Study On A 50kVA Diode-Clamped Three Level Inverter Module

In recent years, multilevel converters have been widely investigated for high power applications. With utilization of power devices with normal voltage rating, these topologies can provide high voltage and high quality output, which are very desirable in high power high voltage applications. Development of multilevel converters is of great significance for industrial drive applications such as variable speed drives for fans and pumps etc.In first chapter, the development of high voltage motor drive systems and the multi-level technique are summarized. The detailed structures and operating principles of several multilevel topologies are presented and explained. In chapter 2, the operating principle of a diode-clamped three level inverter is analyzed in detail. A 50kVA experimental prototype has been built, and the key points of hardware construction are introduced here by: component and material selection, principles and design of gate drive and protection circuits with optical fiber isolation, design methods of the laminated DC buses, the computer aided 3D structure design, test and verification of gate drive, and protection circuits, digital control platform based on DSP and CPLD etc. The experience and essential points in high voltage power converter hardware design are also summarized.In chapter 3, the utilization of the multilevel technique in medium voltage drive applications is discussed, the principle of multilevel variable speed motor drive and PWM control themes are introduced. Based on this prototype, a open-loop constant V/f drive system and a close-loop slip frequency control drive system are built and experimental waveforms are presented.