Research On Modulation Methods And Control Strategies Of VIENNA Rectifier

With the power electronic equipment widely used in the field of power conversion,it also brought lots of harmonic pollution to the grid.Therefore,the study on green and clean PWM rectifier with high power factor and low input current distortion has become a popular issue for the technology of power electronics applications.The VIENNA rectifier which is based on a combination of a three-phase diode bridge and a DC/DC boost converter,has the following advantages: higher power factor than traditional rectifier topologies,low blocking voltage stress on the power switching transistors,high power density,no need to set dead-time and simple control structure.It's main shortcoming is the energy flow is unidirectional.This paper,the prime circuit used on the electric vehicle charger as a research object,researches on the controlling and the modulation methods of VIENNA rectifier.Firstly,this paper focuses on the principle of the VIENNA rectifier;secondly,the mathematical models are deduced based on state-space method in three kinds of common coordinate systems;finally,this paper simplifies the analysis of switching characteristics with ternary logical function.All of these preparations provided a strong foundation for the further study of VIENNA rectifier.Then this paper focuses on the modulation methods of VIENNA rectifier.Two kinds of carrier-based modulation methods which are applicable to VIENNA rectifier are analyzed and compared with the Fourier analysis technology.The conclusion is the synchronized triangular carrier phase current is better than not synchronized saw-tooth carrier.Then this paper classified the space vectors according to vector length,after that what the three kinds of vectors will impact on neutral-point potential balance is analyzed.One simple three level space vector modulation method based on two level space vector modulation method is used in this paper,this method avoided complex trigonometric calculations.On the problem of neutral-point potential unbalance,the method of zero sequence current injection is used when the modulation method is based on carrier;when the modulation method is based on space vector,this paper adopts the method of allocating the time distribution of the redundant vectors in a switching cycle.Simulation model is built based on Simulink,experimental verification for above method is did based on the 7.5kW electric vehicle charger module.