Research And Design Of Three Phase SiC Onboard Charger

In order to comply with the requirements of energy conservation and emission reduction.How to reduce the huge carbon emissions produced by traditional fuel vehicles become a research hotspot which made the electric vehicle industry developing rapidly.At the same time,safe and efficient electric vehicle battery charging has become an important link in the development of electric vehicles.With its convenient charging performance and small size,on-board OBC provides the possibility of long endurance and fast charging of electric vehicles.This paper uses 6.6k W SiC on-board OBC as the main research content,discussing the use of new material power electronic devices to design a high efficiency and high power density vehicle OBC prototype.According to the function and design requirements of 6.6k W three-phase on-board OBC,the common topology of on-board OBC is analyzed,then selecting the two-stage topology.The first stage topology is three-phase six-switch full bridge rectifier circuit,and the second stage is LLC full bridge circuit.The topological structure of the threephase six-switch PFC rectifier circuit at the front stage is illustrated and its working principle is analyzed theoretically.The single-cycle control modulation is used as the control algorithm of the pre-stage PFC,and the control system can eliminate the steadystate and transient errors in one cycle to ensure that the errors of the previous cycle will not accumulate to the next cycle.The typical waveforms and principles of the LLC full bridge circuit under three resonant modes are analyzed.The basic wave analysis method is used to calculate the gain of the converter,and the limitation of the basic wave analysis is pointed out in combination with parasitic parameters.The LLC resonant parameters were designed by comprehensively considering the factors such as device stress,efficiency and converter gain in the converter,and the designed resonant parameters were simulated and verified.The device selection of the main power circuit was carried out and the overall converter loss was calculated.Based on the application requirements of high switching voltage,the influence of parasitic parameters is analyzed and the solution is given.In terms of control,the first stage is digital single-cycle control,and the second stage is single voltage or single current closed-loop control.After the control model is verified by simulation,the peripheral resource allocation of the chip is determined after the selection of the chip according to the control requirements.The control strategy of the whole machine is illustrated by the flow chart.The appearance of the prototype is briefly introduced and the experimental data are listed.With the influence of actual parasitic circuit parameters,the capacitor buffer circuit and RC buffer circuit are paralleled on the SiC MOSFET pins,and the drive clamp is added.According to the above design results,a 6k W experimental prototype is made and debugged.Under this premise,the experimental waveform and experimental data under different power and different output voltage are analyzed to verify the function and various indicators of the prototype.The prototype has achieved a wide range of output requirements,at rated working point,the full load efficiency reaches 94.1%,which meets the design requirements.The experimental results are basically consistent with the theoretical analysis results,which verifies the reliability of the circuit design process and the control process.