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The global trends toward increasing clean and sustainable power generation have brought significant changes and developments in electrical distribution networks. The existing passive networks are being restructured to facilitate renewable distributed generations to ensure high degree of reliability of power supply to customers. A distribution system reliability assessment (DSRA) is crucial to analyze the risk and cost associated with power interruptions and take necessary preventive and corrective actions. This paper presents an approach to DSRA and carries out a comprehensive reliability assessment of an active distribution network (ADN) connected with solar, wind, and tidal energy sources. A multi‐state reliability model is developed, combining the Markov and well‐being frameworks to determine the reliability of a network energized by multiple renewable energy sources (RESs). The load point reliability and worth‐oriented indices, namely SAIDI, SAIFI, CAIDI, AENS, EENS, ECOST and IEAR, are evaluated to analyze the impacts of the three RESs on the reliability of the ADN. The paper also proposes two new metrics to estimate the benefits of adding RESs from the reliability worth and cost perspectives. The analyses have been carried out on the Roy Billinton Test System. The results show that the maximum reliability worth and cost benefits can be extracted from a combined operation of multiple RESs. A combination of solar‐wind‐tidal energy sources, therefore, can be an effective solution for countries having long coastlines to fulfill not only the sustainable energy goals but also to improve the grid's reliability and reduce the monetary losses incurred due to customer interruptions. [ABSTRACT FROM AUTHOR]

Summary: At the present day, the issue of the further development of energy economics, industry, and other areas are quite urgent, taking into account the environmental component and not excluding the economic component of this problem. It is possible to reduce the negative impact on the environment by switching to biofuel. In addition to the environmental benefits, biofuels are beneficial in use, also to the companies themselves, as it is more cost‐efficient. The production and use of energy by the companies involve distributed generation. The purpose of the paper is to analyse the economic prospects of replacing distributed generation with biofuel. Results: within the framework of the study, the concepts of distributed generation, biofuel, its main types, as well as some of the advantages of biofuel are defined. Some economic aspects are considered, mainly in the direction of biofuel‐related benefits. In addition, the paper considers the distributed generation market development and the use of biofuel in Russia in comparison with other countries, the main problems were identified, and the main prospects in this direction were considered. Prospects for further research: due to the subsequent study of biofuel usage, taking into account economic and environmental aspects. The applied value of the material: the paper is of practical value in the framework of generalising data on the distributed generation market and the bioenergy market in the Russian Federation and foreign countries. [ABSTRACT FROM AUTHOR]

Summary: This paper is concerned with the two‐stage hierarchical control of microgrids (MG) that can operate in both grid‐connected and off‐grid modes. The procedure consists in the segmentation of the control scheme in the primary and secondary levels, thus enabling the application of faster and slower dynamics according to the process. A decentralized droop control‐based method is used in the primary level, while a distributed multi‐agent coordination scheme is applied in the secondary one. The multi‐agent system is run on Python Agent DEvelopment (PADE) environment, a FIPA‐compliant agent framework. The key contributions this paper provides are the control strategies of reactive power output of non‐dispatchable sources, dynamic sharing of energy storage systems, and the management of loads of microgrids, all of them based on multi‐agent system. Co‐simulations using PSCADTM and PADE are performed considering several operating scenarios of the MG resources under different load conditions. Simulation results validate the accurate performance of the proposed control strategies. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes a novel control scheme for unified power quality conditioner (UPQC) to minimize voltage sag, swell, and total harmonic distortion (THD) in a distribution grid integrated with distributed generation (DG). UPQC is a power electronics module that can provide, both, series and shunt compensation simultaneously in a distribution system. The whole characteristic of UPQC is dependent on the embedded control algorithms, which are used for generating a reference signal. This work focuses on synchrosqueezing wavelet transform (SWT) based identification, detection, and control of power quality (PQ) events. SWT is a time‐frequency analysis method that analyzes multicomponent signals with oscillating modes. In this paper, first, SWT is used for the detection and identification of various kinds of PQ issues in the DG integrated grid. The SWT based identification scheme provides better resolution and increases the readability of time‐frequency representation. This work further explores to control the PQ issues through UPQC's enhanced compensation capabilities which utilize artificial neural network (ANN) with SWT based shunt controller. The effectiveness of the proposed method is validated through MATLAB/ SIMULINK simulations and is seen that ANN with SWT based controller is better performed in comparison to ANN based controller, in terms of accuracy, and also with respect to THD. Performance analysis of UPQC is carried out with ANN based controller as well as ANN with SWT based controller, under different voltage and current disturbances, in time and frequency domain. [ABSTRACT FROM AUTHOR]

Summary: Identifying maximum penetration level (MPL) of Solar Photo‐Voltaic Generation (SPVG) in the distribution system is crucial for system planners and network operators to keep the system parameters within the acceptable limits. This paper provides a systematic and extensive procedure for evaluation of MPL of SPVG and its enhancement methods in distribution systems. More importantly, it illustrates a novel algorithm for affixing the penetration cap of Solar PV. The methodology initially derives a new stability index for locating SPVGs in the system, including both active and reactive power support from SPVGs. The study shows the utility of redefining MPL of SPVGs by considering the reactive power injection through solar inverters also. Deviating from the practice of considering the conventional constraints of voltage rise and maximum loading for MPL estimation, the paper considers loss minimization as the major constraint. The algorithm has potential to identify distributed integration scenario of SPVGs compared to the limited number of placements in the extant algorithms. This paper provides a novel algorithm to evaluate of maximum penetration level (MPL) of solar photo voltaic generation (SPVG) and its enhancement methods in distribution systems. The utility of redefining the MPL of SPVG by considering the reactive power injection through solar inverter is illustrated. The algorithm has distinct advantages over the extant algorithms in identifying a distributed integration scenario. [ABSTRACT FROM AUTHOR]

Summary: Reconfiguration is one of the most important functions in the distribution network's automation system. Reconfiguration is formulated as an optimization problem with a large number of scenarios, which demands high central processing unit time to check all of them. Therefore, it is necessary to utilize a high‐efficiency optimization method. In this paper, the minimization of active power losses, total voltage deviations of buses, and maximization of system loading margin are integrated as three objective functions of the proposed reconfiguration model. Also, to improve the voltage profile, reduce power losses, and increase system loading margin, shunt capacitors (SCs) and distributed generations (DGs) are located. Seasonal daily load curves are applied to better simulate networks' real conditions. This paper uses the nondominated sorting genetic algorithm II, which generates a set of nondominated solutions. This set includes a wide range of solutions with different weighting coefficients. The multicriteria decision‐making (MCDM) algorithm, as a powerful and flexible decision‐making tool, is utilized to select the best solution based on tuning parameters. Also, it is assumed that DGs are wind farms, thus the uncertainty of DGs' power output is taken into the account, and the three‐point estimate method (3PEM) is utilized to reduce the number of subscenarios generated by 3PEM. Finally, the subscenario aggregation method is utilized to extract the value of objective functions in subscenarios. The developed model determines the optimal location of SCs and DGs in conjunction with the optimal network reconfiguration. The proposed method is implemented on the typical 33 and 69 bus radial distribution systems. [ABSTRACT FROM AUTHOR]

Summary: The continuous increase of the distributed energy resources (DERs) penetration levels leads to voltage stability problems in the distribution system. One of the approaches for the mentioned emerging challenge is the proper placement of automatic voltage regulators (AVRs). This paper investigates the optimal placement and sizing of AVRs in a distribution network by presenting a new modification of the teaching‐learning‐based optimization (TLBO) algorithm. The objective functions consist of minimizing the distribution system voltage deviation, energy generation cost, and electrical losses. The modification improves the convergence velocity and accuracy of the TLBO algorithm using the combination of mutation technique and quasi‐opposition‐based‐learning concept. This paper compares the performance of the proposed algorithm with other famous evolutionary algorithms. The test distribution system contains installed DERs that work more efficiently after the placement of AVRs based on the mentioned objective functions by the proposed optimization algorithm. The simulation results display the best optimization algorithms for AVRs placement with a significant level of less than 0.10 (ie, probability‐value). The proposed multiobjective optimization algorithm's considerable merit is the accuracy and convergence velocity in solving this specific optimization problem. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a new concept for district energy (DE) systems using central battery storage and decentralized hybrid renewable systems. The proposed DE consists of five buildings integrated with centralized 300 (V), 6.5 (A.h) batteries, locally distributed generations such as 8.5 (kW) wind turbines and 10 (kW) solar cells rated at 110 (V) and three‐phase loads. The central battery can be connected to each home for exchanging power. To increase the resilience, the proposed control system connects home 1 to the external 380 (V) and 50 (Hz) network when the battery is operating above the limited power (ie, 50 [kW] for this case study). The connection to the external grid is done by assessing and confirming a set of necessary conditions. The proposed integrated control system for DE is designed to achieve the following objectives: maximum power extraction from local wind/solar units by maximum power point tracking, optimal charge‐discharge process for central battery, connecting DE to the upstream network under outages and supplying the loads under all operating conditions. These goals are investigated by implementing six different scenarios of performance. In scenario 1, wind and solar units produce 6.6 (kW) and 24 (kW), respectively. Therefore, to feed the total load of 42.5 (kW), the central battery produces 15 (kW). In scenario 2, the total load in the first step is 35 (kW) and it is 95 (kW) in the second step. The power of solar and wind units in both loading steps is constant. The battery power increases from 6.5 (kW) absorption in the first step to 22 (kW) injections in the second step. In scenario 3, the solar units are switched off and in scenario 4, both solar and wind units are switched off. In such conditions, the battery responds to supply loads of homes. Increasing the energy resilience of DE during grid outages is modeled in scenario 5; where the battery power increases from 21 to 51.7 (kW) to deal with such outages. The nonlinear simulations in MATLAB/SIMULINK software show that the developed control strategy is able to control local renewable energies as well as the central battery while increasing the resilience and harvesting maximum power from decentralized wind/solar units. [ABSTRACT FROM AUTHOR]

Summary: "Electric vehicles (EVs) are one of the most promising technologies to green the transportation systems. However, high penetration of EVs brings heavy electricity demand to the power grid." Due to the intermittent character of renewable energy sources (RESs), it turns out to be very challenging to manage EV charging with other renewable generation and grid load. This paper aims to introduce a dispatch strategy assisted with the optimization concept for enhancing the economy of the microgrid system. The major objective is to minimize the cost of system operation and environmental control when meeting system load requirements. The output constraints related to the distributed power supply, such as power limits, are subjected to optimization. To solve this optimization issue, a new "Fitness Sorted Moth Search algorithm (FS‐MSA)" is introduced. Finally, the proposed work is compared and validated with other existing works with respect to various measures. The enhanced outcomes prove the efficacy of the implemented FS‐MSA model. This work concentrates on EV adoption integrated with RES for sustainable mobility. On observing the result, it can be noticed that the adopted scheme was 81.97%, 82.03%, 82%, and 81.97%, better than existing genetic algorithm, particle swarm optimization (PSO), moth search algorithm, and lagrange multiplier optimization (LMO) models for mean case scenario. [ABSTRACT FROM AUTHOR]

Summary: Increased green energy presence in distribution power networks can resolve rising energy demands while also reducing fossil fuel consumption, as well as providing economic and technical merits. However, the quantity of power delivered to customers cannot be allowed to take precedence over the quality of that electricity. This is because the high penetration of the renewable‐based power generation comes at the cost of power quality (PQ) deterioration, especially at the point of common coupling (PCC), owing to nonlinear characteristics of renewable‐based distributed generation (DG) systems and pre‐contamination of modern distribution grids. So, the function of PQ improvement technologies unavoidably comes into the picture when the hosting capacity (HC) of renewable energy systems is constrained by any of the grid PQ performance indices. This paper investigates the application of a hybrid active power filter (HAPF) to improve the harmonic‐constrained HC (HC‐HC) of renewable DG systems in harmonically polluted distribution systems. A shunt type HAPF designing to achieve maximum HC‐HC is considered as an optimization problem and solved by the firefly algorithm under several constraints the system particularly related to individual and total harmonic distortion limits in line current and voltage at PCC, harmonic currents overloading of distribution feeder. Aside from harmonics, constraints related to voltage rise and drop limits, as well as power factor, are also taken into account to ensure the optimal use of the HAPF as a compensator. The proposed HAPF‐based HC‐HC improvement approach's findings and efficacy are compared to those acquired from one of the literature's recently proposed techniques. Besides, the study is extended for HC‐HC enhancement by HAPF, under changing the utility‐side's background voltage distortion and the load‐side's nonlinearity level conditions. The performed extended investigation of the system shows that HC‐HC enhancing the effectiveness of the proposed approach is rather less susceptible to utility or customer side contribution to background distortion at the PCC. Highlights: Hybrid harmonic filtering is investigated for enhancing the harmonic‐constrained hosting capacity of distributed generation in distorted grid conditions.A hybrid filter has been found as a better alternative to achieve an advanced level of renewable energy penetration in distorted distribution grids.Along with increasing the penetration level of distributed generation the harmonic distortion is also substantially reduced instead of being at the verge of the standard limit.With the increase in background voltage distortion, the percentage enhancement in HC‐HC degrades.High load‐side's nonlinearity also results in a relatively lower enhancement in HC‐HC.Background nonlinearity negatively influences the percentage of HC enhancement more than the load‐side's nonlinearity.Though the utility, as well as customer‐side nonlinearity, affect the performance of the hybrid filter also yet the variation is significantly lesser than the purely passive filtering‐based approach. [ABSTRACT FROM AUTHOR]

Summary: Integration of renewable energy sources into a distribution system requires adjustments and improvement of the existing relay protection systems. Application of the three‐phase reclosing in radial distribution networks often leads to the island operation of the distributed power generation, which causes the generator's disconnection from the network. The application of the upgraded single‐phase reclosing technique, which is proposed in this paper, enables a partial transfer of energy into the electric power system during the temporary fault. Thus, it contributes to the maintenance of the distributed generator transient stability during temporary faults in the distribution network. Improvement of single‐phase reclosing technique is reflected in the adaptation to eliminate various types of faults that may occur. The analyses include different operation conditions and stability requirements of distributed generators. The proposed solution is presented in the paper by example of different types of distributed generation: a small hydropower plant with a synchronous generator that is directly connected to the distribution network, and a wind power plant with double fed induction generator and photovoltaic systems. The results of the analyses are presented in the form of dynamic simulations performed by DIgSILENT PowerFactory software using IEEE 33‐bus model of distribution network. [ABSTRACT FROM AUTHOR]

Summary: The demand of electric energy is increasing globally, and the fact remains that the major share of this energy is still being produced from the traditional generation technologies. However, the recent trends, for obvious reasons of environmental concerns, are indicating a paradigm shift towards distributed generation (DG) incorporating renewable energy resources (RERs). But there are associated challenges with high penetration of RERs as these resources are unpredictable and stochastic in nature, and as a result, it becomes difficult to provide immediate response to demand variations. This is where energy storage systems (ESSs) come to the rescue, and they not only can compensate the stochastic nature and sudden deficiencies of RERs but can also enhance the grid stability, reliability, and efficiency by providing services in power quality, bridging power, and energy management. This paper provides an extensive review of different ESSs, which have been in use and also the ones that are currently in developing stage, describing their working principles and giving a comparative analysis of important features and technical as well as economic characteristics. The wide range of storage technologies, with each ESS being different in terms of the scale of power, response time, energy/power density, discharge duration, and cost coupled with the complex characteristics matrices, makes it difficult to select a particular ESS for a specific application. The comparative analysis presented in this paper helps in this regard and provides a clear picture of the suitability of ESSs for different power system applications, categorized appropriately. The paper also brings out the associated challenges and suggests the future research directions. [ABSTRACT FROM AUTHOR]

Summary: In an active distribution network (ADN), the optimal micro‐PMU (μPMU) placement problem (OμPP) determines the location set with the minimal number of μPMUs that make the system observable. However, most approaches that solve OμPP provide a single location set limiting electrical power monitoring planning flexibility. Therefore, this paper presents an approach based on nonlinear programming (NLP) for solving the OμPP. The objective of the approach is to provide multiple location sets for OμPP that provide flexibility to electrical power monitoring planning. New constraints of the presence of distributed generations (DGs), zero injection buses (ZIBs), and communication line unavailability are taken into account for OμPP formulation. The proposed approach is implemented on the IEEE 69 distribution feeder, Indian‐85 distribution feeder, and IEEE 123 distribution feeder. The results show that the proposed approach successfully provides multiple location sets with a minimal number of μPMUs. [ABSTRACT FROM AUTHOR]

Summary: This paper aims to advance the recently progressing research on solid‐state transformers (SST) and examines the impact of uncertainty on load demand and distributed generation (DG) units while integrating SST into an active distribution network (ADN) in the presence of battery backed solar photovoltaic (BBSPV) and wind generation. The uncertainty related to solar irradiance, wind speeds, and load demands is modeled through kernel density estimation (KDE), generalized extreme value (GEV) distribution, and Gaussian distribution summed with the maximum likelihood estimation (MLE) approach respectively. The K‐medoid clustering procedure is utilized to group the load demand into multiple load levels, which helps in the intelligent scheduling of charging and discharging of battery energy storage systems (BESS). The distribution network planning process manages two conflicting criterion functions of real power loss (RPL) reduction and sum of square deviations of the expected voltage values, which are optimized utilizing the non‐dominated sorting genetic algorithm (NSGA‐II). The probabilistic power flow uses the direct load flow procedure utilizing bus injection to branch current (BIBC) matrix along with the forward sweep method to investigate each run of Monte Carlo simulation (MCS). Multiple case studies have been conducted on the IEEE 33 bus radial distribution network (RDN). The outcomes demonstrate the potential benefits of RPL reduction and voltage profile improvement (VPI) with increasing penetration levels of SST. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a multi‐objective coyote optimization algorithm (MOCOA) is proposed for techno‐economic benefits of simultaneous placement of fault current limiters (FCLs) and distributed generation (DGs) units in distribution grids. The proposed MOCOA is employed for mitigating the loss of power in distribution lines, minimizing the fault current levels, minimizing the economic costs of FCL size, enhancing the total voltage stability index, and reducing the total voltage deviation. The MOCOA is enhanced by emerging the concept of pareto‐optimal dominance to store the distinguished solutions in each generation. Finally, TOPSIS, a technique is implemented to find the compromise solution to fulfill the operator requirements. Applications are carried out in three distribution systems. The simulation results show the great effectiveness of the proposed MOCOA in acquiring several alternatives with appropriate technical improvements in power losses, voltage stability, fault level reduction, and economical FCL size. [ABSTRACT FROM AUTHOR]

Summary: Brazil has one of the richest river basins in the world and an energy matrix based mostly on hydroelectric power. Current national policy is increasingly promoting renewable sources like wind power and solar photovoltaic power. Technologies used in generation energy via hydro, wind, and solar sources can be employed in decentralized generation. This study describes a turbine for hydro energetic use in flow sites with heads up to 2.5 (m). A hydrodynamic study was performed using computational fluid dynamics (CFD) analysis to evaluate the performance of this turbine. For this, a three‐dimensional model of the turbine was considered, consisting of three computational domains, using periodicity to decrease the computational cost. The variation of the angular velocity and the volumetric flow were the boundary conditions. The turbulence model used was the shear stress transport. The draft tube geometry was modified according to the results of the CFD analysis. The efficiency and performance of the turbine improved from 79% to 80% as a result of this modification. A case study was conducted for a comparative financial analysis of the turbine proposed in this paper, with wind power and solar photovoltaic decentralized generation in Brazil. [ABSTRACT FROM AUTHOR]

Summary: The distributed generation (DG) units are used more in the electrical networks to reduce the energy demand along with reducing the system losses and increasing the voltage profile of the load points. This paper presents an unintentional islanding detection, reliability enhancement, and power loss minimization of the restored system after an islanding event. The detection of islanding is performed by passive detection method of simultaneous measurement of voltage and frequency (vf)‐based technique. The reliability of the system is increased along with the power loss minimization through reconfiguration by Particle Swarm Optimization (PSO) technique. The network reconfiguration is performed by identifying the most vulnerable buses, and reliability indices of the system are evaluated after the islanding event. The reliability indices act as a marker for validating the proposed reconfiguration strategy. The proposed method for islanding detection, reliability enhancement, and power loss minimization is compared with the existing methods available in the literature. The proposed method is tested on two different radial distribution system such as IEEE‐69 and 118 bus systems, and the results obtained after the validation are promising. [ABSTRACT FROM AUTHOR]

Summary: This paper proposes a two‐stage planning approach for the efficient utilization of distributed generation (DG) and capacitor banks (CBs) for the simultaneous grid‐connected and islanded operations of the balanced distribution networks. The first stage determines the optimal installation locations and capacities of DGs and CBs using an improved variant of the Jaya optimization algorithm (IJaya) to minimize the power losses and voltage deviation during the grid‐connected operation of the distribution network. The second stage identifies the optimal operating point of the DG and CB combination to carry the maximum load during the islanded network operation under power supply‐demand imbalance conditions. For the second stage, an analytical approach is proposed to identify the best operating power factor for the DG‐CB combination, calculating the power loss, and under‐utilization of the installed real‐reactive power sources. Simulation results on the IEEE 33‐bus grid‐dependent distribution network demonstrate that the proposed IJaya significantly improved the network performance and outperforms various existing optimization methods. In addition, during the network's islanded operation, maintaining the network power factor equal to the source power factor (pfsource) makes the DG‐CB combination operate at their rated capacities. [ABSTRACT FROM AUTHOR]

The vigorous development of renewable energy has induced multiple sources connected to regional distribution networks. However, the high impedance ground fault that appeared in the distribution network can induce an intermittent arc accompanied by extinction and reignition, which may damage renewable energy generation devices severely. Therefore, the detection of arcing faults is profoundly necessary for practice, but the high impedance arcing fault is easily confused with switches of motor or capacitor bank. In order to solve high impedance arcing fault detection, this paper proposes a high impedance arcing fault detection method that combines complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and Teager energy operator (TEO). Firstly, CEEMDAN algorithm is used to extract the intrinsic mode function (IMF) of transient zero‐sequence current (TZSC). According to the correlation coefficient and waveform similarity, which can select maximum correlation coefficient value as the characteristic component of TZSC; Then, TEO is utilized to track the change of signal in real‐time, meanwhile, wavelet singular entropy (WSE) is applied to calculate the characteristic component of TZSC. In particular, high impedance arcing fault (HIAF), motor switching (MS), and capacitor bank switching (CBS) can be effectively identified by comparing WSE. The effectiveness of CEEMDAN‐TEO detection method is verified by simulation, which owns advantages in extraction accuracy, calculation efficiency, and detection accuracy of feature components. [ABSTRACT FROM AUTHOR]

Summary: Distributed generation (DG) has attracted significant attention due to its great potential for enhancing economical and technical performance of power systems and reducing dependence on fossil fuels. Optimal sizing and placement are critical for stimulating such potential, about which a considerable number of models and algorithms have been proposed in past literature. This paper attempts to undertake a comprehensive review on optimal sizing and placement of DG via a systematic methodology procedure, including definition and classifications of DG, modelling and problem formulation with different technical and economic criteria, and summary of optimization algorithms. Common features and distinctive characteristics of both models and methods are identified, followed by evaluations and comparisons based on their practical performance in various test systems. Selection of DG techniques with respect to application scenarios, indispensable and optional considerations in DG planning models, and pros and cons of algorithms are listed in tables for a clearer understanding. Lastly, a total of 107 algorithms are addressed, which are classified into five categories. Particular, hybrid methods can deal with complex engineering problems with multiple objective functions and constraints most effectively and robustly. Future research trends are also highlighted with the aim of providing a comprehensive and state‐of‐the‐art survey for researchers, engineers, and other stakeholders. [ABSTRACT FROM AUTHOR]

Summary: Renewable energy sources powered distributed generation (RES‐DG) is getting more indispensable to encounter the considerable increase in demand for electric energy owing to its techno‐economic benefits and eco‐friendly nature. An economic solution to this demand can only be obtained with the optimal placement and sizing of RES‐DGs. The optimal siting and sizing of RES‐DG, such as Photovoltaic (PV) and Wind Turbine (WT) is still a hot topic due to the uncertainties in solar irradiance (SI) and wind speed (WS). The main objective of this research paper is to develop a RES‐DG siting and sizing strategy for the discrete, nonlinear siting and sizing pattern of RES‐DGs using a novel hybrid Harris' Hawk optimizer (HHHO), considering the stochastic nature of SI and WS. The Weibull and Beta probability density functions (PDFs) are utilized for modeling the stochastic nature of WS and SI, respectively. The optimization of the multiobjective function comprises active power loss reduction, enhancement in voltage profile, and improvement in voltage stability index (VSI). Different scenarios of single and multiple RES‐DGs and capacitor banks (CB) are examined to validate the efficiency of the proposed novel HHHO based RES‐DGs siting and sizing strategy. The results show a considerable reduction in power loss, enhancement in the system voltage profile, and improvement in VSI. Evaluation of results by comparing withstate‐of‐art hybrid algorithms shows that the proposed solution using HHHO algorithm is globally optimum. [ABSTRACT FROM AUTHOR]

Summary The power grid constructed with electric power router (EPR) will have the ability of flexibly controlling the voltage and power flow on each line of the grid, which will be helpful to maximize the integration of the renewable distributed generation to the grid. Most of the current methods for transmitting energy depend on storage unit or large scale calculation, which are relatively difficult. To avoid these disadvantages, this paper proposed a two‐step routing strategy based on the improved shortest path method for DC power grid with EPRs. The improved shortest path method combines Shortest Path Faster Algorithm (SPFA) with depth first search (DFS) algorithm, which could handle the negative weights and the negative cycle issue in the graph of the power flow paths. The increase of the transmission line power loss and the EPR's power loss are taken as the weight for the path search method to evaluate the cost of the path. Applying the proposed method to each power demand and supply finally helps to obtain the current distribution of the whole grid. By analysis of typical scenarios, compared with the power flow distribution of traditional DC power grid, the one produced by the proposed strategy could improve the power transmission capability as well as reduce the maximum voltage drop in the network. Besides, this strategy introduces less power loss, than many other ways do, in power routing. The effectiveness of the rioting strategy is related to the configuration of the network. [ABSTRACT FROM AUTHOR]

In order to accommodate distributed generation (DG) while ensuring the security and efficiency of distribution networks and considering the reasonable interest of transmission system, this paper proposes a spatial‐temporal comprehensive matching evaluation, analysis and improvement method for distribution network with DG. The method generally uses a two‐stage planning strategy, namely first total then distribution. Firstly, in the first stage, aiming at the total load/DG in a feeder, a comprehensive matching evaluation index system and an evaluation method are proposed, including load and DG matching, net load and feeder capacity matching and transmission and distribution matching. Total matching evaluation indices can evaluate the comprehensive matching level of distribution network with DG from total perspective. Influence factor indices are used to analyze the dominant factors restricting the total matching. In the second stage, under the premise that the total is matched both in size and in time, distribution matching evaluation is further performed in space, namely, considering the location of loads and DGs in the feeder. Secondly, the causes for mismatch are analyzed and improvement measures are proposed for various mismatched scenarios. For total mismatch scenarios, sensitivity analysis is used to find cost‐effective improvement factors and guide the improvement of load or DG power curve to achieve better total matching. For total match and distribution mismatch scenario, an optimal placement method is used to adjust the location of loads and DGs in the feeder to achieve spatial‐temporal matching. Finally, a case study is presented to demonstrate the proposed method. Six scenarios are studied considering different matching evaluations and different combinations of dominant factors and improving factors. The results show that the method can evaluate the DG‐load‐grid matching and provide solutions for mismatching scenarios. Through summarizing and comparing various scenarios, proposals for distribution network planning are concluded: total matching should be ensured first, which is reflected in energy matching and smooth net load curve. Then, the spatial‐temporal matching can be achieved by optimizing the location of loads and DGs in the feeder. [ABSTRACT FROM AUTHOR]

Background: Positive feedback (PFB) based anti‐islanding schemes have gained wide popularity in islanding detection. However, the disturbance injected by the PFB methods can easily cause the destabilization of the grid‐connected distributed generation (DG) system. Therefore, how to effectively balance the normal operation of the grid‐connected system and the effectiveness of the islanding detection is essential. Purpose: In this study, the trade‐off design of the PFB control gain is given, where the requirements of grid‐tied control and islanding detection are simultaneously considered. Design/Method: Firstly, the small‐signal models are established to investigate the stability of a DG system in both islanded and grid‐connected mode. Meanwhile, the minimum and maximum PFB gains are obtained by root loci method, thus, the PFB gain can be accurately determined without trial and error. Additionally, the Sensitivity analysis is conducted for the DG system. Factors such as grid impedance, phase‐locked loop (PLL) bandwidth, proportional‐integral (PI) controller gains, inverter output current rating, and load quality factor are thoroughly taken in account, which provides the guideline of the PFB gain design. Finally, simulations and experiment tests are performed to confirm the theoretical analysis. Results: This paper presents a trade‐off design of the PFB control gain for a DG system from the essence of the PFB algorithm. The essence of PFB as well as the cause of the interconnected system instability are revealed. In addition, the minimum and maximum PFB gains are obtained by the stability analysis. Conclusions: A high PFB gain will contribute to the islanding detection but deteriorate the grid‐connected system stability. Further, it is found that 1) the maximum PFB gain decreases with the grid impedance increasing, 2) the increase in PLL bandwidth and the integral gain in current loop lead to a decrease in the maximum PFB gain, 3) the minimum PFB gain which reflects the islanding detection capability of the VPF scheme is not affected by the load quality factor, 4) when the inverter output current is large, a reasonable PFB gain may not be found as the islanding detection and the normal operation of the grid‐connected system cannot be balanced. [ABSTRACT FROM AUTHOR]

Summary: Higher load growth in the distribution system and its consequences on higher voltage deviation, feeders overloading, and distribution system loss increase have a bad effect on system quality. Global warming and the dwindling supply of fossil fuels also make it imperative to search for more effective alternatives that guarantee appropriate operating level of power losses and voltage profile at different points of the distribution networks. Capacitor banks (CBs), renewable distributed generators (DGs), and automatic voltage regulators (AVRs) can be considered the most suitable enhancement devices for distribution systems that reduce both pollution and power losses, improving the voltage profile, ..., etc, if they are optimally sized and sited. The objective of this paper is to investigate the optimal placement of each of the 3 mentioned solutions (CBs, DGs, and AVRs) on a part of real Egyptian distribution system. This system is an old, long, weak, and heavily loaded distribution system with high power losses (about 29% of system loading) and poor voltage regulation (about 30%). Each introduced solution has been evaluated according to power loss minimization and investment cost minimization. A new modification to the backward‐forward power flow method for radial distribution system embedded AVRs has been proposed, which facilitates the placement procedure of AVRs and reduces computation time as compared to other methods. In this paper, an optimal placement of the combined CBs, DGs, and AVRs has also been introduced based on integrated particle swarm optimization technique and rough set theory. The proposed approach aims to minimize the problem complexity and reduce the storage capacity required for the optimization problem. [ABSTRACT FROM AUTHOR]

Fast and accurate fault location methods will accelerate power system restoration process and then cause improvement on availability and reliability indices. Presenting a modified scheme in order to improve accuracy of impedance-based fault location method in electric power distribution systems (EPDS) equipped with distributed generation (DG) units is the main goal of this paper. To achieve this goal, an iterative algorithm is introduced to compensate load variations. Also, a method is presented based on forward/backward sweep load flow to consider loss in all laterals of EPDS. Then, fault location will be determined by using a comprehensive method that extracts a fifth-order algebraic equation for each type of fault. This method will be modified to consider the presence of DGs in EPDS. In this paper, all the specific characteristics of real distribution systems such as unbalanced nature of network and loads, different types of loads, presence of multi-phase laterals, and capacitive effects of distribution lines are taken into account. The proposed scheme uses only 1 measurement unit at the main substation and 1 measurement unit at the DG bus. In this paper, modified IEEE 34 node test system is simulated by using PSCAD/EMTDC software, and it is used as a test system to evaluate the performance of the proposed method. Different scenarios such as the effect of fault distance, fault type, different fault resistances, and measurement unit errors are evaluated. The results indicate usefulness and precision of the proposed scheme. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a Backward/Forward Sweep (BFS) power flow method in the frequency domain for the analysis of the harmonic distortion in radial distribution systems with distributed generation (DG) units. A detailed procedure for solving the power flow problem at fundamental and harmonic frequencies and the models of distribution system elements in harmonic analysis are presented. In addition, the effects of converter‐based and nonconverter‐based DG units on voltage profile, power losses, and power quality are carried out. Performance of the proposed method is tested and evaluated on the standard IEEE distribution systems. Simulation results, obtained using the proposed BFS method, are compared with those obtained using the Decoupled Harmonic Power Flow (DHPF) method, Harmonic Analysis module of the ETAP program, and Full Harmonic Solution module of the PCFLO program. It is shown that the BFS method provides effective, robust, and high‐quality solutions. Besides that, the proposed method has better computational performance than the commonly used DHPF method, since the bus admittance matrix inverse employed by the DHPF method is not necessary in the solution procedure. [ABSTRACT FROM AUTHOR]

Summary: The integration of distributed energy resources (DERs) with conventional systems emerges as an intelligent solution for providing uninterrupted and secure power even at times of high load demand. Better load management with a mature fault handling mechanism makes AC a viable option which has an efficiency of 78.24%. In contrast with less power loss and slightly better efficiency of 84.6%, DC microgrid is a reliable option in a low power environment. In order to accommodate all operating conditions and load types, a hybrid system can be designed with a theoretical efficiency of more than 90%. Bidirectional power flows, low inertia, the transition between different modes of operations are the challenges for the protection of alternating current (AC) and direct current (DC) microgrid systems. Power balance fluctuation, absence of zero‐crossing currents, selection of suitable grounding, and coordination between different rating devices restrict the hybrid system to achieve the said efficiency constantly. This paper reviews in detail of existing protection along with grid‐connected algorithms for both modes of operation. Finally, the limitation, major hurdles, and future course of action for a reliable, efficient, and secure hybrid grid system are figured out. [ABSTRACT FROM AUTHOR]

Summary: Nowadays, increasing nonlinear loads as well as distributed generation (DG) sources, which are some of these types, not only cause a wide range of voltage fluctuations, but also make it difficult to control the DG sources to produce proper output. Hence, it is necessary to use an approach that evaluates and tracks the voltage fluctuations, and also to have an output with optimal accuracy and smoothness that is suitable for control of DG sources. This paper presents a Teager energy operator (TEO)‐based approach to track and detect the voltage fluctuations in distribution networks in the presence of the inverter‐based DG and nonlinear load that eliminates as much as possible distortion and unwanted signals from the voltage flicker signal. This hybrid algorithm is able to track accurate the amplitude variations of voltage disturbances in industrial systems. To attain this aim, a suitable combination of the TEO and a relevant filter set is adopted. Simulations for a mathematical fluctuation waveform and the grid‐connected inverter‐based DG using the proposed method are conducted and results are compared with each other to evaluate their performance. Simulation results for different voltage fluctuations validate that the new approach is accurate and smooth in tracking the voltage fluctuations. [ABSTRACT FROM AUTHOR]

Summary: Integrating renewable energy hybrid distributed generation (REHDG) into distribution network systems (DNSs) has become increasingly important because of various technical, economic, and environmental advantages accruing from it. However, the output power of REHDGs from photovoltaic (PV) and wind is highly variable because of its dependency on intermittent parameters such as solar irradiance, temperature, and wind speed. Such variability of generated power from large‐scale REHDGs or load introduces small signal instabilities (oscillations). Meanwhile, different locations of integration and sizes of REHDGs in the DNS affect the system oscillation modes by either improving or depriving the small‐signal stability (SSS) of the network. Consequently, a significant number of research has been conducted on the planning of optimal allocation of REHDGs in DNS. In this regard, this paper reviews the existing planning models, optimisation techniques, and resources' uncertainty modelling employed in REHDGs allocations in terms of their capability in obtaining optimal solutions and enhancing SSS of the system. Planning models with optimisation algorithms are evaluated for modelling renewable resource uncertainties and curtailing SSS variables. Research works on planning of optimal allocation of these generations attain minimum cost, but were unable to satisfy the SSS requirements of the system. The existing models for the planning and design of optimal timing, sizing, and placement of REHDGs will need to be improved to optimally allocate REHDGs and satisfy the SSS of the DNS after the integration. [ABSTRACT FROM AUTHOR]

Summary: The distributed generation (DG) is getting extensively integrated in existing power distribution system because of the massive development in green energy technologies and their economical, technical, and environment benefits. However, apart from beneficial aspects, DGs also have various and complex technical limitations, major of which are loss of protection coordination among protection devices which can lead to malfunctioning of protection devices, blind protection, fuse blowing, and permanent outage of power supply due to temporary faults. In this paper, a novel curve fitting technique is designed to restore much influenced recloser‐fuse coordination using the directional properties of midline recloser for upstream and downstream protection devices coordination. It also works on fuse‐saving scheme. Using Electrical Transient Analysis Program (ETAP) Software, the proposed methodology is implemented on a real 11 kV Rajewala radial distribution feeder starting from 132 kV Eimnabad grid station, district Gujranwala, Pakistan. Present here are some key results. Different case studies are carried out and results validate the effectiveness of the proposed methodology, and the coordination among protection devices is sustained even after DGs integration in the system. [ABSTRACT FROM AUTHOR]

Summary: Increased energy demands due to rapid industrialization, environmental concerns with fossil fuel–based generation, diminishing fossil energy resources, transmission network congestion, and technical performance deterioration are the motivations behind the integration of small renewable distributed generation (DG) units and turning the existing power systems into a restructured one. Optimizing the technical benefits offered by DG placement is a well‐known challenge for distribution network operators (DNOs) for both fossil and renewable energy resource–based DGs, but renewable DG systems have several power quality (PQ) challenges associated additionally. Power quality is a very significant characteristic of renewable DG systems because today's loads are more sensitive to PQ disturbances and penetration of renewable energy as well as nonlinear loads is proliferating in distribution power networks. So the need for innovative power quality improvement (PQI) techniques becomes inevitable due to ongoing reformation in traditional distribution networks by the integration of renewable energy. This article presents a comprehensive analysis of power quality challenges with grid integration of renewable DG systems and current research status of associated mitigation techniques. Firstly, this paper puts emphasis on theoretically illustrating all the crucial power quality challenges associated with grid integration of renewable energy, and secondly, a thorough survey, of all PQI techniques introduced till date, is elaborated along with highlighting the opportunities for future research. Furthermore, all the crucial power quality issues, the impact of high penetration of renewable energy and mitigation techniques on power quality, are demonstrated also by simulating a grid integrated PV‐based DG system in MATLAB/Simulink. This article is believed to be very beneficial for academics as well as industry professionals to understand existing PQ challenges, PQI techniques, and future research directions for renewable energy technologies. [ABSTRACT FROM AUTHOR]

Summary: Distributed generation (DG) technologies are environmentally friendly and have low operating costs, and thus, distributed generators are widely used for the energy supplies of buildings. Solar energy used for on‐demand heating of buildings is also a mature technology that is environmentally friendly and inexpensive and has a short recycling life cycle. This paper proposes a high proportion of new energy access–combined cooling, heating, and power (HPNE‐CCHP) system composed of a distributed generator and solar energy heat pump system. To obtain the optimum capacity of the HPNE‐CCHP system, nondominated sorting genetic algorithm‐II (NSGA‐II) was used to optimize the system by considering the life cycle cost (LCC) and life cycle pollutant emissions (LCPE) as the objective functions. A mixed integer economic scheduling model (MIESM) was proposed to make the HPNE‐CCHP system operate more economically. Finally, an HPNE‐CCHP system was constructed for a building in Northern China. The simulation results show that an HPNE‐CCHP system with a moderate proportion of new energy is more economical and environmentally friendly than a traditional CCHP system. Building occupants, depending on their desired spending, can select the best capacity configuration on the Pareto frontier. Although pollutant emissions will be reduced as the proportion of new energy increases, this type of configuration is expensive. [ABSTRACT FROM AUTHOR]

The paper presents a novel detection method based on feature extraction discrete wavelet transform (DWT) combined with artificial neural network (ANN) for identification of islanding condition in distributed generation (DG) system. Islanding detection methods can be classified into two major categories as active and passive methods. The main disadvantages of the passive methods are determined threshold value and related to their large non-detection zone. The emphasis of the proposed approach is eliminating the aforementioned drawbacks. The DWT allows revealing various hidden features of the signal. The aim of this paper is to determine the best wavelet basis function in order to identify islanding occurrence with higher accuracy and lower decomposition level. The proposed approach requires the measure rate of change of frequency at the DG's terminal, and various features are extracted from DWT then these features used as input into ANN. Also, the performance of the different structures of ANN such as feed-forward neural network, radial basis function, and probabilistic neural network are compared for islanding detection purpose. The proposed method is simulated and tested in various operation conditions such as islanding conditions, motor starting, capacitor bank switching, and nonlinear load switching. The test results showed that the proposed method correctly detects the islanding operation and does not mal-operate in the other situations. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A MicroGrid (MG) can be operated in two main situations: grid-connected mode and autonomous mode. Power electronics (PE) are required to interface the DG units with the MG. This paper presents an optimal operating strategy and cost minimization scheme for an electronically weak-coupled MG. The major objective of the paper is to minimize the overall cost considering both the power system and the power electronics constraints in the two modes of operation. The paper presents steady-state models of power electronic converter/inverter systems for coupling distributed generation (DG) units to the grid based on Newton-Raphson method. A Matlab program is developed to represent the proposed algorithm. The program is tested in various network conditions and verified by applying it to an MG with three different DG units. The main contribution of the study is to ensure that the converter constraints are satisfied for both types using DC/AC inverter and AC/AC matrix converter. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY How to decide the location and the capacity of distributed generators (DGs) in the distribution network is a complex and hard work. In this paper, several technical indexes involving energy loss, voltage quality and stability, and line loadability are considered to optimize DG capacity and location. It is an optimization problem wherein both discrete and continuous variables are involved, and cloud theory adapted genetic algorithm (CAGA) is employed to avoid search exploration and long time search. The weights of the indexes are decided by judgment matrix. DGs in a 28-node distributed network are employed to be optimized quickly to improve the indexes aforementioned to demonstrate the CAGA developed in this paper. Meanwhile, the optimization results are compared with traditional GA. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Summary: The addition of photovoltaic (PV)‐based distributed generators introduces several challenges to power system protection and control engineers. In a multi‐source distribution network, power flow becomes bi‐directional, and conventional overcurrent and earth fault protection schemes are threatened. Addition of PV‐based distributed generation could lead to protection blinding, sympathetic tripping, and loss of coordination in conventional overcurrent protection. This paper evaluates the general concerns regarding protection in a PV‐based distributed generation network, by modeling a power system with sequence networks for different types of faults. The power system is simulated with Digsilent PowerFactory. The results show that many of the general concerns can be mitigated by using sequence components to identify faults. A method is presented to adapt conventional overcurrent protection schemes without the need for communication‐assisted protection. [ABSTRACT FROM AUTHOR]

Summary: This paper has proposed a comprehensive coordinated planning framework for solving the network reconfiguration with simultaneous installation of distribution generation (DG) units, with an objective of minimizing the feeder power loss and boosting the voltage profile of the electric distribution system. A meta‐heuristic bit‐shift operator–based particle‐swarm‐optimization (PSO) technique has been used for simultaneous reconfiguration with the optimal siting and sizing of the DG units. The bit‐shift operator–based PSO has been obtained by incorporating a shift operator in the velocity equation of the basic PSO, such that the problem moves in the direction of finding the best optimal reconfigured system. The entire problem has been investigated in the light of both voltage independent and dependent loads, such as residential, industrial, and commercial, to evaluate the performance of the proposed work in a practical scenario. A sensitivity analysis has been applied for finding the optimal location for the DG placement. The efficacy and validation of the proposed method have been tested on a standard IEEE test system under 4 different load models for 5 different cases. [ABSTRACT FROM AUTHOR]

Summary: In recent scenario, there is abundant availability of renewable energy resources to satisfy the significant increase in residential, industrial, and commercial demand. This paper presents a novel framework to determine the preeminent size of renewable distributed generators (RDGs) by optimizing the system components such as area required for solar‐photovoltaic modules, swept area occupied by wind turbine blades, and area used by fuel cell. A microgrid with hybrid RDG (h‐RDG) is integrated in distribution system to minimize the distribution loss, substation energy requirement, and improve the voltage level of the load. The power loss minimization is formulated as a nonlinear problem and optimized by the proposed Hybrid Nelder Mead‐Particle Swarm Optimization algorithm. The microgrid location is identified by voltage stability index to improve the stability of system. Further, the system is analyzed for energy flow in different seasonal loading conditions with mixture of residential, industrial, and commercial load. The effective performance of the proposed technique is applied to standard 12‐bus, 69‐bus, and a practical Tamil Nadu (TN) 84‐bus radial distribution system (RDS) for different hybrid combinations of h‐RDG in microgrid. The result proves that the proposed method provides a simple and efficient tool for optimal and flexible use of h‐RDG in microgrid under different climatic changes by simultaneously reducing distribution energy loss and improving voltage profile. [ABSTRACT FROM AUTHOR]

Summary: This paper presents the design of a current reference used in an inverter‐side current controller for a grid‐connected single‐phase transformerless inverter with an Inductive‐Capacitive‐Inductive of LCL filter. The idea is to indirectly control the inverter‐side current, by directly acting on the grid‐side current. Furthermore, it can be shown that the simple proportional term guarantees damping injection. However, the design of the current reference for such a controller is a more involved process, which turns out to be even more challenging in the case where the grid voltage signal is subject to harmonic distortion. In this case, the distortion propagates into the converter through the LCL filter. Therefore, an inverter‐side current reference must be proposed to be as distorted as necessary to assure indirect tracking of the grid‐side current towards its corresponding reference, which is built as a sinusoidal with a given phase displacement to allow reactive current injection. The inverter‐side controller must then include a harmonic compensation mechanism, to assure perfect tracking of the inverter‐side current towards its distorted reference, and thus, achieve an adequate performance under harmonic distortion. Experiments are performed in a prototype to evaluate the performance of the proposed controller. [ABSTRACT FROM AUTHOR]

Summary: This paper presents a multiobjective method for obtaining optimal size and site of distributed generation (DG), to reduce loss, and DG investment cost while improving the voltage profile in primary distribution networks. To solve the multiobjective problem, a classical technique known as global criterion method is implemented to form a novel objective function equation, which is custom‐built for a distribution system. The application of the global criterion method is explained using a DG that is capable of injecting real power, ie, unity power factor DG, and then extended to DGs capable of injecting reactive power. The method is validated for 2 distribution systems. Results show that the proposed method satisfies the individual objectives simultaneously. The proposed method is also compared with existing methods to exhibit its effectiveness. [ABSTRACT FROM AUTHOR]

It is expected that the use of distributed generation (DG) will increase sharply in distribution systems, especially with the realization of smart grids. In spite of the benefits of DG in distribution systems, high penetration level of DGs could cause some challenges for the network. Therefore, the optimal sizing and siting of DGs should be identified carefully. In addition, different operating conditions have to be taken into account in this process. The DGs are usually installed depending on optimal siting and sizing techniques considering normal operating periods. During repairing fault periods, different locations and capacities of DGs may be preferable. In this paper, 2 scenarios of switching strategies are presented for attaining the optimal sizing and siting of DGs during repairing fault period starting from the optimal allocation obtained for normal operating period. Genetic algorithm is used for solving the optimization problem that is implemented for an actual loop distribution system in Egypt. [ABSTRACT FROM AUTHOR]

With increasing annual energy demand and significant growth in the use of distributed generation (DG), distribution companies are exploring ways to improve the technical specifications of the distribution networks such as power losses, customer interruption costs, and voltage stability and on the other hand to increase the penetration level of DGs. In this paper, a multi-objective optimization model is proposed for distribution network reconfiguration (DNR) to decrease the total costs of energy losses and energy not supplied (ENS) and increase the voltage stability and DG penetration level. Seasonal hourly load curves are applied, and best configuration is determined for each loading condition. Uncertainties regarding the load variations and volatile power production of wind turbine are modeled using a 2-point estimate method, and a benefit-cost analysis is used to assess the effects of depreciation cost in DNR problem. The proposed model is applied on 2 typical test systems. [ABSTRACT FROM AUTHOR]

According to IEEE std. 1547, islanding mode is 'a condition in which a portion of an Electric Power System (EPS) is energized solely by one or more local EPSs through the associated Point of Common Coupling (PCC) while that portion is electrically separated from the rest of the area EPS'. Therefore, the dynamic instability due to islanding may result in power swing and finally loss of synchronism. Hence, many studies have been done for islanding detection and disconnection of distributed generation (DG) in an EPS. But, these conventional methods eventually lead to the disconnection of the DG units. To improve DG dynamic stability, superconducting magnetic energy storage (SMES) can be used effectively, because SMES have a high-energy density and fast response. This paper proposes a new method to damp the power swing after DG islanding and to maintain synchronism conditions based on SMES. Hence, the disconnection of the DG units is not required. Also, new controllers are developed for SMES including voltage source converter (VSC), and DC-DC chopper. The controller structures of VSC and DC-DC chopper are of PI and fuzzy logic-based type, respectively. Superconducting coil charging is controlled by the DC-DC chopper. SMES sizing is performed, based on power swing equations. Hereupon, dynamic load model is considered. Performance of the proposed method is evaluated by defining 12 scenarios such as strong and weak networks with load changing simulated in PSCAD. Simulation results show that the islanded DG stabilization (IDGS) method has good performance to maintain stability margin in a weak network. [ABSTRACT FROM AUTHOR]

This paper identifies a new mode called 'critical voltage mode" in emerging distribution systems. The small-signal stability analysis indicates that load voltage dynamics significantly influence the damping of the newly identified mode. This mode has frequency of oscillation between the electromechanical and subsynchronous oscillation of power systems. A novel voltage controller is designed to damp this voltage mode of the system. The controller is designed using the linear quadratic Gaussian (LQG) method with norm-bounded uncertainty. The approach considered in this paper is to find the smallest upper bound on the H ∞ norm of the uncertain system and to design an optimal controller based on this bound. The design method requires the solution of a linear matrix inequality. The performance of the designed controller is demonstrated on a distribution test system for different types of induction motors. Simulation results show that the proposed controller with a careful uncertainty modeling has significant performance to improve the voltage profile of the distributed generation system compared to the conventional excitation controller and standard LQG controller. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents an application of the chaotic artificial bee colony (CABC) algorithm to identify the optimal location and sizing of the distributed generation (DG) units in order to improve the voltage stability margin in the radial distribution system. Artificial bee colony algorithm is an optimization algorithm based on the intelligent foraging behavior of honey bee swarm. To improve the searching ability of an artificial bee colony algorithm, chaos theory is united with artificial bee colony, called the CABC algorithm. The various impact indices are used to evaluate the multi-objective performance index aimed to identify the optimal location and sizing of combined real and reactive power-based DGs on the distribution systems. The presence of DG in the distribution system has been potential to improve voltage stability of the system. The effect of DG on the weakest bus is analyzed by constructing the PV curve. The effectiveness of the proposed method is tested on 38-node and 69-node radial distribution systems. [ABSTRACT FROM AUTHOR]

This paper proposes a new active islanding detection scheme based on the harmonic impedance measured from distorted current and voltage waveforms. Such distortions are due to periodical short-time phase-to-phase short circuits, caused by firing a thyristor placed between two phases at the distributed generator terminals. Distributed generator islanding is identified by analyzing the change of harmonic impedance. The method was validated by simulation and experimental tests. The results show that the method is effective and robust. Moreover, it was observed that the proposed method is hardly impacted by the interaction among different signals, and its influence on power quality is negligible. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

If sensitive loads are connected to the point of common coupling (PCC), compensation should be carried out in order to reduce PCC voltage harmonics. In this case, compensation is performed by the interface converters of distributed generation (DG) units. In this paper, a novel method is proposed for voltage harmonics compensation in islanded microgrids. The proposed method is capable of adjusting compensation percentage in proportion to the existing level of distortion at PCC. Also, this controller provides a proper sharing of compensation workload, considering the nominal capacity of DGs, which will improve the sharing of nonlinear load. Also, to decrease the asymmetry among phase impedances of microgrid, a novel structure is proposed to generate virtual impedance. At fundamental frequency, the proposed structure for the virtual impedance improves the control of the fundamental component of the power, and at harmonic frequencies, it acts to adaptively improve nonlinear load sharing among DG units. In the structures of the proposed harmonics compensator and the proposed virtual impedance, a self-tuning filter is used for separating the fundamental component from the harmonic components. This self-tuning filter decreases the number of the phase-locked loops. The simulation results in MATLAB/SIMULINK environment show the efficiency of the proposed approach in improving load sharing and decreasing voltage harmonics. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, two-level decentralized optimization power dispatch control strategies are proposed in an islanded microgrid without communication network to ensure frequency security and economic benefit. First, the secondary-level decentralized optimization control strategy is designed only by using local measurement regarding frequency deviation. It is able to implement the optimal power dispatch for all dispatchable distributed generation units in a coordinated way in order to completely restore the system frequency with minimum operation cost. Then, the first-level decentralized droop compensation control strategy is designed to implement real-time optimal power sharing among all energy storage units in order to quickly compensate large supply-demand imbalance and ensure frequency security. Moreover, the proposed control strategies are proved to be able to meet the requirements of the 'plug and play' operation in the absence of communication network. Simulation results verify the validity of the proposed method. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper proposes a solution methodology for optimal allocation and sizing of renewable based DG units in radial distribution systems. The objectives are to minimize total power losses, to minimize system's investment cost and to improve voltage stability. The multi-objective genetic optimization algorithm is used to generate the optimal Pareto front and a fuzzy decision making function is used, as a hybrid function, to obtain the best compromise solution. The proposed technique is applied to typical IEEE bus systems including 33-bus system, 69-bus system and 119-bus system. This technique is implemented using different scenarios including all possible combinations of renewable DG units; to prove the effectiveness of the proposed methodology. The effect of DG based renewable energy allocation on the most sensitive buses to collapse is also carried out considering different load models. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]