Research On A New Z-source Inverter And Its Application

Z-source inverter overcomes the traditional voltage source inverter ’s buck output,output current waveform distortion and other problems,and it alse has the characteristics of allowing the bridge arms to be short circuit or open circuit,which is now widely used in photovoltaic grid-connected power generation,fuel cell and other aspects.However,the traditional Z-source inverter has the problem of freewheeling shoot-through state in the resonant system,which limits its application in the field of wireless power transmission.The traditional shoot-through modulation strategy of the ZSI has a large inductive current ripple.Although the coupled inductor can suppress the input current ripple,the problem of freewheeling shoot-through state in resonant system has not been solved.In this paper,ASC-qZSI is taken as the research object,and its freewheeling shoot-through state in resonant inverter system is studied,and the new modulation strategy to suppress the input current ripple is proposed.The freewheeling shoot-through state of ASC-qZSI is studied in the single-phase resonant inverter system.The critical condition and the characteristic equation of voltage boost ratio are conducted.Then we derived the implicit function of the freewheeling shoot-through duty ratio to the shoot-through duty ratio.By analyzing the boost duty ratio curve and the inductor current curve,we knew that the freewheeling shoot-through state increases the complexity of the controller design process and reduces both the output power quality and the system security.By analyzing the working mode of the ASC-qZSI,an improvement topology and modulation is proposed to eliminate the freewheeling shoot-through state,which is verified in the PLECS simulation model.When ASC-qZSI adopts the traditional through modulation strategy,the inductor current ripple is large.In order to reduce the input current ripple,this paper proposes the PWM2 asynchronous shoot-through modulation strategy for the single-phase inverter system.By analyzing its working mode,we derived the expression of the inductor current ripple.Compared with the traditional PWM1 synchronous shoot-through modulation method,the ripple is reduced by more than50%.According to different insertion of the shoot-through state,the space vector modulation of the traditional ZSI in the three-phase system can be divided into four-segment insertion and six-segment insertion,where the four-segment ZSVM has a smaller input inductor current ripple.Based on the four-stage inserted ZSVM,this paper proposes a ZSVMm ripple suppression modulation strategy for ASC-qZSI,Theoretical analysis and calculations are given in terms of operating mode,DC bus voltage,and maximum inductor current ripple.Compared with the traditional ZSVM,the inductor current ripple is reduced by more than 50%.Finally,the experimental platforms of the single-phase resonant inverter system and the three-phase inverter system were built respectively.The PWM2 asynchronous shoot-through modulation strategy and the ZSVMm asynchronous shoot-through modulation strategy were experimentally verified.The experimental results are consistent with the theoretical value under two different strategy,which proves the correctness of the theoretical analysis.