Abstract: Torsional vibration of permanent magnet synchronous generator (PMSG) shafting not only will increase the fatigue damage of the shafting, but also can seriously affect the stability and reduce the service lifetime of wind turbine generator (WTG).Torsional vibration problem of large WTG becomes increasingly prominent.In order to ensure high efficient and stable operation of the WTG, and restrain shafting torsional vibration effectively, this paper expounds the basic control strategy of permanent magnet synchronous wind power system (PMSWPS) in detail, and discusses and analyzes the influence of control parameters and shafting system damping on the system stability and the shafting torsional vibration.It is found that the instability of the shafting torsional vibration will be caused when inappropriately selecting the control parameter, and that the shafting system damping can suppress the torsional vibration, and improve system stability margin.Because of the stronger nonlinearity and complexity of direct-drive PMSWPS (D-DPMSWPS), there exists certain blindness in the setting of control parameters.This paper effectively restrained the shafting torsional vibration caused by the inappropriate parameter selection.The article puts forward a kind of additional virtual damping control method, that is, under the real condition of insufficient shafting damping, introducing the corresponding compensation current at q axis current control loop, which is equivalent to the introduction of damping torque compensation and increasing the shafting system damping.The proposed control strategy has a certain practical significance and practical value for inhibiting the shafting torsional vibration, and improving the stability and WTG service lifetime of the nonlinear complex system D-DPMSWPS, has the same control effect with the actual increase of shafting damping, and can reduce the requirement for the control parameters.We can get the following conclusions by simulation: 1) It can lead to instable torsional vibration, when the control parameter selection is inappropriate.The article chooses 2 groups of control parameters to confirm this conclusion.The first group of control parameters are kp=0.0005, ki=0.001 and T=0.1 and the second group of control parameters are kp=0.0005, ki=0.01 and T=0.1.It is found that the instable torsional vibration occurs under the first group of control parameters, but does not occur under the second group of control parameters.2) Different control parameters have different requirements on shaft system damping.For example, it only needs to increase the shaft system damping to 300 to maintain system stable under the first group of control parameters, while it need not increase the shaft system damping under the second group of control parameters.3) It can inhibit torsional vibration damping and enhance the stability margin by increasing the shafting.This phenomenon will be found that the instable torsional vibration due to unsuitable control parameter selection can be suppressed effectively by increasing damping of shafting, and the stability margin is enhanced under the first group of control parameters.4) Additional virtual damping control has the same effect with the actual increase of shaft damping and can suppress torsional vibration.The last conclusion can be validated by computer simulation that it can enhance WTG damping and restrain shafting torsional vibration effectively through introducing additional virtual damping under the real condition of insufficient shafting damping.