用于海上风电低频交流输送的柔性化二极管整流背靠背变频器

Flexible Diode Rectifier Back-to-back Modular Multilevel Converter for Low-frequency AC Transmission of Offshore Wind Power

低频交流输电技术在中远距离大容量海上风电送出的应用场景中具有独特优势,但是现有的交交变频器存在成本高、占地大和扩展性差等问题。提出了一种新型的柔性化二极管整流背靠背交交变频器(flexible diode rectifier back-to-back modular multilevel converter,FDR-BTB-MMC)。在低频侧,基于小容量辅助模块化多电平换流器(modular multilevel converter,MMC)与常规12脉动二极管整流器(diode rectifier,DR)串联构成柔性化二极管整流器(flexible DR,FDR),可以利用DR实现降低成本和体积,又能够通过小容量辅助MMC的控制能力使FDR具备交直流电压控制能力、黑启动功率输送能力、低无功和谐波特性。在工频侧仅需采用常规的半桥子模块MMC与FDR直流背靠背连接。之后提出了FDR-BTB-MMC的拓扑结构、控制策略和参数设计方法。与其他现有交交变频器方案进行的经济性比较表明,FDR-BTB-MMC在降低成本和占地上具有显著优势,并且直流母线环节也带来了可灵活扩展的优势。通过仿真结果验证了所提出的FDR-BTB-MMC的有效性。

Low frequency AC transmission technology has unique advantages in the application scenario of large-capacity offshore wind power transmission over long distance.However,existing AC/AC converters suffer from issues such as high cost,large footprint,and poor expandability.This paper proposes a novel flexible diode rectifier back-to-back modular multilevel converter(FDR-BTB-MMC).By connecting a small-capacity auxiliary modular multilevel converter(MMC)and a conventional 12-pulse diode rectifier(DR)in series,a flexible diode rectifier(FDR)can be formed on the low-frequency side.FDR utilizes DR to reduce cost and volume,while also utilizing the control capabilities of the auxiliary MMC to endow FDR with the ability to control AC-and DC-sides voltages,deliver black start power,and exhibit low reactive power and harmonic characteristics.On the line-frequency side,only a conventional half-bridge submodule-based MMC is needed to connect the FDR back-to-back.The topology,control strategy,and parameter design method of FDR-BTB-MMC are proposed.Compared with other existing AC/AC converter solutions,the economic analysis shows that FDR-BTB-MMC has significant advantages in reducing cost and footprint,and the existence of the DC link brings advantages in flexible expandability.The effectiveness of the proposed FDR-BTB-MMC was verified through simulation results.