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Showing papers on "Microgrid published in 2005"


Journal ArticleDOI
TL;DR: In this paper, the authors present the operation of a multiagent system (MAS) for the control of a microgrid and a classical distributed algorithm based on the symmetrical assignment problem for the optimal energy exchange between the production units of the Microgrid and the local loads, as well the main grid.
Abstract: This paper presents the operation of a multiagent system (MAS) for the control of a Microgrid. The approach presented utilizes the advantages of using the MAS technology for controlling a Microgrid and a classical distributed algorithm based on the symmetrical assignment problem for the optimal energy exchange between the production units of the Microgrid and the local loads, as well the main grid.

1,035 citations


Proceedings ArticleDOI
01 Dec 2005
TL;DR: In this paper, a novel wireless load sharing controller for islanding parallel inverters in an ac distributed system is proposed, where the resistive output impedance of the parallel-connected inverters is explored.
Abstract: In this paper, a novel wireless load-sharing controller for islanding parallel inverters in an ac distributed system is proposed. The paper explorers the resistive output impedance of the parallel-connected inverters in an island microgrid

718 citations


Journal ArticleDOI
TL;DR: The optimization is aimed at reducing the fuel consumption rate of the system while constraining it to fulfil the local energy demand and provide a certain minimum reserve power and a penalty is applied for any heat produced in excess of demand.
Abstract: A cost optimization scheme for a microgrid is presented. Prior to the optimization of the microgrid itself, several schemes for sharing power between two generators are compared. The minimization of fuel use in a microgrid with a variety of power sources is then discussed. The optimization of a small power system has important differences from the case of a large system and its traditional economic dispatch problem. Among the most important differences is the presence of a local heat demand which adds another dimension to the optimization problem. The microgrid considered in this paper consists of two reciprocating gas engines, a combined heat and power plant, a photovoltaic array and a wind generator. The optimization is aimed at reducing the fuel consumption rate of the system while constraining it to fulfil the local energy demand (both electrical and thermal) and provide a certain minimum reserve power. A penalty is applied for any heat produced in excess of demand. The solution of the optimization problem strongly supports the idea of having a communication infrastructure operating between the power sources.

509 citations


01 Jan 2005
TL;DR: A benchmark LV network developed within the EU project “Microgrids” and later adopted as a benchmark LV system by CIGRE TF C6.04.02 maintains the important technical characteristic of real utility grids, whereas, at the same time, it dispenses with the complexity of actual networks to permit efficient modeling and simulation of microgrid operation.
Abstract: The increasing penetration of distributed generation resources to the low voltage (LV) grids, such as photovoltaics, CHP micro-turbines, small wind turbines in certain areas and possibly fuel cells in the near future, alters the traditional operating principle of the grids. A particularly promising aspect, related to the proliferation of small-scale decentralized generation, is the possibility for parts of the network comprising sufficient generating resources to operate in isolation from the main grid, in a deliberate and controlled way. These are called Microgrids and the study and development of technology to permit their efficient operation has recently started with a great momentum ([1,2]). Microgrids are foreseen within public distribution grids and therefore suitable study case networks are required to perform simulation and analysis tasks. Moreover, standardizing study case grids to provide “benchmark” networks suitable for Microgrid design would further enhance their merit and utility. The objective of this paper is to present and discuss a benchmark LV network developed within the EU project “Microgrids”, Contract ENK5-CT-2002-00610 and later adopted as a benchmark LV system by CIGRE TF C6.04.02: “Computational Tools and Techniques for Analysis, Design and Validation of Distributed Generation Systems”. The network consists of an LV feeder, while a more extended multi-feeder version is also included in the Appendix. The emphasis is placed on the network itself, rather than on the microsources connected and the control concepts applied. The benchmark network maintains the important technical characteristic of real utility grids, whereas, at the same time, it dispenses with the complexity of actual networks, to permit efficient modeling and simulation of microgrid operation.

381 citations


Journal ArticleDOI
TL;DR: This paper presents recent extensions to the GrADS software framework: a new approach to scheduling workflow computations, applied to a 3-D image reconstruction application; a simple stop/migrate/restart approach to rescheduling Grid applications, application to a QR factorization benchmark; and a process-swapping approach to Rescheduling, applications to an N-body simulation.
Abstract: The goal of the Grid Application Development Software (GrADS) Project is to provide programming tools and an execution environment to ease program development for the Grid. This paper presents recent extensions to the GrADS software framework: a new approach to scheduling workflow computations, applied to a 3-D image reconstruction application; a simple stop/migrate/restart approach to rescheduling Grid applications, applied to a QR factorization benchmark; and a process-swapping approach to rescheduling, applied to an N-body simulation. Experiments validating these methods were carried out on both the GrADS MacroGrid (a small but functional Grid) and the MicroGrid (a controlled emulation of the Grid).

225 citations


Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this paper, the voltage and frequency control of islanded microgrid after intentional and unintentional switching events are investigated. And the studies are performed on a PSCAD simulation software package.
Abstract: In this paper voltage and frequency control of islanded microgrid after intentional and unintentional switching events are investigated. The weak low voltage (LV) network based microgrid consists of two inverter based distributed generation (DG) units. One unit is a storage (battery) unit and the other is a photovoltaic (PV) cell. In this case the battery inverter with rapid response is considered to act as a master and it has the main responsibility to control the voltage and frequency in microgrid when islanded from the main distribution network. The studies are performed on a PSCAD simulation software package. Simulation studies show the voltage - active power and frequency - reactive power dependency in weak LV network. The studies also show that in order to maintain frequency balance in islanded microgrid, there is need for a reference sine wave generator inside master unit which imitates the main network phase voltages and gives the input for master units' (battery storage) PLL (phase locked loop) during islanding

197 citations


Proceedings ArticleDOI
27 Jun 2005
TL;DR: In this paper, the authors present the development of microsource modelling and the definition of control strategies to evaluate the feasibility of operation of a microgrid when it becomes isolated, and an evaluation of the need of storage devices and load shedding strategies is included in the paper.
Abstract: The main objective of this paper is to present the development of microsource modelling and the definition of control strategies to be adopted to evaluate the feasibility of operation of a microgrid when it becomes isolated. Normally, the microgrid operates in interconnected mode with the MV network, however scheduled or forced isolation can take place. In such conditions, the microgrid must have the ability to operate stably and autonomously. An evaluation of the need of storage devices and load-shedding strategies is included in the paper.

167 citations


Proceedings ArticleDOI
16 Nov 2005
TL;DR: The main functions of the microgrid central controller required for the optimization of microgrid operation its interconnected operation are described, including optimizing production of the local DGs and power exchanges with the main distribution grid.
Abstract: Restructuring of power markets has helped in the penetration of distributed generation (DG) in the electricity networks. Microgrids are low voltage distribution networks comprising various distributed generators (DG), storage devices and controllable loads that can operate interconnected or isolated from the main distribution grid, as a controlled entity. This paper describes the main functions of the microgrid central controller required for the optimization of microgrid operation its interconnected operation. This is achieved by maximizing its value, i.e. optimizing production of the local DGs and power exchanges with the main distribution grid

167 citations


Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this paper, two possible control strategies were investigated and are described in order to operate a microgrid under emergency mode, and a sequence of actions for a well succeeded black start procedure, involving microgeneration units, has also been identified contributing for an increase in distribution network reliability.
Abstract: Under normal operating conditions, a microgrid (MG) is interconnected with the medium voltage (MV) network. However, planned or unplanned events like maintenance or faults in the MV network, respectively, may lead to MG islanding. In order to deal with islanded operation and even black start following a general blackout, an emergency operation mode must be envisaged. Two possible control strategies were investigated and are described in this paper in order to operate a MG under emergency mode. A sequence of actions for a well succeeded black start procedure, involving microgeneration units, has also been identified contributing for an increase in distribution network reliability

123 citations


Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this paper, a novel energy management system (EMS) based on the application of neural networks (NN) is proposed, which is able to autonomously make decisions and determine hour by hour the correct dispatch of generators with the final goal of minimizing the global energy costs.
Abstract: The interconnection of large amounts of nontraditional generation causes problems in a network designed for 'conventional' operation. A microgrid consists of a combination of generation sources, loads and energy storage interfaced through fast acting power electronics. The aim of operating microgrid sub-systems is to move away from considering DG as badly behaved system components, of which a limited amount can be tolerated in an area, to 'good citizens'. The paper is focused on the development of a novel energy management system (EMS) based on the application of neural networks (NN). The EMS is able to autonomously make decisions and determine hour by hour the correct dispatch of generators with the final goal of minimising the global energy costs. The application of the EMS to a small test case has showed significant saves in the global energy bill by using typical Italian energy and fuel price data

102 citations


ReportDOI
TL;DR: By viewing a unified microgrid as a system of supply and demand, rather than simply aSystem of on-site generation devices, the benefits of integrated supply andDemand control can be exploited, such as economic savings and improved system energy efficiency.
Abstract: On-site energy production, known as distributed energy resources (DER), offers consumers many benefits, such as bill savings and predictability, improved system efficiency, improved reliability, control over power quality, and in many cases, greener electricity Additionally, DER systems can benefit electric utilities by reducing congestion on the grid, reducing the need for new generation and transmission capacity, and offering ancillary services such as voltage support and emergency demand response Local aggregations of distributed energy resources (DER) that may include active control of on-site end-use energy devices can be called microgrids Microgrids require control to ensure safe operation and to make dispatch decisions that achieve system objectives such as cost minimization, reliability, efficiency and emissions requirements, while abiding by system constraints and regulatory rules This control is performed by an energy manager (EM) Preferably, an EM will achieve operation reasonably close to the attainable optimum, it will do this by means robust to deviations from expected conditions, and it will not itself incur insupportable capital or operation and maintenance costs Also, microgrids can include supervision over end-uses, such as curtailing or rescheduling certain loads By viewing a unified microgrid as a system of supply and demand, rather than simply a system of on-site generation devices, the benefits of integrated supply and demand control can be exploited, such as economic savings and improved system energy efficiency

Proceedings ArticleDOI
19 Dec 2005
TL;DR: In this paper, a technique for determining the optimal location and sizes of DG units in a microgrid, given the network configuration and the heat and power requirements at various load points is presented.
Abstract: This paper presents a method for optimally siting and sizing distributed generation (DG) units in a microgrid The optimization is based on stipulated reliability criteria Power system planning based on reliability gives rise to efficient architectures which can meet the consumer requirements with minimum system upgrade This paper develops a technique for determining the optimal location and sizes of DG units in a microgrid, given the network configuration and the heat and power requirements at various load points The method is based on simulated annealing Thermal output and utilization of combined heat and power (CHP) units are considered The paper presents the development and implementation of the method, and demonstrates its application on a six bus test system

Journal Article
TL;DR: In this article the authors describe how genetic optimization algorithms can be used to find the optimal size and location of distributed generation units in a residential distribution grid.
Abstract: In this article the authors describe how genetic optimization algorithms can be used to find the optimal size and location of distributed generation units in a residential distribution grid. Power losses are minimized while the voltage profile is kept at an acceptable level. The method is applied on a system based on an existing grid topology with production and residential load data based on measurements. Different scenarios are chosen to run the algorithm. The obtained optimal location and size prove to depend strongly on the given conditions.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the economically optimal adoption and operation of distributed energy resources (DER) by a hypothetical California microgrid (μGrid) consisting of a group of commercial buildings over an historical test year, 1999.
Abstract: This paper describes the economically optimal adoption and operation of distributed energy resources (DER) by a hypothetical California microgrid (μGrid) consisting of a group of commercial buildings over an historical test year, 1999. The optimization is conducted using a customer adoption model developed at Berkeley Lab and implemented in the General Algebraic Modeling System. A μGrid is a semiautonomous grouping of electricity and heat loads interconnected with the existing utility grid (macrogrid) but able to island from it. The μGrid minimizes the cost of meeting its energy requirements (consisting of both electricity and heat loads) by optimizing the installation and operation of DER technologies while purchasing residual energy from the local combined natural gas and electricity utility. The available DER technologies are small-scale generators (<500 kW), such as reciprocating engines, microturbines, and fuel cells, with or without combined heat and power (CHP) equipment, such as water and space heating and/or absorption cooling. By introducing a tax on carbon emissions, it is shown that if the μGrid is allowed to install CHP-enabled DER technologies, its carbon emissions are mitigated more than without CHP, demonstrating the potential benefits of small-scale CHP technology for climate change mitigation. Reciprocating engines with heat recovery and/or absorption cooling tend to be attractive technologies for the mild southern California climate, but the carbon mitigation tends to be modest compared to purchasing utility electricity because of the predominance of relatively clean central station generation in California.

Proceedings ArticleDOI
01 Sep 2005
TL;DR: In this paper, the authors presented a telecom power plant that uses local distributed generation resources and the utility grid as power inputs to the system, where microsources are connected to a high voltage main dc bus using multiple-input dc-dc converters.
Abstract: This paper presents a telecom power plant that uses local distributed generation resources and the utility grid as power inputs to the system The microsources are connected to a high voltage main dc bus using multiple-input dc-dc converters Additional converters are used in the secondary power distribution frames The proposed architecture reduces the energy storage requirements and is more reliable than a traditional power plant The system configuration is highly flexible and cost effective This paper also introduces a topology for the multiple-input dc-dc converters and explains some control approaches The analysis is supported by simulation and experimental results

Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this paper, the fault current distribution in a generic microgrid is investigated for different fault contingencies during grid-connected and islanded operation, based on an extensive investigation of earthing systems, a grounding electrode system is then developed for the microgrid study-case so that safe step and touch potentials are obtained.
Abstract: Microgrids are attracting substantial interest because they have the potential to increase the use of renewable generation and micro-CHP. They can also defer investment in distribution capital plant and can improve local power quality. However the primary operational requirement of power systems is that they must operate safely from a user point of view, even during contingencies. Yet electrical safety of microgrids has received little attention to date. This paper addresses this important area. The fault current distribution in a generic microgrid is investigated for different fault contingencies during grid-connected and islanded operation. Based on an extensive investigation of earthing systems, a grounding electrode system is then developed for the microgrid study-case so that safe step and touch potentials are obtained

Journal ArticleDOI
TL;DR: The objective of this paper is to present novel control strategies for MicroGrid operation, especially in islanded mode, that involve mainly the coordination of secondary load-frequency control by a MicroGrid Central Controller that heads a hierarchical control system able to assure stable and secure operation when the islanding of the MicroGrid occurs.
Abstract: The objective of this paper is to present novel control strategies for MicroGrid operation, especially in islanded mode. The control strategies involve mainly the coordination of secondary load-frequency control by a MicroGrid Central Controller that heads a hierarchical control system able to assure stable and secure operation when the islanding of the MicroGrid occurs and in load-following situations in islanded mode.

Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this paper, a fast fault detection method for microgrid system based on micro-sources equipped with power electronics interfaces is explored, which provides reliable and fast detection for different types of faults within the micro-grid.
Abstract: In this paper a fast fault detection method for Microgrid system based on micro-sources equipped with power electronics interfaces is explored. This method provides reliable and fast detection for different types of faults within the micro-grid. The micro-source output voltages are monitored and then converted to dc quantities in the d-q reference frame. Thus, any disturbance at the micro-source output due to any type of fault is reflected as disturbances in the d-q values. The disturbance is used to detect the fault and this leads to the initiation of the associated breaker to isolate the faulted section from the network. Analysis and simulation results are presented for different types of faults within the micro-grid

Journal ArticleDOI
24 Oct 2005
TL;DR: In this paper, an Hinfin controller is designed for the voltage-source-inverter voltage control in a microgrid to compensate the capacitance-parameter variation.
Abstract: Capacitors are widely used for power-factor correction (PFC) in power systems. When a PFC capacitor is installed with a certain load in a microgrid, it may be in parallel with the filter capacitor of the inverter interfacing the utility grid and the local distributed-generation unit and, thus, change the effective filter capacitance. Another complication is the possibility of occurrence of resonance in the microgrid. This paper conducts an in-depth investigation of the effective shunt-filter-capacitance variation and resonance phenomena in a microgrid due to a connection of a PFC capacitor. To compensate the capacitance-parameter variation, an Hinfin controller is designed for the voltage-source- inverter voltage control. By properly choosing the weighting functions, the synthesized Hinfin controller would exhibit high gains at the vicinity of the line frequency, similar to traditional high- performance P+ resonant controller and, thus, would possess nearly zero steady-state error. However, with the robust Hinfin controller, it will be possible to explicitly specify the degree of robustness in face of parameter variations. Furthermore, a thorough investigation is carried out to study the performance of inner current-loop feedback variables under resonance conditions. It reveals that filter-inductor current feedback is more effective in damping the resonance. This resonance can be further attenuated by employing the dual-inverter microgrid conditioner and controlling the series inverter as a virtual resistor affecting only harmonic components without interference with the fundamental power flow. And finally, the study in this paper has been tested experimentally using an experimental microgrid prototype.

Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this article, the results of investigations on various economic, regulatory and commercial issues faced by the development of micro-grids in MICROGRIDS project are presented and described.
Abstract: Concepts of microgrids are proposed to address primarily various issues related to integration of small scale renewables and increased demand of reliable electricity supply. With an active management control approach and ability to operate in islanding mode, a cluster of micro generators, electricity storage and electrical loads can be operated within the microgrids framework to provide higher supply reliability to highly value customers. Solutions are required not only to make these concepts technologically feasible and safe to operate but also to be commercially viable and attractive, economically efficient and supported by electricity regulations. This paper summarises the results of investigations on various economic, regulatory and commercial issues faced by the development of microgrids in MICROGRIDS project. The potential economic benefits and contributions to environment from applications of microgrid technologies are also presented and described in this paper

Journal ArticleDOI
TL;DR: The collaboration between the states and the DOE's Energy Storage Research Program is proving to be an outstanding success as mentioned in this paper, and the selected projects show a good portfolio of advanced energy storage media: a ZnBr flow battery, the NaS battery, supercapacitors, and flywheels.
Abstract: The collaboration between the states and the DOE's Energy Storage Research Program is proving to be an outstanding success. The selected projects show a good portfolio of advanced energy storage media: a ZnBr flow battery, the NaS battery, supercapacitors, and flywheels. The applications are equally varied: mitigation of substation congestion, grid frequency control, load management, and stabilization of a microgrid. The goal of these partnerships with the states is to demonstrate electric energy storage as a technically viable, cost-effective, and broadly applicable option for increasing the reliability of the electricity system and for electric energy management.

Proceedings ArticleDOI
18 Nov 2005
TL;DR: In this paper, the main micro-generation sources are described, in particular, the models of microturbines, fuel cells, photovoltaic systems and wind turbines.
Abstract: The interconnection of small, modular generation and storage technologies at the MV and LV distribution level have the potential to significantly impact power system performance. In this paper models of the main micro-generation sources are described. In particular, the models of microturbines, fuel cells, photovoltaic systems and wind turbines, are described. In addition basic models of their power electronic interfaces are given. The above models have been integrated in a simulation platform able to represent the steady state and dynamic behavior of three phase networks. The simulation tool, which is developed in the framework of the EU funded MICROGRIDS project, is used to define and evaluate operational and control strategies for the microgrid paradigm

01 Jan 2005
TL;DR: In this paper, the authors proposed a distributed energy resources customer adoption model (DER-CAM) to identify the energy bill minimising combination of on-site generation and heat recovery equipment for sites, given their electricity and heat requirements, the tariffs they face, and a menu of available equipment.
Abstract: While demand for electricity continues to grow, expansion of the traditional electricity supply system, or macrogrid, is constrained and is unlikely to keep pace with the growing thirst western economies have for electricity. Furthermore, no compelling case has been made that perpetual improvement in the overall power quality and reliability (PQR) delivered is technically possible or economically desirable. An alternative path to providing high PQR for sensitive loads would generate close to them in microgrids, such as the Consortium for Electricity Reliability Technology Solutions (CERTS) Microgrid. Distributed generation would alleviate the pressure for endless improvement in macrogrid PQR and might allow the establishment of a sounder economically based level of universal grid service. Energy conversion from available fuels to electricity close to loads can also provide combined heat and power (CHP) opportunities that can significantly improve the economics of small-scale on-site power generation, especially in hot climates when the waste heat serves absorption cycle cooling equipment that displaces expensive on-peak electricity. An optimisation model, the Distributed Energy Resources Customer Adoption Model (DER-CAM), developed at Berkeley Lab identifies the energy bill minimising combination of on-site generation and heat recovery equipment for sites, given their electricity and heat requirements, the tariffs they face, and a menu of available equipment. DER-CAM is used to conduct a systemic energy analysis of a southern California naval base building and demonstrates a typical current economic on-site power opportunity. Results achieve cost reductions of about 15% with DER depending on the tariff. Furthermore, almost all of the energy is provided on-site, indicating that modest cost savings can be achieved when the microgrid is free to select distributed generation and heat recovery equipment in order to minimise its overall costs.

Proceedings ArticleDOI
12 Jun 2005
TL;DR: In this paper, the authors present a rational method of building microgrids optimized for cost and subject to reliability constraints, based on dynamic programming and consists of determining the optimal interconnection between microsources and load points, given their locations and the rights of way for possible interconnections.
Abstract: Today's power delivery infrastructure is operating under extreme stress. The last few decades have seen minimal investment in infrastructure, and little has been done to prepare the ageing equipment for increasing load growths and the demands of open access. Consequently, the deployment of distributed energy resources (DER) is becoming an increasingly attractive alternative to the expensive and time consuming processes of upgrading and augmenting the transmission and distribution systems. DERs are small, modular sources (generation or storage) of energy which are often more efficient and controllable than traditional power plants. These devices are installed at or near centers of utilization. Eventually, as their penetration increases considerably, they are interconnected in a grid-like fashion for stability and enhanced reliability. These grids are called 'microgrids'. This paper presents a rational method of building microgrids optimized for cost and subject to reliability constraints. The method is based on dynamic programming and consists of determining the optimal interconnection between microsources and load points, given their locations and the rights of way for possible interconnections. A new approach, called 'unit link addition', is also introduced. The method is demonstrated using a 22-bus system.


01 Oct 2005
TL;DR: In this paper, three possible control strategies (PQ control, Droop control, and Frequency/Voltage control) of the microgrid are described, and simulation results show how the flywheel uses PQ control only when the MicroGrid is operated in grid-connected mode.
Abstract: With large-scale integration of micro generation into low voltage grids, stability becomes an important issue for a MicroGrid. The unique nature of the MicroGrid requires that the MicroGrid is stable in both grid-connected mode and islanded mode. In this paper, the major factors (such as control schemes of the flywheel energy storage system, types of load in the MicroGrid, location of the fault and inertia constants of motor load) influencing the stability of the MicroGrid are investigated. Three possible control strategies (PQ control, Droop control and Frequency/Voltage control) of the MicroGrid are described. Simulation results show how the flywheel uses PQ control only when the MicroGrid is operated in grid-connected mode. During islanded mode, the control scheme of the flywheel has to be switched from PQ control to Droop control or Frequency/Voltage. With fixed PQ load or impedance load in the MicroGrid there is no stability problem. However, motor loads have a significant influence on the transient stability of the MicroGrid. In the MicroGrid, no evidence of small signal instability has been found. Instability of the MicroGrid is likely to result in low voltages. Hence, the stability of the MicroGrid can be improved by using an undervoltage load shedding method on the less important motor loads in the MicroGrid.

Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this paper, an algorithm able to deal with the reconfiguration of distribution systems is proposed to find the optimal combination of micro-grids, in the search of the best configuration among different combinations of microgrids.
Abstract: In the last twenty years power systems observed important changes at the distribution level, due to the presence of distributed generation and the changing towards MV active networks, as well the institutional, regulatory and commercial reorganization. In this new scenario, among the various opportunities related to the use of DG, there is the opportunity of a partition of the distribution network in cells or microgrids. In order to find the optimal combination of microgrids, an algorithm able to deal with the reconfiguration of distribution systems is proposed. In the search of the best configuration among different combinations of microgrids, the algorithm uses a Sequential Monte Carlo simulation technique. The final structure found by the algorithm maximizes the sum of the savings in both the cost of energy purchasing and the cost of service interruptions

Proceedings ArticleDOI
06 Nov 2005
TL;DR: In this article, the authors discussed how the gas turbines absorb the power variation from the wind generation and load, and showed that gas turbine output control is effective method to absorb output fluctuation from load and wind farm.
Abstract: Renewable energies such as wind power or photovoltaic energy are environmentally focused but the output power fluctuation of the renewable energies may cause excess variation of voltage or frequency of the grid (Ramirez et al., 2004; Oliva and Balda, 2003), Marei et al., 2004), Okuyama et al., 2003). Increase of the amount of renewable energies would violate the quality of the grid (McCusker et al., 2002; Gupta and Pahwa, 2004; Bhowmik et al., 2003), Hernandez, 2003). The micro grid in which dispersed energies compensate the variation from the renewable energies can expand the installation limit of the renewable energies by maintaining the quality of the interconnected grid (Guan et al., 2003; Pregelj et al., 2004; Hayashi et al., 2003). In this paper, how the gas turbines absorb the power variation from the wind generation and load is discussed. In order to control output power, gas turbines must run at partial load operation, which results in lower efficiency. Tie-line power flow and frequency fluctuation caused by imbalance between supply and demand is also discussed. It is shown that gas turbine output control is effective method to absorb output fluctuation from load and wind farm. If the exhausted thermal energy from a gas turbine can be used for co-generation, more energy saving is expected

Proceedings ArticleDOI
16 Jun 2005
TL;DR: In this paper, a modified p-q theory is proposed to compensate for voltage and current harmonics, present in the microgrid bus, which is suitable for application in control of single-phase active filters and unified power quality conditioners (UQPC).
Abstract: This paper presents a 400 Hz microgrid, suitable for integration of alternative energy sources in a distributed generation system. The utilization of a higher frequency can bring some advantages, such as weight and size reduction of passive components. To compensate for voltage and current harmonics, present in the microgrid bus, this paper proposes a modified p-q theory, which is suitable for application in control of single-phase active filters and unified power quality conditioners (UQPC). The UPQC can compensate for current and voltage harmonics and also for reactive power. Practical and simulated results show the ability of the proposed method to obtain the harmonic contents of voltage and current, independently of one each other

Journal Article
TL;DR: In this paper, a three-phase four-wire grid-interfacing power quality compensator for microgrid applications is proposed for use with each individual distributed generation (DG) system in the microgrid and consists of two four-phase-leg inverters (a shunt and a series), optimally controlled to achieve an enhancement of both the quality of power within the micro-grid and quality of currents flowing between the micro grid and the utility system.
Abstract: This paper presents a three-phase four-wire grid-interfacing power quality compensator for microgrid applications. The compensator is proposed for use with each individual distributed generation (DG) system in the microgrid and consists of two four-phase-leg inverters (a shunt and a series), optimally controlled to achieve an enhancement of both the quality of power within the microgrid and the quality of currents flowing between the microgrid and the utility system. During utility grid voltage unbalance, the four-phase-leg compensator can compensate for all the unwanted positive-, negative-, and zero-sequence voltage-current components found within the unbalanced utility. Specifically, the shunt four-leg inverter is controlled to ensure balanced voltages within the microgrid and to regulate power sharing among the parallel-connected DG systems. The series inverter is controlled complementarily to inject negative- and zero-sequence voltages in series to balance the line currents, while generating zero real and reactive power. During utility voltage sags, the series inverter can also be controlled using a newly proposed flux-charge current-limiting algorithm to limit the flow of large fault currents between the micro- and utility grids. The performance of the proposed compensator has been verified in simulations and experimentally using a laboratory prototype.