Modular multilevel converters are known to develop high-frequency oscillations (HFOs) with the power system they are connected to, and the root cause is that the system resonance frequencies fall into the delay-induced non-passive region of MMCs. To damp such oscillations, this paper presents a wideband passivation method that can shape the MMC impedance to become completely passive above 100 Hz. This work involves a systematic design approach for using voltage feedforward for passivizing an MMC inverter impedance, and using current feedforward for passivizing MMC rectifier impedance. The effectiveness of the proposed wideband passivation method is verified first by frequency-domain analysis and then validated via EMT simulations.
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Huang et al. (2023) studied this question.