Study On The Large-capacity Silicon Carbide MOSFET Module And Key Technology Of Converter Application

Due to the excellent physical properties of the silicon carbide?SiC?material,the SiC MOSFET becomes the most likely power electronic device to replace the Si IGBT.Especially in the applications of medium/high voltage and high power,the appearance of the SiC MOSFET module is bound to push the power electronics technology into a new stage.In order to make the SiC MOSFET module be better applied in power electronic converters,the following work is carried out in this paper:The dynamic and static performances of the most advanced large-capacity 1700V?300A SiC MOSFET module and Si IGBT module are tested and contrastively analyzed.Four performance characteristics of the SiC MOSFET module are found:?1?The switching losses of the Si IGBT module are greater than those of the SiC MOSFET module with the common external drive resistance even the external gate resistance of the former is reduced to zero;?2?The maximum dv/dt and di/dt?EMI?during switching transients of the SiC MOSFET module are close to those of the Si IGBT module when the external drive resistance is greater than a certain value?such as 8??but the switching loss of the SiC MOSFET module is much smaller than Si IGBT module;?3?Different from the exponential relation between the turn-on current peak of Si IGBT module and the load current?slope decreases gradually?,the turn-on current peak of the SiC MOSFET module has a linear relationship with the load current,so when the load current is large,the turn-on current peak of SiC MOSFET module may be larger than the turn-on current peak of Si IGBT module.It has been explained by a device turn-on current peak model proposed in this paper;?4?The induced negative gate voltage due to the cross-talk effect is more harmful to the SiC MOSFET module than the induced positive gate voltage when the gate off-voltage adopts the commonly used-6V.The loss modeling of the three-phase two-level converter using the SiC MOSFET module is presented.Firstly,through analysis and experiment when the SiC MOSFET is used as the switching device of the converter,there are three main characteristics below:?1?The SiC MOSFET module generally works in the synchronous rectification mode and its output characteristics are asymmetric between the first quadrant and the third quadrant;?2?The switching loss of the SiC MOSFET module is not proportional to the DC-bus voltage;?3?The SiC MOSFET module has a loss caused by the output capacitance.Considering the above three characteristics,on the basis of the traditional three-phase two-level loss model,the SiC MOSFET channel?or the channel and the reverse parallel SiC SBD?reverse continuation loss model?the SiC MOSFET output capacitance loss model are added and the voltage ratio in the traditional switching loss model is replaced by the switching energy ratio under different bus voltages.The experimental results show that the new model is more accurate than the traditional three-phase two-level converter loss model.Using this model,the efficiency of the100kW SiC MOSFET module converter at 5kHz to 80kHz is predicted and compared with the efficiency of the 100kW Si IGBT module converter,which proves the switching frequency and efficiency advantage of the SiC MOSFET module when it is applied to the converter.The switching process of the SiC MOSFET module in the SiC MOSFET converter is analyzed and modeled.Based on the model,the dead-time before the main switching device turns on(pre-dead-time T_d,ahead)and the dead-time after the main switching device turns off(post-dead-time T_d,after)are optimized to reduce the loss within the dead-time.The optimum asymmetry variable dead-time?OAVDT?is proposed by combining the pre-dead-time and post-dead-time after they are optimized and it can improve the efficiency of the converter and reduce the fundamental voltage loss.Experimental results show that compared with the traditional fixed dead-time setting,the OAVDT setting can effectively reduce the loss of the SiC MOSFET three-phase two-level converter,which is more obvious under the light load and the high switching frequency.In order to directly and accurately evaluate the feasibility of SiC MOSFET modules applied to high-power high-power-density converters,a 100kW high power density SiC MOSFET converter was developed.Firstly,the busbar,the heatsink and the three-phase inductor of the 100kW SiC MOSFET converter are designed.In order to reduce the volume of the converter,the optimal structure design of the three-phase inductor is carried out,and the power density of the converter reaches 1.657kW/dm³finally.Electromagnetic,thermal and mechanical properties of the 100kW SiC MOSFET high power density converter was verified by 100kW full power experiment.The volume analysis of the internal space of the 100kW SiC MOSFET converter shows that the proportion of its additional volume is as high as 55.5%,which means that the key to further increase the converter power density is to reduce the additional volume.There are 103 figures,7 tables and 135 references in this dissertation.