Research And Design On Three Level Vienna Rectifier Of Three Phase Three Wire System

Compared with the traditional three-phase uncontrolled bridge rectifiers and thyristor phase controlled rectifier,three-level Vienna rectifier has been widely used because of its advantages of high power density,low harmonic content,high voltage rating,no dead zone,less switching devices and so on.However,due to the particularity of the topology,Vienna rectifier has inherent problems that three-phase current distortion at current zero-crossing.As with the three-level converter,there exists the problem of neutral point potential balance and system leakage current suppression.In order to reduce the harmonics injected into the power grid and ensure the stable and reliable operation of three-level Vienna rectifier system,it is necessary to solve the problem of three-phase current distortion at current zero-crossing,the neutral point potential balance and suppress the system leakage current.Firstly,the paper introduces the research background of three level Vienna rectifier and the present situation of the research on the current distortion at zero-crossing,the neutral point balance control and the suppression of the leakage current.Then the topological structure,basic working principle,neutral point potential unbalance and leakage current of three level Vienna rectifier are introduced.The influence of space vector on the neutral point balance and common mode voltage is analyzed to put forward the new strategy.Secondly,the mechanism of the three-phase current distortion at zero-crossing and the region of three-phase current distortion of Vienna rectifier are analyzed.By using the minimum reactive power compensation and in the region of current distortion injecting a certain zero sequence component,the problem of three-phase current distortion of three level Vienna rectifier is solved.And this method realizes the maximization of power factor.In the region of current distortion,the leakage current of the system is small,but the neutral point potential can't be adjusted.Therefore,the control of neutral point potential is strengthened and the leakage current of the system is small in the region of no current distortion.The specific scheme is: Based on the space vector,a new modulation strategy is proposed in this paper.The neutral point potential balance is controlled by the small vector of which common voltage is small.Not only strengthen the neutral point potential control and the system leakage current is smaller.Finally,the space vector modulation and carrier-based pulse width modulation are unified,and carrier-based pulse width modulation is simple and easy to implement.In order to verify the validity and feasibility of the proposed scheme,set up three-level Vienna rectifier platform.The current distortion at current zero-crossing suppression,neutral point balancing control and leakage current suppression schemes proposed in this paper are verified by simulation and experiment.The simulation and experimental results verify the validity of the theoretical analysis.