Research On High Performance Hybrid Switch Three-level T-type Inverter

Efficiency and cost are two important indicators of photovoltaic(PV)inverters.Achieving high efficiency of PV inverters at a lower cost is a research hotspot.In this dissertation,the current SiC PV inverter technology is first reviewed in terms of efficiency,power density,circuit topology,switching frequency and so on.Then SiC hybrid switch inverter technology is summarized and analyzed.Compared with full SiC inverter,SiC hybrid switch inverter can effectively reduce costs while achieving high efficiency.For low-cost and high-efficiency power conversion requirements,in this dissertation,the research on the key application technology of hybrid switch with the combination of largecurrent silicon(Si)insulated gate bipolar transistor(IGBT)and small-current silicon carbide(SiC)metal-oxide semiconductor field-effect transistor(MOSFET)in three-level T-type grid inverter is carried out.The loss model of the inverter is established after the deep analysis of the commutation state of the three-level T-type hybrid switch grid inverter.Furthermore,the cost and loss model of the hybrid switch inverter is proposed,and the relationship between the cost and loss of the hybrid switch inverter with different ratios is revealed.The influence of different device combinations,turn-on and turn-off time delay on the loss and efficiency of the hybrid switch inverter is proved.In addition,the LTSPICE simulation model of the three-level hybrid switch inverter is established.Finally,the experimental verification is carried out on a 20 k W hybrid switch grid inverter.Theoretical analysis and experimental results show that using hybrid switch in a three-level T-type inverter can achieve high efficiency and increase switching frequency and power density at relatively low cost.In this dissertation,the study of the hybrid switch gate drive modes is carried out from the perspective of inverter efficiency.There are two degrees of freedom in the Si-IGBT/SiC-MOS hybrid switch gate drive modes,so there are many different combinations of drive modes.And different gate drive modes will affect the loss distribution and efficiency of the inverter.Therefore,a comparative study of several gate drive modes is carried out.In view of the overheating risk of small current SiC MOSFETs,gate drive modes with SiC MOSFETs turned off in the middle are proposed.The influence of middle conduction time on inverter efficiency is revealed.Finally,an experimental verification is carried out on a 20 k W hybrid switch grid inverter.In order to slove the problem of large parasitic inductance of the inverter designed by the hybrid switch with discrete devices,this dissertation conducts research on the design method of the low parasitic inductance three-level T-type Si-IGBT/SiC-MOS hybrid module.A layout scheme of the three-level T-type hybrid module is proposed.First,the commutation loops of the three-level T-type hybrid module under non-unity power factor are analyzed.The self-and mutual inductances models of the multi-path segments of commutation loops are established,and the key current commutation loops of the three-level T-type hybrid module are determined.Secondly,for the stacked substrates with low parasitic inductance,the effects of different layout schemes on parasitic inductance and thermal resistance are compared.Finally,a hybrid module solution is proposed with stacked bond wire substrates structure which is easy to produce and cheap.The designed low parasitic inductance three-level T-type Si-IGBT/SiC-MOS module is verified by static on-state voltage drop test,commutation loops’ parasitic inductance measurement,dynamic double pulse test and single-phase hybrid switch inverter grid-connected experiment.The measured loop parasitic inductance is consistent with the simulation results,and the designed single-phase grid inverter based on the hybrid module can operate stably.The work of this dissertation is summarized at last,and the future works are presented.