Research On Some Control Strategies Of Cascaded Multilevel High Voltage Inverter

With the development of electric drive technology, the high voltage inverter brings the important action of motor energy conservation into play. The study of the cascaded multilevel high voltage inverter in our country is one of the research technology which is the international advanced level and has great significance in the field of the national power electronics.This thesis chooses the cascaded multilevel high voltage inverter as the subject to be investigated. Based on the system structure of the inverter, a detailed theoretical analysis and experimental research have been carried out centered on the PWM technology, the flying restart technology, DC brake technology and the power cell bypass technology.The basic principle, structure, relation and function of every part for the inverter are first introduced simply. Then based on the introduction of two-level PWM modulation, the carrier phase-shifted SPWM for cascaded multilevel inverter is analyzed. The validity of the method is validated by the experiment. The output capability of the inverter is analyzed.To improve the performance of the system, based on the particularity of its, two aspect methods of the flying restart technology are proposed. One is based on V/f control system and added the flying restart inspecting device, the other is a frequency search method based on the stator current vectors, together with an effective maximal current limitation controller. To improve the dependability of the system, a method of stepwise rise voltage of realizing DC brake technology is proposed. By experiment, providing over-current operation is proved when breaking. In the thesis, an intelligent power cell bypass technology and several methods of bypass voltage control are proposed. They improve effectively the reliability of the system and can be used universally in industry.