The Isolated Resonant Drive Circuit Design For SiC MOSFET

While the traditional Si MOSFETs is reaching their physical limits in performance,the third generation of wide-bandgap semiconductor power device SiC MOSFETs have been used widely in the field of high frequency and high power density due to their superior physical characteristics concerning high operating temperature,high voltage capability,fast switching speed and so on.However,as switching frequency increases,the driving energy is consumed totally by resistance in the gate path because of no energy recovery feature in conventional drive scheme resulting in lower efficiency and reliability.Therefore,it is very necessary and important to study how to reduce effectively drive loss of SiC MOSFETs in high frequency.In this thesis,a new type of isolated resonant gate drive circuit is proposed for SiC MOSFETs applied in high frequency on the basis of the conventional full-bridge voltage source isolated drive circuit topology.The basis idea is to utilize the resonance between transformer's leakage inductance and the power MOSFET's input capacitor.The energy storaged in the input capacitor is recovered into the leakage inductance,and then charges the input capacitor reversely.It helps SiC MOSFET complete the switching of ON/OFF state and realizes the gate energy recovery.It achieves the purpose of reducing SiC MOSFETs drive loss in high frequency.At the same time,it also works to recover the energy storaged in the gate parasitic inductance,so it can reduce the drive voltage's overshoot and shock.Besides,it achieves the function of driving the high side switch in the bridge converter by employing drive transformer's fuction of electrical isolation Secondly,in view of SiC MOSFETs' special characteristics of the asymmetry maximum gate voltage and the high frequency crosstalk interference,the proposed drive circuit can offer the asymmetry positive and negative driving voltage by using the level shift circuit realizing reliable off-state for SiC MOSFETs and suppress effectively the phenomenon of the false trigger in high frequency field.Finally,the proposed drive circuit topology is verified in a 800W syschronous buck converter.The experiment results show that the gate driver can offer the asymmetry voltage range from-2.27V to +19.58V so as to meet the drive requirement of SiC MOSFET.Compared with the conventional drive scheme,the voltage spike is about 2V reduced by 50%.In the case of the switch frequency up to 1MHz,the converter system peak efficiency is improved from 86.3%to 86.7%(an improvement of 0.4%)and the drive loss is reduced from 3.26W to 1.17W(a reduction of 64%).It can be seen that the drive loss is reduced effectively in high frequency field.So the target in the thesis is reached.