A Frequency Estimation-Based Adaptive Mitigation Approach for High-Frequency Oscillation in MMC-HVDC System

To suppress the high-frequency oscillations (HFOs) in Modular Multilevel Converter based High Voltage Direct Current (MMC-HVDC) transmission system, this article proposes a frequency estimation-based adaptive mitigation approach, including the oscillation frequency estimation (OFE) function and the oscillation suppression function by band-stop filter (BSF). Firstly, the proposed OFE function which is based on the rotating frame transformation and LPF can mitigate the influence of background harmonics, and rapidly identify frequency and amplitude of the HFO. Then, a BSF with adaptively corrected parameters, based on the identified frequency from OFE function, is embedded in the inner control loop of MMC to regulate the system damping in the interested frequency range. Thus, the impedance characteristic of MMC system in the oscillation frequency band can be adaptively reshaped to mitigate the HFO. The working principle of OFE function and suppression function by BSF is presented, and the parameters selection procedures are also provided. Finally, the proposed approach is validated by electromagnetic transient (EMT) simulations and controller hardware-in-the-loop (HIL) experiments. The results show that the presented adaptive mitigation approach shows a favorable identification and oscillation suppression ability for the HFOs.