Research On Control And Modulation Strategy Of VIENNA Rectifier

With the development of the new energy vehicle industry,a large number of DC charging stations are connected to the power grid.As the most common front-end topology of DC charging stations,Vienna rectifier,the input current THD of which will seriously affect the stability of the power grid.In order to reduce the current THD of Vienna rectifier,the following improvements are made in this paper from two aspects of control and modulation.In the aspect of its control,firstly,the vector model of the current inner loop of Vienna rectifier is established by using the complex coefficient transfer function.Based on the vector model of the current inner loop,the phenomenon of system dynamic process overshoot and oscillation caused by the coupling of the current inner loop was analyzed.Due to the inherent errors in the model of the control object in practical applications,the decoupling process is also necessarily incomplete.By comparing the performance of current state with feedback decoupling and complex coefficient vector PI(cPI)controller decoupling in the case of incomplete decoupling,the performance advantages of cPI controller in model tolerance are clarified.Afterwards,the coupling problem caused by digital control delay was analyzed,and the prerequisite for ignoring phase delay and simplifying system parameter tuning was provided.The decoupling approach for phase delay was briefly explained.In terms of modulation,a Hybrid Triangular Carrier Based Discontinuous Pulse Width Modulation Ⅰ(HTCB-DPWM＿Ⅰ)method is proposed,which can generate same pulse sequences as the Space Vector Discontinuous Pulse Width Modulation(SV-DPWM),to solving the problem of sampling frequency improve limitation due to the complex algorithm of SPWM.A HTCB＿DPWM＿Ⅱ method with voltage clamping method is proposed to suppress the current zero crossing distortion,which is caused by the passive commutation characteristics of Vienna rectifier.Afterwards,in order to reduce the impact of midpoint voltage imbalance on the current control loop,the effects of these two modulation methods on the midpoint voltage were analyzed.By effectively combining these two modulation methods,an HTCB＿DPWM method with current distortion suppression ability,capacitor voltage balance ability,and the ability to effectively reduce the computational burden of digital signal processors(DSP)was obtained,which has comprehensive performance.In order to verify the performance of the control and modulation methods mentioned in this paper,an experimental prototype of Vienna rectifier with switching frequency of 25 k Hz and rated power of 1k W is designed.The simulation and experimental results indicate that,in the case of imprecise current inner loop model,compared to current state feedback decoupling,cPI controller decoupling provides better dynamic and static performance;HTCB＿DPWM can effectively reduce the computational burden of DSP and inherit the midpoint voltage balance ability of HTCB＿DPWM＿I and the suppress current zero crossing distortion ability of HTCB＿DPWM＿II.