Research On Control Technology Of Asymmetrical Faults Ride-through For Grid-connected Photovoltaic Power System Based On Rtds

With the fossil energy crisis and the environmental problem,the proportion of the grid-connected renewable energy power generation especially on wind and solar energy become more and more large.Photovoltaic(PV)power generation with its unique advantage has become the focus of new energy power generation.However,the increase of the demand of energy will result in the increase of the rate of the generator of solar power generation,which will influence the grid when it happens to be fault.So the grid have proposed very strict code of the operation of solar power generation,which demands the solar power generation should obtain the Asymmetrical faults ride-through(AFRT)capability and supporting ability of power grid when the grid voltage asymmetry fault happens.Therefore,the theory and control strategy of the PV grid-connected power system under asymmetrical grid fault have been discussed,then a set of 100 kW grid-connected PV power system simulation platform have been established based on real time digital simulator(RTDS).The AFRT capability of the system has been analyzed based on this platform.Firstly,the grid-connected PV power system under normal grid condition is analyzed from mathematical modeling and theoretical analysis in this paper.What's more,simulation study is made for the PV panels,based on these,simulation model with traditional control strategy has been established and it's operating performance under asymmetric power grid fault has been proved by RTDS.To the problems of Grid current distortion,overlarge Inrush current,double frequency oscillation on active power and reactive power,solving ideas have been provided especially from grid synchronization system and current controller.Secondly,the grid synchronization technology under asymmetric power grid fault is analyzed in this paper.Based on the demands of tracking grid phase quickly and accurately when the amplitude falling and phase angle jumping in the grid voltage,Phase locking scheme based on the double second order generalized integrator has been formulated and passes validation.According to the requirement of the grid-connected PV power system preforming normally under asymmetric fault of power grid,the design of current controller is critical.This paper introduces a control strategy based on decoupled double synchronous reference frame and establish the mathematical model,then illustrates thefeasibility and deficiencies of the strategy.For its disadvantages,the paper puts forward an improved control strategy,which adds the feed-forward loop and additional feedback loop.The strategy improves the AFRT ability of the system.The test results demonstrate the validity of the proposed improved controller.Finally,micro power system network model by using RTDS is established in this paper,which simulates the actual condition about asymmetric voltage dropping at the point of common coupling,the improved control strategy is validated by the test.The results prove that the Design Plan proposed by this paper can meet the requirements in system AFRT better,which has a certain practical significance.