Research Of Buck Circuit Based On SiC Power Devices

Compared with traditional vehicles,electric vehicles are more eco-friendly and electric power is renewable,thus electric vehicles have broad prospects for development.However,electric vehicle applications can't live without the support of high-conversion-efficiency,high power density on-board charger and charging point.On-board charger is mainly composed of EMI filter circuit,AC/DC link and DC/DC link.EMI filter can improve the anti-interference ability of the charger,inhibit electromagnetic interference flowing between power grid and equipment.Alternating current from the EMI filter will enter into the AC/DC converter,whose function is rectifying,power factor correcting and filtering.The DC/DC converter transforms the direct current from the front level into high frequency pulse direct current,and then passes it through the filter to form stable,low-voltage direct current,finally provides the DC power supply for battery.Buck converter and Boost converter can form a bridgeless on-board charger with high power density,in which Boost converter plays the role of AC/DC link and Buck converter plays the role of DC/DC link.Therefore,the research of a stable,high-conversion-efficiency,high-power-density Buck circuit is meaningful.In order to keep the output DC voltage stable under the condition of disturbances,the Buck circuit should adopt the closed loop control.The principle of closed loop control is that sample the output changes caused by disturbance,then pass it through error amplifier,comparator and driving circuit,and finally affect the switching devices,thus weaken the output changes.Besides,soft-start circuit can decrease inrush current during the start-up period,which is caused by the closed loop control.In the converter,switching devices will bring in switching losses,which is against the promotion of conversion efficiency.The Zero Voltage Transition technology can decrease the switching losses of switching devices,which is helpful to the promotion of the conversion efficiency.At the same time,it doesn't require that the switching devices should withstand larger current and voltage.In addition,compared with silicon power devices,SiC power devices have a series of excellent properties,which makes them more suitable for application in high frequency converter.For instance,SiC MOSFET's parasitic capacitances are small,and the reverse recovery time of its parasitic body diode is short.SiC schottky diode also has short reverse recovery time and small switching time.The combination of ZVT technology and the excellent characteristics of SiC power devices will further enhance the conversion efficiency of the converter.In this paper,component parameters are designed and components are selected reasonably on the basis of theoretical analysis about each link of the converter.Then several simulations are made with the help of the PSPICE software,including the simulation of drive circuit,the simulation of ZVT,the open loop simulation,the closed loop simulation and so on.After simulating submodules correctly,the simulation of the whole circuit is done.Furthermore,comparison of circuit based on SiC power devices and Si power devices is carried out.The comparison shows that the efficiency of circuit based on SiC devices can reach up to 98.55%,which is 0.69% higher than that of circuit based on Si devices.Finally,draw the PCB of the converter with Altium Designer,produce the prototype,weld the PCB and test the circuit.Its testing efficiency can reach up to 96.03%.