Active Damping for PMSG-Based WECS With DC-Link Current Estimation

An active-damping strategy is proposed for the suppression of speed and torsional oscillations in permanent-magnet synchronous generator (PMSG)-based wind-energy conversion systems (WECSs). Direct-driven configuration with PMSG is an attractive choice for WECS because of the gearbox elimination and cost reduction due to small pole-pitch design. However, speed and torsional oscillations appear when the generator is directly connected to the wind turbine without any assistant damping device. Based on small-signal analysis, a low-bandwidth design for the power or generator torque controller of PMSG can help to reduce the oscillation amplitude, but the system dynamic performance is thus sacrificed. From the power-flow´s point of view, the oscillation is reflected in the dc-link current. With the help of switch function modeling based on the space-vector-modulation scheme, the average dc-link current can be estimated and applied to the compensation strategy, which provides positive damping resulting in stability improvement. The simulation and experiment results verify the theoretical analysis and the validation of the proposed strategy.