Enhanced Fuzzy Logic Controller Design for Alternate Arm Converter in Short and Extended Overlap Modes

Alternate arm converters (AAC) are emerging as one of the most efficient voltage source converter (VSC) topologies in high-voltage direct current (HVDC) systems due to their advantages over conventional modular multilevel converters (MMCs). Compared to conventional MMC, they benefit from fewer number of submodules (SMs), lower capacitance per submodule and DC fault ride-through capability. However, the AAC VSC controller must ensure appropriate regulation of AC currents in both overlap and non-overlap modes while maintaining minimal harmonic distortion. This paper presents an optimized control design method for the half-bridge (HB) AAC VSC using a Fuzzy Logic (FL) controller. The average modeling of multilevel converters is used to reduce computational burden, and the proposed FLC scheme is employed to regulate AC and circulating currents. The performance of the proposed control architecture is evaluated under short and extended overlap operating modes. Sensitivity analysis of the proposed controller against changes in VSC design parameter of overlap period is also investigated to examine the proposed scheme usefulness in different operating conditions. A two-terminal HVDC link using AAC VSC converters is modeled in MATLAB/Simulink and simulation results under different operating conditions are presented to demonstrate the effectiveness of the proposed scheme.