This work will aim to develop advanced computational models for power systems including models that are suitable for solving optimal power flow problem. Models will be developed for VSC-based HVDC links which could be used to form multi-terminal supergrids for connecting multiple wind farms. The optimal power flow problem is a complex nonlinear optimisation problem which can be quite tasking for especially larger scale systems and as such one of the main methodological contributions in this project is to develop suitable approximations such as linearisation methods for reducing the computational expenditure of the optimal power flow problem and at the same time maintain its tractability when scaled up for larger systems. The project will also involve implementation of a suitable day-ahead operational planning framework by solving multiple instances of optimal power flow problem to plan the operation of offshore wind farms within a specific planning timescale (say 24 hours). The planning framework is then implemented to multiple wind farms connected via a multi-terminal HVDC supergrid to provide better power regulation and a more stable, reliable operation even after emergencies such as loss of supply in a specific region. These added flexibilities of operation are necessary for a sustainable growth and integration of offshore wind resource in the future for example in the UK in line with National Grid's Future Energy Scenarios (FES) projections.