Research On Two Types Of Three-phase Medium Frequency PFC Rectifier

Power electronic devices have an outstanding advantage of energy saving,so they are widely used in industrial,commercial and other occasions.Conventional rectifiers have non-linear operating characteristics,which make the harmonic of the network side current larger and cause voltage distortion and harmonic interference.In order to solve this problem,using PFC rectifier has become the common choice of power electronic devices.This thesis studies on two commonly used three-phase PFC rectifier: multi-pulse rectifier and three-phase combined PFC rectifier,which are usually applied in medium frequency occasion.Multi-pulse rectifier has many advantages such as low cost,high reliability and high overload capacity,etc.This article selects P-type 18-pulse isolated transformer rectifier as the object of study and the problem of taking the transformer winding turns as an integer is analyzed.The thesis establishes the mathematical model by introducing the ratio correction coefficient and gives the analysis of the condition that turns ratio changes.The analysis includes the changes of the height and width of each step of the input current,the changes of the amplitudes and commutation angles of the output voltages and the changes of the phase angles on the grid side.A prototype of 10 kW is designed,and the simulation and experimental results verify the correctness of the theoretical analysis.The thesis further systematically studies the three-phase combined PFC system.At first,this thesis analyzes the instantaneous input and output power pulsations in single-phase and three-phase PFC systems and points out that the characteristic of the three-phase PFC system is that the instantaneous input power is constant and the input-output power keeps a balance theoretically.If we can take advantage of the system's internal power balance reasonably,low frequency ripple of the output voltage can be reduced,which is beneficial for reducing the size of the storage capacitor.Based on this idea,different output combinations of three-phase PFC systems,including the module in series combination,the series combination of windings and modules in parallel combination,are analyzed.The thesis gives the choice of topological requirements and control strategies of different combinations and carries out simulation verification.Finally,the three-phase flyback parallel combination scheme is selected.The parameter is designed and the prototype is established.The experimental results verify the correctness of the theoretical analysis.