Research On Improvement Of Power Quality Problem In Photovoltaic Grid-connected System

With the exhaustion of the oil besides other traditional energy sources and the continued deterioration of the ecosystem environment, the development of renewable clean energy receives more attention. Solar energy becomes the main development direction in the world energy field because of its inexhaustible and non-pollution. PV gird is rising in the proportion of grid due to its increase in scale, which cause the change for morphology and control mode of grid. PV itself intermittent output characteristic brings the traditional power grid disturbances as well as affects power quality. The research of photovoltaic grid-connected system power quality problems is an important prerequisite to ensure safe and reliable economic operation of power system.Based on the research of improvement to PV system power quality, this paper analyzed the impact of output filters and control strategy of PV grid to the power quality. And this paper proposed an improved filter, which can effectively attenuate harmonic components around switching frequency of grid current. Combining the improved filter and control strategy improved the injected current quality of grid and well improved the performance of PV system.This paper introduced the structure and characteristics of photovoltaic power grid system and gave the test program in accordance with power quality standards, from which studied the existing output LCL filter to form a new LCL-LC filter by increasing an LC branch series to the LCL filer and gave an simple way of design of the new LCL-LC filter. Then for LCL-LC filter two control schemes were proposed according to capacitive current feedback active damping dual loop control strategy. Finally the theoretical study and simulation result showed that LCL-LC filter could well reduce the switching frequency harmonics nearby.This paper made the simulations of output filter and control strategy using Matlab/Simulink simulation environment, by which made a comparison with LCL filter structure. The result of simulation showed the improved methods can effectively improve power quality of PV grid-connected system and solved the power quality problems well.