Research And Design On Control System For Cascaded Multilevel Inverters

With the development of electrical drive technology recently, High voltage and high power inverter has already become one of research focus in AC drives. 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 widely application in the future.Multilevel power conversion has the ability to make lower voltage semiconductors be stably used to high-voltage and large-capacity applications while reducing the high order harmonics produced by PWM control efficiently. But its topology and control is rather complicated. Due to expanding to medium-voltage fields easily, cascaded multilevel power inverters have been utilized in medium-voltage motor drives and reactive power compensations of power system. This dissertation is devoted to research the topological structure, PWM control method and application in motor drives of cascaded multilevel inverters, so that some effective methods for optimizing topology and improving control performance could be proposed..Cascaded multilevel power inverters are different from traditional 2-level power inverters. Because of an increase of switch components, the distribution of driving impulse is caused. Moreover, there exists some technique difficulty about interface of driving impulse between digital signals process available and switch components of multilevel power inverters. Hence, considering the control system consisted of cascaded multilevel power inverters, this dissertation is devoted to research some fields as follows:1. Based on the main circuit of cascaded multilevel power inverters, analyze the operating mechanism of 3-cell serial inverters in depth.2. Contrast and analyze the Pulse Width Modulation and Space Vector Modulation for Cascaded Multilevel Inverter. The result of experiment is discussed, and the conclusion is significative. This dissertation provides experimental data and guideline of technique.3. Under analysis of theory and emulational validation, it designed the whole experimental system, including the main circuit (based on IPM), control unit, (based on DSP&CPLD), in order to improve the performance of system.