Distributed Control Methods and Cyber Security Issues in Microgrids

Distributed Control Methods and Cyber Security Issues in Microgrids
Author: Wenchao Meng,Xiaoyu Wang,Shichao Liu
Publsiher: Academic Press
Total Pages: 296
Release: 2020-03-22
ISBN 10: 0128169478
ISBN 13: 9780128169476
Language: EN, FR, DE, ES & NL

Distributed Control Methods and Cyber Security Issues in Microgrids Book Review:

Distributed Control and Cyber Security Issues in Microgrids presents a thorough treatment of distributed control methods and cyber security issues for power system researchers and engineers. With the help of mathematical tools, this reference gives a deep understanding of microgrids and new research directions, addressing emerging concepts, methodologies and applications of monitoring, control and protection in smart microgrids with large-scale renewables. With the integration of more distributed or aggregated renewables and the wide utilization of power electronic devices, the smart microgrid is facing new stability and security challenges. Includes global case studies to demonstrate distributed control success stories Offers detailed illustrations and flowcharts to address challenges and technical solutions for those working in power systems in utilities and industry Showcases new challenges faced in the stability and security of smart microgrids

Modeling and Control of Static Converters for Hybrid Storage Systems

Modeling and Control of Static Converters for Hybrid Storage Systems
Author: Fekik, Arezki,Benamrouche, Nacereddine
Publsiher: IGI Global
Total Pages: 355
Release: 2021-09-17
ISBN 10: 1799874494
ISBN 13: 9781799874492
Language: EN, FR, DE, ES & NL

Modeling and Control of Static Converters for Hybrid Storage Systems Book Review:

The energy transition initiated in recent years has enabled the growing integration of renewable production into the energy mix. Microgrids make it possible to maximize the efficiency of energy transmission from source to consumer by bringing the latter together geographically and by reducing losses linked to transport. However, the lack of inertia and the micro-grid support system makes it weak, and energy storage is necessary to ensure its proper functioning. Current storage technologies do not make it possible to provide both a large capacity of energy and power at the same time. Hybrid storage is a solution that combines the advantages of several technologies and reduces their disadvantages. Modeling and Control of Static Converters for Hybrid Storage Systems covers the modeling, control theorems, and optimization techniques that solve many scientific problems for researchers in the field of power converter control for renewable energy hybrid storage and places particular emphasis on the modeling and control of static converters for hybrid storage systems. Covering topics ranging from energy storage to power generation, this book is ideal for automation engineers, electrical engineers, mechanical engineers, professionals, scientists, academicians, master's and doctoral students, and researchers in the disciplines of electrical and mechanical engineering.

Microgrids

Microgrids
Author: Amjad Anvari-Moghaddam,Hamdi Abdi,Behnam Mohammadi-Ivatloo,Nikos Hatziargyriou
Publsiher: Springer Nature
Total Pages: 643
Release: 2021-04-16
ISBN 10: 3030597504
ISBN 13: 9783030597504
Language: EN, FR, DE, ES & NL

Microgrids Book Review:

This book provides a comprehensive overview on the latest developments in the control, operation, and protection of microgrids. It provides readers with a solid approach to analyzing and understanding the salient features of modern control and operation management techniques applied to these systems, and presents practical methods with examples and case studies from actual and modeled microgrids. The book also discusses emerging concepts, key drivers and new players in microgrids, and local energy markets while addressing various aspects from day-ahead scheduling to real-time testing of microgrids. The book will be a valuable resource for researchers who are focused on control concepts, AC, DC, and AC/DC microgrids, as well as those working in the related areas of energy engineering, operations research and its applications to energy systems. Presents modern operation, control and protection techniques with applications to real world and emulated microgrids; Discusses emerging concepts, key drivers and new players in microgrids and local energy markets; Addresses various aspects from day-ahead scheduling to real-time testing of microgrids.

Energy Internet and We Energy

Energy Internet and We Energy
Author: Qiuye Sun
Publsiher: Springer
Total Pages: 325
Release: 2018-07-12
ISBN 10: 9811305234
ISBN 13: 9789811305238
Language: EN, FR, DE, ES & NL

Energy Internet and We Energy Book Review:

This book focuses on the framework and implementation of energy integration systems with energy and smart-control technologies. It describes in detail We-Energy, a novel energy interaction mode based on a cyber-physical-economy-energy model, which can be adopted to solve the problem of energy supply and utilization. It then analyzes the key devices and technologies for developing the Energy Internet, such as converters, energy-conversion devices, system-level connection devices, optimization control strategies, cyber-physical system security, energy-system stability, communication technologies’ operating modes and distributed optimization algorithms, to enable readers to gain a comprehensive understanding of the topic. Lastly, it offers an outlook on the development of the Energy Internet, providing a reference for cross-integration between different disciplines. The book is an indispensable resource for power enterprises, manufacturers in the power-supply industry, and researchers in the field of Energy Internet application. It is also useful for university and college teachers and students seeking to deepen their understanding of the Energy Internet, as well as for readers interested in the Energy Internet correlation techniques.

Advances and Technologies in High Voltage Power Systems Operation Control Protection and Security

Advances and Technologies in High Voltage Power Systems Operation  Control  Protection and Security
Author: Hassan Haes Alhelou,Pierluigi Siano
Publsiher: MDPI
Total Pages: 208
Release: 2021-08-30
ISBN 10: 3036511407
ISBN 13: 9783036511405
Language: EN, FR, DE, ES & NL

Advances and Technologies in High Voltage Power Systems Operation Control Protection and Security Book Review:

The electrical demands in several countries around the world are increasing due to the huge energy requirements of prosperous economies and the human activities of modern life. In order to economically transfer electrical powers from the generation side to the demand side, these powers need to be transferred at high-voltage levels through suitable transmission systems and power substations. To this end, high-voltage transmission systems and power substations are in demand. Actually, they are at the heart of interconnected power systems, in which any faults might lead to unsuitable consequences, abnormal operation situations, security issues, and even power cuts and blackouts. In order to cope with the ever-increasing operation and control complexity and security in interconnected high-voltage power systems, new architectures, concepts, algorithms, and procedures are essential. This book aims to encourage researchers to address the technical issues and research gaps in high-voltage transmission systems and power substations in modern energy systems.

Microgrid Architectures Control and Protection Methods

Microgrid Architectures  Control and Protection Methods
Author: Naser Mahdavi Tabatabaei,Ersan Kabalci,Nicu Bizon
Publsiher: Springer
Total Pages: 781
Release: 2019-08-01
ISBN 10: 3030237230
ISBN 13: 9783030237233
Language: EN, FR, DE, ES & NL

Microgrid Architectures Control and Protection Methods Book Review:

This book presents intuitive explanations of the principles of microgrids, including their structure and operation and their applications. It also discusses the latest research on microgrid control and protection technologies and the essentials of microgrids as well as enhanced communication systems. The book provides solutions to microgrid operation and planning issues using various methodologies including planning and modelling; AC and DC hybrid microgrids; energy storage systems in microgrids; and optimal microgrid operational planning. Written by specialists, it is filled in innovative solutions and research related to microgrid operation, making it a valuable resource for those interested in developing updated approaches in electric power analysis, design and operational strategies. Thanks to its in-depth explanations and clear, three-part structure, it is useful for electrical engineering students, researchers and technicians.

Smart Microgrids

Smart Microgrids
Author: Sasi K. Kottayil
Publsiher: CRC Press
Total Pages: 263
Release: 2020-08-18
ISBN 10: 1000166104
ISBN 13: 9781000166101
Language: EN, FR, DE, ES & NL

Smart Microgrids Book Review:

This book addresses the need to understand the development, use, construction, and operation of smart microgrids (SMG). Covering selected major operations of SMG like dynamic energy management, demand response, and demand dispatch, it describes the design and operational challenges of different microgrids and provides feasible solutions for systems. Smart Micro Grid presents communication technologies and governing standards used in developing communication networks for realizing various smart services and applications in microgrids. An architecture facilitating bidirectional communication for smart distribution/microgrid is brought out covering aspects of its design, development and validation. The book is aimed at graduate, research students and professionals in power, power systems, and power electronics. Features: • Covers a broad overview of the benefits, the design and operation requirements, standards and communication requirements for deploying microgrids in distribution systems. • Explores issues related to planning, expansion, operation, type of microgrids, interaction among microgrid and distribution networks, demand response, and the technical requirements for the communication network. • Discusses current standards and common practices to develop and operate microgrids. • Describes technical issues and requirements for operating microgrids. • Illustrates smart communication architecture and protocols.

Exploring Cyber Security Issues and Solutions for Various Components of DC Microgrid System

Exploring Cyber Security Issues and Solutions for Various Components of DC Microgrid System
Author: Sultana Razia Akhter
Publsiher: Unknown
Total Pages: 135
Release: 2018
ISBN 10: 1928374650XXX
ISBN 13: OCLC:1125015563
Language: EN, FR, DE, ES & NL

Exploring Cyber Security Issues and Solutions for Various Components of DC Microgrid System Book Review:

Nowadays, considering the growing demand for the DC loads and simplified interface with renewable power generation sources, DC microgrids could be cost effective solution for the power supply in small scale area. the supervisory control and data acquisition (SCADA) system maintain the bidirectional power communication through the internet connectivity with the microgrid. However, this intelligent and interactive feature may pose a cyber-security threat to the power grid. this work aims to exploring cyber-security issues and their solutions for the DC microgrid system. To mitigate the adverse effects of various cyber-attacks such as the False Data Injection (FDI) attack, Distributed Denial of Service (DDoS) attack etc., two new techniques based on non-linear and proportional-integral (PI) controllers have been proposed. Simulation results obtained from MATLAB/Simulink software demonstrate the effectiveness of the proposed methods in mitigating the adverse effects of cyber-attacks on the DCMG system performance. .

Networked Microgrids

Networked Microgrids
Author: Peng Zhang
Publsiher: Cambridge University Press
Total Pages: 234
Release: 2021-04-30
ISBN 10: 1108497659
ISBN 13: 9781108497657
Language: EN, FR, DE, ES & NL

Networked Microgrids Book Review:

Discover scalable, dependable, intelligent solutions for integrating complex networked microgrids with this definitive guide. Combining resilient control, fast programmable networking, reachability analysis, and cyber-physical security, this is essential reading for researchers, professional engineers, and graduate students.

Decision Making Applications in Modern Power Systems

Decision Making Applications in Modern Power Systems
Author: Shady H.E. Abdel Aleem,Almoataz Youssef Abdelaziz,Ahmed F. Zobaa,Ramesh Bansal
Publsiher: Academic Press
Total Pages: 576
Release: 2019-09-21
ISBN 10: 0128166266
ISBN 13: 9780128166260
Language: EN, FR, DE, ES & NL

Decision Making Applications in Modern Power Systems Book Review:

Decision Making Applications in Modern Power Systems presents an enhanced decision-making framework for power systems. Designed as an introduction to enhanced electricity system analysis using decision-making tools, it provides an overview of the different elements, levels and actors involved within an integrated framework for decision-making in the power sector. In addition, it presents a state-of-play on current energy systems, strategies, alternatives, viewpoints and priorities in support of decision-making in the electric power sector, including discussions of energy storage and smart grids. As a practical training guide on theoretical developments and the application of advanced methods for practical electrical energy engineering problems, this reference is ideal for use in establishing medium-term and long-term strategic plans for the electric power and energy sectors. Provides panoramic coverage of state-of-the-art energy systems, strategies and priorities in support of electrical power decision-making Introduces innovative research outcomes, programs, algorithms and approaches to address challenges in understanding, creating and managing complex techno-socio-economic engineering systems Includes practical training on theoretical developments and the application of advanced methods for realistic electrical energy engineering problems

Microgrid

Microgrid
Author: Magdi S Mahmoud
Publsiher: Elsevier
Total Pages: 398
Release: 2016-10-24
ISBN 10: 0081012624
ISBN 13: 9780081012628
Language: EN, FR, DE, ES & NL

Microgrid Book Review:

Microgrids: Advanced Control Methods and Renewable Energy System Integration demonstrates the state-of-art of methods and applications of microgrid control, with eleven concise and comprehensive chapters. The first three chapters provide an overview of the control methods of microgrid systems that is followed by a review of distributed control and management strategies for the next generation microgrids. Next, the book identifies future research directions and discusses the hierarchical power sharing control in DC Microgrids. Chapter 4 investigates the demand side management in microgrid control systems from various perspectives, followed by an outline of the operation and controls of the smart microgrids in Chapter 5. Chapter 6 deals with control of low-voltage microgrids with master/slave architecture. The final chapters explain the load-Frequency Controllers for Distributed Power System Generation Units and the issue of robust control design for VSIs, followed by a communication solution denoted as power talk. Finally, in Chapter 11, real-time implementation of distributed control for an autonomous microgrid system is performed. Addresses issues of contemporary interest to practitioners in the power engineering and management fields Focuses on the role of microgrids within the overall power system structure and attempts to clarify the main findings relating to primary and secondary control and management at the microgrid level Provides results from a quantified assessment of benefits from economic, environmental, operational, and social point-of-views Presents the hierarchical control levels manifested in microgrid operations and evaluates the principles and main functions of centralized and decentralized control

Smart Hybrid AC DC Microgrids

Smart Hybrid AC DC Microgrids
Author: Farzam Nejabatkhah,Hao Tian,Yunwei Ryan Li
Publsiher: John Wiley & Sons
Total Pages: 420
Release: 2022-08-17
ISBN 10: 1119598397
ISBN 13: 9781119598398
Language: EN, FR, DE, ES & NL

Smart Hybrid AC DC Microgrids Book Review:

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.

Integration of AC DC Microgrids into Power Grids

Integration of AC DC Microgrids into Power Grids
Author: Fazel Mohammadi
Publsiher: MDPI
Total Pages: 154
Release: 2020-12-02
ISBN 10: 3039361805
ISBN 13: 9783039361809
Language: EN, FR, DE, ES & NL

Integration of AC DC Microgrids into Power Grids Book Review:

AC/DC Microgrids are a small part of low voltage distribution networks that are located far from power substations, and are interconnected through the point of common coupling to power grids. These systems are important keys for the flexible, techno-economic, and environmental-friendly generation of units for the reliable operation and cost-effective planning of smart electricity grids. Although AC/DC microgrids, with the integration of renewable energy resources and other energy systems, such as power-to-gas, combined heat and power, combined cooling heat and power, power-to-heat, power-to-vehicle, pump and compressed air storage, have several advantages, there are some technical aspects that must be addressed. This Special Issue aims to study the configuration, impacts, and prospects of AC/DC microgrids that enable enhanced solutions for intelligent and optimized electricity systems, energy storage systems, and demand-side management in power grids with an increasing share of distributed energy resources. It includes AC/DC microgrid modeling, simulation, control, operation, protection, dynamics, planning, reliability and security, as well as considering power quality improvement, load forecasting, market operations, energy conversion, cyber/physical security, supervisory and monitoring, diagnostics and prognostics systems.

Control and Optimization of Distributed Generation Systems

Control and Optimization of Distributed Generation Systems
Author: Magdi S. Mahmoud,Fouad M. AL-Sunni
Publsiher: Springer
Total Pages: 578
Release: 2015-05-14
ISBN 10: 3319169106
ISBN 13: 9783319169101
Language: EN, FR, DE, ES & NL

Control and Optimization of Distributed Generation Systems Book Review:

This text is an introduction to the use of control in distributed power generation. It shows the reader how reliable control can be achieved so as to realize the potential of small networks of diverse energy sources, either singly or in coordination, for meeting concerns of energy cost, energy security and environmental protection. The book demonstrates how such microgrids, interconnecting groups of generating units and loads within a local area, can be an effective means of balancing electrical supply and demand. It takes advantage of the ability to connect and disconnect microgrids from the main body of the power grid to give flexibility in response to special events, planned or unplanned. In order to capture the main opportunities for expanding the power grid and to present the plethora of associated open problems in control theory Control and Optimization of Distributed Generation Systems is organized to treat three key themes, namely: system architecture and integration; modelling and analysis; and communications and control. Each chapter makes use of examples and simulations and appropriate problems to help the reader study. Tools helpful to the reader in accessing the mathematical analysis presented within the main body of the book are given in an appendix. Control and Optimization of Distributed Generation Systems will enable readers new to the field of distributed power generation and networked control, whether experienced academic migrating from another field or graduate student beginning a research career, to familiarize themselves with the important points of the control and regulation of microgrids. It will also be useful for practising power engineers wishing to keep abreast of changes in power grids necessitated by the diversification of generating methods.

Cooperative Optimal Control of Hybrid Energy Systems

Cooperative Optimal Control of Hybrid Energy Systems
Author: Dong Yue,Huifeng Zhang,Chunxia Dou
Publsiher: Springer Nature
Total Pages: 372
Release: 2021-02-15
ISBN 10: 9813367229
ISBN 13: 9789813367227
Language: EN, FR, DE, ES & NL

Cooperative Optimal Control of Hybrid Energy Systems Book Review:

This book mainly investigates the cooperative optimal control of hybrid energy system, it presents security control, multi-objective optimization, distributed optimization and distributed control approaches for tackling with security, economic and stability problem of the hybrid energy system. It aims to solve some challenging problems including security issue, economic cost or benefits from both power generation side and load demand side, and coordination among different power generators. The methods proposed in this book is novel and attractive, it consists of the hierarchical optimal control strategy for the security issue, multi-objective optimization for both economic and emission issue, and distributed optimal control for coordination among power generators. Readers can learn novel methods or technique for tackling with the security issue, multiple-objective problem, and distributed coordination problem. It also may inspire readers to improve some drawbacks of existing alternatives. Some fundamental knowledge prepared to read this book includes basic principles of the multi-agents system, robust optimization, Pareto-dominance optimization, and background of electrical engineering and renewable energy.

Power Systems Resilience

Power Systems Resilience
Author: Naser Mahdavi Tabatabaei,Sajad Najafi Ravadanegh,Nicu Bizon
Publsiher: Springer
Total Pages: 353
Release: 2018-08-16
ISBN 10: 3319944428
ISBN 13: 9783319944425
Language: EN, FR, DE, ES & NL

Power Systems Resilience Book Review:

This book presents intuitive explanations of the principles and applications of power system resiliency, as well as a number of straightforward and practical methods for the impact analysis of risk events on power system operations. It also describes the challenges of modelling, distribution networks, optimal scheduling, multi-stage planning, deliberate attacks, cyber-physical systems and SCADA-based smart grids, and how to overcome these challenges. Further, it highlights the resiliency issues using various methods, including strengthening the system against high impact events with low frequency and the fast recovery of the system properties. A large number of specialists have collaborated to provide innovative solutions and research in power systems resiliency. They discuss the fundamentals and contemporary materials of power systems resiliency, theoretical and practical issues, as well as current issues and methods for controlling the risk attacks and other threats to AC power systems. The book includes theoretical research, significant results, case studies, and practical implementation processes to offer insights into electric power and engineering and energy systems. Showing how systems should respond in case of malicious attacks, and helping readers to decide on the best approaches, this book is essential reading for electrical engineers, researchers and specialists. The book is also useful as a reference for undergraduate and graduate students studying the resiliency and reliability of power systems.

Distributed Energy Resources in Microgrids

Distributed Energy Resources in Microgrids
Author: Rajeev Kumar Chauhan,Kalpana Chauhan
Publsiher: Academic Press
Total Pages: 554
Release: 2019-08-17
ISBN 10: 0128177756
ISBN 13: 9780128177754
Language: EN, FR, DE, ES & NL

Distributed Energy Resources in Microgrids Book Review:

Distributed Energy Resources in Microgrids: Integration, Challenges and Optimization unifies classically unconnected aspects of microgrids by considering them alongside economic analysis and stability testing. In addition, the book presents well-founded mathematical analyses on how to technically and economically optimize microgrids via distributed energy resource integration. Researchers and engineers in the power and energy sector will find this information useful for combined scientific and economical approaches to microgrid integration. Specific sections cover microgrid performance, including key technical elements, such as control design, stability analysis, power quality, reliability and resiliency in microgrid operation. Addresses the challenges related to the integration of renewable energy resources Includes examples of control algorithms adopted during integration Presents detailed methods of optimization to enhance successful integration

Borrego Springs Microgrid Demonstration Project

Borrego Springs Microgrid Demonstration Project
Author: Thomas Bialek,San Diego Gas and Electric Company,Horizon Energy Group
Publsiher: Unknown
Total Pages: 71
Release: 2013
ISBN 10: 1928374650XXX
ISBN 13: UCSD:31822039255054
Language: EN, FR, DE, ES & NL

Borrego Springs Microgrid Demonstration Project Book Review:

Smart Microgrids

Smart Microgrids
Author: Shahab Bahrami,Ali Mohammadi
Publsiher: Springer
Total Pages: 141
Release: 2019-01-17
ISBN 10: 3030026566
ISBN 13: 9783030026561
Language: EN, FR, DE, ES & NL

Smart Microgrids Book Review:

In this book the authors first provide a comprehensive survey on the available studies on control, management, and optimization strategies in AC and DC microgrids. The authors then provide the design of a laboratory-scale microgrid system. Finally, a real-world implementation of the deigned framework is provided. This book paves the way for researchers working on the smart microgrids spread over the fields of electrical engineering, power systems, and smart infrastructures. Furthermore, it provides the readers with a comprehensive insight to understand an in-depth big picture of smart microgrids as well as an all-inclusive framework for laboratory-scale implementation of a microgrid. It is suitable for senior undergraduate students, graduate students who are interested in research in areas related to future smart grids and microgrids, and the researchers working in the related areas. This book also can be used as a reference book for researchers who want to develop laboratories on smart microgrids for future research.

Microgrid Cyberphysical Systems

Microgrid Cyberphysical Systems
Author: Bidyadhar Subudhi,Pravat Kumar Ray
Publsiher: Elsevier
Total Pages: 298
Release: 2022-06-14
ISBN 10: 0323983995
ISBN 13: 9780323983990
Language: EN, FR, DE, ES & NL

Microgrid Cyberphysical Systems Book Review:

Microgrid Cyberphysical Systems: Renewable Energy and Plug-in Vehicle Integration outlines the fundamental concepts on microgrid system design and control in a cyberphysical framework, focusing on the integration of renewables and EVs into microgrids. Including operational, control and management perspectives, the volume aims to optimize the reliability and economic performance of microgrids, focusing on power quality, storage and voltage and frequency control. The work encompasses generation, transmission, protection and load management under uncertainty and discusses critical drivers in robustness, uncertainty and sustainability management. Focusing on applied implementations, chapters are supported by detailed methods, heavy figurative explication, and comparative and integrative analysis. Case studies range across chapters. In addition, chapters are supported by representative experimental or test bed validations of proposed algorithms or methods which can be directly applied to reader problems. Provides advanced controller methodologies to efficiently optimize the operation of microgrids with high levels of connected renewable generators and electric vehicles Explores powerful approaches for the prevention of cyberattacks in microgrid systems Addresses design issues for power quality filters suitable for microgrid robustness, uncertainty and sustainability handling Includes field-tested methods, heavy case studies and an implementation focus with supporting experimental or test bed validations of proposed algorithms or methods in MATLAB