Study On Control Strategy Of Three-Phase VIENNA Rectifier

With the booming development of China’s manufacturing industry,power electronic converters are widely used.The consequent large amount of reactive power and highfrequency harmonics lead to a decrease in the power factor of the power grid,therefore,improving the power factor of power converters is one of the current research hotspots.Threephase VIENNA rectifiers are widely used in applications with high power factor requirements due to their low input current harmonic content,small output ripple and no need to join the dead band.In this dissertation,a space vector PWM(Space Vector Pulse-Width-Modulation,SVPWM)control strategy and a single-cycle control strategy are investigated for three-phase VIENNA rectifiers with the primary objective of improving the grid-side power factor.In this dissertation,the mathematical model of the VIENNA rectifier is constructed based on its operating principle.In the SVPWM control strategy,the modulation process of this control strategy is simplified by using a three-level to two-level modulation algorithm,reducing the complexity of the control.The sector interval is re-divided and calculated to further optimize the space vector modulation algorithm,achieving a significant improvement in control accuracy and efficiency.To improve the stability of the VIENNA rectifier system and balance the mid-point voltage on the DC side of the circuit,the influence of different fundamental vectors on the mid-point voltage balance is investigated,and the mid-point voltage balance is achieved by controlling the relative action time of the positive and negative short vectors,and the control system is designed.Secondly,under the single-cycle control strategy,small-signal modelling of the controller is carried out according to the derived core control equations,and phase compensation is applied to the input current in order to improve the system power factor and efficiency.In addition,the analysis and control strategy design is carried out for the fluctuation of the mid-point potential on the DC side.The fluctuation caused by the AC component of the capacitor voltage difference is eliminated by controlling the zero-sequence component using the third harmonic current injection,and based on this,a PI controller is introduced to eliminate the DC deviation in the mid-point current flowing through the capacitor on the output side,so as to achieve the balance of the mid-point potential on the output side.Finally,the hardware platform and software system of the VIENNA rectifier are designed and implemented through simulation analysis and experimental platform construction,and the software program ideas and flowcharts are given.Given the simulation parameters,both control strategies can improve the system efficiency to a certain extent and achieve stable and reliable operation of the VIENNA rectifier.The two control strategies studied in this dissertation are of broad research value and application prospect for three-phase VIENNA rectifiers,which have important reference values for improving converter efficiency and power factor,and are conducive to the further promotion and application of VIENNA rectifiers in grid-side power factor regulation.