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• A new communication-less intelligent islanding detection scheme for hybrid DG systems is proposed in this research paper. • The proposed scheme utilizes time-domain FE and LSTM to detect and classify islanding and grid-connected mode events. • By reducing the reliance on communication, the proposed scheme overcomes limitations associated with remote schemes. • Extensive simulations are conducted to validate the performance of the proposed scheme. • The proposed scheme outperforms existing techniques, demonstrating superior accuracy, selectivity, and sensitivity. The proposed scheme in this research paper is a communication-less islanding detection system based on recurrent neural network (RNN) for hybrid distributed generator (DG) systems that include both synchronous and inverter-based DG devices. The scheme consists of three stages: time-domain feature extraction (FE) from the three-phase voltage signal at the point of common coupling (PCC), feature selection using the wrapper method, and detection using a long short-term memory (LSTM) RNN algorithm. To assess the performance of the proposed scheme, a comprehensive set of islanding and grid-connected scenarios was created using the IEC 61850-7-420 test system in MATLAB/Simulink. After feature extraction in MATLAB, the feature selection and LSTM model training/testing steps were conducted in Python. Thirteen features were extracted from the voltage signal, and the most significant features were selected for detection using the wrapper method. The detection process encompassed various events, such as line faults, load switching, and capacitor switching, occurring in both islanded and grid-connected modes. The proposed scheme was compared against existing techniques, artificial neural networks, and support vector machines under the same conditions. The proposed scheme demonstrated excellent accuracy (99.68 %), selectivity (99.44 %), and sensitivity (100 %) under normal conditions with all features. It also performed well in noisy environments, with accuracies of 98.94 % and 97.04 % with 40 dB and 30 dB noise, respectively. This research highlights the importance of quality and quantity of data for training intelligent RNN-based IDSs and demonstrates the effectiveness of the proposed scheme in detecting islanding in hybrid DG systems. [ABSTRACT FROM AUTHOR]

• A modified DC Power Flow with a piecewise linearization of the branch losses based on a modified power balance at the buses. • The consideration of controllable loads as distribution assets based on load shifting for chemical plants. • A partitioning method whose distance computation ensures the cluster connectedness. • The implementation of a fast sequential management procedure with zonal and nodal representations. This paper presents an optimal management (OM) strategy for distributed generation (DG) planning studies. The objective is the reduction of the CO 2 emissions for the power generation on Jurong Island in Singapore. Different DG resources are investigated with solar panels, energy storage units, small gas turbines as well as controllable loads in addition to the centralized generation already in site. Each of those resources is modeled in an optimal scheduling procedure that furtherly allows to test several DG configurations (i.e. different types/sizes/sites) with regards to the CO 2 emissions. The paper mainly focuses on the implementation of the OM and the main challenge is to avoid prohibitive computational times, which is tackled thanks to two approaches. At first, a linearization of the line losses with a modified DC power flow is considered while optimizing the system management over a representative day. A generic clustering method is then developed along with a sequential optimal management (S-OM) lying on both nodal and zonal representations of the electrical network. Different validation tests are performed as well as sets of simulations with several DG configurations. The optimal DG planning procedure itself is not in the scope of that paper and will be part of further developments. [ABSTRACT FROM AUTHOR]

• Efficient dynamic modelling framework for the analysis of fair-sized DC microgrids. • Nodal formulation combined with Newton–Raphson and implicit trapezoidal methods. • BESS, CHP units, PV plants and series connected DC/DC converters can be studied. • Results are validated versus EMT simulation conducted in Simscape Electrical. • Small errors are obtained with a small fraction of time taken by the EMT simulation. This paper introduces a novel modelling framework for conducting dynamic analysis of DC microgrids (MG), considering components such as battery energy storage systems (BESS), combined heat and power (CHP) cogeneration, photovoltaic (PV) plants and DC/DC converters. The MG dynamics are accurately captured using well-founded modelling practices of the power system transient analysis field. Firstly, the power device models are derived based on fundamental operating principles using a lumped-type parameter modelling approach. Secondly, the DC microgrid is formulated using nodal power injections, which is combined with Newton–Raphson and implicit trapezoidal methods to efficiently solve fair-sized networks of arbitrary topology. The dynamic outcomes of a 13-bus MG were compared with those of an electromagnetic transient (EMT) simulation conducted in Simscape Electrical for load and solar irradiance changes and for a DC/DC converter outage. For these events, errors smaller than 2.5% were yielded by the new approach, only requiring 3.1% of the computing time employed by the EMT simulation. The method's applicability was also showcased by assessing the dynamic performance of a larger DC microgrid containing 118 buses, twelve distributed generators and five BESS, which was subjected to typical contingencies such as load increases and distribution line disconnections. [ABSTRACT FROM AUTHOR]

• A novel FL-based VPP modeling approach. • A novel multi-task FL method improvement for non-IID data sets such as data sets in VPP. • The proposed algorithm's superiority is its accuracy and calculation velocity. • Presenting the performance analysis of the optimization process of the proposed method. The Virtual Power Plant (VPP) is a promising solution to power systems' challenges. However, its energy management system (EMS) faces challenges due to centralized Big-Data analysis, i.e., complexity and high computational cost. Decentralized strategies, e.g., federated learning (FL), have been proposed to mitigate these challenges. Although conventional FL can be implemented in VPPs, its effectiveness is limited by its typical structure, which relies on single-pattern modeling. Indeed, this particular structure leads to delays and inaccuracies in optimizing the heterogeneous generator dispatch patterns, particularly renewables. Hence, addressing this critical hindrance is essential for FL's efficient and effective deployment in VPPs. To overcome this drawback, this paper proposes novel VPP modeling utilizing multi-task FL modernized by multi-pattern modeling to decentralize the EMS processing. The proposed FL defines electricity generators' agents as clients collaborating to train the decentralized local data coordinated by a central server. The innovative idea is to create a novel multi-pattern-multi-task FL for electricity generation prediction so that the generator's agents learn to provide an optimized dispatch. Thus, the conventional multi-task FL is improved by proposing an optimized neural-network clustering technique. Simulation results demonstrate that multi-pattern-multi-task FL is 39%-41% faster than the best-reported methods, i.e., teaching–learning-based and honey-bee-mating optimization algorithms. © 2017 Elsevier Inc. All rights reserved. [ABSTRACT FROM AUTHOR]

Highlights • This paper solves the problem of MV/LV distribution system planning. • A new bilevel mathematical model to solve the integrated problem is proposed. • The mathematical model considers the fixed and operation costs of both networks. • Three cases are used: traditional planning, bilevel model and bilevel model with DG. Abstract This paper presents a new model for optimal integrated planning of medium and low voltage distribution systems with penetration of distributed generation (DG) in the low voltage network. The proposed bilevel model takes into account in the upper and the lower levels, the medium and low voltage network planning respectively. This approach considers as conflict between these two agents (upper and lower levels), the size and location of the distribution transformers (DT), i.e. the incidence in both networks of the power flow circulating from the primary to the secondary system. The main objective of this approach is to find a joint global solution that establishes a balance to benefit the planning of both networks, by decomposing the problem in two subproblems (or levels). The upper and lower levels involve the costs of installing and upgrading the new and existing elements (branches, DT, substations and DG) and the cost of the energy technical losses. This problem is formulated as a mixed integer non-linear model, and is solved using a tabu search algorithm (TSA). To verify the efficiency of the proposed methodology, three cases of study are compared: (i) traditional integrated planning, (ii) bilevel integrated planning and (iii) bilevel integrated planning with DG in the LV network. The obtained results show the importance of considering both networks in a simultaneous way in the electric distribution system planning, which allows finding answers of lower global costs. [ABSTRACT FROM AUTHOR]

Distributed Generation (DG) systems are typically interfaced with distribution lines by modern power converter devices, which their controllers and dynamic behaviours are significantly influenced by unbalanced grid faults. The active and reactive power control with positive-negative sequences (PNS) is one of fundamental of power converter control under grid fault conditions. This paper proposes a reference current generator (RCG) based flexible power control strategy to enable regulation of active and reactive power with minimizing active and reactive power oscillations. Current limitation control is embedded into the RCG in order to keep maximum current injection in safety limitation for overcurrent protection under grid faults and harmonic distortions. The proposed control strategy has been also accomplished maximum active power and minimum reactive power transfer capability to electric grid. The analytical expression of active and reactive power oscillations depending on flexible control parameters are comprehensively investigated as theoretically and examined with simulations. Fractional order proportional integral (FOPI) controller is preferred to minimise steady state error of AC current regulation and provide faster processing time instead of conventional PI and proportional resonant (PR) controllers. An important contribution for similar previous studies is that PNS voltage and current components are separated by dual average filter based phase locked loop (DAPLL) which is firstly proposed in this paper. The performance of proposed controller is compared with multiple complex-coefficients filter (MCCF-PLL) based controller. Theoretical analysis and simulation results verify the correctness and effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

The Virtual Power Plant (VPP) is a promising solution to power systems' challenges. However, its energy management system (EMS) faces challenges due to centralized Big-Data analysis, i.e., complexity and high computational cost. Decentralized strategies, e.g., federated learning (FL), have been proposed to mitigate these challenges. Although conventional FL can be implemented in VPPs, its effectiveness is limited by its typical structure, which relies on single-pattern modeling. Indeed, this particular structure leads to delays and inaccuracies in optimizing the heterogeneous generator dispatch patterns, particularly renewables. Hence, addressing this critical hindrance is essential for FL's efficient and effective deployment in VPPs. To overcome this drawback, this paper proposes novel VPP modeling utilizing multi-task FL modernized by multi-pattern modeling to decentralize the EMS processing. The proposed FL defines electricity generators' agents as clients collaborating to train the decentralized local data coordinated by a central server. The innovative idea is to create a novel multi-pattern-multi-task FL for electricity generation prediction so that the generator's agents learn to provide an optimized dispatch. Thus, the conventional multi-task FL is improved by proposing an optimized neural-network clustering technique. Simulation results demonstrate that multi-pattern-multi-task FL is 39%-41% faster than the best-reported methods, i.e., teaching–learning-based and honey-bee-mating optimization algorithms.© 2017 Elsevier Inc. All rights reserved.

This paper introduces a novel modelling framework for conducting dynamic analysis of DC microgrids (MG), considering components such as battery energy storage systems (BESS), combined heat and power (CHP) cogeneration, photovoltaic (PV) plants and DC/DC converters. The MG dynamics are accurately captured using well-founded modelling practices of the power system transient analysis field. Firstly, the power device models are derived based on fundamental operating principles using a lumped-type parameter modelling approach. Secondly, the DC microgrid is formulated using nodal power injections, which is combined with Newton–Raphson and implicit trapezoidal methods to efficiently solve fair-sized networks of arbitrary topology. The dynamic outcomes of a 13-bus MG were compared with those of an electromagnetic transient (EMT) simulation conducted in Simscape Electrical for load and solar irradiance changes and for a DC/DC converter outage. For these events, errors smaller than 2.5% were yielded by the new approach, only requiring 3.1% of the computing time employed by the EMT simulation. The method’s applicability was also showcased by assessing the dynamic performance of a larger DC microgrid containing 118 buses, twelve distributed generators and five BESS, which was subjected to typical contingencies such as load increases and distribution line disconnections.

In a deregulated power system, incentive regulations for network owners are designed to direct the network investment. An innovative method that assesses the incentive regulation in distribution networks is proposed in this paper. The method quantifies the interplay between incentive regulation, network investment, and network performances. It allows regulators and the distribution system operators (DSOs) evaluating the economic effects of investments within the incentive regulation framework. Considered network investments include the investment in network infrastructure and performance improving. The assessment is based on a network investment optimization model considering multi-period optimal power flow and regulatory constraints. The main contributions of this paper include the modeling of the incentive regulations and the quantification of the impacts of incentive regulation on network infrastructure investment and performance improving investment. [ABSTRACT FROM AUTHOR]

The presence of power electronic-based wind turbines and photovoltaic systems in distribution networks has provided distribution companies an opportunity to implement voltage control through using the reactive power of these systems. In this paper, a decentralized method based on fuzzy logic is proposed to control the reactive power of distributed generations (DGs) regarding the technical constraints. The fuzzy system is optimized by gradient descent algorithm (GDA) and then implemented on various DG technologies including a photovoltaic (PV) system, permanent magnet synchronous generator (PMSG) wind turbine and also a doubly fed induction generator (DFIG) wind turbine. The system under study is tied to a real distribution network. Having simulated the system, the paper shows that the fuzzy system can appropriately determine the desired reactive power that should be produced by each DG based on the voltage variation of the bus at which the DG is connected. Furthermore, a centralized voltage control is also applied to the same network to verify the performance of the method proposed. The verification indicates that the method is capable of finding the near-optimal solution. A scenario in which an unwanted conflict appears in the DGs’ function is defined in detail and then a strategy is presented to resolve the situation. In addition to this, the coordination between the stator of the wind turbines and grid side converter (GSC) is examined. To investigate the robustness of the proposed method in different distribution networks, simulation results are also presented for IEEE 33-bus distribution test system. The numerical results show that the fuzzy system can effectively control the voltage of the DG connection bus. [ABSTRACT FROM AUTHOR]

The promotion of the distributed generation and the photovoltaic (PV) energy great potential put this technology in the spotlight of investors. Thus, the optimization of its efficiency is made a priority. In this paper, a complete and versatile remote controller (C&VRC) for PV systems is presented, scalable to any kind and size of installations (with or without partial shading, with or without connection to the grid, housing, small plants or even large-scale solar plants) and valid for any weather conditions. The C&VRC involves the controller itself, which is constituted by a set of sensors and actuators connected to the converters Direct Current (DC)/DC and DC/Alternating Current (AC), if necessary, and a control unit communicated with them through the third-generation mobile telecommunications technology (3G) network. The control strategies can be changed according to the different weather conditions and installations characteristics, which guaranties the optimum performance of the system. The use of the 3G network as communication platform makes the C&VRC useful in remote and low accessibility places, because it is the most extended worldwide. The C&VRC is also based on free software, open hardware and low-cost electronic devices. Experimental results are presented in this paper to show the C&VRC optimum usability. [ABSTRACT FROM AUTHOR]

In this paper a novel approach regarding the optimal penetration of Distributed Generation (DG) in Distribution Networks (DNs) towards loss minimization is proposed. More specific, a Local Particle Swarm Optimization (PSO) variant algorithm is developed in order to define the optimal active and reactive power generation and/or consumption requirements for the optimal number and location of nodes that yield loss minimization. Thus, the proposed approach provides the optimal number, siting and sizing of DGs altogether. In addition, based on the optimal power requirements of the resulted nodes, a combination of potential DG types to be installed is recommended. The proposed objective function in this paper is also innovative since it embeds the constraint of reverse power flow to the slack bus by the formation of a new penalty term. The proposed methodology is applied to 30 and 33 bus systems. The results indicate the optimal number, locations, and capacity of DG units, which were calculated simultaneously. Finally, the impact of the predefined amount of permissible reverse power flow to the optimal solution is also examined through two scenarios: the first considers zero reverse power flow and the second unlimited reverse power flow. [ABSTRACT FROM AUTHOR]

This paper proposes a new analytical method for placement and sizing of distributed generation (DG) units for loss reduction. This analytical method for DG placement in the distribution network is developed based on a new mathematical formulation which does not require bus impedance matrix. This is the main advantage of the proposed method. This paper also proposes the placement and sizing of DG unit considering two novel bus types, i.e., P and PQV buses. The ‘ P ’ bus is represented by real power specification only whereas the ‘ PQV ’ bus is one whose voltage magnitude is remotely controlled by the ‘ P ’ bus. A simple method is suggested to select ‘ P ’ bus in a distribution network to control the voltage magnitude of ‘ PQV ’ bus. The effectiveness of the proposed method is demonstrated through examples of 33 bus and 69 bus distribution networks. [ABSTRACT FROM AUTHOR]

Distributed generation (DG) has an overall positive impact on Microgrids. These DGs are usually located close to the load centers which lead to some benefits such as; system power loss and energy cost reduction; voltage profile and stability improvement; environmental friendliness, postponement system upgrading and reliability enhancement. In this paper, a novel combined method based on Genetic Algorithm (GA) and Intelligent Water Drops (IWD) is proposed to find location and capacity of DG in Microgrids for optimizing some objective functions. The objectives are minimizing network power losses, improving voltage regulation and increasing the voltage stability within the framework of system operation and security constraints in Microgrids. In this paper, DG units are modeled as generators that are able to inject just active power to network. The Intelligent Water Drops (IWD) algorithm is a new swarm-based optimization algorithm inspired by observing natural water drops that flow in rivers. A detailed performance analysis is carried out on 69-bus and 33-bus Microgrids to demonstrate the effectiveness of the proposed methodology. [ABSTRACT FROM AUTHOR]

Energy needs increases day by day in those areas of the world where the electrical distribution lines are not available. This situation limits the industrial and economic development of these areas as well as the establishment of the population, so that it facilitates the exodus and the uprooting of people. At the moment the electrical energy supply in remote areas is based on solutions with generator sets, consuming great amounts of fuel with a great environmental damage. The technological development of renewable energies and the new concepts for their management, make possible proposing off-grid generation solutions for providing great amount of energy with high quality and reliability. Along this paper, a smart-grid configuration is proposed which is developed with products of proved reliability and which uses renewable energies as main generation source. This configuration allows having “standard” grid services anywhere, without the need of connection to the traditional grid. Environmental, economic and operation benefits of using these technologies against traditional solutions are also presented in this paper. This proposed solution allows the economical development and exploitation of areas where due to the lack of energy or to the energy cost it has not been possible until now. [ABSTRACT FROM AUTHOR]

Distribution network expansion planning (DNEP) is one of the most important tools to deal with the demand growth in a system. DNEP is usually carried out through reinforcement or installation of new components. In this paper, a new and combined methodology is used to consider several practical aspects in DNEP such as uncertainty, distributed generation (DG), load growth, electricity market and multi stage dynamic expansion are included in the planning. So that DNEP is addressed in the presence of distributed generation (DG), considering load and price uncertainties under electricity market environment. The proposed planning aims at minimizing investment and operational costs simultaneously. Since DNEP in coordination with DG planning leads to reduce planning cost; therefore, the coordinated DNEP and DG planning are presented in this paper. The proposed planning is implemented by the particle swarm optimization (PSO) technique. Besides, the uncertainties are modeled as the probability distribution function (PDF) and Monte-Carlo simulation (MCS) is used to insert the uncertainties into the programming. The proposed planning is carried out based on the 9-bus as well as Kianpars–Ahvaz test systems (Kianpars–Ahvaz is a practical network in Ahvaz province, Iran). The simulation results demonstrate the ability and effectiveness of the proposed planning to deal with uncertainties under electricity market environment. [ABSTRACT FROM AUTHOR]

The increasing presence of inverter-based distributed generation (DG) units in microgrid application requires control methods that achieve high performance not only during normal operating conditions, but also under unbalanced conditions. These conditions can occur permanently due to distribution of unbalanced loads on the three phases of the microgrid. This paper proposes a robust control strategy for a grid-connected multi-bus microgrid containing several inverter-based DG units. Each of the DG units can supply a combination of balanced and unbalanced local loads. The proposed control strategy employs an adaptive Lyapunov function based control scheme to directly compensate the negative-sequence current components caused by unbalanced loads in some part of microgrid; and a sliding mode based control scheme to directly regulate the positive-sequence active and reactive power injected by DG units to the microgrid. The control method proposed in this paper is shown to be robust and stable under load disturbances and microgrid parameter uncertainties even in the presence of nonlinear and time-variant unbalanced loads. The effectiveness of the presented controller is validated through time-domain simulation studies, under the MATLAB/Simulink software environment. [ABSTRACT FROM AUTHOR]

This paper deals with the subject of finding the site and size of distributed generation in distribution systems. This problem corresponds to a mixed-integer nonlinear problem which is difficult and hard to solve with classical optimization techniques. Many approaches and with different objective functions have been applied to solve it. In this paper, the problem to solve comprises multiple distributed generation sources and the objective of minimizing power losses and generation costs, both for the distributed and conventional generators. Since it is highly combinatorial, a search space reduction is needed. So, an approximate model is used to reduce the search space of the possible buses where the distributed generation has to be located. Then, for each combination of the reduced space search, a nonlinear equations system is solved by a numerical method to get the size of the distributed generation, checking the voltage limits and the lines’ capacities. To test the method, a comparison between the proposed algorithm and a force brute algorithm is performed on a 69 and 118 bus test systems. The obtained results indicate that this method find the optimal or near optimal solution in a reasonable computation time. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of Novel Power Loss Sensitivity, Power Stability Index (PSI), and proposed voltage stability index (VSI) methods for optimal location and sizing of distributed generation (DG) in radial distribution network. The main contribution of the paper is: (i) optimal placement of DGs based on Novel Power Loss Sensitivity and PSI methods, (ii) proposed voltage stability index method for optimal DG placement, (iii) comparison of sensitivity methods for DG location and their size calculations, (iv) optimal placement of DG in the presence of load growth, (v) impact of DG placement at combined load power factor, (vii) impact of DG on voltage stability margin improvement. Voltage profile, the real and reactive powers intake by the grid, real and reactive power flow patterns, cost of energy losses, savings in cost of energy loss and cost of power obtained from DGs are determined. The results show the importance of installing the suitable size of DG at the suitable location. The results are obtained with all sensitivity based methods on the IEEE 12-bus, modified 12-bus, 69-bus and 85-bus test systems. [ABSTRACT FROM AUTHOR]

The introduction of a Distributed Generation (DG) unit in the distribution system improves the voltage profile and reduces the system losses. Optimal placement and sizing of DG units play a major role in reducing system losses and in improving voltage profile and voltage stability. This paper presents in determination of optimal location and sizing of DG units using multi objective performance index (MOPI) for enhancing the voltage stability of the radial distribution system. The different technical issues are combined using weighting coefficients and solved under various operating constraints using a Chaotic Artificial Bee Colony (CABC) algorithm. In this paper, real power DG units and constant power load model and other voltage dependent load models such as industrial, residential, and commercial are considered. The effectiveness of the proposed algorithm is validated by testing it on a 38-node and 69-node radial distribution system. [ABSTRACT FROM AUTHOR]

Because of their small scale and large share of intermittent power sources, islanded microgrids require additional means of flexibility, such as dedicated storage. For controlling the loads and distributed generation (DG) units in an islanded microgrid, the voltage-based droop (VBD) control has been developed. This controller determines the switching actions of these units’ power electronic interfaces in order to ensure a stable islanded microgrid operation. In this paper, the VBD control is extended for storage applications, taking into account the state of charge. As the VBD control automatically fixes the priority of power changes of the microgrid elements, the storage elements are included in this priority list without inter-unit communication. This benefits the coordinated integration of DG units in the system. Simulation examples are included illustrating the transient and dynamic response of the VBD control of all grid assets. The paper also provides an experimental validation of the VBD control for both the DG units and the storage elements in an islanded microgrid. [ABSTRACT FROM AUTHOR]

This paper deals with the influence of distributed generation (DG) on distribution losses in medium voltage (MV) distribution networks. The aim was to minimize the losses and operation costs with only DG reactive power compensation with respect to voltage constraints. Thus, the active power flows are not affected as any attempt of active power curtailment causes financial loss for DG owner. The advantage of technologies that build up new smart grids is the possibility of developing new approaches of network management. In this paper, a coordinated reactive power control is presented which takes advantage of real-time data measurements from the network. The load-flow algorithm is implemented into the coordinated control, which determines the optimal operating point using a modeled network for every generator separately. The aim of the algorithm is to minimize the reactive power flow. The solution is evaluated by means of computer simulations. The simulated network is a part of the Slovenian medium-voltage distribution network. The presented results illustrate that the algorithm results in fast, simple and efficient energy loss allocation with an acceptable level of accuracy. [ABSTRACT FROM AUTHOR]

It is often necessary to investigate the output power against load demand in a system having distributed generation (DG) resources connected to the existing conventional power system. In this paper, the load frequency control (LFC) problem is presented using different optimization algorithms for two types of power system configurations: (i) hybrid configuration of thermal power system (TPS) integrated with DG, comprising wind turbine generators (WTGs), diesel engine generators (DEGs), fuel cells (FCs), aqua-electrolyzer (AE) and battery energy storage system (BESS); (ii) two area interconnected power system with DG connected in area-1. The inclusion of wind energy system in DG, having high variability in its output power, results into a challenging task for the realization of an effective controller design. This difficulty is further enhanced with random variation of load demand. The control scheme proposed in this paper is based on linear matrix inequalities (LMI) with its parameters tuned by particle swarm optimization (PSO), as a new contribution to earlier studies. The robustness of this controller is thoroughly demonstrated in the above hybrid power systems with different conditions of load disturbances, wind power and parameter variations. [ABSTRACT FROM AUTHOR]

With the implementation of competitive electricity supply system all over the world, there is the need of optimal utilization of the existing generation sources at the same time to curtail the generation from the conventional power plants and add the renewable sources generation looking into the environmental concern and limitation of the fossil fuels. This has lead to the motivation for the studies on the integration of distributed resources to the grid. In this paper optimal locations and sizes for DG is determined for weakly meshed distribution networks based on the sensitivity method. Novel method based on loss sensitivity is used in this paper to determine optimal size and location of DGs. The modified Novel method is proposed for DG allocation. The main contribution of the paper is: (i) distributed generation allocation for mesh network using sensitivity approach, (ii) modified Novel method for DG allocation and sizes calculation for meshed distribution system with load variations, (iii) comparison of the results obtained with single and two DG placement with load variations, (iv) the loss savings and overall cost savings per annum with single and two DGs placement with load variations. In this paper we considered the impact of time varying load flow with realistic load model. The realistic ZIP load model has been considered for study. The results have been obtained for a distribution network of UK Distribution Corporation consisting of 38 buses. The results have also been obtained for radial distribution system for comparison. [ABSTRACT FROM AUTHOR]

• A strategy for the operation planning of ADNs considering renewable generation and CVR. • A centralized approach from the distribution system operator viewpoint. • A stochastic formulation proved to be effective in preventing network contingencies. • Tests showed significant benefits of using of CVR for energy savings and power balancing. • The forecast errors of renewable generation can be compensated by using CVR. Energy efficiency and renewable energy are of paramount importance in the search for a sustainable energy system. This paper investigates the effect of conservation voltage reduction (CVR) on the optimal operation scheduling of active distribution networks with high shares of renewable energy sources (RES)-based distributed generation (DG). To this end, a probabilistic optimal power flow-based algorithm, formulated as a two-stage stochastic programming model, is proposed. In the first-stage, based on forecasts of load demand and DG production, the active power exports and imports, and tap settings of the on-load tap changer (OLTC) and voltage regulators (VRs), are scheduled for the 24 h of the next day. This schedule is optimized to minimize the energy imports and maximize the energy exports. The second-stage simulates the real-time operation of the system for scenario realizations of the uncertainties, and seeks to minimize the energy deficits and maximize the energy surplus once the first-stage decisions have been made. To achieve its objective, the second-stage regulates the DG active and reactive power outputs and coordinates its operation with the OLTC and VRs to reduce the energy consumption through the CVR procedure and maximize the energy harvested from RES, while satisfying system constraints. Results of case studies describe important benefits for energy efficiency, maximum utilization RES, and safe, reliable and economic system operation. [ABSTRACT FROM AUTHOR]

• Voltage magnitude and line loading monitoring scheme using artificial neural networks. • Low estimation errors even with distributed generation and different switching states. • The presented hyperparameters are transferable for use in other grids. The increasing number of distributed generators connected to distribution grids requires a reliable monitoring of distribution grids. Economic considerations prevent a full observation of distribution grids with direct measurements. First approaches using a limited number of measurements to monitor distribution grids exist, some of which use artificial neural networks (ANN). The current ANN-based approaches, however, are limited to static topologies, only estimate voltage magnitudes, do not work properly when confronted with a high amount of distributed generation and often yield inaccurate results. These strong limitations have prevented a true applicability of ANN for distribution system monitoring. The objective of this paper is to overcome the limitations of existing approaches. We do that by presenting an ANN-based scheme, which advances the state-of-the-art in several ways: Our scheme can cope with a very low number of measurements, far less than is traditionally required by the state-of-the-art weighted least squares state estimation (WLS SE). It can estimate both voltage magnitudes and line loadings with high precision and includes different switching states as inputs. Our contribution consists of a method to generate useful training data by using a scenario generator and a number of hyperparameters that define the ANN architecture. Both can be used for different power grids even with a high amount of distributed generation. Simulations are performed with an elaborate evaluation approach on a real distribution grid and a CIGRE benchmark grid both with a high amount of distributed generation from photovoltaics and wind energy converters. They demonstrate that the proposed ANN scheme clearly outperforms state-of-the-art ANN schemes and WLS SE under normal operating conditions and different situations such as gross measurement errors when comparing voltage magnitude and line magnitude estimation errors. [ABSTRACT FROM AUTHOR]

• The output current characteristics of V/f-DG and PQ-DG are analyzed. • The coordinating control strategy between V/f-DG and PQ-DG is proposed. • A new fault detection criterion based on the fault components is established. • The fault detection method can be applied to the islanded microgrid with V/f-DG and PQ-DG. The fault characteristic of islanded microgrid is closely related to the control strategy of distributed generation (DG) and it is different from that of grid-connected microgrid. Also, the analysis of fault control strategy is an essential foundation of the fault location. This paper discussed the control strategy and output fault characteristic of V/f and PQ controlled DG. To establish the fault detection criterion of islanded microgrid, the coordinating control strategy between V/f and PQ controlled DG is presented. Based on the above fault analysis, the fault point is located by using a new fault detection method, which is based on the phase differences between the pre-fault bus voltage and the positive- sequence current fault component of the feeders. Finally, examples are simulated in PSCAD/EMTDC and the results verify the accuracy and effectiveness of the proposed fault detection method. [ABSTRACT FROM AUTHOR]

• Estimation of fault distance and section in microgrid by one method. • Measurements are used only at PCC and DG locations. • Grid connected and island modes are considered. • Investigating the ARC fault. • Does not require DG models. The most challenging problem to protect the microgrids is the integration of different types of distributed generations, which leads to the bidirectional load flow and different fault current levels. On the other hand, the use of voltage and current measurements in nodes increases the cost of fault location methods. This paper proposes a technique to calculate the distance and branch of fault for microgrids in islanded and grid-connected modes by calculating the current and voltage difference at the terminals of each branch. This method obtains the voltages and currents of all nodes by installing measuring devices at the point of common coupling and the location of distributed generations. This technique uses a distributed parameter line model and node data to determine fault locations in the microgrid, considering distributed generation such as wind turbines, photovoltaic systems, fuel cells, and electric vehicles. This technique does not require distributed generation models. Moreover, it requires less than a quarter of the data of a cycle. The efficiency of proposed the technique is investigated by a modified IEEE 15-bus in MATLAB/SIMULINK and a 7-bus test system in the power system simulator. Besides, studies are conducted on the impacts of various fault resistance and inductance, different fault locations, different fault inception angles, measurements error, and ARC faults. The results showed that the proposed approach is extremely accurate compared to other fault location methods in microgrids. [ABSTRACT FROM AUTHOR]

This paper presents the design of local PI regulators to control voltage and active power of the Distributed Energy Resources (DERs) in grid-connected Active Distribution Networks (ADNs). The design is developed based on the proposed Multiple-Input Multiple-Output (MIMO) model of ADN. Firstly, the Relative Gain Array (RGA) matrix is used to address the problem of input–output pairing and to show that the voltage control loops are coupled whereas the active power control loops are decoupled. Subsequently the method of the Effective Open-Loop Transfer Function (EOTF) is used to decompose the multi-loop voltage control system into a set of equivalent Single-Input Single-Output (SISO) loops. Then, each PI regulator is independently designed to fulfill some control objectives dictated by the designer. The proposed design procedure is simple and straightforward. The fixed-parameters PI regulators facilitate the integration of DERs into traditional distribution networks which are usually operated without or with limited communication infrastructure. The simulation results presented for various scenarios of two different ADN confirm that performance objectives and regulation at the desired set-points are achieved in a robust sense. • Voltage and active power PI control of DERs. • Square MIMO model of the ADN oriented to the design. • Analysis of the internal and external interactions among control loops. • Independent design based on the concept of Effective Transfer Function. • Robust stability and robust performance in presence of parameters uncertainty and disturbances. [ABSTRACT FROM AUTHOR]

Renewables interfaced through inverters in microgrids, may be controlled using centralized, decentralized or distributed approaches. The decentralized droop control involves mimicking the performance of a synchronous generator of the power system, so as to share load power proportionately amongst parallel connected sources. When the conventional droop control is used, only the fundamental real powers can be shared in proportion to the source ratings, which does not ensure satisfactory performances in the presence of unbalanced/ asymmetrical loads. Several schemes have been worked upon to achieve proportional load power-sharing with power quality aspects: in the presence of harmonic and unbalanced loads. This paper proposes five modifications for the popular virtual conductance vs. negative sequence power (G vs. Q-) approach, aimed at improving the sharing of the unbalanced currents amongst the sources to improve the power quality and microgrid system reliability. The eigenvalue analysis for determining the parameter range for assuring stability and comparisons with fixed virtual conductance values are discussed. The proposed modifications are discussed and demonstrated through simulations on a two inverter-based distributed generator (DG) system, a modified 13 bus system, and using experimental results on a lab-scale microgrid. • The work presented focuses on the power quality of unbalance in islanded AC microgrid systems and proposes five modifications for the popular G vs. Q- approach, aimed at improving the sharing of the unbalanced currents amongst the parallel connected sources. • The proposed modifications are based on local measurements and do not need communication, network and load estimations • The eigenvalue based small signal analysis for determining the parameter range for assuring stability and comparisons with fixed virtual conductance values are presented. • The proposed modifications are discussed and demonstrated through simulations on a two-inverterbased distributed generator (DG) system, a modified 13 bus system, and using experimental results on a lab-scale microgrid. • An overall improvement in the range of 26.0% to 61.0% was observed across the different cases (enhanced unbalanced power-sharing: before and after activating the proposed control). [ABSTRACT FROM AUTHOR]

• The optimization function was expanded with the maximization of the time gap between the backup relay operating time and the thermal stress curves of the protected elements, • A modified genetic algorithm was developed, in which the genetic operators were tailored specifically to remove the unfeasible solution space. • The proposed method was verified on a realistic example of a 16-bus medium voltage ring distribution network with included distributed generation unit, • The results suggest that it is possible to simultaneously minimize the total primary relays' operating time and to widen the time margin before the degradation and/or damage of the protected elements. In this paper, a novel method for optimizing and coordinating directional overcurrent relays in active distribution networks considering thermal equivalent short-circuit current is proposed. A modified genetic algorithm is used as a tool in order to simultaneously minimize the operating times of the primary relays and maximize the time delay between the operation of backup relays and their respective protected elements' thermal stress curves. In other words, the objective function to be minimized is defined as the sum of the operating times of all primary relays and the reciprocal sum of the thermal violation check. The latter part is necessary because a protection engineer needs to be sure that the operation of a backup relay is as far as possible from the thermal stress curve of the protected element. Needless to say, for every solution, the algorithm ensures the proper coordination between primary and backup relay pairs throughout the network. The simulation is carried out for a closed loop medium voltage distribution network and the results are presented to demonstrate the effectiveness of the proposed approach. The main benefit of this optimization process is that it indicates whether the existing protection system can operate safely below the thermal stress curves of the protected elements' or whether additional measures are required. [ABSTRACT FROM AUTHOR]

• This paper gives an effective hybrid planning of distributed generation and distribution automation. • The platform consists of automatic voltage and VAR control and automatic fault management systems. • A stochastic programming approach is also pursued in this paper, aiming to model uncertain parameters. • The proposed strategy is implemented on an IEEE 69-bus radial distribution network. • Different case studies are represented to demonstrate the economic and technical benefits. This paper intends to give an effective hybrid planning of distributed generation and distribution automation in distribution networks aiming to improve the reliability and operation indices. The distribution automation platform consists of automatic voltage and VAR control and automatic fault management systems. The objective function minimizes the sum of the expected daily investment, operation, energy loss and reliability costs. The scheme is constrained by linearized AC optimal power flow equations and planning model of sources and distribution automation. A stochastic programming approach is also implemented in this paper based on a hybrid method of Monte Carlo simulation and simultaneous backward method to model uncertainty parameters of the understudy model including load, energy price and availability of network equipment. Finally, the proposed strategy is implemented on an IEEE 69-bus radial distribution network and different case studies are presented to demonstrate the economic and technical benefits of the investigated model. By allocating the optimal places for sources and distribution automation across the distribution network and extracting the optimal performance, the proposed scheme can simultaneously enhance economic, operation, and reliability indices in the distribution system compared to power flow studies. [ABSTRACT FROM AUTHOR]

Highlights • Propose a joint planning model for active distribution systems. • Develop a new stochastic modelling approach for renewable energy. • Develop a new multi-objective optimization method for the proposed model. Abstract This paper proposes a multi-objective joint planning model for Active Distribution Networks (ADNs). The model determines the location and size of Electric Vehicle Charging Stations (EVCSs), Renewable Energy Sources (RESs), Battery Energy Storage System (BESSs), and distribution network expansion schemes, with the objectives of minimizing the total investment and reliability cost of the distribution network and maximizing the EVCSs' charging service capability. A scenario-based stochastic modelling approach based on Wasserstein distance metric and K-medoids scenario analysis is developed to model the stochastic nature of renewable generation. A multi-objective optimization algorithm, Multi-Objective Natural Aggregation Algorithm (MONAA), is applied to solve the proposed model. Case studies are conducted on a coupled 54-node distribution system and 25-node traffic system to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Highlights • Super twisting technique is innovatively used to control the direct power control. • Kalman filter is formulated to estimate the feedback power. • Kalman filter is formulated to estimate the feedback voltages. • The direct power control is used in a grid-connected mode. • The direct power control is used in a stand-alone mode. Abstract This paper presents an efficient modification of the direct power control scheme employed to precisely control the power of the distributed generation system. This modification is articulated for utilizing the super-twisting technique for controlling the feedforward power and Kalman filter for estimating the feedback power. The combination of the super-twisting technique and Kalman filter for the direct power control achieves a seamless steady-state and dynamic performance for the injected power by the distributed generation system in a grid-connected mode. Furthermore, the concept of direct power control is modified to operate the distributed generation system in a stand-alone mode so as to stabilize the voltage at different loading conditions, where the feedback voltage is estimated by a simple formulation of Kalman filter. The proposed control scheme for the distributed generation system is compared to several control schemes such as the conventional direct power control operated by space vector modulation and another proposed 1st order sliding mode control based direct power scheme. Simulation results are presented to prove the meritorious performance of Kalman filter and the super-twisting technique for the power and voltage control schemes. Experimental results are provided to prove the practicality of the super-twisting technique for the operation of the direct power control in a grid-connected mode. [ABSTRACT FROM AUTHOR]

Highlights • A novel analytical technique to assess the impact of energy storage on reliability. • Energy storage is evaluated for restoration by islanded and by emergency ties. • Chronological charges and discharges during a failure are modelled. • Accuracy and computational efficiency of the methodology are demonstrated. • The contribution and benefit of energy storage to reliability are evaluated. Abstract A wide scale deployment of energy storage systems in power networks for energy balancing applications will lead to network reliability improvements. After a fault occurs in a network, energy storage will be able to help restore supply in the network areas isolated from the primary substation or in those re-connected to adjacent feeders of limited transfer capacity by emergency-ties. The reliability improvements introduced by energy storage need to be evaluated and quantified for both restoration modes. The objective of this paper is to assess the energy storage contribution in these restoration modes and to seek analytical, less computationally intensive solutions for such evaluation. The proposed analytical technique uses a probabilistic model of energy storage to assess the charge and discharge processes over a fault duration and the related operational strategy. In this way, reliability indices are calculated by taking into account the energy storage actions during a fault as well as the time-evolution of renewable generation and demand. These features lead to more realistic modelling of energy storage in analytical techniques. The proposed analytical technique was firstly validated by using a case study where the results obtained by Monte Carlo Simulation were used as a reference. Then, the proposed technique was applied to a distribution network to assess the reliability improvement provided by energy storage and to demonstrate the effectiveness and accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

Highlights • A protection which isolates the SLG fault in neutral non-effectively grounded distribution with DG. • The time setting based on the grading coordination is added to the traveling-wave-protection. • Based on the coordination of relays the fault can be removed from both sides without communication. Abstract Electricity networks are in the era of major transition from stable passive distribution networks with unidirectional electricity transportation to active distribution, and the fault on the distribution lines should be cleared from both sides accordingly. This paper proposes a traveling-wave-based line protection scheme which can isolate the Single-Line-to-Ground (SLG) fault from both sides of the faulted line in neutral non-effectively grounded distribution network including Distributed Generation (DG) sources. In the proposed scheme, when a SLG fault occurs, first, relays distinguish the fault direction by comparing the polarities of the initial voltage and current traveling waves; and then the relays that detect the fault on the downstream and upstream sides operate based on the conventional time grading coordination, and the electrical changes of three-phase in a specified time window, respectively; finally, after operation of the relay upstream of the fault on the faulted line with the fastest time setting, the relay downstream of the fault operates by detecting the tripping of the opposite circuit breaker. In order to validate the efficiency of the proposed scheme, extensive simulations have been performed on a typical active distribution system using ATP-EMTP software. The simulation results indicate that the proposed line protection scheme can accurately and quickly isolate the SLG fault from both sides. [ABSTRACT FROM AUTHOR]

Highlights • A distance protection scheme for meshed distribution systems with DG is proposed. • The scheme is efficient under the effect of DG infeed and fault resistance. • Permissive logic is applied to ensure protection security. • One setting group is applied for both grid-connected and islanded mode. • Existing numerical distance relay technology is considered for the proposed scheme. Abstract This paper proposes a pilot-based distance protection scheme for meshed distribution systems with a high penetration of distributed generation. The proposed scheme assumes distance relays installed at the opponent ends of each main line segment. A forward distance element is enabled in each relay to protect the main line segment, while, a reverse distance element is enabled in each relay for protecting adjacent buses and laterals. The relays protecting a main line segment or a bus/lateral communicate in a permissive logic, ensuring protection sensitivity and security at the same time. The scheme provides efficient primary and backup protection against faults of any type, even with a considerable fault resistance, and under weak-infeed conditions. It is also appropriate for both the grid-connected and the islanded mode of system operation. Coordination of the distance protection scheme with the lateral protection means is also addressed. Existing numerical distance relay technology is considered, to enhance the applicability of the proposed scheme. Offline setting of the distance relays is required, which has to be performed once. Only one setting group is ultimately extracted for each relay, suitable for different fault/system conditions, avoiding the need for adaptive protection techniques. The proposed scheme is applied to a test meshed distribution system and conclusions are drawn. Comparison with directional overcurrent and differential protection shows the advantages of the designed distance-based protection scheme. [ABSTRACT FROM AUTHOR]

Highlights • A scalable optimization method is proposed to maximize a DG hosting capacity. • The method enumerates all possible optimal configurations while simultaneously considering optimal DG placement. • A compressed data structure is utilized to represent the solution space compactly. • The method obtains 1.49 × 1018 optimal configurations in 17.1 h for a network containing 235 switches. Abstract At the stage of planning distributed generation (DG) for a distribution network, the network configuration is a key factor in increasing the DG hosting capacity. The determination of a configuration that maximizes the hosting capacity is a highly complex, nonlinear combinatorial optimization problem. No existing method can yield the global optimal solution for practical-scale networks. Therefore, this paper proposes a scalable optimization method. Specifically, the proposed method enumerates all optimal configurations while simultaneously considering optimal DG placement. The proposed method first optimizes the DG placement for possible partial networks using a second-order cone programming technique. Next, it enumerates possible combinations of the partial networks while avoiding a combinatorial explosion using a highly compressed data structure. Finally, it finds the optimal configurations by exploring solutions over the data structure. In experiments involving a large-scale network containing 235 switches, our enumeration method obtained 1.49 × 10 18 global optimal configurations in 17.1 h. Another powerful feature of our method is that it enables distribution system operators to select the preferred optimal configuration interactively. [ABSTRACT FROM AUTHOR]

Highlights • A two-layer collaborative planning for inverter interfaced DGs and BES units is established for enhanced voltage regulation functions in ADN. • The potential of DG inverter over-sizing design at planning stage, the fully utilization mode of reactive power output of DG inverters at operation stage are discussed. • A time-varying ZIP load model is adopted representing the dynamic load characteristics. • The uncertainties of the DG power output are modeled based on the Taguchi robust test design approach. Abstract Active Distribution Networks (ADNs) are featured by large-scale integration of distributed generation (DG) and energy storage. This paper proposes a novel two-layer co-planning method for optimal placement of inverter-interfaced DG and battery energy storage (BES) units towards enhanced voltage regulation functions in an ADN. The outer-later model determines the planning decision of DG units and the inverter sizing, location, and capacities of BES units, respectively; the inner-layer model corresponds to the operation decision which aims to optimally schedule the BES's charging/discharging and reactive power from inverters for voltage regulation support considering the conservation voltage reduction (CVR). The Taguchi's Orthogonal Array Testing (TOAT) is used to select a small number of scenarios to represent the DG power output uncertainties. The load is represented by a time-varying ZIP load model. The proposed model is tested on a modified IEEE 33-bus radial distribution system and the results to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Highlights • A method is proposed to calculate the optimal oversize of the DG inverters. • The reactive power capability and active power curtailment are considered. • Different control schemes of the inverter are considered in the proposed method. • The effect of OLTC operation on the total costs and inverter oversize is studied. • IEEE 69-bus and IEEE 33-bus distribution systems are used for simulation. Abstract The penetration of renewable distributed generations (DG) is recently being increased in distribution systems. Due to the intermittent nature of these generation units, several technical problems are expected based on the environmental conditions and load profiles, such as voltage rise and increasing losses. A traditional way to alleviate these technical problems is to oversize their interfacing inverters for releasing their capacities to inject/absorb further reactive power. In the literature, the DG inverter is normally oversized by a certain percentage (e.g., 10%) for this purpose. In turn, an optimization-based method is proposed in this paper to calculate the optimal oversize of the interfaced inverter employed in various utility-owned DG types to regulate voltages and to reduce losses with minimum total costs. The proposed method considers the active power curtailment (APC) feature in the DG inverter and the transformer taps. Different control schemes of the interfaced inverter are considered and incorporated in the proposed optimization model. The simulation results demonstrate the effectiveness of the proposed method compared with existing methods. [ABSTRACT FROM AUTHOR]

This paper introduces a novel approach to enhance the stability of islanded grids with multiple virtual synchronous generators (VSGs) in-operation. The proposed method mainly relies on the concept of “center of inertia” (COI) response of the system. We discuss that an islanded grid with ‘ n ’ connected VSGs, can experience up to ‘ n-1 ’ oscillation frequencies due to swing power between VSGs, while the COI-frequency only indicates the major disturbances. The main idea of this method is to control the input power of VSGs to suppress the power fluctuations and reduce oscillations of VSGs relative to COI-frequency. For each VSG, a controller which includes three proportional, integral and derivative terms is used to match the VSG speed with COI-frequency in transient conditions. The state-space analysis shows that these parameters provide a high degree of freedom for adjusting the grid stability-indices to desired values. In addition, the method is able to effectively eliminate the adverse effect of the high impedance of VSGs to achieve desired performances. [ABSTRACT FROM AUTHOR]

This paper proposes the use of Energy Storage (ES) to support frequency fluctuations in weak grids powered by low-power synchronous generators (SGs). Traditionally, large synchronous generators rely on high inertia and governor control to guarantee the frequency stability of the network. The scenario changes in networks with a large penetration of small distributed generators (DGs) with smaller inertia, where load variations can lead to large frequency deviations, violating the over/under frequency protection limits. The proposed energy storage control injects active power during load transients so that the frequency is constrained within predefined thresholds. The system frequency is detected by a Double Second-Order Generalised Integrator Frequency Locked Loop (DSOGI-FLL), eliminating the need for communication between energy storage and synchronous generator and providing “plug-and-play” capability. The proposed method combined with the continuous speed governing supports the frequency well within the primary frequency transient requirements. The solution has been validated using an 8 kW laboratory system. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical approach for optimal allocation of wind DG units in radial distribution networks. Using this analytical approach, size and location of wind DG units are determined at different optimal power factors of a wind DG ( OPF w s ), while different types of time-dependent load models and probabilistic wind DG generation are considered. The proposed approach is based on the partial derivative of a multi-objective index (IMO) including four impact indices of real power loss (ILP), reactive power loss (ILQ), voltage profile (IVD) and voltage stability (IVS). IVS methods based on analytical expression are usually assumed separately (not in an IMO), to find only the optimum location. In this study, the IVS is defined for a new application as an index in the IMO so as to determine both optimal size and location of the wind DG units. Also, the impact of the wind DG penetration on system voltage stability is evaluated. The 33 and 69 bus systems are examined to show the validity of the proposed approach. From the results, the load models have a significant effect on the wind DG penetration in the network, and the match rate between wind DG output and demand curves for each load model is different. [ABSTRACT FROM AUTHOR]

This paper proposes a new multifunctional converter based on a series voltage compensator applied to centralized AC microgrids. Besides the basic functionalities required for a centralized converter in microgrids, such as grid-supporting and grid-forming voltage support and smooth transition from operating modes, the proposed converter can change its connection topology from series to parallel and vice-versa, depending on the system’s condition. Thus, it assumes all the basic defining features of series and shunt power converters. The devised control algorithm allows on-line change of converter operating modes either as voltage- or current-controlled sources. These flexible functionalities allow the converter to operate as: (i) a grid-forming converter providing voltage and frequency references for the entire microgrid, keeping the voltages at the point of common coupling (PCC) synchronized with the utility voltage; (ii) grid-feeding active power into the microgrid; and (iii) grid-supporting, performing ancillary services such as voltage regulation, voltage sag and swell compensation, along with active power filtering, reactive power, unbalance and harmonic compensation. The converter can be applied to both single-phase and three-phase three- or four-wire networks. The multifunctional control is implemented using a Texas Instruments TMS320F28335 digital signal processor, and then validated through a hardware-in-the-loop simulation developed in the Typhoon HIL 600 platform. [ABSTRACT FROM AUTHOR]

Security distance provides a quantitative approach to assess the N-1 security and its margin of distribution systems. In order to support system N-1 secure operation, distributed generations (DGs) should be used in terms of capacity credit (CC). Considering the conductor thermal constraints and voltage constraints after a substation transformer or feeder N-1 contingency, this paper proposes a rapid maximum output assessment method for DGs. With the proposed method, the system operators can better guarantee system security in the presence of active management. The concept of security distance for distribution networks is primarily decomposed into two parts: feeder security distance (FSD) and transformer security distance (TSD). Considering the correlation between the wind speed and illumination intensity, the combined output characteristics of DGs are achieved using the defined wind-photovoltaic conversion coefficient based on coordinate conversion. Then, the initial maximum DG output on each feeder section is approximately calculated by initial FSDs and TSDs. On these bases, the maximum output assessment method is proposed under uncertainties associated with DGs, loads and contingencies. Moreover, several related issues are further discussed: (a) discussion of the proposed use of DGs in terms of CC, (b) consideration of demand response in the proposed method, and (c) feasibility of the proposed method to N-2 contingency analysis. In the end, the proposed method is successfully applied to the expanded IEEE RBTS-Bus4 and a real urban distribution networks and the results verify its high performance when compared to the normal optimal method from static and dynamic views. [ABSTRACT FROM AUTHOR]

• Fault current limiter (FCL) is one of the best choices for solving protection problems in active distribution networks comprising dispersed generation (DG). • Due to the nonlinear nature of protection problems and characteristics of protective devices (PDs), selection of FCL type and specification is one of the main challenges of this approach. • In this paper, a simple and effective analytical method for FCL impedance calculation is proposed. • In this paper, all of the protection issues arising from integration of DGs into distribution network are investigated. Fault current limiter (FCL) is one of the best choices for solving protection problems in active distribution networks comprising dispersed generation (DG). Due to the nonlinear nature of protection problems and characteristics of protective devices (PDs), the selection of FCL type and specification is one of the main challenges of this approach. In this paper, a simple and effective analytical method for FCL impedance calculation is proposed. Knowing only the properties of the fastest fuse of the feeder and the protective device installed at the beginning of the feeder (in this case recloser) suffices for the implementation of the proposed method. The method addresses issues of miscoordination caused by increased fault current levels, reduction of reach of PDs, miscoordination due to reduction of reach, blinding of protection, false tripping of PDs, and fuse-fuse and overcurrent relay-fuse miscoordination. The suggested approach has also been simplified so that the selection of FCL for one feeder only relies on DGs connected to this feeder. In the proposed scheme, the impact of both conventional and inverter-based DGs is considered, and the transient behavior of FCL is elaborated. Effectiveness of the proposed method is demonstrated by various simulations on a test system in MATPOWER 5.1 toolbox. [ABSTRACT FROM AUTHOR]

• This paper presents a Z-source converter integration technique. • The energy management of various renewable energy sources is achieved. • This innovative method connect in series several power sources. • The supply to the load can be maintained without alterations. • The converters can be integrated into a common generation branch. This paper presents a Z-source converter integration technique, with which the energy management of various renewable energy sources is achieved. With a single controller and with serial arrangement of converters, this innovative method connect in series several power sources, with different power and voltage conditions. In this way, the supply to the load can be maintained without alterations, despite the random variations that occur in renewable energy sources. The main innovation is the design of the converters, according to the power and voltage conditions of the sources, so they can be integrated into a common generation branch with a single controller for all converters. The results have been verified by building a laboratory prototype consisting of three unidirectional and two bidirectional converters, which integrate three renewable sources and two electric accumulators. The generation branch management has been implemented in an S7-1500 PLC, each converter has used a DSP TMS320F2812 for the implementation of its switching technique, the branch control has also been implemented in another DSP of the same type. [ABSTRACT FROM AUTHOR]

The increasing penetration of distributed generations (DGs) and variable loads introduces significant power fluctuations to distribution networks, rendering conventional reconfiguration strategies ineffective. In the context of an active distribution network (ADN), remote control switches can be operated in real time through a centralized control scheme. Therein the distribution network topology can be configured in a flexible and dynamic manner capable of adapting to time-varying load demand and DG output. This paper presents a dynamic reconfiguration approach for a three-phase unbalanced distribution network. The ADN topology is optimized for the look-ahead time periods and is adaptive to the time-varying load demand and DG output while minimizing the daily power loss costs. To improve the calculation efficiency, several linearization methods are introduced to formulate the dynamic reconfiguration as a mixed-integer linear programming problem, which can be effectively solved using off-the-shelf solvers. The effectiveness of the proposed approach is verified by the test results obtained on a modified IEEE 34 node test feeder. [ABSTRACT FROM AUTHOR]

Voltage dependent active and reactive power injections are used to improve the grid integration of distributed generators, such as photovoltaic systems. In state-of-the-art literature these power injections are considered during power flow calculations via an external loop, which requires to perform multiple (up to ten or more) power flow calculations in order to obtain one static operation point. In this paper it is shown how to integrate voltage dependent power injections into the nonlinear grid equations in order to solve for a static working point by means of performing one Newton power flow calculation. That makes the external loop unnecessary and save computational time. Furthermore, it is shown for a two-bus system that the integration of voltage dependent power injections into the nonlinear grid equations can exhibit ill-conditioned power mismatch functions. Therefore, a damped Newton method is used in order to avoid numerical oscillations. Simulations of the IEEE 118-bus test system and a real German 234-bus test system show that the damped method converges faster and is computationally more efficient than the external approach currently used in literature and state-of-the-art simulation tools in power systems. In addition, the implemented power flow algorithm is validated in the laboratory for a two-bus system and a numerical example of a low-voltage feeder is given. [ABSTRACT FROM AUTHOR]

Synchronous Machine-based Distributed Generations (SMDGs) are integrated into distribution networks due to their benefits. However, they may cause problems for protection systems, especially in radial distribution networks. In this paper, a coordination algorithm is proposed to modify Time Multiplier Setting (TMS) and pickup current settings of the protective devices, e.g. overcurrent relays, reclosers and fuses, in order to overcome conventional problems of installing SMDGs, e.g. nuisance tripping and fuses blowing, caused by the reverse fault currents of the SMDGs. The proposed algorithm employs the Fault Current Limiter (FCL), as well as re-coordination algorithm, to restore coordination of protection systems in radial distribution networks with high penetration of SMDGs. For this purpose, a multi-objective optimization algorithm is used to determine the minimum size of FCL and optimal setting of protection system. The algorithm is formulated based on hybrid genetic algorithm (GA) and linear programing (LP) method to reduce computation time. Simulations are carried out on a realistic distribution network, and the results demonstrate that the proposed method provides feasible and effective solutions for optimal coordination restoration, while minimizing the FCL size. [ABSTRACT FROM AUTHOR]