Direct Power Control of a Surface-Mounted Permanent Magnet Synchronous Generator Wind Turbine for Offshore Applications

Abstract

This paper proposes a direct power control scheme for an offshore wind turbine-driven surface-mounted permanent magnet synchronous generator with a full back-to-back converter situated onshore to decentralize the weight of the turbine. The proposed model is designed in a stationary reference frame and does not require a phase-locked loop as opposed to the traditional vector current control method. Simple feed-forward and feedback control loops are used in the proposed model to extract the maximum available wind power, maintain constant voltage at the coupling DC link, and ensure power injection into the electric network at unity power factor. Simulation results carried out in MATLAB/SIMULINK show that the proposed model has a fast transient response and steady-state performance consistent with the vector current control model. Furthermore, eigenvalue analysis results demonstrate that the proposed method’s performance is robust to variations in different system parasitic elements, even under both stiff and weak electric network conditions. These results also indicate that the back-to-back converter can operate effectively when located onshore close to the load center while the turbine is in close proximity offshore. This can be suitable for multiple specific offshore applications as it can potentially reduce the overall weight, volume, and cost of the offshore wind turbine infrastructure.

Keywords

• Back-to-back converter
• direct power control
• surface-mounted permanent magnet synchronous generator
• short-circuit ratio
• weak electric networks