Predictive Control of Power Converters and Electrical Drives

Jose Rodriguez, Patricio Cortes

• Publisher: Wiley-IEEE Press
• Year: 2012
• ISBN:
  9781119942641
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Power Resources
• Index: Technology & Engineering

Describes the general principles and current research into Model Predictive Control (MPC); the most up-to-date control method for power converters and drives

The book starts with an introduction to the subject before the first chapter on classical control methods for power converters and drives. This covers classical converter control methods and classical electrical drives control methods. The next chapter on Model predictive control first looks at predictive control methods for power converters and drives and presents the basic principles of MPC. It then looks at MPC for power electronics and drives. The third chapter is on predictive control applied to power converters. It discusses: control of a three-phase inverter; control of a neutral point clamped inverter; control of an active front end rectifier, and; control of a matrix converter. In the middle of the book there is Chapter four - Predictive control applied to motor drives. This section analyses predictive torque control of industrial machines and predictive control of permanent magnet synchronous motors. Design and implementation issues of model predictive control is the subject of the final chapter. The following topics are described in detail: cost function selection; weighting factors design; delay compensation; effect of model errors, and prediction of future references. While there are hundreds of books teaching control of electrical energy using pulse width modulation, this will be the very first book published in this new topic.

• Unique in presenting a completely new theoretic solution to control electric power in a simple way
• Discusses the application of predictive control in motor drives, with several examples and case studies
• Matlab is included on a complementary website so the reader can run their own simulations

Part One

Introduction

Chapter 1

Introduction

In the last few decades, the use of power converters and high-performance adjustable speed drives has gained an increased presence in a wide range of applications, mainly due to improved performance and higher efficiency, which lead to increased production rates. In this way, power converters and drives have become an enabling technology in most industrial sectors, with many applications in a wide variety of systems. Conversion and control of electrical energy using power electronics is a very important topic today, considering the increasing energy demands and new requirements in terms of power quality and efficiency. In order to fulfill these demands new semiconductor devices, topologies, and control schemes are being developed.

This chapter presents a basic introduction and useful references for readers who are not familiar with power converters, motor drives, and their applications. The most common applications that involve the use of power converters are presented, and a general scheme for a drive system is explained. The power converter topologies found in industry are introduced according to a simple classification. A brief introduction to control schemes for power converters, the basic concepts behind them and the digital implementation technologies used today, are discussed.

This chapter provides the necessary context, including a brief motivation for the use of predictive control, to understand the contents of this book.

1.1 Applications of Power Converters and Drives

Power converters and drives are used in diverse sectors, ranging from industrial to residential applications [1, 2]. Several application examples for different sectors are shown in Figure 1.1, where a diagram of the system configuration is shown as an example for each group, marked with *.

Figure 1.1 Power converter applications

From the drive applications used in industry, pumps and fans are those that account for most of the energy consumption, with power ratings up to several megawatts. The use of adjustable speed drives can bring important benefits to these kinds of systems in terms of performance and efficiency. Many interesting applications of high-power drives can be found in the mining industry, for example, in downhill belt conveyors. A block diagram of one of these systems is shown in Figure 1.1, where three-level converters with active front-end rectifiers are used for regenerative operation, that is, power flowing from the motors to the grid [3, 4].

Common applications of drives can be found in transportation, where electric motors are used for traction and propulsion. In electric trains, the power is transferred from the overhead lines to the motors using a power converter like the one shown in the figure. This converter generates the required voltages for controlling the torque and speed of the electric motor. High-power drives can be found in ships, where diesel engines are used as generators and the propulsion is generated by electric motors. Newer applications in transportation can be found in electric and hybrid vehicles, and in aircraft.

The use of power converters in renewable energy conversion systems has been constantly increasing in recent years, mainly due to growing energy demands and environmental concerns. Among the different renewable energy sources, photovoltaic (PV) generation systems are a very interesting example of power converter applications because it is not possible to deliver power from the PV panel to the grid without a converter. An example of a power converter for a PV system is shown in Figure 1.1, composed of a DC–DC converter for optimal operation of the panel and an inverter for injection of sinusoidal currents to the grid. The use of power converters and drives in wind generation systems allows optimization of the amount of energy extracted from the wind and compliance with the new grid regulations that impose restrictions on the power quality and performance of the system [5].

The use of power converters can help to improve the quality and stability of the grid. Some examples of power converters with applications in power systems are active filters, converters for distributed generation, energy storage systems, static VAR compensators (STATCOM), and others. A diagram of an active filter application is also shown in Figure 1.1, where the power converter generates the required currents for compensating the distorted currents generated by a nonlinear load. In this way, distortion of the grid voltage is avoided.

Low-power drives and converters offer many possibilities in residential applications. The use of adjustable speed drives can increase the efficiency of systems like air conditioners and other home appliances [1, 6].

1.2 Types of Power Converters

There are many types of power converters and drive systems, and every application requires different specifications that define the most appropriate topology and control scheme to be used. A general scheme for a drive system and a simple classification of the different types of power converters are presented next.

1.2.1 Generic Drive System

A block diagram and a picture of a real drive system are shown in Figure 1.2. The main components of the system are the line-side transformer, the rectifier, the DC link, the inverter, the electrical machine, and the control unit. Depending on the system requirements, the rectifier can be a diode rectifier or an active front-end rectifier. The DC link is composed of capacitors or inductors, depending on the topology of the inverter and rectifier, whose purpose is to store energy and decouple the operation of the inverter and rectifier. The inverter modulates the DC link voltage (or current) and generates a voltage whose fundamental component can be adjusted in amplitude, frequency, and phase, in order to control the torque and speed of the machine. The control unit samples voltage and current measurements of the most important variables and generates the gate drive signals for the power semiconductor devices.

Figure 1.2 General motor drive system (AFE = Active Front-End)

As can be observed in Figure 1.2, the drive system requires several additional elements for proper operation, such as transformers, input and output passive filters, and a cooling system for the switching devices.

1.2.2 Classification of Power Converters

Power converters are composed of power semiconductor switches and passive components. They can be classified according to several criteria. A very simple and useful classification considers the type of conversion from input to output that the system performs, in terms of alternating current (AC) and direct current (DC). This leads to four main types of power converters:

AC–DC Conversion from AC to regulated or unregulated DC voltage or current.

DC–DC Conversion from a DC input voltage to a DC output voltage, providing regulation of the output voltage and isolation (optional).

DC–AC Conversion from a DC voltage or current to an AC voltage or current with controlled (variable) amplitude, frequency, and phase.

AC–AC Conversion from an AC voltage with fixed magnitude and frequency to an AC voltage with controlled (variable) amplitude and frequency.

Each one of these types includes several subcategories, as depicted in Figure 1.3. Some examples of different types of power converters will be described and analyzed in this book.

Figure 1.3 Power converter classification (PWM − CSI = ...

Table of contents

• Cover
• Title Page
• Copyright
• Foreword
• Preface
• Acknowledgments
• Part One: Introduction
• Part Two: Model Predictive Control Applied to Power Converters
• Part Three: Model Predictive Control Applied to Motor Drives
• Part Four: Design and Implementation Issues of Model Predictive Control
• Appendix A: Predictive Control Simulation—Three-Phase Inverter
• Appendix B: Predictive Control Simulation—Torque Control of an Induction Machine Fed by a Two-Level Voltage Source Inverter
• Appendix C: Predictive Control Simulation—Matrix Converter
• Index