Multi-terminal Direct-Current Grids: Modeling, Analysis, and Control

Chapter 2The Voltage-Sourced Converter (VSC)

2.1 Introduction

The voltage-sourced converter (VSC) would constitute the backbone of future MTDC grids. A VSC interfaces an AC grid with a DC grid and enables an efficient bidirectional trade of energy between the two. More specifically, (1) it may impress the voltage of the DC grid and then let the energy flow result based on the prevailing conditions or, alternatively, (2) operate off an impressed DC voltage (e.g., impressed by one or more other VSCs interfaced with the same DC grid). In addition, it can exchange (in either direction) a pre-specified amount of reactive power with the AC grid. The aforementioned functionalities are realized by a circuit comprising power diodes, semiconductor power switches with turn-off capability, inductors, and capacitors. As circuit elements, resistors are avoided, but they inevitably exist as parasitic elements.

Adopting a generalized approach, this chapter discusses the modeling, control, and simulation of the VSC.

2.2 Ideal Voltage-Sourced Converter

Consider the system of Fig. 2.1 in which a five-terminal device, labeled as the ideal VSC, serves as an energy transfer medium between a DC grid and an AC grid. As Fig. 2.1 indicates, the two left-hand side terminals of the ideal VSC identify a port, referred in this book to as the DC side, whose voltage and current are denoted by, respectively, and (both functions of time, in general); a positive current is assumed to be one entering the ...