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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Serie: Wiley - IEEE
- Sprache: Englisch
SMART HYBRID AC/DC MICROGRIDS
Addresses the technical aspects and implementation challenges of smart hybrid AC/DC microgrids
Hybrid AC/DC Microgrids: Power Management, Energy Management, and Power Quality Control provides comprehensive coverage of interconnected smart hybrid microgrids, their different structures, and the technical issues associated with their control and implementation in the next generation of smart grids. This authoritative single-volume resource addresses smart hybrid microgrids power management, energy management, communications, power converter control, power quality, renewable generation integration, energy storage, and more.
The book contains both basic and advanced technical information about smart hybrid AC/DC microgrids, featuring a detailed discussion of microgrid structures, communication technologies, and various configurations of interfacing power converters and control strategies. Numerous case studies highlight effective solutions for critical issues in hybrid microgrid operation, control and power quality compensation throughout the text. Topics include control strategies of renewable energy and energy storage interfacing converters in hybrid microgrids, supervisory control strategies of interfacing power converters for microgrid power management and energy microgrid, and smart interfacing power converters for power quality control. This volume:
- Includes a thorough overview of hybrid AC/DC microgrid concepts, structures, and applications
- Discusses communication and security enhancement techniques for guarding against cyberattacks
- Provides detailed controls of smart interfacing power electronics converters from distributed generations and energy storage systems in hybrid AC/DC microgrids
- Provides details on transient and steady-state power management systems in microgrids
- Discusses energy management systems, hierarchical control, multi-agent control, and advanced distribution management control of smart microgrids
- Identifies opportunities to control power quality with smart interfacing power electronic converters
- Addresses power quality issues in the context of real-world applications in data centers, electric railway systems, and electric vehicle charging stations
Smart Hybrid AC/DC Microgrids: Power Management, Energy Management, and Power Quality Control is a valuable source of up-to-date information for senior undergraduate and graduate students as well as academic researchers and industry engineers in the areas of renewable energy, smart grids, microgrids, and power electronics.
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Table of Contents
Cover
Title Page
Copyright
Author Biographies
Preface
Part I: Smart Hybrid AC/DC Microgrids
1 Smart Hybrid AC/DC Microgrids
1.1 Introduction to Microgrids
1.2 Smart Hybrid Microgrid Configurations
1.3 Smart Hybrid Microgrid Operations
1.4 Outline of the Book
References
2 Renewable Energy, Energy Storage, and Smart Interfacing Power Converters
2.1 Renewable‐based Generation
2.2 Energy Storage Systems
2.3 Integration of Renewable Energy and Energy Storage
2.4 Summary
References
3 Smart Microgrid Communications
3.1 Introduction
3.2 Communication Technique for Smart Microgrids
3.3 Standards and Protocols in Smart Microgrids
3.4 Network Cyber‐security
3.5 Summary
References
Part II: Power Management Systems (PMSs) and Energy Management Systems (EMSs)
4 Smart Interfacing Power Electronics Converter Control
4.1 Primary Control of Power Electronics Converters
4.2 Virtual Impedance Control of Power Electronic Converters
4.3 Droop Control of Power Electronics Converters
4.4 Virtual Synchronous Generator (VSG) Control of Interfacing Power Electronics Converters
4.5 Unified Control of Power Electronics Converters
4.6 Summary
References
5 Power Management System (PMS) in Smart Hybrid AC/DC Microgrids
5.1 Introduction
5.2 Hierarchical Control of Hybrid Microgrids
5.3 Power Management Systems (PMSs) in Different Structures of Hybrid Microgrids
5.4 Power Management Strategies During Transitions and Different Loading Conditions
5.5 Implemented Examples of Power Management Systems in Hybrid Microgrids
5.6 Black Start in Hybrid Microgrids
5.7 Summary
References
6 Energy Management System (EMS) in Smart Hybrid Microgrids
6.1 Energy Management in Hierarchical Control of Microgrids
6.2 Multi‐agent Control Strategy of Microgrids
6.3 Advance Distribution Management Systems (ADMSs) in Smart Hybrid Microgrids
6.4 Cyber‐security in Smart Hybrid Microgrids
6.5 Summary
References
Part III: Power Quality Issues and Control in Smart Hybrid Microgrids
7 Overview of Power Quality in Microgrids
7.1 Introduction
7.2 Classification of Power Quality Disturbances
7.3 Overview of Power Quality Standards
7.4 Mitigation Techniques of Power Quality Problems
7.5 Power Quality Issues and Compensation in Microgrids
7.6 Summary
References
8 Smart Microgrid Control During Grid Disturbances
8.1 Introduction
8.2 Islanding Detection
8.3 Fault Ride‐through Capability
8.4 Fault Current Contribution and Protection Coordination
8.5 Summary
References
9 Unbalanced Voltage Compensation in Smart Hybrid Microgrids
9.1 Introduction
9.2 Control of Individual Three‐phase IFCs for Unbalanced Voltage Compensation
9.3 Control of Parallel Three‐phase IFCs for Unbalance Voltage Compensation
9.4 Control of Single‐phase IFCs for Three‐phase System Unbalanced Voltage Compensation
9.5 Summary
References
10 Harmonic Compensation Control in Smart Hybrid Microgrids
10.1 Introduction
10.2 Control of Interfacing Power Converters for Harmonic Compensation in AC Subgrids
10.3 Control of Low‐switching Interfacing Power Converters for Harmonics Compensation in an AC Subgrid
10.4 Control of Interfacing Power Converters for Harmonics Compensation in a DC Subgrid
10.5 Coordinated Control of Multiple Interfacing Power Converters for Harmonics Compensation
10.6 Summary
References
A: Instantaneous Power Theory from Three‐phase and Single‐phase System Perspectives
A.1 Introduction
A.2 Principles of Instantaneous Power Theory
A.3 Power Control Using Instantaneous Power Theory from a Three‐phase System Perspective
A.4 Power Control Using Instantaneous Power Theory from a Single‐phase System Perspective
A.5 Discussion
A.6 Summary
References
B: Peak Current of Interfacing Power Converters Under Unbalanced Voltage
B.1 Introduction
B.2 Peak Currents of Interfacing Converters
B.3 Maximizing Power/Current Transfer Capability of Interfacing Converters
B.4 Summary
References
C: Case Study System Parameters
Index
End User License Agreement
List of Tables
Chapter 2
Table 2.1 Characteristics of widely used energy storage technologies.
Chapter 3
Table 3.1 Requirements of communication functions in a smart microgrid/grid...
Table 3.2 Comparison of different wired communication technologies.
Table 3.3 Comparison of different wireless communication technologies.
Table 3.4 Standards and protocols categories and contents.
Chapter 5
Table 5.1 Overview of the power management strategies of an AC‐coupled hybr...
Table 5.2 Overview of power management strategies of a DC‐coupled hybrid mi...
Table 5.3 Overview of power management strategies of the AC‐DC‐coupled hybr...
Table 5.4 Overview of power management during the transition between grid‐c...
Chapter 6
Table 6.1 Review of cyber‐security violations in smart microgrids.
Chapter 7
Table 7.1 Power quality problems: causes and effects.
Table 7.2 Standards for common power quality problems.
Table 7.3 Recommended voltage variation (up to 1000 V).
Table 7.4 IEEE Standard 519‐2014: current distortion limits for general dis...
Table 7.5 Transmission level voltage distortion limits.
Chapter 8
Table 8.1 Islanding detection methods.
Table 8.2 Fuse‐recloser coordination study summary.
Chapter 10
Table 10.1 Summary of harmonics compensation in hybrid AC/DC microgrids usi...
Appendix C
Table C.1 Parameters used in simulation of microgrid system formed by interf...
Table C.2 Parameters used in simulation of virtual impedance based fault rid...
Table C.3 System parameters for experiments of adjustable unbalanced voltage...
Table C.4 System parameters for simulations of parallel three‐phase IFC cont...
Table C.5 System parameters for simulations of parallel three‐phase IFC cont...
Table C.6 Values of
C
1
to
C
10
; coefficients of the amplitude of the PCC curr...
Table C.7 Values of
D
1
to
D
10
; coefficients of amplitude of the PCC current ...
Table C.8 Distributed load modifications connected to Bus#671 (Model: Y‐PQ) ...
Table C.9 Single‐phase IFCs of DG connected to IEEE 13‐Node Test System.
Table C.10 Parameters used for simulation of CCM, VCM and HCM for harmonic c...
Table C.11 Parameters used for experiment of VFF and CFF for harmonic contro...
Table C.12 Parameters used for experiment of virtual impedance based ripple ...
Table C.13 Parameters used in simulation of microgrid system with priority d...
List of Illustrations
Chapter 1
Figure 1.1 Block diagram of modern microgrids.
Figure 1.2 A typical example of an AC‐coupled hybrid microgrid.
Figure 1.3 A typical example of a DC‐coupled hybrid microgrid.
Figure 1.4 A typical example of an AC‐DC‐coupled hybrid microgrid.
Figure 1.5 Examples of a data center: (a) AC‐coupled structure, and (b) DC‐c...
Figure 1.6 Examples of the electric vehicle charging station: (a) AC‐coupled...
Figure 1.7 The more electric aircraft as a high‐frequency AC‐coupled microgr...
Figure 1.8 Functions of a smart microgrid.
Chapter 2
Figure 2.1 Global electricity generation mix, historical and forecast until ...
Figure 2.2 Photon energy converted into electrical energy in a PV cell.
Figure 2.3 Equivalent solar cell electrical model.
Figure 2.4 A PV cell I–V curve.
Figure 2.5 PV configuration from cell to array.
Figure 2.6 (a) I–V and (b) P–V characteristics of a PV panel at different en...
Figure 2.7 General scheme of a PV system with MPPT.
Figure 2.8 (a) The movement of the operating point in MPP tracking operation...
Figure 2.9 Different configurations of PV panels.
Figure 2.10 Dual power stage PV converters configuration: (a) low‐frequency...
Figure 2.11 Single power stage PV converter configuration: (a) with an isola...
Figure 2.12 Main components of a wind power system.
Figure 2.13 Wind turbine classification: (a) VAWT and (b) HAWT.
Figure 2.14 Idealized power curve of a wind turbine.
Figure 2.15 Wind turbine output power versus turbine speed under different w...
Figure 2.16 A typical wind turbine power and rotor efficiency versus wind sp...
Figure 2.17 Four types of wind turbine generator systems.
Figure 2.18 Variable‐speed wind energy conversion system with DC/DC boost co...
Figure 2.19 Diagram of an
n
‐RC model of a battery.
Figure 2.20 Battery energy storage system (BESS) components.
Figure 2.21 Flywheel system components.
Figure 2.22 Superconducting magnetic system components.
Figure 2.23 Generalized energy flow of a hydrogen‐based storage system.
Figure 2.24 Schematic diagram of an alkaline electrolyzer.
Figure 2.25 Electrolyzer equivalent circuit.
Figure 2.26 Typical polymer electrolyte membrane fuel cell power curve.
Figure 2.27 Typical fuel cell system structure.
Figure 2.28 Interfacing power electronics converters (IFCs): (a) two‐port DC...
Chapter 3
Figure 3.1 A typical cyber‐physical smart microgrid.
Figure 3.2 Seven‐layer OSI model of communication techniques.
Figure 3.3 Networks of the communication system in a smart grid.
Figure 3.4 Categories of communication standards in a smart grid.
Chapter 4
Figure 4.1 Typical structure of a three‐phase converter and its control syst...
Figure 4.2 Relationships between the
abc
frame and the
αβ
frame.
Figure 4.3 Relationships between the
abc
frame and the
dq
frame.
Figure 4.4 DC/AC converter with a single inductor as the filter.
Figure 4.5 Block diagrams of typical model predictive control (MPC): (a) FCS...
Figure 4.6 Primary control of IFCs; bi‐directional power control through the...
Figure 4.7 CCM‐based primary control of IFCs – example of different ways to ...
Figure 4.8 Primary control of IFCs: AC voltage control of the power converte...
Figure 4.9 Primary control of IFCs: bi‐directional power control through the...
Figure 4.10 Functions of virtual impedance in a power converter [4].
Figure 4.11 Possible internal virtual impedance positions.
Figure 4.12 Two popular internal virtual impedance positions for a voltage s...
Figure 4.13 Position of the external virtual impedance of an interfacing con...
Figure 4.14 Different ways to realize complex virtual impedance: (a) LPF‐bas...
Figure 4.15 An example control scheme to implement external virtual impedanc...
Figure 4.16 An example control system with both internal and external virtua...
Figure 4.17 General closed‐loop control with internal and external virtual i...
Figure 4.18 Real power sharing through frequency droop control in an AC subg...
Figure 4.19 Reactive power‐sharing with traditional voltage droop control: (...
Figure 4.20 Load demand sharing in a DC subgrid using DC droop control.
Figure 4.21 AC/DC‐coupled hybrid microgrid in islanded operation mode with t...
Figure 4.22 Control block diagram of one AC/DC subgrid IFC in islanded opera...
Figure 4.23 Power sharing by unified droop for IFCs in hybrid AC/DC systems....
Figure 4.24 Virtual inductor realization scheme.
Figure 4.25 Reactive power‐sharing diagram with line impedance (inductive) e...
Figure 4.26 Matching line impedances with virtual impedance.
Figure 4.27 System diagram used for the case study: (a) system structure; (b...
Figure 4.28 Simulation results of the case study: (a) reactive power sharing...
Figure 4.29 Control system of a real synchronous generator.
Figure 4.30 Voltage‐based virtual synchronous a generator control scheme....
Figure 4.31 VSG control as outer loops: (a) full control scheme; (b) virtual...
Figure 4.32 Block diagram of current‐based VSG control.
Figure 4.33 An example of a control system with a mode switch for the IFC.
Figure 4.34 An example of unified control for an IFC.
Chapter 5
Figure 5.1 The structure of hierarchical control in smart microgrids.
Figure 5.2 Centralized structure of supervisory control of IFCs.
Figure 5.3 Distributed structure of supervisory control of IFCs.
Figure 5.4 Decentralized structure of supervisory control of IFCs.
Figure 5.5 A typical structure of an AC‐coupled hybrid microgrid.
Figure 5.6 A typical structure of a DC‐coupled hybrid microgrid.
Figure 5.7 A typical structure of an AC/DC‐coupled hybrid microgrid.
Figure 5.8 Power converter control in grid voltage amplitude and frequency s...
Figure 5.9 Example of a control block diagram for unbalanced voltage compens...
Figure 5.10 Sequential model of three‐phase IFC connected to the AC subgrid....
Figure 5.11 Negative sequence of PCC voltage; an example of IFC negative seq...
Figure 5.12 Example of power balance scheme in DC‐coupled grid‐connected WT/...
Figure 5.13 A typical unified control with a unified droop for an IFC in a h...
Figure 5.14 Simulation results of the case study: (a) IFC under power contro...
Chapter 6
Figure 6.1 A microgrid management in different time scales.
Figure 6.2 Multiple microgrid energy management.
Figure 6.3 Application of AI in power systems.
Figure 6.4 The structure of multi‐agent control for multiple microgrid.
Figure 6.5 Multi‐agent control case study flow chart.
Figure 6.6 SCADA system and components.
Figure 6.7 Diagram of the distributed structure of SCADA systems.
Figure 6.8 GIS and ADMS interaction architecture.
Figure 6.9 The architecture of a DERMS.
Figure 6.10 DC microgrid with the cyber–physical model.
Figure 6.11 The
i
th converter controller for sensors and communication link ...
Chapter 7
Figure 7.1 Typical waveforms of transients.
Figure 7.2 Typical waveforms of short duration variations.
Figure 7.3 Traditional power quality compensation methods.
Figure 7.4 Passive single‐tuned filters: (a) shunt passive filter, (b) serie...
Figure 7.5 Passive damped filters: (a) shunt passive filter (second‐order), ...
Figure 7.6 Shunt passive filter with impedance frequency plots: (a) band‐pas...
Figure 7.7 Series passive filters: (a) single‐tuned filter, (b) damped filte...
Figure 7.8 Different combinations of passive series and shunt filters for hy...
Figure 7.9 An example structure of SVCs – thyristor controlled reactor (TCR)...
Figure 7.10 The control scheme of an SVC.
Figure 7.11 Equivalent model of a STATCOM.
Figure 7.12 Cascaded H‐bridge converter based high‐power medium‐voltage STAT...
Figure 7.13 Structure of a distributed STATCOM (D‐STATCOM).
Figure 7.14 Example control scheme of a D‐STATCOM.
Figure 7.15 Structure of a dynamic voltage restorer (DVR).
Figure 7.16 Phasor diagram for different DVR operating schemes: (a) pre‐sag ...
Figure 7.17 Example pre‐sag control scheme for a DVR.
Figure 7.18 Structure of shunt active power filters.
Figure 7.19 Typical control block diagram of a shunt APF.
Figure 7.20 Unified power quality conditioner (UPQC) system configuration.
Figure 7.21 An example control scheme for distributed generation systems wit...
Figure 7.22 Harmonic interactions between AC and DC subgrids.
Figure 7.23 Parallel IFCs for DC ripple cancelation.
Figure 7.24 DC ripple mitigators in a DC subsystem.
Chapter 8
Figure 8.1 Distorted current waveform for the active frequency drift method....
Figure 8.2 Remote islanding detection scenario.
Figure 8.3 Schematic of intelligent process in islanding detection.
Figure 8.4 Operation of grid‐connected DG based on IEEE Standard 1547‐2018 a...
Figure 8.5 DG response to abnormal voltage and high voltage and low voltage ...
Figure 8.6 A typical example of a resistive type SFCL.
Figure 8.7 Example of LVRT control for a grid‐connected PV system.
Figure 8.8 Simulation results of FRT of PV inverter under balanced faults.
Figure 8.9 A typical example of virtual impedance‐based voltage control for ...
Figure 8.10 Grid disturbance ride‐through using adaptive impedance.
Figure 8.11 Experimental DG performance during PCC voltage sag: (a) with con...
Figure 8.12 Fuse‐recloser protection scheme in distribution feeders.
Figure 8.13 Time–current characteristic curves of recloser superimposed on a...
Figure 8.14 Impact of DG on operation of protection system under low impedan...
Figure 8.15 Equivalent circuit of a distribution system with inverter‐based ...
Figure 8.16 Voltage and current vector diagram of (a) DG provides active pow...
Figure 8.17 Control strategy to determine inverter reference current.
Figure 8.18 IEEE 13‐node test feeder system.
Figure 8.19 Fuse‐recloser coordination in the simulated system.
Figure 8.20 Output current of inverters for a 2 Ω fault in the middle of 645...
Figure 8.21 Inverter output power for a 8 Ω fault in the middle of 645–646....
Figure 8.22 PCC voltage for a 8 Ω fault in the middle of 645–646.
Figure 8.23 Fuse current for a 8 Ω fault in the middle of 645–646.
Chapter 9
Figure 9.1 Typical three‐phase IFC performance under unbalanced condition.
Figure 9.2 Typical individual three‐phase IFC with control block diagram und...
Figure 9.3 Single three‐phase interfacing converter.
Figure 9.4 Sequential model of a three‐phase IFC connected to the AC subgrid...
Figure 9.5 Performance of the IFC under unbalanced voltage when its output a...
Figure 9.6 Performance of the PCC unbalanced voltage compensation and IFC ac...
Figure 9.7 Performance of the PCC unbalanced voltage compensation and IFC ac...
Figure 9.8 Typical parallel three‐phase IFCs with control block diagram unde...
Figure 9.9 Individual IFC output active power and three‐phase currents under...
Figure 9.10 Vector representation of Δ
P
cancelation using the redundant...
Figure 9.11 Parallel IFCs control strategy under unity PF operation when one...
Figure 9.12 Results of three parallel IFCs under unbalanced condition when o...
Figure 9.13 Results of three parallel IFCs under unbalanced condition when a...
Figure 9.14 Hybrid AC/DC microgrids with single‐phase DGs' IFCs connected to...
Figure 9.15 PCC voltage and current.
Figure 9.16 Negative sequence model of the system seen from the PCC.
Figure 9.17 An example of the PCC zero‐sequence current minimization, with a...
Figure 9.18 Zero sequence model of the system seen from the PCC.
Figure 9.19 Phasor diagram of negative and zero sequences of the PCC current...
Figure 9.20 IEEE 13‐node test system with embedded single‐phase IFCs from DG...
Figure 9.21 Performance of negative sequence current compensation (k− = 1; k...
Chapter 10
Figure 10.1 AC subgrid harmonic compensation using interfacing converter () ...
Figure 10.2 The equivalent circuit of the IFC that is connected to the AC su...
Figure 10.3 External virtual impedance control of IFCs through: the current ...
Figure 10.4 IFC control block diagram with CCM‐based harmonic compensation....
Figure 10.5 Performance of CCM‐based harmonic compensation of an IFC: (a) wi...
Figure 10.6 IFC control block diagram with VCM‐based harmonic compensation....
Figure 10.7 The IFC line current harmonic rejection with the VCM using IFC c...
Figure 10.8 Performance of VCM‐based harmonic compensation of an IFC: (a) wi...
Figure 10.9 A typical individual IFC control block diagram with HCM harmonic...
Figure 10.10 Performance of HCM‐based harmonic compensation of an IFC: (a) P...
Figure 10.11 Feed‐forward control methods: (a) full feed‐forward of PCC volt...
Figure 10.12 Virtual impedance feedforward control (FCM): (a) voltage feedfo...
Figure 10.13 Different sampling and PWM methods: (a) synchronous sampling wi...
Figure 10.14 An example of harmonic control of low‐switching IFCs with curre...
Figure 10.15 Equivalent model of a microgrid with IFC and non‐linear loads....
Figure 10.16 An example of harmonic control of low‐switching IFCs with volta...
Figure 10.17 Harmonics compensation with VFF.
Figure 10.18 FFT analysis of the PCC voltage: (a) no harmonic control; (b) h...
Figure 10.19 Harmonics compensation with CFF.
Figure 10.20 FFT analysis of the PCC voltage: (a) no harmonic control; (b) h...
Figure 10.21 Two DC/DC IFC control for DC‐subgrid harmonic compensation.
Figure 10.22 Performance of the two DC/DC IFC control for DC‐subgrid harmoni...
Figure 10.23 AC microgrid structure and the equivalent model: (a) microgrid ...
Figure 10.24 Selective harmonics compensation scheme with
G–S
droop an...
Figure 10.25 THD at each node under different compensation priority schemes....
Appendix A
Figure A.1 Three‐phase power system at the PCC.
Figure A.2 Typical grid‐connected three‐phase interfacing converter with its...
Appendix B
Figure B.1
n
‐parallel three‐phase IFCs.
Figure B.2 Locus of the PCC voltage and the
i
th IFC current: (a) unity power...
Figure B.3 Individual IFC output active power and three‐phase currents under...
Figure B.4 Relation between the phase of the individual
i
th IFC peak current...
Figure B.5 The phase of IFCs peak currents for different values of
ρ
wh...
Figure B.6 The individual
i
th IFC maximum currents in
a, b, c
phases under d...
Figure B.7 The variations of
B
3
(for the redundant IFC) under
k
p
2
= −
k
q
2
= −...
Guide
Cover
Table of Contents
Title Page
Copyright
Author Biographies
Preface
Begin Reading
A: Instantaneous Power Theory from Three‐phase and Single‐phase System Perspectives
B: Peak Current of Interfacing Power Converters Under Unbalanced Voltage
C: Case Study System Parameters
Index
End User License Agreement
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Smart Hybrid AC/DC Microgrids
Power Management, Energy Management, and Power Quality Control
Yunwei Ryan LiFarzam NejabatkhahHao Tian
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Author Biographies
Yunwei Ryan Li received his Bachelor degree from Tianjin University, China, in 2002, and his Ph.D. degree from Nanyang Technological University, Singapore, in 2006. In 2005, Dr. Li was a Visiting Scholar with Aalborg University, Denmark. From 2006 to 2007, he was a Postdoctoral Research Fellow at Toronto Metropolitan University (previously known as Ryerson University), Canada. In 2007, he also worked at Rockwell Automation Canada before he joined University of Alberta, Canada in the same year. Since then, Dr. Li has been with University of Alberta. Dr. Li is among the first few researchers on microgrids, since early 2000, and his research on microgrids, power quality, and interfacing converters has led to over 350 publications. He is recognized as a Highly Cited Researcher by the Clarivate Analytics.
Farzam Nejabatkhah received his Bachelor (Hons) and Master (Hons) degrees in electrical engineering from the University of Tabriz, Tabriz, Iran, in 2009 and 2011, respectively, and his Ph.D. degree in electrical engineering from the University of Alberta, Edmonton, Canada, in 2017. He was a Postdoctoral Fellow from 2017 to 2019 and an instructor in 2019 at the University of Alberta. Since September 2019, he has joined CYME International T&D, EATON, in Montreal, Canada. In 2021, he was also an instructor at Polytechnique Montreal University. His research interests include smart grids, hybrid AC/DC microgrids, power converters, and cyber‐physical systems.
Hao Tian received his Bachelor and Master degrees in electrical engineering from Shandong University, Jinan, China, in 2011 and 2014, respectively, and his Ph.D. degree in energy systems from University of Alberta, Edmonton, Canada, in 2019. Since 2019, he has been working as a Postdoctoral Research Fellow at University of Alberta. His research interests include power quality control of hybrid AC–DC microgrid and multilevel converter topology.
Preface
Smart grids are becoming as the next generation power systems, which encompass interconnected microgrids with high penetration of renewable generations and energy storage. Hybrid AC/DC microgrids are the most likely future microgrid structure since DC subgrids feature high efficiency, better power quality, better current carrying capacity, and faster response; DC subgrids can also be easily interfaced to the century‐long AC utility grid.
During the past decade, smart hybrid AC/DC microgrids have received much attention and experienced significant development. However, as an emerging concept for the future grid structure, their technical details have not been understood very well. For example, with the high percentage of renewable energy and energy storage as well as the wide adoption of interfacing power electronics, there are great challenges in power management among the different elements in a microgrid within a very short time (e.g. a fundamental cycle). Therefore, topics such as power management, power converter control, integration of renewable generation and energy storage, cybersecurity, communication technologies, and power quality are critical for the sound operation of a microgrid. This book thoroughly covers the above topics for smart hybrid AC/DC microgrids and presents effective solutions.
This book contains 10 chapters that cover the basics as well as advanced materials in smart hybrid AC/DC microgrids. The 10 chapters are organized into three main parts: Part 1 Smart Hybrid AC/DC Microgrids, which includes a panoramic introduction to hybrid AC/DC microgrids and different microgrid structures. Renewable based generation and energy storage with their interfacing power converters as well as microgrid communications are presented. Part 2 Power Management Systems (PMSs) and Energy Management Systems (EMSs), which provides thorough discussions on hybrid microgrid planning and operation including interfacing power electronics converter control, instantaneous power management, and microgrid energy management systems. Part 3 Power Quality Issues and Control in Smart Hybrid Microgrids, covers more detailed power quality issues in microgrids as well as their control strategies. Additional opportunities to improve the microgrid power quality with smart interfacing power electronic converters are also addressed.
This book is designed to be suitable for senior undergraduate and graduate students as well as academic researchers and industry engineers in the areas of renewable energy, smart grids, microgrids, and power electronics. The book covers a comprehensive range of topics related to smart AC/DC microgrids and includes a good number of references in each chapter. Acknowledging that this is a rapidly developing field, any comments regarding further improvement to the book are always welcomed by the authors.
The authors wish to express their deep gratitude to their families for support, encouragement, and patience, which was essential to the completion of this book during the challenging pandemic that started in 2020. The authors would also like to thank the members of the ELITE (Electronics and Intelligent) Grid Research Lab at the University of Albert, whose contributions to chapter proofreading, figures, and many helpful comments are much appreciated.
Part ISmart Hybrid AC/DC Microgrids
1Smart Hybrid AC/DC Microgrids: Structures and Technical Challenges
1.1 Introduction to Microgrids
1.1.1 Concept of Microgrids
“Microgrids” became jargon in the electrical engineering field at the beginning of the twenty‐first century. After nearly two decades of development, the core of this concept keeps expanding and growing along with the development of many other fields, such as power electronics and smart grids. In general, a microgrid refers to a less complex form of an electrical grid, consisting of power generation, energy storage, and consumption as well as essential interfaces. Its functions, on the other hand, entail many more differences than conventional grids [1], e.g. (i) it can work in grid‐connected or standalone operation modes; (ii) To the grid, it operates as a self‐controlled entity; (iii) it normally features an advanced control strategy to optimally regulate the intermittence from renewable energies, providing high reliability and high power quality; (iv) it is typically located near the users as well as the power generators in a distributed manner, providing high flexibility and cost‐effectiveness.
Another important concept closely related to microgrids is distributed generation (DG). DG mainly refers to power generation with distributed forms, differing from the traditional centralized power plant. DG technologies can use sources such as: (i) renewable energy resources such as wind, photovoltaic, micro‐hydro, biomass, geothermal, ocean wave, and tides; (ii) clean alternative energy generation technologies such as fuel cells and microturbines; (iii) traditional fossil fuel and rotational machine technologies, such as diesel generators. Due to several benefits of these sources, such as cleanness and simple technologies, compounded with increasing demand for electrical energy and the exhaustible nature of fossil fuels, renewable and clean‐energy‐based DGs play an essential role in microgrids. Generally speaking, the microgrid is a key concept to broadly adopt DGs into the conventional electrical grid.
1.1.2 Development of Microgrids
The affix “micro” in “microgrid” indicates one iconic nature of this technique, which is its scale compared to the utility grid. However, the traditional grid used to be much smaller when the first power plant was constructed in the 1880s – the Manhattan Pearl Street Station. In terms of scale, it is indeed micro, and can essentially fall into the generalized category of microgrids. It was also operated as the very early combined heat and power (CHP) demonstration where steam was used to heat nearby buildings as well as power the generators.
During the dawn of the electrical grid, Thomas Edison's direct current (DC) grid configuration showed superior performance when supporting power at a short distance. By 1886, Edison's firm had installed 58 DC “microgrids.” Things quickly changed after Nikola Tesla, with the Westinghouse company, patented an electric motor in 1888. It exploited the rotating field invented by Galileo Ferraris, showing the promising potential of the alternative current (AC) generator. Further enabled by AC transformer technologies, high voltage AC transmission with high efficiency became possible. In 1891, an experiment regarding such an AC‐based transmission technique took place in Germany, where a 175 km long, 15 kV transmission line was implemented [2]. The success of this experiment soon gained commercial attention, resulting in the monopoly of AC‐type utility grids until now.
During this early stage of the electrical system, power quality issues like harmonic voltages and currents also gained their engineering‐perspective investigation rather than pure mathematical problems. The word “harmonic” firstly appeared in electrical research in 1894 by Houston and Kennelly's work entitled “The Harmonics of Alternating Current.” The active compensation concept came later during the 1920s [3]: an AC‐machine‐based compensator was introduced by Boucherot and Kapp. It can adjust the reactive power produced by the machine which shares the similar methodology of modern static compensation equipment.
Alongside the rapid development of a centralized AC electrical system, electricity generation for remote areas (e.g. small islands, isolated mountain settlements, etc.) was challenging based on the traditional grid infrastructure with remote fuel‐based power plants and long distance transmission. For those areas, small‐scale AC off‐grid systems or standalone‐only microgrids provided electrical power utilizing techniques such as wind‐diesel combinations in the early twentieth century, and even up until now. On the other hand, DC power systems, including DC microgrids, still exist and found their application in systems such as telecommunication systems.
During the last century, worldwide electrical grids experienced significant growth, driven by the everlasting demand for electricity generation. In 1924, the first event of the World Energy Congress was held in London. The concerns regarding limited sources of fossil fuels and dramatically increased energy demand embarked energy experts on exploring alternatives. Solar energy was described as a promising candidate in F. M. Jaeger's article published in Science in 1929 [4]. More detailed discussions of alternative energy forms covering water, wind, solar, and nuclear (at that time it was called atomic) were provided in C.C. Furnas's article published in Science in 1941 [5]. Similar discussions are scattered in historical publications but rarely conveyed into market driving forces toward sustainable energy eco‐systems until the first energy crisis in the twentieth century. The 1973 Arab oil embargo, a turning point for the United States energy strategy, resulted in a chain reaction that soon spread out worldwide. One of the eventual reactions was the establishment of the International Energy Agency (IEA). Born from the oil security crisis, the IEA has evolved through the years, pursuing the enhancement of the reliability, affordability, and sustainability of energy. Another important point of progress in history was the 1992 Energy Policy Act in the United States, further strengthening the cost‐competitiveness of renewable energy technologies.
In addition to utility‐scale regulation, small scale distributed power generation was also taken care of by national policies, e.g. through the 1978 Public Utilities Regulatory Policy Act, the United States became the first country to establish fixed power buy‐back rates (i.e. independent producers are allowed to connect to the grid and sell power). The rapid growth of electricity demand keeps pushing the electrical grids to their design limits. During the 1980s–1990s, the economic value of DG started to be recognized as a good complement to the monopoly of the traditional grid. In addition, DGs can support critical electrical needs in rural areas that are difficult to be covered by the centralized grid infrastructure.
At the end of the twentieth century, distributed‐resources‐based systems received dedicated research attention, which eventually spawned into the concept of modern microgrids, where power electronics serve as vital interfaces bridging renewable energy generation and the load and grid. In 1999, the United States microgrid research development and demonstration program was established under the Consortium for Electric Reliability Technology Solutions (CERTS). The 2005 Energy Policy Act was more energy legislation that was of great significance not only in the United States but also worldwide. It covers a wide scope of renewable energy forms, emphasizes research and development, and promotes the study of advanced energy technologies such as DG, integrated thermal systems, reliability of energy production, etc.
The following years witnessed intense research of microgrids. The trajectory of microgrid technology is shifting from technology demonstration pilot projects to commercial projects, which have grown into a multi‐billion‐dollar market. In addition to pure electrical power generation, microgrids with CHP applications brought significant opportunities by optimally regulating multiple energy forms for local customers to achieve much better overall efficiency. This is particularly true considering the much higher efficiency of transmitting electricity over a relatively long distance and the flexibility of DG locations. The concept of “district heating” presented in 1950 is a typical precedent that promoted the combination of thermal/electric stations to generate all the heat and power for a town [6]. In recent years, the philosophy of integration has been further extended to clusters of microgrids for a broader scope of energy generation, forming the virtual power plant (VPP) concept, which is not restricted to physical locations and can include assets connected to any part of the grid.
Moving forward to the third decade of the twenty‐first century, a number of countries have announced pledges to achieve net‐zero emissions in the future, e.g., IEA 2021 report “Net Zero by 2050” [7]. This is when microgrids as well as their larger interconnected systems will play key roles to better integrate renewable‐based DGs with higher reliability, lower cost, and easier accessibility. The challenges are huge but there has been promising progress in recent years. Considerable research efforts have been dedicated to smarter operation for microgrids, e.g. multi‐function optimization, fast and reliable power regulation, comprehensive power quality management, advanced communication, etc. Moving forward, microgrids also serve as one of the key enabling techniques for next‐generation power systems, i.e. smart grids. These smart grids encompass interconnected microgrids, especially at the distribution level where DGs are increasingly used.
1.1.3 Features of Modern Microgrids
With many years of development of microgrids and the enabling technologies in power electronics, communications, and control, a modern microgrid includes a physical electrical system with renewable and non‐renewable‐based DGs, energy storage systems (ESSs), and various loads, as well as the communication and control systems as shown in Figure 1.1.
Figure 1.1 Block diagram of modern microgrids.
As illustrated, the microgrid has a higher‐level control system that monitors and coordinates the physical components through communication systems. Control system information acquisition and command execution are mainly realized by the actuators, such as sensors, relays, and, most importantly, the interfacing converters (IFCs). IFCs are interfaces between the microgrid network and renewable energy, ESSs, loads, or another microgrid network, performing power conversions required for the interconnections. The modern microgrids are expected to have some distinctive features, as shown in the next sections.
High Percentage of Renewable Energy and Energy Storage
Carbon emission and pollution from fossil‐fuel‐based power generation have been considered as the major challenges confronted by human beings. However, renewable‐based electricity generation, such as the generation from solar and wind, generally suffers intermittencies and lacks complete control. Microgrid technology provides a solution to adopt more renewable‐energy‐based power generation without degrading the reliability and power quality of the grid through the integration of ESSs, controllable loads, and the corresponding coordination control.
High system efficiency. As mentioned earlier, the flexibility of providing CHP systems can significantly improve the energy efficiency of microgrids. In addition, the adoption of DGs closer to the loads can effectively reduce the losses in the traditional transmission and distribution systems. Moreover, much renewable‐based DG such as photovoltaic (PV), fuel cell, ESSs, and modern loads (such as LED lighting) are based on DC technologies, where the many AC–DC conversion processes through IFCs for connecting them to the traditional AC buses can create additional losses. The suitable microgrid configuration where both AC and DC buses exist to interface different types of generation, storage, and load technologies can further improve the system efficiency.
Resiliency. Microgrids are designed to work in both grid‐connected or standalone operation modes. This enables the autonomous operation of microgrids when the utility grid suffers from blackouts or major disturbances. In this case, power systems with microgrids are more resilient than traditional ones. Moreover, with more sensors and actuators, such as the controllable and flexible IFCs, microgrids have enhanced the capability for power control and management, leading to sound system operation and higher reliability.
Intelligent. With the development of information and communication technologies, their role in modern microgrid operation and control is becoming more important than ever. Modern microgrids have the capability of system status monitoring, intelligent power and energy management, operation optimization, and outage control.
Superior power quality. With the increasing penetration of interfacing power converters in microgrids, they can be properly controlled to optimize the network power quality in addition to their power management targets. This is a promising idea since most IFCs are not always operating at full rating due to the intermittent nature of renewable‐based DGs. Therefore, their available rating can be used in a smart way to support microgrids. Such microgrids will benefit from fewer harmonics, better power factors, lower unbalance, and well-regulated voltage amplitude and frequency.
1.2 Smart Hybrid Microgrid Configurations
According to the type (AC or DC) of buses or feeders to integrate the generation or loads, microgrids can be classified into AC microgrids, DC microgrids, and hybrid AC/DC microgrids. In AC‐coupled microgrids, only AC buses or feeders are available and all sources and loads are connected to the AC buses. In a DC‐coupled microgrid, all sources and loads are connected to DC buses, and the DC microgrid is interfaced to the main grid through an AC/DC IFC. In hybrid AC/DC microgrids, both AC and DC buses are available, and the microgrid generation sources and loads are connected to the respective buses to minimize the voltage conversion process or optimize the system operation.
1.2.1 AC‐coupled Hybrid Microgrid
A simple example of an AC‐coupled hybrid microgrid is shown in Figure 1.2. As illustrated, only AC buses are available in an AC‐coupled microgrid, and various DGs and ESSs are connected to the AC buses through their IFCs. The ESSs need bidirectional converters to provide the bidirectional power flow capability. In this configuration, both AC and DC loads are also connected to the AC bus where the DC load will require an DC/AC IFC for such integration. This AC‐coupled structure is commonly used when dominant generation sources in the microgrid produce grid‐level AC voltages directly (such as from diesel generators) or indirectly through interfacing power converters.
Figure 1.2 A typical example of an AC‐coupled hybrid microgrid.
In such an AC‐coupled system, the control strategy and power management scheme are mainly focused on power generation/consumption balance and AC subgrid voltage/frequency control, especially in standalone operation mode. The AC‐coupled microgrid has been the dominant structure in the past due to its simple structure and simple control and power management scheme.
In some AC‐coupled microgrids, instead of using IFCs for each DG or ESS, several power conversion stages can be replaced by multiple‐port converters, which combine different power sources in a single power converter. Moreover, in some systems, high‐frequency (higher than the power frequency) AC coupling can be adopted for the microgrid, where the microgrid then requires an AC/AC IFC to be connected to the main grid at power frequency.
1.2.2 DC‐coupled Hybrid Microgrid
Figure 1.3 shows a DC‐coupled hybrid microgrid, where only DC buses are available for integrating the DGs, ESSs, and loads. The AC‐based source and loads will then require IFCs to be connected to the common DC bus. This DC‐coupled configuration is typically adopted when DC power sources (e.g. PV or battery systems) are the major power generation units in the microgrid. Note that in this structure, all the DGs and ESSs are connected to the DC bus. In this DC‐coupled microgrid, a variable frequency AC load such as adjustable speed motors can be connected to the DC bus with a DC/AC converter. In this case, the traditional front‐end AC/DC grid side rectifier for AC bus connection can be removed, which brings obvious benefits in control, power quality, and efficiency. In this system, the microgrid DC/AC IFCs provide bidirectional power flow between the DC bus and AC bus. Depending on the power exchange requirement between DC and AC buses, parallel IFCs are typically used with increased rating and reliability.
Figure 1.3 A typical example of a DC‐coupled hybrid microgrid.
The DC‐coupled microgrid features a simple structure and does not need any frequency and phase angle related synchronisation when integrating different DGs. The control and power management of parallel microgrid IFCs, and their AC terminal voltage synchronization (with each other or with the grid in grid‐connected mode) can present some challenges. Moreover, both DC and AC voltage control and subsystem power management are necessary for a DC‐coupled system. In some DC‐coupled hybrid microgrids, ESSs are connected to the DC bus directly without converters.
Similar to an AC‐coupled hybrid microgrid, in DC‐coupled hybrid microgrids, multiple‐port power converters can be used to connect different input power sources to a common DC link in a unified structure.
1.2.3 AC‐DC‐Coupled Hybrid Microgrid
The structure of an AC‐DC‐coupled hybrid microgrid is shown in Figure 1.4. As seen, both DC and AC buses are available in such a system to integrate the DGs, ESSs, and loads. The AC and DC buses (or subgrids) are linked by IFCs. Different from the DC‐coupled system, the AC‐DC‐coupled hybrid microgrid has DGs and ESSs on the AC subgrid too, which requires more coordination for the voltage and power control between the DC and AC subgrids. On the other hand, similar to the DC‐coupled microgrid, parallel IFCs are desired to link AC and DC subgrids with increased capacity and reliability. In general, this structure is considered if major power sources include both DC and AC powers. This structure improves overall efficiency and reduces the system cost with a reduced number of power converters by connecting sources and loads to the AC and DC subgrids with minimized power conversion requirements.
Figure 1.4 A typical example of an AC‐DC‐coupled hybrid microgrid.
Considering these benefits, AC‐DC‐coupled hybrid microgrids will be the most promising microgrid structures in the future.
1.2.4 Examples of Hybrid Microgrids
A hybrid microgrid can exist in many different forms, such as a community, campus, institutions, commercial center, or even a microgrid in the sky or ocean like more electric aircraft (MEA) or electrified ships. Considering the rapidly increasing online activities and demand of data centers as well as the wide acceptance of electric vehicles, two examples of hybrid microgrids, data centers, and electric vehicle charging stations, are briefly presented here.
Based on an EPRI report, data centers will consume 20% of electricity in the United States by 2030, and power quality issues are a significant concern in such systems (in the United States, low power quality and unreliable power supply of data centers can result in millions of dollar losses annually). In general, data center structure can be AC‐coupled or DC‐coupled, which are shown in Figure 1.5. The traditional configuration of the data center is an AC‐couple structure, where the AC/DC and DC/DC voltage conversion happens right before the server load. In recent years, the research and implementation of DC data centers (400 V DC distribution) have seen increasing demand. This DC‐based structure effectively reduces the current and losses in the system. They also have better performance compared to AC architecture in terms of reliability, efficiency, and power quality.
Figure 1.5 Examples of a data center: (a) AC‐coupled structure, and (b) DC‐coupled structure.
The charging stations of EVs can have AC or DC structures, which are shown in Figure 1.6. For commercial EV charging stations, level 2 (single/three‐phase AC charger, around 20 kW) and level 3 (typically DC‐based fast charger greater than 20 kW) chargers are popular. In the AC‐coupled structure, all fast DC chargers are connected to a common AC‐bus through AC/DC converters, while in a DC‐coupled structure they are connected to a common DC bus. Considering the DC voltage requirement for EV batteries, the possibility of integrating renewable energy sources, higher efficiency, and better power quality, DC structures are more promising for charging stations.
Figure 1.6 Examples of the electric vehicle charging station: (a) AC‐coupled structure, and (b) DC‐coupled structure.
Moreover, EV charging stations with level 2 or 3 chargers can easily consume power in the MW level, introducing significant peak power and stress to the station's electrical system (with potentially costly upgrades required). One solution for this is to also include local energy storage to reduce peak power demand. Again, the DC‐coupled microgrid solution will ensure less AC/DC voltage conversion is required in such a charging station with battery energy storage.
As mentioned earlier, some standalone microgrids in the sky exist in the form of an MEA with a high‐frequency AC bus. In Figure 1.7, an example of an MEA structure is shown. As can be seen, in this AC‐coupled hybrid microgrid, the loads and power generators are connected to a common AC bus. The traditional loads such as starter, deicing, etc., are also powered by an electrical system to improve the overall system efficiency. The AC bus is a high‐frequency bus with variable frequency in the range 350–800 Hz. Compared to the traditional 400 Hz fixed frequency, the variable frequency allows more efficient engine operation.
Figure 1.7 The more electric aircraft as a high‐frequency AC‐coupled microgrid.
Similarly, electric ships can be considered as a standalone microgrid in the ocean. In an electric ship, the generators and loads are connected to the medium voltage DC bus on the ship to allow maximum controllability of the generators and loads to optimize the system operation with significant fuel savings.
1.3 Smart Hybrid Microgrid Operations
Different operation aspects or functions of a smart microgrid are executed at different time scales. For example, the primary control functions of IFCs (i.e. voltage and current controls) must be executed over a very short time (with control bandwidths of hundreds or thousands of hertz), especially when harmonics regulation is needed. The power and power quality management functions are also mostly waveform‐based control and need to be implemented with a high control bandwidth. On the other hand, the energy management functions with long‐term optimization objectives can be done over a relatively long time scale.
Figure 1.8 shows the basic and smart functions of smart microgrids with their expected time scales. The basic functions mainly focus on individual IFC operations while the smart functions improve smart microgrid stability, reliability, energy efficiency, and power quality. In the following, the key aspects of smart microgrid operation are briefly introduced.
Figure 1.8 Functions of a smart microgrid.
1.3.1 Distributed Generation and Energy Storage Systems
Renewable and non‐renewable energy‐based DG systems are now widely adopted in microgrids. They can supply loads without long‐distance power transmission, reducing power losses compared to traditional power grids. However, despite the benefits of DG systems, challenges are also raised due to their integration. For example, the power flow within the microgrid is bidirectional, leading to complexity in operation control and system protection. Also, the output powers of DGs are usually not compatible with the grid; thus, appropriate power converters structures with high reliability, efficiency, controllability, and power quality are essential. As another challenge, the intermittence of renewable energy‐based DG systems, such as wind or PV power systems, could lead to power fluctuations, power quality issues, or even stability problems, especially in high penetration levels.
Due to the intermittent nature of such renewable energy‐based DGs and their low inertia, the load demands and their variations cannot be satisfied at all times, particularly in standalone operation. Therefore, ESSs are required, such as batteries, fuel cells, pumped‐hydroelectric, flywheels, and supercapacitors. Some ESSs require proper power converters to be integrated into the microgrid. The ESSs should be appropriately sized to deal with the DG output variations and load demand variations. They should also be placed in a proper location, where different objectives such as improving voltage profile, reducing the system power loss, or reducing the occurrence and levels of abnormal conditions (overloads and over/under voltages) can be targeted. Furthermore, ESSs should be appropriately controlled and coordinated with DG systems to ensure system stability in steady‐state and transition operation modes of microgrids.
1.3.2 Smart Interfacing Converters
As mentioned, a key component in a modern microgrid is smart IFCs, which enable flexible power flow control and are the actuators of smart functions. Those IFCs connect renewable/non‐renewable energy‐based DGs, ESSs, and loads to the AC and DC subgrids of microgrids. The main smart functions of IFCs can be classified into three categories: (i) information‐level functions, (ii) microgrid‐level functions, and (iii) converter‐level functions.
The information‐level functions of smart IFCs are mainly focused on data communication through a cyber system. In smart microgrids, physical components, such as IFCs, are usually interconnected to cyber systems, and their operations are coupled to cyber system functionality. Smart IFCs can communicate with control centers and each other either by wireline (such as power line communication and low bandwidth communication) or wireless technologies (such as a ZigBee, WiFi, and cellular communication networks). The data communications of IFCs can help to control microgrid operations in steady‐state and transient conditions properly. Also, smart IFCs can be controlled remotely. However, as evident, an efficient, reliable, and timely data flow is required, and any cyber incidents can have devastating effects on the microgrid's operation.
The microgrid‐level functions of smart IFCs are used to realize power and energy management system objectives in a microgrid. In general, microgrid energy and power management strategies can be realized in hierarchical control. There are three control layers in hierarchical control: primary, secondary, and tertiary layers. The primary control layer contains voltage and current regulations. The objectives of the second layer include system frequency regulations and power quality compensations such as unbalanced voltage compensation, and harmonic compensation. In tertiary control, an optimization problem is usually run to achieve a global optimum operation point and determine the operating power of each power source. The short‐term power management system objectives are realized in the primary and part of the secondary control layers, while the tertiary control and part of the secondary control contain the long‐term energy management system.
The converter‐level functions are focused on proper power conversion. The IFCs track their reference powers provided by the power management and energy management strategies, using current or voltage controls. In addition, microgrid power quality control using IFCs is also part of the converter‐level functions.
1.3.3 Cyber Systems
In general, cyber networks are important for smart microgrids to coordinate, monitor, and manage distributed devices, such as power converters, circuit breakers, and meters. In detail, the cyber system provides sensor information to control units (distributed or central) and transfers the control signals to the physical components such as IFCs and relays. Although smart IFC operation in microgrids is generally autonomous, cyber network presence can improve their control performance. Also, the cyber network is critical for the entire microgrid optimal operations (i.e. energy management scheme) and restoration and black start after faults occurrence.
Since the cyber network operation can impact the physical system performance and functionality, the cyber system's high reliability and security are expected. Malfunctions of cyber systems, such as communication failure or cyber‐attacks, could adversely affect the smart microgrids' operation and stability.
1.3.4 Power Management and Energy Management Systems
In microgrids, the terms “energy management” and “power management” are different considering control tasks and time scales. The long‐term energy management schemes match the total power production to the demand. The energy management strategies use measured data from sensors and predictions data (e.g. renewable sources prediction) and consider microgrid operational requirements (e.g. appropriate level of power reserve capacity) to optimize the microgrid operation. Generally, the energy management system needs to coordinate the various devices, such as power generators, energy storage, and loads in the microgrid, or even coordinate multiple microgrids.
The objective of the short‐term power management system is to control the instantaneous operational conditions toward specific desired parameters such as voltage, current, power, and frequency within a very short time (e.g. a fundamental cycle). In other words, the power management strategies include voltage and frequency regulations, and real‐time power dispatching among the microgrid different power sources. The power management strategies should also provide a seamless and smooth transition during microgrids transition between grid‐connected and standalone modes (with minimum voltage and frequency disturbances and deviations, and ensure instantaneous power balancing of generation and demand to prevent DGs overloading and circulating powers).
1.3.5 Power Quality
Power quality issues are becoming urgent for future microgrids. They affect the operation of devices in the microgrid, including power converters, protection devices, and loads, while such device malfunctions can lead to further power quality issues. In microgrids, the integration of unbalanced/non‐linear loads and unbalanced distributed sources cause the most significant power quality issues. In addition to conventional methods to improve power quality, IFCs from DGs and ESSs can be appropriately controlled to help address such power quality challenges.
In general, the power quality issues
