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

Chapter 1Fundamentals

1.1 Introduction

Commercial supply of electric power began in the late 1880s through electrification of the Wall Street area in New York City using direct current (DC) technology pioneered by Thomas Alva Edison. It was driven by the availability of DC generators and incandescent bulbs working with DC. Use of DC was the only option for electric supply until Nicola Tesla advocated for the use of alternating current (AC) form. Amidst fierce competition and lobbying for both DC and AC options, historically known as war of currents [1], AC started to win primarily due to more efficient power transmission enabled by use of transformers to step up or down voltage levels to reduce the power losses. As the need for long distance power transmission grew, the efficiency became a predominant consideration, which worked in favor of AC. For the first half of the twentieth century, AC transmission enjoyed unrivaled popularity and growth while DC was virtually ruled out for electric power transmission.

During the early 1950s, there was renewed interest in the use of DC technology primarily driven by the need for long distance cable transmission. It was realized that the power capacity of an AC cable reduces drastically due to excessive charging current even for moderate distances and voltage levels necessitating the use of DC cables where no such limitation exists. This led to the first DC cable link between mainland Sweden and Gotland island in 1953. Although DC reappeared ...