Zero-Inertia Offshore Grids: N-1 Security and Active Power Sharing

With Denmark dedicated to maintaining its leading position in the integration of massive shares of wind energy, the construction of new offshore energy islands has been recently approved by the Danish government. These new islands will be zero-inertia systems, meaning that no synchronous generation will be installed in the island and that power imbalances will be shared only among converters. To this end, this paper proposes a telecommunication-free frequency droop controller to maintain the active power balance in the offshore system and guarantee N-1 security. Although offshore systems are the main focus of this paper, the presented methodology could be applied to any other zero- or low-inertia system. The frequency droop gains are calculated solving an optimization problem which takes into consideration the small-signal and transient stability of the system. As a consequence, the proposed controller allows for greater loadability of the offshore converters at pre-fault state and guarantees their safe operation in the event of any power imbalance.