Research On Three-phase And Three-wire VIENNA Rectifier Control And Modulation Methods

Non-linear load is an important part of the power electronic system,but it may cause plenty of harmonic harm in the power grid.Therefore,it is necessary to suppress harmonics from the root,and this prompt the application of power factor correction(PFC).VIENNA rectifier as a three-level topology using PFC technology has many advantages.And also can reduced the quantity of power devices by a large extent.Because of the special reverse series structure of the power switch,each power switch withstand a relatively small voltage stress,and the design of the drive signal is also relatively simple.A better control effect can be achieved with a small power density.And the capability of current tracking is strong so the power factor is unitization.The main task of this paper is to study the control and modulation of VIENNA rectifiers.In order to further improve the efficiency of the system,a new modulation method has been studied and verified through simulations and experiments.Firstly,the development background of the power factor correction technology is briefly introduced.After comparing the advantages and disadvantages of several common three-phase three-level rectifier topologies,the advantages of VIENNA rectifier are demonstrated.Secondly,after analyzing the work principle of the system,the mathematical model of input currents and output voltages are builded in three different coordinate systems.This is the first step in understanding the VIENNA rectifier system and it is also the basis for designing the system controller.Thirdly,based on the established mathematical model,the structure of the two controlled object models of the system is analyzed,namely input current and output voltage,and a double-loop proportional-integral controller is designed accordingly.At the same time,the analysis of the controller,system stability,and the chosing of PI coefficient is performed.Fourthly,the space vector modulation and midpoint balance of VIENNA rectifier are studied.The model of midpoint voltage of the DC bus is obtained and its controller is designed whitch is then added to the SVPWM modulation algorithm.The simplification of the three-level SVPWM is analyzed in detail,and the midpoint potential of the DC side is controlled by adjusting the action time of the redundancy vector.Fifthly,though the advantages of the simplified method of three-level vector modulation are obvious and the algorithm is simple and easy to implement,in order to further improve the system efficiency,a vector modulation method that combines the five-step intermittent modulation and switching action prohibition for large current is proposed.In this paper,the principle of the two methods to reduce the loss is analyzed in detail,and the implementation scheme of combining the two strategies and simultaneously solving the midpoint imbalance problem is presented.Finally,the feasibility of the scheme is proved by simulation and experimental data.