The Research of Sub Synchronous Oscillation in PMSG Wind Farm

Under some certain conditions, the wind power farm which accesses to the power system may appears the phenomenon of sub synchronous oscillation (SSO). Doubly fed induction generator (DFIG) connected to power grid usually transports power energy by series compensated AC transmission or DC transmission, and the theory of SSO in DFIG wind farm is relatively clear and has been researched mostly. Permanent magnet synchronous generator (PMSG) wind farm connected to weak AC power grid also appears more SSO accidents, which causes multiple PMSG to take off the power grid and the damage of crowbar circuits. Because PMSG wind farm still appears sub synchronous oscillation accidents in the absence of series compensation or DC transmission when transmitted to the outside, SSO in PMSG wind farm is a new type of oscillation waiting to be researched. In order to investigate the mechanism of problem, the equivalent system model of D-PMSG connected with power grid was established in this paper. Through the transfer function, eigenvalue value analysis and electromagnetic transient simulation, the mechanism of sub synchronous oscillation was revealed. The influence on its characteristics from many factors was also analyzed, including delay time and the wind speed. The results show that the voltage delay link of controller feed forward in network side is the direct cause of sub synchronous oscillation. Finally, potential danger and its suppression measures of the SSO problem were discussed according to the characteristics of sub synchronous oscillation of D-PMSG wind farm.