Strategy Design and Parameter Optimization of High-Frequency Resonance Suppression for Modular Multilevel Converter

Addressing the issue of high-frequency oscillations in converter stations during flexible DC grid integration and transmission, a suppression scheme combining active and passive damping, along with a method for optimizing the design of its parameters, is proposed. This scheme aims to alter the impedance characteristics of the converter station from a passive perspective, thereby achieving reliable suppression of high-frequency oscillations. Firstly, by analyzing the negative damping characteristics within the simplified high-frequency impedance model of the converter station, the principle is revealed that the active damping in the suppression scheme should shift the negative damping of the converter station to higher frequencies. Secondly, based on the impedance model, the principle for selecting the parameters of the active damping controller for virtual series impedance is derived, and appropriate parameters are obtained using a coefficient fitting method. Subsequently, with the goal of reducing investment costs and the constraint of completely eliminating high-frequency negative damping, an optimization algorithm is employed to determine the parameters of the passive filter. By comparing the parameter changes of the passive filter before and after the addition of virtual series impedance, the economic benefits of the coordinated suppression scheme are highlighted. Finally, electromagnetic transient simulations verify the correctness and effectiveness of the suppression scheme under the optimized parameter design method.