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

Chapter 3Modeling, Analysis, and Simulation of AC–MTDC Grids

3.1 Introduction

It is envisaged that a subsea MTDC grid based on the VSC technology would be built around the North Sea to tap the rich wind resource of the region and also interconnect the UK and Nordic pool with continental Europe [27]. Sections 1.1 and 1.2 described the business case and rationale behind such an MTDC grid. It was also mentioned in Sections 1.4.1 and 1.4.2 that the VSC technology is the obvious choice over the LCC technology for this application.

For system planning and operation, both steady-state and dynamic simulation of the MTDC grid in conjunction with the surrounding AC network is essential. From the network operators’ point of view, the possibility of an enormous loss of in-feed (tens of gigawatts) due to a single-point failure in such VSC based MTDC grid is one of the major concerns. Following DC side faults, isolating only the faulty component (a converter or a cable) of the MTDC grid is a challenge. Besides protection and DC breaker development issues, there are primary control problems such as autonomous sharing of power imbalance among the converters following a converter or cable outage. Moreover, the MTDC grid could be required to provide AC system support such as allowing exchange of frequency reserves. To study these issues, interaction between multi-machine AC systems and an MTDC grid along with the impact on the overall stability of the combined AC–MTDC system needs investigation, ...