Robust Adaptive Control of MMC-HVDC System Integrating Offshore Wind Farms Using Cascade High-Gain State and Perturbation Observer

This paper proposes a novel cascade high-gain state and perturbation observer (CHGSPO)-based robust adaptive control (RAC) strategy of modular multi-level converter based high voltage direct current (MMC-HVDC) system integrating offshore wind farms. The sending-end MMC and receiving-end MMC are decomposed into four subsystems by input-output linearization, respectively. The CHGSPO is designed to estimate the states and perturbations of each subsystem accurately. Then the estimated states and perturbations are used by the feedback linearization controller (FLC) to eliminate the nonlinearities of the system. Compared with traditional vector control (VC), the design of the proposed controller does not rely on the accurate model of MMC-HVDC, and it has strong robustness to model uncertainties, parameter variations, and external disturbances. Moreover, there are no physical connections between the control loops. Thus, it can achieve complete decoupling control of MMCHVDC. Simulation studies are undertaken in an MMC-HVDC system connecting a modified 4Generator-13Bus system with two offshore wind farms. The results reveal that the CHGSPO-based RAC has better performance under various conditions than VC.