Research On Driving Techniques Of Series Connected SiC MOSFET

In the past few decades,Silicon-based power devices have dominated the power electronics applications.However,due to the restraint of physical properties,silicon-based technology is difficult to meet the growing power device performance requirements for powerhandling and switching-frequency capabilities nowadays.The third generation semiconductor material Silicon Carbide is an ideal material for replacing Si owing to its superior properties(e.g.,higher thermal conductivity and higher mobility).Si C-based MOSFETs have already entered the industrial market with the advantages of high blocking voltage,fast switching speed,small conduction losses and high temperature endurance.However,the performance of SiC power devices is still limited by immature material and device technology at present.The capability of commercial available discrete Si C MOSFET is about 1700V/40 A now.These devices still do not meet voltage requirement for building medium voltage power electronic equipment.In order to improve the application range,Si C MOSFET can be connected in series to improve the withstand voltage level.However,due to device characteristic difference and asymmetric circuit layout,static and dynamic voltage imbalance occurs and affects the safety of the circuit.Static and dynamic voltage balancing of series-connected Si C MOSFET are demanded to prevent overvoltage breakdown.Static voltage balancing is relatively easy to implement by parallelling voltage shunt resistors with each MOSFETs.However,due to the extremely fast switching speed of Si C MOSFET,dynamic voltage balancing is arduous.Therefore,dynamic voltage balancing in series-connected Si C MOSFET is critical.First of all,this paper elaborates published domestic and foreign research methods for series connected power device and points out their strengths and weaknesses.Then this paper analyzes the characteristics of MOSFET switching processes and various factors that influence voltage sharing of series-connected Si C MOSFET.Then determines key factors that influence voltage sharing by software simulation.A novel series connected Si C MOSFET topology based on clamping circuit has been introduced in this paper.This topology can effectively preclude the occurrence of static and dynamic overvoltages in series-connected Si C MOSFETs.The novel series connected Si C MOSFET topology based on clamping circuit has simple structure.This paper analyzes the working principle of clamping circuit and the requirement of component parameter values.The diode and capacitance clamping circuit can insure that the drain-source voltage of Si C MOSFET does not exceed the voltage of clamping capacitance and prevent overvoltage breakdown.In order to limit the voltage of clamping capacitors,this paper introduces clamping assisted circuit and energy recovery circuit.According to needs and features,a dual switches flyback converter is designed as energy recovery circuit.This circuit can limit the voltage of clamping capacitors and recycle the excess energy.Circuit principles of energy recovery circuit has been analyzed.The control strategy of energy recovery circuit is that dual switches will switch on when the voltage of clamping capacitor exceeds rated voltage.Then the voltage of clamping capacitors decrease and the excess energy of clamping capacitors will be transferred to bus capacitors.This paper designs corresponding transformer isolated drive circuits on the basis of requirements of series-connected Si C MOSFET main circuit and energy recovery circuit respectively.The working principles of transformer isolated drive circuits and the requirement of component parameter values have been illustrated.Simulation of the proposed topology has been done in the Cadence Pspice platform.2800 V Si C MOSFET module has been implemented by three serial Si C MOSFETs.The function of transformer isolated drive circuits have been tested.The function of main circuit,clamping circuit and energy recovery circuit have been verified.The simulation results show that the proposed topology can prevent the occurrence of static and dynamic overvoltages.The PCB schematic and layout of the series-connected Si C MOSFET topology are drawn under Altium Designer and test of the prototype is made to verify the above design.The design function of driving circuit,clamping circuit and energy recovery circuit is consistent with simulation results.The feasibility of the proposed topology is confirmed.