Study On Control Technology Of Photovoltaic Power Generation System

The global energy system is moving towards green,environment-friendly,low-carbon and efficient.The proportion and growth rate of new energy and renewable energy in the modern energy system are increasing.The high proportion of renewable energy power system and electronic power energy system are gradually replacing the traditional energy system.It is urgent to realize the large-scale application of photovoltaic power generation system,improve the rapid and reliable connection of photovoltaic system to the power grid,and reduce the impact of intermittent photovoltaic system on the power grid.The distributed photovoltaic power generation system is especially miniaturized,easy to install,and can satisfy the household electricity consumption,realize the surplus electricity to surf the Internet.Based on the two-stage three-phase photovoltaic power generation system,this thesis conducts an indepth study on its maximum power tracking technology,grid-connected current control technology and phase-locked loop technology.The main research contents are as follows:1.The output power curve of photovoltaic cells is easy to be affected by ambient temperature and light intensity.The maximum power tracking technology can realize the maximum utilization rate of photovoltaic cell array.Due to the selection of disturbance step size,the traditional disturbance observation method is unable to give consideration to the tracking speed and steady-state accuracy of maximum power.However,due to the poor adaptability of the disturbance factor,the traditional method of disturbance observation with variable step size cannot realize the tracking with variable step size under full conditions.In this thesis,an adaptive variable step length perturbation observation method is adopted to achieve the consistency of disturbance factors under different light intensification,and the tracking speed and steady-state accuracy of the maximum power tracking algorithm are effectively solved.2.Due to the intermittent fluctuation of the output power of the photovoltaic system,the traditional grid-connected current control technology cannot guarantee the rapid response of current loop control to power changes.Therefore,the grid-connected current control technology based on model predictive control is adopted in this thesis.A discrete mathematical model of inverter in two-phase stationary coordinate system is established.On this basis,the MPC controller is designed,the prediction model and the evaluation function are designed,and the time delay of the controller is compensated.The steady-state performance and dynamic performance of grid-connected inverter are improved.3.In order to synchronize the grid-connected current with the grid voltage,the phaselocked loop needs to provide accurate phase information of grid voltage.However,due to the three-phase imbalance in the grid voltage and a large number of high harmonics problems,the phase tracking accuracy of the phase-locked loop in the traditional synchronous rotating coordinate system is poor and there is oscillation.The phase-locked loop structure based on DSOGI can suppress the harmonic of the grid voltage,but it cannot solve the phase tracking error caused by the three-phase imbalance.In this thesis,a positive sequence voltage phaselocked loop structure based on DTOGI is adopted.By extracting the positive sequence component of the fundamental wave voltage,the effective tracking of the grid phase is realized.Meanwhile,the dc component,the negative sequence component of the fundamental wave and the high-order harmonic component of the grid voltage are effectively suppressed.