Boarding Control System - for Improved Accessibility to Offshore Wind Turbines

This paper considers the dynamic modelling and motion control of a Surface Effect Ship (SES) for safer transfer of personnel and equipment from vessel to-and-from an offshore wind-turbine. Such a vessel is a key enabling factor for operation and maintenance (O&M) of offshore wind-energy infrastructure. The control system designed is referred to as Boarding Control System (BCS). We investigate the performance of this system for a specific wind-farm service vessel–The Wave Craft. A two-modality vessel model is presented to account for the vessel free motion and motion whilst in contact with a wind-turbine. On a SES, the pressurized air cushion carries the majority of the vessel mass. The control problem considered relates to the actuation of the pressure such that wave-induced vessel motions are minimized. This leads to a safer personnel transfer in developed sea-states than what is possible today. Results for the BCS is presented through simulation and model-scale craft testing.

Some aspects of multilevel load-frequency control of a power system

The application of multilevel control strategies for load-frequency control of interconnected power systems is assuming importance. A large multiarea power system may be viewed as an interconnection of several lower-order subsystems, with possible change of interconnection pattern during operation. The solution of the control problem involves the design of a set of local optimal controllers for the individual areas, in a completely decentralised environment, plus a global controller to provide the corrective signal to account for interconnection effects. A global controller, based on the least-square-error principle suggested by Siljak and Sundareshan, has been applied for the LFC problem. A more recent work utilises certain possible beneficial aspects of interconnection to permit more desirable system performances. The paper reports the application of the latter strategy to LFC of a two-area power system. The power-system model studied includes the effects of excitation system and governor controls. A comparison of the two strategies is also made.