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Microgrids 2016

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (30 September 2016) | Viewed by 209499

Special Issue Editor


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Guest Editor
Department of Electronic Engineering, Technical University of Catalonia, Barcelona, Spain
Interests: microgrids; renewable energy systems; neuroscience-based artificial intelligence; digital twins; cybersecurity
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

During the last decade, microgrids have been developed as a tool to conceive different kinds of energy generation, storage, and consumption, locally. A microgrid is an autonomous entity that can operate connected to the main utility grid or disconnected in islanded mode. These small-scale grids can also be connected, forming energy clusters. This Special Issue of Energies will explore the latest developments in technology to enable the widespread diffusion of microgrids throughout the globe. While papers concerning control of microgrids systems are welcomed, we would particularly welcome those that offer insights about microgrid architectures and sites. The issue will include, but is not be limited to:

*    Decentralized, distributed and centralized controllers for microgrids

*    Power quality for grid-connected and islanded microgrids

*    Communication systems oriented to microgrids

*    Energy management systems for microgrids

*    Demonstration and pilot projects

We welcome papers on primary, blue-skies research, as well as cutting-edge exemplars from industrial practice that can be used to encourage sustainable development and performance of energy microgrids worldwide.

Prof. Dr. Josep M. Guerrero
Guest Editor

Manuscript Submission Information

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Keywords

  • microgrids
  • distributed generation
  • islanded systems
  • renewable energy

Published Papers (31 papers)

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2726 KiB  
Article
Stability Analysis of DC Distribution Systems with Droop-Based Charge Sharing on Energy Storage Devices
by Despoina I. Makrygiorgou and Antonio T. Alexandridis
Energies 2017, 10(4), 433; https://doi.org/10.3390/en10040433 - 27 Mar 2017
Cited by 21 | Viewed by 5355
Abstract
Direct current (DC) distribution systems and DC microgrids are becoming a reliable and efficient alternative energy system, compatible with the DC nature of most of the distributed energy resources (DERs), storage devices and loads. The challenging problem of redesigning an autonomous DC-grid system [...] Read more.
Direct current (DC) distribution systems and DC microgrids are becoming a reliable and efficient alternative energy system, compatible with the DC nature of most of the distributed energy resources (DERs), storage devices and loads. The challenging problem of redesigning an autonomous DC-grid system in view of using energy storage devices to balance the power produced and absorbed, by applying simple decentralized controllers on the electronic power interfaces, is investigated in this paper. To this end, a complete nonlinear DC-grid model has been deployed that includes different DC-DERs, two controlled parallel battery branches, and different varying DC loads. Since many loads in modern distribution systems are connected through power converters, both constant power loads and simple resistive loads are considered in parallel. Within this system, suitable cascaded controllers on the DC/DC power converter interfaces to the battery branches are proposed, in a manner that ensures stability and charge sharing between the two branches at the desired ratio. To achieve this task, inner-loop current controllers are combined with outer-loop voltage, droop-based controllers. The proportional-integral (PI) inner-loop current controllers include damping terms and are fully independent from the system parameters. The controller scheme is incorporated into the system model and a globally valid nonlinear stability analysis is conducted; this differs from small-signal linear methods that are valid only for specific systems, usually via eigenvalue investigations. In the present study, under the virtual cost of applying advanced Lyapunov techniques on the entire nonlinear system, a rigorous analysis is formulated to prove stability and convergence to the desired operation, regardless of the particular system characteristics. The theoretical results are evaluated by detailed simulations, with the system performance being very satisfactory. Full article
(This article belongs to the Special Issue Microgrids 2016)
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6971 KiB  
Article
Multi-Agent-Based Controller for Voltage Enhancement in AC/DC Hybrid Microgrid Using Energy Storages
by Ahmadali Khatibzadeh, Mohammadreza Besmi, Aminollah Mahabadi and Mahmoud Reza Haghifam
Energies 2017, 10(2), 169; https://doi.org/10.3390/en10020169 - 3 Feb 2017
Cited by 33 | Viewed by 6805
Abstract
Development of renewable energies and DC loads have led microgrids toward the creation of DC networks. The predictions show that the hybrid microgrids will be used widely in the future. This article has studied the voltage stability in the presence of sources of [...] Read more.
Development of renewable energies and DC loads have led microgrids toward the creation of DC networks. The predictions show that the hybrid microgrids will be used widely in the future. This article has studied the voltage stability in the presence of sources of energy storage in AC/DC hybrid networks. However, because the different dynamics of hybrid networks applying centralized and distributed controllers will be faced with different problems, in this study, a multi-agent control for the microgrid has been used. A new structure referred to here as an event-driven microgrid control management (EDMCM) has been developed to control the microgrid. This method increases response speed and accuracy of decision making. Hybrid Network Simulation results confirm the validity of the developed model. Full article
(This article belongs to the Special Issue Microgrids 2016)
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14611 KiB  
Article
Balanced Current Control Strategy for Current Source Rectifier Stage of Indirect Matrix Converter under Unbalanced Grid Voltage Conditions
by Yeongsu Bak, June-Seok Lee and Kyo-Beum Lee
Energies 2017, 10(1), 27; https://doi.org/10.3390/en10010027 - 27 Dec 2016
Cited by 13 | Viewed by 8067
Abstract
This paper proposes a balanced current control strategy for the current source rectifier (CSR) stage of an indirect matrix converter (IMC) under unbalanced grid voltage conditions. If the three-phase grid connected to the voltage source inverter (VSI) of the IMC has unbalanced voltage [...] Read more.
This paper proposes a balanced current control strategy for the current source rectifier (CSR) stage of an indirect matrix converter (IMC) under unbalanced grid voltage conditions. If the three-phase grid connected to the voltage source inverter (VSI) of the IMC has unbalanced voltage conditions, it affects the currents of the CSR stage and VSI stage, and the currents are distorted. Above all, the distorted currents of the CSR stage cause instability in the overall system, which can affect the life span of the system. Therefore, in this paper, a control strategy for balanced currents in the CSR stage is proposed. To achieve balanced currents in the CSR stage, the VSI stage should receive DC power without ripple components from the CSR stage. This is implemented by controlling the currents in the VSI stage. Therefore, the proposed control strategy decouples the positive and negative phase-sequence components existing in the unbalanced voltages and currents of the VSI stage. Using the proposed control strategy under unbalanced grid voltage conditions, the stability and life span of the overall system can be improved. The effectiveness of the proposed control strategy is verified by simulation and experimental results. Full article
(This article belongs to the Special Issue Microgrids 2016)
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3994 KiB  
Article
Research on a Micro-Grid Frequency Modulation Strategy Based on Optimal Utilization of Air Conditioners
by Qingzhu Wan, Yuan Bian and Yalan Chen
Energies 2016, 9(12), 1085; https://doi.org/10.3390/en9121085 - 19 Dec 2016
Cited by 2 | Viewed by 5062
Abstract
With the proportion of air conditioners increasing gradually, they can provide a certain amount of frequency-controlled reserves for a micro-grid. Optimizing utilization of air conditioners and considering load response characteristics and customer comfort, the frequency adjustment model is a quadratic function model between [...] Read more.
With the proportion of air conditioners increasing gradually, they can provide a certain amount of frequency-controlled reserves for a micro-grid. Optimizing utilization of air conditioners and considering load response characteristics and customer comfort, the frequency adjustment model is a quadratic function model between the trigger temperature of the air conditioner compressor, and frequency variation is provided, which can be used to regulate the trigger temperature of the air conditioner when the micro-grid frequency rises and falls. This frequency adjustment model combines a primary frequency modulation method and a secondary frequency modulation method of the energy storage system, in order to optimize the frequency of a micro-grid. The simulation results show that the frequency modulation strategy for air conditioners can effectively improve the frequency modulation ability of air conditioners and frequency modulation effects of a micro-grid in coordination with an energy storage system. Full article
(This article belongs to the Special Issue Microgrids 2016)
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2164 KiB  
Article
A Decentralized Control Method for Distributed Generations in an Islanded DC Microgrid Considering Voltage Drop Compensation and Durable State of Charge
by Chul-Sang Hwang, Eung-Sang Kim and Yun-Su Kim
Energies 2016, 9(12), 1070; https://doi.org/10.3390/en9121070 - 16 Dec 2016
Cited by 20 | Viewed by 5237
Abstract
This paper presents a decentralized control method for distributed generations (DGs) in an islanded direct current (DC) microgrid. In most typical DC microgrids, a decentralized control method is based on a voltage droop control method. However, the grid voltage differs from node to [...] Read more.
This paper presents a decentralized control method for distributed generations (DGs) in an islanded direct current (DC) microgrid. In most typical DC microgrids, a decentralized control method is based on a voltage droop control method. However, the grid voltage differs from node to node due to line voltage drop, and hence the power sharing ratio among DGs cannot be matched with as desired value. Especially in an islanded DC microgrid including an energy storage system as a voltage source, it is difficult for DGs to maintain the charge state of the ESS in a decentralized way. To overcome this problem, state of charge (SOC)-voltage droop control is applied to the ESS. By using the proposed droop method, the SOC information can be assigned to the grid voltage, and hence the other DGs are able to support the SOC in a decentralized way. For DGs to enhance the accuracy of the SOC estimation, voltage drop is compensated for based on forecasting data and line impedance data. The simulation is modeled and implemented using Power System Computer Aided Design/Electromagnetic Transients for DC (PSCAD/EMTDC, version 4.2, Winnipeg, Manitoba, Canada) and the simulation results show that the capability to maintain SOC as well as the system voltage profile are improved by using the proposed method. Full article
(This article belongs to the Special Issue Microgrids 2016)
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Article
Adaptive Droop Control for Microgrids Based on the Synergetic Control of Multi-Agent Systems
by Zhiwen Yu, Qian Ai, Xing He and Longjian Piao
Energies 2016, 9(12), 1057; https://doi.org/10.3390/en9121057 - 15 Dec 2016
Cited by 13 | Viewed by 4907
Abstract
In this paper, a distributed synergetic control based on multi-agent systems is proposed to solve the problems of frequency and voltage errors, system stability and power sharing accuracy in the traditional droop control of microgrids. Starting with power flow equations, we build the [...] Read more.
In this paper, a distributed synergetic control based on multi-agent systems is proposed to solve the problems of frequency and voltage errors, system stability and power sharing accuracy in the traditional droop control of microgrids. Starting with power flow equations, we build the secondary-order dynamic model of DG, which consists of three parts: (1) active power allocation; (2) active power-frequency; and (3) reactive power-voltage droop control. Considering time-delays in communication networks, a leaderless synergetic control algorithm is proposed to allocate the active power in inverse proportion to the droop coefficient, and the synergetic control with a virtual leader is proposed to control the system frequency and voltage to keep at the expected value. Besides, the direct Lyapunov method is introduced to verify the globally asymptotical stability. Moreover, the impacts of communication disturbance are also discussed from the aspects of control precision and system stability. Finally, based on a test microgrid, numerous cases are designed as illustration, and the simulation results validate the proposed method. Full article
(This article belongs to the Special Issue Microgrids 2016)
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12016 KiB  
Article
Study of Unwanted Emissions in the CENELEC-A Band Generated by Distributed Energy Resources and Their Influence over Narrow Band Power Line Communications
by Noelia Uribe-Pérez, Itziar Angulo, Luis Hernández-Callejo, Txetxu Arzuaga, David De la Vega and Amaia Arrinda
Energies 2016, 9(12), 1007; https://doi.org/10.3390/en9121007 - 30 Nov 2016
Cited by 44 | Viewed by 6539
Abstract
Distributed Energy Resources might have a severe influence on Power Line Communications, as they can generate interfering signals and high frequency emissions or supraharmonics that may cause loss of metering and control data. In this paper, the influence of various energy resources on [...] Read more.
Distributed Energy Resources might have a severe influence on Power Line Communications, as they can generate interfering signals and high frequency emissions or supraharmonics that may cause loss of metering and control data. In this paper, the influence of various energy resources on Narrowband Power Line Communications is described and analyzed through several test measurements performed in a real microgrid. Accordingly, the paper describes the effects on smart metering communications through the Medium Access Control (MAC) layer analysis. Results show that the switching frequency of inverters and the presence of battery chargers are remarkable sources of disturbance in low voltage distribution networks. In this sense, the results presented can contribute to efforts towards standardization and normative of emissions at higher frequencies higher, such as CENELEC EN 50160 and IEC/TS 62749. Full article
(This article belongs to the Special Issue Microgrids 2016)
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9565 KiB  
Article
Conventional P-ω/Q-V Droop Control in Highly Resistive Line of Low-Voltage Converter-Based AC Microgrid
by Xiaochao Hou, Yao Sun, Wenbin Yuan, Hua Han, Chaolu Zhong and Josep M. Guerrero
Energies 2016, 9(11), 943; https://doi.org/10.3390/en9110943 - 11 Nov 2016
Cited by 50 | Viewed by 7974
Abstract
In low-voltage converter-based alternating current (AC) microgrids with resistive distribution lines, the P-V droop with Q-f boost (VPD/FQB) is the most common method for load sharing. However, it cannot achieve the active power sharing proportionally. To overcome this drawback, [...] Read more.
In low-voltage converter-based alternating current (AC) microgrids with resistive distribution lines, the P-V droop with Q-f boost (VPD/FQB) is the most common method for load sharing. However, it cannot achieve the active power sharing proportionally. To overcome this drawback, the conventional P-ω/Q-V droop control is adopted in the low-voltage AC microgrid. As a result, the active power sharing among the distributed generators (DGs) is easily obtained without communication. More importantly, this study clears up the previous misunderstanding that conventional P-ω/Q-V droop control is only applicable to microgrids with highly inductive lines, and lays a foundation for the application of conventional droop control under different line impedances. Moreover, in order to guarantee the accurate reactive power sharing, a guide for designing Q-V droop gains is given, and virtual resistance is adopted to shape the desired output impedance. Finally, the effects of power sharing and transient response are verified through simulations and experiments in converter-based AC Microgrid. Full article
(This article belongs to the Special Issue Microgrids 2016)
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1549 KiB  
Article
Power Quality Disturbances Feature Selection and Recognition Using Optimal Multi-Resolution Fast S-Transform and CART Algorithm
by Nantian Huang, Hua Peng, Guowei Cai and Jikai Chen
Energies 2016, 9(11), 927; https://doi.org/10.3390/en9110927 - 9 Nov 2016
Cited by 30 | Viewed by 4780
Abstract
In order to improve the recognition accuracy and efficiency of power quality disturbances (PQD) in microgrids, a novel PQD feature selection and recognition method based on optimal multi-resolution fast S-transform (OMFST) and classification and regression tree (CART) algorithm is proposed. Firstly, OMFST is [...] Read more.
In order to improve the recognition accuracy and efficiency of power quality disturbances (PQD) in microgrids, a novel PQD feature selection and recognition method based on optimal multi-resolution fast S-transform (OMFST) and classification and regression tree (CART) algorithm is proposed. Firstly, OMFST is carried out according to the frequency domain characteristic of disturbance signal, and 67 features are extracted by time-frequency analysis to construct the original feature set. Subsequently, the optimal feature subset is determined by Gini importance and sorted according to an embedded feature selection method based on the Gini index. Finally, one standard error rule subtree evaluation methods were applied for cost complexity pruning. After pruning, the optimal decision tree (ODT) is obtained for PQD classification. The experiments show that the new method can effectively improve the classification efficiency and accuracy with feature selection step. Simultaneously, the ODT can be constructed automatically according to the ability of feature classification. In different noise environments, the classification accuracy of the new method is higher than the method based on probabilistic neural network, extreme learning machine, and support vector machine. Full article
(This article belongs to the Special Issue Microgrids 2016)
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5680 KiB  
Article
SoC-Based Output Voltage Control for BESS with a Lithium-Ion Battery in a Stand-Alone DC Microgrid
by Seung-Yeong Yu, Hyun-Jun Kim, Jae-Hyuk Kim and Byung-Moon Han
Energies 2016, 9(11), 924; https://doi.org/10.3390/en9110924 - 8 Nov 2016
Cited by 15 | Viewed by 7557
Abstract
This paper proposes a new DC output voltage control for a battery energy storage system (BESS) with a lithium-ion battery based on the state of charge (SoC). The proposed control scheme was verified through computer simulations for a typical stand-alone DC microgrid, which [...] Read more.
This paper proposes a new DC output voltage control for a battery energy storage system (BESS) with a lithium-ion battery based on the state of charge (SoC). The proposed control scheme was verified through computer simulations for a typical stand-alone DC microgrid, which consists of a BESS, photovoltaic (PV) panel, engine generator (EG), and DC load. A scaled hardware prototype for a stand-alone DC microgrid was set up in the lab, in which the proposed control scheme was loaded in a DSP controller. The experimental results were compared with the simulation results for performance verification. The proposed control scheme provides relatively lower variation of the DC grid voltage than the conventional droop control. Full article
(This article belongs to the Special Issue Microgrids 2016)
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3971 KiB  
Article
Master–Slave Based Hierarchical Control for a Small Power DC-Distributed Microgrid System with a Storage Device
by Seung-Woon Lee and Bo-Hyung Cho
Energies 2016, 9(11), 880; https://doi.org/10.3390/en9110880 - 27 Oct 2016
Cited by 21 | Viewed by 8201
Abstract
In this paper, we analyze one of the main drawbacks of droop control-based DC microgrid systems, and propose a novel control method to overcome this problem. Typically, DC microgrid systems use droop control techniques to enable communication independency and expandability. However, as these [...] Read more.
In this paper, we analyze one of the main drawbacks of droop control-based DC microgrid systems, and propose a novel control method to overcome this problem. Typically, DC microgrid systems use droop control techniques to enable communication independency and expandability. However, as these advantages are based on bus quality and regulation abandonment, droop-based schemes have limitations in terms of high bus impedance and bus regulation. This paper proposes a novel master–slave based hierarchical control technique for a DC distribution system, in which a DC bus signaling method is used to overcome the communication dependency and the expandability limitations of conventional master–slave control methods. The concept and design considerations of the proposed control method are presented, and a 1 kW simulation under a Powersim (PSIM) environment and hardware prototype—built to verify the system—is described. Full article
(This article belongs to the Special Issue Microgrids 2016)
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1073 KiB  
Article
Marginal Generation Technology in the Chinese Power Market towards 2030 Based on Consequential Life Cycle Assessment
by Guangling Zhao, Josep M. Guerrero and Yingying Pei
Energies 2016, 9(10), 788; https://doi.org/10.3390/en9100788 - 29 Sep 2016
Cited by 9 | Viewed by 6311
Abstract
Electricity consumption is often the hotspot of life cycle assessment (LCA) of products, industrial activities, or services. The objective of this paper is to provide a consistent, scientific, region-specific electricity-supply-based inventory of electricity generation technology for national and regional power grids. Marginal electricity [...] Read more.
Electricity consumption is often the hotspot of life cycle assessment (LCA) of products, industrial activities, or services. The objective of this paper is to provide a consistent, scientific, region-specific electricity-supply-based inventory of electricity generation technology for national and regional power grids. Marginal electricity generation technology is pivotal in assessing impacts related to additional consumption of electricity. China covers a large geographical area with regional supply grids; these are arguably equally or less integrated. Meanwhile, it is also a country with internal imbalances in regional energy supply and demand. Therefore, we suggest an approach to achieve a geographical subdivision of the Chinese electricity grid, corresponding to the interprovincial regional power grids, namely the North, the Northeast, the East, the Central, the Northwest, and the Southwest China Grids, and the China Southern Power Grid. The approach combines information from the Chinese national plans on for capacity changes in both production and distribution grids, and knowledge of resource availability. The results show that nationally, marginal technology is coal-fired electricity generation, which is the same scenario in the North and Northwest China Grid. In the Northeast, East, and Central China Grid, nuclear power gradually replaces coal-fired electricity and becomes the marginal technology. In the Southwest China Grid and the China Southern Power Grid, the marginal electricity is hydropower towards 2030. Full article
(This article belongs to the Special Issue Microgrids 2016)
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10374 KiB  
Article
A Riding-through Technique for Seamless Transition between Islanded and Grid-Connected Modes of Droop-Controlled Inverters
by Shang-Hung Hu, Tzung-Lin Lee, Chun-Yi Kuo and Josep M. Guerrero
Energies 2016, 9(9), 732; https://doi.org/10.3390/en9090732 - 9 Sep 2016
Cited by 5 | Viewed by 5812
Abstract
This paper presents a seamless transition method for a droop-controlled inverter. The droop control is suitable to make the inverter work as a voltage source in both islanded and grid-connected modes, however, the transfer between theses modes can result in a big inrush [...] Read more.
This paper presents a seamless transition method for a droop-controlled inverter. The droop control is suitable to make the inverter work as a voltage source in both islanded and grid-connected modes, however, the transfer between theses modes can result in a big inrush current that may damage the system. The proposed method allows the droop-controlled inverter to improve the transient response when transferring between modes, by detecting the inrush current, activating a current control loop during transients, and then transferring back to droop-controlled mode smoothly by using a virtual inductance loop. In addition, a local phase-locked-loop (PLL) is proposed to align the inverter voltage with the grid in order to reduce the transient current during the transition. Therefore, the droop-controlled inverter is able to operate in both grid-connected and islanded modes, providing as well a smooth transition between them, requiring neither synchronization signals nor grid-side information. The control algorithm and design procedure are presented. Experimental results from a laboratory prototype validate the effectiveness of the proposed method. Full article
(This article belongs to the Special Issue Microgrids 2016)
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2480 KiB  
Article
Comparative Life Cycle Cost Analysis of Hardening Options for Critical Loads
by Sungmin Park, Sung-Yeul Park, Peng Zhang, Peter Luh, Michel T. J. Rakotomavo and Camilo Serna
Energies 2016, 9(7), 553; https://doi.org/10.3390/en9070553 - 18 Jul 2016
Cited by 4 | Viewed by 5934
Abstract
In order to determine the most cost effective alternative among hardening options of power systems, the direct monetary benefits should be evaluated above all other things. Therefore, this paper presents a life-cycle cost model which describes total monetary costs experienced in annual time [...] Read more.
In order to determine the most cost effective alternative among hardening options of power systems, the direct monetary benefits should be evaluated above all other things. Therefore, this paper presents a life-cycle cost model which describes total monetary costs experienced in annual time increments during the project with consideration for the time value of money. In addition, to minimize the risks associated with estimated cost errors due to uncertainties of input data, the stochastic input data are considered. Using the Monte Carlo method, the probabilities and cost ranges in the case studies can be predicted, in turn resulting in better decisions in the selection of hardening options which are cost effective. Full article
(This article belongs to the Special Issue Microgrids 2016)
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5021 KiB  
Article
A Feed-Forward Control Realizing Fast Response for Three-Branch Interleaved DC-DC Converter in DC Microgrid
by Haojie Wang, Minxiao Han, Wenli Yan, Guopeng Zhao and Josep M. Guerrero
Energies 2016, 9(7), 529; https://doi.org/10.3390/en9070529 - 11 Jul 2016
Cited by 6 | Viewed by 5660
Abstract
It is a common practice for storage batteries to be connected to DC microgrid buses through DC-DC converters for voltage support on islanded operation mode. A feed-forward control based dual-loop constant voltage PI control for three-branch interleaved DC-DC converters (TIDC) is proposed for [...] Read more.
It is a common practice for storage batteries to be connected to DC microgrid buses through DC-DC converters for voltage support on islanded operation mode. A feed-forward control based dual-loop constant voltage PI control for three-branch interleaved DC-DC converters (TIDC) is proposed for storage batteries in DC microgrids. The working principle of TIDC is analyzed, and the factors influencing the response rate based on the dual-loop constant voltage control for TIDC are discussed, and then the method of feed-forward control for TIDC is studied to improve the response rate for load changing. A prototype of the TIDC is developed and an experimental platform is built. The experiment results show that DC bus voltage sags or swells caused by load changing can be reduced and the time for voltage recovery can be decreased significantly with the proposed feed-forward control. Full article
(This article belongs to the Special Issue Microgrids 2016)
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5327 KiB  
Article
Combined Two-Stage Stochastic Programming and Receding Horizon Control Strategy for Microgrid Energy Management Considering Uncertainty
by Zhongwen Li, Chuanzhi Zang, Peng Zeng and Haibin Yu
Energies 2016, 9(7), 499; https://doi.org/10.3390/en9070499 - 30 Jun 2016
Cited by 45 | Viewed by 7237
Abstract
Microgrids (MGs) are presented as a cornerstone of smart grids. With the potential to integrate intermittent renewable energy sources (RES) in a flexible and environmental way, the MG concept has gained even more attention. Due to the randomness of RES, load, and electricity [...] Read more.
Microgrids (MGs) are presented as a cornerstone of smart grids. With the potential to integrate intermittent renewable energy sources (RES) in a flexible and environmental way, the MG concept has gained even more attention. Due to the randomness of RES, load, and electricity price in MG, the forecast errors of MGs will affect the performance of the power scheduling and the operating cost of an MG. In this paper, a combined stochastic programming and receding horizon control (SPRHC) strategy is proposed for microgrid energy management under uncertainty, which combines the advantages of two-stage stochastic programming (SP) and receding horizon control (RHC) strategy. With an SP strategy, a scheduling plan can be derived that minimizes the risk of uncertainty by involving the uncertainty of MG in the optimization model. With an RHC strategy, the uncertainty within the MG can be further compensated through a feedback mechanism with the lately updated forecast information. In our approach, a proper strategy is also proposed to maintain the SP model as a mixed integer linear constrained quadratic programming (MILCQP) problem, which is solvable without resorting to any heuristics algorithms. The results of numerical experiments explicitly demonstrate the superiority of the proposed strategy for both island and grid-connected operating modes of an MG. Full article
(This article belongs to the Special Issue Microgrids 2016)
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4214 KiB  
Article
State of Charge-Based Active Power Sharing Method in a Standalone Microgrid with High Penetration Level of Renewable Energy Sources
by Yun-Su Kim, Chul-Sang Hwang, Eung-Sang Kim and Changhee Cho
Energies 2016, 9(7), 480; https://doi.org/10.3390/en9070480 - 23 Jun 2016
Cited by 20 | Viewed by 5252
Abstract
Standalone microgrids, which are mainly constructed on island areas have low system inertia, may result large frequency deviations even for small load change. Moreover, increasing penetration level of renewable energy sources (RESs) into standalone microgrids makes the frequency stability problem even worse. To [...] Read more.
Standalone microgrids, which are mainly constructed on island areas have low system inertia, may result large frequency deviations even for small load change. Moreover, increasing penetration level of renewable energy sources (RESs) into standalone microgrids makes the frequency stability problem even worse. To overcome this problem, this paper proposes an active power sharing method with zero frequency deviations. To this end, a battery energy storage system (BESS) is operated as constant frequency (CF) control mode, whereas the other distributed generations (DGs) are operated as an active and reactive power (PQ) control mode. As a result, a state of charge (SOC) of the BESS is changed as the system load varies. Based on the SOC deviation, DGs share the load change. The SOC data is assumed to be sent via communication system, hence the communication time delay is considered. To enhance reliability, controllers of DGs are designed to take account of the failure of communication system. The simulation results show that active power can be shared among DGs according to desired ratio without frequency deviations even for large variation of output power of RESs. Full article
(This article belongs to the Special Issue Microgrids 2016)
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2514 KiB  
Article
Optimal Electric and Heat Energy Management of Multi-Microgrids with Sequentially-Coordinated Operations
by Nah-Oak Song, Ji-Hye Lee and Hak-Man Kim
Energies 2016, 9(6), 473; https://doi.org/10.3390/en9060473 - 21 Jun 2016
Cited by 12 | Viewed by 4980
Abstract
We propose an optimal electric and heat energy management for a cooperative multi-microgrid community. The sequentially-coordinated operation for heat energy is proposed in order to distribute the computational burden as an extension of “Optimal Energy Management of Multi-Microgrids with Sequentially Coordinated Operations” and [...] Read more.
We propose an optimal electric and heat energy management for a cooperative multi-microgrid community. The sequentially-coordinated operation for heat energy is proposed in order to distribute the computational burden as an extension of “Optimal Energy Management of Multi-Microgrids with Sequentially Coordinated Operations” and is following the sequentially-coordinated operations for electric energy in it. This sequentially-coordinated operation for heat energy is mathematically modeled and how to obtain the global heat energy optimization solution in the cooperative multi-microgrid community is presented. The global heat energy optimization is achieved for the cooperative community by adjusting the combined electric and heat energy production amounts of combined heat and power (CHP) generators and the heat energy production amount of heat only boilers (HOBs) which satisfy all heat loads, as well as optimize the external electric energy trading in order to minimize the unnecessary cost from the external electric trading, and/or maximize the profit from the external electric trading. To validate the proposed mathematical energy management models, a simulation study is also conducted. Full article
(This article belongs to the Special Issue Microgrids 2016)
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9404 KiB  
Article
Development of a Novel Bidirectional DC/DC Converter Topology with High Voltage Conversion Ratio for Electric Vehicles and DC-Microgrids
by Ching-Ming Lai
Energies 2016, 9(6), 410; https://doi.org/10.3390/en9060410 - 26 May 2016
Cited by 36 | Viewed by 10523
Abstract
The main objective of this paper was to study a bidirectional direct current to direct current converter (BDC) topology with a high voltage conversion ratio for electric vehicle (EV) batteries connected to a dc-microgrid system. In this study, an unregulated level converter (ULC) [...] Read more.
The main objective of this paper was to study a bidirectional direct current to direct current converter (BDC) topology with a high voltage conversion ratio for electric vehicle (EV) batteries connected to a dc-microgrid system. In this study, an unregulated level converter (ULC) cascaded with a two-phase interleaved buck-boost charge-pump converter (IBCPC) is introduced to achieve a high conversion ratio with a simpler control circuit. In discharge state, the topology acts as a two-stage voltage-doubler boost converter to achieve high step-up conversion ratio (48 V to 385 V). In charge state, the converter acts as two cascaded voltage-divider buck converters to achieve high voltage step-down conversion ratio (385 V to 48 V). The features, operation principles, steady-state analysis, simulation and experimental results are made to verify the performance of the studied novel BDC. Finally, a 500 W rating prototype system is constructed for verifying the validity of the operation principle. Experimental results show that highest efficiencies of 96% and 95% can be achieved, respectively, in charge and discharge states. Full article
(This article belongs to the Special Issue Microgrids 2016)
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5693 KiB  
Article
Black Start Strategy for PV-ESS Multi-Microgrids with Three-Phase/Single-Phase Architecture
by Zhirong Xu, Ping Yang, Zhiji Zeng, Jiajun Peng and Zhuoli Zhao
Energies 2016, 9(5), 372; https://doi.org/10.3390/en9050372 - 16 May 2016
Cited by 22 | Viewed by 7205
Abstract
With the rapid development of microgrids (MGs) in recent years, it is anticipated that combinations of multiple microgrids—multi-microgrids (MMGs)—will gradually become a new form of power grid. A safe and efficient black start strategy for MMGs is in urgent demand because of their [...] Read more.
With the rapid development of microgrids (MGs) in recent years, it is anticipated that combinations of multiple microgrids—multi-microgrids (MMGs)—will gradually become a new form of power grid. A safe and efficient black start strategy for MMGs is in urgent demand because of their complicated structure and control systems. In this paper, first, we analyze the topology and control system of residential-type MMGs with three-phase/single-phase (TP/SP) architecture. Second, a black start strategy based on a hierarchical control scheme is presented, including the selection strategy for the main power supply and master microgrid, the stand-alone operation strategy, and the grid-connected operation strategy. After the selection of the main power supplies, the master MG is determined. Hereby, all sub-microgrids (SMGs) execute the stand-alone algorithm. When the synchronous connection condition is satisfied, the slave SMGs connect to the master MG who provides the voltage and frequency support. Meanwhile, the control algorithm transfers to the grid-connected algorithm, with the grid dispatching value set to zero. Finally, experimental results from the MMG experimental setup in the Clean Energy Technology Laboratory (CETLAB) are presented to verify the effectiveness and feasibility of the proposed black start strategy. Full article
(This article belongs to the Special Issue Microgrids 2016)
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3483 KiB  
Article
Optimal Day-Ahead Scheduling of a Smart Distribution Grid Considering Reactive Power Capability of Distributed Generation
by Rongxiang Yuan, Timing Li, Xiangtian Deng and Jun Ye
Energies 2016, 9(5), 311; https://doi.org/10.3390/en9050311 - 25 Apr 2016
Cited by 9 | Viewed by 5803
Abstract
In the traditional paradigm, large power plants provide active and reactive power required for the transmission system and the distribution network purchases grid power from it. However, with more and more distributed energy resources (DERs) connected at distribution levels, it is necessary to [...] Read more.
In the traditional paradigm, large power plants provide active and reactive power required for the transmission system and the distribution network purchases grid power from it. However, with more and more distributed energy resources (DERs) connected at distribution levels, it is necessary to schedule DERs to meet their demand and participate in the electricity markets at the distribution level in the near future. This paper proposes a comprehensive operational scheduling model to be used in the distribution management system (DMS). The model aims to determine optimal decisions on active elements of the network, distributed generations (DGs), and responsive loads (RLs), seeking to minimize the day-ahead composite economic cost of the distribution network. For more detailed simulation, the composite cost includes the aspects of the operation cost, emission cost, and transmission loss cost of the network. Additionally, the DMS effectively utilizes the reactive power support capabilities of wind and solar power integrated in the distribution, which is usually neglected in previous works. The optimization procedure is formulated as a nonlinear combinatorial problem and solved with a modified differential evolution algorithm. A modified 33-bus distribution network is employed to validate the satisfactory performance of the proposed methodology. Full article
(This article belongs to the Special Issue Microgrids 2016)
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5848 KiB  
Article
Decentralized Renewable Hybrid Mini-Grids for Sustainable Electrification of the Off-Grid Coastal Areas of Bangladesh
by Majbaul Alam and Subhes Bhattacharyya
Energies 2016, 9(4), 268; https://doi.org/10.3390/en9040268 - 6 Apr 2016
Cited by 45 | Viewed by 10787
Abstract
Lack of access to energy is considered as a serious bottleneck for the socio-economic development of Bangladesh. Despite earning recognition for promoting solar home systems, most of the rural areas and remote islands of the country still remain non-electrified due to very high [...] Read more.
Lack of access to energy is considered as a serious bottleneck for the socio-economic development of Bangladesh. Despite earning recognition for promoting solar home systems, most of the rural areas and remote islands of the country still remain non-electrified due to very high unit cost and low quality of electricity from solar home systems (SHS) coupled with only few hours of restricted usages in the evening. Considering the resource potential and demand characteristics at the local level, the present study investigates the hybrid renewable mini-grid approach as a possible solution for universal electricity access in the country. Using Hybrid Optimisation of Multiple Energy Resources (HOMER) simulation model, the study, covering the whole coastal region of Bangladesh, shows that it is possible to offer a much better quality electricity for 12 h to 18 h a day for as low as USD 0.29–USD 0.31/kWh. Hybrid models suggested in this study can be replicated along the coastal belt and remote islands to obtain maximum diffusion of this technology and hence universal electrification. Full article
(This article belongs to the Special Issue Microgrids 2016)
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3864 KiB  
Article
A Novel Secondary Control for Microgrid Based on Synergetic Control of Multi-Agent System
by Zhiwen Yu, Qian Ai, Jinxia Gong and Longjian Piao
Energies 2016, 9(4), 243; https://doi.org/10.3390/en9040243 - 26 Mar 2016
Cited by 20 | Viewed by 5726
Abstract
In power systems, the secondary control is a very useful way to restore the system frequency and voltage to the rated value. This paper tries to propose a secondary frequency and voltage control of islanded microgrids based on the distributed synergetic control of [...] Read more.
In power systems, the secondary control is a very useful way to restore the system frequency and voltage to the rated value. This paper tries to propose a secondary frequency and voltage control of islanded microgrids based on the distributed synergetic control of multi-agent systems. In the proposed control, since each distributed generation only requires its own information and that of the neighbors, the secondary control is fully distributed. The system is more reliable because the central controller and complex communication network are reduced in the distributed structure. Based on multi-agent systems, the dynamic model is established, and distributed synergetic control algorithms are given to design the secondary control of the islanded microgrid. Meanwhile, the system has globally asymptotic stability under the proposed control, which is proved by the direct Lyapunov method. Simulation results about a test microgrid are given to verify the effectiveness of the proposed control. Full article
(This article belongs to the Special Issue Microgrids 2016)
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3486 KiB  
Article
Tunneling Horizontal IEC 61850 Traffic through Audio Video Bridging Streams for Flexible Microgrid Control and Protection
by Michael Short, Fathi Abugchem and Muneeb Dawood
Energies 2016, 9(3), 204; https://doi.org/10.3390/en9030204 - 16 Mar 2016
Cited by 13 | Viewed by 7742
Abstract
In this paper, it is argued that some low-level aspects of the usual IEC 61850 mapping to Ethernet are not well suited to microgrids due to their dynamic nature and geographical distribution as compared to substations. It is proposed that the integration of [...] Read more.
In this paper, it is argued that some low-level aspects of the usual IEC 61850 mapping to Ethernet are not well suited to microgrids due to their dynamic nature and geographical distribution as compared to substations. It is proposed that the integration of IEEE time-sensitive networking (TSN) concepts (which are currently implemented as audio video bridging (AVB) technologies) within an IEC 61850 / Manufacturing Message Specification framework provides a flexible and reconfigurable platform capable of overcoming such issues. A prototype test platform and bump-in-the-wire device for tunneling horizontal traffic through AVB are described. Experimental results are presented for sending IEC 61850 GOOSE (generic object oriented substation events) and SV (sampled values) messages through AVB tunnels. The obtained results verify that IEC 61850 event and sampled data may be reliably transported within the proposed framework with very low latency, even over a congested network. It is argued that since AVB streams can be flexibly configured from one or more central locations, and bandwidth reserved for their data ensuring predictability of delivery, this gives a solution which seems significantly more reliable than a pure MMS-based solution. Full article
(This article belongs to the Special Issue Microgrids 2016)
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662 KiB  
Article
Electric Vehicle Charging and Discharging Coordination on Distribution Network Using Multi-Objective Particle Swarm Optimization and Fuzzy Decision Making
by Dongqi Liu, Yaonan Wang and Yongpeng Shen
Energies 2016, 9(3), 186; https://doi.org/10.3390/en9030186 - 11 Mar 2016
Cited by 39 | Viewed by 7740
Abstract
This paper proposed a optimal strategy for coordinated operation of electric vehicles (EVs) charging and discharging with wind-thermal system. By aggregating a large number of EVs, the huge total battery capacity is sufficient to stabilize the disturbance of the transmission grid. Hence, a [...] Read more.
This paper proposed a optimal strategy for coordinated operation of electric vehicles (EVs) charging and discharging with wind-thermal system. By aggregating a large number of EVs, the huge total battery capacity is sufficient to stabilize the disturbance of the transmission grid. Hence, a dynamic environmental dispatch model which coordinates a cluster of charging and discharging controllable EV units with wind farms and thermal plants is proposed. A multi-objective particle swarm optimization (MOPSO) algorithm and a fuzzy decision maker are put forward for the simultaneous optimization of grid operating cost, CO2 emissions, wind curtailment, and EV users’ cost. Simulations are done in a 30 node system containing three traditional thermal plants, two carbon capture and storage (CCS) thermal plants, two wind farms, and six EV aggregations. Contrast of strategies under different EV charging/discharging price is also discussed. The results are presented to prove the effectiveness of the proposed strategy. Full article
(This article belongs to the Special Issue Microgrids 2016)
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4571 KiB  
Article
A Half-Bridge Voltage Balancer with New Controller for Bipolar DC Distribution Systems
by Byung-Moon Han
Energies 2016, 9(3), 182; https://doi.org/10.3390/en9030182 - 10 Mar 2016
Cited by 19 | Viewed by 7217
Abstract
This paper proposes a half-bridge voltage balancer with a new controller for bipolar DC distribution systems. The proposed control scheme consists of two cascaded Proportional Integral (PI) controls rather than one PI control for balancing the pole voltage. In order to confirm the [...] Read more.
This paper proposes a half-bridge voltage balancer with a new controller for bipolar DC distribution systems. The proposed control scheme consists of two cascaded Proportional Integral (PI) controls rather than one PI control for balancing the pole voltage. In order to confirm the excellence of voltage balancing performance, a typical bipolar DC distribution system including a half-bridge voltage balancer with proposed controller was analyzed by computer simulations. Experiments with a scaled prototype were also carried out to confirm the simulation results. The half-bridge voltage balancer with proposed controller shows better performance than the half-bridge voltage balancer with one PI control for balancing the pole voltage. Full article
(This article belongs to the Special Issue Microgrids 2016)
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6723 KiB  
Article
A New Robust Decoupled Control of the Stator Active and Reactive Currents for Grid-Connected Doubly-Fed Induction Generators
by Ahmad Bashar Ataji, Yushi Miura, Toshifumi Ise and Hiroki Tanaka
Energies 2016, 9(3), 179; https://doi.org/10.3390/en9030179 - 9 Mar 2016
Cited by 4 | Viewed by 5218
Abstract
This paper addresses the grid-connected variable speed doubly-fed induction generator, and proposes a new decoupled control to replace the conventional decoupled active and reactive powers (P-Q) control. The proposed decoupled control is based on decoupling the stator active and reactive currents, in contrast [...] Read more.
This paper addresses the grid-connected variable speed doubly-fed induction generator, and proposes a new decoupled control to replace the conventional decoupled active and reactive powers (P-Q) control. The proposed decoupled control is based on decoupling the stator active and reactive currents, in contrast with the conventional decoupled P-Q control, which is based on decoupling the stator active and reactive powers by forcing the stator d- or q-voltage to zero. The proposed decoupled control has all the advantages of the conventional decoupled P-Q control such as constant switching frequency and robustness against slip angle inaccuracy, and it has some additional advantages: The proposed control requires less machine parameters; for the controller design, it requires the stator-to-rotor turns ratio only; for the online calculation, it does not requires any machine parameter. The proposed decoupled control is more flexible and robust since the control is independent of the grid voltage orientation. It is robust against variation in the grid voltage amplitude. Several experiments are carried out using a 1.1 kW doubly-fed induction generator (DFIG), and the results support the proposed decoupled control and demonstrate some of its advantages. Full article
(This article belongs to the Special Issue Microgrids 2016)
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5305 KiB  
Article
Constant Jacobian Matrix-Based Stochastic Galerkin Method for Probabilistic Load Flow
by Yingyun Sun, Rui Mao, Zuyi Li and Wei Tian
Energies 2016, 9(3), 153; https://doi.org/10.3390/en9030153 - 3 Mar 2016
Cited by 13 | Viewed by 6363
Abstract
An intrusive spectral method of probabilistic load flow (PLF) is proposed in the paper, which can handle the uncertainties arising from renewable energy integration. Generalized polynomial chaos (gPC) expansions of dependent random variables are utilized to build a spectral stochastic representation of PLF [...] Read more.
An intrusive spectral method of probabilistic load flow (PLF) is proposed in the paper, which can handle the uncertainties arising from renewable energy integration. Generalized polynomial chaos (gPC) expansions of dependent random variables are utilized to build a spectral stochastic representation of PLF model. Instead of solving the coupled PLF model with a traditional, cumbersome method, a modified stochastic Galerkin (SG) method is proposed based on the P-Q decoupling properties of load flow in power system. By introducing two pre-calculated constant sparse Jacobian matrices, the computational burden of the SG method is significantly reduced. Two cases, IEEE 14-bus and IEEE 118-bus systems, are used to verify the computation speed and efficiency of the proposed method. Full article
(This article belongs to the Special Issue Microgrids 2016)
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2597 KiB  
Article
Intentional Islanding Algorithm for Distribution Network Based on Layered Directed Tree Model
by Jian Su, Hao Bai, Pipei Zhang, Haitao Liu and Shihong Miao
Energies 2016, 9(3), 124; https://doi.org/10.3390/en9030124 - 24 Feb 2016
Cited by 5 | Viewed by 5850
Abstract
In this study, a novel intentional island model of a distribution system with distributed generations (DGs) is presented and the improved Dijkstra algorithm is used to solve this model. This paper abstracts the distribution network with DGs to the layered directed tree according [...] Read more.
In this study, a novel intentional island model of a distribution system with distributed generations (DGs) is presented and the improved Dijkstra algorithm is used to solve this model. This paper abstracts the distribution network with DGs to the layered directed tree according to its radial structure and power restoration process. In consideration of grade, controllability, capacity, level and electrical betweenness of load, the model weights load and maximizes total load weight in the island. The proposed model considers power balance, node voltage, phase angle and transmission capability of the branch, and network connectivity to meet practical engineering requirements. The improved Dijkstra algorithm formulates a search rule to select the load that can be divided into an island in descending order of the shortest path between the load node and DG node. An optimal island partition scheme is achieved through three stages: origin island, baby island and mature island. Meanwhile, scheme adjustment and constraint checking are used alternately to balance objective functions and constraints. The improved IEEE 43-bus distribution network is applied to verify the validity of the algorithm. A comparison of two island methods shows that the proposed algorithm can generate a reasonable scheme for island partitioning. Full article
(This article belongs to the Special Issue Microgrids 2016)
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13535 KiB  
Article
Provision of Supplementary Load Frequency Control via Aggregation of Air Conditioning Loads
by Lei Zhou, Yang Li, Beibei Wang, Zhe Wang and Xiaoqing Hu
Energies 2015, 8(12), 14098-14117; https://doi.org/10.3390/en81212417 - 14 Dec 2015
Cited by 14 | Viewed by 5754
Abstract
The integration of large-scale renewable energy poses great challenges for the operation of power system because of its increased frequency fluctuations. More load frequency control (LFC) resources are demanded in order to maintain a stable system with more renewable energy injected. Unlike the [...] Read more.
The integration of large-scale renewable energy poses great challenges for the operation of power system because of its increased frequency fluctuations. More load frequency control (LFC) resources are demanded in order to maintain a stable system with more renewable energy injected. Unlike the costly LFC resources on generation side, the thermostatically controlled loads (TCLs) on the demand side become an attractive solution on account of its substantial quantities and heat-storage capacity. It generally contains air conditioners (ACs), water heaters and fridges. In this paper, the supplementary LFC is extracted by the modeling and controlling of aggregated ACs. We first present a control framework integrating the supplementary LFC with the traditional LFC. Then, a change-time-priority-list method is proposed to control power output taking into account customers’ satisfaction. Simulations on a single-area power system with wind power integration demonstrate the effectiveness of the proposed method. The impact of ambient temperature changes and customer preferences on room temperature is also involved in the discussion. Results show that the supplementary LFC provided by ACs could closely track the LFC signals and effectively reduce the frequency deviation. Full article
(This article belongs to the Special Issue Microgrids 2016)
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Review

Jump to: Research

6930 KiB  
Review
Capacitor Current Feedback-Based Active Resonance Damping Strategies for Digitally-Controlled Inductive-Capacitive-Inductive-Filtered Grid-Connected Inverters
by Iman Lorzadeh, Hossein Askarian Abyaneh, Mehdi Savaghebi, Alireza Bakhshai and Josep M. Guerrero
Energies 2016, 9(8), 642; https://doi.org/10.3390/en9080642 - 17 Aug 2016
Cited by 30 | Viewed by 10079
Abstract
Inductive-capacitive-inductive (LCL)-type line filters are widely used in grid-connected voltage source inverters (VSIs), since they can provide substantially improved attenuation of switching harmonics in currents injected into the grid with lower cost, weight and power losses than their L-type counterparts. However, the inclusion [...] Read more.
Inductive-capacitive-inductive (LCL)-type line filters are widely used in grid-connected voltage source inverters (VSIs), since they can provide substantially improved attenuation of switching harmonics in currents injected into the grid with lower cost, weight and power losses than their L-type counterparts. However, the inclusion of third order LCL network complicates the current control design regarding the system stability issues because of an inherent resonance peak which appears in the open-loop transfer function of the inverter control system near the control stability boundary. To avoid passive (resistive) resonance damping solutions, due to their additional power losses, active damping (AD) techniques are often applied with proper control algorithms in order to damp the LCL filter resonance and stabilize the system. Among these techniques, the capacitor current feedback (CCF) AD has attracted considerable attention due to its effective damping performance and simple implementation. This paper thus presents a state-of-the-art review of resonance and stability characteristics of CCF-based AD approaches for a digitally-controlled LCL filter-based grid-connected inverter taking into account the effect of computation and pulse width modulation (PWM) delays along with a detailed analysis on proper design and implementation. Full article
(This article belongs to the Special Issue Microgrids 2016)
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