Linear Feedback Dead-Beat Control for Modular Multilevel Converters: Validation Under Faults Grid Operation Mode

The cascaded control approach is widely used to control the modular multilevel converter (MMC). Such approach allows to manage all MMC state variables in a decoupling manner based on modes separation. This separation introduces conditions related to control objectives response time resulting in slow dynamics. This will limit the use of the potential of MMC energy that is considered as a freedom for ac and dc grids ancillary services. On another side, robustness properties for a given control are also of a great interest when considering unmodeled uncertainties and disturbances. Starting from these requirements, a linear feedback dead-beat control is proposed in this article to accelerate the inner loops and consequently the outer ones (control objectives). The proposed control, based on exact discrete-time model of the MMC in which the sampling period is considered a priory in the control design, is synthetized by taking into account the control outputs saturation. The stability proof of the control and the robustness analysis as well as experimental results under fault grid operations highlighted on small-scale MMC will be presented in this article. The comparison with a continuous-time sliding mode control shows the advantage of the proposed control regarding the response time and undesired oscillation reduction.