Assessment of the impact of MMC‐VSC intrinsic energy on power system stability

Abstract

Synchronous generation is increasingly being displaced by renewable energy sources and HVDC interconnectors that both have dissimilar characteristics and operating principles compared to synchronous generators. These factors will lead to a diminishing provision of ancillary services that are normally used to provide network support and grid stabilisation. Conventional services tendered to provide network support rely on the availability of synchronous generation and because of this, future power system operators will have to develop new ways to obtain the ancillary services required. A technology rapidly gaining in popularity for the connection of wind power plants and interconnectors is voltage source converter (VSC) based HVDC. Further advances in the technology have led to the modular multilevel converter (MMC). Due to the design of an MMC there is intrinsic electrostatic energy that could potentially be utilised to provide ancillary services. This paper determines the electrostatic energy available from a typical grid-scale MMC VSC for network support during disturbances and for power oscillation damping. Supporting simulations are provided to ascertain the impact that this electrostatic energy could have on network performance if utilised. Findings in this paper display that although an MMC possesses intrinsic energy, utilising it for frequency response would provide negligible system benefits. However, for POD, the available intrinsic MMC energy did improve system stability which leads to the potential of using multiple MMCs to increase the level of energy and further improve system stability.