Research On Coupled-inductor Impedance Source Inverter

Conventional inverter can not achieve boost-buck function at the same time,and not be used in the circumstances of input voltage with wider range.However,all the inverter systems that achieve boost-buck voltage function through introducing dc-dc converter are secondary systems,and the mutual restriction among switches and the coupling control parameters greatly increase the control difficulty and lower the system reliability.In order to improve the aforementioned problems,the single-stage boost-buck technology based on Z-source inverter is proposed,but Z-source inverter itself also has some disadvantages such as lower voltage gain,no common ground between input and output and discontinuous input current.In view of the problems above,this paper improves the topology structure s of impedance source inverter on the basis of summarizing previous studies,and studies suppression methods of input current ripple,inductor current intermittent compensation methods,boost control strategy and output voltage closed-loop control strategy.The detailed contents are as follows:Based on the study of boost converter,Z-source converter and Quasi-Z-source converter,a series of generalized coupled-inductor impedance network topology structures are proposed through combining the aforementioned converters and coupled-inductor boost technology.Through summarizing the change rule of the four kinds of coupled-inductor cells(Y-shape,T-shape,Γ-shape and flliped Γ-shape),deriving the impedance source inverter topology structures based on the aforementioned coupled-inductor cells to improve the boost ability,realize the continuous input current and lower the device voltage stresses.Aiming at the problem that the coupled-inductor cells will produce larger current ripple when charging and discharging,this paper obtains the input current ripple suppression methods based on topology itself through analyzing the input current ripple mechanism of coupled-inductor impedance source inverters.On this basis,this paper propsoes a series of coupled-inductor impedance source inverter topology structures with low input current ripple.Through analyzing the influence of shoot-through segmenting mode on the input current ripple,the multi-stage shoot-through space vector pulse wide modulation(SVPWM)strategy is proposed to further lower the input current ripple of coupled-inductor impedance source inverters.In order to solve the dc-link drop problem of impedance source inverter in discontinuous inductor current state,a kind of Quasi-DC-DC output cell(QDDOC)is proposed by analyzing the operation characteristics of DC-DC converter which flexibly can work in continuous and discontinuous inductor current states.Aiming at QDDOC,this paper propsoes the generalized compensation method of discontinuous inductor current to ensure the stable output of the dc-link voltage of impedance source inverter in discontinuous inductor current state,and make impedance source inverter flexibly work in continuous and discontinuous inductor current states.At the same time,the proposed compensation method increases the boost ability,lowers the device voltage stresses and improves the output voltage quality.In view of the structural characteristics of the coupled-inductor impedance source inverter based on QDDOC,the theoretical analysis process and specific implementation method of the corresponding simple SVPWM boost strategy and maximum SVPWM boost strategy are presented.In this paper,the dual-feedback output voltage control strategy based on gain linearization is proposed to overcome the shortcomings of conventional output voltage closed-loop control strategy for impedance source inverters.This strategy can reduce the control mistakes caused by the device voltage drop through the input and output dual-feedback control,realize the stable voltage output even when the input voltage fluctuates in the wider range,and realize the linear relationship between the gain and t he shoot-through duty ratio by adjusting the modulation index so as to improve the performance of the control system.