The Design Of A Three-Phase/Level VIENNA Rectifier And Researches On Its Neutral Point Voltage Balancing Control

Compared with the traditional three-phase two-level PWM rectifier,the three-phase three-level VIENNA rectifier has the advantages of low voltage stress and low input current THD.Compared with other three-level PWM rectifier topologies,it has fewer circuit components and no bridge arm straight-through problem.Therefore,as a low-cost and high-performance three-phase AC/DC solution,VIENNA rectifier has been widely used in communication power supply,electric vehicle charging pile,UPS(uninterruptible power supply)and renewable energy application.Firstly,this paper studies the operating principle of VIENNA rectifier,and deduces the mathematical model of VIENNA rectifier.Based on those,the design method of VIENNA rectifier control system is analyzed.Then the implementation method of VIENNA rectifier carrier modulation and space vector modulation is analyzed.The simulation model of VIENNA rectifier is built in the paper,and the model is used to verify the analysis,derivation and control system design.The DC side neutral point voltage unbalance is a inherent problem of three-level topologies.In this paper,the VIENNA rectifier is used to study the neutral point voltage unbalance.The paper divides the neutral point voltage unbalance into AC unbalance and DC unbalance.And studied it separately.Aiming at the neutral point voltage AC unbalance(ie,neutral point voltage oscillation),this paper analyzes its formation mechanism,deduces the time domain equation of the oscillating voltage,and establishes the quantitative relationship between the amplitude of the neutral point voltage oscillation and the circuit parameters.Aiming at the neutral point voltage DC imbalance,this paper studies the estimation method of DC unbalance voltage,proposes a DC imbalance suppression method based on PI regulator,and analyzes the design method of PI parameters.Aiming at the suppression of the neutral point voltage imbalance in the VIENNA rectifier,this paper starts from the relationship between the midpoint current of the DC side and the unbalance voltage in neutral point,and derives the ideal zero sequence component which can make the midpoint current of the DC side zero.By suppressing the midpoint current on the DC side by injecting the ideal zero sequence component into the modulation wave,the suppression of the neutral point voltage oscillation is realized.Combined with the DC unbalance suppression method,a composite neutral point voltage balancing control strategy is proposed.The composite balancing strategy can simultaneously achieve the suppression of DC unbalance and AC unbalance in neutral point.Then,through simulation analysis and experimental verification,the effectiveness of the composite neutral point voltage balancing strategy is proved.Finally,this paper designs a prototype of VIENNA rectifier,and introduces the design process of the software and hardware system of the prototype.Based on the prototype,the control system design,voltage modulation method,and the aforementioned neutral point voltage balancing strategy of the VIENNA rectifier were experimentally verified.