Modeling And Stability Analysis Of Multi-time-scale Photovoltaic Power System

The development and utilization of photovoltaic power generation on the one hand has alleviated the current severe energy shortage and environmental pollution problems,and on the other hand has also brought new challenges to the stable operation of power systems.Oscillation is one of its main problems.In the context of increasing photovoltaic penetration,a large number of power electronic conversion elements make different time scales exist in the power system,and the model complexity continues to increase.If the original model of each module is still used for stability analysis or simulation calculation,problems such as model validity,large memory consumption,long simulation time,and dimensional disaster are easy to be brought.Therefore,it is necessary to study a simple and practical simplified model of photovoltaic power generation system to facilitate calculation and simulation,and to conduct in-depth discussion and research on system stability based on the simplified model.Firstly,this paper comprehensively considers the main circuit and control part of the photovoltaic power generation system,establishes the mathematical model of each module,and linearizes the nonlinear model of the system at the equilibrium point to obtain a small interference analysis model for the photovoltaic power generation system.The simulation of photovoltaic array output characteristics and system operating characteristics was performed in MATLAB.The simulation results show that after suffering small interference,the photovoltaic power generation system can correctly track the maximum power point and keep the DC voltage stable,but the stability is not good and needs to be further improved.Secondly,the small disturbance stability of the photovoltaic power generation system is analyzed by the eigenvalue method and the sensitivity method.The analysis results show that the system has three oscillation modes,and the control parameters have a great influence on the small disturbance stability.The singular perturbation theory is used to divide the fast and slow variables in the photovoltaic power generation system,and the fast variables are ignored in order to quickly reduce the dynamic order,and four models of reduced order for the photovoltaic system are obtained.The small interference stability of the original model and the four reduced-order models is analyzed and compared.The results show that the reduced-order model can retain the original oscillation mode of the system to varying degrees,and provides suggestions for studying the influence of control parameters on the small-interference stability.Finally,an appropriate reduced-order model is selected to analyze the influence of the control parameters on the stability of small disturbances,and the controller parameters that have a greater effect on the oscillation mode are determined in combination with the results of the sensitivity analysis.In order to ensure the globality of the optimization results,an objective function whose weight changes with the change of the sub-function is established.The BSA algorithm is used for optimization,and the small disturbance stability and dynamic response curve of the photovoltaic power generation system before and after parameter optimization are simulated and compared.The research results show that the optimization results of the original model and the reduced-order model are basically the same,and they can quickly return to a stable operating state under small disturbances,with good damping characteristics and improved stability.Moreover,the optimization method based on reduced-order model has faster calculation speed and higher efficiency,which verifies the effectiveness of the proposed method.