Subsynchronous Oscillation Suppression of Direct-Drive Wind Turbines Based on Improved Linear Active Disturbance Rejection Control and Analysis of Impedance Stability

ObjectivesIn response to the impact of the bandwidth of the current inner loop PI controller on the stability of the grid connected system of direct drive wind turbines under the background of weak electricity network, which leads to the induction of sub synchronous oscillation (SSO) phenomenon, a linear active disturbance rejection control (LADRC) was proposed to replace the current inner loop PI controller with an improved linear state error feedback control law (LSEF) to suppress SSO.MethodsFirstly, the LSEF of the LADRC controller was improved, and the tracking errors and anti-interference capabilities were studied. Moreover, an impedance model for the system considering frequency coupling effects was developed, and the Nyquist criterion was employed to assess the impact of line impedance values on the stability of the grid-connected converter system. Finally, the analysis and validation were performed using PSCAD/EMTDC simulation software.ResultsCompared with traditional LADRC, the improved LADRC can reduce the DC side voltage fluctuation range by 85% and the active power fluctuation range by 89%.ConclusionsCompared with traditional LADRC controllers, improved LADRC controllers can better reduce the range of power fluctuations, DC side voltage fluctuations, and tracking errors.