Research On Stability Analysis And Control Strategy Of Photovoltaic Grid-Connected Inverter Under Weak Grid

Along with the energy crisis and increasing environmental pollution,photovoltaic power generation systems have been developed with their characteristics of cleanliness,safety and regenerability.However,due to factors such as line impedance and transformer leakage inductance,the power grid is increasingly showing weak grid characteristics.Under the weak grid,the stability of grid-connected inverters is seriously threatened,and the quality of grid-connected power is also deteriorated.Therefore,this paper takes photovoltaic grid-connected inverters under weak grid as the research object,study the operating characteristics of grid-connected inverters under weak grid and proposes a reasonable improvement strategy.For the grid-side current feedback control inverter,this paper model and analyze under ideal condition and weak grid condition respectively,derives the system-dependent transfer function under two conditions,and uses the frequency domain analysis method to judge the stability of the system.The analysis shows that additional positive feedback introduced by weak grid impedance is the main reason for reducing the stability of the system.Based on the above analysis,this paper proposes an improved strategy to improves the stability of the system,then designs the relevant parameters of the complex filter and verify the effectiveness of the improved strategy.For the inverter-side current feedback control inverter,this paper analyze and model the structure of the control structure firstly.Then this paper analyzes the reasons for the system stability degradation under the weak grid condition,and research the reason why non-unit power factor of the inverter-side current feedback control,based on the above analysis,this paper proposes a comprehensive improved control strategy for inverter-side current feedback control.Theoretical analysis and simulation results show that the comprehensive improvement strategy not only has better adaptability to weak grids,but also reduces the number of sensors used and unit power factor correction is achieved.At the end of the paper,the RT-LAB platform is used as the controller,and the grid-connected inverter prototype is built with the peripheral hardware circuit.The prototype is used to verify the proposed improvement strategy.The experimental results are consistent with the relevant simulation results,and the effectiveness of the improved control strategy proposed in this paper is verified.