Research On PV Generation System And Power Quality Control Strategy

With the development of science and technology,people’s awareness of environmental protection is getting stronger and stronger.Environmental pollution caused by traditional energy,such as thermal power,is becoming more and more serious.Clean energy is gradually paid attention by people,and photovoltaic power generation is gradually coming into people’s vision.At the same time,with the application of various power electronic converters and the complexity of industrial load types,the power quality of power grid is threatened,and power quality problem has also become one of the most important research issues.In this thesis,aiming at the photovoltaic grid-connected power generation system and power quality detection and control issues,the photovoltaic grid-connected converter and its power quality control strategy are studied.Firstly,the topology and control strategy of grid-connected photovoltaic converter are studied.Based on the two-level grid-connected photovoltaic converter,the circuit topology is designed.The parameters of the first stage Boost circuit are calculated,the control strategy of double loop which are inductance current and input voltage is designed,and the PI parameters are designed by engineering method.Starting from the characteristics of photovoltaic cells,the maximum power tracking strategy for Boost circuit is studied.Aiming at the problems existing in the current maximum power tracking strategy,a perturbation observation method based on optimal gradient is designed as the maximum power tracking strategy.The problem of fluctuation at the maximum power point is avoided and the tracking speed is becoming faster.The topology structure and control strategy of the second-level inverter of the converter are studied.The double loop control strategy of DC bus voltage and grid-connected current,which,on the one hand,provides a stable voltage source for Boost circuit;on the other hand,it guarantees the stability of grid-connected current control.Finally,the SVPWM modulation technology suitable for the three-phase two-level inverter is also studied based on the analysis of several modulation method.Secondly,the power quality control strategy based on photovoltaic grid-connected converter is studied,reactive power detection technology based on instantaneous reactive power theory is designed.Compared with the traditional harmonic detection technology,a harmonic detection technology based on parallel second-order generalized integrator is designed.The power quality is comprehensively controlled by combining passive and active methods.Parallel capacitors are used to compensate reactive power and LC high-pass filters are used to control harmonics passively.On the basis of passive compensation,the active precise compensation of reactive power and harmonics is realized by adding current compensation control strategy to the control strategy of the inverter.Thirdly,the PV grid-connected converter is modeled and verified by simulation.The Boost topology and control strategy are modeled to verify the rationality of the Boost circuit topology and control strategy.The maximum power tracking ability of the Boost circuit is tested,and the effectiveness of the disturbance observation method based on the optimal gradient is verified.The topology and control strategy of the inverter are also modeled and verified by simulation.Finally,the overall design of the topology and control strategy is carried out.Considering about the limit of hardware experiment,Matlab/Simulink is used for simulation in order to verify the method in the paper.By simulating the harmonic and reactive power sources,the effectiveness of harmonic and reactive power detection algorithm is tested.The simulation operation of the whole system verifies the feasibility and rationality of the photovoltaic grid-connected converter to realize grid-connected generation and power quality control functions simultaneously.