Robust DC-Link Voltage Control of a Full-Scale PMSG Wind Turbine for Effective Integration in DC Grids

DC grids are gaining widespread acceptance under the smart grid paradigm. A full-scale permanent-magnet synchronous generator wind turbine can be interfaced to a dc grid by a voltage-source converter (VSC). Under weak ac grid connections or isolated operation of the dc grid, the machine-side VSC regulates the dc-link voltage via changes in the generator speed. However, several control difficulties are yielded; important among these are: 1) the nonlinear plant dynamics with wide range of operating point variation; 2) the control lever is mainly the generator speed, which complicates the dc-link voltage control dynamics; 3) the presence of uncertain disturbances associated with dynamic loads (e.g., power-converter-based loads) connected to the dc grid and wind speed variation; and 4) the presence of parametric uncertainty associated with the equivalent dc-link capacitance due to connecting/disconnecting converter-based loads. This paper presents a robust dc-link voltage controller that addresses such control difficulties. The proposed controller is based on the robust structured singular values $(\mu)$-synthesis approach and a functional fuzzy model. Analysis and comparative simulation and experimental results validate the effectiveness of the proposed controller.