海上风电中频汇集和分布式串联直流输电系统

A Novel HVDC System Integrating Offshore Wind Farms Using Series-connected Distributed MMCs and Medium-frequency AC Collection Network

随着海上风电向远海和大容量发展,采用新型的柔性直流输电技术实现远海风电输送已成为必然选择。但是,现有集中换流方式存在换流器体积大、平台建设难度高等问题。该文提出一种新型的海上风电中频汇集和分布式串联直流输电系统,将集中式模块化多电平换流器(modular multilevel converter,MMC)拆分为多个分布的小型MMC,并将各MMC分布安装于既有的分布交流升压平台,可以避免集中换流平台建设。在直流侧采用串联直流组网的方式,各分布MMC可以设计为相对较低的电压等级。基于所提的系统方案,对不同拓扑MMC的成本、体积和损耗进行详细分析和对比。对比分析结果表明,基于新型中频单向电流型全桥MMC,可以大幅降低分布MMC的体积和成本,使海上交流升压平台集成分布MMC具有可行性。提出了分布串联直流输电系统的关键控制策略,仿真结果验证了所提出的新型海上风电直流组网方案和控制策略的可行性。

With the development of long-distance and large-capacity offshore wind power, voltage source converter based high voltage direct current transmission(VSC-HVDC)has become an inevitable choice. However, the huge conversion platform in the prevailing centralized conversion solution results in great difficulties in transportation and construction. In this study, a novel VSC-HVDC solution for integrating offshore wind farms using series-connected distributed converters and medium-frequency AC accumulation was proposed. Within this architecture, each distributed modular multilevel converter(MMC) was installed on the existing distributed AC substation, thereby avoiding the construction of a centralized converter platform. The distributed MMCs could be designed with relatively low rated voltage because a series DC network was adopted. The cost,size, and loss of different MMCs were analyzed and compared in detail. Analysis results show that the size and cost of distributed MMC can be greatly reduced on the basis of the novel medium-frequency unidirectional-current H-bridge MMC, which makes the installation of the proposed MMC on the offshore AC substation feasible. The control schemes for the HVDC system based on series-connected distributed MMCs were also proposed. Simulation results verify the feasibility of the proposed scheme and control strategy.