Study On Low Voltage Ride Through Technology Of Grid-connected Photovoltaic Inverter

Photovoltaic (PV) power generation is one of the most effective solutions fortoday’s energy crisis. While providing people with green and renewable energy, highpenetration of photovoltaic power has brought great influence to the stability of thegrid. When grid fault happens, sudden logging-out of grid-connected inverters willdeteriorate the condition. Thus, low voltage riding through (LVRT) technology is thekey technology to ensure the stability of the grid.This thesis researches the grid-connected PV inverter’s control system undernormal and fault grids. First, model of grid-connected PV inverter is built and thisthesis designed the traditional control system under ideal grid conditions. Theeffectiveness of the system is verified by simulation. This paper also researches theeffect of grid voltage sag on the traditional control system, including balanced andunbalanced voltages. Then, with regard to unbalanced voltage sag, this paper studiedthesequence extraction method based on DSOGI-FLL, proposed a sequence currentcontrol method based on quasi proportional resonant controller and optimized thecontrol targets during grid faults. At last, this thesis builds a5kW experimentalplatform and carried out experiments to test performance of the traditional andproposed LVRT control systems under grid fault conditions. The experimental resultsverified the validness of theoretical derivation.