High Efficiency Optimization Of Micro-inverter Based On The High Frequency AC Link

PV grid-connected inverters can be divided into three types: centralized inverters,series inverters and micro-inverters. Micro-inverters with the features of high MPPTefficiency, high system efficiency, low installation cost, plug-and-play, enhancingsystem flexibility and modularity, had become the development trend of photovoltaicgrid-connected inverters in recent years.The efficiency of the micro-inverters determines the energy utilization, and moreimportantly, high-efficiency means the low total cost of the network system, whichmakes the product more attractive. At present most of the grid-tied micro-inverterschoose flyback topology or high frequency link with multi-stage topology. Forflyback topology, the high conduction loss and the current loop existing in PN sectionlimited the total efficiency, while it is hard to guarantee the overall efficiency formulti-stage topology as well. In order to improve the efficiency of the micro-inverter,in this thesis a topology based on high frequency AC link, adopted single-stage gridstructure, realizing ZVS of all switching while eliminating the current loop in PNsection.Based on the high-frequency AC chain topology proposed and studiedpre-adoption phase modulation and corresponding post-stage matrix converterswitching strategies, so that all the switches operate at the same switching frequencyand fixed duty cycle, eliminating the pre-conversion the drawbacks. Pre-seriesresonant inverter, phase modulation by the DC voltage into a50Hz frequencyenvelope of the high frequency AC resonant current, the corresponding matrixconverter current zero crossing switch to the resonator, the resonant high frequencyalternating current direct conversion of50Hz grid current. While using the Fourierseries method, considering the main harmonics, simple and accurate deduced resonantinductor-capacitor design parameters analytically.The genetic algorithm is applied to optimize the design of magnetic componentsto further improve efficiency through multi-objective optimization, from the databaseto quickly select the right core, wires and winding way to achieve high effic iencymagnetic component design. By optimizing the design, the optimized value of themagnetic element relative to AP-based design of a magnetic element, the efficiencycan be increased by3%to5%.According to frequency AC single-phase single stage topology of the chaincorresponding to the overall control strategy proposed to improve enhanced PLL, toimprove their ability to inhibit the DC bias, incremental conductance improvedmethod based on the maximum power point tracking, improve noise immunity,thereby reducing the number of wrong judgment, thereby increasing the maximumpower point tracking speed.Against the overall topology control strategy is proposed based on the enhanced PLL active islanding detection strategy, by adding a reference phase current isproportional to the phase of the grid disturbance, and then apply the Goertzelalgorithm to extract the amplitude of the second harmonic grid determine the island,compared to other active islanding detection, detection area while achieving nothingand net current THD increased by only0.5%.Theoretical analysis is verified through simulation and experimental, under200w,CEC efficiency was92%, the maximum efficiency of93.2%.