Research On Three-level VIENNA Rectifier

The traditional rectification device will cause the decrease of the voltage quality of the power grid and the power utilization rate.How to suppress the power grid pollution and improve the power quality effectively has become an urgent problem to be solved.The rectifier based on PWM control has the characteristics of sinusoidal input current waveform,low total harmonic current and unit power factor unit power factor operation,so the rectifier as a switching power supply is widely used at present.Compared with the traditional three phase half bridge two-level rectifier,the three-level VIENNA rectifier has the characteristics of low stress,no dead time and less total harmonic distortion,which has become a hot spot of research.Firstly,the current flow path of three-level VIENNA rectifier under the polarity of single-phase and three phase current is analyzed in detail.The corresponding mathematical models of VIENNA rectifier in abc and dq coordinate systems are established respectively,and the corresponding matrix equations and equivalent circuits are derived.Secondly,the three-level SVPWM space vector distribution is analyzed.In view of the complexity of modulation algorithm for the general three-level SVPWM,the SVPWM equivalent modulation method based on the square of two electricity is used in this paper,and the detailed derivation is given.For the problem of neutral point voltage imbalance in the DC output side of the VIENNA rectifier,the influence of the basic vector to the change of the middle point voltage is analyzed in detail,and the balance factor method is used to control the unbalance of the middle point voltage.According to the matrix equations obtained by the modeling,the control system of the current inner loop and the voltage outer loop of the three-level VIENNA rectifier is designed.In view of the poor effect of the current loop PI control on the harmonic suppression of the power grid current,a parallel complex control strategy of "PI+ repetitive control" is adopted in this paper,and the structure of the repetitive controller is analyzed in detail.Finally,the control method designed by the simulation comparison has a certain effect on the suppression of harmonic current.Finally,a prototype of a 5kW three-level VIENNA rectifier is completed and the roast machine runs for a long time.The data and test results of the roast machine show the rationality of the control method and parameter design adopted by the three-level VIENNA rectifier,which shows the preliminary effect of the whole design.