Impedance-Adaptive Optimal Control Strategy for Grid-Connected Converters Delivered Via Flexible DC Transmission Systems

In modern power systems, the operation of grid-connected converters delivered via flexible DC transmission systems has become more complex due to the coexistence of flexible DC links and weak AC grids. This setup brings new challenges for converters, especially in handling parameter changes and maintaining stable control. In weak grid or long-distance transmission scenarios, the grid impedance can change quickly, which affects both control performance and system stability. To solve these problems, we propose an adaptive control method that senses grid impedance and adjusts the converter’s behavior accordingly. First, a real-time estimation model is developed to track the inductance at the point of connection. This estimated value is then used in an optimization-based control framework that adapts switching behavior based on the average switching frequency. The proposed algorithm uses rolling optimization and constraint separation to improve dynamic performance while reducing energy loss and electromagnetic interference from frequent switching. Simulation results under typical flexible DC delivery conditions verify the effectiveness of the method.