Stability and Dynamic Analysis of the PMSG-Based WECS With Torsional Oscillation and Power Oscillation Damping Capabilities

The direct-drive permanent-magnet synchronous generator (PMSG) based wind energy conversion system (WECS) with a soft drivetrain shaft is vulnerable to torsional oscillation when it participates in power oscillation damping (POD) services for the AC grid. This paper investigates three possible scenarios of incorporating both torsional oscillation damping (TOD) and POD controllers into PMSG-based WECS. A model of a PMSG-based offshore wind farm (OWF) connected to the IEEE 39-bus AC grid is developed and utilized to analyze the stability and dynamic performances of the WECS within these three scenarios. Comprehensive modal analysis is carried out to analyze the interaction between the torsional and power oscillations, and to tune the TOD and POD controllers to damp these oscillations simultaneously in each scenario. Furthermore, the dynamic performances of the PMSG-based WECS within these scenarios are evaluated through time-domain simulations. Then an optimal scenario for PMSG-based WECS to damp both oscillation types with close frequencies is identified, which is modulating the DC-link voltage for the TOD and the grid-side active power for the POD. This result can provide useful guidance for the future industrial application of the TOD and POD control in the PMSG-based WECS.