Effect of power injections from multiterminal HVDC systems on the operational risk of the AC grid

摘要

The transmission grid is a key enabler for the European low-carbon energy future. Large investmentsare required in the next years in order to strengthen the integration between national electricitysystems and to replace ageing infrastructures, thus allowing the integration of a large share offluctuating renewable electricity, mainly from wind and solar energy sources. In fact, renewableelectricity – at least as far as wind power is concerned – is often produced in places away from mainconsumption centres and it needs to be transported over long distances; transmission is also needed toallow conventional generators cover the demand during low wind periods. R&D activities are moreand more focused on the use of super-grids, off-shore grids, HVAC cables, HVDC technology and theperspective of using smart grids technologies.In this context, the adoption of multi-terminal (MT), possibly meshed, HVDC networks based on VSC(Voltage Source Converter) technology to convey large amounts of off-shore wind power into the bulkAC grid seems very appealing, even though several aspects are still under investigation (DC breakertechnology, control paradigms, etc.). The introduction of Multi-Terminal Direct Current (MTDC)networks may determine new issues in power system operation, however, because large powerinjections are expected from VSC terminals into the AC grid. This would affect the security of theoverall (AC and DC) system. To help operators manage these new scenarios characterised bysignificant variability and uncertainty, new analysis techniques based on risk concept have beenintroduced in recent years.This paper presents the application of a probabilistic risk-based approach to analyze the effect ofpower injections from MT-HVDC networks on the security of the AC bulk system, evaluated in termsof risk of loss of load, high currents and low voltages. In particular, risk assessment is performed fordifferent load levels in the grid, and different amounts and configurations of MT-HVDC powerinjections, in order to evaluate the dependence of the proposed risk indices on the mentioned quantitieswhich are important for AC system operation.