Research And Design On Three-level Svpwm Rectifier

With the rapid development and wide application of the modern power and electronic technology, the harmonic pollution of the power grid caused by the common diode rectifier is increasingly serious. Improving the power factor of the grid and eliminating the harmonic pollution have become the trend of the technology development of rectifier.The three-level NPC rectifier can eliminate the harmonic pollution of the grid, not only realizing the unity power factor control, but also achieving the bidirectional transmission of the energy between the AC side and the DC side. At the same time, the DC voltage of the rectifier DC side is adjustable and stable in a certain range. This thesis takes three-level NPC rectifier as the study object, analyzing the principle and topological structure of the three-level NPC rectifier and derives the mathematical model on the basis of the principle. Establishing the mathematical model is a effective method to study the three-level NPC rectifier and provides the theoretical basis for the study of the control strategy.Based on the mathematical model of the three-level NPC(neutral-point-potential control) rectifier, a high performance control method based on d-q axis feed-forward decoupling control strategy is presented. In order to avoid the abrupt change of output voltage vectors, a novel space vector modulation algorithm is proposed, which negative small vectors are adopted as first active ones. Action Sequences of output voltage vectors to synthesize the desired vector are given and the duty time of active vector corresponding triangle vertex is deducted. The neutral point potential stability is realized by detecting three phase AC side current and the direction of neutral point current and capacitance voltage and assigning the real effect time of positive and negative space vectors in reason. Finally the correctness of proposed SVPWM method is confirmed by experiment results.At last, the thesis introduces the design of the hardware circuit of and software the whole three-level NPC rectifier control system. This circuit takes the chip TMS320F240 as the controller.