Research On Control Strategy Of Photovoltaic Grid-Connected System Considering The Influence Of Short-Circuit Faults

A reasonable and efficient fault ride-through control strategy of photovoltaics grid-connected system is a key core technology to ensure safe and reliable grid operation of photovoltaics.Short circuit is a common and main form of fault in the power grid,which can be divided into symmetrical short circuit and asymmetric short circuit.The transient characteristics of the photovoltaic grid-connected system under the above two short-circuit faults are quite different.Therefore,this paper has carried out detailed research and analysis on the control strategies of photovoltaic grid-connected systems under two different types of short-circuit faults.The main work is as follows:Firstly,the influence of grid symmetrical short-circuit fault on photovoltaic grid-connected system is analyzed in detail.Combined with relevant national technical regulations,the grid-connected control strategy of photovoltaic system under grid symmetrical short-circuit fault is determined by reactive current injection method.Secondly,based on the analysis of the influence of the asymmetric short-circuit fault of the power grid on the photovoltaic grid-connected system,DSOGI-PNSC is used to solve the positive and negative sequence separation of the unbalanced voltage.In order to solve the problem that the current loop proportional integral controller can not guarantee the static tracking of the input quantity,the current loop control system based on the quasi-proportional resonance controller is designed and analyzed.Thirdly,the problem of calculating the current reference value of photovoltaic grid-connected control system with the aim of suppressing active/reactive power fluctuation or balanced grid-connected current is studied under the asymmetric short-circuit fault of power grid.The relationship between the reactive power injected into the power grid by the photovoltaic grid-connected system and the voltage asymmetry of the grid connection point is analyzed qualitatively and quantitatively.The control system can provide reactive power support to the grid according to the magnitude of the voltage asymmetry while suppressing the reactive power fluctuation.Finally,the research on flexible power control strategy of photovoltaic grid-connected system based on voltage mismatch is carried out.The threshold of voltage asymmetry is determined by the maximum peak value of the grid-connected current.By calculating the control coordination coefficient under different voltage asymmetry,synergistic optimization of various control effects is realized.The system simulation model is built based on Matlab/Simulink,and the feasibility and effectiveness of the above control strategy are verified.The control effect of photovoltaic grid-connected system is simulated and analyzed for grid symmetrical and asymmetric short-circuit faults.The simulated waveforms and data are all as expected.