Performance and economic comparisons between point-to-point HVDC transmission and hybrid back-to-back HVDC/AC transmission

Two alternative schemes for interconnecting asynchronous or independent AC systems by a limited capacity link are presented. The first alternative is a conventional point-to-point HVDC transmission system; the second alternative comprises an AC line terminated by an HVDC back-to-back link. Technical and operational properties of both schemes are illustrated with emphasis on VAr (volt-ampere reactive) regulation capability and control flexibility to improve the overall performance of the interconnected AC systems. Cost comparisons for the principal components of the two alternatives are made. A brief description of two existing HVDC installations is given to demonstrate the practical implementation of the schemes