Investigation of dynamic characteristics of planetary gear stage in wind turbine considering voltage dip

The transient variation of electrical parameters makes system loads fluctuate and reduces bearing capacity when the grid voltage dips. This work proposes an electromechanical coupling dynamic model of the wind turbine drivetrain to build a dynamic interconnection between the electric and drivetrain subsystems. The drivetrain subsystem that includes an improved model of the planetary gear stage is developed and validated. This improved model considers the carrier and planet bearing clearances, the connection relationship among the carrier, main shaft, and planets as well as the flexibilities of the main shaft and parallel stage shafts. The influences of the carrier bearing clearances, non-torque load and planet position angle on planet bearing loads are investigated under the low-voltage ride through (LVRT) event. The results indicate that as the LVRT occurs, the planet bearing loads reduce below the minimum requisite with a high, fluctuating system speed; considering the bearing clearances, the impacts occur in the planet bearing in the minimum load zone followed by significant stress variation; the non-torque load suppresses the planet bearing impacts in a limited range of carrier bearing clearance; the planet position angle has a significant effect on the planet bearing impacts because of the asymmetry of load and structure of the planetary gear stage.