Research And Design Of Micro-grid On-grid And Off-grid Inverter

Background with the country energetic developing smart grid and full use of renewableenergy，this thesis design and develop a micro-grid connected/off grid inverter. The differencewith common grid inverter is that micro-grid connected/off grid inverter can accurate detectanti-island and working state switch between grid and off-grid seamlessly and to ensuremicro-grid important load uninterrupted power supply. The work done by this thesis is asfollows:First, according to the study of micro-grid structure and distributed power, and consideringexperimental conditions, It is using analog AC micro-grid, multi-inverter parallel master-slavemode. Main inverter in case of off-grid using U/f control strategy, to provide a standard ofvoltage and frequency reference for other inverter in micro-grid. And in case of grid, the maininverter use P/Q control strategy, to provide rated power electricity. The other inverter is alwaysusing the P/Q control strategy, to output power.Second, it is researching on the problem of island detection that is in the case ofmulti-inverter parallel. Considering the conventional method in island detection thatmulti-inverter parallel arise dilution effect and the area of corresponding undetectable expand,islanding detection method use frequency-shift method that is based on positive feedback, toimprove the accuracy of islanding detection.Third, to ensure the large power grid in the case of fails, the critical loads that micro-gridconnect uninterrupted power supply, inverters need to switch seamlessly between grid and offgrid. The state switch method that is based on indirect current control, reduce the influence of thevoltage phase and frequency mutations in switching.Forth, on the base of complete the above research questions, it is start the hardware andsoftware design of the micro-grid on-grid and off-grid inverter. And through the grid voltage andcurrent waveforms, off-grid voltage and current waveforms and the accuracy of state switchingthat are obtained from experiments, verify the feasibility of the above method.