Three-phase Power Factor Correction And Digital Control System

Three-level power converter has the advantage of low device stress, high power density, and has been widely used in Industrial applications. Because of its special Three-level structure, it shows much difference when compared with the traditional two level rectifier, such as the method of control and analysis.In order to improve the performance of three-level Vienna rectifier and power factor correction, a mathematical model is built up,the basic structural characteristics, working process and overall performance are analyzed. The analysis on power factor correction includes two aspects, one is traditional phase-oriented PWM-based control, and the other is the technology of space vector control. What is more, an improved three-level space vector synthesis technology is proposed. With the help of the technology geometric projection, complex three-level problems are simplified to traditional two level ones. The position of reference vector is calculated according to the direction of three phase current. Compared with the traditional method, it can make use of existing two-level synthesis method, makes the complex process of vector synthesis easily understand and grasped.Besides the power factor correction of single equipment, the parallel operation of multiple devices is analyzed too. The analysis process is based on two mathematical models, one analysis the two devices as a whole on the AC side, the other from the DC side. Through the above work, problems such as the flow path of circulating current between devices, the mutual influence between devices and so on, are simplified. At the same time, the important role of zero sequence components is revealed under parallel operation conditions. Based on Thevenin's equivalent principle, the mathematical model of DC output side is constructed. The results of the analysis show that DC output voltage has an effect on the generation on the circulating current. At the same time, the theory of virtual resistance is used in the control process. With the help of the theory of virtual resistance, power factor correction can be realized and circulating current can be kept to the minimum.From the point of structure, mathematical model of three-level Vienna rectifier, the power factor correction method, problems about single and multiple equipments are analyzed in detail.