Research Of The Vienna Rectifier Based On SiC Power Devices

While the extensive application of power electronic devices in various fields provides convenience for industry and life,it also injects a large amount of harmonic current and reactive power into the grid,which affects the normal operation of both the grid and other gridconnected devices.The current quality and power factor of three-phase rectifiers are particularly valued.Therefore,active power factor correction devices using controlled switching devices have received increasing attention.The three-phase three-level Vienna rectifier has bright application prospects in the fields like electric vehicle charging infrastructure and aviation power supply due to its advantages of good current harmonic characteristics,high power factor,low voltage stress of semiconductors,simple structure and high reliability.The efficiency and power density of the rectifier have also become key indicators in some fields.Compared with Si power devices,the new generation of power devices represented by SiC MOSFETs has the advantages of low on-resistance,high switching speed and strong thermal stability,so it can promote power electronic devices to higher efficiency,higher power density and higher reliability.This thesis focuses on the Vienna rectifier based on full SiC power devices,including both hardware design and control algorithm.First,the working principle and working mode of the Vienna rectifier are analyzed in detail,and its mathematical models in the abc static coordinate system and the d-q rotating coordinate system are established respectively as the theoretical basis for subsequent work.Secondly,based on the established loss model of SiC MOSFET and Schottky diode,the model of the switching circuit of the Vienna rectifier is derived.In order to promote the efficiency of the Vienna rectifier,the loss of several SiC and Si power devices in the Vienna rectifier are evaluated,fully demonstrating the advantage of high efficiency of SiC power devices in the Vienna rectifier.With the loss model used,the power devices selection of the Vienna rectifier is optimized.In addition,a forced air cooler for the switching circuit is designed,and the effectiveness of the cooler is verified through thermal simulation.Furthermore,the input and output filters are also designed.Thirdly,aiming at reducing the harmonics of the input current,the harmonic composition of the two Carrier-Based PWM modulation methods is analyzed from the perspective of inductor current ripple.For power factor correction and controlling the output voltage,a double closed-loop PI control method is analyzed and designed in the d-q rotating coordinate system.With the root cause of the neutral-point voltage unbalance analyzed,an optimized CarrierBased modulation algorithm is proposed to supress the neutral-point voltage unbalance,of which the effectiveness is verified by simulation.Finally,a 55 kW Vienna rectifier prototype is designed and is verified through experiments.The experimental results show that the prototype achieves a power factor close to 1 with a low current THD and a controllable DC voltage with small ripple,also the neutral-point voltage unbalance is significantly suppressed under the optimized Carrier-Based modulation algorithm.