Research On Modulation Method And Control Strategy Of Three-phase Vienna Rectifier

The three-phase three-level Vienna rectifier has the advantages of high power factor,low stress of switching devices,and high power density,which makes it have good application value and broad development prospects in the fields of uninterruptible power supply,electric vehicle charging pile,and wind power generation.Many key performances of Vienna rectifier are affected by its modulation method and control strategy.The performances of the rectifier are affected by the modulation method,such as the capacitor voltage sharing characteristics,switching losses,etc.The redundant small vectors are used in pairs in the commonly used continuous space vector modulation method,so its switching loss performance needs to be improved.On the other hand,when designing the control strategy of the Vienna rectifier,in addition to meeting the basic control requirements,the dynamic performance and anti-interference ability of the system should also be improved as much as possible.Traditional PI double closed-loop control is a typical linear control strategy.Although the structure is simple and easy to implement,it has problems such as poor dynamic performance.Therefore,the three-phase Vienna rectifier is taken as the research object,and its modulation method and control strategy are studied in this paper.Firstly,according to the main circuit topology of Vienna rectifier,the working principle of its single-phase and three-phase circuits is analyzed.And based on the three-valued logic switching function,Kirchhoff’s law and coordinate transformation theory,the mathematical models and equivalent circuits of Vienna rectifier in three coordinate systems are deduced.Secondly,referring to the basic principle of conventional space vector pulse width modulation(SVPWM),a discontinuous SVPWM method with the ability to adjust the neutral-point potential is studied.The method is implemented based on a specified vector space partitioning method,which mainly includes basic steps such as sector judgment,vector sequence selection,and vector action time calculation.The amount of charge was analyzed to analyze the neutral-point potential regulation ability of the method,and based on the analysis results,the neutral-point potential control algorithm was designed;the switching loss of the discontinuous modulation method is compared with a continuous modulation method;The power factor variable range of the rectifier under the discontinuous modulation method is derived.In addition,the design process and characteristics of the traditional PI control strategy of Vienna rectifier are analyzed in detail.Meanwhile,considering the shortcomings of traditional PI control and the nonlinear characteristics of the system,a backstepping Control(BSC)strategy of Vienna Rectifier is proposed in this paper.Based on the traditional PI double closed-loop structure,the control equation of the BSC strategy is deduced,and the adjustment process of its core coefficients is studied.Finally,the Matlab/Simulink simulation model of traditional PI control system and the BSC system based on the discontinuous modulation method is built,and the dynamic and steady-state characteristics of the two control systems are analyzed and compared.Finally,the hardware platform of the three-phase Vienna rectifier is built,and the two control systems are experimentally verified and comparatively analyzed.The experimental results are basically consistent with the simulation results.The wave content is lower,the dynamic response speed is faster,and the neutral-point potential control effect is better when the BSC strategy is adopted,which verifies the correctness and feasibility of the BSC control system proposed in this paper.