Showing papers on "Islanding published in 2013"
TL;DR: In this article, an enhanced distributed generation (DG) unit virtual impedance control approach is proposed, which can realize accurate regulation of DG unit equivalent impedance at both fundamental and selected harmonic frequencies.
Abstract: In order to address the load sharing problem in islanding microgrids, this paper proposes an enhanced distributed generation (DG) unit virtual impedance control approach. The proposed method can realize accurate regulation of DG unit equivalent impedance at both fundamental and selected harmonic frequencies. In contrast to conventional virtual impedance control methods, where only a line current feed-forward term is added to the DG voltage reference, the proposed virtual impedance at fundamental and harmonic frequencies is regulated using DG line current and point of common coupling (PCC) voltage feed-forward terms, respectively. With this modification, the impacts of mismatched physical feeder impedances are compensated. Thus, better reactive and harmonic power sharing can be realized. Additionally, this paper also demonstrates that PCC harmonic voltages can be mitigated by reducing the magnitude of DG unit equivalent harmonic impedance. Finally, in order to alleviate the computing load at DG unit local controller, this paper further exploits the band-pass capability of conventionally resonant controllers. With the implementation of proposed resonant controller, accurate power sharing and PCC harmonic voltage compensation are achieved without using any fundamental and harmonic components extractions. Experimental results from a scaled single-phase microgrid prototype are provided to validate the feasibility of the proposed virtual impedance control approach.
425 citations
TL;DR: In this paper, the virtual inertia method is used to improve the system dynamic behavior, which imitates the kinetic inertia of a synchronous generator, and the proposed method focuses on short-term oscillations and incorporates no long-term power regulation.
Abstract: Although wind power as a renewable energy is assumed to be an advantageous source of energy, its intermittent nature causes difficulties especially in the islanding mode of operation. Conventional synchronous generators can help to compensate for wind fluctuations, but the slow behavior of such systems may result in stability concerns. Here, the virtual inertia method, which imitates the kinetic inertia of synchronous generator, is used to improve the system dynamic behavior. Since the proposed method focuses on short-term oscillations and incorporates no long-term power regulation, it needs no mass storage device. Thus, the method is economical. To prevent any additional cost, the rotating mass connected to the DFIG shaft or a super-capacitor connected to the DC-link of a back-to-back inverter of a wind power generator could be used. The concept and the proposed control methods are discussed in detail. Eigen-value analysis is used to study how the proposed method improves system stability. The advantages and disadvantages of using DFIG rotating mass or super-capacitor as the virtual inertia source are compared. The proposed approach also shows that while virtual inertia is not incorporated directly in long-term frequency and power regulation, it may enhance the system steady-state behavior indirectly. A time domain simulation is used to verify the results of the analytical studies.
379 citations
TL;DR: In this paper, a low-voltage bipolar-type dc microgrid with two energy storage units and a dc/dc converter was proposed to achieve both power sharing and energy management.
Abstract: Installation of many distributed generations (DGs) could be detrimental to the power quality of utility grids. Microgrids facilitate effortless installation of DGs in conventional power systems. In recent years, dc microgrids have gained popularity because dc output sources such as photovoltaic systems, fuel cells, and batteries can be interconnected without ac/dc conversion, which contributes to total system efficiency. Moreover, high-quality power can be supplied continuously when voltage sags or blackouts occur in utility grids. We had already proposed a “low-voltage bipolar-type dc microgrid” and described its configuration, operation, and control scheme, through experiments. In the experiments, we used one energy storage unit with a dc/dc converter to maintain the dc-bus voltage under intentional islanding operation. However, dc microgrids should have two or more energy storage units for system redundancy. Therefore, we modified the system by adding another energy storage unit to our experimental system. Several kinds of droop controls have been proposed for parallel operations, some of which were applied for ac or dc microgrids. If a gain-scheduling control scheme is adopted to share the storage unit outputs, the storage energy would become unbalanced. This paper therefore presents a new voltage control that combines fuzzy control with gain-scheduling techniques to accomplish both power sharing and energy management. The experimental results show that the dc distribution voltages were within 340 V ± 5%, and the ratios of the stored energy were approximately equal, which implies that dc voltage regulation and stored energy balancing control can be realized simultaneously.
364 citations
TL;DR: In this article, a review of the existing microgrid control methods in the literature and different industry solutions is presented, along with an initial platform for different types of microgrids stability assessment.
Abstract: This paper investigates some aspects of stability in microgrids. There are different types of microgrid applications. The system structure and the control topology vary depending on the application and so does the aspect of stability in a microgrid. This paper briefly encompasses the stability aspects of remote, utility connected and facility microgrids depending on the modes of operation, control topology, types of micro sources and network parameters. The small signal, transient and the voltage stability aspects in each type of the microgrid are discussed along with scope of improvements. With a brief review of the existing microgrid control methods in the literature and different industry solutions, this paper sets up an initial platform for different types of microgrids stability assessment. Various generalized stability improvement methods are demonstrated for different types of microgrids. The conventional stability study of microgrids presented in this paper facilitates an organized way to plan the micro source operation, microgrid controller design, islanding procedure, frequency control and the load shedding criteria. The stability investigations are presented with different control methods, eigen value analysis and time domain simulations to justify different claims.
358 citations
TL;DR: A survey of various islanding detection techniques and their advantages and disadvantages is presented in this article, where a conventional and intelligent technique is used to detect islanding of distributed generations (DGs).
Abstract: Islanding detection of distributed generations (DGs) is one of the most important aspects of interconnecting DGs to the distribution system. Islanding detection techniques can generally be classified as remote methods, which are associated with islanding detection on the utility sides, and local methods, which are associated with islanding detection on the DG side. This paper presents a survey of various islanding detection techniques and their advantages and disadvantages. The paper focused on islanding detection using a conventional and intelligent technique. A summary table that compares and contrasts the existing methods is also presented.
265 citations
TL;DR: An analytical derivation of node voltages and line currents as a function of the nodal power injections and transformers tap-changers positions is provided, based on the use of the [Y] compound matrix of a generic multi-phase radial unbalanced network.
Abstract: The problem of optimal control of power distribution systems is becoming increasingly compelling due to the progressive penetration of distributed energy resources in this specific layer of the electrical infrastructure. Distribution systems are, indeed, experiencing significant changes in terms of operation philosophies that are often based on optimal control strategies relying on the computation of linearized dependencies between controlled (e.g., voltages, frequency in case of islanding operation) and control variables (e.g., power injections, transformers tap positions). As the implementation of these strategies in real-time controllers imposes stringent time constraints, the derivation of analytical dependency between controlled and control variables becomes a non-trivial task to be solved. With reference to optimal voltage and power flow controls, this paper aims at providing an analytical derivation of node voltages and line currents as a function of the nodal power injections and transformers tap-changers positions. Compared to other approaches presented in the literature, the one proposed here is based on the use of the [Y] compound matrix of a generic multi-phase radial unbalanced network. In order to estimate the computational benefits of the proposed approach, the relevant improvements are also quantified versus traditional methods. The validation of the proposed method is carried out by using both IEEE 13 and 34 nodes test feeders. The paper finally shows the use of the proposed method for the problem of optimal voltage control applied to the IEEE 34 node test feeder.
256 citations
TL;DR: In this article, an autonomous three-level control strategy is proposed for dc micro-grids with selective slack terminal(s) assigned to each operation level, where the system operational status is acknowledged via the common dc voltage and the transitions between different operational levels are triggered by its variation.
Abstract: System control for dc microgrids with variable generations and energy storage is proposed in this paper. An autonomous three-level control strategy is proposed for dc microgrids with selective slack terminal(s) assigned to each operation level. The system operational status is acknowledged via the common dc voltage and the transitions between different operational levels are triggered by its variation. A four-terminal sample dc microgrid system with a grid-connected voltage-source converter, a wind turbine, an energy storage system, and dc loads are established and a specific control scheme is outlined to demonstrate the proposed strategy during various operating conditions, such as load step, generation fluctuation, islanding, grid reconnection, load shedding, and generation curtailment. The control strategy and the specific scheme are validated by experimental results conducted on a prototype dc microgrid system.
233 citations
TL;DR: In this article, a two-step controlled islanding algorithm that uses spectral clustering to find a suitable islanding solution for preventing the initiation of wide area blackouts by un-damped electromechanical oscillations is proposed.
Abstract: Controlled islanding is an active and effective way of avoiding catastrophic wide area blackouts. It is usually considered as a constrained combinatorial optimization problem. However, the combinatorial explosion of the solution space that occurs for large power systems increases the complexity of solving it. This paper proposes a two-step controlled islanding algorithm that uses spectral clustering to find a suitable islanding solution for preventing the initiation of wide area blackouts by un-damped electromechanical oscillations. The objective function used in this controlled islanding algorithm is the minimal power-flow disruption. The sole constraint applied to this solution is related to generator coherency. In the first step of the algorithm, the generator nodes are grouped using normalized spectral clustering, based on their dynamic models, to produce groups of coherent generators. In the second step of the algorithm, the islanding solution that provides the minimum power-flow disruption while satisfying the constraint of coherent generator groups is determined by grouping all nodes using constrained spectral clustering. Simulation results, obtained using the IEEE 9-, 39-, and 118-bus test systems, show that the proposed algorithm is computationally efficient when solving the controlled islanding problem, particularly in the case of a large power system.
229 citations
TL;DR: The objective is to minimize the fuel cost during the grid-connected operation, while ensuring stable operation after islanding, to achieve this goal, the economic dispatch (ED) problem and related constraints are formulated.
Abstract: This paper is concerned with the power dispatch problem of distributed generators (DGs) for optimal operation of a microgrid. The objective is to minimize the fuel cost during the grid-connected operation, while ensuring stable operation after islanding. To achieve this goal, the economic dispatch (ED) problem and related constraints are formulated. The constraints considered in this study are: i) reserve for variation in load demand, ii) reserve for variation in the power outputs of non-dispatchable DGs, iii) flow limits between two adjacent areas, and iv) reserve for the stable islanded operation. The first three constraints, which have been employed in ED problem for conventional power systems, are modified to apply to Microgrids. We also provide a detailed formulation of the constraint for stable islanded operation in accordance with two power-sharing principles: i) fixed droop and ii) adjustable droop. The problem is solved using a modified direct search method, and the effect of the constraints on the operational cost is investigated via numerical simulations.
194 citations
TL;DR: In this paper, the voltage-based droop (VBD) control is developed for islanded lowvoltage microgrids with a high share of renewable energy sources to enable a smooth transition between the islanded and the grid-connected mode of the microgrid.
Abstract: Microgrids are able to provide a coordinated integration of the increasing share of distributed generation (DG) units in the network. The primary control of the DG units is generally performed by droop-based control algorithms that avoid communication. The voltage-based droop (VBD) control is developed for islanded low-voltage microgrids with a high share of renewable energy sources. With VBD control, both dispatchable and less-dispatchable units will contribute in the power sharing and balancing. The priority for power changes is automatically set dependent on the terminal voltages. In this way, the renewables change their output power in more extreme voltage conditions compared to the dispatchable units, hence, only when necessary for the reliability of the network. This facilitates the integration of renewable units and improves the reliability of the network. This paper focusses on modifying the VBD control strategy to enable a smooth transition between the islanded and the grid-connected mode of the microgrid. The VBD control can operate in both modes. Therefore, for islanding, no specific measures are required. To reconnect the microgrid to the utility network, the modified VBD control synchronizes the voltage of a specified DG unit with the utility voltage. It is shown that this synchronization procedure significantly limits the switching transient and enables a smooth mode transfer.
190 citations
TL;DR: In this paper, the authors present innovative functionalities to run online, which are able to manage microgrid storage considering the integration of electric vehicles and load responsiveness, and the effectiveness of the proposed algorithms is validated through extensive numerical simulations.
Abstract: Microgrids are assumed to be established at the low voltage distribution level, where distributed energy sources, storage devices, controllable loads and electric vehicles are integrated in the system and need to be properly managed. The microgrid system is a flexible cell that can be operated connected to the main power network or autonomously, in a controlled and coordinated way. The use of storage devices in microgrids is related to the provision of some form of energy buffering during autonomous operating conditions, in order to balance load and generation. However, frequency variations and limited storage capacity might compromise microgrid autonomous operation. In order to improve microgrid resilience in the moments subsequent to islanding, this paper presents innovative functionalities to run online, which are able to manage microgrid storage considering the integration of electric vehicles and load responsiveness. The effectiveness of the proposed algorithms is validated through extensive numerical simulations.
TL;DR: The proposed hybrid voltage and current control method allows the coordinated closed-loop control of the DG unit fundamental voltage and line harmonic currents and guarantees smooth transition during the grid-connected/islanding operation mode transfer.
Abstract: This paper presents a hybrid voltage and current control method to improve the performance of interfacing converters in distributed generation (DG) units. In general, current-controlled methods have been widely adopted in grid-connected converters nowadays. Nevertheless, in an islanded system, the voltage control of DG units is desired to provide direct voltage support to the loads. Due to the absence of closed-loop line current controller, the voltage control scheme can hardly regulate the DG unit's line current harmonics. Furthermore, if not addressed properly, the transfer between the grid-connected operation and autonomous islanding operation will introduce nontrivial transient currents. To overcome the drawbacks of voltage- and current-controlled DG units, this paper develops a hybrid voltage and current control method (HCM). The proposed method allows the coordinated closed-loop control of the DG unit fundamental voltage and line harmonic currents. With the HCM, local harmonic loads of the DG unit can even be compensated without using harmonic current extraction. In addition, the HCM guarantees smooth transition during the grid-connected/islanding operation mode transfer. Simulated and experimental results are provided to verify the feasibility of the proposed approach.
TL;DR: In this paper, a wavelet singular entropy (WSE)-based islanding detection method was proposed for distributed generation interfaced to the microgrid. But, the proposed method is limited to detecting islanding within 10 ms (half cycle) from the event inception.
Abstract: The paper presents wavelet singular entropy (WSE)-based islanding detection in distributed generation (DG) interfaced to the microgrid. Initially, the three-phase voltage signals retrieved at the target DG location are processed through wavelet transform (WT) to derive detailed coefficient at different levels of decomposition. From the detailed coefficients, the singular value matrix is generated and the WSE for each phase is calculated. Finally, the WSE index (WSEI) for islanding detection is computed by adding the WSE of each phase. The proposed WSEI is able to detect islanding within 10 ms (half cycle) from the event inception, showing the speed of the developed technique. It is observed that WSEI is highly effective in islanding detection, including different islanding and nonislanding conditions in the initial test system and standard microgrid with wide variations in operating parameters.
TL;DR: In this paper, a comprehensive review of islanding detection methods (comparing their non-detection zones and detection speeds) and anti-islanding standards is presented, and a few information and clearer vision for researchers to determine the best method for their product.
Abstract: Islanding is undesired because it may impair the safety of maintenance service workers and/or damage load equipment through unsynchronized re-closure. In principle, islanding detection is the monitoring of islanding—indicating changes in inverter output parameters or other system parameters. This paper aims to aid design efforts through its comprehensive review of islanding detection methods (comparing their non-detection zones and detection speeds) and anti-islanding standards. As a result, this paper shall provide a handful information and clearer vision for researchers to determine the best method for their product.
TL;DR: In this article, a new passive local multicriteria-based islanding detection algorithm with fault detection and islanding verification logic is presented, measuring voltage unbalance and voltage total harmonic distortion from all phases, is able to detect very fast and selectively islanding situations in a perfect power balance without NDZ.
Abstract: Islanding detection methods can be divided into communication-based and local detection-based methods. Proposed local passive detection methods have traditionally been dependent on the distributed generation unit type. A large nondetection zone (NDZ) near a power balance situation and unwanted distributed generation tripping due to other network events have also been major drawbacks of traditional, passive local islanding detection methods. In this paper, a new passive local multicriteria-based islanding detection algorithm with fault detection and islanding verification logic is presented. This new islanding detection algorithm, measuring voltage unbalance and voltage total harmonic distortion from all phases, is able to detect very fast and selectively islanding situations in a perfect power balance without NDZ with a simultaneous utilization of the available fault detection information and novel islanding verification logic. In addition to the new multicriteria-based islanding detection method, the fault detection information and islanding verification logic could also be used together with any other known passive islanding detection methods, that is, parameters which are not specified in the fault-ride-through (FRT) requirements of the future grid codes, to improve the performance of these methods in terms of reliability and speed of detection.
TL;DR: A new integrated diagnostic system for islanding detection by means of a neuro-fuzzy approach for grid-connected inverter-based distributed generation and is capable of detecting islanding accurately within the minimum standard time.
TL;DR: Three techniques are proposed for solving and reducing the consequences of wind speed fluctuations in microgrids, including a new fuzzy logic pitch angle controller and an energy-storage ultracapacitor which directly smoothes the output power of the wind turbine and enhances the performance of the MG during the islanding mode.
Abstract: The necessity to solve global warming problems by reducing CO2 emission in the electricity generation field had led to increasing interest in microgrids (MGs), particularly those containing the renewable sources such as solar and wind generation. Wind speed fluctuations cause high variations in the output power of a wind turbine which cause fluctuations in frequency and voltage of the MG during islanding mode and originate stability problems. In this paper, three techniques are proposed for solving and reducing the consequences of this problem. In the first technique, we develop a new fuzzy logic pitch angle controller. In the second technique, we design an energy-storage ultracapacitor which directly smoothes the output power of the wind turbine and enhances the performance of the MG during the islanding mode. In the third technique, storage batteries are used to support the MG in the islanding mode.
TL;DR: An islanding detection method for a grid-connected inverter incorporating intermittent bilateral (IB) reactive power variation (RPV) is described in this article, where the inverter output with IB reactive power enables the detection of an islanding.
Abstract: An islanding detection method for a grid-connected inverter incorporating intermittent bilateral (IB) reactive power variation (RPV) is described. The inverter output with IB reactive power enables the detection of an islanding. The RPV range is derived in order to eliminate the nondetection zone. The design scheme of variation time in the method is obtained by estimating the transient response due to islanding occurrence. In addition, the effect of the proposed detection strategy on power quality is investigated. The proposed islanding detection method has been experimentally verified on a three-phase grid-connected 6-kW inverter.
TL;DR: In this article, a seamless control methodology has been proposed for a photo voltaic (PV)-diesel generator (DG) microgrid to operate both in the grid connected and islanded mode.
Abstract: In this paper, a seamless control methodology has been proposed for a photo voltaic (PV)-diesel generator (DG) microgrid to operate both in the grid connected and islanded mode It does not require any islanding detection mechanism, to change the control philosophy from the grid connected mode to the islanded mode A second order sliding mode control has been used to control the voltage source converter of the PV source whose set points have been generated by PI controllers The maximum power point tracking algorithm for the PV system has been augmented with an auxiliary signal obtained using the electrical power output of the DG to reduce the output power of the PV system for economical operation of the DG unit The DG unit is regulated with the frequency of the microgrid while the inverter used in the PV system regulates the voltage at the point of common coupling Similarly, if the DG is uncontrollable due to any reason, the PV system is further added with an auxiliary signal based on the frequency deviation to maintain frequency stability Simulation of the system has been carried out in MATLAB/SIMULINK with different levels of insolation and load to verify the proposed control scheme
TL;DR: In this article, the authors proposed two islanding detection methods, the frequency difference method and the change of angle difference method, based on the data collected by the frequency disturbance recorder (FDR) deployed in the North American power grid.
Abstract: A fast islanding detection tool can help power dispatchers monitor and control power system operations. Frequency monitoring network (FNET) is a low cost and quickly deployable wide-area phasor measurement system at the distribution system level. The frequency disturbance recorder (FDR) in FNET is actually a single-phase phasor measurement unit (PMU) installed at ordinary 120 V outlets in the sense that it measures the voltage phase angle, amplitude, and frequency from a single-phase voltage source. Based on the data collected by the FDRs deployed in the North American power grid, two islanding detection methods, the frequency difference method and the change of angle difference method, are proposed. The nine real cases recorded, including islanding cases, generation trip cases, load shedding cases and oscillation cases, are presented to verify the proposed methods of islanding detection. Sensitivity analysis on the thresholds of the frequency deviation and angle deviation is done based on the real measurement data for obtaining the insensitive interval of two thresholds. The results show that the proposed methods can correctly detect power system islanding, and will not be falsely triggered by generation trips, load shedding and system oscillations.
TL;DR: In this article, power smoothing and frequency controlling of wind power in islanding systems has been investigated, and the results show that wind plant power output can be smoothed in short time frame, and support frequency in both primary and secondary frequency control timescales including droop functionality.
Abstract: Conventionally operated full power converter wind plants show high short-term power output variability caused by variable winds, and does not contribute to the power system inertia due to the decoupled generator speed and grid frequency. There is, however, abundant inertial resources in wind plant rotors for both smoothing of output power and for synthetic inertia contribution. Together with added frequency controlling functionality, this could facilitate inclusion of wind power in islanding systems, enabling greater system loads and enhancing power system stability. This paper describes modeling of power smoothing and frequency controlling wind plants and assesses different control strategies as well as the grid frequency performance gains achievable over hydro powered islanding systems and over islanding systems incorporating both hydro power and conventional wind plants. The results show that wind plant power output could be smoothed in the short time frame, and support frequency in both primary and secondary frequency control timescales including droop functionality.
TL;DR: In this paper, a mixed integer linear programming (MILP) formulation is given for the problem of deciding simultaneously on the boundaries of the islands and adjustments to generators, so as to minimize the expected load shed while ensuring no system constraints are violated.
TL;DR: In this article, the load parameters are estimated online and the SFS parameter is adaptively tuned to eliminate NDZ using fuzzy load parameter estimation (FLPE) method, and the simulation results verify the excellent performance of the proposed method.
Abstract: Sandia Frequency Shift (SFS) is one of the active islanding detection methods that rely on frequency drift to detect an islanding condition. Recently, SFS has been widely applied to inverter-based distributed generations due to its small Non-Detection Zone (NDZ). The NDZ in SFS method highly depends on its design parameters. Improper tuning of these parameters may result in failure of the method. In the proposed method in this paper, the load parameters are estimated online and the SFS parameter is adaptively tuned to eliminate NDZ using fuzzy load parameter estimation (FLPE) method. Simulation results verify the excellent performance of the proposed method.
TL;DR: The problems encountered in analyzing prospective microgrid economics and environmental and reliability performance are described and some results from the software tools developed for these tasks are presented.
Abstract: A vision shared by many experts is that future communities (residential and commercial developments, university and industrial campuses, military installations, and so on) will be self-sufficient with respect to energy production and will adopt microgrids. With power generation capacities of 10-50 MW, microgrids are usually intended for the local production of power with islanding capabilities and have capacity available for sale back to macrogrids. A typical microgrid portfolio includes photovoltaic (PV) and wind resources, gas-fired generation, demand-response capabilities, electrical and thermal storage, combined heat and power (CHP), and connectivity to the grid. Advanced technologies such as fuel cells may also be included. This article describes the problems encountered in analyzing prospective microgrid economics and environmental and reliability performance and presents some results from the software tools developed for these tasks.
TL;DR: In this paper, a photovoltaic (PV) generation system interfaced with a dc distribution system is discussed for energy-efficient and reliable system implementation, and a new anti-islanding technique for dc distribution as a system protection scheme.
Abstract: This paper proposes a photovoltaic (PV) generation system interfaced with a dc distribution system. DC interface allows for the improvement of system efficiency by fully utilizing dc-based renewable sources and storage devices. In this paper, issues on PV interface for dc distribution systems are discussed for energy-efficient and reliable system implementation. AC and dc PV interfaces are mathematically analyzed. In dc distribution, eliminating electrolytic capacitors in PV interfaces improves system reliability, increases system efficiency, and reduces cost. In addition, this paper proposes a new anti-islanding technique for dc distribution as a system protection scheme. The operating principle is presented in detail and analysis shows that the proposed injected current perturbation technique is an effective solution for anti-islanding operation. A prototype converter features a simple structure with no electrolytic capacitor, which ensures a longer lifetime of the PV power circuit. Experimental results of the prototype circuit show a maximum efficiency of 98.1% and a European efficiency of 97.5%. The proposed anti-islanding technique shows fast response to the islanding condition in less than 0.2 s. It also shows that the average maximum power point tracking efficiency is 99.9% in normal conditions, which verifies the performance of the proposed scheme.
18 May 2013
TL;DR: This paper examines several prediction approaches for day and week ahead electrical load of a community of houses that are supplied by a common residential transformer, in particular: artificial neural networks; fuzzy logic; auto-regression;auto-regressive moving average; auto"-regressive integrated moving average"; and wavelet neural networks.
Abstract: Applications such as generator scheduling, household smart device scheduling, transmission line overload management and microgrid islanding autonomy all play key roles in the smart grid ecosystem. Management of these applications could benefit from short-term load prediction, which has been successfully achieved on large-scale systems such as national grids. However, the scale of the data for analysis is much smaller, similar to the load of a single transformer, making prediction difficult. This paper examines several prediction approaches for day and week ahead electrical load of a community of houses that are supplied by a common residential transformer, in particular: artificial neural networks; fuzzy logic; auto-regression; auto-regressive moving average; auto-regressive integrated moving average; and wavelet neural networks. In our evaluation, the methods use pre-recorded electrical load data with added weather information. Data is recorded from a smart-meter trial that took place during 2009-2010 in Ireland, which registered individual household consumption for 17 months. Two different scenarios are investigated, one with 90 houses, and another with 230 houses. Results for the two scenarios are compared and the performances of the evaluated prediction methods are discussed.
TL;DR: In this article, the authors proposed a new islanding detection technique that is suitable for multiple mini-hydro type DG units based on the rate of change of reactive power and load connecting strategy to detect islanding within the system.
21 Jul 2013
TL;DR: A two-step controlled islanding algorithm that uses spectral clustering to find a suitable islanding solution for preventing the initiation of wide area blackouts by un-damped electromechanical oscillations is proposed.
Abstract: Controlled islanding is an active and effective way of avoiding catastrophic wide area blackouts. It is usually considered as a constrained combinatorial optimization problem. However, the combinatorial explosion of the solution space that occurs for large power systems increases the complexity of solving it. This paper proposes a two-step controlled islanding algorithm that uses spectral clustering to find a suitable islanding solution for preventing the initiation of wide area blackouts by un-damped electromechanical oscillations. The objective function used in this controlled islanding algorithm is the minimal power-flow disruption. The sole constraint applied to this solution is related to generator coherency. In the first step of the algorithm, the generator nodes are grouped using normalized spectral clustering, based on their dynamic models, to produce groups of coherent generators. In the second step of the algorithm, the islanding solution that provides the minimum power-flow disruption whilst satisfying the constraint of coherent generator groups is determined by grouping all nodes using constrained spectral clustering. Simulation results, obtained using the IEEE 9, 39 and 118-bus test systems, show that the proposed algorithm is computationally efficient when solving the controlled islanding problem, particularly in the case of a large power system.
TL;DR: It is determined that using only one input (voltage) signal not only improves speed and simplicity and reduces costs, also makes accuracy of the proposed relay better than other intelligent and passive methods.
Abstract: In this paper, a method for islanding detection based on analysis of transient state signals is provided. Decision tree (DT) is trained for classifying the transient events. The required features for classifying are extracted through discrete wavelet transform (DWT) of signals. The proposed method is then simulated on a medium voltage distribution system of CIGRE with two kinds of distributed generations (DGs) using DIgSILENT, MATLAB and WEKA softwares. By analysis performed on type of input signal, type of mother wavelet and required transform level, among 162 relay designs, an optimum relay is selected for distributed generations (DGs) based on accuracy, speed, simplicity and cost parameters. By evaluation, it is determined that using only one input (voltage) signal not only improves speed and simplicity and reduces costs, also makes accuracy of the proposed relay better than other intelligent and passive methods. The final selected relay for each DG is V-db4-D3 which has accuracy equal 98%.
TL;DR: Two grid partitioning methods based on modularity, properly modified to take into account the power flow model are proposed, modifications of the Fast Greedy algorithm and the Bloom algorithm, and are polynomial in running time.
Abstract: Intentional islanding of a power system can be an emergency response for isolating failures that might propagate and lead to major disturbances. Some of the islanding techniques suggested previously do not consider the power flow model; others are designed to minimize load shedding only within the islands. Often these techniques are computationally expensive. We aim to find approaches to partition power grids into islands to minimize the load shedding not only in the region where the failures start, but also in the topological complement of the region. We propose a new constraint programming formulation for optimal islanding in power grid networks. This technique works efficiently for small networks but becomes expensive as size increases. To address the scalability problem, we propose two grid partitioning methods based on modularity, properly modified to take into account the power flow model. They are modifications of the Fast Greedy algorithm and the Bloom algorithm, and are polynomial in running time. We tested these methods on the available IEEE test systems. The Bloom type method is faster than the Fast Greedy type, and can potentially provide results in networks with thousands of nodes. Our methods provide solutions which retain at least 40-50% of the system load. Overall, our methods efficiently balance load shedding and scalability.