Showing papers on "Microgrid published in 2013"
TL;DR: In this article, the authors present a comprehensive literature review of AC and DC microgrid (MG) systems in connection with distributed generation (DG) units using renewable energy sources (RESs), energy storage systems (ESS) and loads.
Abstract: This paper presents the latest comprehensive literature review of AC and DC microgrid (MG) systems in connection with distributed generation (DG) units using renewable energy sources (RESs), energy storage systems (ESS) and loads. A survey on the alternative DG units' configurations in the low voltage AC (LVAC) and DC (LVDC) distribution networks with several applications of microgrid systems in the viewpoint of the current and the future consumer equipments energy market is extensively discussed. Based on the economical, technical and environmental benefits of the renewable energy related DG units, a thorough comparison between the two types of microgrid systems is provided. The paper also investigates the feasibility, control and energy management strategies of the two microgrid systems relying on the most current research works. Finally, the generalized relay tripping currents are derived and the protection strategies in microgrid systems are addressed in detail. From this literature survey, it can be revealed that the AC and DC microgrid systems with multiconverter devices are intrinsically potential for the future energy systems to achieve reliability, efficiency and quality power supply.
1,004 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
TL;DR: In this paper, a decentralized controller for DC microgrid is proposed to achieve high reliability, low-voltage regulation, and equal load sharing, utilizing low-bandwidth communication.
Abstract: DC microgrids are gaining popularity due to high efficiency, high reliability, and easy interconnection of renewable sources as compared to the ac system. Control objectives of dc microgrid are: 1) to ensure equal load sharing (in per unit) among sources; and 2) to maintain low-voltage regulation of the system. Conventional droop controllers are not effective in achieving both the aforementioned objectives simultaneously. Reasons for this are identified to be the error in nominal voltages and load distribution. Though centralized controller achieves these objectives, it requires high-speed communication and offers less reliability due to single point of failure. To address these limitations, this paper proposes a new decentralized controller for dc microgrid. Key advantages are high reliability, low-voltage regulation, and equal load sharing, utilizing low-bandwidth communication. To evaluate the dynamic performance, mathematical model of the scheme is derived. Stability of the system is evaluated by eigenvalue analysis. The effectiveness of the scheme is verified through a detailed simulation study. To confirm the viability of the scheme, experimental studies are carried out on a laboratory prototype developed for this purpose. Controller area network protocol is utilized to achieve communication between the sources.
768 citations
TL;DR: In this article, the authors proposed a distributed secondary voltage control of micro-grids based on the distributed cooperative control of multi-agent systems, where each distributed generator only requires its own information and the information of some neighbors.
Abstract: This paper proposes a secondary voltage control of microgrids based on the distributed cooperative control of multi-agent systems. The proposed secondary control is fully distributed; each distributed generator only requires its own information and the information of some neighbors. The distributed structure obviates the requirements for a central controller and complex communication network which, in turn, improves the system reliability. Input-output feedback linearization is used to convert the secondary voltage control to a linear second-order tracker synchronization problem. The control parameters can be tuned to obtain a desired response speed. The effectiveness of the proposed control methodology is verified by the simulation of a microgrid test system.
728 citations
TL;DR: To address the intrinsically stochastic availability of renewable energy sources (RES), a novel power scheduling approach is introduced that involves the actual renewable energy as well as the energy traded with the main grid, so that the supply-demand balance is maintained.
Abstract: Due to its reduced communication overhead and robustness to failures, distributed energy management is of paramount importance in smart grids, especially in microgrids, which feature distributed generation (DG) and distributed storage (DS). Distributed economic dispatch for a microgrid with high renewable energy penetration and demand-side management operating in grid-connected mode is considered in this paper. To address the intrinsically stochastic availability of renewable energy sources (RES), a novel power scheduling approach is introduced. The approach involves the actual renewable energy as well as the energy traded with the main grid, so that the supply-demand balance is maintained. The optimal scheduling strategy minimizes the microgrid net cost, which includes DG and DS costs, utility of dispatchable loads, and worst-case transaction cost stemming from the uncertainty in RES. Leveraging the dual decomposition, the optimization problem formulated is solved in a distributed fashion by the local controllers of DG, DS, and dispatchable loads. Numerical results are reported to corroborate the effectiveness of the novel approach.
718 citations
TL;DR: The proposed EMS is implemented for a microgrid composed of photovoltaic panels, two wind turbines, a diesel generator and an energy storage system and the results show the economic sense of the proposal.
Abstract: A novel energy management system (EMS) based on a rolling horizon (RH) strategy for a renewable-based microgrid is proposed. For each decision step, a mixed integer optimization problem based on forecasting models is solved. The EMS provides online set points for each generation unit and signals for consumers based on a demand-side management (DSM) mechanism. The proposed EMS is implemented for a microgrid composed of photovoltaic panels, two wind turbines, a diesel generator and an energy storage system. A coherent forecast information scheme and an economic comparison framework between the RH and the standard unit commitment (UC) are proposed. Solar and wind energy forecasting are based on phenomenological models with updated data. A neural network for two-day-ahead electric consumption forecasting is also designed. The system is tested using real data sets from an existent microgrid in Chile (ESUSCON). The results based on different operation conditions show the economic sense of the proposal. A full practical implementation of the system for ESUSCON is envisioned.
686 citations
TL;DR: A fuzzy logic expert system is used for battery scheduling and the results show considerable minimization on operation cost and emission level compared to literature microgrid energy management approaches based on opportunity charging and Heuristic Flowchart (HF) battery management.
Abstract: In this paper, a generalized formulation for intelligent energy management of a microgrid is proposed using artificial intelligence techniques jointly with linear-programming-based multiobjective optimization. The proposed multiobjective intelligent energy management aims to minimize the operation cost and the environmental impact of a microgrid, taking into account its preoperational variables as future availability of renewable energies and load demand (LD). An artificial neural network ensemble is developed to predict 24-h-ahead photovoltaic generation and 1-h-ahead wind power generation and LD. The proposed machine learning is characterized by enhanced learning model and generalization capability. The efficiency of the microgrid operation strongly depends on the battery scheduling process, which cannot be achieved through conventional optimization formulation. In this paper, a fuzzy logic expert system is used for battery scheduling. The proposed approach can handle uncertainties regarding to the fuzzy environment of the overall microgrid operation and the uncertainty related to the forecasted parameters. The results show considerable minimization on operation cost and emission level compared to literature microgrid energy management approaches based on opportunity charging and Heuristic Flowchart (HF) battery management.
561 citations
TL;DR: In this article, a double-layer coordinated control approach for microgrid energy management is proposed, which consists of two layers: the schedule layer and the dispatch layer, which provides power of controllable units based on real-time data.
Abstract: There are two operation modes of microgrids: grid-connected mode and stand-alone mode. Normally, a microgrid will be connected to the main grid for the majority of time, i.e., operates in the grid-connected mode. In the stand-alone mode, a microgrid is isolated from the main grid; the highest priority for microgrids is to keep a reliable power supply to customers instead of economic benefits. So, the objectives and energy management strategies are different in two modes. In this paper, a novel double-layer coordinated control approach for microgrid energy management is proposed, which consists of two layers: the schedule layer and the dispatch layer. The schedule layer obtains an economic operation scheme based on forecasting data, while the dispatch layer provides power of controllable units based on real-time data. Errors between the forecasting and real-time data are resolved through coordination control of the two layers by reserving adequate active power in the schedule layer, then allocating that reserve in the dispatch layer to deal with the indeterminacy of uncontrollable units. A typical-structure microgrid is studied as an example, and simulation results are presented to demonstrate the performance of the proposed double-layer coordination control method in both grid-connected mode and stand-alone mode.
537 citations
TL;DR: In this paper, a full scope review of the principal energy storage technologies being developed so far, and the features and benefits of energy storage systems (ESSs) within the MG are analyzed in details including ESS configuration and topologies, power electronics interfaces, ESS control schemes for charging/discharging, control strategy of hybrid ESS as well as optimization of the renewable sources and ESS.
531 citations
TL;DR: In this article, a semidefinite programming (SDP) relaxation technique is advocated to obtain a convex problem solvable in polynomial-time complexity, and numerical tests demonstrate the ability of the proposed method to attain the globally optimal solution of the original nonconvex OPF.
Abstract: Optimal power flow (OPF) is considered for microgrids, with the objective of minimizing either the power distribution losses, or, the cost of power drawn from the substation and supplied by distributed generation (DG) units, while effecting voltage regulation. The microgrid is unbalanced, due to unequal loads in each phase and non-equilateral conductor spacings on the distribution lines. Similar to OPF formulations for balanced systems, the considered OPF problem is nonconvex. Nevertheless, a semidefinite programming (SDP) relaxation technique is advocated to obtain a convex problem solvable in polynomial-time complexity. Enticingly, numerical tests demonstrate the ability of the proposed method to attain the globally optimal solution of the original nonconvex OPF. To ensure scalability with respect to the number of nodes, robustness to isolated communication outages, and data privacy and integrity, the proposed SDP is solved in a distributed fashion by resorting to the alternating direction method of multipliers. The resulting algorithm entails iterative message-passing among groups of consumers and guarantees faster convergence compared to competing alternatives.
518 citations
TL;DR: This study proposes a secondary voltage and frequency control scheme based on the distributed cooperative control of multi-agent systems that is fully distributed such that each distributed generator only requires its own information and the information of its neighbours on the communication digraph.
Abstract: This study proposes a secondary voltage and frequency control scheme based on the distributed cooperative control of multi-agent systems. The proposed secondary control is implemented through a communication network with one-way communication links. The required communication network is modelled by a directed graph (digraph). The proposed secondary control is fully distributed such that each distributed generator only requires its own information and the information of its neighbours on the communication digraph. Thus, the requirements for a central controller and complex communication network are obviated, and the system reliability is improved. The simulation results verify the effectiveness of the proposed secondary control for a microgrid test system.
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.
TL;DR: In this paper, the authors proposed a virtual-harmonic-resistance-based active damping method for a parallel-inverter-based grid-interactive microgrid.
Abstract: This paper addresses the resonance problem in a parallel-inverter-based grid-interactive microgrid. Unlike the single grid-connected inverter system where the resonance frequency is mainly fixed by the inverter output LCL filter parameters, the parallel-inverter-based grid-interactive microgrid system presents a more challenging picture where inverter interactions will excite complex resonances at various frequencies. As a result, line currents of inverters can be severely distorted even when the control schemes and filter circuits are properly designed based on the single-inverter model. This paper first develops a microgrid model using discrete time-domain closed-loop Norton's equivalent circuit. Multiple resonances can then be evaluated with the developed model. To improve the microgrid power quality, this paper also designs a virtual-harmonic-resistance-based active damping method. The proposed damping method can be seamlessly incorporated into the conventional deadbeat control scheme through the direct control reference modification. Therefore, the active damping method is able to address both the transient and steady-state resonances within the deadbeat current control bandwidth. Simulation and experimental results are provided to validate the correctness of the developed resonance modeling and active damping methods.
TL;DR: In this article, an optimization model including battery life loss cost, operation and maintenance cost, fuel cost, and environmental cost is established to obtain a set of optimal parameters of operation strategy considering the lifetime characteristics of lead-acid batteries, a multiobjective optimization to minimize power generation cost and to maximize the useful life of leadacid batteries has been achieved via the NSGA-II.
Abstract: Standalone microgrids with renewable sources and battery storage play an important role in solving power supply problems in remote areas such as islands To achieve reliable and economic operations of a standalone microgrid, in addition to the consideration of utilization of renewable resources, the lifetime characteristics of a battery energy storage system also need to be fully investigated In this paper, in order to realize the economic operation of a recently developed standalone microgrid on Dongfushan Island in China, an optimization model including battery life loss cost, operation and maintenance cost, fuel cost, and environmental cost is established to obtain a set of optimal parameters of operation strategy Considering the lifetime characteristics of lead-acid batteries, a multiobjective optimization to minimize power generation cost and to maximize the useful life of lead-acid batteries has been achieved via the nondominated sorting genetic algorithm (NSGA-II) The results show that the proposed method can optimize the system operations under different scenarios and help users obtain the optimal operation schemes of the actual microgrid system
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.
TL;DR: In this paper, the optimal control of the microgrid's energy storage devices is addressed, where stored energy is controlled to balance power generation of renewable sources to optimize overall power consumption at the micro-grid point of common coupling.
Abstract: Energy storage may improve power management in microgrids that include renewable energy sources. The storage devices match energy generation to consumption, facilitating a smooth and robust energy balance within the microgrid. This paper addresses the optimal control of the microgrid's energy storage devices. Stored energy is controlled to balance power generation of renewable sources to optimize overall power consumption at the microgrid point of common coupling. Recent works emphasize constraints imposed by the storage device itself, such as limited capacity and internal losses. However, these works assume flat, highly simplified network models, which overlook the physical connectivity. This work proposes an optimal power flow solution that considers the entire system: the storage device limits, voltages limits, currents limits, and power limits. The power network may be arbitrarily complex, and the proposed solver obtains a globally optimal solution.
TL;DR: A microgrid protection scheme that relies on optimally sizing fault current limiters and optimally setting directional overcurrent relays is proposed, and is tested on two medium-voltage networks.
Abstract: Microgrids can be operated either grid-connected to reduce system losses and for peak shaving or islanded to increase reliability and provide backup power during utility outage. Such dual configuration capability imposes challenges on the design of the protection system. Fault current magnitudes will vary depending on the microgrid operating mode. In this paper, a microgrid protection scheme that relies on optimally sizing fault current limiters and optimally setting directional overcurrent relays is proposed. The protection scheme is optimally designed taking into account both modes of operation (grid-connected and islanded). The problem has been formulated as a constrained nonlinear programming problem and is solved using the genetic algorithm with the static penalty constraint-handling technique. The proposed approach is tested on two medium-voltage networks: a typical radial distribution system and on the IEEE 30-bus looped power distribution system equipped with directly connected conventional synchronous generators.
TL;DR: In this article, an active rectifier and voltage regulator are modeled in nonlinear state-space form, linearized around an operating point, and joined to network and inverter models, and participation analysis of the combined system identified that the low-frequency modes are associated with the voltage controller of the active rectifiers and the droop controllers of the inverters.
Abstract: Rectifiers and voltage regulators acting as constant power loads form an important part of a microgrid’s total load. In simplified form, they present a negative incremental resistance and beyond that, they have control loop dynamics in a similar frequency range to the inverters that may supply a microgrid. Either of these features may lead to a degradation of small-signal damping. It is known that droop control constants need to be chosen with regard to damping, even with simple impedance loads. Actively controlled rectifiers have been modeled in nonlinear state-space form, linearized around an operating point, and joined to network and inverter models. Participation analysis of the eigenvalues of the combined system identified that the low-frequency modes are associated with the voltage controller of the active rectifier and the droop controllers of the inverters. The analysis also reveals that when the active load dc voltage controller is designed with large gains, the voltage controller of the inverter becomes unstable. This dependence has been verified by observing the response of an experimental microgrid to step changes in power demand. Achieving a well-damped response with a conservative stability margin does not compromise normal active rectifier design, but notice should be taken of the inverter–rectifier interaction identified.
TL;DR: Simulation results clearly indicate that the agent-based management is effective in resource management among multiple microgrids economically and profitably.
Abstract: Microgrid is a combination of distributed generators, storage systems, and controllable loads connected to low-voltage network that can operate either in grid-connected or in island mode. High penetration of power at distribution level creates such multiple microgrids. This paper proposes a two-level architecture for distributed-energy-resource management for multiple microgrids using multiagent systems. In order to match the buyers and sellers in the energy market, symmetrical assignment problem based on naive auction algorithm is used. The developed mechanism allows the pool members such as generation agents, load agents, auction agents, grid agents, and storage agents to participate in market. Three different scenarios are identified based on the supply-demand mismatch among the participating microgrids. At the end of this paper, two case studies are presented with two and four interconnected microgrids participating in the market. Simulation results clearly indicate that the agent-based management is effective in resource management among multiple microgrids economically and profitably.
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.
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.
TL;DR: In this article, a droop control method with a restoration mechanism is proposed to improve reactive power sharing in a microgrid, and its operation principle and control method are explained and analyzed.
Abstract: Microgrid is widely accepted as an effective mean of integrating various distributed energy resources (DERs) through their interface converters to provide electric power of high quality and reliability. These distributed resources interface converters can operate in an autonomous fashion without any communication for enhanced system reliability and reduced complexity. Conventionally, the real power-frequency droop control and the reactive power-voltage magnitude droop are adopted as the decentralized control strategies in these DERs interface converters for the autonomous power sharing operations. However, the reactive power sharing of $Q\hbox{--}V$ droop control often deteriorates due to its dependence on the line impedances. In this paper, a $Q\hbox{--}\dot{V}$ droop control method with $\dot{V}$ restoration mechanism is proposed to improve reactive power sharing. Its operation principle and control method are explained and analyzed. Simulation and experimental results are presented to validate the effectiveness of the proposed method.
TL;DR: In this article, a novel controller for inverters is proposed to improve the frequency response of microgrid under disturbances involving large frequency deviations, which is simulated using Simulink/MATLAB software to test the proposed control strategy.
Abstract: Generation is shifting from a centralized power generating facility having large synchronous generators to distributed generation involving sources of smaller capacity. Most of these sources require inverters on the front end while being connected to the grid. Lower available kinetic energy, coupled with less short-circuit current ratio compared to large synchronous generators, compromises the transient stability of the microgrid when isolated from the main grid. Sources in the microgrid use droop control to share power according to their capacity without any form of communication. This paper proposes a novel controller for inverters to improve the frequency response of microgrid under disturbances involving large frequency deviations. It also discusses design of various parameters defined for the proposed control. The microgrid, which has two inverters and two synchronous generators, is simulated using Simulink/MATLAB software to test the proposed control strategy.
16 Jun 2013
TL;DR: In this article, a comprehensive literature review on VSM and a possible classification of the different schemes is provided, and the small-signal response of the inertia emulation characteristics of VSM-based control is proved to be equivalent to conventional droop-based controller for standalone and microgrid operation of converters.
Abstract: The concept of Virtual Synchronous Machines (VSM) is emerging as an alternative approach for control of power electronic converters operating in the power system. One main motivation for applying VSM-based control is to achieve a simple approach for emulating the inertia effect of traditional synchronous machines. This paper provides a comprehensive literature review on VSM and a possible classification of the different schemes. In addition, the small-signal response of the inertia emulation characteristics of VSM-based control is proved to be equivalent to conventional droop-based control for standalone and microgrid operation of converters. Thus, the droop gain and the filter time constant of the power feedback in a droop controller can be directly related to the damping factor and the inertia constant of a Virtual Synchronous Machine. The derived results are providing additional physics-based insight into the operation and tuning of both types of controllers.
TL;DR: In this paper, an appropriate control scheme is developed for controlling the interlinking converter to keep the hybrid microgrid in autonomous operation with active power proportionally shared among its distributed sources.
Abstract: The coexistence of ac and dc subgrids in a hybrid microgrid is likely given that modern distributed sources can either be ac or dc. Linking these subgrids is a power converter, whose topology should preferably be not too unconventional. This is to avoid unnecessary compromises to reliability, simplicity, and industry relevance of the converter. The desired operating features of the hybrid microgrid can then be added through this interlinking converter. To demonstrate, an appropriate control scheme is now developed for controlling the interlinking converter. The objective is to keep the hybrid microgrid in autonomous operation with active power proportionally shared among its distributed sources. Power sharing here should depend only on the source ratings and not their placements within the hybrid microgrid. The proposed scheme can also be extended to include energy storage within the interlinking converter, as already proven in simulation and experiment. These findings have not been previously discussed in the literature, where existing schemes are mostly for an ac or a dc microgrid, but not both in coexistence.
TL;DR: A stationary-frame control method for voltage unbalance compensation in an islanded microgrid is proposed, based on the proper control of DGs interface converters, which demonstrates the effectiveness of the proposed method in the compensation of voltage un balance.
Abstract: Recently, there has been an increasing interest in using distributed generators (DGs) not only to inject power into the grid but also to enhance the power quality. In this paper, a stationary-frame control method for voltage unbalance compensation in an islanded microgrid is proposed. This method is based on the proper control of DGs interface converters. The DGs are properly controlled to autonomously compensate for voltage unbalance while sharing the compensation effort and also active and reactive powers. The control system of the DGs mainly consists of active and reactive power droop controllers, a virtual impedance loop, voltage and current controllers, and an unbalance compensator. The design approach of the control system is discussed in detail, and simulation and experimental results are presented. The results demonstrate the effectiveness of the proposed method in the compensation of voltage unbalance.
TL;DR: In this article, a fault protection and location method for a dc bus microgrid system is presented, where the bus is segmented into overlapping nodes and links with circuit breakers (CBs) to isolate the segment in the event of a fault.
Abstract: A fault protection and location method for a dc bus microgrid system is presented in this paper. Unlike traditional ac systems, dc bus systems cannot survive or sustain high-magnitude fault currents. And if a fault causes the dc bus to de-energize completely, it makes locating faults very difficult. The main goal of the proposed scheme is to detect and isolate faults in the dc bus without de-energizing the entire system and identifying the fault location. In order to achieve this, a ring-type bus was used in this paper. The bus was segmented into overlapping nodes and links with circuit breakers (CBs) to isolate the segment in the event of a fault. Backup protection is implemented for circuit breaker failures to improve system reliability. A noniterative fault-location technique using a probe power is also presented in this paper. This probe power can also be used for a pilot test before main CB reclosing to avoid system issues that can be expected when the reclosing fails due to a permanent fault. The proposed algorithm can be implemented and executed by an intelligent electrical device for individual node. The proposed concepts have been verified with computer simulations and hardware experiments.
TL;DR: In this paper, an energy management system (EMS) with fuzzy control for a dc microgrid system is presented, where the authors use MATLAB/Simulink for modeling, analysis, and control of distributed power sources and energy storage devices.
Abstract: This paper presents the design and implementation of an energy management system (EMS) with fuzzy control for a dc microgrid system. Modeling, analysis, and control of distributed power sources and energy storage devices with MATLAB/Simulink are proposed, and the integrated monitoring EMS is implemented with LabVIEW. To improve the life cycle of the battery, fuzzy control manages the desired state of charge. The RS-485/ZigBee network has been designed to control the operating mode and to monitor the values of all subsystems in the dc microgrid system.
TL;DR: In this article, the optimal scheduling of smart homes' energy consumption is studied using a mixed integer linear programming (MILP) approach, in order to minimise a 1-day forecasted energy consumption cost, DER operation and electricity consumption household tasks are scheduled based on real-time electricity pricing, electricity task time window and forecasted renewable energy output.
TL;DR: For urban areas, a building integrated photovoltaic (BIPV) primarily for self-feeding of buildings equipped with PV array and storage is proposed, with an aim of elimination of multiple energy conversions.
Abstract: The utility grid challenge is to meet the current growing energy demand. One solution to this problem is to expand the role of microgrids that interact with the utility grid and operate independently in case of a limited availability during peak time or outage. This paper proposes, for urban areas, a building integrated photovoltaic (BIPV) primarily for self-feeding of buildings equipped with PV array and storage. With an aim of elimination of multiple energy conversions, a DC network distribution is considered. The BIPV can supply a tertiary building at the same time as PV array may produce power through a hierarchical supervision able to exchange messages with the smart grid and metadata. The hierarchical control is designed as an interface to expand the system ability for advanced energy management control having regard to the grid availability and user's commands. It consists of four layers: human-machine interface, prediction, cost management, and operation. The operation layer, implemented in an experimental platform, takes into account the grid supply power limits and constrains the DC load. The experimental results validate the approach that may be a solution for the future smart grid communication between BIPV and utility grid.