主从式级联多电平变换器及其控制方法的研究

针对混合级联多电平变换器的输出电压等级和中间单元功能不明确的缺点,提出了一种主从式级联多电平功率变换器的拓扑组合结构.主变换器用来实现基波功率输出,从变换电路用来改善输出波形质量.该主从式级联多电平变换器具有输出波形质量高、开关损耗小、系统整体效率高等显著优点,特别适用于高压或超高压功率变换系统,是一种非常实用的电路拓扑组合方式.文中给出了适合于该功率变换器拓扑结构的两种控制策略:三角载波调制控制策略和特定谐波消除(SHEPWM)控制策略,并给出了50Hz下三角载波控制策略的仿真结果.仿真结果证明了所提的主从式级联多电平功率变换及其控制策略的有效性和实用性.

Research on Composite Cascade Multilevel Converters and Its Control Strategies

This paper proposes a new kind of topology of composite cascade multilevel converter, each phase of which is composed of a main converter and an auxiliary converter connected in cascade mode. The main converter is a multilevel converter composed of devices with high blocking voltage such as GTO and operates at the fundamental frequency of output voltage, and the difference between every two adjacent level is 2E or 3E. The large voltage synthesis is contributed by the main converter. The auxiliary converter is a H-bridge composed of fast switching devices such as IGBT and modulates at a higher frequency to enhance the quality of output voltage, and the voltage of the independent DC source of the H-bridge is E. A synergistic approach which combines the fast switching ability of IGBT and large voltage blocking capability of GTO is proposed. The proposed converter is well suited for application in high voltage or ultra-high voltage situations with high performance requirements and has advantages in high quality of output waveform, high efficiency, high voltage capacity etc. Two control strategies applicable to composite cascade multilevel converter are discussed. One is triangle-carrier method and another is SHEPWM method. Simulations of triangle-carrier method at 50Hz are carried out which proves the practicability and validity of proposal topology and control strategy.