中文摘要：

CPS．SPWN（载波相移脉宽调制）技术算法简单，适于快速实时控制场合。介绍了柔性直流输电中两电平级联变流器的结构和CPS．SPWM的基本调制原理；计算了两电平级联主要参数的选择，讨论了两电平级联条件下通过CPS．SPWM调制方法的提高电能质量的可行性，并通过PSCAD建模仿真，证明了CPS—SPWM调制和两电平级联结合在的显著优势。

英文摘要：

The practical and simple CPS-SPWM method is applicable for quick and real-time control. This paper in- troduces the structure of VSC-HVDC two-level cascade converter and the basic modulation principles of CPS-SPWM, calculates the main parameter choices for the two-level cascade, and discusses the feasibility of using CPS-SPWM method to improve the power quality in the state of two-level cascade. PSCAD modeling and simulation verifies the significant advanta~,e of the combination between CPS-SPWM and two-level cascade.