Research And Realization Of I-type NPC Three-level Rectifier

Clean energy replacing fossil energy has become the inevitable trend of the development of energy. With the continuous breakthroughs in the development of clean energy technology, the high voltage transmission line should be built to guarantee the development of large-scale clean energy bases and the reliable grid-connect. As an emerging variable conversion technology, three-phase three-level rectifier technology has received more and more attention in energy and power field, especially in high voltage power transmission field because of less harmonic pollution and lower device voltage. The I-type diode clamped is widely used in the three-level rectifier for its less harmonic output and high control efficiency. In this thesis, the three-level rectifier has been deeply studied based on the diode clamped topology. The control strategy and modulation strategy of the three-level rectifier have been adapted. And a balance control method has been carried out to inhibit the unbalance of neutral point voltage.Firstly, two different topologies of three-level rectifier have been analyzed. The operational principles have been introduced to obtain the mathematical model of three-level rectifier. Secondly, based on the grid voltage orientation, combining the voltage/current double closed loop control with current feed forward decoupling, the control system of the rectifier has been designed. The three-level voltage vector modulation strategy has been specifically analyzed and then the method of neutral point voltage balancing has been proposed. A large number of simulation experiments have been carried out in Matlab/Simulink to verify the control system, modulation strategy and balance method.Then, based on the theoretical derivation and simulation experiments, a three-level 2kW rectifier prototype has been designed. Finally, by the experimental prototype, the debugging experiments have been carried out. The data and waveforms of the dynamic adjustment condition and stable condition of the experiments have been both recorded. These records have been compared with the simulation and theoretical results. Comparison of the experimental results has fully proved the feasibility of the design scheme of three-level rectifier.