基于混合型多电平换流器的柔性直流输电系统

针对一种混合型多电平换流器（Hybrid Multilevel Converters, HMC）在柔性直流输电系统（VSC-HVDC）中的应用进行了研究。阐述HMC的电路拓扑和工作原理，从功率角度分析子模块电容电压均衡条件，介绍了换流器的基本控制策略，提出了一种改进控制策略和HMC子模块串的均压控制策略。提出了基于HMC的前馈交叉解耦控制策略，包括有功无功解耦控制器，以及直流侧电压控制器。利用PSCAD/EMTDC建立了基于HMC双端三相35 kV，240子模块的VSC-HVDC详细仿真模型，验证了所提出的主电路拓扑和控制策略。

VSC-HVDC system based on hybrid multilevel voltage sourced converters

This paper researches the application of hybrid multilevel converters (HMC) in the VSC-HVDC system. First, the circuit configuration and working principle are introduced. Then the conditions about capacitor voltage balancing of each sub-module are analyzed from the power perspective. A basic control strategy of converters is introduced. An advanced control strategy of converters and a voltage-balancing scheme are proposed. Feed forward cross decoupling control strategies based on the HMC are used to design the controller which includes decoupling control of active power and reactive power, and the DC voltage control. Finally, a two terminals, three phases, 35 kV, 240 sub-modules VSC-HVDC detailed simulation model is built based on PSCAD/EMTDC. The principle of the main circuit and the control strategies are verified.