基于 CET 变换器的串联型风电全直流系统研究

The series-connected collection and transmission scheme is considered as the most feasible solution for large-scale offshore wind power full DC systems. To avoid overvoltage phenomena and wind power loss caused by the characteristics of series-connected DC wind turbines, to enable the system to achieve high-voltage DC transmission, and self-cleaning capability during DC faults, a novel series-connected system based on the capacitive energy transfer principle DC/DC transformer (CET-DCT) is proposed. The proposed system integrates CET-DCT into an offshore booster station and uses hybrid modular multilevel converters (MMC) for the DC wind turbines and the onshore converter station. To achieve maximum power point tracking under all operating conditions and crossing various DC faults, the control and protection strategies of the system are designed. Simulation models for both the conventional and the novel series-connected systems are developed using PSCAD/EMTDC. By simulating the unbalanced power condition between wind turbines in the traditional series-connected system, the overvoltage and wind power loss phenomena in wind turbines are validated. Using simulations for steady-state and fault conditions of the novel series-connected systems, the operational characteristics and the effectiveness of the proposed strategies in the novel systems are verified.