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In this paper, the operation of electrical, heat and gas networks with flexible energy hubs is presented, where hubs is contributed in energy market that is based on market clearing price. This scheme maximizes the difference between energy hubs profit and operation cost of generation units subjected to operation model of sources, storages and responsible load in hub format, flexibility limits of hubs, and optimal power flow model of energy networks. This formulation is based on market clearing price model, so that it obtain value of energy price according to balancing between the generation and demand in different buses if energy networks. Penalty function method in this paper uses to calculate of primal variables and some dual variables (energy prices). In the following, the stochastic optimization uses to model the uncertainties of load and renewable power. Finally, the obtained numerical results show the capabilities of the proposed scheme in the improving flexibility and economic situations of hubs. Also, optimal operation of hubs is able to improve the economic and operation induces of energy networks in comparison to load flow study, and it improves the social welfare based on reducing of energy price. So that 100% flexibility condition obtains for Hubs. In this condition, the operation cost, energy loss, voltage drop and temperature drop are reduced about to 19.8%, 7.1%, 19.5% and 16.7%, respectively, with respect to load flow analysis, but the pressure drop increases about to 4.9%. [ABSTRACT FROM AUTHOR]

This paper presents the optimal scheduling of active distribution network (ADN) with linear and non‐linear loads in the presence of an integrated unit of electric spring and electric vehicle parking lot (IUEE). The proposed scheme is formulated in the form of three‐objective optimization, which minimizes the expected operating cost of the ADN, voltage deviation function (VDF), and the total harmonic distortion (THD) of the voltage in separate objective functions. Constraints include harmonic power flow (HPA) equations, operation and power quality limits, and operation model of the IUEE. This scheme has uncertainties of load, energy price, and energy demand of EVs, which are modelled here using stochastic programming. Next, the sum of the weighted functions method as a subset of the Pareto optimization technique is adopted to extract the integrated single‐objective problem. Then, Sine‐Cosine Combined Algorithm (SCA) and Gray Wolf Optimization (GWO) are used to achieve an optimal solution. In the end, by examining the numerical results obtained from the implementation of the proposed scheme on a 69‐bus ADN, the capability of the design in enhancing the economic situation, operation, and power quality of the ADN compared to network power flow studies obtained by optimal scheduling of the IUEE is confirmed. [ABSTRACT FROM AUTHOR]

With the emergence of smart grids, accurate very short-term load forecasting (VSTLF) has become a crucial tool for competitive energy markets. The number of behind-the-meter photovoltaic solar panels, which usually are not monitored are increasing. This could reduce the load visibility and also affects the VSTLF accuracy. While most of the research works focus on demand forecasting of large areas, the performance of VSTLF methods for the future scenario of high solar power penetration in the microgrid environment is unclear. This paper investigates the impact of high solar power integration on the forecasting accuracy of machine learning VSTLF models for microgrids. The performance of Neural Network, Support Vector Regression are evaluated for high penetration scenario and no solar penetration. The accuracy of these models is examined for three different forecasting horizons through various comparative experiments for two real-world microgrid datasets. According to simulation results, using the most relevant variables is highly recommended. Furthermore, the results demonstrate that machine-learning methods can tackle the nonlinear characteristics of net load forecasting as well as total load forecasting. These simulations show that high penetration of solar power generation could not significantly affect the accuracy of machine learning VSTLF if most relevant variables are selected and applied as model inputs. [ABSTRACT FROM AUTHOR]

This paper presents a fault detection and faulty area identification algorithm in double-circuit transmission lines (DCTLs) compensated by the generalized unified power flow controller (GUPFC) for the first time. The topology of the GUPFC-compensated DCTL is threatened by three types of faults: single-circuit faults, inter-circuit faults, and grounded double-circuit cross-country faults. In the first step, the suggested scheme can determine the time of fault in this type of topology using a very fast method that is based on the analysis of a current index called the current jump index. In the second step, the fault type and area are identified with the help of two other indices, i.e., voltage difference index and current difference index. The test network presented in this paper, which includes a DCTL and a GUPFC, along with the proposed algorithm, is implemented in the MATLAB software package. The results of the simulation and sensitivity analysis of the algorithm confirm the correct performance of the algorithm. [ABSTRACT FROM AUTHOR]

Power management in microgrids is a major challenge due to its low total inertia and capacity. The lower the microgrid generation capacity is, the higher the share of each generation unit in total power will be, and the higher the frequency deviation in less time will be when an outage occurs. So, preventive actions can be more reasonable and affordable than corrective actions for microgrid power and frequency control. In this regard, a new primary frequency response-constrained unit commitment model is presented here to prevent excessive frequency deviations by more commitment of higher inertia power plants and more contribution of renewable energy resources or energy storage systems' fast inertia response. To have a mixed-integer linear programming model, the primary frequency response constraints are linearized. The model is solved by the combination of two commercial solvers named MOSEK and YALMIP in the MATLAB 2018 environment. The proposed model is examined on a real isolated microgrid (an island). The results show that by activating the primary frequency support of distributed energy resources, the power can be managed with lower costs because there will be less need to start up fast (and expensive) gas turbine generation units. In addition, although comparing the model with others shows the more expensive management procedure, better frequency stability is obtained in contingencies. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive characteristic for eliminating the adverse effects of fault resistance and static synchronous compensator (STATCOM) on the performance of distance relays in transmission line and collector lines of doubly‐fed induction generator (DFIG)‐based wind farms in the case of single‐phase‐to‐ground resistive faults. The proposed method improves the performance in distance relaying and maintains the coordination between relay pairs in the transmission line and wind farm collector lines. In this method, an adaptive coefficient that can modify the zone settings of conventional distance relays is added to their characteristic to improve the accuracy and coordination under the mentioned conditions. Using analytical relationships and numerical results from simulations in Matlab/Simulink environment, the efficiency of the proposed method is confirmed. [ABSTRACT FROM AUTHOR]

Internet of Things (IoT)-based energy management systems (EMSs) are considered a new technology in which consumers can manage their electricity payments according to their preferences, such as reducing costs or increasing satisfaction. Each consumer has its own program for communicating with a central control unit. In addition, the central control unit that is responsible for energy pricing can access consumer information and network performance status through the IoT infrastructure. Therefore, technical analysis can be performed using big data to determine the optimal price in order to make a compromise between the buyer and the goals of the distribution system operators. This paper presents a model to accurately assess the impact of pricing on the behavior of IoT-based energy systems. Then, according to the load specifications of each item and the technical limitations of the distribution network, the best time to use pricing is determined. The results show that the higher the price variance, the more discomfort the consumer and the lower the daily payment. Therefore, in this paper, the main goal of energy management is to minimize the total weight of the costs paid and their discomfort level. The paper could facilitate further penetration of IoT-based EMSs into smart grids. The study was performed on an IEEE standard 33-bus network. Optimization was implemented using YALMIP and MOSEK toolboxes. Therefore, it can be concluded that IoT technology allows consumers to enjoy the benefits of the network and makes optimal consumption management possible. [ABSTRACT FROM AUTHOR]

An accurate inter‐circuit fault location algorithm for double‐circuit transmission lines compensated by a generalized unified power flow controller based on phasor analysis is presented. The proposed algorithm utilizes synchronous currents and voltages of the buses on both sides of the line to accurately calculate the fault location. Using the equations of sequence component circuits, the algorithm calculates voltage and current of the fault point on both circuits. Then, using boundary conditions equations for 98 types of inter‐circuit fault on the double‐circuit transmission lines, the accurate location of the fault is obtained. The number of boundary conditions equations varies depending on the type of faulty phases of the two circuits and the number of unknowns in the current and voltage equations of the fault point. The calculation of these boundary equations are also described. The results presented in the simulation section verify the validity and accurate performance of the proposed algorithm under different fault conditions. [ABSTRACT FROM AUTHOR]

Network reconfiguration (NR) has undergone new changes to adapt to smart grid evolution. Internet of things (IoT) has found its way to smart grids especially in the distribution systems. Demand‐side management can be more efficient in the presence of IoT. IoT‐based energy management systems can have bidirectional communication with smart grids and decide according to their preferences, time‐of‐use (TOU) pricing, and their flexible devices. Therefore, customers would consume electricity more interactively. Consequently, the total load profile will be changed and a new NR approach must be adopted to meet load demands. So, the selection of critical switches must be modified to achieve the most effective network resource utilisation. For this purpose, a mixed‐integer linear programming model for feeder reconfiguration is presented considering the customers' behaviours in the IoT environment. At first, the customer manner is investigated at different prices and preferences. Then the total load profile is calculated considering the normal distribution of uncertain customer preference factors. Finally, the identification of critical switches is obtained using the proposed method. The optimisation is done in YALMIP and MOSEK toolboxes. Results show the effectiveness of the proposed method to efficient utilisation of IoT potentials and renewable energy benefits. [ABSTRACT FROM AUTHOR]

In this paper, a bi‐level power management strategy is presented for an active distribution network (ADN) in the presence of virtual power plant (VPP). In the proposed strategy, VPP contains renewable energy source (RES), energy storage system (ESS) and electric vehicles (EVs) parking lot coordinated with VPP operator (VPPO), and there is a coordinated framework between VPPO and distribution system operator. The proposed power management strategy (PMS) is considered in the context of the bi‐level optimization problem. In the first level, the optimal harmonic power flow formulation of the ADN is considered by minimizing the summation of energy cost, voltage deviation function and voltage THD% as a normalized objective function. In the second level, the VPP is modeled according to the framework of day‐ahead energy and ancillary services markets. In the next step, the linear format of the proposed non‐linear original problem is obtained with an optimal solution and low calculation burden. Also, the Karush‐Kuhn‐Tucker condition is used to convert the proposed bi‐level PMS approach to a single‐level model, and the scenariobased stochastic programming models the uncertainty of load, energy price, RES power, and EVs demand. Finally, the proposed strategy is applied on the 33‐bus distribution network using GAMS software. [ABSTRACT FROM AUTHOR]

In this study, on the basis of a new agent‐based situational awareness platform, the amount of severity in closeness to voltage instability occurrence is determined. In the proposed platform (with the aid of the agents of the disturbance detection unit that are responsible for perception of environmental events and understanding the current situation and the agents of the early enough instability prediction unit that predicts instability occurrence), the novelty is in creating the agents of clustering units that are responsible for prediction of the future status, i.e. severity in closeness to voltage instability occurrence through determining the severity class. This clustering unit maps the reactive power‐based features obtained from unconstrained power flow analyses, to the instability time; without any need of post‐disturbance data, i.e. the method belongs to just‐after‐disturbance algorithms. Then, it estimates the severity of the closeness to instability for any test scenario according to its membership degree related to the pre‐defined severity clusters. The simulation results show acceptable overall accuracy (up to 99%) in performing early warning task for operators of power systems. [ABSTRACT FROM AUTHOR]

The rapid growth and development of manufacturing technology for controlling processors and high-power semiconductor devices has led to the enhancement of flexible AC transmission system (FACTS) controllers, thus improving the performance of power systems. The generalized unified power flow controller (GUPFC) is today introduced as the most advanced generation of the FACTS family, which is based on voltage source converter (VSC). It can, hence, control all the five parameters of a power system given above. The paper, for the first time, presents the accurate modeling of different parts of the control system and power electronics of the 72-pulse VSC-based GUPFC in detail to satisfy operation constraints and improve power quality in terms of harmonic level reduction. There is no need to use active or passive filters in the proposed model for reducing harmonic level of the GUPFC. In this regard, the calculation of four main parameters, namely D_alpha, alpha, angular speed, and sigma, as inputs of the pulse-firing system for the 72-pulse VSC is performed dynamically and optimally to meet all expected constraints in terms of operation, power quality, and harmonic reduction of a network with a GUPFC. The presented modeling is implemented on a 230 kV GUPFC-compensated double-circuit transmission line in MATLAB/Simulink environment, and the desired results of the presence of the 72-pulse VSC-based GUPFC are shown to meet the desired constraints of operators. [ABSTRACT FROM AUTHOR]

In this study, a simple, fast, and adaptive network reduction procedure is presented for long‐term voltage stability analyses, to speed up the simulation time. The proposed procedure consists of two parts including disturbance detection based on data from synchronised measurement devices; and the rest, up to the final estimated values, based on simulations and calculations. In turn, simulations and calculations result in an adaptive dynamic‐oriented determination of external sub‐network (according to the disturbance occurred) and substituting an appropriate equivalent for that subsystem. The external subsystem is determined without any need to measure post‐disturbance data, while the detection criteria are calculated by simulations at 0.8 s after disturbance occurrence. The results have shown considerable reduction in the simulation time while providing acceptable accuracy in delivering the time of voltage instability occurrences, especially when applying the proposed error compensation procedure. [ABSTRACT FROM AUTHOR]

In this study, the proposed algorithm is a help for utilities to find out when voltage instability will happen, as soon as they realise that a disturbance may/will result in voltage instability. In this regard, the data gathered, on‐line, by a wide area monitoring system (WAMS) is supposed to be processed in an energy management system, where, finally, voltage instability inception time will be determined. The proposed algorithm employs k‐nearest neighbour algorithm as an instance‐based learning algorithm. This estimation uses only pre‐disturbance information and exact disturbance data, so it is fast enough for real‐time applications. A comprehensive investigation of the input features has resulted in introducing the most appropriate feature set and the most effective search procedure in estimating the instability time. The simulation results show an acceptable accuracy in estimation of voltage instability time. [ABSTRACT FROM AUTHOR]

This paper deals with a control design based on amplitude adaptive notch filter (AANF) for a four-leg distributed static compensator (DSTATCOM) in a three-phase four-wire distribution grid to overcome current-related problems of power quality. Extracted reference currents of DSTATCOM are obtained using AANF because of its simple structure, exact measuring of frequency and amplitude, suitable estimation of the desired signal, and capability of tracking the changes of the input signal amplitude. To improve the dynamic performance of DSTATCOM, two fuzzy logic controllers are utilized to regulate DC link voltage and the voltage of point of common coupling (PCC). Furthermore, an adaptive hysteresis band current controller is applied for generating the gate pulses of IGBT switches. The proposed control scheme is robust to power system oscillations, especially when the main voltage suffers from disturbances and unbalancing. Different surveys are performed to study the efficacy of the proposed method, and results are verified through the simulation results in MATLAB/Simulink environment. [ABSTRACT FROM AUTHOR]

An ultra‐high‐speed, accurate and reliable algorithm is proposed in this study for the identification and faulted phases selection of inter‐circuit faults. For this purpose, modal components of current samples just before they arrive to the relay location are extracted. Teager energy operator is used here for the extraction of current travelling waves (TWs). The amplitude of the TWs in different modal components and their ratios in similar modal components are used for the inter‐circuit fault identification and finding the faulted phases. Test signals are simulated in PSCAD/EMTDC software and the algorithm is implemented in MATLAB. Results show that the proposed algorithm is a really ultra‐high‐speed algorithm which can be reliably used for the identification and classification of the inter‐circuit faults. [ABSTRACT FROM AUTHOR]

Considering the advantages of DC microgrids, the extension of the conventional AC distribution grid can be implemented using a DC microgrid. This justifies the realization of a hybrid AC/DC microgrid. In the present study, a new global solution is presented to improve the power quality and to fully compensate the reactive power of an AC microgrid using DC bus capacity while introducing a new design for a hybrid AC/DC microgrid. In the new design, back- to-back connections of two series and parallel converters, as well as the presentation of new controllers and simultaneous utilization of an earthing switch, are proposed. The proposed method guarantees the quality of the delivered voltage to consumers and the drawn current from the network according to the IEEE-519 and IEEE-1159 standards under different power quality problems (e.g., interruptions, sags, harmonics, and any variation in voltage/current signals from pure sinusoidal). Through the proposed design of the new hybrid AC/DC microgrid, as a new feature, the operation of the network in islanded mode can be achieved in accordance with power quality standards even in the worst load quality conditions. It should be noted that in common hybrid microgrids in islanded mode, the delivered voltage quality is proportional to the quality of the consumer's load current. Another possibility of the proposed design is the instantaneous VAR compensation of nonlinear and induction loads of consumers to keep the power factor of the distribution transformer close to unit value. Simulation results indicate that there are acceptable levels of compensation for different types of power quality problems. Total harmonic distortions and total demand distortions are below 3% in both the grid-connected and isolated modes of the hybrid AC/DC microgrid. [ABSTRACT FROM AUTHOR]

This paper presents a new hybrid islanding detection approach for microgrids (MGs) with multiple connection points to smart grids (SGs) which is based on the probability of islanding (PoI) calculated at the SG side and sent to the central control for microgrid (CCMG). The PoI values are determined using a combination of passive, active, and communication islanding detection approaches based on the utility signals measured at the SGs sides which are processed by discrete wavelet transform using an artificial neural network (ANN). If \textPoI{\rm{ANN}} is larger than the threshold value (indicating high possibility of islanding) then a more accurate approach based on fuzzy network is used to recompute it (\textPoI{\rm{FUZZY}}) where the fuzzy parameters are determined by an adaptive neuro-fuzzy inference system. In the proposed technique, an active islanding is only performed when PoI is high and the amplitudes of the disturb signals are proportional to \textPoI{\rm{FUZZY}}. Furthermore, if the PoI is not correctly received by CCMG, two auxiliary tests will be performed in the MG side to detect islanding. These tests include an intentional passive islanding detection in a short preset time and an active islanding detection with disturb signals proportional to the calculated PoI. Detailed simulations are performed and analyzed to evaluate the performance of the proposed method. [ABSTRACT FROM AUTHOR]

Due to the limited operations of three-phase machines in open-phase fault conditions, the multiphase induction generators are now introduced in high-performance power generation systems. In the case of six-phase induction generators, the operation with opened phases is associated with torque and consequently power oscillations even in steady state conditions. Previous works have reported different methods to reduce these oscillations but they only deal with sensored control issues. Therefore, this paper deals with on-line modification of a sensorless control system applied to a squirrel cage six-phase induction generator (SC6PIG) when one to three phases of the machine are lost. Designing ten different off-line Luenberger speed observers as well as ten control systems corresponding to the different possible fault types and switching between them as a function of a detection system is proposed in this paper. Furthermore, on-line imposing of the nonzero initial conditions induces a smooth switching between the observers as well as the controllers with minimum associated transient at switching instants. The proposed strategy is tested on a wind turbine simulator driven by a permanent magnet dc motor. The experimental results in healthy and faulty modes assess the validity of the proposed strategy. [ABSTRACT FROM AUTHOR]

This study proposes an intelligent traveling‐wave (TW)‐based protection algorithm for parallel transmission lines. In the proposed algorithm, Karenbauer's phase to modal transform is applied on three phase current signals. Teager energy operator is then applied on the modal components to extract TWs. First extracted TW of each modal component along with well‐designed fuzzy systems are used for internal fault identification and fault type classification. In order to find the fault location, the time difference between the first and the second TWs and the TW propagation speed are utilised. Test signals are generated in PSCAD/EMTDC software and the algorithm is implemented in MATLAB. Results show that the proposed algorithm is an ultra‐high‐speed algorithm for the reliable protection of parallel transmission lines. [ABSTRACT FROM AUTHOR]

The cuckoo search (CS) algorithm is a simple and effective global optimization algorithm. It has been successfully applied to solve a wide range of real- world optimization problem. In this paper, a modified CS algorithm is applied to determine the feasible optimal solution of the economic load dispatch problem considering various generator constraints. In order to solve the problem of being trapped into the local optima, a new mutation scheme, inspired by the DE/current-to-gr_best/1, is incorporated in standard CS to enrich the searching behavior and solution quality and to avoid being trapped into local optimum. In order to verify the performance of our approach, the proposed approach is tested with two power system cases consisting of 3, 6, 15, and 40 thermal units with generator constraints. State-of-the-art optimization techniques are compared with simulation results obtaining proposed method to illustrate the efficiency of the proposed method and to show that the improved CS could be used as a reliable tool for solving economic load dispatch problems with generator constraints. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study presents a new voltage control algorithm for multilevel inverters which are used to connect the distributed generation (DG) sources (like photovoltaic cells) to the network, which is called the voltage look-up table method (VLUTM). This method can build up an almost sinusoidal voltage at the inverter output with the least number of switching in the power circuit, and the best possible harmonic spectrum without the need to any big filtering. On the other hand, in some specific applications where the DG has been set up beside a non-linear load, VLUTM can make a reference voltage based on the reference current to take a desired current form the DG. This way the DG can compensate the major low-order load current harmonics and improve the source side current THD greatly. Decreasing the switching frequency as much as possible, which leads to better efficiency and less EMI problems, the capability of implementation both in single phase and three phase circuitry, and the very simple and desired current control, would be the major benefits of this method. The simulation results taken from Matlab/Simulink and the experimental results on a 1 kVA experimental prototype are presented to evaluate the performance of this method. [ABSTRACT FROM AUTHOR]

There are many types of distributed-generation (DG) sources that cannot be connected to the network directly and use an inverter-based interface. In harmonic compensators [like active power filters (APFs)], the coupling transformer disrupts the compensation capability, therefore the transformerless inverter schemes have grown up in recent years. A new cascaded multilevel transformerless inverter topology is introduced in this study to connect the DG sources to power utility. The proposed circuit of this study can compensate the current harmonic of the non-linear load (as in APF) and inject maximum possible active power as a DG source interface, simultaneously. A fixed gain called KC is obtained based on the load nature, and is used to adjust the set point of the inverter between two operating modes. Proposed scheme has been simulated in Matlab/Simulink to evaluate the circuit performance both in the maximum active power injection mode and the load harmonic compensation mode. Then a 2.2 kW single-phase prototype of the circuit is used for experimental evaluation of the study. Both simulative and experimental results prove that such a circuit minimises the total harmonic distortion of the source side current to an acceptable margin, while injecting the maximum possible active power. [ABSTRACT FROM AUTHOR]

This paper presents an effective technique for tracking and finding the direction of switched capacitor banks in distribution system generating switching transient when certain number of power quality meters exist. The proposed method is comprised of two independent algorithms. Algorithm utilizing the steady-state power quality data based on changes of the phase-angle difference between voltage and current and algorithm utilizing the transient state power quality data based on branch voltage and current changes immediately before and after the capacitor switching instant. This technique uses modal current and voltage signals that can be constructed by combining three-phase current and three-phase voltage. Wavelet transform is used to detect the exact instant of switching transient. The efficiency of proposed method was validated using IEEE 34-bus distribution system, modeled in PSCAD. [ABSTRACT FROM AUTHOR]

The practical aspects of constructing an ironless axial flux direct-drive generator for Mind applications are presented in this paper. In other words, the design procedure for this 50 kW-generator is discussed in details as well as the construction procedure. This generator provides various advantages which are distinctly discussed in this work In this structure, both rotor and stator are designed without any ferromagnetic materials. Because of the absence of ferromagnetic materials and gearbox, the total mass of system is less than equivalent designs based on iron-cored magnetic circuits. The genetic algorithm is used to optimize machine structure and to achieve high power density and ejftciency. As a result, the constructed 50kW-generator has been found to have a proper volume as well as an appropriate efficiency. Unlike other generator structures, the iron losses are completely omitted in this structure. This issue contributes to achieve high efficiency. In addition, the armature reaction effect is considerably reduced because of the significant decrease in the synchronous reactance. In this structure, like slotless machines, there Is no cogging torque. The generator operation is investigated in both simulation and implementation. The validity of this generator structure is demonstrated by great agreement between simulation and implementation results. [ABSTRACT FROM AUTHOR]

Summary: The use of phase shifting transformer (PST) is one of the common methods of power flow control in complex transmission systems. Changing the power distribution in lines by the PST will change the voltage and the current signals of the power system. Loss of excitation relay in a synchronous generator is one of the important relays of the generator that measures the voltage and current signals of generator output to identify the loss of excitation of the generator. This study shows that the presence of PST in the transmission line interferes with the performance of the loss of excitation (LOE) relay. The LOE relay in this paper is of the Berdy type, which detects loss of excitation by measuring the voltage and current of the generator and calculating the impedance from them. In this paper, the way this impedance is calculated has been modified, as this impedance is calculated from the modified values of the active and reactive powers of the generator. As a result, it has been shown that with the help of this method, the effect of PST on the operation of the LOE relay is significantly eliminated. In the proposed method, PST information is not required to be sent to the relay location, and so the communication channel is not needed. A decision tree‐based method is used as a backup protection to guarantee proper operation in power swing conditions. [ABSTRACT FROM AUTHOR]