Basic Research Of Medium-High Voltage Variable-Frequency Technology

The variable-frequency technology is to meet the needs of AC induction motor stepless speed regulating coming into being. With the development of new power electronic component and computer technology, the variable-frequency technology becomes more mature day by day. The variable-frequency variable-speed system for high voltage motor is a burgeoning technology in recent years, which has realized high voltage and high power induction motor stepless speed regulating. It not only could enhance the turnout and quality of products, but also could economize large numbers of power energy and reduce production cost if high voltage motor could change their velocity smoothly using high voltage inverter. It has huge market potential and wide application in the future. High voltage and high power inverter has already become one of research focus in AC drives.Cascaded multilevel power conversion has the ability to make lower voltage semiconductors be stably used to high-voltage and high-power applications. As one of the most popular multilevel topologies, cascaded multilevel power conversion has been applied widely in the high voltage and high power drive fields. Input circuit adopting multi-winding phase-shifting isolation transformer technology and output circuit using multilevel PWM control technology are two outstanding features of the cascaded multilevel power conversion. In the paper, analyzed the operating principle of the cascaded multilevel power conversion, and expounded the multi-winding phase-shifting isolation transformer technology which adopted extensional triangle connection manner, and also proven that multi-winding phase-shifting isolation transformer could eliminate inputting harmonic current. Base on the analysis of operation principle for the cascaded inverter, in this thesis the modulation principle of multilevel phase-shifting SPWM control technology has been explained in detail, and the superiority of harmonic elimination under this SPWM modulation has been demonstrated also. Base on the theoretical analysis for the experimental system, the experimental equipment of cascaded inverter with two power cells cascaded every phase was set up, this equipment adopted a phase-shifting isolation transformer, and the contravariant main circuit used Intelligent Power Module, the core of the controller was made up of Digital Signal Processor and Complex Programmable Logic Device devices. Based on this experiment platform, the software and hardware was debugged, no-load test of asynchronous motor driven by the inverter was performed. These works establishes a basis for further studies.