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Advanced Operation and Control of Smart Microgrids

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

Deadline for manuscript submissions: closed (30 November 2017) | Viewed by 54540

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Dr. Wenxin Liu

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Smart Microgrid and Renewable Technology (SMRT) Research Laboratory, Department of Electrical and Computer Engineering, Lehigh University, 19 West Memorial Drive, Bethlehem, PA 18015, USA
Interests: power and energy (smart grid, microgrid, renewable energy, power electronics, energy internet, etc.); control systems (optimal control, cooperative control, networked control, cyber-physical systems, etc.); computational intelligence (neural networks, swarm intelligence, etc.).

Prof. Dr. Il-Yop Chung

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Guest Editor

School of Electrical Engineering, Kookmin University, Seoul 02707, Republic of Korea
Interests: power system control and operation; renewable energy integration to grids; microgrids; power distribution systems; shipboard power systems
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Dr. Hao Xu

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Guest Editor

Department of Electrical and Biomedical Engineering, University of Nevada, Reno 1664 N. Virginia Street, Reno, NV 89557-0260, USA
Interests: intelligent control; networked control for power systems; resilient control for power systems; machine learning-based optimal control; cross-layer control and communication co-design; cyber-physical systems and wireless passive sensor network.

Special Issue Information

Dear Colleagues,

Microgrid is defined as a cluster of distributed generators (DGs) and loads serviced by a distribution network that can operate in both grid-connected and autonomous modes. Major benefits of microgrids include increased reliability, increased usage of renewable energy, and timely response to growing consumer demand. Microgrids will play an important role in smart grids and the study of smart microgrids is vital for their successful deployment. Due to renewable integration, an increasing number of power converters are used to interface the DGs with the distribution network. The reduced inertia of the inverter-based microgrids together with the uncertainty of the renewable generation make effective control of microgrids very challenging. To achieve good static and dynamic control performance, the control solutions for microgrids need to be very fast and accurate, which is beyond the capability of traditional control solutions for large-scale power systems. Designing advanced control solutions for microgrids requires integrating multidisciplinary expertise, including modeling, optimization, controls, and power electronics. This Special Issue seeks original contributions from all related fields that can promote the research on microgrid operation and control. The research effort will not only endorse this research on microgrids, but also benefit studies on renewable energy, smart grids, and Energy Internet.

Dr. Wenxin Liu
Dr. Il-Yop Chung
Dr. Hao Xu
Guest Editors

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Keywords

microgrid
smart grid
renewable energy
intelligent control
distributed control
adaptive control
stochastic optimization
computational intelligence

Published Papers (11 papers)

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Research

7224 KiB

Open AccessArticle

Distributed Variable Droop Curve Control Strategies in Smart Microgrid

by Changhong Deng, Yahong Chen, Jin Tan, Pei Xia, Ning Liang, Weiwei Yao and Yuan-ao Zhang

Energies 2018, 11(1), 24; https://doi.org/10.3390/en11010024 - 22 Dec 2017

Cited by 3 | Viewed by 3671

Abstract

In micro grid (MG), active/reactive power sharing for all dis-patchable units is an important issue. To meet fluctuating loads’ active and reactive power demands, the units generally adopt primary P-f and Q-U droop control methods. However, at different state of charge (SOC) values, the capability of Lead Acid Battery Bank (LABB) based units to take loads varies in a large range; active power should not be shared according to the units P capacities in a constant ratio. Besides, influenced by the output and line impedance between units, reactive power is not able to be shared in proportion to the units Q capacities. Another problem, after MG power balance requirement is satisfied, frequency and voltage are deviating from their rated values thus power quality is reduced. This paper presents a new smart MG which is based on the multi agent system. To solve the problems mentioned above, P-f and Q-U droop curves are adjusted dynamically and autonomously in local agents. To improve the power quality, secondary restoration function is realized in a decentralized way, the computation tasks are assigned to local, the computation capability and communication reliability requirements for central PC are low, and operation reliability is high. Simulation results back the proposed methods. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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2642 KiB

Open AccessArticle

Improved Linear Active Disturbance Rejection Control for Microgrid Frequency Regulation

by Xiao Qi and Yan Bai

Energies 2017, 10(7), 1047; https://doi.org/10.3390/en10071047 - 20 Jul 2017

Cited by 12 | Viewed by 4563

Abstract

The frequency regulation has become one of the major subjects in microgrid power system due to the complexity structure of microgrid. In order to solve this problem, this paper proposes an improved linear active disturbance rejection control algorithm (ILADRC) that can significantly improve system performances through changing feedback control law to reduce the disturbance estimation error of extended state observer. Then, the proposed algorithm is employed in microgrid power system frequency regulation problem, which demonstrates its effectiveness. The parameters of controllers are optimized by particle swarm optimization (PSO) algorithm improved by genetic algorithm (GA). Simulations with different disturbances including sudden and stochastic change of load demand and wind turbine generation are carried out in comparison with previous studies. And robustness testing based on Monte-Carlo approach also shows better performance. So frequency stability of microgrid power system can be well guaranteed by proposed control algorithm. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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2866 KiB

Open AccessArticle

Efficient Model Predictive Control Strategies for Resource Management in an Islanded Microgrid

by Seaseung Oh, Suyong Chae, Jason Neely, Jongbok Baek and Marvin Cook

Energies 2017, 10(7), 1008; https://doi.org/10.3390/en10071008 - 16 Jul 2017

Cited by 21 | Viewed by 4007

Abstract

The energy research community is continuously pursuing improvements in power system resiliency and reliability. Microgrids offer a unique opportunity for enhanced reliability and resiliency by utilizing localized generation and energy storage when grid power is unavailable or too expensive. Energy management is a critical aspect of these systems to ensure proper balancing of sources and ensuring power supply to critical loads with minimum cost, especially in an islanded microgrid. This paper presents a hierarchical real-time optimization with mathematical formulations to achieve optimal operation for an islanded microgrid. The optimization is implemented using simple numerically tractable model predictive control strategies and enables appropriate decisions in response to constantly changing conditions. The optimization method is extended for experimentation within the real-time simulation. Simulation results show that the proposed resource management algorithm shows near-optimal performance while effectively dealing with uncertainties in forecasting. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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9868 KiB

Open AccessArticle

Multi-Frequency Control in a Stand-Alone Multi-Microgrid System Using a Back-To-Back Converter

by Hyeong-Jun Yoo, Thai-Thanh Nguyen and Hak-Man Kim

Energies 2017, 10(6), 822; https://doi.org/10.3390/en10060822 - 17 Jun 2017

Cited by 37 | Viewed by 5339

Abstract

A stand-alone multi-microgrid (MMG) system can be formed by connecting multiple stand-alone microgrids (MGs). In the stand-alone MMG system where the frequencies of each MG system are different, a back-to-back (BTB) converter can be used for interconnecting the adjacent MG system. The frequency control performance of the MMG system can be improved by designing the suitable controller of the BTB converter. This study proposes a multi-frequency control in the BTB converter to improve the performance of frequency regulation in the MMG system. Autonomous power sharing between each MG system is achieved by using the proposed multi-frequency control. The stand-alone MMG system where two stand-alone MG systems with different nominal frequencies are interconnected using the BTB converter is simulated in this study to show the feasibility of the proposed multi-frequency controller. Each stand-alone MG system consists of an inverter-based distributed generator (DG) that uses a grid-forming converter with a conventional frequency droop controller. The inverter-based DG is responsible for the primary frequency control in each MG system. To show the effectiveness of the proposed multi-frequency control, a comparison study of the multi-frequency control and the single frequency control is presented in this study. Simulation results show that the system stability can be improved by using the proposed multi-frequency controller. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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7925 KiB

Open AccessEditor’s ChoiceArticle

A Novel Decentralized Economic Operation in Islanded AC Microgrids

by Hua Han, Lang Li, Lina Wang, Mei Su, Yue Zhao and Josep M. Guerrero

Energies 2017, 10(6), 804; https://doi.org/10.3390/en10060804 - 13 Jun 2017

Cited by 29 | Viewed by 4656

Abstract

Droop schemes are usually applied to the control of distributed generators (DGs) in microgrids (MGs) to realize proportional power sharing. The objective might, however, not suit MGs well for economic reasons. Addressing that issue, this paper proposes an alternative droop scheme for reducing the total active generation costs (TAGC). Optimal economic operation, DGs’ capacity limitations and system stability are fully considered basing on DGs’ generation costs. The proposed scheme utilizes the frequency as a carrier to realize the decentralized economic operation of MGs without communication links. Moreover, a fitting method is applied to balance DGs’ synchronous operation and economy. The effectiveness and performance of the proposed scheme are verified through simulations and experiments. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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8600 KiB

Open AccessArticle

Robust Frequency and Voltage Stability Control Strategy for Standalone AC/DC Hybrid Microgrid

by Furqan Asghar, Muhammad Talha and Sung Ho Kim

Energies 2017, 10(6), 760; https://doi.org/10.3390/en10060760 - 30 May 2017

Cited by 33 | Viewed by 7178

Abstract

The microgrid (MG) concept is attracting considerable attention as a solution to energy deficiencies, especially in remote areas, but the intermittent nature of renewable sources and varying loads cause many control problems and thereby affect the quality of power within a microgrid operating in standalone mode. This might cause large frequency and voltage deviations in the system due to unpredictable output power fluctuations. Furthermore, without any main grid support, it is more complex to control and manage the system. In past, droop control and various other coordination control strategies have been presented to stabilize the microgrid frequency and voltages, but in order to utilize the available resources up to their maximum capacity in a positive way, new and robust control mechanisms are required. In this paper, a standalone microgrid is presented, which integrates renewable energy-based distributed generations and local loads. A fuzzy logic-based intelligent control technique is proposed to maintain the frequency and DC (direct current)-link voltage stability for sudden changes in load or generation power. Also from a frequency control perspective, a battery energy storage system (BESS) is suggested as a replacement for a synchronous generator to stabilize the nominal system frequency as a synchronous generator is unable to operate at its maximum efficiency while being controlled for stabilization purposes. Likewise, a super capacitor (SC) and BESS is used to stabilize DC bus voltages even though maximum possible energy is being extracted from renewable generated sources using maximum power point tracking. This newly proposed control method proves to be effective by reducing transient time, minimizing the frequency deviations, maintaining voltages even though maximum power point tracking is working and preventing generators from exceeding their power ratings during disturbances. However, due to the BESS limited capacity, load switching (load shedding scheme) as last option is also introduced in this paper. Simulation results prove the effectiveness of the proposed control strategy from both frequency and voltage perspectives. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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1494 KiB

Open AccessArticle

Optimal Control Based on Maximum Power Point Tracking (MPPT) of an Autonomous Hybrid Photovoltaic/Storage System in Micro Grid Applications

by Ibrahem E. Atawi and Ahmed M. Kassem

Energies 2017, 10(5), 643; https://doi.org/10.3390/en10050643 - 07 May 2017

Cited by 26 | Viewed by 6024

Abstract

This paper investigates how to increase the efficiency of a photovoltaic/energy storage generation unit supplying dynamic loads by regulating and managing both the photovoltaic generator and the storage battery charge-discharge modes. The proposed photovoltaic/energy storage unit is proposed to supply an induction motor driven industrial pump with controlled speed and/or a DC motor driven water pump. An optimal proportional-integral-derivative control based on an Artificial Bee Colony Optimization algorithm is used to regulate the photovoltaic generator in case of normal operation or in case of maximum power point tracking (MPPT) and to also control the battery storage charge discharge modes. A vector control based on the proposed optimal control is used to regulate the induction motor rotor speed at its low reference values needed by the industrial pump. First, a total model of the entire system is obtained. The controller performance with the proposed system is studied with both a DC motor and/or induction motor loads. Simulation results show that the proposed photovoltaic/storage generator is able to supply the suggested dynamic loads under different conditions and with good performance. Also, it is noticed that operating the photovoltaic base on maximum power point tracking condition will give about 43% extra generation power than the normal operation case. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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3677 KiB

Open AccessArticle

A Novel Optimal Control Method for Islanded Microgrids Based on Droop Control Using the ICA-GA Algorithm

by Hamed Moazami Goodarzi and Mohammad Hosein Kazemi

Energies 2017, 10(4), 485; https://doi.org/10.3390/en10040485 - 04 Apr 2017

Cited by 14 | Viewed by 4150

Abstract

Microgrids are small scale power systems with local resources for generation; consumption and storage, that can operate connected to the main grid or islanded. For the islanding operation of microgrids, two important tasks are to share the load demand and maintain the voltage and frequency stabilities. In order to achieve this goal, a hierarchical control structure can be employed. This research presents a solution technique for finding the optimal site, production and droop coefficients of distributed generation (DG) units in microgrids. In this paper, three main factors are scrutinized through a multi-objective optimization approach. These factors include fuel consumption cost, stability and variations of voltage. To solve this optimization problem, an Imperialist Competitive Algorithm-Genetic Algorithm (ICA-GA) is presented. A fuzzy approach is used to search in non-dominated outcomes and to find the best answer. To show the effectiveness of the proposed method, it is implemented on 33-buses IEEE test systems. The simulation results exhibit the ability and efficiency of the proposed scheme to find the optimal solutions. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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8990 KiB

Open AccessArticle

Analyzing the Impacts of System Parameters on MPC-Based Frequency Control for a Stand-Alone Microgrid

by Thai-Thanh Nguyen, Hyeong-Jun Yoo and Hak-Man Kim

Energies 2017, 10(4), 417; https://doi.org/10.3390/en10040417 - 23 Mar 2017

Cited by 24 | Viewed by 4197

Abstract

Model predictive control (MPC) has been widely studied for regulating frequency in stand-alone microgrids (MGs), owing to the advantages of MPC such as fast response and robustness against the parameter uncertainties. Understanding the impacts of system parameters on the control performance of MPC could be useful for the designing process of the controller to achieve better performance. This study analyzes the impact of system parameters on the control performance of MPC for frequency regulation in a stand-alone MG. The typical stand-alone MG, which consists of a diesel engine generator, an energy storage system (ESS), a wind turbine generator, and a load, is considered in this study. The diesel engine generator is in charge of primary frequency control whereas the ESS is responsible for secondary frequency control. The stand-alone MG is linearized to obtain the dynamic model that is used for designing MPC-based secondary frequency control. The robustness of MPC against the variation of system parameters is also analyzed in this study. A comparison study of MPC and proportional–integral (PI) control is presented. Simulation results show that MPC has a faster response time and lower overshoot compared to PI control. In addition, the robustness of MPC against the system uncertainties is stronger than conventional PI control. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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4561 KiB

Open AccessArticle

An Energy-Based Control Strategy for Battery Energy Storage Systems: A Case Study on Microgrid Applications

by Rui Hou, Thai-Thanh Nguyen, Hak-Man Kim, Huihui Song and Yanbin Qu

Energies 2017, 10(2), 215; https://doi.org/10.3390/en10020215 - 13 Feb 2017

Cited by 6 | Viewed by 4772

Abstract

Battery energy storage systems (BESSs) with proportional-integral (PI) control methods have been widely studied in microgrids (MGs). However, the performance of PI control methods might be unsatisfactory for BESSs due to the nonlinear characteristics of the system. To overcome this problem, an energy-based (EB) control method is applied to control the converter of a BESS in this study. The EB method is a robust nonlinear control method based on passivity theory with good performance in both transient and steady states. The detailed design process of the EB method in the BESS by adopting an interconnection and damping assignment (IDA) strategy is described. The design process comprises three steps: the construction of the port-controlled Hamiltonian model, the determination of the equilibrium point and the solution of the undetermined matrix. In addition, integral action is combined to eliminate the steady state error generated by the model mismatch. To establish the correctness and validity of the proposed method, we implement several case simulation studies based on a test MG system and compare the control performance of the EB and PI methods carefully. The case simulation results demonstrate that the EB method has better tracking and anti-disturbance performance compared with the classic PI method. Moreover, the proposed EB method shows stronger robustness to the uncertainty of system parameters. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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5810 KiB

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Integration of Electric Springs and Multi-Port Transformers—A New Solution for AC Microgrids with Renewable Energy Sources

by Qingsong Wang, Ming Cheng and Giuseppe Buja

Energies 2017, 10(2), 193; https://doi.org/10.3390/en10020193 - 09 Feb 2017

Cited by 10 | Viewed by 5080

Abstract

The new concept of integrating electric springs (ESs) and multi-port transformers (MTPs) as an active solution for energy management in alternating current (AC) microgrids is proposed. With an ES located at the port where storage devices previously were, the so-called critical flux is regulated to a constant value within the core of the transformer. The voltage on each winding is then clamped so that critical load (CL) voltage is regulated to a predefined value. The integration of ESs and MPTs can ensure a safer environment for ES utilization. Thus, the power generated by renewable energy sources can be safely used at residential locations with no need to worry about voltage fluctuations across CLs. Moreover, users can sell electricity to the power companies considered as CLs when the electricity generation of the AC microgrids or the home-installed renewable energy resources exceeds the personal consumption. In the paper, isolated topologies for ESs with three- and four-port transformers are examined, and a theoretical analysis of the ES operation is carried out. Then, equivalent circuits of the isolated ES topologies have been derived. Analysis of the ES operation and effectiveness of the isolated ES topologies are validated by both simulations and experiments. Full article

(This article belongs to the Special Issue Advanced Operation and Control of Smart Microgrids)

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