MITIGATION OF SUBSYNCHRONOUS OSCILLATION IN THE LARGE-SCALE WIND ENERGY TRANSMISSION SYSTEM WITH HVDC LINK BASED ON THE LOCAL GAIN-VARYING CONTROL

摘要

The interaction between large-scale wind farms and HVDC transmission system may cause the risk of subsynchronous oscillation (SSO). Studies have shown that the SSO tends to arise from small signal amplitude oscillation at the early stage. Meanwhile, the dominant SSO mode of the wind energy transmission system with HVDC link is strongly correlated to HVDC control parameters and the risk of SSO can be reduced by decreasing the gain of HVDC control. Based on the above analysis, the local gain-varying controller (LGVC) is proposed to suppress SSO, which is added in the current control loop of HVDC rectifier. LGVC's gain depends on the input representing the SSO amplitude of the system. When the input amplitude is below the threshold value, the gain is adjusted according to the input. Otherwise, it is kept unchanged to maintain original control performance. Obviously, LGVC is nonlinear, so the describing function (DF) method is used to representing its characteristics. Then, the influence of LGVC on the system stability can be determined by Nyquist stability criterion. The simulation results show that LGVC can suppress SSO with no change in the system original control performance.