Model-Free Adaptive Control for Mitigation of SSO in PMSG-Based Wind Farms With VSC-HVDC

Due to the variation of operating conditions, the frequency of subsynchronous oscillation (SSO) varies with time in permanent magnet synchronous generator based wind farms integrated with voltage source converter based high-voltage direct current transmission (VSC-HVdc) systems. Existing SSO mitigation strategies generally share limited mitigation capacity owing to their fixed controller parameters relative to various operating conditions. To address this issue, an adaptive VSC-side supplementary control strategy is proposed based on model-free adaptive control theory, which is driven by real-time data rather than the comprehensive dynamic model of the system. It comprises 1) a pseudo gradient (PG) estimator and 2) a predictive controller. The PG estimator utilizes real-time data to estimate the dynamic characteristics of the system, while the predictive controller generates appropriate signals based on the estimated PG. Considering the ac voltage is regulated by VSC-HVdc, the voltage SSO signal is utilized as the input signal of the proposed strategy to generate voltage compensation, without additional signal measurements. Case studies under various operating conditions are conducted to verify the adaptiveness of the proposed strategy through controller hardware-in-the-loop experiments. Results indicate the proposed strategy has better mitigation performance compared to the supplementary subsynchronous damping controller and has a minor impact on the performance of the VSC controller.