Multi-Objective Optimization and Stable Operation Control Strategy for Fractional Frequency Transmission System Based on Large Signal Stability Analysis

Fractional frequency transmission systems perform well in offshore wind power transmission, yet analyzing the large signal stability of the whole system still remains a significant challenge. Particularly, the absence of optimized stable operation control strategy under large signal disturbances threatens the system's long-term reliability and stability. To tackle the issues, this paper develops the multiple T-S fuzzy model, incorporating equivalent models for offshore wind farms, M3C, and industrial frequency loads, and analyzes stability under large signal disturbances, considering coupling effects and interactions with different frequencies. Furthermore, to address the challenge of system inability to directly transition to a new steady-state point after encountering large signal disturbances, such as load transients, a multi-objective optimization method based on Normalized Boundary Intersection (NBI) is proposed. This method aims to solve the problem by determining one optimal intermediate transition point for the stable operation control strategy. By comprehensively considering stability margins and operational efficiency, the system adopts an optimal operational mode during transient processes to smoothly transition to the target operating point. Finally, simulation and experimental results validate the effectiveness of large signal stability analysis findings and the stable operation control strategies.