Control And Design Of Threephase Multilevel Current Source Rectifier Based On SVPWM

The multilevel rectifier can realize the sine of the AC side current,and make the system operate at unit power factor and achieve adjustable power factor and low harmonic content.With the maturity of superconducting technology,some of the disadvantages of multilevel current source rectifier have been improved,and their applications have continued to expand.The multilevel current source rectifier can complete the bidirectional flow of energy between the DC side and the AC side,that is,energy can flow back from the DC side to the AC side to achieve the inverter effect,and the energy can also be transmitted from the AC side to the load side to complete the rectification effect.There are many control strategies for multilevel current source rectifier.Among them,the SVPWM control strategy has the advantages of easy digital realization,lower switching loss and better dynamic performance,and can be applied to multilevel current source rectifier.This article mainly studies the theory of three-phase multilevel current source rectifier based on SVPWM algorithm.(1)This paper studies the mathematical model of a three-phase multilevel current source rectifier.According to the low-frequency equivalent circuit of the single-module three-phase current-type rectifier,the low-frequency equivalent circuit of the three-phase multilevel current source rectifier is analyzed and the three-phase circuits on the AC side are independent of each other,and there is no coupling In conclusion,one-phase circuit can be analyzed separately and then three-phase circuit can be analyzed in the same way,considering its switching tube function model,analyzing its harmonics,and obtaining a high-frequency mathematical model of three-phase multilevel current source rectifier.(2)This paper studies the theory of SVPWM algorithm in a single-module three-phase current source rectifier,and conducts experiments and simulations to verify it.The control system of the three-phase current source PWM rectifier adopts a double closed loop design to control two variables,one is the DC side current to make it equal to the given value,and the other is the three-phase grid-side current,which controls the grid-side power factor It is 1,so that the system maintains the unit power factor operation,and controls the grid side current and voltage to be in phase.And built MATLAB/Simulink simulation model and experimental platform for simulation and experimental verification.(3)This paper presents the theory of a three-phase multilevel current source rectifier in which multiple modules are connected in parallel with the SVPWM algorithm.The space vector diagram of the three-phase current source 7-level rectifier is made,the vector diagram is analyzed,the vectors are classified,and the vectors are further filtered,so that the filtered vector achieves a 7-level vector synthesis effect.On the basis of the vector diagram,according to the principle of equivalence,the vector action mode is analyzed,and the vector action time is calculated.Finally,a basic definition is made to the composite vector and the basic vector,the relationship between the composite vector and the basic vector is analyzed,and the corresponding relationship between the composite vector,the basic vector and the switching tube is determined,and the combination sequence of the switching tube is determined,so that the 7-level rectifier The vector analysis is more concise,and the principle of sector independence is proposed,which provides a theoretical basis for the principle of current sharing in the next chapter.Build a simulation model in MATLAB/simulink for simulation verification.(4)This paper studies the current sharing problem of parallel modules,and proposes a current sharing method between modules.First,analyze the current sharing of the rectifiers connected in parallel with two modules.Based on the SVPWM algorithm,different vector synthesis methods are studied,and a vector control method is proposed to realize the current sharing of the two modules.On this basis,the current sharing theory of the three modules is analyzed,and the current sharing theory method of the three modules is proposed.This paper proposes a current sharing method based on the feedback of the shunt inductor current on the DC side.The thesis carried out simulation verification on three current sharing methods.(5)Finally,an experimental platform based on TMS320F28335 DSP was designed and built,and the parameters and specifications of the experimental equipment were designed.Design the hardware circuit,design the AC side LC filter parameters and load side smoothing inductance.Finally,the SVPWM algorithm of the single-module current-mode rectifier is verified.