Islanded Network Research Articles

LOAD SHEDDING SCHEMES FOR ISLANDING DISTRIBUTION NETWORK OPERATION

One case of contingency or unplanned power outage occurs in the event of large mismatch between the power demand and the power generated. During overloads in islanded networks, the load curtailment applied to interruptible loads is often the only solution to keep them in operation. The loads participating in load shedding schemes experience minimal discomfort. This work proposes an approach to the load shedding schemes that can be employed in islanding distribution networks to guarantee the correct electrical system operation. This new proposed methodology includes the average and the priority shedding schemes and is based on a corrective load shedding optimizer (CLSO) algorithm. The CLSO evaluates and compares the network dynamic responses with the network frequency and voltage stability criteria for each distributed generation to optimize the amount of load shedding requirements. This work presents an in-depth investigation of the operation and robustness of the proposed method under various case studies on a typical IEEE distribution network. The results are then analysed and discussed.

GENERALISED GRID-FORMING VSC CONTROL FOR GRID CONNECTION AND ISLAND NETWORK

This study proposes a generalised grid-forming VSC control for grid connection and island network for distributed generations. The proposed control scheme is based on grid-forming direct voltage control to establish the AC voltage and frequency for island network, while it works as a controlled AC voltage source to regulate the active and reactive power flowing to the local load and AC grid during grid-connected operation. Strategy for fault current limiting is also proposed to overcome the overcurrent problem brought by the grid-forming direct voltage control. Simulation results during three-phase AC fault and transition from grid-connected operation to islanding operation are presented to confirm the feasibility and effectiveness of the proposed control strategy.

A Three-Phase Weather-Dependent Power Flow Approach for 4-Wire Multi-Grounded Unbalanced Microgrids With Bare Overhead Conductors

Conventional power flow algorithms assume that the network resistances and reactances remain constant regardless of the weather and loading conditions. Although the impact of the weather in power flow analysis has been recently investigated via weather-dependent power flow (WDPF) approaches, the magnetic effects in the core of Aluminum Conductor Steel Reinforced (ACSR) conductors have not been explicitly considered. ACSR conductors are widely used in distribution networks. Therefore, this manuscript proposes a three-phase weather-dependent power flow algorithm for 4-wire multi-grounded unbalanced microgrids (MGs), which takes into consideration the impact of weather as well as the magnetic effects in the core of ACSR conductors. It is shown that the magnetic effects in the core can significantly influence the power flow results, especially for networks composed of single-layer ACSR conductors. Furthermore, the proposed algorithm explicitly considers the multi-grounded neutral conductor, thus it can precisely simulate unbalanced low voltage (LV) and medium voltage (MV) networks. In addition, the proposed approach is generic and can be applied in both grid-connected and islanded networks. Simulations conducted in a 25-Bus unbalanced LV microgrid (MG) highlight the accuracy and benefit of the proposed approach, while its computation performance is tested in the IEEE 8500-Node network.

An efficient framework for integrating distributed generation and capacitor units for simultaneous grid‐connected and islanded network operations

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.

Research on power control strategy of household-level electric power router based on hybrid energy storage droop control

In the light of user-side energy power control requirements, a power control strategy for a household-level EPR based on HES droop control is proposed, focusing on the on-grid, off-grid and seamless switching process. The system operating states are divided based on the DC bus voltage information with one converter used as a slack terminal to stabilize the DC bus voltage and the other converters as power terminals. In the on-grid mode, the GCC and the HES are used as the main control unit to achieve on-grid stable operation, whereas in the off-grid mode, the PV, HES and LC are used as the main control unit at different voltages to achieve stable operation of the island network. Finally, a DC MG system based on a household-level EPR is developed using the PSCAD / EMTDC simulation platform and the results show that the control strategy can effectively adjust the output of each subunit and maintain the stability of the DC bus voltage.

An ensemble approach of classification model for detection and classification of power quality disturbances in PV integrated microgrid network

In this study, different Power Quality Disturbances (PQDs) in Photovoltaic (PV) integrated Microgrid (MG) network have been detected and classified using a voting method of ensemble classification model along with Discrete Wavelet Transform (DWT) analysis. The proposed ensemble classification model is useful to classify the most common PQDs (voltage sag, voltage swell, and harmonics) in islanded MG network, and different PQ transients in both grid-connected and islanded MG network. For this study, a PV integrated MG model has been developed in the Matlab/Simulink software environment with introduction of different PQDs. The result obtained reveals that the performance of proposed ensemble classification model-2 (combination of Bayesian net, Multi-layer perceptron (MLP) and J48 decision tree (JDT) classifiers) attains higher classification accuracy (100%) as compared to other ensemble classification model-1 (combination of Bayes net and MLP classifiers) and base classifiers such as Bayesian net, MLP and JDT. Further, the effectiveness of classifiers has been assessed using performance indices (PI) such as Kappa statistics, Mean absolute error (MAE), Root mean square error (RMSE), Precision, Recall, F-measure, and Receiver operating characteristics (ROC). From the results of PI, it can be concluded that the proposed ensemble model-2 outperforms ensemble model-1 and other base classifiers.

Understanding ecological groups under landscape fragmentation based on network theory

In the context of landscape fragmentation, a variety of ecological conservation theories have been proposed to maintain habitat connectivity. These theories focus on the connectivity of the ecological corridors in ecological space but ignore the community structure of ecological space. However, community structure is ubiquitous in ecological space. Our study predicted habitat quality of ecological patches by using an artificial neural network and species occurrence points. Then, the ecological space network (ESN) was proposed and constructed by taking large ecological patches and fragmented patches as habitat nodes. Based on island biogeography theory (TTIB) and network community detection, the ecological groups in the ESN were proposed and identified. They are considered to be collections of ecological land with close species connections. After that, the hierarchy of the ecological group was analyzed, and the existing policy was evaluated. The results show that there were 39 ecological groups in the ESN. The dendrogram of the hierarchy shows that all ecological groups can form five bigger ecological groups. The extent of the bigger groups proves that the ecological groups in the eastern part are closely connected. By analyzing the protection of ecological control lines on the linkages among ecological groups, we found that the existing policy could protect most of the ecological groups separately, but could not maintain connectivity among ecological groups, leading to habitat isolation. We believe that the concept of “ecological group” makes up for the lack of “habitat isolation” in the existing theory. The idea can understand the hierarchical structure of ecological space, which is conducive to the maintenance of ecological integrity.

Analysis of Renewable Integrated DG Investment Planning Based on Emission Cost

The prospect of distributed power generation investment planning (DGIP) is particularly important in island networks due to multiple reasons such as energy security, emissions, and renewable energy integration goals. Against this background, this article proposes a consideration that includes various types of DGIP models including renewable energy. The planning process includes an economic analysis that takes into account emissions costs, reliability and other related cost components. In addition, the variability and uncertainty of model parameters for distributed generation comprehensive sensitivity analysis of the impact of investment decisions. The ultimate goal is to determine the parameters that have an important impact on the decision-making process and quantify their degree of impact. The results show that uncertainty has an important impact on DG investment decisions. In fact, the degree of impact varies depending on the parameters. However, in general, ignoring or not fully considering the uncertainty and variability in model parameters is a quantifiable cost. The analysis made in this article is the most relevant to determine the need for special attention in planning practice the model parameters are very useful.

Scaling Laws of Collective Ride-Sharing Dynamics.

Ride-sharing services may substantially contribute to future sustainable mobility. Their collective dynamics intricately depend on the topology of the underlying street network, the spatiotemporal demand distribution, and the dispatching algorithm. The efficiency of ride-sharing fleets is thus hard to quantify and compare in a unified way. Here, we derive an efficiency observable from the collective nonlinear dynamics and show that it exhibits a universal scaling law. For any given dispatcher, we find a common scaling that yields data collapse across qualitatively different topologies of model networks and empirical street networks from cities, islands, and rural areas. A mean-field analysis confirms this view and reveals a single scaling parameter that jointly captures the influence of network topology and demand distribution. These results further our conceptual understanding of the collective dynamics of ride-sharing fleets and support the evaluation of ride-sharing services and their transfer to previously unserviced regions or unprecedented demand patterns.

Average dynamical frequency behaviour for multi-area islanded micro-grid networks

A micro-grid is a part of power system which able to operates in grid or islanding mode. The most important variable that able to give us information about the stability in islanded micro-grid network is the frequency dynamical responses. The frequency analysis for multi-area micro-grid network model may involve a complicated of mathematical equations. This makes the researcher intending to omit several unnecessary parameters in order to simplify the equations. The purpose of this paper is to show an approach to derive the mathematical equations to represent the average behavior of frequency dynamical responses for two different micro-grid areas. Both of networks are assumed to have non-identical distributed generator behavior with different parameters. The prime mover and speed governor systems are augmented with the general swing equation. The tie line model and the information of rotor angle was considered. Then, in the last section, the comparison between this technique with the conventional approach using centre of inertia (COI) technique was defined.

Optimal design and operation of an islanded water-energy network including a combined electrodialysis-reverse osmosis desalination unit

This paper proposes an optimization framework to simultaneously optimize the saline and freshwater water sources as well as decentralized renewable and conventional energy sources, which consequently results in an economic and efficient water-energy system operation. The inextricable links between water and energy systems are taken into considerations, and a mixed integer nonlinear programming formulation is used to solve the proposed optimization model. A hybrid electrodialysis-reverse osmosis is integrated in the water distribution system and its electricity consumption is minimized. Also, the day-ahead economic dispatch problem of the energy system incorporates the random behavior of solar and wind generation units, along with charging and discharging modes of battery storage systems. The outcomes of the proposed models highlight: 1) integrating the hybrid desalination module in the water-energy system will reduce peak demands by more than 30% if the water and energy systems are solely supplied by saline water and renewable energy sources, respectively; 2) presence of an extra water storage tank also decreases peak demands by 13%. The impact of key elements of the combined system such as pumps’ speeds, water tank constraints, and presence of renewable sources on the output cost, generated energy, and hydraulic parameters is investigated through case studies.

Impact of faults on bus stability on an island 330kV mesh network on the Nigerian grid

This study carried out an assessment on the impact of faults on bus stability along the Benin-IkejaWest-Aiyede-Oshogbo-Benin (BIAOB) 330kV island network. The sensitivity of BIAOB as a ring network on the Nigerian grid aroused the interest behind its choice for this study. The network parameters were collated from the National Control Centre, Oshogbo and the network was modeled on the MATLAB 2015 environment using the obtained data. A high reactive power flow was observed in all the buses while the lowest voltage profile was observed on the Line-Line-Line-Ground (L-L-L-G) simulated in bus 1. This is an indication that symmetrical faults have the greatest impact on the network. Further results showed that the BIAOB network has a better voltage profile when compared with other radial network from existing literature. The paper concluded by recommending the closure of more radial network on the grid in order to improve its performance.

Chiral topologically ordered insulating phases in arrays of interacting integer quantum Hall islands

We study networks of Coulomb-blockaded integer quantum Hall islands with even fillings $\nu=2k$ ($k$ being an integer), including cases with $2k$ layers each of $\nu=1$ fillings. Allowing only spin-current interactions between the islands (i.e., without any charge transfer), we obtain solvable models leading to a rich set of insulating $SU(2)_k$ topologically ordered phases. The case with $k=1$ is dual to the Kalmeyer-Laughlin phase, $k=2$ to Kitaev's chiral spin liquid and the Moore-Read state, and $k=3$ contains a Fibonacci anyon that may be utilized for universal topological quantum computation. Additionally, we show how the $SU(2)_k$ topological phases may be obtained also in an array of islands with $\nu=2k$ integer quantum Hall states and critical spin chains in a checkerboard pattern. The array and checkerboard constructions gap out the charge mode and additional "flavor" modes by virtue of their geometry. Furthermore, we find that a fine tuning of the system parameter is not needed in the checkerboard configuration and the $\nu=2$ case. We also discuss their bulk excitations, and show that their thermal Hall conductance is universal, reflecting the central charge $c=3k/(k+2)$ of the chiral edge modes.

The Integrated Energy System with Multiple Resources Integration in Future Distribution Network of Pelagic Clustering Islands

Sang, Z.; Huang, J.; He, J.; Fang, R.; Yan, J., and Lei, H., 2020. The integrated energy system with multiple resources integration in future distribution network of pelagic clustering islands. In: Yang, D.F. and Wang, H. (eds.), Recent Advances in Marine Geology and Environmental Oceanography. Journal of Coastal Research, Special Issue No. 108, pp. 42–47. Coconut Creek (Florida), ISSN 0749-0208.In the overall strategy of national security, the pelagic clustering islands have a special geostrategic significance as an important fulcrum and platform to safeguard national coastal defense and maritime rights and interests. Reliable energy supply is the artery of the development and construction of the pelagic clustering islands. Still, the current research is mostly aimed at the offshore islands, lacking relevant theories and methods for the pelagic clustering islands. Therefore, the current situation of the island grid research, with its limitations and defects when applied to the pelagic clustering islands, are inquired and analyzed in the paper firstly. Furthermore, an integrated energy system (IES) as a future distribution network of pelagic islands is proposed for the purpose of taking full advantage of the abundant renewable energy to optimize the configuration of multiple resources of the islands as a whole. The IES breaks the isolated development pattern of island grid, taking the islands as a whole, interconnected through the originality energy storage vessels (ESVs). Finally, the key technologies required to construct the IES of pelagic islands are summarized, and the design of ESVs as well as the case study are given in order to provide a reference for the development and construction of pelagic clustering islands in China.

Energy demand and quality management of standalone diesel/ PV /battery microgrid using reconfiguration

Power quality has become one of the most vital challenges in the planning of smart distribution grids due to popularity and myriad applications of power electronic devices. This paper introduces a new method based on network reconfiguration to efficiently deliver the energy demand of standalone Diesel/PV/Battery microgrids with improved power quality. The feeder reconfiguration is performed to decrease power loss, decrease the total harmonic distortion (THD), and improve voltage sag indices. Mathematical models of Diesel/PV/Battery standalone system are integrated with harmonic power flow algorithms to implement the concept. Reconfiguration algebraic equations along with nonlinearities introduced by Diesel/PV/Battery standalone system are solved by means of Non-Dominated Sorting Differential Evolution Algorithm (NDSDEA). The proposed methodology is carried out on a 33-bus standalone microgrid. The results have shown that reconfiguration not only improves the overall performance of the standalone energy system but also is effective to improve the quality of power delivered to the significant consumers. The method has both economic and technical benefits for such islanded networks.

Power Supply Reliability Assessment Including Island Division and Network Reconfiguration

After the power distribution system (DS) fails, a single power supply recovery method will cause certain loads to fail to recover in time. To improve the reliability of distribution systems with distributed generation, this paper proposes a two-stage network restoration reliability assessment method considering island division and network reconfiguration. In the process of network fault recovery, firstly, distributed generation is used to supply power to the load point of power loss, islanding of the network after fault with the aim of minimizing power loss. Then the residual network is reconstructed and optimized by considering the network loss and voltage quality. Finally, the improved ieee33 node network is simulated based on Monte Carlo simulation method. The results show that this method is superior and can realize real-time load transfer, reduce power loss, improve the reliability of DS and the economy of system operation, Considering the continuous change of the network structure, the running state of the system can be described more accurately.

A Simplified Optimization Model for Sizing Proton-Exchange Membrane Fuel Cells

The fluctuations in the cost of energy coupled with the gradual decrease in natural resources (i.e., oil, natural gas, coal) and the environmental issues caused by the extensive use of fossil fuels, demand the urgent need for the development of advanced and clean energy systems. The European Union has requested new measures to target climate and energy deterioration by developing renewable energy sources by 2030. The stochastic character of the energy sources and the fluctuation in demand for the energy systems poses a hindrance to achieving these targets. In this direction, hydrogen technology, that can be produced by electrolysis carried out in the presence of electricity from renewable energy systems can contribute as an energy carrier. It does not emit hazardous gasses and can be stored in the metal hydride canisters for future use via fuel cells (FCs). Modeling these systems is important for achieving their optimal size and to increase the penetration of renewable energy. They are beneficial both from the energy and economic point of view. For the accurate understanding of the hydrogen systems and especially FCs, it is important to understand the thermodynamic and electrochemical operating principles. In the present study, an integrated mathematical model is proposed concerning the electrical and thermal behavior of the FC. The model developed can simulate the operation of an FC by using the FC’s technical specifications. The reliability of the model was validated under three different hydrogen flow patterns applied in the experimental configuration (NEXA 1.2 kW). The proposed model was applied to a specific case study for the optimum sizing of an FC in terms of maximum hydrogen absorption. A hydrogen production pattern from electrolysis was used, and the excess energy from a wind park installed in an autonomous grid island network was utilized.

Coordinated Control Design for Reconnection of Islanded Generation

In countries with large hydroresources, generation formed by small hydropower plants may have a significant participation in distributed power generation. Small hydropower plants are connected at subtransmission or distribution level and usually are disconnected after contingencies and islanding. Islanded operation requires adequate system dynamics after disconnection and smooth reconnection. The increase in wind generation and photovoltaic sources requires that utilities consider these sources in islanded operation. In this paper, the design of coordinated controllers for reconnection of distributed generation including hydro- and wind power plants after islanding is considered. The design method is based on constrained optimal control, which allows the design of structured controls such as PI, PID and decentralized. The proposed method is applied to a test system with two small hydropower plants and a wind farm. The results show that the proposed method provides a systematic design approach to ensure smooth reconnection of the islanded network to the main network.

Island networks: Transformations of inter-community social relationships in the Lesser Antilles at the advent of European colonialism

The Caribbean Sea was a conduit for human mobility and the exchange of goods and ideas during the whole of its pre-colonial history. The period cal. AD 1000-1800, covering the Late Ceramic Age and early colonial era, represents an archaeologically understudied time during which the Lesser Antilles came under increasing influence from the Greater Antilles and coastal South America and participated in the last phase of indigenous resistance to colonial powers. This article summarizes the results of the Island Network project, supported by the Netherlands Organisation for Scientific Research (NWO) in which a multi-disciplinary set of archaeological, archaeometric, geochemical, GIS, and network science methods and techniques have been employed to disentangle this turbulent era in regional and global history. These diverse approaches reveal and then explore multi-layered networks of objects and people and uncover how Lesser Antillean communities were created and transformed through teaching, trade, migration, movement, and exchange of goods and knowledge.

Formation and dissolution of conductive channels in an Ag2S-islands network

A network that shows dynamical change in response to each input pattern works as a reservoir. In this study, we propose to use a network of Ag2S islands for reservoir computing. Input of a small number of electrons to an Ag2S island from a neighbored island causes Ag nanowire growth, which eventually connects the two islands. Shrinkage of an Ag nanowire also occurs depending on the distribution of a local electric potential. Thus, growth and shrinkage of Ag nanowires among Ag2S islands shows dynamical change in conductive channels responding to input bias, which is demonstrated by an Ag2S-island network surrounded by input/output electrodes. The Ag2S islands that are electrically connected to a surrounding electrode are identified using a conductive-atomic force microscope, confirming the operating mechanism.