Research On Efficiency Optimization And Control Methods Of Mixed-Conduction-Mode Inverters

With the continuous expansion of the application field,it is a trend to continuously optimize the power density of inverters,which is of great significance to study the related technologies.This paper focuses on the related technologies of mixed-conduction-mode inverters to optimize the efficiency and reduce the size of passive components,and handles the issues of waveform control when inverters operating in mixed conduction mode.Firstly,this paper gives the analysis and comparison of the switching process and operation characteristics of inverters in different current mode.To gain the advantages of both discontinuous current mode and continuous current mode,mixed conduction mode is introduced into this paper,which makes the inverter reduce the switching losses in discontinuous current mode and lower the current stresses in continuous current mode of SiC MOSFETs.Furthermore,to handle the problems when modelling the inverters in mixed conduction mode,this paper proposed a new unified model which took the inductor charge as the control variable.Based on this model,the inverter in mixed conduction mode can be controlled flexibly and feasibly.Aiming at the mixed-conduction-mode inverter,this paper analysed its losses in detail,and established the dissipation model of each component.Based on this model,this paper discussed the relationship between the inverter efficiency and both the proportion coefficient of discontinuous and continuous current mode in the mixed conduction mode and the value of the filter inductor.Therefore,the optimal coefficient and the value of the filter inductor are determined as follow.The inverter can achieve highest operating efficiency with full load based on this design.On this basis,this paper further studied the related techniques on the waveform control of output voltage with the direct charge model.In this paper,four control methods were applied respectively,and the control effects of the waveform of output voltage were fully analysed and compared with different loads.The study shows that the waveform can beoptimized effectively with load current feedforward.The control method in parallel operation control of PI controller and repetitive controller with load current feedforward is most suitable for the mixed-conduction-mode inverter.It can obtain excellent quality of the output voltage waveform with either linear loads or non-linear loads.A 1.21kW-SiC MOSFET-inverter prototype platform was established and the experimental verification was accomplished on the platform.The experiment results verified that the mixed-conduction-mode inverter was of high-efficiency and with excellent quality of the output voltage waveform,and it also validated that the SiC-mixed-conduction-mode inverter possessed an excellent engineering application prospect.