Islanded Mode Of Operation Research Articles

Wavelet-Based ensembled intelligent technique for advanced fault detection and classification in AC microgrids

This research introduces a novel intelligent protection technique for microgrids, leveraging Discrete Wavelet Transform (DWT) and an Ensemble Bagged Decision Tree (EBDT) classifier for precise fault detection and classification across various scenarios. Non-stationary voltage and current signals are analysed using DWT to extract wavelet detailed coefficients, which are then used to compute the energy of these coefficients as input features for the EBDT. The hyperparameters of the EBDT are optimized using a random search algorithm to enhance robustness in fault classification. The proposed protection scheme’s efficacy is validated on a modified IEC test microgrid model, incorporating both inverter-interfaced Distributed Generators (DGs) and synchronous DGs, under different fault conditions simulated in the MATLAB/SIMULINK environment. Results demonstrate that the method is both fast and accurate, achieving fault detection and classification accuracies of 100% in both grid-connected and islanded modes of operation. The performance of the proposed model is benchmarked against state-of-the-art methods, including Decision Tree and Random Forest classifiers. Additionally, the robustness of the proposed technique is confirmed under conditions of DG uncertainty and in the presence of noise. The effectiveness of the technique is assured across various fault conditions, and it is further validated in an OPAL-RT real-time environment. This study significantly enhances the reliability and resilience of microgrid protection systems, offering a robust solution for real-time fault management, which is crucial for the stability of modern power networks integrating renewable energy sources.

Energy management system for multi interconnected microgrids during grid connected and autonomous operation modes considering load management

This study focuses on improving power system grid performance and efficiency through the integration of distributed energy resources (DERs). The study proposes an artificial intelligence (AI) based effective approach for economic dispatch and load management for three linked microgrids (MGs) that operate in both grid-connected and autonomous modes. A day-ahead scheduling method is suggested to calculate the optimal set points for various energy sources in MGs considering various system constraints for safe operation. In addition, a load management approach that shifts the controllable loads from one interval to another is applied to reduce the operating cost of MG. To handle the optimization challenges of energy scheduling and load shifting such complexity and non-linearity, an advanced meta-heuristic method known as the one-to-one based optimizer (OOBO) is used. Overall, the paper proposes a viable and efficient methodology for economical distribution in linked microgrids, which takes advantage of renewable energy resources and incorporates scheduling optimization via the OOBO algorithm. The proposed energy management strategy enhances the system performance, increases energy efficiency, and reduces the daily operational cost by 1.6% for grid connected mode and by 0.47% for islanded operation mode.

A novel differential protection scheme for AC microgrid based on loss function

Differential protection stands out as the optimal choice for protecting AC microgrids, compared to overcurrent and distance-based schemes, because of its adaptability to different network topologies, ability to manage bi-directional power flow, and better selectivity for system transients and variable fault current. However, high impedance faults, time synchronization error, and high bandwidth communication requirements are significant challenges faced by differential protection schemes. Considering such issues, this paper has proposed a novel differential protection scheme based on loss function (Percentage Bias Error), evaluated by using line's both end superimposed positive and negative sequential currents magnitude, which enhances the sensitivity in identifying internal fault that occurs in either grid-connected or islanded microgrid mode of operation. Its effectiveness is validated on ring and radial distribution networks with high impedance fault (500 Ω) at different fault locations. Additionally, the relaying scheme is stable under different system transients, CT error in noisy environments, and robust for time synchronization error. Moreover, the proposed scheme is compared with the existing techniques to illustrate its high sensitivity, fast operation (within one cycle), and high accuracy. The proposed scheme is simulated in a MATLAB Simulink environment, and results are validated using a laboratory-level hardware setup.

Privacy-preserving distributed frequency control for AC microgrids with constrained communication

Distributed control of AC microgrids is one of the most popular methods in the islanded operation mode. Whereas, most of the existing studies either do not consider the potential threat of privacy security or rely on the assumption of ideal communication networks. To this end, this paper presents a novel privacy-preserving distributed secondary frequency control strategy for the privacy protection problem of an islanded AC microgrid with constrained communication. The key contributions of this paper are threefold. (1) Different from the existing privacy-preserving approaches used in AC microgrids, a time-varying function is introduced to mask interactive information such that the frequency cannot be reconstructed by malicious attackers. (2) An event-triggered communication scheme is employed to cope with the constrained communication environment. (3) A privacy-preserving distributed event-triggered control strategy with communication delay is developed such that the frequency restoration and active power sharing of the microgrid are guaranteed. Moreover, the maximum communication delay that the proposed control can withstand is analyzed. Simulation results show the properties of the privacy preservation, the decrease of communication load, and the bounded communication delay allowed in the proposed control strategy.

Techno-economic microgrid design optimization considering fuel procurement cost and battery energy storage system lifetime analysis

The importance of microgrids (MGs) lies in their capacity to enhance energy reliability, integrate renewable resources, and bolster resilience, yet their optimal design and sizing pose intricate challenges in balancing investment and operational cost while dispatching the MG equipment efficiently. This paper presents the optimal MG design problem formulated as an integer linear program (ILP) aimed at minimizing total investment and operational cost of MG as well as optimal hourly dispatch of MG asset over the project lifetime. Furthermore, a comprehensive analysis of the fuel procurement cost and the impact of ESS technical parameters, such as depth of discharge (Dod), ESS lifetime, and battery C-rate, on the optimal MG design, ESS lifetime and relevant costs is presented in this work for a MG operating in islanded and grid-connected modes. The simulation results demonstrate that the optimal design of a MG with the maximum load demand of 300 kW operating in the grid-connected mode can save about 28 k$ equivalent to 14% in total annual cost compared with the islanded mode operation thanks to the flexibility provided by the utility purchases and efficient MG equipment sizing. This study’s unique contributions provide significant insights into the practical implications of MG design optimization, potentially influencing regulatory policies and business strategies.

Coordination of SRF-PLL and Grid Forming Inverter Control in Microgrid with Solar PV and Energy Storage

Recently, there has been a huge advancement in renewable energy integration in power systems. Power converters with grid-forming or grid-following topologies are typically employed to link these decentralized power sources to the grid. However, because distributed generation has less inertia than synchronous generators, their use of renewable energy sources threatens the electrical grid’s reliability. Suitable control approaches for ensuring frequency and voltage stability in the grid-connected form of operation are established in this study, which offers dynamic, seamless power switching in the islanded mode of operation. In this research, effective Phase Locked Loop (PLL) techniques for grid-forming (GFM) and grid-following (GFL) converters are designed to achieve a smooth transition from grid-tied to islanded mode of operation. In this work, PLL configurations are implemented while considering the active and reactive power, frequency, voltage, and current parameters of the system, and ensuring voltage and frequency stability. The simulation results in a microgrid network that ensures a smooth transition of power transfer while switching between modes of operation, and supports the voltage and frequency stability of the system.

Optimal configuration of distributed energy storage considering intending island recovery in faulty distribution networks

With the rapid development of distributed generation, represented by photovoltaic power, the access of a large number of distributed generation poses threats to the security and reliable operation of islanded distribution networks. However, relying on the distributed energy storage system can stabilize the island power supply, which can effectively improve the reliability of the island distribution network. To this end, under the premise of knowing photovoltaic output and load forecast curve, this paper proposes a distributed energy storage optimization configuration method in the active islanding operation mode of multi-source distribution network, which satisfies the “N-1″ safety criterion. First, this paper establishes an optimization configuration model for distributed energy storage with multiple objectives, including minimizing the load shedding in the non-fault loss of power zone, the initial investment cost of distributed energy storage, the node voltage deviation and the system frequency offset. Then, aiming at the islanded power flow calculation process mentioned above, an improved trust region algorithm is proposed, and integrating this method with the harmony search algorithm and ”N-1″ safety criterion solves the model. Finally, the IEEE 33-node distribution system is used to test the performance of the proposed algorithm. The results show that the proposed improved trust region algorithm has the advantages of fast convergence speed and short time-consumption compared with the traditional trust region algorithm. And the proposed optimization configuration scheme for distributed energy storage can satisfy the “N-1″ safety criterion of the distribution network under different fault scenarios.

Smooth Transition Control Strategy for Operation Modes of Optical Storage Microgrid based on VSG

Addressing the challenge of suppressing voltage and frequency oscillations during mode transitions and achieving smooth transitions between grid-connected and islanded operation modes in peer-to-peer structured optical storage microgrids, is an urgent technical issue. This paper proposes a control strategy for smooth mode transitions based on numerical soft starters, focusing on the dynamic characteristics of voltage and frequency in optical storage microgrids during grid-connected and islanded operation modes. The numerical soft starter smoothens the input reference value of the current inner loop, reducing the impact of transient surge current on the current inner loop during transitions, thus ensuring the oscillations of bus voltage and frequency during microgrid mode transitions. In islanded operation mode, a VSG control strategy is introduced by constructing a small signal model to analyze the frequency response characteristics of the system under different inertia and damping characteristics, setting appropriate control parameters to provide strong frequency support for the system during islanded operation. Finally, an optical storage microgrid system is established using Matlab/Simulink to conduct simulation experiments under conditions such as grid-connected/islanded mode transitions, load fluctuations, and sudden changes in photovoltaic output power, validating the effectiveness of the proposed smoothing strategy.

Fault identification, classification, and localization in microgrids using superimposed components and Wigner distribution function

The integration of Distributed Energy Resources (DERs) into distribution grids has become increasingly feasible and sustainable due to the development of microgrids. However, the development of an effective protection strategy remains a challenge in the implementation of microgrids. To address this challenge, this paper presents a simple and novel microgrid protection method based on superimposed components, Wigner distribution function (WDF) and alienation index-based. The proposed method develops a new fault detection index (FDI) by applying the alienation coefficient and WDF on a superimposed current signal to detect faulty events in the microgrid. The scheme is inherently phase segregated because the FDI is obtained for each phase individually. In addition, the proposed strategy introduces a new fault zone identification method based on the superimposed positive sequence reactive power (SPSQ). After obtaining the complete fault information, a relevant trip signal is generated to isolate the faulty section from the rest of the grid. The proposed methodology is evaluated through simulations using MATLAB/SIMULINK software. Various fault types, with varying parameters are simulated to validate the proposed approach. The results indicate that the proposed methodology is capable of recognizing, classifying, and locating all fault types in both grid-connected and islanded modes of operation.

Novel protection method for AC microgrids with multiple distributed generations using Unscented Kalman filter

Traditional protection methods were inadequate in multiple distributed generations (MDG) microgrids due to the bidirectional power flow/high fault current in the grid-connected (GC) mode, and reduced fault current in the islanded (ID) mode. Therefore, a reliable and robust protection method has become of paramount importance for such MDG-based microgrids. This article suggests an Unscented Kalman filter (UKF) to detect, classify, and locate faults in such MDG-based microgrids. Initially, the harmonic content is generated from the UKF-estimated current signal to compute the total harmonic RMS factor (THRF). Then the changes in the THRF of each phase are cross-checked to a pre-specified threshold level to distinguish the fault conditions. Furthermore, the cumulative covariance-dependent reactive energy (CCDRE) is computed from both the estimated state and covariance matrix of voltage and current signals provided by UKF. Finally, the directional trends in the CCDRE are used to identify the fault zone in the microgrids. The effectiveness of the proposed method is validated through ample simulations on CIGRE and IEC 61,850–7–420 microgrid test system via MATLAB® Simulink. The results illustrate that the presented strategy is robust in both the GC mode and the ID mode of operation in meshed and radial topologies with 99.9% accuracy.

Performance Evaluation of Microgrid Management Function in KERI pilot plant

As usual, the microgrid operates in grid-connect mode, but, when a fault occurs in the upstream grid, it should disconnect and shift into islanded operation mode. In grid-connect mode, the controlling power flow at PCC is necessary management function rather than the frequency and voltage. However, the controlling the frequency and voltage is asked in islanded mode. To achieve these management goals appropriately, the cooperative control strategy among microsources is needed. This supervisory control action is executed at MMS. In this paper, the cooperative control strategy of microgrid components is presented and the management performance is evaluated by using microgrid pilot plant. The pilot plant consists of the PV, PV/Wind Hybrid system, BESS, diesel generators, and RLC loads, which are connected to 380V low voltage lines. The test results show that the proper control strategy can ensure stability of microgrid in islanded mode and maintain the power flow of PCC at desired value successfully.

New Control Algorithms for Microgrids Based on Microturbines

This paper analyses the performance of a low voltage microgrid, based on microturbines, and presents new control algorithms to improve the efficiency and reliability of microgrids. Due to the importance of islanding and focusing on the efficiency and the harness of the heat of the exhaust gasses in islanded operation mode, a new control algorithm has been developed. Additionally, a new control strategy is presented for the seamless transition between islanded and grid connected operation modes based on changing the control algorithms of the microturbines. synchronization, have been studied in [1]-[2]. Moreover, automatic fault detection in the utility network for the necessary transition between connected and islanded mode has been studied in [3]. However, it is still necessary to develop control strategies applied to generation systems to automatically transition between both modes with reduced voltage and current transients. The new proposed control algorithms are tested by simulation using a low voltage network fed by 5 microturbines. Lasseter model is used to represent the dynamic behaviour of the microturbines. The paper shows the simulation results and the main conclusions of the validation process. The new proposed control algorithms are tested by simulation using a low voltage network fed by 5 microturbines. Lasseter model is used to represent the dynamic behaviour of the microturbines. The paper shows the simulation results and the main conclusions of the validation process.

Preliminary steady state and dynamic analysis of a microgrid system

The objective of this paper is to analyse the steady state and dynamic behaviour of a MicroGrid system containing one microturbine generating Combined Heat and Power feeding some small local loads in islanded mode of operation. Future operating scenarios were also analysed and simulated, namely considering the installation of photovoltaic panels near consumers

The Performance and Robustness of Power Protection Schemes for Grid‐Connected PV Systems Under Varied Smart Inverter Controllers

The increasing use of inverter‐based distributed generation requires a comprehensive study of its effects on fault analysis and the effectiveness of protection systems in distribution networks. This study examines the impact of different inverter control modes on multiple types of protective relay schemes. These include different overcurrent relay (OCR) schemes, both standard and nonstandard tripping characteristics, optimal coordination approaches, and different grid operation scenarios. The investigation is conducted through the utilization of grid‐connected and islanding operation modes, with fault resistance values of 0 and 5 Ω. The study is carried out on a 14‐bus CIGRE network which includes two photovoltaic (PV) farms with a capacity of 10 MVA each. The research provides several significant contributions, including the analysis of fault current contributions, examination of issues in OCR protection, investigation of the influence of fault impedance levels on OCR performance, evaluation of ideal coordination methods, and carrying out a comparative analysis utilizing optimization technique by using the water cycle optimization algorithm (WCA) and the particle swarm optimization algorithm (PSO). In addition, to guarantee the robustness of the suggested protection strategy, this work adopts a hardware‐in‐the‐loop approach. The OMICRON‐256 system is utilized to carry out real‐time testing on a SIPROTEC 7SJ62 multifunction protection relay, which validates the effectiveness of the proposed method in protecting microgrids under different PV control strategies. The total operating time for the nonstandard tripping scheme was 12.077–12.3003 s for PSO and WCA, respectively, while for the standard tripping scheme, it was 12.1226 and 12.1564 s. Moreover, these findings offer practical insights that can assist operators in effectively designing the power networks with grid‐connected PV systems by showing OCR miscoordination and no tripping events in power systems with PVs under inverters controllers.

Estimation of Area Frequency Response in Island Operation Mode by Utilizing Interconnected Power System Measurements

Estimation of Area Frequency Response in Island Operation Mode by Utilizing Interconnected Power System Measurements

Multiple Control Strategies for Distributed Battery Energy Storages in Microgrid DC Fast Charging Stations to Improve Load Voltage Variations, Mutual Power Exchange with the Grid and Islanded Mode Operation

Multiple Control Strategies for Distributed Battery Energy Storages in Microgrid DC Fast Charging Stations to Improve Load Voltage Variations, Mutual Power Exchange with the Grid and Islanded Mode Operation

Advanced hardware-in-the-loop testing chain for investigating interactions between smart grid components during transients

Aiming to investigate the possible interactions between smart grid components during transient events, an advanced hardware-in-the-loop testing chain for the validation of novel smart grid solutions is proposed in this paper. The testing chain is directed towards both academic and industrial hardware-in-the-loop users, e.g., relay manufacturers, power electronics manufacturers and DSOs/TSOs. All different hardware-in-the-loop simulation setups, ranging from simple local simulations up to more elaborate, power hardware-in-the-loop simulations, are discussed, forming a solid testing chain. The interactions during transients, which can be investigated at each step, are analytically derived to emphasize the insights that each step can offer to the performed component validation. To highlight the applicability of the proposed hardware-in-the-loop testing chain, when validating smart grid components, a case study concerning the testing of a microgrid transition algorithm, between the interconnected and islanded modes of operation, is considered for a real microgrid. Particularly, the interactions between an advanced grid-forming inverter and the already existing grid-following inverters of the microgrid are investigated during normal and abnormal grid conditions, while following the appropriate steps of the proposed testing chain.

Optimal single settings based relay coordination in DC microgrids for line faults

A novel time–current-rate-based inverse characteristic curve for relays in a DC microgrid is proposed in this paper. Line current rise rate is used as actuating quantity, ensuring quick line fault clearing (relay operating time is in order of a few μs). The advantage of using line current rise rate as actuating quantity is that for a line short-circuit fault, it does not vary significantly for grid-connected and islanded modes of operation and varying network topologies of DC microgrid. Consequently, using the proposed characteristic, a single set of optimal relay settings is obtained using an optimization solver in MATLAB. The obtained settings ensure reliable and selective coordination between primary and backup relays for various pole-to-ground and pole-to-pole line faults under different operating conditions with multiple sources in two different 4-bus 400V low voltage DC microgrids. The maximum relay operating time for a high resistance fault with the proposed curve is 394.9μs for the first considered low voltage DC microgrid. Simulations in the Real Time Digital Simulator and comparisons with previous schemes (one comparison on the second considered DC microgrid), conventional standard inverse, and extremely inverse curves for DC microgrid protection indicate the effectiveness of the proposed scheme.

Enhanced four-port dual-active-bridge converter employing power decoupling capability for DC microgrid islanding mode operation

Enhanced four-port dual-active-bridge converter employing power decoupling capability for DC microgrid islanding mode operation

Collaborative Optimization Scheduling of Resilience and Economic Oriented Islanded Integrated Energy System under Low Carbon Transition

With the development of new energy sources and the increase in the installed scale of energy coupling equipment, the low-carbon transformation of the energy supply of the integrated energy system (IES) has a serious impact on the reliability of the IES supply, and there is an urgent need for a reasonable and accurate assessment and trade-off between the IES resilience and economics. In this regard, this paper models the overall optimization of the resilience and economic configuration and operation scheduling of the IES in the islanded operation mode after grid faults, proposes a two-layer optimization strategy model of resilience and economy, and solves the unit configuration, coupled output characteristics, and optimal scheduling of the islanded IES using the Markov decision-making process and forbearing stratified sequencing method, and evaluates and analyzes the resilience and cost of the various types of IES configuration schemes. Resilience and cost are also evaluated and analyzed. Finally, an example analysis is carried out in an electric-heat-cooling integrated energy system. The results show that the proposed two-tier optimization strategy model can optimize the IES configuration scheme and coordinate the scheduling of each equipment, and the overall annualized cost of the energy system decreases by CNY 45.21 thousand, or a percentage decrease of 5.24%, compared to the same configuration of the conventional strategy. The typical day toughness index improved by 7.33%, 7.56%, and 13.01% in the spring, summer, and autumn, respectively.