Research On Low Voltage Ride-Through Technique Of Grid-tied Photovolaic Inverters

Nowadays, as the public began to realize the disadvantages of fossil fuel, which has driven climate change and goes exhausted, Photovoltaic (PV) generation systems have been broadly applied. However, as the penetration level of PV generation systems in the grid is increasing significantly, the impacts they bring to the grid promote the updates of grid codes, resulting in the introduction of Low Voltage Ride-Through (LVRT), which has been proposed and applied in Wind Power System.The introduction of LVRT brings benefits to the grid while increases the design difficulty of PV inverters. And the performances, as well as the basic functions that to be connected and supply reactive power support to the grid during fault condition call for more attention from research area.Based on the research of the behaviors of PV inverters with conventional control strategy, the problems need to be solved are discovered. In order to solve these problems, some specific solutions are studied and then an overall control strategy is proposed. Concerning the request of the development of LVRT, two novel control strategies are proposed to further improve the performance of PV inverters under fault condition. The main contents are as follows:1) Backgrounds of LVRT and its detailed requirements.2) Analysis on PV inverter topologies and conventional control strategies, whose behavior under grid faults is simulated in Matlab.3) Based on the simulation results of conventional control method under low voltage faults, problems need to be solved in LVRT is concluded and according solutions are studied. Then an overall control strategy is proposed to realize the LVRT.4) Two novel strategies are proposed to enhance the performance during LVRT:one improves the dc-link voltage and output performance by configuring super-capacitor in single-stage PV inverters; another one takes the basic rule that the output quality decreases when the modulation index is low into account and improves the output quality by employing an adaptive dc-link voltage control method.5) Simulation verifications.