Abstract:

In order to meet the micro-power photovoltaic inverter input voltage range wide,and the characteristics of the high efficiency requirements,this paper proposed a two-stage type micro-inverter of high frequency power transformation plan.The top level LLC resonant full bridge converter at the switching frequency is higher than the resonant frequency,at the same time using frequency PFM and phase shift PWM control strategy,which not only meets the requirements of the photovoltaic panels wide voltage range,but also realizes the efficient power transformation of the wide voltage range.The MPPT control method with the latter stage power disturbance is simple to control and avoids the shortage of many control variables in the former stage disturbance.The optimal design method of resonant tank was presented,which can optimize the efficiency of the converter.A 250 W/220 V AC/50 Hz grid-connected photovoltaic inverter was developed.The experimental prototype has good grid-connected current performance index,high efficiency of the prototype,and fast tracking speed and accuracy of MPPT,which verifies that the proposed scheme,design and control method are correct and effective.

Key words: photovoltaic mciro-inverter, LLC resonant converter, PFM, phase-shift PWM, MPPT