| Three-phase Vienna rectifier,as a kind of superior three-level rectifier topology,has the advantages of low device stress,high power density,low harmonic current pollution and so on.It has been widely used in the industrial field.Similar to the traditional three-level rectifier,the DC voltage is set by step,and there is an impulse current on the side of the network and an overshot of the DC bus voltage in the start-up stage.Excessive impulse current increases the stress of the switch tube,which seriously affects the stable operation of the rectifier.In addition,in steady-state operation,current distortion is easily generated at the grid side current crossing point based on conventional carrier PWM modulation strategy,which increases the harmonic current of the grid.To solve the VIENNA rectifier at startup and steady-state problems produced during the operation,based on the three phase six switch VIENNA rectifier topology as the research object,analyzes in detail its working principle,mathematical model and equivalent circuit model,and then puts forward a method of two sections of soft start and improvement of the distortion of the net side current control strategy,and through the simulation and experiment of the proposed control strategy is verified.This paper first introduces the working principle of three-phase three-level Vienna rectifier,establishes the mathematical model based on Cartesian coordinate system,twophase static coordinate system and two-phase rotating coordinate system,deduces the related function expression,and calculates the switching stress when the switching device works,which provides the theoretical basis for the equipment selection.Secondly,through the established mathematical model,the traditional double-closed loop control strategy is used to design the parameters,and the traditional sector division method of space vector modulation and the sector division method of space vector modulation based on two levels are elaborated respectively.For the unbalance of midpoint potential in three-level rectifier,the reason of unbalance of midpoint voltage in rectifier is analyzed,and a control strategy of changing midpoint voltage by controlling the action time of positive and negative small vectors is proposed based on the influence of small vectors on the fluctuation of midpoint potential.In view of the VIENNA rectifier in the process of start a web side impact current and dc bus voltage overshoot problem,puts forward a twopart startup strategy,with three phase half controlled rectifier bridge as the charging circuit,slow curve function as the inner ring current for a given value,makes the implement no impact on the current in the startup phase rectifier,dc bus voltage overshoot,and through the simulation and experiment verify the validity of the proposed method.Then,study a modulation wave voltage compensation methods to eliminate the net side current waveform distortion when passing zero,the current in a zero to satisfy constraints,design of zero voltage compensation strategy,calculated the modulation wave voltage compensation scope,eliminates the distortion of the current,solve the problem of the net side current distortion,reduces the power grid harmonic current,and through the simulation and experiment verified the effectiveness of the proposed control strategy.Finally,according to the application situation and performance requirements of the research direction,the hardware experimental selection design of Vienna rectifier is given,and an experimental prototype with DSP28335 as the control chip is built,and the experimental results are analyzed to verify the feasibility of the method proposed in this paper. |
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