Two meshed grids were considered in DEMO 3 (see Figure 1): a meshed HVDC network version of the “DC backbone grid” layout, and a mixed topology (including both meshed and radial DC connections to the grid) which was tested in an HVDC multi-terminal grid mock-up to prove the effectiveness and robustness of various control algorithms, both in normal operation and during contingencies.
This is the first DCG mock-up with physical cables (15 km) and protection devices that was ever designed and tested, as illustrated during a live demonstration in Université de Lille in April 2013. This small-scale hybrid mock-up enabled the experimental assessment of various embedded control devices in the converters and designed for this DCG (master-slave control, voltage control, and coordinated control), thus proving their viability and robustness using Hardware-in the-loop (HIL) simulation on both actual and simulated equipment.
During the project innovative and selective protection algorithms (for DC fault detection) were developed to be efficient for DC cables up to 200 km long. The protection system relies on fast communication. Both selective detection and backup protection were also successfully tested on the DCG mock-up.
Fig. 1 – Meshed grid examples: a meshed backbone (left) and the DEMO 3 DCG mock-up topology (right).