Research On Parallel Photovoltaic Inverters In Microgrid

As the problems of energy’s drastic reduction, power’s growing demand and load’srequirement on the power supply reliability and security become increasingly serious,the technologies of new energy and distributed generation systems has become aresearch hotspot. In the microgrid system based on distributed generation, the inverterparallel technology is widely used because of its unique advantage in improving powerdensity of the system and enhancing system reliability. Consequently, this paper hasresearched on PV parallel-inverters system, for the purpose of enhancing the capacityand reliability of power supply in microgrid.Through comparative analysing of the common inverter topologies, a appropriatemain circuit topology suitable for PV was designed, which was Boost circuit infirst-class and full-bridge structure in second-class. And an equivalent full-bridgeinverter circuit model was established. Meanwhile, a reasonable closed-loop controllerdesign method was put forward, based on the strategy of double closed-loop withinstantaneous inductor current and output voltage. Finally, simulation analysis verifiesthe inverter’s stability and reliability.Based on the analysis of the inverter unit, the overall control scheme ofparallel-inverter system was proposed. Through analyzing the circulation of parallel-inverter system, traditional droop control methods was improved, which only applies tothe situation when the impedance is purely inductive. Also, by analyzing thesmall-signal model for the parallel system and the drawing the system’s root locus,proper droop coefficient was designed to ensure stable operation of the system and rapidresponse. On this basis, a current-sharing link with a virtual impedance loop was addedto the control scheme, and the inhibitory effect of circulation caused by non-idealfactors to the the introduction of virtual impedance was analyzed. At last,MATLAB/Simulink simulation verified that current-sharing control method based onvirtual impedance loop was correct and feasible.The design of overall structure and hardware circuit as well as the software controlfor the parallel-inverter system was completed, and a experimental platform composedof two1kW PV inverters was built. The experimental results show that the proposeddesign scheme of parallel-inverter system can achieve the system’s stability and reliableoperation.