面向新型电力系统的柔性直流换流器统一控制架构

Unified High Voltage Direct Current Converter Control Dedicated for New Power Systems

新型电力系统的发展对柔性直流输电技术提出了更高需求,随着异构串联型直流换流器拓扑架构的提出,柔直换流器已在拓扑层面实现结构统一。然而,在控制层面,传统柔直换流器控制虽然具备功率解耦控制能力,但交流电压、直流电压和子模块电容电压之间存在紧密耦合,难以发挥柔直换流器全控型器件运行灵活性高的优势。首先,基于现有直流换流器控制架构,提出控制自由度的概念,并引入调制比的表征方法,构建模块化多电平换流器(modular multilevel converter,MMC)的多自由度控制体系;然后,通过分析MMC换流器内部的电压耦合机理及其与调制比的关系,系统地揭示了现有MMC换流器的各种控制策略之间的关联性,形成具备“功能统一、结构统一”的MMC换流器的4自由度统一控制架构。并针对柔直系统中不同控制目标的MMC换流器分析4自由度控制架构的应用及其控制潜能;最后,在单端MMC物理动模实验系统中对MMC换流器4自由度控制在典型应用场景下的性能进行实验验证。

The development of new power systems has put forward higher demands for flexible DC transmission technology.With the proposal of the heterogeneous series converter,the flexible DC converter has been unified at the topology level.However,at the control level,although the traditional control has the power decoupling ability,there is a close coupling between AC voltage,DC voltage,and submodule capacitor voltage,which makes it difficult to fully utilize the advantages of flexible operation of fully controlled devices based converters.This article first proposes the concept of control degree of freedom based on traditional DC converter control structures,and introduces a characterization method of modulation ratio to construct a multi-degree of freedom control system for MMC converters.By analyzing the voltage coupling mechanism inside MMC and its relationship with modulation ratio,the correlation between various MMC control strategies is systematically revealed,forming a 4-degree of freedom unified control structure for MMC converters with“unified function and unified structure”.And the applications and potentials of the 4-degree of freedom control structure are analyzed for MMC converters with different control objectives in flexible DC transmission systems.Finally,the performances of MMC 4-degree of freedom control in typical application scenarios are verified in a single-end MMC physical dynamic simulation experimental system.