Active damping for torsional vibrations in PMSG based WECS

Multi-pole permanent magnetic synchronous generator (PMSG) applied in the direct driven wind energy conversion system (WECS) usually has a relative ¿soft¿ drive train. Because of no internal damping winding, torsional vibrations are easily excited in the PMSG based WECS. For the maximum power extraction requirement, the vibrations can be automatically damped with optimal torque (OT) or power signal feedback (PSF) scheme implemented in the generator side. However, if the WECS is required to output a smoothed or constant power for the power regulation, the vibrations will not be damped with the control strategy. Thus additional active damping control is necessary. Active damping can be achieved with power control in both grid and generator sides or just dc link voltage control. With additional compensator in the power or dc voltage control loop, the damping torque is introduced to suppress the vibrations in the generator torque. Different active damping strategies for different output power requirements are designed and verified with simulation results in the paper.