Improved control strategy of an active crowbar for directly-driven PM wind generation system under grid voltage dips

Permanent magnet synchronous generation (PMSG) has been more and more used in the wind power generation system due to its advantage of simpler structure, higher generation efficiency and more reliable operation. However, the behavior of wind power system during grid disturbances becomes more important with an increasing amount of wind energy installed. Nowadays the grid code demands that the wind power generation must possess the ability of riding through the grid voltage dips in order to prevent the more severe successive grid faults. To protect the converter from suffering damage, it is needed to limit the high current in grid-side converter and high voltage in the DC bus. A crowbar has to be provided as a bypass for overflowing power, which can short circuit the DC bus when needed to protect the total power converter. In this paper, an improved crowbar control strategy is proposed to limit the over current and voltage of the converter. Moreover, a capacitive current is injected to assist the recovery of the grid voltage. Simulation results validated that the proposed strategy is able to ride through the severe grid voltage dips.