Research Of Grid-Connected Photovoltaic Solar Micro Inverter

Micro inverters have high efficiency, plug and play, low cost, and many other advantages which are widely used in daily life. The micro inverter topologies and the maximum power point tracking algorithm are the keys to the high efficiency and performance of the inverter technology.Now the staggered parallel flyback topology, isolation boost topology and high frequency AC chain topology are more commonly used and effective micro inverter topologies. This paper analyzed the circuit diagrams, working principle and control strategy of the three kinds of topologies. The staggered parallel flyback type and isolation boost type topologies have more power transformations, higher conduction loss of power switch tubes and more complex control strategy. While the power switch tubes of the high frequency AC chain micro inverter topology which is single-stage transformation, all realize the soft switching technology to improve the efficiency of the system. Because of the bad micro inverter working environment, the reliability of the system is also crucial in addition to considering the factor of system efficiency when we are choosing a topology. By the components counting method we analyzed the main circuit topologies of the staggered parallel flyback type and high frequency AC chain micro inverters. Through calculating the life of the two systems, the voltage stress of power switch tubes and the capacitance value, we can conclude that:the life cycle of the high frequency AC chain micro inverter is about 25 years and the voltage stress of power switch tubes is moderate.This topology has higher reliability.With the phase shift modulation, the series resonance circuit of the high frequency AC chain micro inverter outputs the high frequency AC current of 50Hz sine envelope, and the matrix transformation circuit outputs 50Hz low frequency current into the grid. According to the principle above,we designed the main circuit of the high frequency AC chain micro inverter including the selection of the power switch tubes and the drive circuit, the series resonant circuit, the transformer, etc. In order to further improve the efficiency of the system, the MOSFET based on SiC is selected which has high working voltage, high switching frequency, low loss, etc. In addition, we designed the control strategy of the full bridge inverter and the matrix converter.At the same time, this paper studied the perturbation and observation method, the incremental conductance method and the new variable step size maximum power point tracking algorithm based on three kinds of Step lengthes. With the MATLAB/Simulink simulation software the three algorithms were analyzed, and the results showed that the new variable step size method had the advantages of high efficiency and rapidity.Finally, we designed the simulation parameters of the main circuit of the high frequency AC chain micro inverter, set up the system simulation model through the Multisim software platform, and compared the switch waveforms of the full bridge inverter and the matrix converter and harmonic current waveform. The results showed that all the power switch tubes achieved the soft switching technology. The matrix converter was applied to make the harmonic current injected into the grid or back to the circuit, which improved the energy utilization rate. Using the SiC materials, the prototype based on the FPGA validated that the high frequency AC chain micro inverter had good output voltage and current waveforms, and the system efficiency is higher than 96%, conforming to the theoretical research.