Modeling And Research On Control Of The Extended-boost Quasi-z Source Cascaded Multilevel Photovoltaic Inverter

The fossil energy crisis and environmental pollution have become the global key issues,and solar photovoltaic power generation is regarded as one of the most prospective clean energy sources.However,solar photovoltaic power generation is susceptible to environmental conditions and the output voltage of a single photovoltaic cell is low.The key to solve these problems is the power converter.In view of the shortcomings of traditional single-stage or two-stage power converters in the application of photovoltaic power generation,a large number of studies have been dedicated on the combination of cascade multilevel inverter(CMI)and quasi-Z source inverter(qZSI),which result in quasi-Z source cascade multilevel inverter(qZS-CMI).Aiming at low input voltage and wide range input voltage of the photovoltaic power generation,the extended-boost quasi-Z source(EqZS)network is applied to cascade multilevel system and the dissertation puts forward extended-boost quasi-Z source cascade multilevel inverter(EqZS-CMI).Then its basic theory is investigated and the corresponding modulation strategy and grid-tie control scheme are proposed.The specific research details are as follows:(1)A parameter design method to limit the double-line-frequency(2?)ripples is presented.In order to limit the inherent 2? voltage and current ripples in the single-phase EqZS inverter(EqZSI)module,the equivalent model based on EqZSI module is established.The relationship between the 2? component of each state variable and the EqZS network parameters is analyzed.The 2? ripples are suppressed within the required range by designing the parameters of impedance source network.(2)A novel phase-shifted pulse-width-amplitude modulation technique based on dual switch frequency modulation(DFM-PWAM)is proposed.By analyzing the existing phase-shifting sinusoidal pulse width modulation(PS-SPWM)and phase-shifted pulse-width-amplitude modulation(PS-PWAM),the combination of DFM and PWAM causes input and output sides of the H-bridge module to operate at different switching frequencies.The switching losses under PS-SPWM,PS-PWAM and DFM-PWAM techniques are compared in detail,and the proposed modulation strategy mitigates the switching frequency effect on the switching losses.(3)The control strategy of photovoltaic power generation system based on EqZS-CMI is proposed.The traditional PI controller and proportional resonant(PR)controller are applied to the grid-connected control to realize distributed MPPT control,independent DC-link voltage control and the grid-connected control with unity power factor.The simulation model of the system is established,which verifies the effectiveness of the whole control method.(4)A low-power experimental prototype is designed and an experimental platform is built.The experimental results further verify the EqZS-CMI,the established mathematical model and the proposed modulation technology.