Active/Passive Method-Based Hybrid High-Frequency Damping Design for MMCs

High-frequency resonance (HFR) is a key issue of power electronics-based systems. Two solutions can be applied for addressing HFRs, including active damping method and passive damping method. For modular multilevel converters (MMCs), most of the existing harmonic resonance suppression methods are focused on active methods, including active filtering and virtual resistance. However, the active filtering may lead to negative damping in its attenuation band and the virtual resistance may become negative in high-frequency range when influenced by control delay. In order to avoid the negative effects of control delay and increase the damping of MMCs in high-frequency range, this article reconsiders the arm inductor in MMCs and proposes a passive damper design method for MMCs. With the coordinated design between active controller and passive damper, the negative damping of MMCs in high-frequency range can be effectively eliminated and the system stability can be improved. Also, the proposed passive damper has little impact on the steady-state operation and increases few losses of the MMC. The effectiveness of the proposed passive damper is validated by electromagnetic transient (EMT) simulations in PSCAD/EMTDC.