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• A multiple criteria analysis method is proposed to compare renewable energy and traditional solutions for off-grid island power supply. • Life cycle cost is used to build the economic model. • The fuzzy analytic hierarchy process is used to quantify the risk level. • A simulation platform is built to obtain the energy utilization. • Applied to the actual project to verify the feasibility of the method. Renewable energy microgrids are a new option for powering remote islands. To explore the feasibility of constructing island microgrid in China, based on the failed Dongfushan Island Demonstration Microgrid Project caused by equipment failure, low economic benefits, low residents' satisfaction, and poor power supply stability, this paper compares two power supply methods, microgrid and submarine cable. A systematic multiple criteria analysis method is established to compare these two methods, including economic analysis, risk assessment, energy spilled and energy shortage. Net present value and the life-cycle cost method are used to establish the economic cost model. Fuzzy analytic hierarchy process is used to establish the risk assessment model. Additionally, the simulation using PVsyst software is used to calculate the energy spilled and energy shortage. Furthermore, future trends are predicted with data to provide suggestions for decision-makers. Multiple criteria analysis results showed that energy spilled and shortages are inevitable for the use of microgrid on seasonally tourist islands like Dongfushan Island, with energy spilled and shortages rate as high as 50.11% and 37.57% in the worst case. The microgrid risk level is relatively low risk, higher than the lowest risk level for submarine cables. At full capacity, the cost of microgrid (34.03 million yuan) is comparable to submarine cables (30.31 million yuan), making the latter more suitable for power supply due to its better reliability. [Display omitted] [ABSTRACT FROM AUTHOR]

• Random-fuzzy multi-objective optimal power flow. • Transmission and distribution interaction. • Security region constraints. In order to deal with the static voltage stability region problem of the power system caused by the penetration of distributed energy resources, this paper presents an interactive random-fuzzy optimal power flow method for transmission-distribution network considering security region constraints. Firstly, based on the random-fuzzy theory, the output of wind power and multi-energy coupling energy hub connected to transmission-distribution network are obtained. On this basis, the security region model of transmission-distribution network is established. As the interaction and cooperation between multiple distribution networks and transmission network throughout the system are described, the global random-fuzzy model of transmission-distribution interaction is established. Then, the security domain opportunity constraints are incorporated into the multi-objective optimization model of transmission-distribution network. Finally, based on the improved IEEE30 bus transmission system and IEEE33 bus distribution system, the power flow of transmission-distribution interactive network under the proposed model is calculated. The simulation results validate the effectiveness of the proposed model and algorithm. The safe operation distance of the power grid system can be improved and the active power network loss and power generation cost can be reduced. [ABSTRACT FROM AUTHOR]

• To detect islanding, the 4th harmonic is injected into the output current. • A modified Goertzel filter is employed to measure the harmonics of voltage. • The method is robust to variation of load quality factor and resonant frequency. • The impact of reactive power on frequency after islanding is compensated. • The method is fast and detects islanding within two cycles of fundamental frequency. Islanding occurs when a utility-interactive distributed generator (DG) is disconnected from the utility grid and continues to supply power to local loads. This condition has several consequences including damage to the equipment and personnel safety risks. Therefore, it is required by utility interconnection standards for the DG to stop energizing local loads in the case of islanding. In this paper, an active islanding detection method (IDM) based on injecting a disturbance into the phase-locked loop (PLL) of a grid-connected photovoltaic (PV) inverter and monitoring the harmonic components of the point of common coupling (PCC) is proposed. A modified Goertzel algorithm is utilized to detect the injected harmonic which is effective for a wide range of load conditions in terms of load quality factor, resonant frequency, and reactive power. The simulation results in MATLAB/Simulink show that the proposed technique is fast with minimum side effects on power quality features such as output current total harmonic distortion (THD). This method is implemented on a single phase 5 kW grid-tied PV inverter and is tested experimentally. The experimental results verify that the proposed technique is fast with zero non-detection zone (NDZ) which is effective for a variety of load conditions. [ABSTRACT FROM AUTHOR]

With the development of virtual synchronous generators (VSG), microgrids can choose a synchronous generator (SG) or a virtual synchronous generator (VSG) as the main power supply of an isolated island system. The governor of a synchronous generator and the active power control loop of a virtual synchronous generator may cause the transient power angle instability of the system, while the excitation device and reactive power control loop may cause the transient voltage instability. At present, there have been many studies on these two aspects. However, when a synchronous generator and a virtual synchronous generator are used as the main power sources to supply power to the isolated island system, the mutual coupling between the synchronous generator and the virtual synchronous generator may cause transient power angle and voltage instability. At present, there is little research in this field. Therefore, this paper focuses on the influence of the parallel mutual coupling of synchronous generator and virtual synchronous generator on the system stability, derives the mutual coupling model of a parallel system, it is also revealed that the coupling relationship between the SG and VSG parallel systems will produce a positive feedback mechanism that will be constantly amplified, which will greatly affect the system's stability. At the same time, the influence of coupling on the stability of a parallel system is carefully analyzed using large signal analysis, and the corresponding coupling suppression strategy and adaptive inertia control (AIC) is proposed. Finally, the correctness and feasibility of the proposed method are verified by time-domain simulation, and the experimental results are analyzed. [ABSTRACT FROM AUTHOR]

• Novel protection technique for microgrids with inverter-based resources. • Effective both in grid-connected and islanded modes of operation unlike other relays such as differential relays. • Not affected by inverter-type and its control strategy, microgrid topology and level of generation. Due to the unavailability of a suitable relay for microgrid protection, various utilities are fitting available IEDs for the protection of microgrids. At present, microgrid protection is achieved using a combination of conventional numerical relays. These numerical relays are not suitable for all kinds of microgrid architectures and do not provide complete protection with inverter-based generators. Since these relays were designed considering the fault characteristics of synchronous generators, they fail to respond to the fault characterized by inverter-based generators. This paper proposes a new protection technique that is independent of the type of generating sources, control philosophy of inverters as well as microgrid architecture. Simulations are performed using PSCAD/EMTDC and performance of the protection scheme is also evaluated in real-time using RTDS. Pertinent results are presented which demonstrate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

• The structure scheme of hybrid pumping unit is proposed for the first time in this paper. New forms of wind energy can effectively reduce oil field energy consumption by 90%. • The Mechanical-hydraulic energy storage transmission scheme is proposed for the first time. The coupling of wind energy and electric energy can be realized through the new hybrid transmission structure. • A double pump energy supply system is proposed for the first time in this paper. Double pump energy supply system can improve the utilization efficiency of wind energy. Wind energy can replace electric energy to drive pumping units. Wind power generation is used in oil fields, but the energy saving effect is not obvious. This paper proposes a new method of wind energy utilization. Wind energy directly drives pumping unit by new mechanical-hydraulic transmission system without the intermediate conversion into electricity for the first time. This new system can realize hybrid power of wind and electricity and adjust the output energy of the system to meet load requirements. It can effectively address the problems of wind energy utilization and is especially suitable for oil fields in remote areas where electricity is insufficient and its exploitation is difficult. This paper studies the performance of wind-pump system and mechanical-hydraulic system, respectively. Mathematical model is verified by numerical simulation and experiment studies. The economic matching model is established and the parameters of the system are optimized. Finally, this paper puts forward the optimization matching design theory of wind-motor hybrid system. Wind energy utilization rate is higher 60% under optimal parameter combination. [ABSTRACT FROM AUTHOR]

• The significant active power injection provided by high-capacity distributed generation (DG) units associated with the high R/X ratio of MV feeders may cause overvoltage at the point of common coupling. • High-capacity DG units can adversely affect step voltage regulator (SVR) control operations in reverse active power flow scenarios. • Reverse power tap changer runaway events are a threat to voltage security of active and reconfigurable distribution feeders containing SVRs. • The application of SVRs in long rural feeders with high-capacity DG units is crucial for maintaining voltage levels at all buses within predetermined operating ranges in the context of decentralized network operation. • The proposed optimal DG rescheduling approach prevents voltage issues and ensures reconfiguration options for the network whilst still benefiting the independent power producer. This paper investigates and discusses voltage issues currently faced by engineers from a Brazilian utility in the high-capacity dispatchable distributed generation (DG) interconnection planning study on a real reconfigurable distribution network with cascaded step voltage regulators (SVRs). Based on this investigation, this paper proposes an optimal rescheduling approach applied to high-capacity dispatchable DG considering two additional technical constraints to the optimization problem for mitigating voltage issues, such as over/undervoltage violations and SVR runaway, while still allowing network reconfiguration schemes and benefiting the independent power producer (IPP). With this approach, the active power supplied by the IPP's DG is adjusted throughout the day with respect to the feeder load forecast, avoiding reverse power flow situations on SVRs and ensuring suitable control operation on reconfigurable distribution networks. The problem is formulated as a constrained optimization and solved through the primal-dual interior point technique. Simulation results on a real Brazilian reconfigurable distribution network demonstrate that the proposed method is effective to mitigate the identified voltage issues without affecting network reconfiguration operations and the weekly average active power injected by the DG. [ABSTRACT FROM AUTHOR]

• Boundary eigenvalue approach is used to identify the worst-case scenarios • Look-ahead approach is proposed for Hopf bifurcation stability margin (HBSM) monitoring • Formulation of HBSM enhancement problem using boundary active power loss evaluation • Optimal rescheduling of power system controllers under non-statistical uncertainties Uncertainties in the forecasted load and generation can have a catastrophic impact on power system stability. For a reliable power supply, a sufficient dynamic stability margin is always desired. This paper introduces a novel boundary eigenvalue-based approach for the determination of Hopf Bifurcation Stability Margin (HBSM), which, explicitly, accounts for the impact of uncertainties in specified renewable generation and loads. Since the Hopf bifurcation stability problem is nondeterministic, it requires large computational efforts to determine the HBSM. Most of the available methods are based on statistical data, which are computationally less efficient for such applications. In this paper, a non-statistical uncertainty based control rescheduling strategy is proposed to enhance the stability margin of the system. To balance the trade-off between solution quality and computation time, the proposed approach is composed of two stages: i) determination of boundaries of critical eigenvalues; and ii) optimal setting of the controllers by minimization of a boundary active power loss based objective function under the given range of uncertainties. The proposed approach is demonstrated on standard IEEE test systems with promising results to show the importance and its reliability. [ABSTRACT FROM AUTHOR]

• The flexibility potential of a smart home is estimated for providing flexibility services • The flexibility services adopted from the smart home help system operators to operate their networks more effectively • Air conditioner, electric water heater, electric vehicle, and battery energy storage are considered the controllable appliances of the smart home • The flexibility of each controllable device is estimated using its flexible and non-flexible operations The high penetration of intermittent renewable-based power into modern power systems increases the need for more technical ancillary services from flexible energy resources. Smart homes could provide different flexibility services related to active power control services and therefore fulfill a part of the flexibility needs of system operators. In this regard, the estimation of the flexible capacities of each smart home's flexible device is of key importance. Correspondingly, this paper first estimates the flexible capacities of a smart home with controllable devices as flexible resources. The flexible capacity of each appliance is estimated considering its flexible and non-flexible operations. Besides, the local and system-wide flexibility services are introduced and the paper discusses whether a smart home can provide these types of services. In the simulations of this paper, the flexible capacity of each household appliance is estimated and compared to each other. Finally, the profitability of the smart home's battery energy storage multi-use is analyzed when it is providing three different types of flexibility services for the transmission system operator's needs. The results demonstrate that in some scenarios, the smart home's battery energy storage can increase its profits by providing transmission-system-level flexibility. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, a large number of Distributed Generation units (DG units) such as Wind Turbines (WTs) and Combined Heat and Power plants (CHPs) have been penetrating the distribution systems. Meanwhile, an intentional island operation of distribution systems is proposed as a potential measure against power supply outages by continuously running DG units during system emergencies. However, there are some challenging security issues for an island operation, such as the power imbalance during the islanding transition and the coordination of feeder protection systems. To tackle the former issue, which is the focus of this paper, available resources including both DG units and demand should be fully utilized as reserves. The control and coordination among different resources requires an integral architecture to serve the purpose. This paper develops the Islanding Control Architecture (ICA) for future smart grid, based on the Islanding Security Region (ISR) concept. With the ISR, system operators can assess beforehand if an island operation can be successful for a given distribution system at its current operating state. In case of unfavorable assessment, control measures will be suggested to coordinate different resources, aiming at pulling the system back into the ISR to ensure a successful island operation on time. [Copyright &y& Elsevier]

• Application of the ampacity control system is necessary for wind energy integration. • DLR application reduced the time in which wind farms were out of service by 4100 h in 44 months. • DLR application increased the energy supplied by wind farms by 70.9 GWh in 44 months. • DLR application saved more than 7800 t of CO 2 in 44 months. The total renewable wind energy capacity of Spain currently accounts for more than 20% of the total installed energy capacity, which makes integration into the grid challenging for wind farm owners as well as Distribution System Operator (DSO). Electrical companies require new techniques to integrate renewable energies safety and with low investment costs. Dynamic line rating (DLR) is one of these techniques, and is used by DSOs to maximise the capacity of existing infrastructure. This paper presents a successful case of DLR application by a DSO over several years to reduce the time that wind farms were out of service due to an excess of electrical energy generated. Over the period from January 2015 to September 2018, the application of the DLR technique prevented 4,100 hours of out-of-service time, increasing the energy supplied by the wind farms by 70.9 GWh and by extension saving 7,800 tons of CO2. [ABSTRACT FROM AUTHOR]

• Proposed voltage control method is based on proximity of controlling unit. • A proximity index independent of load variation is proposed. • Voltage control is achieved by changing generator output/shifting flexible load. In any power system the voltage profile is a crucial performance factor which must be contained in a specific tolerance range with respect to the nominal voltage value. This paper proposes a voltage control method for smart distribution system using a novel electrical proximity index. This index is independent of the system load dynamics. The method works on the electrical proximity of the control units, viz. distributed energy resources (DER) and flexible loads, from the point where voltage control needs to be incorporated. Depending on proximity of control units from the point of operation, the contribution of these units on voltage deviation are calculated for different time steps spanning over the day. The generation or demand of the control units, which are in close electrical proximity of the point of voltage deviation, are updated. Use of electrical proximity in choice of control units makes the control strategy faster and effective in controlling system voltage profile. The effectiveness of the proposed technique is demonstrated and evaluated for different types of distribution systems. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an agent-based simulation of a Financial Transmission Rights (FTR) auction for both types of point-to-point FTRs, obligation and option, is presented. Each auction participant is simulated as an adaptive agent who has the ability of evaluating its environment and acting accordingly, following the decision rules of the naïve reinforcement learning algorithm presented in the paper. Initially, a Locational Marginal Pricing (LMP) based ex-ante energy market is assumed. From the solution of the ex-ante energy market the agents calculate their initial FTR bid prices. Subsequently, the ISO solves the FTR auction problem and the agents profits equal the reimbursement they receive in the ex-post energy market for holding the FTR. The agent-based simulator repeats the FTR auction under the same conditions; in each repetition the agents update their bids according to the implemented algorithm and they “learn” their bidding strategies, through exploration by repetition. A five bus test system with five agents is used to illustrate the presented method. The results demonstrate the impact of contingency constraints and the effect of speculation in FTR auctions. Furthermore, the difference between bidding for FTR-obligations and FTR-options is shown. [Copyright &y& Elsevier]

Highlights • Smart-grid based based electrical railway network through the use of a Yd transformer with multiple phase connections. • Intelligent control method for RPFC implementing the central Steinmetz-based intelligent (SICS) control system. • Calculating the optimal amounts of active and reactive powers transferring in different phases. • The SICS proposed method performance verification by the FPGA-based real-time laboratory setup results. • Significantly reduction of RPFC converter's power rating and installation costs. Abstract Adoption of smart grids has led to significant opportunities in the optimal operation of systems and energy consumption in utility grid loads. Among the various grid loads, electrical railway networks (ERNs) are known as one of the most important and critical end users due to their high power consumption. Energy management and power quality domination in such a network are already concerns of researchers. The railway power flow controller (RPFC) is a commonly used system to manage the optimal energy consumption and power quality problems of ERNs. This paper presents a comprehensive study of an RPFC power rating and a new compensation strategy with the objective of reducing the installed capacity in several consecutive traction power substations (TPSs). This technique is implemented through the use of a Yd transformer with multiple phase connections and the central Steinmetz-based intelligent control system (SICS). Through coordination with the internal control systems, the optimal mode of the active and reactive powers transferring in different phases is calculated by the central SICs and applied to each TPS. The proposed control strategy substantially diminishes the RPFC converter's power rating and installation costs. A real-time laboratory platform for the smart-grid based proposed method is provided using Opal-RT emulator to confirm the theoretical analysis with the desired precision representing the real power system behavior. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a rule based comprehensive approach to study distribution network reconfiguration (DNRC). The DNRC model with line power constraints is set up, in which the objective is to minimize the system power loss. In order to get the precise branch current and system power loss, a power summation based radiation distribution network load flow (PSRDNLF) method is applied in the study. The rules that are used to select the optimal reconfiguration of distribution network are formed based on the system operation experiences. The proposed rule based comprehensive approach is implemented in distribution network in Guiyang South Power Supply Bureau. For the purpose of illustrating the proposed approach, two distribution network systems are tested and analyzed in the paper. [Copyright &y& Elsevier]

• Increase speed and accuracy in compensating for voltage and frequency fluctuations. • Intelligent power and energy management based on MPC and INN algorithms. • Optimal performance of primary and secondary controllers based on uncertainties. • Optimal control of power generation sources and energy storage units. This paper presents an intelligent energy management method to control the voltage and frequency at the primary and secondary control levels of micro-grids. The proposed model is based on the model predictive control (MPC) at the primary and intelligent neural network (INN) at the secondary. The purpose of this paper is to control the voltage and frequency based on the uncertainties of power generation resources and loads. In order to validate, the results of the proposed model are compared in different scenarios with other methods such as Fuzzy and PID controllers. The performance of the proposed method in primary and secondary as well as the coordination of this method with a high degree of sensitivity along with HESS and diesel generator units, in addition to increasing stability and reliability, protects the operation of the micro-grid against fluctuations based on uncertainties. The results show that this method, in addition to accuracy, has a higher operating speed than other controllers. As a result, the voltage and frequency restoration in the primary and the compensation of deviations from the reference in the secondary are associated with acceptable results. In order to validate the simulation results and experimental results are also presented. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses the design, implementation, experimental validation and performances of a fully digital fast power switch fault detection and compensation for three-phase shunt active power filters. The approach introduced in this paper minimizes the time interval between the fault occurrence and its diagnosis. This paper demonstrates the possibility to detect a faulty switch of the active filter in less than 10μs by using simultaneously a “time criterion” and a “voltage criterion”. In order to attain this fast detection time a FPGA (Field Programmable Gate Array) is used. The other feature introduced in this approach is that the control scheme used to compensate the current load harmonics and fault tolerant scheme are both programmed in only one FPGA. “FPGA in the loop” prototyping results and fully experimental results based on a real active power filter verify satisfactory performances of the proposed method. [Copyright &y& Elsevier]

Abstract: This paper proposes a differential protection scheme for transmission lines using the energy conservation law. The real power signals at both ends (sending and receiving) of the line are compared with a pre-specified value, if the resultant is more than this value, an internal fault is indicated in the transmission line zone. The proposed technique is evaluated using PSCAD/EMTDC program configurated to model the effect of faults on typical 500kV transmission line. Extensive simulation studies show that this protection scheme has the ability to discriminate internal faults fast and accurately, and is more reliable than conventional biased differential protection scheme, and suitable for all types of lines. Details of the proposed relay design are given in the paper; also results of some performance studies are given. [Copyright &y& Elsevier]

Abstract: Reconfiguration involves changing the status (OFF/ON) of switches, and reconfiguration for restoration involves changing the switch status to maximize the supply to loads that are left unsupplied after fault removal. Shipboard Power Systems (SPS) need automated reconfiguration for restoration schemes to restore vital loads quickly and efficiently in order to improve fight-through and survivability capabilities. The restoration in this paper is achieved using optimization with multiple objectives—maximizing the restored load and giving priority to vital loads. A restoration scheme for SPS with an integrated power system (IPS) and distributed generation (DG) involving islanding has been developed. This formulation includes a hybrid power system that has both ac and dc parts. The restoration formulation in this paper also considers the unbalanced nature of SPS operation with mutual coupling. [Copyright &y& Elsevier]

Abstract: This paper presents two novel control schemes for static synchronous series compensator (SSSC) for dynamic series compensation and voltage regulation. The SSSC model comprises a harmonic neutralized multilevel 48 pulse voltage source converter. This paper investigates two novel control schemes for optimal series compensation, which are indirect control (constant reactance control) and direct control (constant voltage control) using pulse width modulation (PWM) switching techniques. The proposed model of SSSC within the power system is performed in Matlab/Simulink using the power system blockset. The performance of the SSSC schemes connected to the 230kV grid is evaluated in both capacitive and inductive modes of operation under load excursions. The operation of the proposed controllers is also tested in a weak power in order to compare their performance for securing SSSC stability in response to system contingencies. [Copyright &y& Elsevier]

Abstract: The paper presents an analysis of very fast-transient overvoltages that occur because of the capacitive surge transfer from the high-voltage (HV) transformer winding to the low-voltage (LV) transformer winding. The study is done on a 6.6kV single-phase test transformer. By applying a pulse with a short rise time at the HV terminal, the voltage at the LV side is measured and calculated. The voltage distribution along the LV winding is calculated by applying the transmission line theory, so that the foils of the LV winding are represented as transmission lines. For the studied transformer with a nominal transformer ratio of 95.6, a maximum voltage ratio of 3.3 was measured during the rate of rise of the applied impulse. The present paper also shows that in some specific cases, the mutual inductance between the primary and the secondary side can be ignored during determination of the transients along the secondary winding. The computation and measurement of the voltage at the LV side is validated by making use of the vector fitting method. [Copyright &y& Elsevier]

The parameterized fast decoupled power flow (PFDPF), versions XB and BX, using either θ or V as a parameter have been proposed by the authors in Part I of this paper. The use of reactive power injection of a selected PV bus (QPV) as the continuation parameter for the computation of the maximum loading point (MLP) was also investigated. In this paper, the proposed versions obtained only with small modifications of the conventional one are used for the computation of the MLP of IEEE test systems (14, 30, 57 and 118 buses). These new versions are compared to each other with the purpose of pointing out their features, as well as the influence of reactive power and transformer tap limits. The results obtained with the new approaches are presented and discussed. The results show that the characteristics of the conventional FDPF method are enhanced and the region of convergence around the singular solution is enlarged. In addition, it is shown that these versions can be switched during the tracing process in order to efficiently determine all the PV curve points with few iterations. A trivial secant predictor, the modified zero-order polynomial, which uses the current solution and a fixed increment in the parameter (V, θ, or μ) as an estimate for the next solution, is used for the predictor step. [Copyright &y& Elsevier]

In a deregulated power system customers have the freedom to choose their reliability. They can purchase spinning reserve directly from electric power providers. In this case, an individual customer is concerned more with its own load point reliability rather than with the system reliability. This paper introduces bulk load point (BLP) well-being indices for supply customers, with the primary objective of determining their spinning reserve based on desired reliability levels in a bilateral market model. The system well-being model used in conventional power systems is extended to the load point model in a restructured power system. The impacts of spinning reserve purchase on these indices were investigated and are reported in the paper. A reliability test system is used to illustrate how customers can determine their spinning reserve in the deregulated environment. [Copyright &y& Elsevier]

In the paper, a general analytical method for the probabilistic evaluation of power system transient stability is discussed and a new statistical inference approach for this evaluation is proposed. In particular, the transient stability probability (TSP) is defined and evaluated by taking into account the random nature of both the system loads and the fault clearing times (FCT). The paper is focused upon the aspect of statistical estimation of the TSP—a topic generally neglected in literature—on the basis of the obvious consideration that the parameters affecting the TSP (e.g. mean value and variance of loads, FCTs, etc.) are not known, but must be estimated. New properties of point and interval estimations of the TSP are derived and, in particular, an efficient “lower confidence bound” for the TSP estimation is proposed, based upon a suitable Beta probability distribution. In order to show the feasibility of the proposed approach, a numerical application to the Cigre test network is illustrated. Moreover, extensive Monte Carlo simulations to evaluate the estimator efficiency are performed. In the final part of the paper, also a practical example of possible application to the optimization of system design is illustrated. The application of the method is illustrated and performed by using the potential energy boundary surface method, but the estimation results hold their validity irrespective of the method adopted for the transient stability problem formulation and resolution. [Copyright &y& Elsevier]

The integration of Distributed Energy Resources (DERs) in distribution networks comes with challenges, like power quality concerns, but also opens up new opportunities, e.g., DERs can offer competitive energy prices for final users by leveraging time arbitrage. A suitable method to fully exploit such opportunities is to compute the optimal DER schedule, either with a full three-phase network model or a more computationally efficient single-line equivalent. This paper presents under which conditions a single-line equivalent can and cannot be used to properly represent a modern and unbalanced power distribution network able to dispatch high levels of DER integration optimally. Results show that single-line equivalents might be helpful when the problem objective function limits counterflows, for example, when minimizing active power losses. Moreover, single-line equivalents might be helpful for low levels of DER integration. However, enabling single-line equivalents results in a lower hosting capacity for high levels of DER integration. • Three-phase models ensure safe network operation, but with more computation time. • Increase of Distributed Energy Resources may increase unbalances in the network. • Maintaining balanced conditions may require more curtailment. • Single-line equivalent models are effective when minimizing network losses. • Case studies include 144 simulations on the 34 node IEEE test feeder. [ABSTRACT FROM AUTHOR]

This paper presents a model for photovoltaic (PV) distributed generators that operates in abnormal electrical voltage scenarios — Voltage Ride Through (VRT), following the Brazilian standard NBR 16149 of 2013. The model includes various modes of operation, such as interruption of energy supply, disconnection, and reconnection of the PV system to the grid. Two types of simulations were performed to test the model's performance: the first involved using a ramp function to test the activation of different operating modes, while the second connected the PV model to a distribution feeder and tested its response to a short circuit. The results showed that the model met the requirements established by the standard and was efficient in representing the behavior of the PV system in real-world scenarios. • Photovoltaic solar energy has been gaining considerable space. • Dynamic modeling of photovoltaic generators. • The recommendations of the Brazilian standard RS 16149 for PV connections. • The simplified generator model reduces computational costs. [ABSTRACT FROM AUTHOR]

In this paper, an alternative approach to power loss calculation in a transformer supplying a nonlinear load is presented. The advantage of the proposed approach is that it relies on readily available transformer technical data in contrast to the data required by the methodology described in IEEE std. C57.110–2018. Experimental verification of the proposed approach was carried out using a 4.5kVA laboratory dry type power transformer. The results obtained experimentally show high compatibility with theoretical model featuring an error margin smaller than 0.2%. [ABSTRACT FROM AUTHOR]

• To solve the issues related to ignoring network constraints in the peer matching process, we apply NUF based on sensitivity analysis to evaluate the impact of each agent's equivalent load on network constraints. The proposed NUF can fully and fairly diagnose the portion of each agent on power loss, congestion and voltage violation. • This work extends the existing primal-dual subgradient algorithm by adding Peer-to-Grid (P2G) energy trading and NUF. • The proposed TEM framework would innovatively ensure the individual TE agent privacy while facilitating energy trading. • As part of the proposed TEM framework, the DSO operation (e.g., VVC and network reconfiguration) is considered, which may assist in providing the optimal network topology to facilitate peer matching and minimize interference with the scheduling of the TE agents. A growing number of distributed energy resources (DERs) connected to the distribution network presents operational challenges. Therefore, it is crucial to develop an effective framework to address these challenges. In this paper, a novel transactive energy market (TEM) framework is proposed in two levels based on the concept of a network usage fee (NUF) to address technical issues. We perform the peer matching process using a primal-dual algorithm at a lower level. We consider distribution system operation (DSO) operations (e.g., Volt/VAR control and network reconfiguration) and NUF to maintain network constraints and to provide an optimal network topology to facilitate energy trading. The proposed framework has been tested on an IEEE 33-bus distribution network. A key issue relating to the coordination of DERs in distribution networks is addressed in the results. In the proposed NUF, the sensitivity analysis is used to fully diagnose the portion of each TE agent in power loss, congestion, and voltage violations. A fair penalty or incentive signal can be generated to ensure that the network operates within the limits. Furthermore, the proposed framework ensures that the privacy of agents is protected. DSO operation facilitates the trading of energy and minimizes interference with their schedules. [ABSTRACT FROM AUTHOR]

• This paper focuses on boosting the diesel generator (DG) set's utilization by exploiting the solar photovoltaic plant (SPVP) power converter's available capacity as DSTATCOM. The key highlights of this work are as follows. • The power factor of the DG set is regulated at unity irrespective of the SPVP generation or load behavior, enhancing the efficiency of the diesel engine and electric generator. Consequently, fuel consumption is decreased, lowering the cost of electricity. • The SPVP carries the burden of the entire load's reactive power. Hence, the DG set's surplus capacity, initially reserved to supply the reactive power to the load, can be utilized now to commit the additional load on the same rating system. • Due to the DSTATCOM operation, the SPVP operates 24 hours, raising the overall utilization factor of the SPVP. Hence, the payback time is less compared to the existing system. • The DSTATCOM operation of the SPVP boosts the power quality performance of the microgrid without causing any high additional costs to the system. Thus, the IEEE std. 519 [21] is followed at POI, with improved utilization of the microgrid. • A least mean 2L th (LM2L) rule-based adaptive filter has been developed for a quick and accurate estimation of the load's fundamental component current. It is a hybrid adaptive filter algorithm that uses the conventional normalized least mean square (N-LMS) and normalized least mean fourth (N-LMF) algorithms to improve the steady state and transient response. In the existing solar photovoltaic (SPV) and diesel generator (DG) based standalone microgrid, the power factor of the DG set reaches around 0.5-0.6. Further, it encounters poor power quality performance due to harmonics currents of the local loads, coupled at the microgrid's point of interconnection (POI). All these issues significantly affect the DG set performance, causing additional losses and reducing its fuel efficiency. In addition, the SPV plant does not provide any ancillary services in the existing system and remains ideal most of the time, causing the under-utilization of microgrid's power converters. In this context, this work presents a least mean 2L th (LM2L) rule-based adaptive filter-controlled SPV system, where its power converters are regulated to deliver multifunctional capabilities such as enhancing the DG set's power factor and power quality performance. As a result, the DG set power factor improves to unity, and the %THD value of its voltage and current reduce to below 5%. Hence, the fuel efficiency of the DG set is improved, line losses are decreased, and the additional load can be committed to the DG set capacity, which is kept reserved to supply reactive power to the load. Moreover, the modifications, which are earlier required in the DG set design to accommodate the distortion in its voltages and currents due to the nonlinear load, can be avoided. The LM2L algorithm is used as a prefilter for the measured load currents and determines their fundamental component. It has two operating rules, which decide the fundamental component's estimation depending on the system conditions. As a result, it demonstrates an improved steady state and dynamic performances compared to the existing adaptive filter algorithms. Test results verify the control and design of the microgrid on a laboratory prototype. [ABSTRACT FROM AUTHOR]

• A method to preplan segmentation of power distribution system into MGs with flexible boundaries to enhance resiliency. • A three-stage algorithm to enable resiliency of the PDS subjected to natural disasters and/or multiple faults, using MILP. • Assessed the impact of the controllable MGs with flexible boundaries on power system resiliency performance with a composite metric. With the increased frequency of adverse weather and manmade events in recent years, the issue of the power distribution system (PDS) resiliency has become drastically important. Microgrids with various types of distributed energy resources (DERs) have capabilities to enhance the PDS's resiliency against high impact low probability (HILP) events. Resiliency is defined as the ability of the system to keep supplying critical loads even during and after extreme contingencies. This paper presents a systematic method to segmentize parts of a PDS into microgrids with flexible boundaries to enhance resiliency and mitigate negative impacts from anticipated threats. The method is aimed at anticipation and preparation to HILP events in advance: alternative flexible boundaries of the microgrids must be preplanned during normal operation and dynamically changed prior to or during disturbances. The Mixed-Integer Linear Programming (MILP) is formulated and applied to select switching actions to adjust microgrids' boundaries as well as to supply critical loads, while meeting system constraints. Networked microgrids are merged and reconfigured as necessary to maximize supply to critical loads, driven by a factor-based resiliency metric, which is obtained using the Analytical Hierarchy Process (AHP). The modified IEEE 123 bus system was utilized for validation of the proposed method. Compared with the traditional fixed-boundary microgrids, this approach determines the most resilient network configuration to supply high-priority critical loads. The developed method can be employed in power system planning, operation, and in decision-making to enhance operational resiliency and invest in system upgrades appropriately. [ABSTRACT FROM AUTHOR]

• A novel GNA optimized FOPTID+1 controller is suggested to supress the fluctuations in frequency in multi-source one and two-area multi-source power systems. • The supremacy of the controller is established over published techniques. • The effect of capacitive energy storage device is tested. • Robustness of the controller is scrutinized under extensive variation in system parameters and tie-line outages. The demand for power increases during the peak hours and the power supply can't exceed its limitations. This results into mismatch between the supplied and demanded powers causing fluctuations in the frequency. Extreme power-frequency deviations may cause power system blackouts. To maintain the constant frequency of power system, automatic generation control (AGC) should be embedded with a reliable controller. In this paper, a fractional order proportional tilt integral derivative plus one (FOPTID+1) controller is introduced in the design of AGC to retain frequency constancy. This controller has the ability to regulate the frequency hastily during load disruptions. The controller parameters are optimized by exploiting global neighbourhood algorithm (GNA). Firstly, the investigation is directed on a one-area multi-source thermal-hydro-gas generating system. To authenticate the expandability of the method, the study is then extended to multi-source interconnected two-area thermal-hydro-gas power system without/with nonlinearities. The dominance of the suggested controller is recognized over various recently published results of I/PI/PID/TID/FOTID and GNA tuned PID/FOPID controllers. Inspection of results authorizes the worthier performance of FOPTID+1 over other controllers regarding least overshoot/undershoot/settling time of frequency/tie-line power change and error criteria at disturbances. To further advance the system performance, capacitive energy storage (CES) units are incorporated to compensate the power demanded by the load disturbances. The obtained results demonstrate that CES is capable to improve system performance effectively. With CES, FOPTID+1 produces less cost function value for both one-area (9.52%) and two-area (8.97% for linear and 11.38% for nonlinear) systems. The control system stability is verified by the study of bode diagram. The resilience behaviour of the controller is confirmed by the stout conduct of controller under ±25% variation of system parameters and tie-line outages. [ABSTRACT FROM AUTHOR]

• The ADMM-based method is extended to solve the MISOCP optimization problems with minimum information exchange. The main contributions and innovations of this work are as follows: • A decentralized stochastic optimization model has been developed to collaboratively optimize the expansion of interconnected national energy networks, while considering the impact of cross-border interconnection and trade. • The economic benefits of cross-border electricity and gas trading in cross-border network expansion planning problem are analyzed. • An ADMM-based algorithm has been extended to decompose the centralized MISOCP optimization model to protect data privacy, with adaptive adjustment of penalty parameters and Lagrangian multipliers to accelerate convergence. Cross-border interconnection and trade (CBIT) can effectively leverage the differences in resource endowments and energy demand between regions and countries, making cross-border cooperation a potential option for addressing the high penetration of variable renewable energy. This paper presents centralized and decentralized planning approaches for the cross-border energy transmission expansion planning (TEP) problem. The proposed centralized mixed-integer second-order cone programming (MISOCP) model collaboratively optimizes the expansion of national energy networks, while considering the impact of CBIT. To protect the privacy of energy data in each country, the alternating direction method of multipliers (ADMM) algorithm is extended to decompose the centralized optimization formulation into mutually independent sub-optimization issues, and adaptively adjust the penalty parameters and Lagrangian multipliers to improve convergence. This study also quantifies the effect of cross-border cooperation in such co-expansion problems as a comparative consideration. Numerical simulations on the modified cross-border integrated energy network validates the correctness and effectiveness of the proposed model and solution methodology. The results show that cross-border cooperation can reduce a country's internal energy network congestion, thus postponing the expansion investment decisions. It also shows that the distributed coordinated planning is more efficient in terms of lower cost and renewable generation curtailment that than independent optimization method. Therefore, cross-border collaboration brings economic, environmental, and renewable integration benefits to interconnected countries. [ABSTRACT FROM AUTHOR]

• Considering the internal contingencies of virtual power plant (VPP), such as sudden unit losses and significant demand changes, a scheduled power tracking control method is proposed to simultaneously track the assigned power required by the transmission system operator in order to avoid the punishment of the mismatched generation. • The proposed control considers the inclusion of both the grid-forming and grid-following DER and the constraints from the DER capacity and communication delays and proposes the parameter designing method to ensure a safe and stable VPP operation. • A Matlab/Simulink serves to verify the function of the proposed control on the scheduled power tracking in the various scenarios, and a IEEE 39-bus system case study is used to verify the proposed control on the frequency stability enhancement for the entire power system. The Virtual Power Plant (VPP) has been proposed to aggregate Distributed Energy Resources (DERs) to act like a single power plant, thus, it also has functions on the frequency and voltage support. The most of the previous works have been conducted on the use of VPP for economic dispatch and energy management. However, now the VPP as an alternative to the traditional power plant has to be engaged with the power system dynamics, especially be in response to the contingencies. Up-to-date, none of the previous work considers the response of the VPP in relation to the internal contingencies, such as a sudden units lost and a significant demand change. This VPP internal contingency would at one aspect lead to economical punishment due to the miss-scheduled generation and another aspect results in the entire system dynamics. In order to confront the VPP internal contingency, this paper proposes a Scheduled Power Tracking Control (SPTC) strategy to ensure the VPP power generations. Such a method simultaneously forces the remaining online units of the VPP to track the dispatched power set by the Transmission System Operator (TSO) after the contingency occurs within the VPP. Considering the communication delays and DER capacity limitations, the parameter design for the SPTC is proposed to ensure a safe and stable VPP operation. The Matlab/Simulink simulations are used to validate the function of the SPTC in terms of the power tracking and resetting, while a modified IEEE 39-bus benchmark system serves to verify the effectiveness of the SPTC on the frequency stability enhancement for the entire power system. [ABSTRACT FROM AUTHOR]

• Grid stability, grid reliability, and grid resilience are the key performance indicators for a grid-connected PV system to obtain grid synchronization [ 18 , 19 ]. • In [20] proposed constant coupling effect based PLL to maintain stability in grid connected power system. In conventional and weak grid systems, authors demonstrated high grid impedance variation robustness and anti-interference capabilities [21]. • Grid synchronization is attained by achieving stability, reliability, and resiliency parameters. To achieve stability and resilience in the system, advanced DC-DC converters, in particular, HGCB, as well as the proposed GW-RUCA algorithm, are beneficial. • Reliability assessment is achieved by making the appropriate adjustments to the duty ratio of HGCB converter so that an uninterrupted power supply can be provided without decreasing overall power quality. It is crucial to combine a range of different energy sources and power electronic converters to appropriately meet the load demands under dynamic environmental conditions. This paper presents an effective implementation of a single-phase, two-stage Photovoltaic (PV) system linked to the grid under Standard Test Conditions (STC). The first step incorporates the usage of various DC-DC converters with a Maximum Power Point Tracking (MPPT) controller. Artificial Bee Colony integrated Perturb and Observation (ABC-PO) and proposed Grey-Wolf Robust Unified Control Algorithm (GW-RUCA) MPPT maximizes solar module power. The second stage synchronizes with the grid using DC–AC converter, LCL filter, and Phase Locked Loop (PLL). To analyse a 2 kW grid-connected solar power system, grid current, and voltage were synchronized during load and irradiance changes. The duty ratio for the proposed GW-RUCA MPPT algorithm tracks much faster than ABC-PO. The novelty of this work is to simulate all DC-DC converters such as Non-isolated Buck- Boost based Zeta (NBBZ) converter, single input dual output (SIDO) DC-DC converters, and High Gain Cascaded Boost (HGCB) converter to differentiate grid-connected PV system efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

• A PSO-based optimization method for VRCD coordination control parameters of shipboard MVDC system is proposed. • Models of gas turbine and MVDC power system are established, leading to the quantification of evaluation indicators considering gas turbine capacity and HESS configuration. • The simulation results validate the effectiveness of the proposed control strategy and optimization method, contributing to improved transient power flow. Supplying power for large pulsed power load with shipboard MVDC system has continued to be a challenge. Due to limited grid capacity and power ramp rate of prime movers, the high-power load mutation will cause intolerable impact, which is an essential issue to be solved. In this paper, hybrid energy storage system is configured for transient power compensation, and the distributed virtual resistive capacitive droop is introduced to power coordination for MVDC sources. The transient flow evaluation function considering the speed state of the genset and the configuration cost of hybrid energy storage system is defined, models of the gas turbine and MVDC power system are established, and the optimization method of control parameters and system flow based on PSO and model simulation is proposed. The effectiveness of the proposed control strategy and optimization method is verified by MATLAB/Simulink simulations. [ABSTRACT FROM AUTHOR]

• This paper introduces a passive islanding detection approach that uses deep learning combined with the continuous wavelet transform. • The proposed approach does not require the identification of the islanding features a priori as in the existing islanding detection approaches. • Instead the coefficients of the CWT are directly fed to the CNN networks, which are then used to train the model and automatically learn the features. • This approach is simulated and tested on a test system that includes a grid-connected photovoltaic system while considering different operating conditions. • The results have shown that the testing accuracy of the proposed approach may reach 98.6% with a fast detection time of 0.21 s. The renewable-based distributed energy resources (R-DERs) are extensively used in the smart distribution systems. Despite the advantages of the R-DER, they also introduce some operational challenges such as the unintentional islanding, reverse power flow, and several protection issues. Due to the unpredictable faults, an island or multiple islands can be formed throughout the electrical power systems. The island may have R-DER that shall be tripped within 2 s of the islanding formation as per IEEE 1547 and hence the islanding must be detected. This paper introduces a passive islanding detection approach that uses deep learning combined with the continuous wavelet transform and hence no need for identifying the islanding features a priori as in the existing islanding detection approaches. The numerical examples demonstrating the effectiveness of the proposed approach are presented and the conclusion is drawn. [ABSTRACT FROM AUTHOR]

• We proposed an adaptive (two-stage) robust energy management for an isolated microgrid considering renewables uncertainty. • Minimization of the expected total operating costs of the microgrid is the objective function. • Reactive power costs from diesel generators are considered and are co-optimized with active power costs • The reactive power capability of the inverter-interfaced distributed energy resources is considered. • Detailed modeling of the diesel generators and inverter interfaced distributed energy resources by the consideration of their capability curves is provided. • The results obtained validate the effectiveness of the proposed solution. This paper presents an adaptive robust Energy Management (EM) model for an isolated Microgrid (MG) to decide for the day-ahead optimal dispatch to effectively manage the MG power sources considering uncertainties in Renewable Energy Sources (RESs). The aim of this model is to minimize the operation costs, reactive power costs, spinning reserve and load shedding. Usually, fuel consumption costs of diesel generators are considered to be dependent on active power generation only. However, neglecting the related reactive power costs might result in increased operation costs and deviations from optimal dispatches. Hence, this paper optimizes the costs related to both active and reactive powers of diesel generators. Furthermore, simultaneous active/reactive power dispatch can lead to accurate operation decisions compared to separate dispatch for active or reactive power alone. In addition, this study considers the reactive power capability of inverter-interfaced Distributed Energy Resources (DERs) so that reactive powers can be supplied from inverter-interfaced DERs. Moreover, detailed models for the different resources are presented, especially for diesel generators and inverter interfaced DERs where actual capability curves are used instead of the widely used box constraints. The problem is formulated as nonlinear programming problem using GAMS program and solved by the CONOPT solver. [ABSTRACT FROM AUTHOR]

This paper discusses the optimal selling price and energy procurement strategies for a retailer in an electricity market [Electric Power Syst. Res. 79 (2009) 246-254] while the optimal strategy of a retailer over a time period is presented to decide on the optimal energy purchase portfolio from several sources. The risk is assessed using linearized Conditional Value at Risk (CVaR) while CVaR is considered with the coherency properties (translation invariance, sub additivity, positive homogeneity and monotonicity). Indeed, CVaR lacks the monotonicity property. Therefore, this paper intends to prove this issue. [ABSTRACT FROM AUTHOR]

• A new control scheme is proposed to benchmark performance of the power control strategies. • The DC-link voltage oscillations originated from active power oscillations are eliminated. • Increasing lifetime of inverter as well as eliminating third order current harmonics at AC side. • Protection of overvoltage at DC-side of inverter and overcurrent at AC-side of inverter. • Comparative analyses for state of the art proposed control scheme are performed. Voltage and current oscillations have become a primary power quality issues for DC and AC systems. In this respect, this paper presents a new control scheme for analytical implementation of reference current generator (RCG) based power control strategies to eliminate oscillations both DC and AC sides. Benchmarking of the RCG based power control strategies are examined in terms of elimination of the power oscillations, reducing DC-link voltage oscillations, avoiding DC-side overvoltage and preventing AC-side overcurrent. Compared to the existing strategies, controlling reference active power is provided with a closed-loop control system. A noteworthy contribution of this paper is to eliminate active power oscillations, which is an effective method to suppress the DC-link voltage oscillations resulting in third-order harmonic at the grid side. This helps to reduce the size of the DC-side capacitor and also improves the lifetime of the inverter, safety and stability of the grid connected primary energy resources (PERs). Detailed comparative analysis with the most recent strategies have been performed for state of the art proposed control scheme. Finally, various case studies are presented to support the proposed control scheme can mitigate the DC-link voltage oscillations, effectively. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage prevention and emergency control strategy that consists of coordinately arranging multiple reactive power sources in order to handle the point of common coupling (PCC) voltage fluctuation and stability in large-scale PV power plants. When a disturbance occurs at the PCC, dynamic reactive power compensation devices are coordinated preferentially to support the PCC voltage. After the disturbance is cleared, the reactive power in dynamic and fast devices is transferred into static and slow devices so that the static VAR generation (SVG) can maintain a large power margin for coping with the next disturbance. Moreover, the reactive power output of the individual inverter in PV power plants is coordinately allocated using a model to optimize the in-station voltage distribution. Finally, the effectiveness of the proposed control strategy is verified by an example simulation of a practical large-scale PV power plant. [ABSTRACT FROM AUTHOR]

In this paper, a hierarchical control structure with voltage unbalanced compensation scheme in ac islanded microgrid is proposed to improve Critical Load Bus (CLB) voltage quality and address inaccurate power sharing problems. The hierarchical scheme includes primary and secondary control levels. The primary control mainly contains the power droop controllers, voltage and current controllers, selective virtual impedance loop, and voltage unbalanced compensation. The virtual impedance loop includes virtual positive- and negative-sequence impedance loops at fundamental frequency and virtual variable harmonic impedance loop at harmonic frequencies. The secondary control is designed to restore frequency and amplitude of the CLB voltage. In order to compensate the CLB voltage, an unbalanced compensation is proposed to change the voltage reference of the distributed generation (DG) units. This strategy also employs the low bandwidth communication (LBC) technique to send the proper signals of the secondary control from the microgrid control center (MGCC) to the primary control. To evaluate the performance of the proposed control strategy, simulations are conducted on two islanded microgrid prototype. The results demonstrate the effectiveness of the proposed control structure in the unbalance and harmonic compensation of the CLB voltage and proper power sharing of reactive, unbalanced and harmonic powers among the DG units. [ABSTRACT FROM AUTHOR]

The stated aim of the European Commission has been the unbounded flow of energy across Europe and the effective functioning of a single European power market so as to achieve secure, sustainable and affordable energy supplies, as well as to foster competition and increase the utilization of electricity networks and generation capacity. Most countries have already adapted or are gradually adapting their wholesale markets to the provisions of the so called Target Model for the internal electricity market in Europe, however Greece still lies behind in this binding target. In this paper, the basic design variables and respective options for the integration of the Greek wholesale electricity market with the other European markets under the Target Model paradigm are presented. The design variables refer to all market instances and mechanisms. The proposed choices are justified in terms of effectiveness and market power mitigation, considering the current market structure in Greece. A transitional phase for the full integration of the Greek Intraday and Balancing Markets is proposed, considering the relevant evolutions in the wholesale markets of Greece’s neighboring countries. Finally, a simulation analysis is performed in order to highlight the implications on schedules of utilizing European-based order formats in the restructured Greek electricity market. [ABSTRACT FROM AUTHOR]

• Voltage relays showed high dependability and are promising for microgrid protection. • The enhanced method efficiently improved the reliability of voltage-based protection. • The method was tested for sympathetic trips and changes in the microgrid operation. • The improvements did not imply an increase in the complexity of the protection method. • The voltages and currents were analyzed for the islanded and grid-connected microgrid. Microgrids emerged as an efficient way to integrate distributed energy resources and local loads into power distribution systems, allowing the local system operation in grid-connected and islanded modes. However, the microgrids imply several challenges for the protection systems, such as the changes in fault current path and the decrease of the fault current amplitude during islanded operation. Therefore, conventional overcurrent protection does not guarantee selectivity, coordination, reliability, and adequate trip time in AC microgrids. Under this perspective, voltage-based relays have been widely investigated as a potential protection for AC microgrids. Thus, this paper critically reviews voltage-based protection and proposes improvements to an existing technique, aiming to simplify the settings and guarantee reliability and selectivity among various voltage-based protection devices. The results showed that our modifications improved the selectivity and reliability of the voltage-based protection compared with the original technique and the traditional overcurrent protection devices for different topologies of an AC microgrid. [ABSTRACT FROM AUTHOR]

• The uniformity of electric field in insulation is a sign of its health. • Insulation voids lead to inhomogeneous distribution of the electric field. • Insulation defects cause to increasing of the leakage current. • Changing the void dimensions is effective in non-uniformity of field distribution. • The inner void of insulation is worse than the surface void of insulation. The growing population and the need to use clean and safe energy for public and industrial use, has led engineers to look for safe ways to supply energy. Meanwhile, the use of GIS substations has increased due to the need for less maintenance and faster installation, but these equipments have weaknesses that will affect their safe operation if inattention. In a GIS compartment, solid insulation is one of the parts that becomes defective usually which this causes a non-homogenous distribution of electric field inside the insulation and partial discharges in the void in insulation and leads to insulation failure finally. In this paper, by assuming an elliptical void on the surface (not inside) of a 145 kV gas insulation switchgear spacer, non-uniformity in potential distribution, electric field distribution, current density and leakage current are investigated. Also, in cases of the constant and variable volume of the elliptical void, the effect of changing void dimensions on the desired parameters is analyzed. The results comparison shows that although changing the void radius is effective on the parameters, but the effect of changing the depth of the void on the non-uniformity of the potential distribution, field distribution and leakage current are greater. [ABSTRACT FROM AUTHOR]

• LF signal injection for faulty feeder detection in unearthed MV network is possible. • LF signal is injected through primary windings of group of three IVTs. • It is possible to influence the IVT design to make it suitable for signal injection. • The capacitance to ground topology influences the signal distribution the most. Unearthed neutral is often used in industrial networks, which require continuous power supply, and in distribution networks where the network capacitive current is not too high; or it is uneconomical to move to compensated grounding. Unearthed networks can remain in operation during an earth-fault, but fast determination of the faulty line is the key for prevention of further fault escalation. Signal injection is one of the fault location methods often used in LV unearthed networks. The possibility of application of this method in MV networks is dependent on how to inject the signal into unearthed phases with voltages ranging from 10 to 35 kV. This paper presents the signal injection circuit, which consist of three inductive voltage transformers (IVTs). The specifics of IVT design for signal injection are discussed. The application of the LF signal injection during an earth-fault was simulated on the model of an unearthed distribution network in EMTP. An intermittent fault and ring-type network connection were considered as possible cases. [ABSTRACT FROM AUTHOR]

• Interharmonics caused by MPPT operation and nonlinear loads in grid-tied PV system. • Shunt Active Power Filter (SAPF) is employed for interharmonics mitigation. • Proposed optimal technique MSCA to optimize the control parameters of MPPT and SAPF. • Proposed methodology validated by laboratory-based real-time system. Interharmonics are generated by nonlinear loads, interfacing converters that connect renewable energy sources to the grid, and the Maximum Power Point Tracking (MPPT) in photovoltaic systems. Interharmonics can also have negative impacts on power supply lines by interfering with control and protection signals. This will result in significant energy losses and stability issues with the system for large-scale PV systems. Several harmonic mitigation strategies have been developed such as the optimal selection of various control parameters related to MPPT controller and Shunt Active Power Filters (SAPF). The optimal design of SAPF parameters requires significant computational effort when they are solved by conventional optimization techniques. In this paper, a Multi Sine Cosine Algorithm (MSCA) based methodology has been incorporated for the optimal design of SAPF with the goal of reducing interharmonics. The effectiveness of the proposed methodology is verified by simulation using MATLAB Simulink and validated using two case studies, viz rectifier with RL load and UPS load. From the results, it is established that the interharmonics in grid current due to MPPT perturbation are restricted to less than 2% of the magnitude at the fundamental frequency and interharmonics from nonlinear loads are totally eliminated. Further, the proposed methodology was also implemented on a laboratory-based real-time system to reduce the effects of interharmonics in the grid-tied PV system. [ABSTRACT FROM AUTHOR]

• A cost-efficient centralized topology integrated with distribution system is proposed to compensate the voltage drops. • Mathematical modelling is formulated to reveal the compensation mechanism, required compensation rating, and dc voltage. • A more generalized and practical power loss model based on scaling laws is formulated to analyze the loss reduction mechanism. • A comprehensive control scheme is developed to achieve the voltage quality improvement. Recently, an intelligent substation by the L-coupling static synchronous compensator integrated with a primary tapped transformer (L-STATCOM PTT) has been developed to perform multifunction operations, including stable power supply and desired power quality. While previous works mainly focus on current quality, the cost-effective compensation of voltage quality is still not involved. This paper firstly formulated the mathematical model of voltage compensation to reveal the compensation mechanism, and determine the required inverter rating and reasonable dc voltage for acceptable performance. Then its power rating reduction under different voltage drops has been mathematically revealed compared with conventional STATCOM. Furthermore, by considering the potential differences in IGBT switching time and collector-emitter on-state resistance, a more generalized and practical power loss model based on scaling laws is formulated. The proposed voltage compensation method can reduce compensator rating by 28.1% and power loss by 12.2% at the 10% voltage drop. Simulation and experiments are performed to prove the validity and effectiveness of the proposed topology over cost-effectiveness and load voltage support. [ABSTRACT FROM AUTHOR]

In the light of the rapid advances in renewable energy technologies, they have become an appropriate option to supply energy with numerous advantages. Besides, the coordination of different energy resources and the proliferation of energy conversion technologies such as Combined Heat and Power (CHP) has facilitated the raising of new energy prosumers called Smart Energy Hub (S.E.Hub). This paper utilizes an innovative model to propose a secured decentralized energy market architecture that consists of S.E.Hubs, energy utility grids, energy consumers, and an aggregator. The interaction among these players is modeled as a bilevel optimization problem. This problem has been transformed into a single-level mixed integer linear problem by means of the Strong duality theorem. Numerical results show how the pricing method influences S.E.Hubs' motivation to provide more energy on high-demanded hours. Furthermore, two-sided cooperations could be seen among S.E.Hubs that facilitate their energy bill reduction. • Aggregators' behavior towards S.E.Hubs in LEM is modeled by a bilevel problem. • The model balances energy prices in all hours. • Our design optimizes multi-energy consumers' cost and S.E.Hubs' profit. • The stochastic behavior of renewables is modeled with Beta and Weibull functions. • Results validate the effectiveness of the proposed design of local energy markets. [ABSTRACT FROM AUTHOR]

• Protection against electric shock and protection selectivity in collective prosumer electrical installations (cPEI) are investigated. • A cPEI can be easily established based on LV distribution system. • Original protective devices implemented in LV distribution system must be verified while the cPEI is planned to operate in island mode. • The case study demonstrates the whole process of protection verification to meet the requirements. • The case study prove the original protection devices and introducing molded case circuit breakers can satisfy the protection requirements. IEC 60364-8-2 introduces many safety issues concerning a new concept of integration of electricity consumers and local power generation and energy storage, i.e., prosumer's low-voltage electrical installations. A collective type of them is several consumer installations connected to the same public distribution system and sharing one common set of local power supplies and energy storage unit. The transition to island mode raises technical challenges related to ensuring the protection selectivity and the effectiveness of protection against electric shock. They result from the expected short-circuit currents, much smaller compared to other modes. In this paper, the first approach for protection verification and design concerning collective prosumers' electrical installation to be established based on an existing low-voltage distribution system in each area (group of prosumers) is proposed. It includes the following: calculation of short-circuit currents while operating in island mode, selection of the currents relying on the current limit of an energy storage unit, verification of the protection devices, and design of the additional protection. The case study confirms the approach allows for the investigation of the common protection devices in terms of meeting both the safety and selectivity requirements. Otherwise, advanced protection schemes and strategies should be considered to meet the same safety requirements. [ABSTRACT FROM AUTHOR]

The Non-Utility Distributed Energy Resources (nDERs) are those not responsible for supporting the distribution system operation. These resources are crucial for improving the Energy mix's sustainability due to their majority renewable nature. However, integrating these resources into distribution systems has become a challenge for Distribution Companies (DisCos) due to their intermittent behavior. This challenge is even more significant when a gap in distribution system modernization (smart meters and communication systems) exists. This paper proposes an approximate method to evaluate the nDERs' impact on the distribution system's steady-state voltage. The method is based on a linear approximation of voltage drop/rise and the impedance matrix. It has been validated on two distribution systems considering five scenarios. Numerical comparison with exact solution has shown good results in four scenarios with maximum absolute errors around 0.01 p.u. in low-risk and high-risk voltage violation situations. The proposed method can be used in the planning or operation stage as a first estimation where no real-time monitoring is available, or the power-flow calculation is difficult to obtain. • The method does not require running a power flow simulation for each analysis. • The nDERs' voltage impact can be easily estimated by matrix/vector operation. • The DisCo can define power limits for operation without real-time monitoring. • A first estimation of nDERs' voltage impact in common scenarios. [ABSTRACT FROM AUTHOR]