基于CET变换器的串联型风电全直流系统研究

A series connected wind power full DC system based on a CET converter

串联型汇集送出方案被认为是规模化远海风电全直流系统最可能实现的方案。为避免串联型直流风电机组因风电机组间耦合特性引起的过电压现象和风功率损失,使系统实现高压直流送出和具备直流故障自清除能力,提出了基于容性能量转移原理DC/DC变换器(capacitive energy transfer principle based DC/DC transformer, CETDCT)的新型串联系统。该系统拓扑中海上升压站为CET-DCT结构,并采用基于混合型模块化多电平换流器(modular multilevel converter, MMC)的直流风电机组和岸上换流站。以实现风电机组全工况下的最大功率点跟踪、穿越多种直流故障为目标,设计了系统的控制与保护策略。基于PSCAD/EMTDC搭建了传统串联系统和新型串联系统的仿真模型。对传统串联系统风电机组间功率不平衡工况的仿真,验证了风电机组的过电压和风功率损失现象。对新型串联系统稳态工况和故障工况的仿真,验证了新型串联系统的运行特性及所提策略的有效性。

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.