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The operational performance of grid‐connected active front‐end converters (AFEs) faces challenges arising from the intricate interplay among phase‐locked loop (PLL) non‐linearities, grid impedance, and conventional control strategies, resulting in compromised stability. This study introduces a refined approach to dynamic model predictive control (MPC) by integrating recursive least squares (RLS) for the precise estimation of physical model parameters, thereby addressing stability concerns. Unlike conventional methodologies, the proposed enhanced RLS‐based MPC approach, equipped with an auto‐tuning feature, allows for the design of controllers without a prerequisite understanding of exact external dynamics. Notably, this technique exhibits exceptional disturbance rejection capabilities. The evaluation of the cost function at each sampling interval facilitates the determination of optimal switching states based on predicted variables. Gate pulses for the switches of the AFEs are generated accordingly. Employing a simulation platform, the proposed control structure's performance across varied conditions is comprehensively assessed, encompassing alterations in grid impedance and system non‐linearities. The method adeptly integrates inherent non‐linearities within the system, showcasing exceptional robustness in diverse dynamic scenarios. To further substantiate the efficacy of the proposed control system over conventional approaches, simulation results are validated using a laboratory hardware platform equipped with Typhoon HIL and dSPACE real‐time emulators, providing tangible evidence of the proposed control system's effectiveness in real‐world hardware setups. The multifaceted approach, encompassing precise parameter estimation, predictive control, auto‐tuning, disturbance rejection, robust design, and real‐time evaluation, collectively establishes a resilient foundation for enhancing and maintaining the overall stability of the system across diverse operating scenarios. [ABSTRACT FROM AUTHOR]

This article investigates the impacts of proper modeling of the wake effects and wind speed delays, between different wind turbines' rows, on the dynamic performance accuracy of the wind farms models. Three different modeling scenarios were compared to highlight the impacts of wake effects and wind speed time-delay models. In the first scenario, wind wake effect and time delay are ignored. Consequently, all wind turbines are assumed subjected to the same wind speed profile. The second scenario considers the wind wake effect, and it was modeled by reducing the incident wind speed values by 0.5 m/s from one row to the next row facing the wind. The last scenario, the proposed model, used the wind wake effect model developed for wind turbines micrositting applications and considered the effect of the delay time between the wind speed profiles incident on the different wind turbines' rows. (Contains 17 figures.)

Currently, the architecture of Line Current Differential Relays (LCDRs) is designed to respond to internal faults on the protected line using local and remotely-communicated current measurements. However, this architecture cannot distinguish between real faults and cyber-induced attacks whose goal is to cause false tripping of the line protected by the LCDR. In this paper, we propose an Anomaly-Based Scheme (ABS) for detecting false-tripping attacks against LCDRs, in the form of relay attacks, replay attacks, general false-data-injection attacks, and time-synchronization attacks. The ABS employs the Isolation Forest algorithm, which is trained on features determined from local current measurements to confirm real faults and differentiate them from false-tripping attacks. No trip command will be issued unless the sensed fault is confirmed as a non-attack by the ABS. The performance of the proposed ABS is tested and validated using the IEEE 9-bus benchmark in PSCAD/EMTDC environment. Simulation results show that the proposed ABS: (i) can accurately detect different categories of cyberattacks, (ii) does not negatively impact the accuracy of the fault-detection function, and (iii) is robust to the change in the power system’s operating point. [ABSTRACT FROM AUTHOR]

This paper presents an improved feedback controller and optimal management system to operate a battery storage system in a microgrid. The aim is to optimize the storage usage by reducing the battery degradation. The feedback controller regulates the battery current to track a reference despite uncertainties. It includes a disturbance observer to compensate unknown uncertainties and improve its tracking performance. The current reference is carried out using a management system based on the power balance in the microgrid connected to the main grid. Furthermore, the management system uses a coefficient to operate the battery depending on its constraints and the grid electricity price. This allows online optimization of the battery operation based on the price variations to reduce its degradation. The control and management systems are validated by simulation and the results are provided to demonstrate their effectiveness. Furthermore, experimentation is conducted to evaluate the control performance. The results show that the proposed feedback controller and disturbance observer provide better mean absolute error (0.0846) for the current tracking compared to only feedback controller (0.2073) and conventional proportional-integral controller (0.1126). Moreover, the proposed management system represents a reduction in the battery degradation by 74.56% compared to the conventional management system. [ABSTRACT FROM AUTHOR]

This paper proposes a new approach for optimal operation of an Electric Vehicle (EV) battery-swapping station (BSS) based on Rolling-Horizon optimization (RHO). The BSS has several swapping bays such that each can accommodate an EV for swapping single or multiple battery units. The proposed BSS model considers serving different types of EVs using a heterogeneous battery stock. The charging of the depleted batteries (DBs) is performed using continuously controlled variable chargers which makes it more flexible for providing grid services. While previous studies focused on day-ahead modeling of BSSs, our study considers BSS dynamic scheduling. The goal is to maximize the daily profit using an RHO mechanism to provide optimal swapping and charging/discharging processes. The problem is defined as mixed-integer nonlinear programming (MINLP), then it’s linearized into a mixed-integer linear problem (MILP) to reduce the computational complexity. To predict the EV’s swapping demand, a long short-term memory (LSTM) recurrent neural network is utilized as a time series forecasting engine. The proposed model is validated through a set of case studies comparing the LSTM-based RHO mechanism versus unscheduled operation and day-ahead scheduling. Simulation results demonstrate that the proposed dynamic scheduling mechanism increases the profit between 10% and 25.7% compared to the day-ahead scheduling. Furthermore, the number of EVs served using the proposed approach increases between 11% and 14% compared to the day-ahead model. [ABSTRACT FROM AUTHOR]

Keen interest in the development and utilization of wind-based distributed generations (DGs) has been currently observed worldwide for several reasons. Among those is controlling the emission of environmentally harmful substances, limiting the growth in energy costs associated with the use of conventional energy sources and encouraging the independent power producers for participation in the electricity market system. One of the most important issues is to quantitatively assess the impact of such type of DGs on the distribution system reliability. This paper presents a probabilistic technique to evaluate the distribution system reliability utilizing segmentation concept and a novel constrained Grey predictor technique for wind speed profile estimation. Index Terms--Distributed power generation, distribution system reliability, uncertainty, wind power.

Islanded microgrids have specific features that should be considered in their harmonic analysis. First, microgrids’ distributed generators (DGs) are typically droop-based, and accordingly, the steady-state frequency is different from the nominal one. This affects the harmonics produced by DGs and nonlinear loads. Second, there is no slack bus, which affects the distribution of the fundamental currents, and thus, the harmonics. Third, DGs usually have voltage source converters (VSCs) as an interface for energy transfer to microgrids. The control structures and output filters of DGs affect the voltage and current distortions, and hence, they should be considered in the harmonic analysis. This paper introduces a sequential algorithm for the harmonic analysis of droop-based islanded microgrids that considers these features. For being accurate and yet computationally efficient, DGs’ cascaded control loops are modeled in the proposed algorithm through their transfer functions. Due to its quadratic convergence, a Newton-based approach is proposed for modeling nonlinear loads that relies on an analytical Jacobian matrix to further speed up its convergence. The meritorious advantage of the proposed approach is the consideration of the mutual coupling between different harmonics. The effectiveness of the proposed algorithm is confirmed through comparative evaluations with time-domain simulations. [ABSTRACT FROM AUTHOR]

This paper presents a new control strategy for enhancing the dc voltage regulation and the transient response in the multi-terminal VSC-HVDC system by ensuring swift power-sharing among converters when encountering large disturbance such as converter loss or ac fault at one of the converter stations. The quick power sharing can be realized using direct power control (DPC) since it has a merit of fast power dynamic response. On the other hand, to limit the converter current during ac fault, a new coordination strategy between DPC and vector current control (VCC) is proposed. Furthermore, a new simplified model of the MTDC system is developed to study the performance of DPC in enhancing the dc voltage dynamics response analytically. The time-domain simulation of the detailed model of the four converter stations MTDC system verify that the proposed control strategy significantly reduces the overshoot in the transient dc voltage response following an outage or ac fault. As a result, together with the droop gain selection for the maximum permissible steady-state dc voltage deviation, the proposed control strategy can help to reduce the size of the dc chopper in the MTDC grid or even avoiding it. Moreover, the comparative analysis based on time-domain simulation depicts that the proposed simplified model has the same dc voltage response compared to the detailed model of the MTDC system except for a steady-state error of 0.47% and a little bit longer settling time (1.5 ms) at transient. [ABSTRACT FROM AUTHOR]

This paper develops a new control strategy for voltage source converter (VSC) based multi-terminal high voltage dc (MT-HVDC) grids for enhancing the mutual frequency support between MT-HVDC interconnected asynchronous ac systems. The existing droop control structure of VSCs is augmented with an additional feedback voltage-based loop that generates a voltage shifting term to be added to the original dc voltage reference. The addition of this integrator-based controller nullifies the difference between voltage errors seen at adjacent converter stations. This action helps to overcome inaccuracies in the mutual frequency support caused by the uneven voltages across a dc system. The proposed strategy uses only local variables for the continuous-time control; thus, it does not rely on a high-bandwidth communication network, and its performance is not affected by the change of ac systems’ parameters. Modal analysis is carried out to investigate the stability of the proposed controller. Finally, comprehensive simulation studies are used to verify the proposed strategy’s performance and compare it with recently reported alternative controllers. [ABSTRACT FROM AUTHOR]

The wide integration of all battery electric buses (BEB) in the operation of public transit services is identified as one of the most promising means toward decarbonizing public transport systems. In response, public bus transit (PBT) and utility grid operators are currently in need of developing analytical techniques that enable them to conduct tradeoff analyses for the many available options of BEBs, charging infrastructure, and their associated system impacts. To that end, this article proposes a systematic and effective technique for feasibility check and configuration design of electrified PBT fleets without the need for the sophisticated optimization toolbox and high performance computing. The configuration design aims at determining the number of BEBs and their on-board battery capacities to meet the PBT prespecified schedule under different sizes of chargers. The proposed model is tailored for BEBs designed to either boost their batteries on-route at intermediate bus stations using fast chargers (opportunity charging) or charge while parked at the depot (in-depot charging). The developed model is also utilized to generate the aggregated power demand profiles of electrified PBT fleets under different charging practices. Based on the generated power demand profile, a lifecycle cost analysis is conducted to compare BEB-based PBT options to their diesel counterparts. [ABSTRACT FROM AUTHOR]

This paper addresses the low-frequency relative stability problem in paralleled inverter-based distributed generation (DG) units in microgrids. In the sense of the small-signal dynamics of a microgrid, it can be shown that as the demanded power of each inverter changes, the low-frequency modes of the power sharing dynamics drift to new locations and the relative stability is remarkably affected, and eventually, instability can be yielded. To preserve the power sharing stability, an adaptive decentralized droop controller of paralleled inverter-based DG units is presented in this paper. The proposed power sharing strategy is based on the static droop characteristics combined with an adaptive transient droop function. Unlike conventional droop controllers, which yield 1-DOF tunable controller, the proposed droop controller yields 2-DOF tunable controller. Subsequently, the dynamic performance of the power sharing mechanism can be adjusted, without affecting the static droop gain, to damp the oscillatory modes of the power sharing controller. To account for the power modes immigration at different loading conditions, the transient droop gains are adaptively scheduled via small-signal analysis of the power sharing mechanism along the loading trajectory of each DG unit to yield the desired transient and steady-state response. The gain adaptation scheme utilizes the filtered active and reactive powers as indices; therefore, a stable and smooth power injection performance can be obtained at different loading conditions. The adaptive nature of the proposed controller ensures active damping of power oscillations at different operating conditions, and yields a stable and robust performance of the paralleled inverter system. Index Terms--Adaptive control, decentralized control, distributed generation (DG), microgrid, parallel operation, power sharing stability.

This paper presents an adaptive discrete-time grid-voltage sensorless interfacing scheme for grid-connected distributed generation inverters, based on neural network identification and deadbeat current regulation. First, a novel neural network-based estimation unit is designed with low computational demand to estimate, in real-time, the interfacing parameters and the grid voltage vector simultaneously. A reliable solution to the present nonlinear estimation problem is presented by combining a neural network interfacing-parameters identifier with a neural network grid-voltage estimator. Second, an adaptive deadbeat current controller is designed with high bandwidth characteristics by adopting a delay compensation method. The delay compensation method utilizes the predictive nature of the estimated quantities to compensate for total system delays and to enable real-time design of the deadbeat controller. Third, the estimated grid voltage is utilized to realize a grid-voltage sensorless average-power control loop, which guarantees high power quality injection. Theoretical analysis and comparative evaluation results are presented to demonstrate the effectiveness of the proposed control scheme. Index Terms--Deadbeat current control, digital control, distributed generation (DG), grid-voltage sensorless control, neural network identification, pulsewidth modulated (PWM) inverters.

This paper presents a robust high bandwidth discrete-time predictive current control scheme for voltage-source pulsewidth-modulated (VS-PWM) converters. First, to achieve high bandwidth current control characteristics, a digital predictive current controller with delay compensation is adopted. The compensation method utilizes a current observer with an adaptive internal model for system uncertainties. The predictive nature of both the current observer and the internal model forces the delays elements to be equivalently placed outside the closed loop system. Second, to ensure perfect tracking of the output current in the presence of uncertainties and providing means for attenuating low- and high- frequency system disturbances, the frequency modes of the disturbances to be eliminated should be included in the stable closed loop system. Toward this, an adaptive internal model for the estimated uncertainty dynamics is proposed. To cope with the high bandwidth property of the lump of uncertainties in VS-PWM converter applications, the disturbance slowly varying assumption is relaxed in the proposed controller. The relaxation is achieved by adopting a curbing sliding-mode-based feedback gain vector within the internal model observation system. Comparative evaluation tests were carried out on a grid-connected VS-PWM converter and a direct drive permanent magnet synchronous motor (DD-PMSM) drive system to demonstrate the validity and effectiveness of the proposed control scheme at different operating conditions. Index Terms--Adaptive estimation, digital current control, internal model, predictive control, robust control, voltage-source pulsewidth modulated (VS-PWM) converters.

The dynamic voltage restorer (DVR) is an effective solution for power quality problems related to voltage. One of the most common control algorithms that are used for the DVR is the symmetrical components method. This paper introduces a new approach for the estimation of the symmetrical components. A modified delta rule structure is proposed and developed which is capable of dealing with multioutput systems for the parameters estimation. An innovative feedforward control, based on the new delta rule structure, is proposed for the series compensator not only to compensate for the zero and negative sequence components, but also to regulate the positive sequence component at the nominal load voltage. One advantage of the proposed control scheme is its insensitivity to parameter variation, a necessity for the series compensator. Experimental verification of the new delta rule algorithm, by using a DSP, is provided. Numerical simulations of the proposed control strategy are conducted to show the robustness, high accuracy, and fast dynamic performance of this novel control algorithm. Index Terms--Delta rule, dynamic voltage restorer (DVR), estimation, flicker, power quality, sag, symmetrical components, voltage regulation.

Distributed measurement architecture, due to its efficiency, is used to monitor the power quality in the electric systems. This paper introduces a novel algorithm to determine the optimum allocations of power quality monitors to reduce the cost of the distributed monitoring system taking into account the data redundancy. The optimization problem is formulated as a covering and packing one which can be manipulated by integer linear programm algorithms. The appropriate constraints are deduced by the electrical circuit topology independent of the load parameters. In addition, the problem is adopted to a general form which can be implemented by any optimization package. The proposed algorithm is applied to five different systems for validation. Then, the results are discussed in terms of the cost and data redundancy. Index Terms--Covering and packing, deregulation, linear integer programming, power quality, power quality info nodes (PQIN), power quality monitoring, TOMLAB.

Distributed Generation (DG) exists in distribution systems and is installed by either the utility or the customers. This paper proposes a novel utilization of the existing DG nonlinear interface not only to control the active power flow, but also to mitigate unbalance and harmonics, and to manage the reactive power of the system. The proposed Flexible Distributed Generation (FDG) is similar in functionality to FACTS, but works at the distribution level. Moreover, a novel ADAptive LINEar neuron (ADALINE) structure is presented. The new structure is applied to multi output (MO) systems for parameter tracking/estimation, and is called MO-ADALINE. It is dedicated to symmetrical components estimation. The control loop combines a Fuzzy Logic Controller (FLC) for voltage regulation, and a processing unit-based ADALINE to deal with unbalance, harmonics and reactive power compensation. One advantage of the proposed control system is its insensitivity to parameter variation, a necessity for distribution system applications. Simulations of the suggested FDG based control algorithm are conducted to evaluate the performance of the novel system. Index Terms--Adaptive estimation, distributed generation, fuzzy control, harmonic distortion, power quality, reactive power control, voltage control.

This paper proposes a new model for the optimal partitioning of active distribution networks into a number of islanded microgrids. The objective of the developed model is to maximize the minimum value of maximum loadability amongst formed islands to create resilient islanded microgrids against unexpected local disturbances and power mismatches. The model takes key aspects such as the operation of islanded microgrids using droop control, system tie-lines, and line capacity limit into consideration. An ear decomposition-based method is proposed in order to preserve the radiality of formed islands. Besides the formulated exact optimization model, which is a nonconvex formulation, two convex mixed-integer models are introduced to achieve a trade-off between solution accuracy and computational time. The numerical results demonstrate the effectiveness and robustness of the proposed models in forming droop-controlled islanded microgrids with optimum loadability. [ABSTRACT FROM AUTHOR]

As the penetration rate of flexible loads and distributed energy resources in the distribution networks increases, congestion management techniques that utilize demand-side management (DSM) have been developed. These are indirect methods that rely on information exchange between the distribution network operator, aggregators, and consumers’ meters to encourage customers to change their demand to relieve congestion. Cyber attacks against aggregators can compromise the operation of DSM-based congestion management methods, and hence, affect the security and reliability of electrical networks. In this article, the vulnerability of indirect congestion management methods to load-altering attacks is studied. An optimization algorithm is developed to determine the aggregators a cyber attacker would compromise, via minimum alteration of their load profiles, to cause congestion problems. The impact of such attacks on congestion and consumers’ electricity bill is then studied. A mitigation scheme is formulated to determine the most critical aggregators in the network. The security of these aggregators is then reinforced to mitigate such cyber attacks. [ABSTRACT FROM AUTHOR]

Synchronverters are inverters that imitate the behavior of synchronous generators to enhance the dynamics of renewable energy sources (RESs) powering microgrids. However, the synchronverter's inrush currents during faults could reach intolerable levels. Limiting the synchronverter's fault currents could obstruct protection relays from identifying faulted phase(s) during unbalanced faults, and hence, jeopardizing selective phase tripping (SPT). This paper unveils the root causes behind the deviation in phase selection that hinder SPT in microgrids powered by synchronverters. Virtual-impedance fault current limiters (VI-FCLs) are proposed for synchronverters to ensure accurate SPT by commercial relays and limit their sequence and DC inrush currents. Based on a short-circuit analysis, the positive- and negative-sequence VI-FCLs, as well as the active-to-reactive power ratio of synchronverters, are regulated to enable SPT and protect synchronverters from inrush currents. Simulation results using PSCAD/EMTDC ensure the effectiveness of the proposed control scheme in enabling reliable SPT in microgrids with synchronverters. The efficacy of the proposed scheme is assured by examining various fault types, a wide range of fault resistances, and the grid-connected and islanded modes. [ABSTRACT FROM AUTHOR]

Line-switching operations introduce several concerns to microgrid operators since they trigger reliability and power quality issues in addition to increasing the wear and tear cost of switching devices. This paper proposes a novel methodology for achieving seamless line-switching in low-inertia islanded microgrids. The proposed methodology aims at mitigating the detrimental line-switching impacts by minimizing the power flow in the switched lines at the moments of executing the switching operations. The minimization of the power flow is realized by optimizing the droop control parameters of the DGs during the transition from one network topology to another. Besides, during executing a series of line-switching operations, the sequence of switching is also optimized to minimize the total switched power. While optimizing the line-switching execution sequence, the transitional droops are optimized for each line-switching operation within that sequence. A dynamic mixed-integer nonlinear programming problem is formulated to find both the optimized dynamic transitional droops and line-switching sequence simultaneously. Simulation results demonstrate the effectiveness of the proposed seamless line-switching methodology where the switched power can be reduced by more than 80% for a single line-switching operation and 54% considering a series of four switch exchanges in addition to achieving several instances of zero-current switching. As a result, a significant decrease in the peak of voltage transients has been recorded for some cases. [ABSTRACT FROM AUTHOR]

The DC microgrid (DC MG) concept enables the hosting of DC-type renewable energy resources. However, their intermittent nature means that a high penetration of renewables can jeopardize supply adequacy and voltage provision during islanding. The work presented in this paper was therefore directed at developing a probabilistic graphical approach based on Bayesian networks (BNs) for the reliability analysis of renewables-dominated DC MGs. The proposed BN model incorporates a family of novel reliability indices for quantifying the impact of a high penetration of renewables on MG reliability, including loss of renewable power supply, rise in voltage, and reversal of power flow. The model is supported by a newly formulated fast and accurate linearized power flow algorithm for probability calculations. The accuracy of the BN model has been verified against a Monte-Carlo simulation (MCS). The effective application of the new BN model for reasoning and impact assessment reveals that a high penetration of renewables affects reliability indices differently. Case study results suggest that the proposed BN model shows promise as a valuable tool for the reliability analysis of renewables-dominated MGs that feature islanding capability. [ABSTRACT FROM AUTHOR]

Technical developments in communication technology and measurement synchronization have facilitated the design of advanced protection schemes, such as Line Current Differential Relays (LCDRs). However, the superior performance of LCDRs is achieved at the expense of exposing them to cyber-threats, since cyber-induced intrusions against protective relays—which take advantage of the direct control of relays over circuit-breakers—can cause protection system mis-operations. To address this problem, this paper presents a Learning-based Framework (LBF) for detecting False Data Injection Attacks (FDIAs) and Time Synchronization Attacks (TSAs) against LCDRs, and for differentiating them from faults. In the proposed LBF, a Multi-Layer Perceptron (MLP) model is trained based on differential and super-imposed features, which are selected using the Recursive Feature Elimination method. After implementing the proposed LBF in LCDRs, when an LCDR picks up, it initially extracts the features and sends them to the trained MLP model. The LCDR trips the line if the proposed LBF confirms a fault. The performance of the proposed LBF is corroborated using the IEEE 39-bus test system. Evaluation results show that the proposed LBF (i) works independently of a system's operating point and configuration, (ii) is not considerably affected by instrumentation errors, and (iii) can accurately detect FDIAs and TSAs. [ABSTRACT FROM AUTHOR]

The interconnection of microgrids to form a network known as the multi‐microgrid (MMG) brings higher resilience and support in providing power to the loads. The dynamic response during interconnection is usually bypassed with the addition of synchro‐checkers installed on all the microgrids and the exchange of critical setting points between the microgrids prior to interconnection via a low‐bandwidth communication. This paper introduces a novel decentralized framework for maintaining the voltage and frequency of the microgrids within permissible operating range during the interconnection. The proposed control strategy is triggered when the microgrids violate the defined states of operation and the fast control action from each type of Distributed Generation (DG) in the microgrid is designed to tackle the transients in the voltage and frequency in order to regulate them within the IEEE standards. Moreover, the study is extended to evaluate the performance of interconnecting single microgrids to form MMG using the decentralized proposed control strategy and then sectionalizing the MMG back into separate autonomous microgrids. The results have been verified using PSCAD/EMTDC. The proposed control strategy demonstrates superior performance and simplicity for carrying out the energy management for interconnecting and sectionalizing of MMG without any kind of communication and synchro‐check infrastructures. [ABSTRACT FROM AUTHOR]

Inverter-interfaced distributed generators (IIDGs) introduce a major challenge for the protection of inverter-based islanded microgrids (IBIMs) due to their limited fault current contribution. This paper proposes a new strategy for the protection of IBIMs, founded on two novel aspects including a soft current limiter and an interharmonic differential relay. In addition to limiting the fault current, the proposed current limiter performs an amplitude modulation of the output fault current from the IIDG which occurs only during fault conditions. This modulation produces interharmonic currents with specific signatures that flow towards the fault. The process of injecting interharmonics is spontaneously initiated by a subset of the IIDGs upon the fault occurrence without a need for a fault detection scheme. Thereafter, based on the locally detected interharmonics, an interharmonic differential relay requiring low bandwidth communication is proposed to identify and isolate the fault. The proposed strategy has been validated using PSCAD/EMTDC. The results confirm the ability of the proposed protection strategy to protect IBIMs considering different fault types, locations, and values of the fault resistance without the need for additional fault detection components or high-bandwidth communication which may constraint the applicability and reliability of the protection schemes. [ABSTRACT FROM AUTHOR]

Inverter-interfaced distributed generators (IIDGs) are characterized by their low fault current contributions that impose a major challenge for microgrid protection. This article proposes a new overcurrent protection strategy that utilizes a third harmonic voltage generated by the IIDG controller during short-circuit faults. By generating harmonic voltages, a new current flow layer in the harmonic domain is created during faults and is independent of the fundamental fault current, which is limited by IIDGs. A harmonic time-current-voltage directional relay is developed based on the measured harmonic currents and voltages at the relay location to ensure optimal protection coordination (OPC) for isolated microgrids. The OPC with the proposed relay characteristics is formulated as a nonlinear program and equipped with a harmonic short-circuit current calculation method to determine the optimal relay settings. The 9-bus Canadian test system and the IEEE 33-bus system are adopted to validate the operation of the proposed OPC. Simulation results demonstrate that the proposed harmonic time-current-voltage directional relay is capable of detecting the direction of the fault current and maintaining precise protection coordination without the need for communication. [ABSTRACT FROM AUTHOR]

Peer-to-peer (P2P) energy trading in a blockchain framework has revealed an imminent potential to complement the conventional trading mechanisms. To that end, this article proposes a new framework for the economic consortium of energy storage systems. A new formulation is presented that would create operational and economic feasibility areas for choosing feasible bids traded in a blockchain framework. The former indicates the area in which the request for the energy trade is within the operational/physical limitations of the energy trader, while the latter is related to the area where the operation of the trader is economically profitable. Although the formulation provided for the feasibility areas is generic and can be utilized as a tool in various P2P applications, it is tailored in this article for energy storage scheduling. Using the proposed formulation for feasibility areas, the concept of feasibility area estimator is presented. The estimator is, then, integrated with the optimal scheduling model in order to capture operationally and economically viable bids traded in a blockchain system. Through numerical results, the efficacy and validity of the proposed model in this article are evaluated. It is demonstrated that different characteristics can be created for filtering the feasible bids to be utilized for storage scheduling. It is also shown that storage can effectively respond to and operate based on such feasible bids. Storage can exploit the arbitrage opportunities and trade energy with other peers to maximize its revenue. [ABSTRACT FROM AUTHOR]

AC/DC hybrid microgrids (HMGs) represent a promising architecture that allows the hosting of a mix of ac/dc energy resources and ac/dc loads. Despite their potential, when islanded, HMGs impose operational challenges among of which are precise and stable power sharing, frequency restoration, and voltage regulation. Imprecise power sharing can result in some distributed generators (DGs) being overloaded, while others being underloaded. This article proposes an optimal-power-flow-based optimal power sharing (OPS) scheme to optimize the droop characteristics of DGs and interlinking converters for global power sharing in a multi-DG HMG regardless of DG location and type. The optimized droop parameters might jeopardize the microgrid stability. Thus, the proposed OPS scheme preserves stable power sharing through stability-constrained optimization of the droop characteristics. In addition to DG overloading because of unequal power sharing, voltage-sensitive loads could possibly suffer from voltage deviations because of drooping the voltage with the load increase. The proposed OPS strategy enjoys the ability to regulate the ac/dc voltage within a desired range and restore the nominal frequency. Steady-state and time-domain simulations verify the effectiveness of the proposed sharing scheme in achieving the underlying objectives. Test results also prove the capability of the OPS scheme in zonal power sharing in the case of a distribution grid with multizone ac/dc microgrids. [ABSTRACT FROM AUTHOR]