Microgrid

Advanced Control Methods and Renewable Energy System Integration

Magdi S. Mahmoud

• Publisher: Butterworth-Heinemann
• Year: 2016
• Print ISBN: 9780081017531
• eBook ISBN: 9780081012628
• Topic: Tecnologia e ingegneria
• Subtopic: Ingegneria elettronica e telecomunicazioni

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

Chapter 1

Microgrid Control Problems and Related Issues

M.S. Mahmoud King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia

Abstract

A microgrid comprises distributed generation, energy storage, loads, and a control system that is capable of operating in grid-connected mode and/or islanded mode. As operation modes are shifted, the microgrid should successfully manage the voltage and frequency adjustment so as to protect the grid and any loads connected to the system. This chapter presents an overall description and a comprehensive study of energy storage devices, microgrid loads, distributed energy resources, and power electronic interface modules in microgrids. It is emphasized that the coordinated control of distributed energy resources can be achieved by various techniques, ranging from a basically centralized control approach to a fully decentralized approach, depending on the share of responsibilities assumed by a central controller and the local controllers of the distributed generation units and flexible loads.

Keywords

Microgrid components; Microgrid operation; Microgrid control; Distributed generation

Acknowledgments

This work is supported by the Deanship of Scientific Research (DSR) at King Fahd University of Petroleum and Minerals (KFUPM) through book writing research project no. BW 151004.

1 Introduction

Economic challenges, technological advancements, and environmental impacts are now demanding distributed generation in place of conventional centralized generation [1]. Power supply companies are now confronted with unprecedented difficulties in terms of meeting the load requirements, consumer satisfaction, and environmental considerations. Thus distributed generation has received much attention because of its potential to alleviate pressure from the main transmission system by supplying a few local loads [2]. The waste heat generated from the fuel-to-electricity conversion is used by the distributed generation system with the help of microturbines, reciprocating engines, and fuel cells to provide heat and power to customers. Adding to the system distributed energy sources such as photovoltaic panels, wind turbines, energy storage devices such as batteries and capacitors, generators extracting energy from other renewables, and controllable loads can provide momentous contributions to future energy generation and distribution. Another noteworthy feature is that the carbon dioxide emission is reduced to a large extent, satisfying the commitment of many nations concerning a decrease of carbon footprints [3]. However, distributed generation faces technical issues regarding its connection to intermittent renewable generation and feeble areas of the distribution network. Further, owing to the distinct behavior of distributed generation unlike the conventional load, alteration in power flow results in problems. To counter the irregular behavior and increasing penetration of distributed generation, the microgrid was introduced.

The microgrid has entered into distributed generation and looks promising for future aspects. It has the ability to respond to changes in the load, while decreasing feeder losses and improving local reliability. Basically designed to cater for the heat and power requirements of local customers, it can serve as an in-interruptible power supply for critical loads.

The concept of a microgrid has received considerable attention owing to its potential to serve as an alternative power source, utilizing unconventional sources and supplying the most critical loads of the main grid in the case of a network failure. Microgrids are low-voltage networks or distributed energy systems that provide heat and power to a particular area by employing generators and loads. They have the ability to operate independently and isolate themselves from the main grid in the case of a fault [4–16].

If proper control techniques are implemented, they may improve the reliability of electrical energy supply. A microgrid can have microturbines, wind turbines, fuel cells, photovoltaic cells, etc., as sources of energy that are interfaced with the help of power electronic converters. All these units are connected to the main grid through a point of common coupling and look like a solitary unit to the distribution network. No additional inertia is added to the system from the distributed generation units. However, because of this, the power balance among generation and load and the network frequency becomes complicated to maintain, especially when the microgrid is in islanded mode [17]. The microgrid operates in two modes: namely, grid-connected mode and islanded mode.

A comparison between a conventional power grid and a microgrid is presented in Table 1.1 to appreciate the role of renewable energy resources.

Table 1.1

Comparison between the conventional grid and a microgrid [18]

Conventional grid	Smart grid
Electromechanical	Digital
One-way communication	Two-way communication
Centralized generation	Distributed generation
Few sensors	Senors throughout
Manual monitoring	Self-monitoring
Manual restoration	Self-healing
Failures and blackouts	Adaptive and islanding
Limited control	Pervasive control
Few customer choices	Many customer choices

2 Microgrid Review

Following the standards of the Consortium for Electric Reliability Technology Solutions (CERTS) architecture [19, 20], a basic microgrid architecture is shown in Fig. 1.1.

Fig. 1.1 Wide-sense microgrid architecture.

A microgrid is an interconnection of [3]:

• Distributed energy sources, such as microturbines, wind turbines, fuel cells, and photovoltaics.

• Storage devices for energy integration, such as batteries, flywheels, and power capacitors on low-voltage distribution systems.

• A group of radial feeders, which could be part of a distribution system. There are three sensitive-load feeders (feeders A–C) and one nonsensitive-load feeder (feeder D):

1. The sensitive-load feeders contain sensitive loads that must always be supplied; thus each feeder must have at least a microsource rated to satisfy the load at that feeder.

2. The nonsensitive-load feeder is the feeder that ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• About the Editor
• Preface
• Acknowledgments
• Chapter 1: Microgrid Control Problems and Related Issues
• Chapter 2: Distributed Control Techniques in Microgrids
• Chapter 3: Hierarchical Power Sharing Control in DC Microgrids
• Chapter 4: Master/Slave Power-Based Control of Low-Voltage Microgrids
• Chapter 5: Online Adaptive Learning Control Schemes for Microgrids
• Chapter 6: An Optimization Approach to Design Robust Controller for Voltage Source Inverters
• Chapter 7: Demand Side Management in Microgrid Control Systems
• Chapter 8: Towards a Concept of Cooperating Power Network for Energy Management and Control of Microgrids
• Chapter 9: Power Electronics for Microgrids: Concepts and Future Trends
• Chapter 10: Power Electronic Converters in Microgrid Applications
• Chapter 11: Power Talk: Communication in a DC Microgrid Through Modulation of the Power Electronics Components
• Chapter 12: Pilot-Scale Implementation of Coordinated Control for Autonomous Microgrids
• Index