Control techniques of Dispersed Generators to improve the continuity of electricity supply
07 Aug 2002-Vol. 2, pp 789-794
TL;DR: In this article, the authors present a control technique for distributed generation (DG) plants that use feedback of only locally measurable variables, which allows correct system operation and switching between parallel and isolated modes without needing online communication of control signals between the generators.
Abstract: It is expected that dispersed generation (DG) will play an increasing role in electric power systems in the near future. Among the benefits that DG can give to the power system operators and to the electricity customers, one of the most attractive is the possibility of improving the continuity of power supply. DG plants can be designed to supply portions of the distribution grid in the event of an upstream supply outage. Techniques for controlling DG plants that use feedback of only locally measurable variables are presented. This solution allows correct system operation and switching between parallel and isolated modes without needing online communication of control signals between the generators. The control technique is described with particular reference to inverter-interfaced systems (micro-turbines, fuel cells). Simulations of sample cases including different size and type of generators are presented.
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01 Nov 2009
TL;DR: The hierarchical control derived from ISA-95 and electrical dispatching standards to endow smartness and flexibility to MGs is presented and results are provided to show the feasibility of the proposed approach.
Abstract: DC and AC Microgrids are key elements to integrate renewable and distributed energy resources as well as distributed energy storage systems. In the last years, efforts toward the standardization of these Microgrids have been made. In this sense, this paper present the hierarchical control derived from ISA-95 and electrical dispatching standards to endow smartness and flexibility to microgrids. The hierarchical control proposed consist of three levels: i) the primary control is based on the droop method, including an output impedance virtual loop; ii) the secondary control allows restoring the deviations produced by the primary control; and iii) the tertiary control manage the power flow between the microgrid and the external electrical distribution system. Results from a hierarchical-controlled microgrid are provided to show the feasibility of the proposed approach.
4,145 citations
Cites background from "Control techniques of Dispersed Gen..."
...AC microgrids are now in the cutting edge of the state of the art [20]-[25]....
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TL;DR: In this article, the feasibility of control strategies to be adopted for the operation of a microgrid when it becomes isolated is evaluated and the need of storage devices and load shedding strategies is evaluated.
Abstract: This paper describes and evaluates the feasibility of control strategies to be adopted for the operation of a microgrid when it becomes isolated. Normally, the microgrid operates in interconnected mode with the medium voltage 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 this paper.
2,276 citations
Cites background from "Control techniques of Dispersed Gen..."
...The fuel-cell includes a fuel processor that converts the used fuel in hydrogen, a power section, where chemical reactions take place, and a power conditioner that converts dc to ac power....
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...…value in the interior of the electrodes, the temperature in the fuel-cell is presumed to be always stable, only ohmic losses are considered, assuming that the working conditions are far away from the upper and lower extreme values of current, and the Nernst equation is assumed to be applicable....
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TL;DR: In this paper, a novel control strategy for parallel inverters of distributed generation units in an AC distribution system is presented, based on the droop control method, using only locally measurable feedback signals.
Abstract: This paper presents a novel control strategy for parallel inverters of distributed generation units in an AC distribution system. The proposed control technique, based on the droop control method, uses only locally measurable feedback signals. This method is usually applied to achieve good active and reactive power sharing when communication between the inverters is difficult due to its physical location. However, the conventional voltage and frequency droop methods of achieving load sharing have a slow and oscillating transient response. Moreover, there is no possibility to modify the transient response without the loss of power sharing precision or output-voltage and frequency accuracy. In this work, a great improvement in transient response is achieved by introducing power derivative-integral terms into a conventional droop scheme. Hence, better controllability of the system is obtained and, consequently, correct transient performance can be achieved. In addition, an instantaneous current control loop is also included in the novel controller to ensure correct sharing of harmonic components when supplying nonlinear loads. Simulation and experimental results are presented to prove the validity of this approach, which shows excellent performance as opposed to the conventional one.
1,003 citations
Cites background from "Control techniques of Dispersed Gen..."
...In addition, every unit must be able to operate independently when communication is too difficult due to the long distance between its connection points [7]....
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TL;DR: The paper explorers the resistive output impedance of the parallel-connected inverters in an island microgrid and proposes a novel wireless load-sharing controller for islanding parallel invertes in an ac distributed system.
Abstract: In this paper, a novel wireless load-sharing controller for islanding parallel inverters in an ac-distributed system is proposed This paper explores the resistive output impedance of the parallel-connected inverters in an island microgrid The control loops are devised and analyzed, taking into account the special nature of a low-voltage microgrid, in which the line impedance is mainly resistive and the distance between the inverters makes the control intercommunication between them difficult In contrast with the conventional droop-control method, the proposed controller uses resistive output impedance, and as a result, a different control law is obtained The controller is implemented by using a digital signal processor board, which only uses local measurements of the unit, thus increasing the modularity, reliability, and flexibility of the distributed system Experimental results are provided from two 6-kVA inverters connected in parallel, showing the features of the proposed wireless control
928 citations
TL;DR: This work shows that a network of loads and DC/AC inverters equipped with power-frequency droop controllers can be cast as a Kuramoto model of phase-coupled oscillators, and proposes a distributed integral controller based on averaging algorithms, which dynamically regulates the system frequency in the presence of a time-varying load.
819 citations
Cites background from "Control techniques of Dispersed Gen..."
...Some representative references for the basic methodology are [30,2,21,22,20] and [17]....
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References
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TL;DR: In this article, the authors focus on some technical aspects, but not on the impact on the quality of supply and on tariff signals, and they focus on the technical aspects only.
Abstract: The insertion of dispersed generation into existing electric power systems has a great impact on real-time operation and planning. Several uncertainties characterize the ability of the existing power system to integrate this form of generation, Hence, dispersed generation must be taken into consideration in power system performance so that operation and security are not disturbed. Dispersed generation increases the complexity of controlling, protecting and maintaining power distribution systems. This article focuses on some technical aspects, but not on the impact on the quality of supply and on tariff signals.
459 citations
TL;DR: In this article, the authors consider distributed generation (DG) can be incorporated into distribution planning as an option along with traditional feeder and substation options, and the planning process needs to incorporate more detailed simulations of capacity constraints and customer damage costs.
Abstract: Distributed generation (DG) can be incorporated into distribution planning as an option along with traditional feeder and substation options. In place of rigid capacity planning rules, the planning process needs to incorporate more detailed simulations of capacity constraints and customer damage costs because utilities now assume more risk. Planning tools need to simulate load variations, contingencies, dispatch and control action to more accurately determine the capacity limits and related costs. This is especially important when considering DG because the siting and dispatch have an important impact on the benefits to the utility. Equally important is the evaluation of economic risk given uncertainties such as load growth. Because of the added complexities associated with these analysis techniques, the planning process must incorporate appropriate screening tools to determine the depth of analysis needed for particular projects, thereby making more efficient use of already scarce planning resources.
241 citations
"Control techniques of Dispersed Gen..." refers methods in this paper
...This big change requires a new approach to system operation, protection and planning [1, 2 ]....
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TL;DR: In this paper, the optimal number and location of switching devices for both radial and meshed power distribution systems was found based on the Bellmann's optimality principle, combined with thinning techniques, yielding the optimal solution in a few ms for real size problems.
Abstract: Automatic devices that locate and automatically sectionalize faulted branches in MV power distribution systems restrict drastically the extent of disruption caused by long power interruptions when properly positioned. Some algorithms and automatic calculation procedures are proposed for determining the optimum number and location of automatic sectionalizing switching devices. Using these algorithms, the optimal solution can be found for both radial and meshed systems. The procedure is based on Bellmann's optimality principle which, combined with thinning techniques, yields the optimal solution in a few ms for real size problems.
157 citations
28 Jan 2001
TL;DR: In this paper, the results of an investigation regarding the electrical performance characteristics of a new, three-phase, 480 V (L-L), 30 kW, micro-turbine generator and its suitability as an electrical power source for applications at the electrical power distribution voltage level.
Abstract: This paper presents the results of an investigation regarding the electrical performance characteristics of a new, three-phase, 480 V (L-L), 30 kW, micro-turbine generator and its suitability as an electrical power source for applications at the electrical power distribution voltage level. This unit is fueled by natural gas and may be used as a dispersed generation source. The unit was purchased by the local utility company and given to the University of Nevada, Reno, USA, for the investigation. The Electrical Machine and the Power System Laboratory was used to perform the study. Testing was performed at several load set-point levels. The investigation includes the turbine behavior under a weak system that consists of the micro-turbine, a variable three-phase load, and a three-phase 15 kVA synchronous machine in the laboratory. The speed of this machine is controlled by a fuzzy logic algorithm. Conclusions are made regarding the suitability of the unit as a distributed generation source.
35 citations
28 Jan 2001
TL;DR: In this paper, the authors proposed a control and command infkstructure around critical installations to sense the presence of a disturbanced attack in any frequency and initiate the generator running process, and start distributed generators as needed to maintain acceptable operational levels.
Abstract: Distributed generation has the potential to improve the security of the electric power infkwtructure in many ways, includ~ the possibility of deliberate operation of the powel grid in small islands centered around critical installations. Once the effects of disturbances (random or intentional) are isolated to an island or two, existing technology could then be used to track down and eliminate the source of the disturbance. Such a scenario will require the development of a control and command infkstructure around critical installations to sense the presence of a disturbancedattack in any fo~ initiate the iskmding process, and start distributed generators as needed to maintain acceptable operational levels.
29 citations