Voltage-Sourced Converters in Power Systems

5

Two-Level, Three-Phase Voltage-Sourced Converter

5.1 INTRODUCTION

Chapter 2 introduced the principles of operation of the DC/AC half-bridge converter and based on the method of averaging presented an equivalent circuit and a dynamic model for the converter. In Chapter 3, the control of the half-bridge converter was studied. Chapter 4 introduced the abc- to αβ-frame transformation to reduce the complexity of the control problem for a three-phase converter system. Chapter 4 further presented the abc- to dq-frame transformation to enable the control scheme of a three-phase converter system to process DC rather than sinusoidal signals and thus to provide a simpler structure.

This chapter employs the half-bridge converter as the building block for the three-phase voltage-sourced converter (VSC). A three-phase VSC can be realized based on a variety of configurations. However, in this book we consider two main configurations: the two-level VSC and the three-level neutral-point clamped (NPC) VSC. This chapter introduces the two-level three-phase VSC as the composition of three identical half-bridge converters. In Chapter 6, we will introduce the three-level NPC three-phase VSC as the composition of six identical half-bridge converters. Hereinafter, throughout this book we refer to the two-level three-phase VSC as two-level VSC and to the three-level NPC three-phase VSC as three-level NPC.¹

5.2 TWO-LEVEL VOLTAGE-SOURCED CONVERTER

5.2.1 Circuit Structure

Figure 5.1 shows a schematic diagram ...