低成本混合型海上风场直流换流器

Cost-effective Hybrid HVDC Converter for Offshore Wind Farms

随着柔性直流输电技术的快速发展,基于模块化多电平变换器（modular multilevel converter,MMC）的海上换流站成为深远海风场接入直流输电系统的首选方案,但由于MMC换流器子模块数量众多、体积与重量较大,使得基于MMC的海上换流站系统较为复杂、成本较高。该文提出一种由二极管整流器和高变比辅助变换器组成的低成本混合型换流器。辅助变换器在风场启动阶段建立风场内网电压、返送功率,实现风场的黑启动;在风场正常发电阶段补偿风场的无功功率和二极管整流器的电流谐波。二极管整流器在风场正常发电阶段承担全部功率输送任务。与采用全功率MMC换流器方案相比,提出的低成本混合型换流器能够大幅减少换流器子模块数量,从而降低体积与重量,减少系统总成本,并能够提高输电效率。以一个160MW的海上换流器为案例,通过仿真分析验证所提出的换流器拓扑、控制原理及降低成本的有效性。

With the rapid development of voltage source converter based high-voltage direct current （VSC-HVDC） technology, modular multilevel converter （MMC） based offshore converter station has become the most attractive solution for dc power delivery of an offshore wind farm. However, an offshore MMC station has a large number of submodules, and the volume and weight of the converter is high, so the system is complex and has high cost. In this paper, a cost-effective hybrid converter was proposed. The proposed converter consists of an MMC based high-conversion-ratio auxiliary AC/DC converter and a diode rectifier. The auxiliary converter sets up the AC voltages of the wind farm and supplies power the during the start-up procedure. The auxiliary converter also provides reactive power and compensates the harmonic currents when the wind farm is generating power. Comparing with the full-power MMC solution, proposed hybrid converter highly decreases the number of submodules, leading to lower volume, weight, and cost. The conversion efficiency is also enhanced. To verify the proposed converter and control scheme, a simulation model of a 160MW offshore wind power system was built, and the simulation results prove the effectiveness of proposed system.