Fuzzy-Adaptive Droop Gain Selection for Enhanced Frequency Support and DC Voltage Regulation in MTDC System

The provision of frequency support and DC voltage regulation from converters of VSC-based MTDC system requires conflicting control actions from their droop controllers. This paper proposes a fuzzy-adaptive droop scheme to effectively compromise between the two conflicting control actions and enhance the robustness of the droop controllers to parameter variations while eliminating the need for complicated mathematical modeling in droop control design. The proposed droop controller uses a fuzzy inference system which selects DC voltage and frequency droop gains considering prevalent conditions of DC voltage, AC frequency, and available power capacity at each VSC station using local measurements. In this context, DC voltage and power indices are formulated to enhance the computational efficiency of the fuzzy inference system by reducing the number of rules in the fuzzy rule base. In addition, modal analysis is performed to ensure system stability when defining the working ranges of droop gains at controller outputs. The performance of the proposed fuzzy-adaptive droop controller is compared with fixed and adaptive droop control strategies using time-domain simulations on a five-terminal IEEE 68-bus MTDC system in MATLAB/Simulink environment demonstrating the compromising ability and robustness of the proposed fuzzy-adaptive droop controller for frequency support and DC voltage regulation.