Scope

The paper presents the development of a novel grid-forming predictive control scheme applied to the integration studies for an offshore wind plant, which is interfaced to the network mains through a Matrix Modular Multilevel Converter, enabling the interconnection of assets operated at different nominal frequencies. The proposed approach significantly improves the robustness of converter-based transmission infrastructures against long-cable resonance conditions and enables higher penetration of renewables in the system.

Main results

The main results of the paper are the following:

• Development of an enhanced predictive grid-forming algorithm that combines the features of a feedback architecture with the inherent predictive capabilities of model predictive control. Compared to more traditional approaches, this scheme enables the minimization of undesired resonance conditions under long transmission cables, without the need for dedicated damping controllers—which are often difficult to design and tune under real operating conditions.
• Application of the proposed strategy to the emerging direct AC-AC power conversion technology for cost-effective interconnection of renewable-based offshore generation, and investigation of the inherent transient stability improvements provided by this solution.

Methods

The approach has been validated through EMT simulations, comparing the interconnection performances with respect to transient stability and low-voltage ride-through events, total harmonic distortion (THD), robustness against physical parameters uncertainty.

Relevance

The relevance of the work is associated to the emerging direct-conversion technologies for interfacing networks operated at different nominal frequencies, as well as deployment of advanced control strategies in combination with the grid-forming characteristics of converter devices.

In addition, the relevance of the work falls within the general scenario of more power electronics-based transmission infrastructures as flexibility enhancers for network operations, and as enablers for higher penetration of renewable generation in public networks.

Conclusions

A novel enhanced predictive grid-forming control strategy to improve transient support and cable resonance damping will be illustrated, both from the mathematical, application and implementation perspectives. This strategy leverages the predictive capabilities of MPC and a deeper understanding of the plant to anticipate the system's dynamic evolution, providing enhanced dynamic stability to the transmission cable. More broadly, the paper highlights the superior dynamical performance of Static Frequency Converters towards the integration of offshore wind plants.