Smart Grid: Technology and Applications

9

Power Electronic Converters

9.1 Introduction

The future power system increasingly will include more controllable power electronic devices to make the best use of existing circuits, maintain flexibility and optimum operation of the power system, and to facilitate the connection of renewable energy resources at all voltage levels. Figure 9.1 illustrates a future power system that is rich in power electronics.

Current Source Converter High Voltage DC (CSC-HVDC¹) is presently used for the connection of asynchronous power systems (for example, 50–60 Hz), for long overhead line transmission and submarine cable circuits as well as for the connection of geographically extensive or weak systems [1–3]. It is anticipated that CSC-HVDC connections will be increasingly used in future for inter-country and inter-state connections.

Voltage Source Converter HVDC (VSC-HVDC¹) is used for offshore wind farm connections. Offshore wind farms up to 50–80 km from shore can be connected to the terrestrial grid using an AC connection. However, the submarine cables generate significant reactive power limiting the distance over which an AC cable connection can be used. The decision on whether to use AC or DC depends on the cable route length, the number of cables required to transmit the wind farm output, acceptable losses and capital costs.

Flexible AC Transmission Systems (FACTS) are used to increase the power transfer capability of existing AC lines, to control steady state and dynamic power flow through ...