Research On Sensorless Current Photovoltaic Micro-inverter Technology

In recent years, photovoltaic technology has become one of the most popularresearch focus. In domestic, large-scale grid-connected PV power stations have beenwidely used currently. Since high power photovoltaic inverter is unable to realize themaximization of generation efficiency and not to be maintained easily, the researcherspropose the photovoltaic inverter with small power level which is called micro-inverter.Recent years, micro-inverters have been very popular in western countries, especially inthe USA.Micro-inverter is usually connected with a single photovoltaic module, and iteffectively solves the problem of maximum efficiency of photovoltaic power generation.What’s more, the miniaturization of micro-inverter system make the technology ofdistributed power generation more flexible. In this thesis, in-depth research and analysisabout micro-inverter technology on the basis of the existing hardware platform will bedone.According to the efficiency advantages, interleaved flyback topology is selected asa micro inverter main circuit in this thesis. Then the principle of flyback converter ispresented and the properties of two modes of flyback circuit are analyzed and compared.Based on the analysis, the discontinued operation mode is chosen as the mainoperational mode to realize sinusoidal modulation.The research and analysis of control strategy about grid-connected micro-inverterof the flyback are completed. After which, two control algorithms of constant frequencyand variable frequency are introduced. The calculation of switching period and duty arededuced in the ideal case, and the control cycle variation range of BCM is also analyzedby using matlab software. Ultimately a control algorithm based on two operation modesis determined to act as the main strategy of this thesis.The control strategy of sensorless current MPPT is analyzed and studied. On thebase of the comparison between P&O method and Incremental Conductance method,the effect of the coupling capacitor of the pv-side in the entire PV system is theoreticallyanalyzed.Depending on the character of the whole system, the corresponding controlstrategy is presented. According to control strategy of primary side and secondary side,the corresponding software design of digital control is proposed. And the analysis andcontrol strategy are verified by experiments.