Research On High Frequency Isolated Photovoltaic Grid-connected Inverter Based On DSP

Recent years, with the rapid development of photovoltaic technology andappearing of the energy crisis, green and contamination free solar energy has attractpeople’s attention, the large-scale application of photovoltaic power generationtechnology will be the inevitable trend in the future. This paper uses a DSP basedtwo-stage high frequency isolated photovoltaic grid-connected inverter as theresearch object, introduces the design principle of hardware circuit of photovoltaicgrid-connected inverter, and the maximum power point of photovaltic array tracking,analys the phase-shift full bridge soft switching circuits in different model loop,employ the two-closed loops control the inverter side, and research the reliability ofthe photovoltaic grid-connected inverter.The design of the hardware circuits are important links in the design of gridptotovoltaic system. The paper makes play of a5KW high frequency isolated inverteras the research object, and apply the TMS320F28069DSP as the main controlchip,and carries on the detailed analysis of the hardware circuit design and theprinciple of the circuit.In order to improve the conversion of photovoltaic cells, they shall work in theirmaximum power point.Based on the analysis of the output characteristics of thephotovoltaic cells, to achieve the maximum power point tracking, the incrementalconductance method is a good choice.For the sake of eliminating the tail current of IGBT,reducing the duty cycle lossof the soft switching condition, the thesis adopts a phase-shiftf full bridge circuit withsaturated inductor, analyses the phase-shift full bridge circuit in the half switchingperiod under different working modes.The control of grid-connected current is the key to control the grid connectedphotovoltaic system, which establishes a mathematical model of the inverter outputstage circuit, analys the disturbance of the grid-connected current principle and gridvoltage of the LCL filter, puts forward the grid voltage feed-forward compensationcontrol the grid connected current based on the digital PI.The reliability research of the system mainly on the hardware, software,islanding detection and other aspects of the system.Reliability of the hardware circuitmainly in the view of the deficiency of the system hardware circuit design andthe matters, proposes the corresponding improvement measures. And the softwareones chiefly introduces the principle of software protection, and gives the threshold ofprotection. Aiming at the lacking of detection of islanding detection in passiveislanding detection blind zone and active islanding introduce interference, thedissertation puts forward a method based on passive islanding detection ofgrid-connected of grid-connected current, obtained a better effect of islandingdetection.Finally, photovoltaic system on the design of the experiment, the experimentalresults show the feasibility and rationally of the system designing, gains a reliableand stable results.