2020-01-27
  • An efficient power-flow approach based on Heun and King-Werner’s methods for solving both well and ill-conditioned cases
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-27
    Marcos Tostado-Véliz; Salah Kamel; Francisco Jurado

    Solving the Power-Flow in ill-conditioned cases is still challenging as most of the available robust methodologies are not efficient enough to be widespread used in industry applications. This paper addresses this issue by developing a novel approach suitable for both ill and well-conditioned power cases. Since the developed approach arises from the combination of the King-Werner and Heun’s methods, it is called Heun-King-Werner method. The developed approach naturally performs as a robust method in ill-conditioned cases and as a high order Newton-like method in well-conditioned systems, which makes it very suitable for solving both cases. The developed approach is tested using various realistic well and ill-conditioned cases under different demanding scenarios. Its performance is compared with other well-known Power-Flow methods. Results show that the developed approach is robust, reliable and computationally much more efficient than other well-known methods. In well-conditioned systems, it performs similar to the standard NR method but improving its convergence features in some cases. Based on the results, the developed approach may be widespread used in industry tools.

    更新日期:2020-01-27
  • Design of integral terminal sliding mode controller for the hybrid AC/DC microgrids involving renewables and energy storage systems
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-24
    Hammad Armghan; Ming Yang; Ammar Armghan; Naghmash Ali; M.Q. Wang; Iftikhar Ahmad

    Traditional power generation is in the midst of a major transformation, and renewable based microgrids are playing a key role in this energy structure transition. This paper investigates the design of a centralized nonlinear controller based on the integral terminal and fast integral terminal sliding mode control for hybrid AC/DC microgrid involving renewable distributed generator as a primary source, fuel cell (FC) as a secondary source, and battery-ultracapacitor as hybrid energy storage system (HESS). At first, the detailed mathematical model of the hybrid AC/DC microgrid is established. Then, the controller is designed with the main objective to ensure the constant DC and AC bus voltage during islanding and grid-connected mode. During grid-connected mode, the controller is capable of providing frequency support to the utility grid. After that, the asymptotic stability of the hybrid AC/DC microgrid is proved using Lyapunov stability criteria. Then, the performance and robustness of the proposed control approach are tested by simulating it on MATLAB/Simulink, and the results are compared with sliding mode controller and Lyapunov redesign. Finally, real-time hardware in the loop tests are conducted to validate the effectiveness of the proposed framework.

    更新日期:2020-01-24
  • Analysis of the impact of sub-hourly unit commitment on power system dynamics
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-24
    T. Kërçi; J. Giraldo; F. Milano

    This paper discusses the impact of the sub-hourly unit commitment problem on power system dynamics. Such an impact is evaluated by means of a co-simulation platform that embeds a sub-hourly stochastic mixed-integer linear programming security constrained unit commitment (sSCUC) into a time domain simulator, as well as includes a rolling planning horizon that accounts for forecast updates. The paper considers different sub-hourly sSCUC resolutions (i.e., 5 and 15 min) and different wind penetration levels (i.e., 25 and 50%). The focus is on the transient response of the system and on frequency variations following different sSCUC strategies, and different sSCUC wind power uncertainty and volatility. The case study consists of a comprehensive set of Monte Carlo simulations based on the 39-bus system.

    更新日期:2020-01-24
  • A Low Voltage Ride Through Strategy of DFIG based on Explicit Model Predictive Control
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-24
    Jia Luo; Haoran Zhao; Shuning Gao; Mingzhe Han

    In this paper, an improved demagnetization control, based on Explicit Model Predictive Control (E-MPC) is proposed to improve Low Voltage Ride Through (LVRT) capability of Doubly Fed Induction Generators (DFIGs). By injecting an additional rotor current component, the demagnetization control can efficiently eliminate the free and negative flux to avoid saturation of the rotor converter. The conventional demagnetization control is based on fixed scaling factors, whose control performance can’t be guaranteed for different fault conditions. The proposed E-MPC approach can fully explore the potential of rotor side converter. Besides, the control parameters of E-MPC are derived offline and very efficient for online control. In addition, the proposed E-MPC structure is simple and easy to be implemented. The mechanism of proposed E-MPC is presented in detail and verified in Matlab/Simulink. The results show that the proposed control scheme has a good performance and can improve the LVRT capability of DFIGs under various fault conditions, especially unbalanced faults.

    更新日期:2020-01-24
  • IEC 61850 based energy management system using plug-in electric vehicles and distributed generators during emergencies
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-22
    S.M. Suhail Hussain; Mohd. Asim Aftab; Ikbal Ali; Taha Selim Ustun

    During emergencies, alternative power system operation that utilizes local assets to energize local loads will change the face of the situation. While distributed generators (DGs) such as PV or wind turbines can be utilized for generation, plug-in electric vehicles (PEVs) can act as mobile generators. Different strategies for forming dynamic and networked microgrids utilizing the local generation during emergencies have been widely proposed in literature. However, the underlying communication required for optimal formation of dynamic microgrids and energy management during emergencies is not discussed. Addressing this gap, this paper develops a communication-based energy management system for emergency cases based on IEC 61850 standard. The IEC 61850 based communication modeling provides interoperability and serves for plug-and-play purposes. Furthermore, for establishing communication during emergencies the concept of Cognitive Radio (CR) is proposed in this scheme. Simulation results show the feasibility of modeling and acceptability of its performance.

    更新日期:2020-01-23
  • Sustainable microgrids with energy storage as a means to increase power resilience in critical facilities: An application to a hospital
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-21
    Alexis Lagrange; Miguel de Simón-Martín; Alberto González-Martínez; Stefano Bracco; Enrique Rosales-Asensio

    This manuscript proposes to study different cases that require the use of renewable energies in addition to diesel generators and energy storage systems with the aim of increasing the resilience of a microgrid feeding critical facilities. The aim of the work here presented is to quantify the benefits provided by an improvement of the energy resilience that could be achieved by installing a microgrid in a hospital fed by renewable energy sources. The microgrid will use a scheme based on solar PV in addition to diesel generators and an energy storage system based on electrochemical batteries. First, it has been evaluated how the implant of the microgrid increases the resilience of the power supply when a power failure occurs, considering that the main application in a hospital, even in the event of breakdowns, is to ensure the continuity of the surgical procedures and safely store drug stocks. Thus, these have been defined as the critical loads of the system. The components sizes have been optimized by considering both economic profitability but also the resilience capacity, observing that, by installing solar photovoltaic modules, Li-ion batteries and diesel generators, according to simulations performed in REopt® software, the microgrid could save approximately $ 440,191 on average over a 20-year life cycle of the facility (both considering the mitigation of energy provide by the power grid and the avoided losses during probable power services interruptions), while increasing the minimum resilience of the installation more than 34 h.

    更新日期:2020-01-22
  • Comparative analysis of the measurement methods for the supraharmonic range
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-17
    Thais M. Mendes; Carlos A. Duque; Leandro R. Manso da Silva; Danton D. Ferreira; Jan Meyer; Paulo R. Ribeiro

    This paper provides an in-depth analysis of the methodologies proposed by the IEC 61000-4-7 and IEC 61000-4-30 standards for the supraharmonic frequency range. The paper presents the stat-of-the-art concerning supraharmonics and describes the existing standardized measurements for supraharmonics. The different ways of performing the measurements proposed by such standards are compared. The main contribution and novelty of the paper are the comparative analysis of the standardized measurement methods which considers both efficiency and computational complexity of them. Analyzes considering real signals, a real time signal, a time-varying synthetic signal and the influence of the noise level for the methodologies proposed by the IEC 61000-4-7 and IEC 61000-4-30 standards were performed. Finally, alternative ways of measuring supraharmonics are suggested. One may conclude that the method described in IEC 61000-4-30 showed to be less immune to noise and less complex (in terms of mathematical operations required during processing) than that described in the IEC 61000-4-7, but loses accuracy in estimating high-amplitude supraharmonic components.

    更新日期:2020-01-21
  • IEC 61970 standard based common information model extension of electricity-gas-heat integrated energy system
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-20
    Shouxiang Wang; Zihan Meng; Shuangchen Yuan

    Power system, natural gas system, and thermal system are traditionally managed by different types of companies, resulting in information islands among different systems. In order to break the information islands phenomenon and realize the unified management of electric-gas-heat integrated energy system, this paper thoroughly analyses the composition and characteristics of the electricity-gas-heat integrated energy system and extends the common information model by using object-oriented modeling concept based on the IEC 61970 to meet the needs of integrated energy systems, such as multi-energy flow calculation, optimal scheduling, and operational control. The complete extended model of natural gas system, thermal system, coupling links and multi-energy storage systems is built. In addition, the attributes of key classes in the electricity-gas-heat integrated energy system are described, such as the classes of natural gas source, natural gas transporting unit, natural gas pipeline, natural gas load, motor-driven compressor, power-to-gas unit, power-to-heat unit, natural gas storage system, thermal storage system and hydrogen storage system. The extended common information model of electricity-gas-heat integrated energy system is built under the Rational Rose platform and an example verification is carried out to generate XML file and partial code of header file and source file in order to test the rationality of the extended common information model.

    更新日期:2020-01-21
  • A resilience assessment approach for power system from perspectives of system and component levels
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-21
    Xiaonan Liu; Kai Hou; Hongjie Jia; Junbo Zhao; Lamine Mili; Yunfei Mu; Jusong Rim; Yunkai Lei

    This paper proposes a novel resilience assessment approach for power system. Two resilience indices are developed from the perspectives of the system and individual component levels, respectively. The former one quantifies the resilience of a power system in a system-wide manner, while the latter is intended to assess the individual component through the pre-disruption and post-disruption indices. Specifically, the pre-disruption index is used to determine the weak points of the system before the occurrence of disruptions, while the post-disruption index is for designing the optimal restoration strategies. We advocate the use of impact-increment-based state enumeration method to calculate the presented indices in an efficient way without loss of accuracy. Numerical results carried out on the IEEE RTS-79 test system and the IEEE 118-bus system validate the effectiveness of the proposed approach and indices.

    更新日期:2020-01-21
  • Grid inadequacy assessment for high power injection diversity. Part I: Framework and metrics
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-16
    Adonis E. Tio; David J. Hill; Jin Ma

    The integration of more intermittent generation, energy storage, and dynamic loads on top of a competitive market environment requires future grids to handle increasing diversity of power injection states. Grid planners need new tools and metrics that can assess the vulnerability of grids in this future. To this end, we propose a new grid inadequacy assessment framework and a set of metrics that expose a grid’s inherent inability to accommodate high power injection diversity without intervention. We define the metrics based on a previously unexplored characterization of grid inadequacy, that is, we use the size of the power flow infeasible set relative to the size of the power injection set as indicator of inherent grid inadequacy. We circumvent the difficulty of characterizing the high-dimensional sets involved using three approaches: one scenario-based approach and two novel approaches that project the sets in lower dimensions. Illustrative examples show how the metrics can reveal useful insights about existing grid bottlenecks resulting from diverse operating states that may otherwise go unnoticed. As with other metrics, the proposed metrics are only valid relative to the assumptions used and cannot capture all intricacies of assessing grid inadequacy. Nevertheless, the metrics provide a new way of quantifying grid inadequacy that is potentially useful in future research and practice. Part II of the paper studies the application of the metrics in identifying and assessing grid expansion options that are less inherently inadequate than others.

    更新日期:2020-01-17
  • An improved fault current limiting circuit for VSC-HVDC transmission system
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-15
    Muhammad Ahmad; Wang Zhixin; Zhang Yong

    In order to maximize the utility of renewable energy resources, long-distance power transmission lines are essentially required. To accomplish this purpose, the voltage-source-converter (VSC) based high voltage direct current (HVDC) transmission is considered an attractive option. However, due to DC-link capacitors and their discharge currents, the VSC-HVDC based transmission networks are more vulnerable to short circuit faults. The direct current circuit-breakers (DCCBs) are considered a reliable option to protect the transmission line against short circuit faults. The DCCBs with increased voltage rating and fault-current interruption capability are still considered a gigantic problem. The capacity issues of DCCBs can be alleviated using some external circuits to reduce the intensity of fault-current. This paper introduces an external fault-current limiting circuit (FCLC), which is non-superconducting in nature, and it consists of power electronics-based bidirectional switches, current limiting inductor, and power dissipating resistor. This circuit is placed in series with a DCCB, to escalate the response time in the advent of fault, to restrict the maximum value of fault-current, and to reduce the stresses on energy absorption components in DCCB. The circuit is activated only when fault-current limitation operation is required, thereby, the proposed FCLC has zero power-loss in the nonoperational state, and has no influence on the steady-state performance of the system. Furthermore, regarding FCLC, the detailed working principle, parametric analysis, and rigorous evaluation of performance are accomplished in this paper. The theoretical concepts are validated using a three-terminal VSC-HVDC model and equivalent circuit analysis, in PSCAD/EMTDC simulation-based environment. The results of FCLC are compared with other solutions in the literature. The comparison of results concludes that the proposed FCLC own better characteristics, in terms of control features, fault clearing time, and power losses.

    更新日期:2020-01-15
  • Gain normalized adaptive observer for three-phase system
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-15
    Hafiz Ahmed; Miao Lin Pay; Mohamed Benbouzid; Yassine Amirat; Elhoussin Elbouchikhi

    This paper proposes the estimation of parameters and symmetrical components of unbalanced grid using adaptive observer framework. Recent adaptive observers proposed in the literature doesn’t employ any gain normalization in their frequency estimation loop. This can be problematic in the presence of large voltage dip. This paper proposes a solution to overcome this limitation using a novel gain normalized - frequency-locked loop (GN-FLL). Technical details of GN-FLL, stability analysis and tuning are provided in this paper. Comparative experimental results with adaptive Luenberger observer, second-order generalized integrator - phase-locked loop (SOGI-PLL) and enhanced PLL (EPLL) are provided to demonstrate the effectiveness the proposed technique in the single-phase case. Comparative experimental results with double SOGI-FLL (DSOGI-FLL) and adaptive notch filter (ANF) are provided to demonstrate the effectiveness the proposed technique in the three-phase case.

    更新日期:2020-01-15
  • Temperature characteristics and influence of water-saturated soil resistivity on the HVDC grounding electrode temperature rise
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-14
    Xishan Wen; Maoheng Jing; Hansheng Cai; Yanhui Zhang; Shangmao Hu; Yun Teng; Gang Liu; Lei Lan; Hailiang Lu

    The temperature rise process has always been the main factor for the safe operation of high-voltage direct current (HVDC) grounding electrodes, and the soil resistivity is the key parameter affecting the temperature rise of the grounding electrode. In some region where rainfall is high or groundwater is abundant, the soil moisture content at the electrode site may be very high or saturated. Therefore, studying the temperature characteristics of soils with saturated water content (water-saturated soil) for grounding electrode heating is particularly important. In this study, the resistivity measurement of temperature rise was conducted on different types of water-saturated soil. On the basis of this measurement result, an electro-thermal coupling finite element model of grounding electrode in water-saturated soil was established. Then the reliability of the coupled model is verified through an experiment of the vertical electrode in water-saturated soil. The comparison of experimental and simulation results shows that the maximum temperature error is 3.5%. Finally, the influence of water-saturated soil resistivity on practical engineering application was analyzed. Under the condition of water-saturated soil, the saturation of electrode temperature rise curve gets more pronounced as the current injection time increases. Thus, the temperature rise rate of the actual grounding electrode is lower than the calculation result without considering the water-saturated soil resistivity. Therefore, using the temperature characteristics of water-saturated soil resistivity to simulate the temperature rise of the grounding electrode can provide a theoretical basis for the grounding electrode to work under water-saturated soil conditions.

    更新日期:2020-01-15
  • A frequency-based economical-sharing strategy for low-voltage DC microgrids
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-15
    Ramin Babazadeh-Dizaji; Mohsen Hamzeh; Arsalan Hekmati

    This paper introduces a frequency-based control strategy to minimize the total generation cost in low-voltage dc microgrids. In dc microgrids, although the voltage is the only variable for controlling the outputs of sources, it is not a common variable for all sources due to the different line resistances. Hence, applying the conventional voltage-based droop control will not be able to share the load among the sources accurately. Within the context alluded above, to realize an accurate load sharing in dc microgrids, the communication-based approaches are employed. However, any link failure in these approaches may impair the controller functionality and consequently, render the whole system inoperable. To cope with the associated problems of the communication-based approaches, the frequency-based control strategy has been introduced for accurate load sharing in dc microgrids which operates without any communication network. This study proposes a frequency-based economical-sharing control strategy that has the capability to minimize the total generation cost and regulate the voltage of sources. The main advantage of this strategy over the previously addressed frequency-based strategies is providing an optimal combination of dispatchable sources to supply the required load on the grid. Through the employed control strategy, the incremental costs of all dispatchable sources will be equal in the steady state which causes the optimal operation of the dc microgrid. The small-signal modeling of the proposed strategy is also carried out to analyze the system stability and parameter sensitivity. A complete set of simulation studies is provided in PLECS software to verify the effectiveness of the proposed control strategy.

    更新日期:2020-01-15
  • Detection and classification of short-circuit faults in distribution networks based on Fortescue approach and Softmax regression
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-13
    Chao Zhang; Jiandong Wang; Jian Huang; Pengfei Cao

    This paper proposes a method to detect and classify ten short-circuit faults in distribution networks, where the presence of distributed generators makes fault diagnosis a challenging problem. The main idea is to consider operating modes of distributed generators in analyzing fault characteristics via the Fortescue approach, and exploit the softmax regression to alleviate negative effects of transient data samples on the fault classification. The proposed method is developed in three main steps. First, the relationship between measurable currents and unavailable currents of the fault point is developed for the grid-connected mode or the islanding mode of distributed generators. Second, the Fortescue approach is used to formulate fault characteristics from the positive-, negative- and zero-sequence components of measurable currents. Third, the softmax regression is introduced to alleviate negative effects of transient data samples on the fault classification. The effectiveness of the proposed method is demonstrated via numerical examples on balanced and unbalanced distribution networks.

    更新日期:2020-01-14
  • A novel EHV transmission line protection of adequate fault-resistance sensitivity and faulted-phase selectivity
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-13
    Xiao Ma; Xiangning Lin; Fanrong Wei; Zhengtian Li; Zixuan Wang; Yuqing Ye

    The summation impedance relay (SIR) is characterized by a strong sensitivity to high-resistance faults. However, previous studies have not made SIR completely immune to the adverse influence of distributed capacitive currents and have ignored its inherent deficiency of faulted-phase selectivity. Therefore, a novel protection scheme is proposed. First, by compensating distributed capacitive currents, an improved ground-type SIR (composed of ground distance relays) is created. Using this SIR, the identification of internal high-resistance faults is performed while guaranteeing security under external faults. Then, a novel phase-type SIR (composed of phase distance relays) is designed, based on which a suitable phase-selection algorithm is proposed to distinguish single-phase faults and multi-phase faults. Comprehensive simulations show the security and dependability of the proposed protection scheme in various fault scenarios, including non-linear high-impedance faults and series compensation scenarios. Moreover, the approach’s performance under power swings is investigated, revealing its complementarity with existing protection principles.

    更新日期:2020-01-14
  • A hybrid algorithm for the load flow analysis of VSC-HVDC systems based on 1+2 order Newton-Raphson and simplified Newton
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-11
    Yanfang Wei; Qiankun Li; Kang-Zhi Liu; Peng Wang; Zhihui Zeng; Xiaowei Wang

    With the rapid increase of multi-terminal and multi-infeed VSC-HVDC lines, the dimension and scale of AC/DC system equation and Jacobian matrix (JM) increase sharply, which makes the load flow (LF) analysis very complicated. In this paper, a new hybrid method is proposed to address this issue. This hybrid algorithm is composed of a 1+2 order Newton-Raphson (NR) method and a simplified Newton (SN) method. Specifically, the 1+2 order NR method is executed up to a preset number of iterations first, then the algorithm is switched to the SN until the system accuracy is met. A good compromise between the solution accuracy and computation burden can be achieved once a suitable iteration number is preset. To this end, a unified iterative form suitable for solving the LF of AC/DC systems with VSC-HVDC is derived in detail: a dimension reduction treatment is proposed to solve the problem of increasing dimension of JM; a rule of thumb is provided for the determination of the iteration number of 1+2 order NR. Then, the proposed hybrid method is validated on the modified IEEE-14, 30, 57 and 118 test systems. Comparisons and analyses are made for numerous scenarios, including the basic test of LF, different control modes and control objectives, influence of active and reactive powers on VSC parameters, algorithm performance under various initial states and heavy loading, etc. Compared with Newton and 1+2 order NR methods, the hybrid method shows a significantly shortened convergence time, 30% of 1+2 order NR and 47% of Newton on average.

    更新日期:2020-01-13
  • Forecast-based overcurrent relay coordination in wind farms
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-11
    Sujo P. George; S. Ashok

    Relay coordination ensures the appropriate isolation of healthy feeders from the faulty areas in a power system. The dynamic nature of renewable sources such as wind generators (WGs) can create variations in fault levels which affect the relay settings. This causes coordination problems, which can lead to the faulty operation of overcurrent relays (OCRs). The settings of the relay need to be modified appropriately in line with the variations of fault levels, which in turn change with the wind dynamics. As a solution, wind forecast based technique for the coordination of the OCRs in wind-integrated substations is suggested in this work. In the proposed algorithm, wind speed and its direction are predicted and the settings of the relay are predetermined using an optimization technique. This reduces the computation time required for the algorithms in the current period. The algorithm is implemented in the modified IEEE 9-bus system with wind farms and also in a typical wind-integrated substation. Further, it is validated through an experimental setup in the laboratory. The results were found to be promising and the algorithm can be applied to any substations integrated with wind farms for avoiding relay mal-operations.

    更新日期:2020-01-13
  • Grid inadequacy assessment for high power injection diversity Part II: Finding grid expansion options
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-11
    Adonis E. Tio; David J. Hill; Jin Ma

    Power injection scenarios will become more diverse in the future as intermittent renewable generation, dynamic loads, and energy storage devices become more prevalent especially under a market environment. Grid planners need new planning tools to find long-term grid expansion options that promote competition and equitable market access by accommodating diverse scenarios. Part I of the paper presented a framework and a set of metrics for measuring inherent grid inadequacy for high power injection diversity using the power flow infeasible set. This paper uses the ideas in Part I to develop an approach that finds grid expansion options by directly minimizing inherent grid inadequacy as objective. We present one implementation using a robust-like optimization model that minimizes the size of a scenario-based representation of the power flow infeasible set. We show using case studies that the proposed approach using inherent grid inadequacy metrics can identify solutions distinct from other approaches and better in some measure.

    更新日期:2020-01-13
  • A new differential protection algorithm for power reactors based on the second central moment
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-10
    Ernesto Vázquez; Manuel A. Andrade; Héctor Esponda; Jesús Ávila

    Power shunt reactors are critical elements in electric power systems for controlling reactive power and maintaining voltage within a permissible range in transmission systems. Protection schemes for shunt reactors are similar to those used in power transformers, e.g., the differential, overcurrent, and distance protection schemes. However, these protection schemes may misoperate for several reasons such as a decaying DC component when the reactor is energized, or the occurrence of current transformer saturation when an external fault occurs. In this context, a novel differential protection algorithm for power shunt reactors is proposed. This algorithm uses the magnitude of the second central moment as a basis for identifying whether the event corresponds to an internal fault. The proposed algorithm was tested and implemented using PSCAD and the MATLAB software. Current transformer saturation and noise were considered in all the events evaluated. The results show that the proposed algorithm accurately discriminates between internal and external faults as well as transient events such as inrush currents. Furthermore, the algorithm exhibits a limited capability for detecting turn-to-turn faults until 2% of short-circuited turns.

    更新日期:2020-01-11
  • Hierarchical service restoration scheme for active distribution networks based on ADMM
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-10
    Feifan Shen; Qiuwei Wu; Yan Xu; Fangxing Li; Fei Teng; Goran Strbac

    Effective self-healing schemes enhance the resilience of active distribution networks (ADNs). As a critical part of self-healing, service restoration aims to restore outage areas with minimal un-supplied demands. With the increasing complexity and size of ADNs, distribution system operators (DSOs) face a more complicated service restoration problem. Thus, it is important to obtain optimal service restoration plans and reduce computational complexity. To achieve this goal, a hierarchical service restoration scheme is proposed to obtain service restoration plans based on the alternating direction method of multipliers (ADMM). The optimal service restoration problem is formulated as a mixed-integer linear programming (MILP) model considering the switching sequence, distributed generation (DG) units and controllable loads, and is solved using the ADMM-based algorithm in a hierarchical manner. In the proposed scheme, each zone of the ADN has a local service restoration controller solving its sub-problem with information from a central service restoration controller. The central controller solves a global coordination problem with information from all the zones. Three case studies were conducted with the 44-node test system, modified IEEE 123-node system and Brazil 948-node system. The results show that the proposed hierarchical service restoration can obtain optimal service restoration plans and reduce computational complexity. Moreover, computation time can be reduced substantially by using the proposed hierarchical scheme for large-scale ADNs.

    更新日期:2020-01-11
  • Study of Corona Configurations under DC Conditions and Recommendations for an Identification Test Plan
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-10
    Saliha Abdul Madhar; Petr Mráz; Armando Rodrigo Mor; Robert Ross

    Corona is one of the most common forms of partial discharge (PD) occurring in high voltage (HV) energy systems. The corona mechanism in air is not exclusive to the field of energy applications but has also been widely studied by physicists to theorize mechanisms of charge transfer during the different phases of gas discharge. The phases of the discharge and its corresponding behavior with alternating voltage (AC) are well established and represented through various discharge trends, patterns and stages. This not only makes the identification of the PD defect possible but also helps evaluate the risk. This paper investigates corona configurations under DC stress in an attempt to create a similar outline of the defect as exists under AC. The defect is studied in terms of the pulse sequence information. The measurement system requirements are kept within a realistic realm to preserve applicability to industrial measurements. Finally, it makes selective recommendations for the effective identification of the discharge condition under DC stress.

    更新日期:2020-01-11
  • A protection scheme for hybrid multi-terminal HVDC networks utilizing a time-domain transient voltage based on fault-blocking converters
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-10
    Xinquan Chen; Haifeng Li; Yuansheng Liang; Gang Wang

    Combining the advantages of the line commutated converter (LCC) and modular multilevel converter (MMC), hybrid multi-terminal HVDC (Hybrid-MTDC) systems have become the most competitive candidate for future power transmission systems. However, for conditions of high fault resistance (HFR), large transmission networks and lacks of boundary components between adjacent lines, economic and practical traveling-wave (TW) protection is an immediate challenge for Hybrid-MTDC networks. In this paper, the fault-generated TW characteristics of Hybrid-MTDC networks are elaborated, and a time-domain transient voltage with different sampling periods is constructed to adapt to the attenuation of HFRs and the band-stop characteristic of T areas. Utilizing the ratio of the transient voltage indexes and based on a fault-blocking converter (FBC), the coordination of relays can be designed to realize internal fault detection and faulty line location for Hybrid-MTDC networks. Furthermore, a comprehensive FBC-based protection scheme for Hybrid-MTDC networks is proposed. Finally, the proposed protection scheme is validated based on the Wudongde project using PSCAD/EMTDC. The protection results show the high sensitivity and reliability of the proposed protection scheme.

    更新日期:2020-01-11
  • Influence of residual charges on the vibration of filter capacitor components
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-10
    Pengning Zhang; Lin Li; Jianye Cui; Bin Wang; Qiang He

    The noise of filter capacitors in high voltage direct current (HVDC) transmission converter stations has raised wide concern. In this paper the influence of residual charges on the surface of dielectric film on the vibration of capacitors is studied by experiments and simulation. A component of filter capacitor is made by enwinding two aluminum foils between them with three layers polypropylene films, and pressed into a rectangular plate form, then packed by insulation paper. A stack of filter capacitor consisted of some components in series or parallel connection. An electrometer is used to test the electric potentials under the unfolded one layer of dielectric film of a component of capacitor, and the residual charge densities of the dielectric film are calculated by means of the measured electric potentials. The results show that the residual charge density distribution on dielectric film is uneven and irregular. The electric field force of the dielectric film with residual charges of different orders of magnitude is simulated by using finite element software. Finally, a programmable power supply is used to apply sinusoidal voltage with different amplitude to a capacitor component, and the vibration of the component surface is tested by a laser vibration meter. The test results show that the residual charges on the dielectric film have significant impact on the vibration of capacitor component.

    更新日期:2020-01-11
  • ADMM-based distributed optimal reactive power control for loss minimization of DFIG-based wind farms
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-10
    Sheng Huang; Peiyao Li; Qiuwei Wu; Fangxing Li; Fei Rong

    In this paper, a distributed optimal reactive power control (DORPC) scheme is proposed for minimizing the total losses of doubly fed induction generator (DFIG)-based wind farms (WFs), including the losses of generators, converters, filters, and networks. The DORPC minimizes total WF losses by optimally coordinating reactive power outputs of the DFIG stator and the grid-side converter. The optimal control problem is solved in a distributed manner by using the consensus alternating direction method of multipliers (ADMM). With the consensus ADMM, the total WF loss optimization problem is transformed into a distributed optimal power flow problem considered with DFIGs’ optimal operation. The optimization problem with local constraints considers the reactive power limit of DFIG-based wind turbines (WTs) and the voltage limits at all WT terminal buses inside the WF. In the DORPC, the optimal control problem is solved by the collector bus station controller and WT controllers in parallel, only with the information exchange between immediate neighbors. It eliminates the need of a central controller and centralized communication, implying better robustness and plug-and-play capability. A WF with 20 DFIG-based WTs was used to validate the proposed DORPC scheme.

    更新日期:2020-01-11
  • Wind power prediction based on high-frequency SCADA data along with isolation forest and deep learning neural networks
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-10
    Zi Lin; Xiaolei Liu; Maurizio Collu

    Wind power plays a key role in reducing global carbon emission. The power curve provided by wind turbine manufacturers offers an effective way of presenting the global performance of wind turbines. However, due to the complicated dynamics nature of offshore wind turbines, and the harsh environment in which they are operating, wind power forecasting is challenging, but at the same time vital to enable condition monitoring (CM). Wind turbine power prediction, using supervisory control and data acquisition (SCADA) data, may not lead to the optimum control strategy as sensors may generate non-calibrated data due to degradation. To mitigate the adverse effects of outliers from SCADA data on wind power forecasting, this paper proposed a novel approach to perform power prediction using high-frequency SCADA data, based on isolate forest (IF) and deep learning neural networks. In the predictive model, wind speed, nacelle orientation, yaw error, blade pitch angle, and ambient temperature were considered as input features, while wind power is evaluated as the output feature. The deep learning model has been trained, tested, and validated against SCADA measurements. Compared against the conventional predictive model used for outlier detection, i.e. based on Gaussian Process (GP), the proposed integrated approach, which coupled IF and deep learning, is expected to be a more efficient tool for anomaly detection in wind power prediction.

    更新日期:2020-01-11
  • An adaptive time-resolution method for ultra-short-term wind power prediction
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-08
    Lijuan Li; Yuan Li; Bin Zhou; Qiuwei Wu; Xiaoyang Shen; Hongliang Liu; Zheng Gong

    Accurate wind power prediction (WPP) plays an important role in the secure operation and dispatch of power systems. This paper proposes an adaptive time-resolution method to improve the accuracy of ultra-short-term wind power prediction (USTWPP). Firstly, the hidden prediction error (HPE) with its fluctuation magnitude and rate indicators is defined to reveal the fluctuation characteristics of real-time wind power. Then, the adjustment time of time-resolution can be dynamically determined by evaluating the fluctuation magnitudes, and the adjustment rules are formulated by mining the regularities of fluctuation rate of historical wind power data and establishing the interval grouping optimization model. Finally, by coupling the adjustment time and rules into the prediction model of back propagation neural network (BPNN), the rolling prediction with adaptive adjustment of time-resolution is achieved. Extensive tests have not only demonstrated the validity of the proposed method, but also confirmed its capability to cope with the USTWPP especially under situations of extremely violent fluctuations of wind power.

    更新日期:2020-01-09
  • Energy storage behind-the-meter with renewable generators: Techno-economic value of optimal imbalance management
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-08
    Vincenzo Trovato; Bharath Kantharaj

    There is a growing body of evidence that energy storage systems can provide significant flexibility to the electricity grid. This study introduces a system comprising an energy storage unit connected behind-the-meter with a large-scale wind power generator. The associated constraints are derived from storage device and wind power parameters, and then implemented to carry out energy arbitrage, manage imbalance of the wind farm, and help the grid during times of peak demand in the winter. A suitable representation of the system components enables the straightforward implementation of energy storage dynamics in a purely linear rolling-planning optimisation framework. A case study is constructed for the simultaneous optimal allocation of energy to maximise profits, followed by a detailed financial investment analysis. It is demonstrated that a business case can be constituted only for the proposed energy imbalance management strategy, which also extends the cyclic lifetime of the storage unit.

    更新日期:2020-01-09
  • A delta-connected MMCC-based active power conditioner for unbalanced load compensation and harmonic elimination
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-08
    Han Huang; L. Zhang; O.J.K. Oghorada; Mingxuan Mao

    Modular multilevel cascaded converters (MMCC) are seen in medium and high voltage applications and have gained attention from industry. This paper presents new control techniques to improve accuracy and control response speed when applied to a delta-connected MMCC- based Active Power Conditioner used for negative sequence and harmonic current elimination. A novel reference current generation scheme combining a notch filter with Decoupled Double Synchronous Reference Frame (DDSRF) is proposed which can extract the negative sequence and a selection of dominant harmonic currents accurately with the minimum time delay. Fast and accurate tracking the extracted reference current is obtained by using a model-based predictive controller with a derivative reference current term. The control strategy is applied to an experimental delta-connected MMCC-APC and the resultant waveforms are shown and analysed, confirming that the grid current quality after compensation has improved significantly.

    更新日期:2020-01-08
  • Incorporating flexibility requirements into distribution system expansion planning studies based on regulatory policies
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-08
    Sahand Karimi-Arpanahi; Mohammad Jooshaki; Moein Moeini-Aghtaie; Ali Abbaspour; Mahmud Fotuhi-Firuzabad

    Increasing penetration of renewable energy sources with intermittent generation calls for further flexibility requirements for efficient as well as the safe operation of power systems. Considering the significant growth of distributed energy resources in distribution systems, a promising approach to fulfill such requirements is to deploy local flexibility sources at the distribution level. Nonetheless, due to the monopoly nature of electricity distribution business, effective regulations are required to direct distribution companies toward fulfilling such goals. Accordingly, this paper aims at proposing various policies to motivate distribution companies to enhance the flexibility of their networks. In order to assess the effectiveness of these rules, we present a novel multi-stage distribution expansion planning model considering flexibility requirements. In this model, installation of conventional dispatchable distributed generation units and battery energy storage systems, as well as demand response programs, are considered available flexibility sources for distribution system planners. The proposed framework is applied to a test distribution network with 18 nodes, and the obtained results are thoroughly discussed. Finally, a sensitivity analysis is conducted to assess the effects of the key parameters of the proposed model on expansion planning of the test system.

    更新日期:2020-01-08
  • Dynamical analysis of the fractional-order centrifugal flywheel governor system and its accelerated adaptive stabilization with the optimality
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-07
    Shaohua Luo; Junyang Li; Shaobo Li; Jianjun Hu

    This paper investigates the issues of dynamical analysis and accelerated adaptive stabilization of the fractional-order (FO) centrifugal flywheel governor system with optimality. The dynamic behavior of the centrifugal flywheel governor system is revealed and its local stability is discussed in the fractional calculus (FC). A speed function is introduced to accelerate convergence rate within a pre-given time and a hierarchical type-2 fuzzy neural network (HT2FNN) is employed to play an approximating role for unknown nonlinear items. An extended state tracking differentiator which overcomes repetitive differentiation problem is used to approximate the derivative of virtual control input. Then, a stabilization controller is designed by integrating with the speed function, neural network and tracking differentiator in the framework of backstepping. It is proved that the proposed scheme guarantees the boundedness of all signals of the closed-loop system by using the frequency distributed model and makes the predefined cost function smallest. Finally, simulation results verify the effectiveness of the presented scheme.

    更新日期:2020-01-07
  • Dependable power extraction in wind turbines using model predictive fault tolerant control
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-06
    Kamyar Ghanbarpour; Farhad Bayat; Abolfazl Jalilvand

    In this paper, a fault tolerant model predictive control scheme is proposed for wind turbines in the partial-load region to meet the control objectives in the presence of disturbances, uncertainties, sensor and actuator faults. The aim of wind turbine control systems in the partial-load region is to capture maximum power by tracking the optimal generator speed. But any fault in the sensors and actuators can take away the closed-loop system from the main objectives and maybe make the system unstable in some cases. At first, an online model predictive controller (MPC) is designed as a nominal controller to track the maximum power and guarantee all constraints satisfaction without considering any fault. In the next step, an adaptive sliding mode observer (SMO) is designed to estimate the actual states and sensor faults, simultaneously. Finally, an additive control law is represented and shown that it is able to tolerate the actuator faults effectively. Using extensive simulation results it is shown that the proposed strategy is able to handle the uncertainties, sensor and actuator faults in the control system, simultaneously.

    更新日期:2020-01-07
  • Home energy management system based on task classification and the resident’s requirements
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-06
    Amir Samadi; Hossein Saidi; Mohammad Amin Latify; Mehdi Mahdavi

    In this paper, an approach for home energy management system is introduced that is based on task classification. The problem is to find the best task activation plan regarding the resident’s requirements and appliances constraints, considering time of use pricing. We show that to have a best task activation plan it is necessary to specify four specific values for each task. In this regard, a quadratic utility function is derived based on the law of diminishing marginal utility in microeconomic. With the parameters such as sensitivity index and monetary equivalent value, each task’s utility function can be configured in accordance to the resident’s personal preferences. In this model, the concept of tasks interaction are also taken into account, for the first time. The problem is transformed to a mixed integer nonlinear programming problem, so that the available commercial solvers can successfully solve it in an acceptable solving time. The outputs of numerical examples show that they are reasonable and can be considered as optimal or near optimal results. The results indicate that the less sensitive the resident is to changing his/her desire task parameters, the more profit he/she will get. It is also shown that by increasing the monetary equivalent value, the task activation is shifted toward the times that are more preferable or has more favorite environment conditions. These results as well as the acceptable solving times, show that the proposed approach can be a promising model for home energy management systems in the future smart homes.

    更新日期:2020-01-07
  • A fast and flexible nearest-level-equivalent space vector modulation algorithm for three-phase multilevel converters
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-07
    Hongjian Lin; Ruoyu Li; Leilei Zhu; Han Yan; Lan Ma; Jiaxuan Yao; Zeliang Shu

    This paper presents a nearest-level-equivalent space vector modulation (SVM) algorithm for three-phase multilevel converters. The proposed algorithm provides a simple approach to obtain three modulation vectors online based on basic vectors. In addition, the principle of nearest-level modulation (NLM) is applied in the proposed SVM to make its superior performance to the generalized SVM algorithms, which present: (1) Merely one modulation vertex need to be detected and three-phase duty cycles are obtained. Therefore, the unbalanced voltages of inner cell of neutral-point-clamped cascaded multilevel converter (NPC-CMC) can be addressed; (2) Redundant and optimized switching sequences are automatically generated to minimize the number of switching transition; (3) Different modulation modes can be flexibly chosen to optimize the harmonic benefit. The proposed SVM scheme is independent of level numbers and finally verified by simulation and experimental results.

    更新日期:2020-01-07
  • Objective transmission cost allocation based on marginal usage of power network in spot market
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-07
    Zhifang Yang; Xingyu Lei; Juan Yu; Jeremy Lin

    Transmission cost allocation is important for a liberalized market with open access to transmission facilities. However, it remains controversial how to objectively allocate the transmission costs because there is no unique answer for the mapping between the power injections at buses and the power flows on branches. However, the marginal usage of the power network can be uniquely determined according to the market-clearing solution. In this paper, an objective transmission cost allocation method is proposed based on the marginal usage of the power network. The influence of the loss modeling on the proposed method is discussed. The “extent of use” of transmission facilities is determined based on the economic principles without subjective assumptions, which obeys the fairness requirement of spot markets. The proposed method is computationally efficient, in which only matrix manipulations are involved. Moreover, the proposed approach is compatible with the standards and procedures of the current spot market operation in the U.S., China, and many other countries and holds promise for industrial applications.

    更新日期:2020-01-07
  • A proposal for the improvement of electrical energy quality by energy storage in flywheels applied to synchronized grid generator systems
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-07
    Renato Kazuo Miyamoto; Alessandro Goedtel; Marcelo Favoretto Castoldi

    In its industrial application, three-phase induction motors are subject to the drive of high inertial loads. This fact results in the storage of kinetic energy during their operation. Thereby, this work presents a method to connect the electric grid of a Squirrel Cage Induction Generator rotor (SCIG) coupled to a cylindrical flywheel of high inertial content to reduce small disturbances in the electric grid. The proposal is validated by means of experimental tests on a bench using toroidal inductors to mitigate the effects of the current transients in the injection of kinetic energy converted into electrical energy in the grid. The results showed that this system can supply a short-time undervoltage disturbance of up to 0.2 pu three-phase and 0.4 pu per phase.

    更新日期:2020-01-07
  • A consensus approach for economic dispatch problem in a microgrid with random delay effects
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-07
    Mei Yu; Chao Song; Shixian Feng; Wen Tan

    In this paper, we propose a consensus approach to solve the economic dispatch problem (EDP) with the effect of random delay. The algorithm is distributed and the supply-demand balance is always satisfied. The impact of random time delay on the stability of the algorithm is investigated. Furthermore, one allowable delay bound is calculated based on the Lyapunov stability condition. Some cases are presented to verify the effectiveness of the proposed scheme.

    更新日期:2020-01-07
  • Two stage risk based decision making for operation of smart grid by optimal dynamic multi-microgrid
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-06
    M. Zadsar; S.Sina. Sebtahmadi; M. Kazemi; S.M.M. Larimi; M.R. Haghifam

    Resect severe economic losses caused by distribution system equipment outage have highlighted the importance of improving the system resiliency and reliability. In active distribution networks (ADNs), the distributed energy resources (DERs) managed by dynamic isolated microgrids in contingency mode provide an alternative approach to enhance the system resiliency and continue supplying critical loads after equipment outage. How to incorporate this ADNs capability into a short-term DERs scheduling is a challenging issue. In response to this challenge, in this paper, a two stage risk based decision making framework for operation of ADNs is proposed to coordinate 24-h DERs’ scheduling and outage management scheme, in a way to be immune against contingency by creating optimal dynamic multi-micrigrid, micro-turbine and energy storage island operating and load shed plan. The first stage is the normal operation condition that operation cost should be minimized considering of the uncertainties of renewable resources, the electricity price and customers loads. The second stage is the operation in contingency condition. In the second stage, the main objective is to keep the shed load at minimum level. Numerical results and sensitivity analysis from modified 33-bus IEEE network are further discussed to demonstrate the efficiency of the solution approach.

    更新日期:2020-01-07
  • AC/AC grid connection of six-phase wind power generator based on enneagon MMC converter
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-03
    Shijia Zhou; Fei Rong; Wenlong Sun; Sheng Huang; Qiuwei Wu

    In this paper, an enneagon multi-level converter (E-MMC) is proposed, which can directly connect six-phase wind power generator to AC grid. It has the advantages of high efficiency, small fluctuation of capacitor voltage of sub-modules (SMs), and no need of step-up transformer. The working principle of the converter is analyzed, and the optimal phase shifting angle between the two windings of the six-phase wind turbine is determined under different boost ratios. The voltage stability control strategy of the converter and the current tracking control strategy based on proportional resonance (PR) are proposed. The simulation and experiment verify the effectiveness of the proposed system and its control strategy from both steady and transient aspects.

    更新日期:2020-01-04
  • An improved virtual inductance control method considering PLL dynamic based on impedance modeling of DFIG under weak grid
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-03
    Xueguang Zhang; Yage Zhang; Ran Fang; Dianguo Xu

    Impedance-based method is an effective method to analyze the system stability. Based on the impedance stability theory, an improved virtual inductance control method considering PLL dynamic is presented for the stability of doubly-fed induction generator (DFIG) under weak grid condition. Firstly, equivalent input admittance model of the DFIG system including all its controller is developed in the synchronous reference (d-q) frame. Secondly, the generalized Nyquist criterion (GNC) proves that the stability of the DFIG system can be improved by increasing the rotor inductance. Then, a virtual inductance term is introduced into the RSC current controller to emulate additional inductance in the rotor. However, the virtual inductance method may be ineffectual due to the influence of the PLL dynamic under weak grid condition. Therefore, an improved virtual inductance control method considering the PLL dynamic is implemented to improve the stability of the DFIG system under weak grid condition, and the simulation is used to verify the effectiveness of the improved virtual inductance control strategy.

    更新日期:2020-01-04
  • Sustainable community based PV-storage planning using the Nash bargaining solution
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2020-01-03
    Junkai Liang; Ashwin Shirsat; Wenyuan Tang

    A dramatic increase in the penetration of customer-sited solar and storage has increased the concerns over utility revenues. A novel business model where the utility and the households within a community cooperatively deploy solar and storage is proposed in this paper. The potential increased payoffs are allocated by the Nash bargaining solution with efficiency and symmetry. Community-based expansion planning highly relies on local meteorology and geography. A convolutional neural network based scenario generation method is used to capture the locally driven uncertainties. The numerical results demonstrate that the players can improve their payoffs using the cooperative approach as compared to the non-cooperative approach. The case studies shed light on the future customer-utility relationship.

    更新日期:2020-01-04
  • Real-time optimization of the integrated gas and power systems using hybrid approximate dynamic programming
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-31
    Hang Shuai; Xiaomeng Ai; Jiakun Fang; Tao Ding; Zhe Chen; Jinyu Wen

    This paper proposes a hybrid approximate dynamic programming (HADP) approach for the optimal operation of integrated gas and power systems (IGPS) under the stochastic environment. The proposed HADP, combining the advantages of the model predictive control (MPC) and approximate dynamic programming (ADP), decomposes the multi-time-period optimization into multiple sequential subproblems by solving Bellman’s equation forward through time. Historical data is utilized to build the approximate value functions so that the influence of current decisions on the future is estimated. And hence, the HADP algorithm can obtain a near-optimal solution through the whole time horizon of interest. Meanwhile, the MPC policy is embedded in the HADP to replace the long-term forecast with short-term or even real-time prediction. This further improves the optimality of the decisions made by the proposed HADP. The simulation results on the IGPS demonstrate the proposed HADP outperforms alternative solutions.

    更新日期:2020-01-01
  • Optimal power tracking of PMSG based wind energy conversion systems by constrained direct control with fast convergence rates
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-31
    Hoach The Nguyen; Ameena Saad Al-Sumaiti; Van-Phong Vu; Ahmed Al-Durra; Ton Duc Do

    This paper proposes a simple direct control with fast convergence rates under constraints for tracking optimal power of permanent magnet synchronous generator (PMSG) based wind energy conversion system (WECS). The simplicity features are on neglecting the following: predicted control performances, measurement of aerodynamic torque/wind speed and stator currents. The superior features are on very fast and accurate tracking performances with asymptotic convergence and well-regulated stator currents. First, a nonlinear observer is designed to observe both aerodynamic torque and stator currents. The wind speed is then inferred from the estimated aerodynamic torque and consequently, the optimal speed reference is identified. Next, the conditions of asymptotic stability for the closed-loop dynamics are formulated. Finally, a simple direct control is proposed to maximize the convergence rates in transient states and reduce switching frequency in steady states. Comparative studies with finite set model predictive control are presented to validate the advantageous features of the proposed method. The comparative results show that the superiority of the proposed method is proved by better controlled outputs with lower ripples, smaller steady-state tracking errors, faster response in transient-states, good tracking performance even for fast-varying aerodynamic torque, and lower average switching-frequency.

    更新日期:2019-12-31
  • An improved digital integral algorithm to enhance the measurement accuracy of Rogowski coil-based electronic transformers
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-31
    Zhenhua Li; Xin Xiang; Tinghe Hu; Ahmed Abu-Siada; Zhenxing Li; Yanchun Xu

    In order to promote the practical application of the Rogowski coil-based electronic transformers, it is of great necessity to handle the issues associated with the measurement error and interference in the integral process of the electronic transformer. In this paper, an improved digital integral algorithm with frequency self-adaption ability that aimed at overcoming the above-mentioned issues is proposed. Based on the electronic transformer calibration and harmonic measurement requirements, two specific applications of the proposed integral algorithm are carried out to validate the practical feasibility of the proposed algorithm. Experimental results reveal the improved performance of the Rogowski coil-based electronic transformer equipped with the proposed digital integral algorithm. Errors in harmonic currents measurement (up to 50th order) can be significantly reduced to a level less than 0.01% at a sampling frequency of 12.8 kHz by employing the proposed algorithm. For calibrating electronic transformers, results show that the performance of the proposed algorithm is better than the conventional trapezoidal integral algorithm and Simpson algorithm. Furthermore, the proposed algorithm has the ability to eliminate the impact of frequency fluctuation around the power frequency.

    更新日期:2019-12-31
  • Power transformer condition assessment based on online monitor with SOFC chromatographic detector
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-31
    Jingmin Fan; Chenyang Fu; Hao Yin; Yu Wang; Qinji Jiang

    Power transformer is vital for energy conversion in power system, the condition assessment of which based on dissolved gas analysis (DGA) is used worldwide. In this paper, an online monitor based on solid oxide fuel cell (SOFC) detector is designed to address the poor stability, low sensitivity of other online-monitoring system. The system is composed of a gas measurement subsystem, a central controlling unit, and an intelligent fault diagnosis subsystem. A portable gas chromatography module developed using SOFC detector. The quantificational algorithm is derived, on basis of which calibration can be skipped. Due to the essential role of the chromatography column as well as gas the detector’s temperature, proportional-integral-differential (PID) controller is implemented in the controlling unit. To evaluate the effectiveness of the developed online monitor, the quantitative analysis and engineering application have been performed; then, based on the measured results, the RVM-ANFIS algorithm is adopted to diagnosis the latent transformers faults. Using the developed online monitor, the results indicate that five characteristic gases, H2, CH4, C2H4, C2H6, and C2H2 can be measured accurately, and incipient faults can be detected, validate the effectiveness of this system.

    更新日期:2019-12-31
  • Day-ahead photovoltaic power forecasting approach based on deep convolutional neural networks and meta learning
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-31
    Haixiang Zang; Lilin Cheng; Tao Ding; Kwok W. Cheung; Zhinong Wei; Guoqiang Sun

    The outputs of photovoltaic (PV) power are random and uncertain due to the variations of meteorological elements, which may disturb the safety and stability of power system operation. Hence, precise day-ahead PV power forecasting is crucial in renewable energy utilization, as it is beneficial to power generation schedule and short-term dispatch of the PV integrated power grid. In this study, a novel day-ahead PV power forecasting approach based on deep learning is proposed and validated. Firstly, two novel deep convolutional neural networks (CNNs), i.e. residual network (ResNet) and dense convolutional network (DenseNet), are introduced as the core models of forecasting. Secondly, a new data preprocessing is proposed to construct input feature maps for the two novel CNNs, which involves historical PV power series, meteorological elements and numerical weather prediction. Thirdly, a meta learning strategy based on multi-loss-function network is proposed to train the two deep networks, which can ensure a high robustness of the extracted convolutional features. Owing to the learning strategy and unique architectures of the two novel CNNs, they are designed into relatively deep architectures with superb nonlinear representation abilities, which consist of more than ten layers. Both point and probabilistic forecasting results are provided in the case study, demonstrating the accuracy and reliability of the proposed forecasting approach.

    更新日期:2019-12-31
  • A novel control strategy for the seamless transfer of microgrids based on disturbance observer
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-30
    Guannan Lou; Wei Gu; Junpeng Zhu; Peng Li; Xuesong Zhang

    This paper presents a novel seamless transfer strategy for microgrids (MGs) that enables both grid-connected and islanding modes, with no need of forced controller switching between different controllers and with improved performance in both reference tracking and disturbance attenuation. A unified control structure based on droop technique is utilized to generate the voltage and frequency references, accommodating all operation modes. Alternatively, the dynamical feedforward with reference model control and disturbance observer are introduced into the cascaded voltage-current control, which not only estimates and compensates the influences of power fluctuation as well as model uncertainties timely, but also provides the perfect reference tracking capability. Then the detailed analysis on the deduced mathematical model of inverter is carried out, and the superiority of the proposed strategy is demonstrated in tracking performance, disturbance attenuation and robustness. Simulation and experimental results show that the harmful transients during the operation mode transition can be effectively eliminated with the overall dynamic performance improved so that the effectiveness of the proposed control scheme is verified.

    更新日期:2019-12-30
  • Frequency-limited pseudo-optimal rational Krylov algorithm for power system reduction
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-27
    Umair Zulfiqar; Victor Sreeram; Xin Du

    In this paper, a computationally efficient frequency-limited model reduction algorithm is presented for large-scale interconnected power systems. The algorithm generates a reduced order model which not only preserves the electromechanical modes of the original power system but also satisfies a subset of the first-order optimality conditions for H2,ω model reduction problem within the desired frequency interval. The reduced order model accurately captures the oscillatory behavior of the original power system and provides a good time- and frequency-domain accuracy. The proposed algorithm enables fast simulation, analysis, and damping controller design for the original large-scale power system. The efficacy of the proposed algorithm is validated on benchmark power system examples.

    更新日期:2019-12-29
  • Condition-based midterm maintenance scheduling with rescheduling strategy
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-28
    Yijing Xu; Xueshan Han; Ming Yang; Mingqiang Wang; Xingxu Zhu; Yumin Zhang

    This paper proposes a condition-based midterm maintenance scheduling with rescheduling strategy. Different from existing methods, the prescheduled maintenance tasks in the proposed method can be rescheduled according to the updated information received from asset condition monitors. To realize the rescheduling strategy, a new decision variable called time-varying maintenance threshold is introduced in the optimization model. When the state measurement of a device is identified to reach the time-varying maintenance threshold, the prescheduled maintenance task should be executed ahead of time to prevent failures. In the proposed method: (1) a stochastic degradation process considering the prescheduled maintenance tasks and the rescheduling strategy is expressed; (2) an optimization model is formulated to minimize the sum of the individual operating risk and the system operating risk through co-optimizing prescheduled maintenance tasks and time-varying maintenance thresholds; (3) a decomposition algorithm is designed to solve the optimization model. Case studies are presented to demonstrate the validity and significant operating risk reduction of the proposed method.

    更新日期:2019-12-29
  • Individual-based distributed parallel optimization for operation of integrated energy systems considering heterogeneous structure
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-27
    L.X. Wang; J.H. Zheng; Z.X. Jing; Q.H. Wu

    This paper proposes an individual-based distributed parallel (IBDP) method for the operation optimization of integrated energy systems considering heterogeneous structure. The proposed IBDP method utilizes individual-based models (IBMs) to describe integrated energy systems. In this model, three basic modelling units are summarized, from which, a general three-level model of integrated energy systems is inherited. Utilizing IBMs, the high-dimensional integrated energy system model is decoupled into distributed heterogeneous individuals. The individuals are with local information inside to protect their information privacy and independent operation from the environment. Meanwhile, global information, which provides with environmental boundary conditions, can be obtained through individual interactions. To solve the IBMs of integrated energy systems efficiently, an Proximal Jacobian alternating direction multiplier algorithm (Proximal Jacobian ADMM) is adopted to implement the IBDP where the subproblems of individuals run in parallel. To verify the veracity and stability of the proposed method, the IBDP is applied to optimize the operation strategy of integrated energy systems in four different scales, and the results are compared with that obtained by centralized optimization method.

    更新日期:2019-12-29
  • Sizing power transformers in power systems planning using thermal rating
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-27
    Olivier Arguence; Florent Cadoux

    It has already been shown in the literature that power transformers may be more accurately sized by their thermal limits than by their rated power limit. In practice however, thermal limits are usually considered only in operations; but not at planning stage, where the more usual notion of rated power is used. This paper proposes a novel method to take into account (and benefit from) thermal limits directly at planning stage. This is made possible by quantifying separately the impact of each generator and load on the temperature of the distribution transformer. Decoupling the effect of individual generators and loads is achieved by linearizing and rewriting the analytical expression of the hot-spot transformer temperature. The practical value of the method is assessed using a real-world dataset, by estimating the increase in the hosting capacity of the considered transformer for additional generators and loads. Significant gains are obtained when the transformer is sized by generation, in particular when photovoltaic (PV) generators are involved.

    更新日期:2019-12-27
  • Impact of rapid PV fluctuations on power quality in the low-voltage grid and mitigation strategies using electric vehicles
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-23
    N.B.G. (Nico) Brinkel; M.K. (Marte) Gerritsma; T.A. (Tarek) AlSkaif; I. (Ioannis) Lampropoulos; A.M. (Arjan) van Voorden; H.A. (Henk) Fidder; W.G.J.H.M. (Wilfried) van Sark

    Cloud transients cause rapid fluctuations in the output of photovoltaic (PV) systems, which can significantly affect the voltage levels in a low-voltage (LV) grid with high penetration of PV systems. These voltage fluctuations may lead to violation of the existing power quality standards. This study estimates the impact of rapid PV output fluctuations on the power quality in an existing LV grid by performing load flow analyses for scenarios in the years 2017, 2030 and 2050 using PV data with 20-second resolution. In this study, we propose a system for the mitigation of PV output fluctuations by altering the charging processes of electric vehicles (EVs) and we assess the effectiveness of the proposed system. Results indicate that PV output fluctuations have minor impact on the voltage levels in the year 2030, but PV output fluctuations induce considerable voltage fluctuations in the year 2050. The magnitude of the voltage fluctuations is dependent on the location in the grid, the installed PV capacity and the grid configuration. These voltage fluctuations can induce visible and annoying light flicker for a significant part of the day in the year 2050. Implementing the proposed system shows that EV technology can contribute in reducing the amount of visible and annoying light flicker considerably, however at the expense of increased charging costs for EV owners.

    更新日期:2019-12-27
  • A new isolated renewable based multi microgrid optimal energy management system considering uncertainty and demand response
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-26
    Seyed Ehsan Ahmadi; Navid Rezaei

    This paper proposes a novel energy management system (EMS) for an isolated structure of networked microgrids (NMGs). The interconnected microgrids consist of the cyber-physical connections for information and power exchanges. A bi-level EMS is presented in which the outer-level EMS is aimed to exchange the required information and power between the interconnected microgrids, and the inner-level EMS is intended for energy scheduling of each on-fault microgrid in case of separation from other microgrids. This paper focuses on the operation of interconnected microgrids. A step-wise demand response program (DRP) is also considered in the energy management to attain the cost-effective operation. Furthermore, a new pricing model based on microgrid marginal pricing (MGMP) is introduced for the power exchanges between the interconnected microgrids. To cope with the uncertainties of the renewable energy sources and loads, some scenarios are generated using the scenario-based analysis. Also, a backward scenario reduction method is used to reduce the number of the scenarios. Besides, a mixed integer linear programming (MILP) is applied to the stochastic optimization problem of the NMGs. The proposed model is implemented on a test system with five NMGs. The simulation is run over a 24-hour scheduling time horizon. Both cases without and with demand response program (DRP) are compared in the numerical results. The results of the simulation demonstrate that using the proposed DRP in the energy management increases the performance of the generation units and decreases the total operational cost of the proposed NMGs. Also, the voltages of the buses converge to their rated values.

    更新日期:2019-12-27
  • Impact of harmonic limits on PV penetration levels in unbalanced distribution networks considering load and irradiance uncertainty
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-19
    Ibrahim Cagri Barutcu; Engin Karatepe; Mutlu Boztepe

    Photovoltaic (PV) system is one of the most important technologies among the renewable energy resources. With the increasing penetration of PV systems in distribution networks, harmonic distortions also rise due to the inevitable effects of PV inverters. Therefore, determination of the optimal PV penetration level is a vital issue in terms of preventing power quality problems. In this paper, probabilistic and deterministic approaches are proposed to determine the optimal penetration levels of PV systems in unbalanced distorted distribution networks by taking into account the uncertainty of load profile and the intermittent characteristic of PV system output power due to changes in solar irradiance. The Interior Point (IP) method is applied to solve the optimization problem in conjunction with the Monte Carlo Simulation (MCS) and K – means clustering, respectively. The methodology is based on the dependence of the harmonic spectrum of PV injected current on solar irradiance. The harmonic power quality parameters are calculated by using loop frame of reference based three phase harmonic power flow method in the unbalanced distribution network, where the nonlinear loads and PV systems are interfaced. The allowable PV penetration levels are determined based on power quality parameters comprising of total harmonic voltage and individual harmonic voltage distortions, and RMS bus voltage limits.

    更新日期:2019-12-27
  • A general PMU placement approach considering both topology and system aspects of contingencies
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-19
    Mohammad Hossein Rezaeian Koochi; Mohammad Hasan Hemmatpour

    In a wide area measurement system, line tripping as well as the following transient and dynamic post-contingency conditions affect the full observability of power systems and possibly the accuracy of the wide area monitoring system. In this paper, a general methodology is presented to solve the phasor measurement unit (PMU) placement problem considering both the system and the topology aspects of disturbances. To do that, the connectivity matrix-based PMU placement problem is firstly formulated in its basic binary integer form to meet the full observability of power systems. Next, the post-disturbance variations in power systems, as the system aspect, are integrated with the conventional placement problem to ensure the more accurate pre- and post-disturbance monitoring of power systems. In addition, the algorithm is developed to achieve the highest possible reliability for single transmission line outages, i.e. N – 1 contingencies, as the topology aspect. Other topology-related issues, including zero injections, PMU channel limitations, and pre-existing measurements are included in the new formulation as well. Since the effects of the two aspects of disturbances on the placement solution are conflicting, and as the magnitude of the system aspect is much stronger than that of topology aspects, compensations are added to balance the conflicting effects by mitigating the strong effect of the system aspect on the overall formulation. Therefore, the proposed methodology will lead to a placement scheme, by which providing the full observability of the system under a high number of single line outages as well as obtaining the more accurate post-disturbance monitoring of power systems are assured. The performance and effectiveness of the proposed methodology are demonstrated in two medium and large test systems.

    更新日期:2019-12-27
  • Iterative harmonic load flow by using the point-estimate method and complex affine arithmetic for radial distribution systems with photovoltaic uncertainties
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-19
    F.J. Ruiz-Rodriguez; J.C. Hernandez; F. Jurado

    Load and generation variations and the random nature of harmonics in non-linear devices (NLDs) are the source of multiple uncertainties that can be handled in harmonic load flows (HLFs) by probabilistic or interval formulations. The paper presents a new combined analytical technique (CAT) for iterative HLFs in the presence of correlated input uncertainties from photovoltaic (PV) systems in radial distribution systems (RDSs). This technique merges the point-estimate method (PEM), a probabilistic formulation, and complex affine arithmetic (AA), an interval formulation. It then uses the information derived in Legendre series approximation (LGSA) to approximate harmonic voltage distributions. Unlike other methods, this CAT includes iterative harmonic penetration (IHP), which provides a way to deal with the interaction of background harmonic voltage on PV harmonic current. The CAT was examined in a real ENDE 100 RDS system. Thanks to PEM and AA, the CAT significantly reduced the computational burden, an evident improvement over the Monte-Carlo simulation (MCS). Furthermore, the simulation results showed that it accurately reconstructed the harmonic voltage distributions (magnitude and phase angle). The iterative approach also underlines the relevance of background harmonic interaction. The CAT outperformed the incomplete CAT (ICAT), which was based solely on a probabilistic HLF formulation.

    更新日期:2019-12-27
  • A medium/long-term auction-based coalition-forming model for a virtual power plant based on stochastic programming
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-19
    Mehran Jafari; Asghar Akbari Foroud

    This paper presents a methodology based on auction theory to form a virtual power plant (VPP) coalition of heterogeneous distributed energy resources (DERs). Moreover, in this procedure, the competition between VPPs for attracting DERs is considered. In this model, the VPP has the ability to participate in the day-ahead energy market, become involved in the future energy market and sign bilateral contracts in a medium or long-term time horizon. Also, the ability of arbitrage between different markets is considered for the VPP. Moreover, the risk of energy trading is taken into account with the risk measure method, conditional value at risk. Due to the uncertain nature of pool prices, a stochastic programming approach consist of two stages is developed for modeling the decision-making problem. In the first stage, the VPP participates in an auction and signs the renting capacity contracts with DERs based on auction results. The future market contracts are signed in this stage as well. In the next stage, the decisions regarding bilateral contracts, pool participation, and DERs planning will be made. Also, the uncertainty of the quantity and the price of bilateral contracts are considered. The efficiency of the model is analyzed in a few case studies.

    更新日期:2019-12-27
  • Structure and properties of the hybrid and topological transformer models
    Int. J. Electr. Power Energy Sys. (IF 4.418) Pub Date : 2019-12-19
    Jianhui Zhao; Sergey E. Zirka; Yuriy I. Moroz; Cesare M. Arturi

    Three topological transformer models for low-frequency transient simulations are considered in increasing order of their topology. It is first shown that the well-known hybrid model is not a strictly topological one, but despite this, it can be used in many applications. The next is the simplified model, which is a strict electric equivalent of the popular magnetic model, and the last is a detailed electric model, which takes into account thicknesses of transformer windings. This model improvement allows one to reproduce experimentally observed behaviors of the magnetic fluxes in the legs and yokes under short circuit conditions.

    更新日期:2019-12-27
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