Switching Frequency Characteristics and Optimization of Medium-Frequency MMC for Offshore Wind Farm Integration

The medium-frequency operation is a very promising technological route to achieve the lightening and compactness of Modular Multilevel Converters (MMC) in offshore converter platforms. However, as the operating frequency increases, the operating characteristics of the offshore AC system will be affected to some extent. To minimize the impact of increased operating frequency on the converter valve losses, this paper investigates the switching characteristics and loss optimization methods for MMCs operating at medium frequencies. Based on the reduced switching frequency submodule capacitor voltage balancing control, this paper proposes a method for optimizing the switching frequency based on the adjusting the voltage loop width of the submodule capacitor. The $1100 \mathrm{MW} / \pm 400 \mathrm{kV}$ case reveals that with the proposed strategy, reducing switching frequency in the medium-frequency MMC is possible.