Research And Design Of Soft Switch Photovoltaic Grid-connected Micro Inverter

With the promotion of smart grid technology and distributed power generation technology,as well as the promotion of the "carbon neutral" strategy,increasing the proportion of clean renewable energy such as wind and photovoltaic in the power grid has become an important development trend in the power industry in the next few decades.As an important equipment of distributed photovoltaic power generation,microinverters which are widely used in household and public infrastructure have always been a research hotspot in power electronics field.This paper focuses on the research and design of two-stage micro inverter with soft-switch.In this paper,a two-stage isolation structure is selected as the basic structure of the micro inverter.The front stage and the rear stage are composed of full-bridge converters,and a highfrequency transformer is used to realize current isolation to improve the safety of the inverter.In this paper,the piecewise linearization method is used to simplify the photovoltaic module external characteristic model,and the front stage topology of the inverter is modeled mathematically under the steady-state condition,and the controller is designed according to the system model.For the inverter stage,the hysteresis current modulation mode with constant loop width is adopted in this paper to realize the soft switch of the whole bridge without auxiliary devices at the rear stage.At the same time,the current modulation link is modeled and the stability analysis is carried out,and the error of the loop width caused by transmission delay is compensated.Considering the attenuation effect of switching noise and the inhibition ability of resonance,this paper selects the mixed passive damped LCL filter with split capacitor as the output harmonic filter of the rear stage,and gives the design scheme of output harmonic filter and EMI filter.In addition,the multi-element inspired maximum power point tracking algorithm is experimentally studied on the photovoltaic model experimental platform,and a hybrid algorithm of variable step size perturbation observation and particle swarm is proposed to reduce the possibility of the algorithm falling into the local optimal and reduce the maximum power point tracking error.In hardware design,a calculation method of initial and final driving voltages is used to simplify the design process of gallium nitride driver parameters.Finally,this paper uses STM32G4 as the main controller to build a 300 W micro inverter experimental prototype for grid-connection experiment and anti-island test.The 4.30% THD and 91% efficiency meet the design requirements.