Research On Three-phase Vienna Rectifiers Control Strategy Without Grid Voltage Sensors

Compared with the two-level rectifier,the three-phase Vienna rectifier has the advantages of low grid-side current harmonic content and low switching tube stress;compared with the traditional three-level rectifier,it has fewer power switching devices,no need to set dead time,etc.advantage.At present,the three-phase Vienna rectifier is gradually being used in aviation power supply,electric vehicle charging piles and other fields.It is a three-level rectifier with great research value and has a wide range of application prospects.The thesis takes the three-phase three-level six-switch Vienna rectifier as the research object to reduce the system hardware cost and complexity,improve the dynamic and steady-state performance,and suppress the start-up inrush current as the research objectives.Three-phase Vienna rectifier control strategy without grid voltage sensors is studied,which mainly includes a simplified SVPWM method that can take into account midpoint potential control,grid voltage sensorless predictive control strategy,and a two-stage soft start method that suppresses inrush current.The thesis firstly introduces the working principle of Vienna rectifier,establishes the mathematical model of Vienna rectifier in three-phase static coordinate system according to Kirchhoff’s voltage law and Kirchhoff’s current law,and converts the mathematical model to two-phase static coordinate system by using Clarke variation.Secondly,the three-level SVPWM method based on two-level space is derived by referring to the space vector PWM method of two-level rectifier.This method can use the two-level space vector synthesis method to synthesize the three-level space vector,which reduces the algorithm computation and complexity.In addition,according to the effect of positive and negative small vectors on neutral point potential is opposite,a control strategy is designed to adjust the action time of positive and negative small vectors to suppress the fluctuation of neutral point potential.A simplified SVPWM method considering neutral point potential balance is formed by combining SVPWM method based on two-level space with neutral point potential balance control.Furthermore,the mathematical relationship between the ac side voltage and the switching signal and the dc side capacitor voltage is derived,and the Vienna rectifier grid voltage estimation algorithm is obtained,and the second-order low-pass filter is used to improve it,the improvement avoids the operation of pure differentiation and integration without increasing the complexity of the algorithm.Although the accuracy of the Vienna rectifier grid voltage estimation algorithm is very high,there is inevitably a certain error.Therefore,model predictive control with low parameter accuracy but high control quality is used as the controller.The predictive power control of Vienna rectifier is derived from the instantaneous power theory,and aiming at the signal lag problem caused by the acquisition and processing links in the actual system,put forward two steps predictive control compensation lag signal as much as possible to improve the effect of system control,the grid voltage estimation algorithm combine with predictive power control to form a predictive power control strategy for grid voltage sensorless.Then,in view of the problem that the Vienna rectifier is prone to happen inrush current during the startup process,which makes it difficult to start the rectifier,so the thesis designs a two-stage soft start method with a current limiting resistor and slow curve given dc side voltage reference value to suppress the inrush current,solving the problem of difficulty in starting the rectifier,thus forming a more perfect three-phase Vienna rectifier control strategy without grid voltage sensors.Finally,the simulation model and the experimental prototype are established to validate the control strategy,the results show that when removing the grid voltage sensors,Vienna rectifier still has the grid side current total harmonic distortion rate is low,the dc side voltage accurately track the reference,keep unity power factor running,the inrush current suppressed effect is good,and the dynamic steady-state performance is good,which proves the correctness and effectiveness of the proposed strategy.