Research On Reliability Of Quasi-z Source Inverter Power Module In Different Modulation Strategies

The performance of the electric vehicle is affected by the reliability of inverter directly.The quasi-Z source inverter has the function of buck and boost with single-stage system,allowing the upper and lower devices of each phase leg to conduct at the same time(shoot-through),which can improve reliability of inverter and has attracted much attention in the field of electric vehicle applic ations.However,the reliability of power devices of quasi-Z source inverter will be affected by the shoot-through state.The shoot-through state is implemented by modulation strategies.While,the switching frequency and shoot-through current of power devices depend on modulation strategies,which leads to the differences of power losses and temperature in different modulation strategies.In this paper,three kinds of SVPWM modulation strategies of three-phase voltage type quasi-Z source inverter are selected to analyze the reliability of IGBT power module,and a hybrid modulation is proposed based on the foregoing.The correctness of the above theoretical analysis and the effectiveness of the proposed hybrid modulation strategy are verified by the simulation results.Firstly,the principle of three kinds of SVPWM strategies of quasi-Z source inverter are explained in this paper.And then the DC bus voltage,the number of shoot-through phase legs,switching frequencies and shoot-through duty ratio of the power devices under each strategy are analyzed,so as to provide the basis for power device loss analysis of each modulation strategy.Secondly,the formulas for calculating the average loss of IGBT under three modulation strategies are derived according to the switching frequencies and the shoot-through current of the IGBT of each modulation strategy.The steady-state average junction and temperature fluctuation of IGBT are analyzed in detail based on the average loss and instantaneous loss.And then,IGBT l ife expectancy is predicted by Coffin-Manson life model.Losses,average junction temperatures,junction temperature fluctuations and lifetime of IGBT in three modulation strategies are compared.The circuit model of three-phase voltage type quasi-z source inverter and IGBT loss,junction temperature and life prediction model are built in MATLAB/Simulink under three kinds of modulation strategies.The correctness of IGBT reliability analysis of the above three kinds of modulation strategies is verified by the simulation results.Finally,a hybrid modulation strategy suitable for output current variation is proposed based on the characteristics of the IGBT reliability with two maximum boost modulation strategies,which can improve the reliability of power mod ule of quasi-Z source inverter.The simulation results show that the proposed hybrid modulation strategy can achieve the purpose of reducing IGBT junction temperature fluctuation and extending its lifetime under the working condition of changing output cur rent,so as to improve the IGBT reliability of the power module of the quasi-z source inverter...