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Designing a robust controller for Modular Multilevel Converters (MMCs) is crucial to ensure stability and optimal dynamic performance under various operating conditions, including faulty and disturbed scenarios. The primary objective of controlling grid-connected MMCs (GC-MMCs) is to accurately track real and reactive power references while maintaining excellent harmonic performance in the output response. This paper proposes a novel model-free control strategy for GC-MMCs, employing a Fractional Order Proportional-Integral (FOPI) controller and a Fractional Order Fuzzy type-II Proportional-Integral (FOFPI) controller. The FOFPI controller utilizes a type-II Fuzzy Inference System (FIS) to adaptively adjust the proportional and derivative gains during the control process, enabling effective control of the MMC under diverse operating conditions. The type-II FIS, which leverages type-II fuzzy sets, can mitigate uncertainty and nonlinearity in the system. Furthermore, the incorporation of fractional-order mathematics enhances the flexibility of the proposed controllers. To optimize the initial parameters of the proposed controllers, the Whale Optimization Algorithm (WOA), a meta-heuristic algorithm, is employed. The results demonstrate that the proposed controllers exhibit superior performance under voltage disturbance conditions, varying input voltage, and can ensure the stability of the MMC.

Power electronic converters enable wind turbines, operating at variable speed, to generate electricity more efficiently. Among variable speed operating turbine generators, permanent magnetic synchronous generator (PMSG) has got more attentions due to low cost and maintenance requirements. In addition, the converter in a wind turbine with PMSG decouples the turbine from the power grid, which favors them for grid codes. In this paper, the performance of back-to-back (B2B) converter control of a wind turbine system with PMSG is investigated on a faulty grid. The switching strategy of the grid side converter is designed to improve voltage drop caused by the fault in the grid while the maximum available active power of wind turbine system is injected to the grid and the DC link voltage in the converter is regulated. The methodology of the converter control is elaborated in details and its performance on a sample faulty grid is assessed through simulation.