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Open AccessArticle

An Embedded System in Smart Inverters for Power Quality and Safety Functionality

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Rafael Real-Calvo

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Antonio Moreno-Munoz

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Juan J. Gonzalez-De-La-Rosa

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Victor Pallares-Lopez

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Miguel J. Gonzalez-Redondo

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Isabel M. Moreno-Garcia

Energies 2016, 9(3), 219; https://doi.org/10.3390/en9030219 - 18 Mar 2016

Cited by 9 | Viewed by 7171

Abstract

The electricity sector is undergoing an evolution that demands the development of a network model with a high level of intelligence, known as a Smart Grid. One of the factors accelerating these changes is the development and implementation of renewable energy. In particular, [...] Read more.

The electricity sector is undergoing an evolution that demands the development of a network model with a high level of intelligence, known as a Smart Grid. One of the factors accelerating these changes is the development and implementation of renewable energy. In particular, increased photovoltaic generation can affect the network’s stability. One line of action is to provide inverters with a management capacity that enables them to act upon the grid in order to compensate for these problems. This paper describes the design and development of a prototype embedded system able to integrate with a photovoltaic inverter and provide it with multifunctional ability in order to analyze power quality and operate with protection. The most important subsystems of this prototype are described, indicating their operating fundamentals. This prototype has been tested with class A protocols according to IEC 61000-4-30 and IEC 62586-2. Tests have also been carried out to validate the response time in generating orders and alarm signals for protections. The highlights of these experimental results are discussed. Some descriptive aspects of the integration of the prototype in an experimental smart inverter are also commented upon. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Optimal Power Flow in Islanded Microgrids Using a Simple Distributed Algorithm

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Eleonora Riva Sanseverino

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Maria Luisa Di Silvestre

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Energies 2015, 8(10), 11493-11514; https://doi.org/10.3390/en81011493 - 15 Oct 2015

Cited by 19 | Viewed by 6031

Abstract

In this paper, the problem of distributed power losses minimization in islanded distribution systems is dealt with. The problem is formulated in a very simple manner and a solution is reached after a few iterations. The considered distribution system, a microgrid, will not [...] Read more.

In this paper, the problem of distributed power losses minimization in islanded distribution systems is dealt with. The problem is formulated in a very simple manner and a solution is reached after a few iterations. The considered distribution system, a microgrid, will not need large bandwidth communication channels, since only closeby nodes will exchange information. The correction of generated active powers is possible by means of the active power losses partition concept that attributes a portion of the overall power losses in each branch to each generator. The experimental part shows the first results of the proposed method on an islanded microgrid. Simulation results of the distributed algorithm are compared to a centralized Optimal Power Flow approach and very small errors can be observed. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Integrated Electrical and Thermal Grid Facility - Testing of Future Microgrid Technologies

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Sundar Raj Thangavelu

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Energies 2015, 8(9), 10082-10105; https://doi.org/10.3390/en80910082 - 16 Sep 2015

Cited by 10 | Viewed by 7372

Abstract

This paper describes the Experimental Power Grid Centre (EPGC) microgrid test facility, which was developed to enable research, development and testing for a wide range of distributed generation and microgrid technologies. The EPGC microgrid facility comprises a integrated electrical and thermal grid with [...] Read more.

This paper describes the Experimental Power Grid Centre (EPGC) microgrid test facility, which was developed to enable research, development and testing for a wide range of distributed generation and microgrid technologies. The EPGC microgrid facility comprises a integrated electrical and thermal grid with a flexible and configurable architecture, and includes various distributed energy resources and emulators, such as generators, renewable, energy storage technologies and programmable load banks. The integrated thermal grid provides an opportunity to harness waste heat produced by the generators for combined heat, power and cooling applications, and support research in optimization of combined electrical-thermal systems. Several case studies are presented to demonstrate the testing of different control and operation strategies for storage systems in grid-connected and islanded microgrids. One of the case studies also demonstrates an integrated thermal grid to convert waste heat to useful energy, which thus far resulted in a higher combined energy efficiency. Experiment results confirm that the facility enables testing and evaluation of grid technologies and practical problems that may not be apparent in a computer simulated environment. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Congestion Control Algorithm in Distribution Feeders: Integration in a Distribution Management System

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Energies 2015, 8(6), 6013-6032; https://doi.org/10.3390/en8066013 - 18 Jun 2015

Cited by 2 | Viewed by 4999

Abstract

The increasing share of distributed energy resources poses a challenge to the distribution network operator (DNO) to maintain the current availability of the system while limiting the investment costs. Related to this, there is a clear trend in DNOs trying to better monitor [...] Read more.

The increasing share of distributed energy resources poses a challenge to the distribution network operator (DNO) to maintain the current availability of the system while limiting the investment costs. Related to this, there is a clear trend in DNOs trying to better monitor their grid by installing a distribution management system (DMS). This DMS enables the DNOs to remotely switch their network or better localize and solve faults. Moreover, the DMS can be used to centrally control the grid assets. Therefore, in this paper, a control strategy is discussed that can be implemented in the DMS for solving current congestion problems posed by the increasing share of renewables in the grid. This control strategy controls wind turbines in order to avoid congestion while mitigating the required investment costs in order to achieve a global cost-efficient solution. Next to the application and objective of the control, the parameter tuning of the control algorithm is discussed. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

A Flywheel Energy Storage System Based on a Doubly Fed Induction Machine and Battery for Microgrid Control

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Thai-Thanh Nguyen

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Hyeong-Jun Yoo

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Hak-Man Kim

Energies 2015, 8(6), 5074-5089; https://doi.org/10.3390/en8065074 - 01 Jun 2015

Cited by 23 | Viewed by 10099

Abstract

Microgrids are eco-friendly power systems because they use renewable sources such as solar and wind power as the main power source. However, the stochastic nature of wind and solar power is a considerable challenge for the efficient operation of microgrids. Microgrid operations have [...] Read more.

Microgrids are eco-friendly power systems because they use renewable sources such as solar and wind power as the main power source. However, the stochastic nature of wind and solar power is a considerable challenge for the efficient operation of microgrids. Microgrid operations have to satisfy quality requirements in terms of the frequency and voltage. To overcome these problems, energy storage systems for short- and long-term storage are used with microgrids. Recently, the use of short-term energy storage systems such as flywheels has attracted significant interest as a potential solution to this problem. Conventional flywheel energy storage systems exhibit only one control mode during operation: either smoothing wind power control or frequency control. In this paper, we propose a new flywheel energy storage system based on a doubly fed induction machine and a battery for use with microgrids. The new flywheel energy storage system can be used not only to mitigate wind power fluctuations, but also to control the frequency as well as the voltage of the microgrid during islanded operation. The performance of the proposed flywheel energy storage system is investigated through various simulations using MATLAB/Simulink software. In addition, a conventional flywheel energy storage system based on a doubly fed induction machine is simulated and its performance compared with that of the proposed one. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Optimization and Analysis of a Hybrid Energy Storage System in a Small-Scale Standalone Microgrid for Remote Area Power Supply (RAPS)

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Fengbing Li

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Kaigui Xie

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Jiangping Yang

Energies 2015, 8(6), 4802-4826; https://doi.org/10.3390/en8064802 - 26 May 2015

Cited by 31 | Viewed by 5413

Abstract

The analysis and application of hybrid energy storage systems (HESSs) in small-scale standalone microgrids for remote area power supply (RAPS) has received extensive attention. This application mode has its own characteristics which must be considered but have not been considered in the existing [...] Read more.

The analysis and application of hybrid energy storage systems (HESSs) in small-scale standalone microgrids for remote area power supply (RAPS) has received extensive attention. This application mode has its own characteristics which must be considered but have not been considered in the existing research. To reflect the common satisfaction of load demands and maximize the utilization of renewable energy in a standalone microgrid, a new index named effective rate of energy storage system (ESS) is proposed. To reflect the true work state of supercapacitor ESS (SC-ESS), the second-level data of field measurements is used in calculation and analysis. To further enhance the operational performance of the HESS, a coordinated control strategy based on state cooperation is adopted. To get a more reasonable and more credible HESS optimization model, the comparison of existing models and proposed model with different considerations on cost and life is provided. In addition, a comparative analysis of technical and economic characteristics improvements is presented for different ESS application schemes in practical projects. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Adaptive Micro-Grid Operation Based on IEC 61850

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Energies 2015, 8(5), 4455-4475; https://doi.org/10.3390/en8054455 - 18 May 2015

Cited by 24 | Viewed by 7169

Abstract

Automatically identifying the new equipment after its integration and adjusting operation strategy to realize “plug and play” functionality are becoming essential for micro-grid operations. In order to improve and perfect the micro-grid “plug and play” function with the increased amount of equipment with [...] Read more.

Automatically identifying the new equipment after its integration and adjusting operation strategy to realize “plug and play” functionality are becoming essential for micro-grid operations. In order to improve and perfect the micro-grid “plug and play” function with the increased amount of equipment with different information protocols and more diverse system applications, this paper presents a solution for adaptive micro-grid operation based on IEC 61850, and proposes the design and specific implementation methods of micro-grid “plug and play” function and system operation mode conversion in detail, by using the established IEC 61850 information model of a micro-grid. Actual operation tests based on the developed IED and micro-grid test platform are performed to verify the feasibility and validity of the proposed solution. The tests results show that the solution can automatically identify the IEC 61850 information model of equipment after its integration, intelligently adjust the operation strategies to adapt to new system states and achieves a reliable system operation mode conversion. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

A Methodology for Assessing Islanding of Microgrids: Between Utility Dependence and Off-Grid Systems

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Antonio Colmenar-Santos

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Carlos De Palacio

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Lorenzo Alfredo Enríquez-García

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África López-Rey

Energies 2015, 8(5), 4436-4454; https://doi.org/10.3390/en8054436 - 18 May 2015

Cited by 8 | Viewed by 5489

Abstract

This paper presents a novel methodology for assessing islanding microgrids from the economical and functional perspective, for various stakeholders. The paper proposes the triggers for competitive deployment of microgeneration, storage, microgrid islanding, the market conditions that apply, and discusses the future tendencies and [...] Read more.

This paper presents a novel methodology for assessing islanding microgrids from the economical and functional perspective, for various stakeholders. The paper proposes the triggers for competitive deployment of microgeneration, storage, microgrid islanding, the market conditions that apply, and discusses the future tendencies and the policy recommendations to foster microgrid benefits. The validation of the proposed scheme is based on real market cases, where the triggers for autogeneration and islanding microgrids are present. Additionally, the new concept of grid independence cycle is presented and analyzed. The policy implications of a situation where grid consumption reduction leads to higher energy prices are presented and discussed. The paper concludes with a summary of prioritized technical and regulatory recommendations, proposed as a result of the assessment. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Simulation of Distributed Generation with Photovoltaic Microgrids—Case Study in Brazil

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Gustavo Azevedo Xavier

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Delly Oliveira Filho

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José Helvecio Martins

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Paulo Marcos de Barros Monteiro

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Antônia Sônia Alves Cardozo Diniz

Energies 2015, 8(5), 4003-4023; https://doi.org/10.3390/en8054003 - 07 May 2015

Cited by 18 | Viewed by 6559

Abstract

Elevated prices and lack of proper legislation and government incentives have been the main barriers in the development of the photovoltaic market in Brazil. In an attempt to overcome those barriers, a microgrid model was proposed and simulated. In the proposed microgrids, residential [...] Read more.

Elevated prices and lack of proper legislation and government incentives have been the main barriers in the development of the photovoltaic market in Brazil. In an attempt to overcome those barriers, a microgrid model was proposed and simulated. In the proposed microgrids, residential consumers are connected to each other to maximize the investment return by trading the surplus of generated energy among them. Different topologies and scenarios were studied from electrical energy and economic standpoints. Stochastic data of solar radiation were simulated for the city of Viçosa, Minas Gerais, Brazil, for the period of one year, considering the statistical behavior of a series over 20 years. The system output power and energy balance were calculated considering a model for photovoltaic generators and the radiation simulated data. By determining the generated energy and electrical needs of the microgrid members, the cash flow and economic feasibility were calculated. Sensitivity analyses were performed by varying economic parameters to determine situations where investment becomes feasible. This paper shows that microgrid contributes to improve the economics and the initial investments. The number of participants in a microgrid, the electricity and the equipment costs are important parameters to speed up the economic and technical feasibility process. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Utilization of Electric Vehicles and Their Used Batteries for Peak-Load Shifting

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Energies 2015, 8(5), 3720-3738; https://doi.org/10.3390/en8053720 - 30 Apr 2015

Cited by 108 | Viewed by 8266

Abstract

The utilization of electric vehicles (EV) and their used batteries in supporting small-scale energy management systems were studied. Both theoretical study and practical demonstration were performed to measure the feasibility of the developed system. Each five EVs and used EV batteries were used [...] Read more.

The utilization of electric vehicles (EV) and their used batteries in supporting small-scale energy management systems were studied. Both theoretical study and practical demonstration were performed to measure the feasibility of the developed system. Each five EVs and used EV batteries were used along with 20 kW photovoltaic (PV) panels as a renewable energy source. The main objective of the developed system is performing a peak-load shifting by utilizing EVs, used EV batteries and PV panels. The planning of load leveling was performed 24 h ahead for each 30 min period. The studies showed that the application of EVs and used EV batteries in supporting certain small-scale energy management systems is feasible. In addition, some findings during the demonstration test were listed and analyzed for the purpose of further system development and deployment. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Enhanced Load Power Sharing Accuracy in Droop-Controlled DC Microgrids with Both Mesh and Radial Configurations

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Energies 2015, 8(5), 3591-3605; https://doi.org/10.3390/en8053591 - 29 Apr 2015

Cited by 23 | Viewed by 8088

Abstract

The rational power sharing among different interface converters should be determined by the converter capacity. In order to guarantee that each converter operates at the ideal condition, considering the radial and mesh configuration, a modified strategy for load power sharing accuracy enhancement in [...] Read more.

The rational power sharing among different interface converters should be determined by the converter capacity. In order to guarantee that each converter operates at the ideal condition, considering the radial and mesh configuration, a modified strategy for load power sharing accuracy enhancement in droop-controlled DC microgrid is proposed in this paper. Two compensating terms which include averaging output power control and averaging DC voltage control of neighboring converters are employed. Since only the information of the neighboring converter is used, the complexity of the communication network can be reduced. The rational distribution of load power for different line resistance conditions is realized by using modified droop control that can be regarded as a distributed approach. Low bandwidth communication is used for exchanging sampled information between different converters. The feasibility and effectiveness of the proposed method for different network configurations and line resistances under different communication delay is analyzed in detail. Simulation results derived from a DC microgrid with three converters is implemented in MATLAB/Simulink to verify the proposed approach. Experimental results from a 3 × 10 kW prototype also show the performance of the proposed modified droop control scheme. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Optimizing Capacities of Distributed Generation and Energy Storage in a Small Autonomous Power System Considering Uncertainty in Renewables

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Energies 2015, 8(4), 2473-2492; https://doi.org/10.3390/en8042473 - 30 Mar 2015

Cited by 32 | Viewed by 6417

Abstract

This paper explores real power generation planning, considering distributed generation resources and energy storage in a small standalone power system. On account of the Kyoto Protocol and Copenhagen Accord, wind and photovoltaic (PV) powers are considered as clean and renewable energies. In this [...] Read more.

This paper explores real power generation planning, considering distributed generation resources and energy storage in a small standalone power system. On account of the Kyoto Protocol and Copenhagen Accord, wind and photovoltaic (PV) powers are considered as clean and renewable energies. In this study, a genetic algorithm (GA) was used to determine the optimal capacities of wind-turbine-generators, PV, diesel generators and energy storage in a small standalone power system. The investment costs (installation, unit and maintenance costs) of the distributed generation resources and energy storage and the cost of fuel for the diesel generators were minimized while the reliability requirement and CO₂ emission limit were fulfilled. The renewable sources and loads were modeled by random variables because of their uncertainties. The equality and inequality constraints in the genetic algorithms were treated by cumulant effects and cumulative probability of random variables, respectively. The IEEE reliability data for an 8760 h load profile with a 150 kW peak load were used to demonstrate the applicability of the proposed method. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Current Harmonics Compensation in Microgrids Exploiting the Power Electronics Interfaces of Renewable Energy Sources

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Ioannis Bouloumpasis

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Panagis Vovos

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Konstantinos Georgakas

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Nicholas A. Vovos

Energies 2015, 8(4), 2295-2311; https://doi.org/10.3390/en8042295 - 25 Mar 2015

Cited by 17 | Viewed by 6718

Abstract

This work presents a method of current harmonic reduction in a distorted distribution system. In order to evaluate the proposed method a grid with high-order current harmonics is assumed. The reduction of current distortion is feasible due to the pulse modulation of an [...] Read more.

This work presents a method of current harmonic reduction in a distorted distribution system. In order to evaluate the proposed method a grid with high-order current harmonics is assumed. The reduction of current distortion is feasible due to the pulse modulation of an active filter, which consists of a buck-boost converter connected back-to-back to a polarity swapping inverter. For a practical application, this system would be the power electronic interface of a Renewable Energy Source (RES) and therefore it changes a source of harmonics to a damping harmonics system. Using the proposed method, the current Total Harmonic Distortion (THD) of the grid is reduced below the acceptable limits and thus the general power quality of the system is improved. Simulations in the MATLAB/SIMULINK platform and experiments have been performed in order to verify the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Load Frequency Control in Isolated Micro-Grids with Electrical Vehicles Based on Multivariable Generalized Predictive Theory

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Energies 2015, 8(3), 2145-2164; https://doi.org/10.3390/en8032145 - 18 Mar 2015

Cited by 124 | Viewed by 11866

Abstract

In power systems, although the inertia energy in power sources can partly cover power unbalances caused by load disturbance or renewable energy fluctuation, it is still hard to maintain the frequency deviation within acceptable ranges. However, with the vehicle-to-grid (V2G) technique, electric vehicles [...] Read more.

In power systems, although the inertia energy in power sources can partly cover power unbalances caused by load disturbance or renewable energy fluctuation, it is still hard to maintain the frequency deviation within acceptable ranges. However, with the vehicle-to-grid (V2G) technique, electric vehicles (EVs) can act as mobile energy storage units, which could be a solution for load frequency control (LFC) in an isolated grid. In this paper, a LFC model of an isolated micro-grid with EVs, distributed generations and their constraints is developed. In addition, a controller based on multivariable generalized predictive control (MGPC) theory is proposed for LFC in the isolated micro-grid, where EVs and diesel generator (DG) are coordinated to achieve a satisfied performance on load frequency. A benchmark isolated micro-grid with EVs, DG, and wind farm is modeled in the Matlab/Simulink environment to demonstrate the effectiveness of the proposed method. Simulation results demonstrate that with MGPC, the energy stored in EVs can be managed intelligently according to LFC requirement. This improves the system frequency stability with complex operation situations including the random renewable energy resource and the continuous load disturbances. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Hierarchical Load Tracking Control of a Grid-Connected Solid Oxide Fuel Cell for Maximum Electrical Efficiency Operation

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Yonghui Li

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Qiuwei Wu

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Haiyu Zhu

Energies 2015, 8(3), 1896-1916; https://doi.org/10.3390/en8031896 - 11 Mar 2015

Cited by 13 | Viewed by 5804

Abstract

Based on the benchmark solid oxide fuel cell (SOFC) dynamic model for power system studies and the analysis of the SOFC operating conditions, the nonlinear programming (NLP) optimization method was used to determine the maximum electrical efficiency of the grid-connected SOFC subject to [...] Read more.

Based on the benchmark solid oxide fuel cell (SOFC) dynamic model for power system studies and the analysis of the SOFC operating conditions, the nonlinear programming (NLP) optimization method was used to determine the maximum electrical efficiency of the grid-connected SOFC subject to the constraints of fuel utilization factor, stack temperature and output active power. The optimal operating conditions of the grid-connected SOFC were obtained by solving the NLP problem considering the power consumed by the air compressor. With the optimal operating conditions of the SOFC for the maximum efficiency operation obtained at different active power output levels, a hierarchical load tracking control scheme for the grid-connected SOFC was proposed to realize the maximum electrical efficiency operation with the stack temperature bounded. The hierarchical control scheme consists of a fast active power control and a slower stack temperature control. The active power control was developed by using a decentralized control method. The efficiency of the proposed hierarchical control scheme was demonstrated by case studies using the benchmark SOFC dynamic model. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Microgrid Stability Controller Based on Adaptive Robust Total SMC

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Energies 2015, 8(3), 1784-1801; https://doi.org/10.3390/en8031784 - 04 Mar 2015

Cited by 27 | Viewed by 5710

Abstract

This paper presents a microgrid stability controller (MSC) in order to provide existing distributed generation units (DGs) the additional functionality of working in islanding mode without changing their control strategies in grid-connected mode and to enhance the stability of the microgrid. Microgrid operating [...] Read more.

This paper presents a microgrid stability controller (MSC) in order to provide existing distributed generation units (DGs) the additional functionality of working in islanding mode without changing their control strategies in grid-connected mode and to enhance the stability of the microgrid. Microgrid operating characteristics and mathematical models of the MSC indicate that the system is inherently nonlinear and time-variable. Therefore, this paper proposes an adaptive robust total sliding-mode control (ARTSMC) system for the MSC. It is proved that the ARTSMC system is insensitive to parametric uncertainties and external disturbances. The MSC provides fast dynamic response and robustness to the microgrid. When the system is operating in grid-connected mode, it is able to improve the controllability of the exchanged power between the microgrid and the utility grid, while smoothing the DGs’ output power. When the microgrid is operating in islanded mode, it provides voltage and frequency support, while guaranteeing seamless transition between the two operation modes. Simulation and experimental results show the effectiveness of the proposed approach. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Energy Coordinative Optimization of Wind-Storage-Load Microgrids Based on Short-Term Prediction

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Energies 2015, 8(2), 1505-1528; https://doi.org/10.3390/en8021505 - 16 Feb 2015

Cited by 17 | Viewed by 7461

Abstract

According to the topological structure of wind-storage-load complementation microgrids, this paper proposes a method for energy coordinative optimization which focuses on improvement of the economic benefits of microgrids in the prediction framework. First of all, the external characteristic mathematical model of distributed generation [...] Read more.

According to the topological structure of wind-storage-load complementation microgrids, this paper proposes a method for energy coordinative optimization which focuses on improvement of the economic benefits of microgrids in the prediction framework. First of all, the external characteristic mathematical model of distributed generation (DG) units including wind turbines and storage batteries are established according to the requirements of the actual constraints. Meanwhile, using the minimum consumption costs from the external grid as the objective function, a grey prediction model with residual modification is introduced to output the predictive wind turbine power and load at specific periods. Second, based on the basic framework of receding horizon optimization, an intelligent genetic algorithm (GA) is applied to figure out the optimum solution in the predictive horizon for the complex non-linear coordination control model of microgrids. The optimum results of the GA are compared with the receding solution of mixed integer linear programming (MILP). The obtained results show that the method is a viable approach for energy coordinative optimization of microgrid systems for energy flow and reasonable schedule. The effectiveness and feasibility of the proposed method is verified by examples. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Reliability Evaluation of a Distribution Network with Microgrid Based on a Combined Power Generation System

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Energies 2015, 8(2), 1216-1241; https://doi.org/10.3390/en8021216 - 04 Feb 2015

Cited by 18 | Viewed by 7408

Abstract

Distributed generation (DG), battery storage (BS) and electric vehicles (EVs) in a microgrid constitute the combined power generation system (CPGS). A CPGS can be applied to achieve a reliable evaluation of a distribution network with microgrids. To model charging load and discharging capacity, [...] Read more.

Distributed generation (DG), battery storage (BS) and electric vehicles (EVs) in a microgrid constitute the combined power generation system (CPGS). A CPGS can be applied to achieve a reliable evaluation of a distribution network with microgrids. To model charging load and discharging capacity, respectively, the EVs in a CPGS can be divided into regular EVs and ruleless EVs, according to their driving behavior. Based on statistical data of gasoline-fueled vehicles and the probability distribution of charging start instant and charging time, a statistical model can be built to describe the charging load and discharging capacity of ruleless EVs. The charge and discharge curves of regular EVs can also be drawn on the basis of a daily dispatch table. The CPGS takes the charge and discharge curves of EVs, daily load and DG power generation into consideration to calculate its power supply time during islanding. Combined with fault duration, the power supply time during islanding will be used to analyze and determine the interruption times and interruption duration of loads in islands. Then the Sequential Monte Carlo method is applied to complete the reliability evaluation of the distribution system. The RBTS Bus 4 test system is utilized to illustrate the proposed technique. The effects on the system reliability of BS capacity and V2G technology, driving behavior, recharging mode and penetration of EVs are all investigated. Full article

(This article belongs to the Special Issue Microgrids)

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Power Quality Disturbances Recognition Based on a Multiresolution Generalized S-Transform and a PSO-Improved Decision Tree

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Energies 2015, 8(1), 549-572; https://doi.org/10.3390/en8010549 - 15 Jan 2015

Cited by 40 | Viewed by 5963

Abstract

In a microgrid, the distributed generators (DG) can power the user loads directly. As a result, power quality (PQ) events are more likely to affect the users. This paper proposes a Multiresolution Generalized S-transform (MGST) approach to improve the ability of analyzing and [...] Read more.

In a microgrid, the distributed generators (DG) can power the user loads directly. As a result, power quality (PQ) events are more likely to affect the users. This paper proposes a Multiresolution Generalized S-transform (MGST) approach to improve the ability of analyzing and monitoring the power quality in a microgrid. Firstly, the time-frequency distribution characteristics of different types of disturbances are analyzed. Based on the characteristics, the frequency domain is segmented into three frequency areas. After that, the width factor of the window function in the S-transform is set in different frequency areas. MGST has different time-frequency resolution in each frequency area to satisfy the recognition requirements of different disturbances in each frequency area. Then, a rule-based decision tree classifier is designed. In addition, particle swarm optimization (PSO) is applied to extract the applicable features. Finally, the proposed method is compared with some others. The simulation experiments show that the new approach has better accuracy and noise immunity. Full article

(This article belongs to the Special Issue Microgrids)

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Hybrid Multi-Agent Control in Microgrids: Framework, Models and Implementations Based on IEC 61850

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Energies 2015, 8(1), 31-58; https://doi.org/10.3390/en8010031 - 24 Dec 2014

Cited by 12 | Viewed by 7241

Abstract

Operation control is a vital and complex issue for microgrids. The objective of this paper is to explore the practical means of applying decentralized control by using a multi agent system in actual microgrids and devices. This paper presents a hierarchical control framework [...] Read more.

Operation control is a vital and complex issue for microgrids. The objective of this paper is to explore the practical means of applying decentralized control by using a multi agent system in actual microgrids and devices. This paper presents a hierarchical control framework (HCF) consisting of local reaction control (LRC) level, local decision control (LDC) level, horizontal cooperation control (HCC) level and vertical cooperation control (VCC) level to meet different control requirements of a microgrid. Then, a hybrid multi-agent control model (HAM) is proposed to implement HCF, and the properties, functionalities and operating rules of HAM are described. Furthermore, the paper elaborates on the implementation of HAM based on the IEC 61850 Standard, and proposes some new implementation methods, such as extended information models of IEC 61850 with agent communication language and bidirectional interaction mechanism of generic object oriented substation event (GOOSE) communication. A hardware design and software system are proposed and the results of simulation and laboratory tests verify the effectiveness of the proposed strategies, models and implementations. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Using the Direct Search Method for Optimal Dispatch of Distributed Generation in a Medium-Voltage Microgrid

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Wei-Tzer Huang

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Kai-Chao Yao

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Chun-Ching Wu

Energies 2014, 7(12), 8355-8373; https://doi.org/10.3390/en7128355 - 12 Dec 2014

Cited by 39 | Viewed by 7373

Abstract

This paper proposes a simple and efficient approach for the optimal dispatch in a medium-voltage microgrid (MG) with various types of distributed generation (DG). The fuel costs generated by these DGs are determined using quadratic and linear functions dependent on the types of [...] Read more.

This paper proposes a simple and efficient approach for the optimal dispatch in a medium-voltage microgrid (MG) with various types of distributed generation (DG). The fuel costs generated by these DGs are determined using quadratic and linear functions dependent on the types of DGs. Instead of using the traditional Lagrange multiplier method for power system economic dispatch, the proposed direct search method (DSM) approach is able to handle several inequality constraints without introducing any multipliers and furthermore it can solve the non-derivative problems or the fuel cost functions being much more complicated. Accordingly, the DSM is proposed for determining the optimal dispatch of MGs with various types of DG to minimize generation costs under grid-tied and autonomous operations. Results demonstrate that the proposed DSM is a highly suitable and simple approach to determining the optimal dispatch in medium-voltage MGs with various types of DG. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

New Power Quality Analysis Method Based on Chaos Synchronization and Extension Neural Network

by

Meng-Hui Wang

and

Her-Terng Yau

Energies 2014, 7(10), 6340-6357; https://doi.org/10.3390/en7106340 - 08 Oct 2014

Cited by 13 | Viewed by 6993

Abstract

A hybrid method comprising a chaos synchronization (CS)-based detection scheme and an Extension Neural Network (ENN) classification algorithm is proposed for power quality monitoring and analysis. The new method can detect minor changes in signals of the power systems. Likewise, prominent characteristics of [...] Read more.

A hybrid method comprising a chaos synchronization (CS)-based detection scheme and an Extension Neural Network (ENN) classification algorithm is proposed for power quality monitoring and analysis. The new method can detect minor changes in signals of the power systems. Likewise, prominent characteristics of system signal disturbance can be extracted by this technique. In the proposed approach, the CS-based detection method is used to extract three fundamental characteristics of the power system signal and an ENN-based clustering scheme is then applied to detect the state of the signal, i.e., normal, voltage sag, voltage swell, interruption or harmonics. The validity of the proposed method is demonstrated by means of simulations given the use of three different chaotic systems, namely Lorenz, New Lorenz and Sprott. The simulation results show that the proposed method achieves a high detection accuracy irrespective of the chaotic system used or the presence of noise. The proposed method not only achieves higher detection accuracy than existing methods, but also has low computational cost, an improved robustness toward noise, and improved scalability. As a result, it provides an ideal solution for the future development of hand-held power quality analyzers and real-time detection devices. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessArticle

Optimization Models and Methods for Demand-Side Management of Residential Users: A Survey

by

Antimo Barbato

and

Antonio Capone

Energies 2014, 7(9), 5787-5824; https://doi.org/10.3390/en7095787 - 04 Sep 2014

Cited by 180 | Viewed by 12103

Abstract

The residential sector is currently one of the major contributors to the global energy balance. However, the energy demand of residential users has been so far largely uncontrollable and inelastic with respect to the power grid conditions. With the massive introduction of renewable [...] Read more.

The residential sector is currently one of the major contributors to the global energy balance. However, the energy demand of residential users has been so far largely uncontrollable and inelastic with respect to the power grid conditions. With the massive introduction of renewable energy sources and the large variations in energy flows, also the residential sector is required to provide some flexibility in energy use so as to contribute to the stability and efficiency of the electric system. To address this issue, demand management mechanisms can be used to optimally manage the energy resources of customers and their energy demand profiles. A very promising technique is represented by demand-side management (DSM), which consists in a proactive method aimed at making users energy-efficient in the long term. In this paper, we survey the most relevant studies on optimization methods for DSM of residential consumers. Specifically, we review the related literature according to three axes defining contrasting characteristics of the schemes proposed: DSM for individual users versus DSM for cooperative consumers, deterministic DSM versus stochastic DSM and day-ahead DSM versus real-time DSM. Based on this classification, we provide a big picture of the key features of different approaches and techniques and discuss future research directions. Full article

(This article belongs to the Special Issue Microgrids)

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Open AccessReview

Power Quality in DC Power Distribution Systems and Microgrids

by

Stephen Whaite

,

Brandon Grainger

and

Alexis Kwasinski

Energies 2015, 8(5), 4378-4399; https://doi.org/10.3390/en8054378 - 15 May 2015

Cited by 85 | Viewed by 14664

Abstract

This review paper discusses power quality considerations for direct current (DC) electric power distribution systems, particularly DC microgrids. First, four selected sample DC architectures are discussed to provide motivation for the consideration of power quality in DC systems. Second, a brief overview of [...] Read more.

This review paper discusses power quality considerations for direct current (DC) electric power distribution systems, particularly DC microgrids. First, four selected sample DC architectures are discussed to provide motivation for the consideration of power quality in DC systems. Second, a brief overview of power quality challenges in conventional alternating current (AC) distribution systems is given to establish the field of power quality. Finally, a survey of literature addressing power quality issues in DC systems is presented, and necessary power quality considerations in DC distribution system design and operation are discussed. Full article

(This article belongs to the Special Issue Microgrids)

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