Broadband Impedance Shaping Control Scheme of MMC-Based STATCOM for Improving the Stability of the Wind Farm

Sub and super-synchronous resonance problems caused by the increasing penetration of wind energy in the grid usually can be solved by reshaping the impedance of wind farms. Considering the feasibility and economics, the static synchronous compensator (STATCOM), which is already part of the wind farm in certain regions, becomes a preferred option for impedance shaping to improve the system stability. However, due to the difference between the application object and the application scenario, the control schemes for impedance shaping that widely used in the two-level voltage source converter are difficult to apply directly to the MMC-based STATCOM to solve the resonance problems in the practical wind farm. Therefore, in this article, a broadband impedance shaping control scheme for MMC-based STATCOM is proposed to generate an active parallel impedance, thus reshaping the impedance characteristics of the wind farm over the sub and super-synchronous frequencies for enhancing the system stability. Then, a passivity-based design method for this impedance is developed to ensure that the proposed control can provide sufficient damping at the desired frequency. With this broadband impedance shaping control scheme, the STATCOM can effectively suppress resonance in the wind farm under various operation conditions, which is confirmed by the hardware-in-the-loop experimental results.