Overview of control technologies for variable-speed constant-frequency wind turbines

This paper analyses and compares domestic and international grid codes, which define the requirements on the wind turbine control and objectives. The focuses are on the topologies of asynchronous doubly-fed induction generator (DFIG) and multi-pole permanent magnet direct-drive synchronous generator (PMSG), as well as their control schemes aimed at MPPT. A summary and comparison of control schemes is made. The control schemes in the LVRT situation of VSCF wind turbines and the protective measures are illuminated. The paper also stresses the PMSG control scheme and the protective measures. In the end of this paper, a brief description of the present research situation on wind turbines to improve power quality, frequency regulation capability as control objective is given, and fractional frequency wind power system with fractional frequency transmission technology is discussed.