Research And Optimization Of Vienna Rectifier Modulation Strategy

For high-power DC charging equipment of electric vehicles(EVs),the two-stage structure of front-stage AC-DC rectification and rear-stage isolated DC-DC conversion is usually used for electric energy conversion.As a three-phase Power Factor Correction(PFC),the Vienna rectifier has the advantages of low input current distortion rate,high power density and high efficiency.Compared with the ordinary three-level neutral point clamped rectifier(NPC),the Vienna rectifier has the advantages of simple structure,simple driving scheme and few power devices.It is widely used in the front stage of DC charging equipment of EVs.Taking Vienna rectifier as the research object,this paper studies and optimizes the modulation strategy of the Vienna rectifier.The main research contents are as follows:Firstly,the research status of the Vienna rectifier is introduced,the working principle of the Vienna rectifier is analyzed,and the mathematical model of the Vienna rectifier in different coordinate systems is established.A double closed-loop control strategy is adopted according to its mathematical model in the Synchronous Reference Frame(SRF).The inner current loop and the outer voltage loop are adjusted by using the PI controller’s characteristic of no static adjustment of the DC quantity.When designing the parameters of the PI controller,two methods,the frequency domain parameter design and the root locus parameter design are used and compared to obtain the best controller gain.Then,the Vienna rectifier’s simplified SVPWM and neutral point potential balance control based on three-level to two-level are analyzed.By injecting the zero sequence component with neutral point potential control into the reference voltage,the equivalent CB-SVM is realized based on dual carriers.The digital implementation process of carrier-based pulse width modulation(CB-PWM)is analyzed.Combining the advantages of SVPWM and CB-SVM,a simplified space vector modulation strategy is proposed,and the influence of small non-redundant vectors and medium vectors ignored in neutral point potential balance control is analyzed.Further,a CB-NSVM(carrier-based new space vector modulation)modulation strategy with a neutral point dynamic compensation factor is proposed to suppress the low-frequency oscillation of neutral point potential after balance control.Then,the influence of the phase offset angle of the input filter and the DC side voltage imbalance on the zero-crossing distortion of the input current of the multi-port Vienna rectifier is analyzed.The suppression strategy of the zero-crossing distortion of the input current under the DC side voltage balance condition is introduced.The importance of the clamping area is analyzed,and it is further determined that the multi-port Vienna rectifier operates under the DC side voltage balance and imbalance condition,Clamping area under different operating conditions.The influence of neutral point current fluctuation is analyzed,and the corresponding optimized zero sequence component is calculated.By adding the clamping compensation component in the clamping area and the optimal component in the non-clamping continuous area,the CB-OCSVM(carrier-based optimal clamping space vector modulation)modulation strategy is proposed,which can take into account the low harmonics of the input current on the AC side and the low voltage fluctuation on the DC side.Finally,the simulation analysis of the Vienna rectifier is carried out through MATLAB /Simulink to verify the parameter design of the proposed double closed-loop controller,the effectiveness of CB-NSVM and CB-OCSVM optimized modulation strategy and the correctness of the theoretical analysis.The hardware platform of the Vienna rectifier is built for experiments to verify the feasibility of the proposed controller parameter design and optimized modulation strategy.