| Impedance source inverter(ISI)has been recognised as the most promising single stage power converter with both boost and buck capabilities and inverter legs shortcircuit immunity.ISI provides a cost-effective solution in renewable energy systems applications,such as photovoltaic,wind power generation and electric vehicle,which make them a superior alternative to the conventional two-state inverters.Reliablity and output harmonic performance are critical issues for ISI when operate at harsh environments.This thesis presents a detailed analysis of various modulation strategies and their effect on the reliability and harmonic performance of ISI.Afterwrd,two space vector pulse width modulation(SVPWM)strategies are proposed to improve the reliability and output harmonic performance.A comparative evaluation was carried out based on the ISI electro-thermal model built in the MATLAB/Plecs and the experimental prototype.This thesis starts by analyzing the operation principle of the three phase ISI,under which the shoot through(ST)state and non-shoot through state have been intensively analysed.Besides,the factors that affect the generation of ST state are explored and three basic schemes of inserction the ST state are investigated.Then,the conventional modulation strategies including three sinusoidal pulse width modulation(SPWM)and five SVPWM are fully analysed.Considering the seen drawbacks of prior art modulation strategies,two novel SVPWM strategies are proposed to improve the reliability and harmonic performance of ISI.Subsequently,the impact of modulation strategies on the reliability performance of ISI have been comprehensively investigated with regards to the current stress,power loss,junction temperature number of cycles to failure.And therewith the harmonic impact of ISIs under various modulation strategies have been explored by gaining insight into the relationship between the inductor current ripples and phase current.To intuitively demonstrate the reliability and harmonic impact of modulation strategies on the ISI,and validate the effectiveness of the proposed modulation strategies,a three phase ISI were simulated in MATLAB/Plecs and experiment results were presented with the established prototype.Both simulation and experimental results confirmed that the modulation strategies would affect the reliability and harmonic performances of the ISIs.More importantly,the proposed modulation strategies can significantly improve the reliability and harmonic of the ISI.It’s noteworthy that this thesis provides valuable theoretical foundation and technical support for evaluating reliability and harmonic performance of ISI.Additionally,the benchmarking in this thesis enables identifying the most appropriate modulation strategy for ISI to achieve better performances in terms of reliability and output harmonic. |
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