Research On Control Method Of Photovoltaic Inverter Considering Harmonic Impact

In recent years, looking for new energy has been the main task in the process ofsocial development under the circumstances of growing threat from energy crisis andenvironment pollution. Solar energy is of a bright future owning to the abundant solarresources in China. With more concern focused on photovoltaic power generation,photovoltaic grid-connected inverter has been a hot issue nowadays. With theestablishment of large-scale photovoltaic power generation system, multi invertergrid-connected power generation technology has been a main tendency. However,after applying the single inverter’s research on the multi inverters’ system, thesimulation results show that: when using the grid-connected inverter equivalentimpedance model in a multi inverter system, the mutual impacts among harmonics isstill existing in it, and it can be even more serious. Around this problem, the researchcontents of this thesis can be categorized as the following aspects:In the first part, the author analyzes the topological structure and mathematicalmodel of photovoltaic grid-connected inverters with respective L, LC, and LCL filterbased on non-isolate inverter. After comparing the function of different filters, thewriter chooses the superior LCL grid-connected inverter as the research object andconducts a study on the parameter designing methods of it. Then, the LCLphotovoltaic grid-connected inverter, which is of great advantage, is chosen as theresearch object. A study on its control strategy is done in this thesis. The authoradopts the double closed loop control strategy based on the capacitor current feedback.The outer loop chooses PI, PR, and quasi PR controller respectively. After comparingthe function simulation results of the three kinds of controller, the writer decides totake quasi PR controller as the final controller type of multi grid-connected inverter.Lastly, the author builds a type of grid-connected inverter equivalent impedancemodel based on the capacitor current feedback control strategy of LCLgrid-connected inverter in this thesis. Associated with the mutual impacts of harmonics in the output current of a single grid-connected inverter, such mutualimpacts existing in multi photovoltaic grid-connected inverter is analyzed in thisthesis. And the simulation results show that the mutual impacts of harmonics existingin multi inverter grid-connected system is more pernicious.