Showing papers on "Islanding published in 2017"
TL;DR: In this paper, an extensive review on control schemes and architectures applied to dc microgrids (MGs) is presented, covering multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms.
Abstract: This paper performs an extensive review on control schemes and architectures applied to dc microgrids (MGs). It covers multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms. Islanding detection, protection, and MG clusters control are also briefly summarized. All the mentioned issues are discussed with the goal of providing control design guidelines for dc MGs. The future research challenges, from the authors’ point of view, are also provided in the final concluding part.
452 citations
TL;DR: A stochastic framework for day-ahead scheduling of microgrid energy storage systems in the context of multi-objective (MO) optimization is presented and the obtained results demonstrate the applicability and efficiency of this framework in dealing with conflicting requirements of micro grid security and economic operation.
Abstract: This paper presents a stochastic framework for day-ahead scheduling of microgrid energy storage systems in the context of multi-objective (MO) optimization. Operation cost of microgrid in normal conditions and load curtailment index in case of unscheduled islanding events (initiated by disturbances in the main grid) are chosen as main criteria of the proposed scheme. In practice, duration of disconnection from the upstream network is unknown in unscheduled islanding incidents and cannot be predicted with certainty. To properly handle the uncertainties associated with time and duration of such events as well as microgrid load and renewable power generation, stochastic models are involved in the MO scheduling framework and they are formulated as mixed integer linear programming problems. The non-dominated sorting genetic algorithm II is employed to effectively cope with the MO optimization problem and a fuzzy decision making approach is employed for appropriate representation of microgrid operator’s preferences in compromising between the two objectives. The proposed scheme is implemented on a test microgrid and the obtained results demonstrate the applicability and efficiency of this framework in dealing with conflicting requirements of microgrid security and economic operation.
181 citations
TL;DR: In this paper, the authors proposed a new hybrid method for the islanding detection of distributed-generation (DG) units, which is based on the combination of an active and a passive method, for which the optimized Sandia frequency shift (SFS) method is used as the selected active method, and rate of change of frequency relay (ROCOF) is employed as the passive method.
Abstract: This paper is aimed at proposing a new hybrid method for the islanding detection of distributed-generation (DG) units. Hybrid method operation is based on the combination of an active and a passive method, for which the optimized Sandia frequency shift (SFS) method is used as the selected active method, and rate of change of frequency relay (ROCOF) is used as the passive method. In order to demonstrate the effectiveness of the proposed technique on islanding detection, several simulation studies based on IEEE 1547 and UL1741 anti-islanding test requirements are carried out. The evaluation of simulation results reveals that the control system, based on the proposed hybrid algorithm, meets the DG islanding protection requirements efficiently. Moreover, it will be demonstrated that the proposed hybrid method is capable of accurately operating under multiple DG units, load switching in the grid-connected mode, as well as different load quality factor conditions.
156 citations
TL;DR: In this article, the effect of active islanding detection on the performance of ROCOF relays has been investigated for an inverter-based distributed generation (DG) and an algorithm along with the new threshold settings to enable it to operate inside the nondetection zone (NDZ) of the conventional frequency relays is proposed.
Abstract: Intentional frequency perturbation by recently researched active islanding detection techniques for inverter based distributed generation (DG) define new threshold settings for the frequency relays. This innovation has enabled the modern frequency relays to operate inside the non-detection zone (NDZ) of the conventional frequency relays. However, the effect of such perturbation on the performance of the rate of change of frequency (ROCOF) relays has not been researched so far. This paper evaluates the performance of ROCOF relays under such perturbations for an inverter interfaced DG and proposes an algorithm along with the new threshold settings to enable it work under the NDZ. The proposed algorithm is able to differentiate between an islanding and a non-islanding event. The operating principle of relay is based on low frequency current injection through grid side voltage source converter (VSC) control of doubly fed induction generator (DFIG) and therefore, the relay is defined as “active ROCOF relay”. Simulations are done in MATLAB.
147 citations
TL;DR: A stochastic framework for optimal scheduling of microgrid resources over unscheduled islanding events, initiated by disturbances in the main grid, that addresses the prevailing uncertainties of islanding duration as well as prediction errors of demand and renewable power generation.
Abstract: This paper deals with energy management of microgrids during unscheduled islanding events, initiated by disturbances in the main grid. In these situations, the main challenge is uncertainty about duration of disconnection from the main grid. In order to tackle this issue, a stochastic framework is proposed for optimal scheduling of microgrid resources over this period. The presented framework addresses the prevailing uncertainties of islanding duration as well as prediction errors of demand and renewable power generation. According to this framework, the probability distribution of islanding duration needs to be estimated, instead of predicting its exact value. The objective is to minimize the expected value of operation cost over the estimated islanding interval, while restricting the load loss risk imposed by uncertain parameters within an acceptable level. Moreover, the impact of microgrid scheduling on the subsequent grid-connected operation is considered via a simple method. The associated stochastic optimization problem is formulated as a mixed integer linear programming model. The developed framework is implemented on a test microgrid and various case studies are presented to demonstrate its effectiveness.
136 citations
TL;DR: In this paper, a real-time mutli-period artificial bee colony (MABC) topology type central energy management system (CEMS) for home micro-grids in islanding mode is proposed to maximize operational efficiency and minimize operational cost of the H-MG with full degree of freedom in automatically adapt the management problem under variations in the generation and storage resources in real time as well, suitable for different size and types of generation resources and storage devices with plug-and-play structure.
132 citations
TL;DR: In this article, an overview of advanced control methods for microgrids, especially the islanded and inverter-based, are presented and categorized in terms of their respective features.
Abstract: Increased penetration of distributed generation (DG) into the power systems has created fundamental challenges from the viewpoints of control and reliable operation of systems. Microgrids (an aggregation of DG units, loads, and storage elements) with proper control strategies can be a good solution for removing or facilitating these challenges. The introduction of inverter-based microgrid in a distribution network has facilitated the utilization of renewable energy resources, distributed generations, and storage resources; furthermore, it has improved power quality and reduced losses, thus improving the efficiency and the reliability of the system. As most DG units are connected via a power electronic interface to the grid, special control strategies have been developed for inverter interfaces of DG units in islanded microgrids. This paper presents an overview of advanced control methods for microgrids, especially the islanded and inverter-based. Moreover, various control methods are compared and categorized in terms of their respective features. It also summarizes microgrid control objectives with their most problematic solutions as well as their potential advantages and/or disadvantages. Finally, some suggestions are put forward for the future research.
108 citations
TL;DR: An energy storage management system based on distributed secondary level control, which promotes charge/discharge control and provides SOC equalization simultaneously is proposed.
Abstract: DC microgrids have been known to be a promising solution for improving renewable energy integration with electrical grid and enhancing the system’s overall energy efficiency. A key component of this microgrid is the energy storage system, which besides smoothing the intermittent behavior of renewable sources, also allows intentional islanding and the execution of optimization routines to improve the microgrid performance. Assuming that storage systems in commercial and residential buildings will mostly be composed of multiple storage units, an energy storage management system, which provides charge/discharge monitoring and state-of-charge (SOC) equalization, is needed to prevent overcharging the units or their uneven use, which can lead to faster deterioration of battery banks. This paper proposes an energy storage management system based on distributed secondary level control, which promotes charge/discharge control and provides SOC equalization simultaneously. The SOC imbalance compensation alters the energy storage unit virtual droop resistance according to the difference between the unit SOC and the microgrid average SOC, thus the compensation intensity is dependent on the imbalance level being suitable to be employed in dc bus signaling controlled microgrids.
102 citations
TL;DR: In this paper, the authors provide a comprehensive review of the major concepts associated with the μgrid, such as constant power load (CPL), incremental negative resistance or impedance (INR/I), and its dynamic behaviors on the μ-grid, and power system distribution.
Abstract: This paper provides a comprehensive review of the major concepts associated with the μgrid, such as constant power load (CPL), incremental negative resistance or impedance (INR/I) and its dynamic behaviours on the μgrid, and power system distribution (PSD). In general, a μgrid is defined as a cluster of different types of electrical loads and renewable energy sources (distributed generations) under a unified controller within a certain local area. It is considered a perfect solution to integrate renewable energy sources with loads as well as with a traditional grid. In addition, it can operate with a conventional grid, for example, by energy sourcing or a controllable load, or it can operate alone as an islanding mode to feed required electric energy to a grid. Hence, one of the important issues regarding the μgrid is the constant power load that results from the tightly designed control when it is applied to power electronic converters. The effect of CPL is incremental negative resistance that impacts the power quality of a power system and makes it at negative damping. Also, in this paper, a comprehensive study on major control and compensation techniques for μgrid has been included to face the instability effects of constant power loads. Finally, the merits and limitations of the compensation techniques are discussed.
101 citations
TL;DR: In this paper, a new concept, probability of successful islanding (PSI), indicating the probability that a microgrid maintains enough spinning reserve (both up and down) to meet local demand and accommodate local renewable generation after instantaneously islanding from the main grid, is developed.
96 citations
TL;DR: In this article, a single-stage three-phase four-wire grid-connected photovoltaic (PV) system operating with a dual compensating strategy and feedforward control loop (FFCL) is proposed.
Abstract: This paper proposes a single-stage three-phase four-wire grid-connected photovoltaic (PV) system operating with a dual compensating strategy and feedforward control loop (FFCL). Besides injection of active power into the grid, the PV system operates as a unified power quality conditioner (UPQC), suppressing load harmonic currents and compensating reactive power. Furthermore, regulated, balanced, and harmonic-free output voltages are provided to the load. Since the PV-UPQC is based on a dual compensation strategy, the series converter operates as a sinusoidal current source, whereas the parallel converter operates as a sinusoidal voltage source. Thus, seamless transition can be achieved from the interconnected to the islanding operation modes, and vice versa, without load voltage transients. Moreover, to overcome problems associated with sudden solar irradiation changes, fast power balance involving the PV array and the grid is obtained, since the FFCL acts on the generation of the series inverter current references. As a result, the dynamic responses of both inverter currents and dc-bus voltage are improved. Detailed analysis involving the active power flow through the inverters is performed allowing proper understanding of the PV-UPQC operation. Experimental results are presented to evaluate both dynamic and static performances of the PV-UPQC tied to the electrical distribution system.
TL;DR: With proper robust level, the solution of the proposed scheduling model ensures successful islanding of the microgrid with minimum load curtailment and guarantees robustness against all possible realisations of the modelled operational uncertainties.
Abstract: This study proposes a robust optimisation-based optimal scheduling model for microgrid operation considering constraints of islanding capability. The objective is to minimise the total operation cost, including generation cost and spinning reserve cost of local resources as well as purchasing cost of energy from the main grid. To ensure the resiliency of a microgrid and improve the reliability of the local electricity supply, the microgrid is required to maintain enough spinning reserve (both up and down) to meet local demand and accommodate local renewable generation when the supply of power from the main grid is interrupted suddenly, i.e. microgrid transitions from grid-connected into islanded mode. Prevailing operational uncertainties in renewable energy resources and load are considered and captured using a robust optimisation method. With proper robust level, the solution of the proposed scheduling model ensures successful islanding of the microgrid with minimum load curtailment and guarantees robustness against all possible realisations of the modelled operational uncertainties. Numerical simulations on a microgrid consisting of a wind turbine, a PV panel, a fuel cell, a micro-turbine, a diesel generator and a battery demonstrate the effectiveness of the proposed scheduling model.
TL;DR: In this article, an improved model predictive control (MPC) algorithm is used to regulate various parameters such as output voltage, frequency and power of the inverters in the MMG system.
Abstract: This study presents a control method to regulate load voltage and system frequency during microgrid islanding in a multi-area multi-microgrid (MMG) system. In the event of islanding of a microgrid from the distribution grid in the proposed MMG system, load voltage of the islanded microgrid and system frequency are affected. To overcome these problems, a control system for the MMG system is proposed. The proposed control system facilitates desired power exchange between grid-connected and islanded microgrids, and achieves effective voltage and frequency regulation in the MMG system. The main significance of the proposed MMG system is that multiple microgrids in different locations can be interconnected to meet larger bulk power demands. This ensures improved reliability and security of power supply in the MMG system. An improved model predictive control (MPC) algorithm is used to regulate various parameters such as output voltage, frequency and power of the inverters in the MMG system. The proposed MMG system is tested during islanding and load shedding using simulation studies. The simulation studies show that the inverters can operate effectively using MPC to provide the desired voltage, frequency and power during islanding and load shedding.
TL;DR: Numerical simulations study a test provisional microgrid for exploring its merits, as well as demonstrating its benefits when compared with deployment of a traditional microgrid.
Abstract: The optimal planning problem of provisional microgrids, as a new class of microgrids, is investigated in this paper. Unlike traditional microgrids, provisional microgrids do not possess the islanding capability and are dependent on one or more electrically connected microgrids, called coupled microgrids, for islanding purposes. Provisional microgrids can be considered as enablers of rapid integration of renewable energy resources in distribution networks, while at the same time providing economic benefits for local consumers and environmental benefits for the entire system. The provisional microgrid planning problem is defined and formulated in this paper, considering anticipated interactions between the provisional microgrid, the coupled microgrid, and the utility grid during grid-connected and islanded modes. Robust optimization is used to efficiently consider physical and financial uncertainties in the problem. Numerical simulations study a test provisional microgrid for exploring its merits, as well as demonstrating its benefits when compared with deployment of a traditional microgrid.
TL;DR: The feasibility of using a simple power factor-frequency inverse droop control for series-connected islanding microconverters and the accuracy of power sharing is not affected by the variations of microgrid feeder parameters or the disturbance of the point of common coupling (PCC) nonlinear loads.
Abstract: Series-connected microconverters have been used to integrate distributed energy resources into grid mains through a single-stage power conversion. When this string converter is switched to islanding operation mode, it is preferred to share the local load demand by series microconverter modules in a decentralized manner. Due to the characteristics of series connection, the well-understood P–f droop and Q–E droop control for parallel distributed generation units in a conventional islanding microgrid is not applicable in this case. To solve this problem, the feasibility of using a simple power factor-frequency inverse droop control for series-connected islanding microconverters is discussed in this paper. The proposed method can achieve simultaneous real and reactive power sharing without the assistance of any communications between series microconverters. Furthermore, the accuracy of power sharing is not affected by the variations of microgrid feeder parameters or the disturbance of the point of common coupling (PCC) nonlinear loads. Simulated and experimental results are provided to verify the correctness of the proposed method.
TL;DR: An active islanding detection method based on frequency-locked loop (FLL) for constant power controlled inverter in single-phase microgrid is proposed, which generates a phase shift comparing the instantaneous frequency obtained from FLL unit with the nominal frequency to modify the reference phase angle.
Abstract: An active islanding detection method based on frequency-locked loop (FLL) for constant power controlled inverter in single-phase microgrid is proposed. This method generates a phase shift comparing the instantaneous frequency obtained from FLL unit with the nominal frequency to modify the reference phase angle. An initial low frequency variable triangular disturbance is added to the phase shift in order to reduce non-detection zone and accelerate the detection process especially in the case of power matching. With the modified phase angle, the frequency at point of common coupling will be drifted away from the nominal frequency until exceeding the threshold because of the frequency positive feedback after islanding. Besides, FLL is introduced to this method in order to lock frequency quickly considering that the frequency is time-varying during the islanding detection process. Simulation and experiment have been done to evaluate this method.
TL;DR: In this article, the authors proposed a scheme for reduction in losses and improvement of bus voltages in the active distribution network, where a DG in the form of small renewable energy resources such as solar PV, wind, biomass, is placed optimally for reduction of losses in the network.
Abstract: Due to rapid depletion of fossil fuels availability and huge environmental pollution, focus is now changing from traditional method of power generation to the non-conventional DERs located at distribution voltage level. Technological advancement and more researches in the use of DERs result in the formation of microgrids and active distribution network. Small DER units when placed in a network near to load, makes the network stable as it can work in islanding mode in case of any fault outside the network. This paper proposes a scheme for reduction in losses and improvement of bus voltages in the active distribution network. A DG in the form of small renewable energy resources such as solar PV, wind, biomass, is placed optimally for reduction of losses in the network. However, placement of DG does not result in fulfilment of reactive power needs of the network, resulting in under voltage at several buses. This under voltage problem is solved by the optimal placement of DSTATCOM. DLF technique is used in this paper for load flow calculations and LSF along with voltage deviation is used in objective function for optimal location of DG on MATLAB platform. The methodology is tested on 33-bus radial distribution system.
TL;DR: In this paper, a spectral clustering algorithm is presented to obtain an islanding solution, which results in minimal power flow disruption across boundaries of islands, based on generator coherency grouping.
Abstract: Intentional islanding is often conducted as the last resort to preserve the electric grid from severe blackouts. The intentional islanding scheme deliberately segregates the power system into a number of self-sustained islands to enhance the transient stability of the power network. In this study, a spectral clustering algorithm is presented to obtain an islanding solution, which results in minimal power flow disruption across boundaries of islands. The constraint in the spectral clustering method is introduced based on generator coherency grouping. The proposed scheme ensures that each island is only comprised of generators, which are synchronized with each other. The proposed clustering scheme utilizes a more computationally efficient and accurate k -medoids algorithm comparing to k -means ones. The proposed intentional islanding method is scrutinized using the IEEE 9-bus and IEEE 118-bus models. The results of simulations demonstrate that the proposed method can effectively prevent blackouts by separating the systems into stable islands.
TL;DR: In this article, the authors present the positive-sequence, negative-sequence and zero-sequence voltage and current control schemes in the dq frame for the voltage-source converter (VSC)-based distributed generation (DG) units in order to compensate for voltage unbalance in a microgrid.
Abstract: This paper presents the positive-sequence, negative-sequence, and zero-sequence voltage and current control schemes in the dq frame for the voltage-source converter (VSC)-based distributed generation (DG) units in order to compensate for voltage unbalance in a microgrid. The objective of these schemes is to control the positive-, negative-, and zero-sequence components (separately and independently) of the voltage at the point of common coupling and the VSC currents to their respective reference commands. Dynamically varying limits have been proposed for the positive- and negative-sequence references for the current control schemes in order to protect the VSC from overloading (under unbalanced conditions) and unsymmetrical faults. The active power control, frequency control, and the reactive power–voltage droop control schemes decide the references of the positive-sequence voltage control scheme in order to fulfill the objective of using the same control schemes for the grid-connected and the islanded modes of operation of the microgrid, thereby eliminating the need for islanding detection. The performance of the various control schemes employed for controlling the VSC-based DG unit has been tested on two identical VSC-based DG units feeding power to the IEEE 34 node distribution network implemented in PSCAD/EMTDC.
TL;DR: In this paper, the authors focused on enhancing the resiliency of hybrid micro-grids considering feasible islanding and survivability of critical loads, and proposed a strategy for minimisation of load curtailment during switching of scheduling windows.
Abstract: Microgrids have the capability to enhance the resiliency of power systems by supplying local loads during emergency situations. However, the disturbance incident and clearance times cannot be predicted precisely. Therefore, this study is focused on enhancing the resiliency of hybrid microgrids considering feasible islanding and survivability of critical loads. The optimisation problem is decomposed into normal and emergency operation problems. In normal operation, unit commitment status of dispatchable generators and schedules of batteries are revised to ensure a feasible islanding following a disturbance event. In emergency operation, the decision between charging of batteries for future dispatch and feeding of lesser critical loads is considered. In addition, a strategy for minimisation of load curtailment during switching of scheduling windows is also considered. These two considerations can mitigate the curtailment of critical loads during the emergency period. Finally, a resiliency index is formulated to evaluate the performance of the proposed strategy during emergency operation. Numerical simulations have demonstrated the effectiveness of the proposed strategy for enhancing the resiliency of hybrid microgrids.
TL;DR: In this article, the authors proposed an approach based on Hilbert-Huang transform (HHT) and Extreme learning machine (ELM) to detect an islanding condition in a distribution system with distributed generations (DGs).
TL;DR: In this paper, intelligent techniques, such as genetic algorithm and particle swarm optimization, have been applied for reconfiguration of shipboard microgrid power system (SMPS) in order to isolate system damage and restore lost loads/or optimize certain characteristics of the system in real time.
Abstract: The distribution power system in ship is almost similar to an islanded microgrid and supplies energy to navigation, service, and operation system, as well as sophisticated systems of weapons and communications in future ships. After a fault occurs, reconfiguration refers to changing the topology of the shipboard microgrid power system (SMPS) in order to isolate system damage and restore lost loads/or optimize certain characteristics of the system in real time. Reconfiguration problem in shipboard microgrid is nonlinear with numerous discrete variables and additional constraints. Traditional optimization methods are not the best solution due to tendency of getting stuck to a suboptimal solution and/or not providing solution in real time. In this study, intelligent techniques, such as genetic algorithm and particle swarm optimization, have been applied for reconfiguration of SMPS. Proposed methods consider all the operational constraints and load priorities. Graph theory is utilized to model the SMPS and mathematically represent the shipboard system. Proposed intelligent reconfiguration algorithms were implemented using MATLAB and tested on 8-BUS and 13-BUS SMPS models including distributed generations and islanding. Test systems were reconfigured in three different possible scenarios by considering load priority, load magnitude, and by combining these two simultaneously. Developed reconfiguration algorithm was also implemented in real time using controller-in-the-loop with real-time digital simulator. Simulation results show satisfactory performance for several test operating scenarios.
TL;DR: In this paper, the potential failure mechanism of the f-Q (frequency-reactive power) drifting active method in multiple-DG situations was analyzed and a novel high-frequency transient injection-based islanding detection method was proposed for both single and multiple DGs.
Abstract: Active islanding detection methods are generally employed for grid-connected inverter-based distributed generation (DG). However, there might be mutual influences and power quality issues caused by the disturbance signal when multiple inverters are involved. To address those problems, this paper analyzes the potential failure mechanism of the f-Q (frequency-reactive power) drifting active method in multiple-DG situations. Then, a novel high-frequency transient injection-based islanding detection method that is suitable for both single and multiple DGs is proposed. Compared with the conventional injection methods, a high-frequency impedance model for DG is provided for better theoretical analysis. By means of the intermittent time-domain low-voltage condition injection control, this method can achieve good accuracy and reduce disturbances to power system.
TL;DR: This paper presents a new hybrid islanding detection approach for microgrids (MGs) with multiple connection points to smart grids (SGs) which is based on the probability of islanding (PoI) calculated at the SG side and sent to the central control for microgrid (CCMG).
Abstract: This paper presents a new hybrid islanding detection approach for microgrids (MGs) with multiple connection points to smart grids (SGs) which is based on the probability of islanding (PoI) calculated at the SG side and sent to the central control for microgrid (CCMG). The PoI values are determined using a combination of passive, active, and communication islanding detection approaches based on the utility signals measured at the SGs sides which are processed by discrete wavelet transform using an artificial neural network (ANN). If ${\text{PoI}}_{{\rm{ANN}}}$ is larger than the threshold value (indicating high possibility of islanding) then a more accurate approach based on fuzzy network is used to recompute it ( ${\text{PoI}}_{{\rm{FUZZY}}}$ ) where the fuzzy parameters are determined by an adaptive neuro-fuzzy inference system. In the proposed technique, an active islanding is only performed when PoI is high and the amplitudes of the disturb signals are proportional to ${\text{PoI}}_{{\rm{FUZZY}}}$ . Furthermore, if the PoI is not correctly received by CCMG, two auxiliary tests will be performed in the MG side to detect islanding. These tests include an intentional passive islanding detection in a short preset time and an active islanding detection with disturb signals proportional to the calculated PoI. Detailed simulations are performed and analyzed to evaluate the performance of the proposed method.
04 Oct 2017
TL;DR: The concepts of both FACTS and RACDS for a smart grid are introduced and the current efforts as a concept of resilient ac distribution systems (RACDS) are summarized.
Abstract: Transmission and distribution (T&D) networks are a critical part of the power grid. As moving towards a smart-grid, it is essential to modernize the T&D networks and make it “Smart-grid ready”. The concept of flexible ac transmission systems (FACTS) has been well-known for three decades. Rapid advancements in power electronics technology in the past decades have led to a new generation of FACTS devices. The Modern FACTS technology helps the transition of transmission networks to “smart”. With increasing penetration of distributed generation, the distribution network is seeing unprecedented variation in terms of its fundamental operation and control, from renewable energy integration to microgrid, from active control of power quality, volt/var and frequency to self-healing and islanding operation. As a key part of smart-grid at the distribution level, we summarize the current efforts as a concept of resilient ac distribution systems (RACDS). The concepts of both FACTS and RACDS for a smart grid are introduced in this paper. Different configurations, key benefits, operating principles and world-wide installations of FACTS and RACDS devices are presented in detail. The ongoing and future direction of R&D leading to newer generations of FACTS and RACDS are also discussed.
TL;DR: A fast and effective service restoration method is proposed for medium-voltage distribution system with distributed generators by combining intentional islanding of distributed generators with network reconfiguration to maximize restoration of out-of-service loads.
Abstract: A fast and effective service restoration method is proposed for medium-voltage distribution system with distributed generators by combining intentional islanding of distributed generators with network reconfiguration to maximize restoration of out-of-service loads. The whole process is divided into four stages: 1) matching islanding schemes; 2) restoration of network connectivity and distributed generators; 3) network reconfiguration; and 4) optimization of load shedding. Whether the last three stages are executed or not depends on violations of operational constraints. In accordance with the topological feature of distribution system, a new concept of fundamental loop matrix is presented and applied in detecting out-of-service areas, restoration of network connectivity, and network reconfiguration. Simulation studies on the PG&E 69-bus system shows the effectiveness of the proposed approach.
TL;DR: In this paper, a robust hybrid islanding detection technique (HIDT) has been proposed for identifying the islanding event early and accurately in the distribution networks with DGs installed by a two-step GA process.
Abstract: The integration of Distributed Generation (DG) units in the existing power system has made the reliable operation of the system more complex. This has necessitated a comprehensive approach in planning the expansion of the system with the incorporation of DG units for effective and reliable operation of the system. In this study, a robust Hybrid Islanding Detection Technique (HIDT) has been proposed for identifying the islanding event early and accurately in the distribution networks with DGs installed by a two-step Genetic Algorithm (GA) process. As the reliability of power supply to the customer is of utmost importance, a priority-based load shedding scheme is proposed. The proposed load shedding scheme sheds only the vulnerable loads in the island for regaining the frequency and voltage stabilities. By the proposed methods, a comprehensive solution for system planning and emergency control actions can be obtained for effective operation of the system with DG units. The proposed methods are investigated on standard IEEE 33 and 69 bus distribution systems under different loading conditions. The results obtained show that the proposed methods are able to identify the islanding event more effectively and also regain the stability in the island with less amount of load shedding.
TL;DR: Graph spectra-based controlled islanding method is used to identify the impact of reduced inertia on the spectral properties of power system graphs and, thus, coherent generator grouping and validate the effectiveness of the proposed algorithm in the case of low inertia systems.
Abstract: The inertia of modern power systems is decreasing and becoming more variable as more inverter-connected renewable energy sources and loads are integrated. This leads to a low and time-varied inertia power system that is more sensitive to disturbances and may not be robust enough to survive large disturbances. How to protect such a low and time-varied inertia system from blackouts is in question. This paper tries to answer this question using a graph spectra-based controlled islanding method. Eigenvector sensitivity, with respect to inertia, is used to identify the impact of reduced inertia on the spectral properties of power system graphs and, thus, coherent generator grouping. Constrained spectral clustering is then used to find the islanding boundary with minimal power-flow disruption to island low inertia systems. Simulation results, obtained using the IEEE 9-bus and 118-bus test systems, validate the effectiveness of the proposed algorithm in the case of low inertia systems.
TL;DR: In this paper, a medium-voltage solid-state transformer (SST)-interfaced permanent magnet synchronous generator system with integrated active power management and reactive power compensation functions is presented.
Abstract: The higher penetration of wind energy poses increasing demand for grid support and power management functions of a wind energy conversion system (WECS). This paper investigates a medium-voltage solid-state transformer (SST)-interfaced permanent magnet synchronous generator system with integrated active power management and reactive power compensation functions. Specifically, a WECS consisting of wind turbines, SSTs, and dc loads is presented. In addition, a distributed power management algorithm is proposed for a dc network with local wind turbine controls incorporated to achieve a self-contained power-balanced condition without the need for energy storage or communication devices. Scenarios considered include the grid-connected mode, the islanding mode, and the mode transitions. Simulation results are provided to verify the effectiveness of the proposed strategy. Additionally, the concept is experimentally verified using a scaled-down laboratory prototype.
TL;DR: This study proposes a novel, fast, and reliable method to identify islanding conditions using feature vectors associated with different operation conditions such as islanding and non-islanding events to train artificial neural networks (ANNs).
Abstract: One of the most important challenges in microgrid operation is the unintentional islanding occurrence. Unintentional islanding can cause serious safety hazards and technical issues. Islanding detection methods can be classified into active and passive methods. The main disadvantages of the passive methods are large non-detection zone as well as determination of suitable threshold value to avoid unwanted distributed generations tripping in normal network events. In order to overcome these drawbacks, this study proposes a novel, fast, and reliable method to identify islanding conditions. The proposed method calculates different transient states in the rate of change of frequency signal in two consecutive cycles. Various features of the differential signal are extracted. The extracted feature vectors associated with different operation conditions such as islanding and non-islanding events are used to train artificial neural networks (ANNs). The performances of different structures of ANNs and also other machine learning methods such as support vector machine and adaptive neuro fuzzy inference system are evaluated for islanding detection purposes. The simulation results indicate that the proposed method provides more accurate and faster responses compared with other conventional islanding detection methods.