Mitigating Subsynchronous Oscillation Using Adaptive Virtual Impedance Controller in DFIG Wind Farms

Abstract

Subsynchronous oscillation(SSO) may occur in doubly-fed induction generator (DFIG)-based wind farms transmission system with series capacitive compensation. However, the uncertainties of wind farm have non-negligible impact on SSO. The traditional suppression method based on the virtual impedance controller may be unable to adapt to the variation of uncertainties in the wind farms due to its fixed parameters. Meanwhile, the variation of uncertainties will cause the change of the wind turbine impedance, which further affects the mitigation effect of the virtual impedance controller. To solve this problem, this paper proposes an SSO mitigation strategy based on an adaptive virtual impedance controller that takes into account the uncertainties of multiple wind farms. First, the DFIG impedance model considering the RSC outer control loop is established, and then the influence mechanism of DFIG active power output and reactive power output on SSO is revealed. Next, based on the suppression principle of the virtual impedance controller and the derived DFIG impedance model, an adaptive virtual impedance controller is proposed and its parameter update strategy and overall control structure are designed. Finally, considering multiple uncertainties in wind farms, the suppression effect and adaptability of the proposed strategy are demonstrated.