Research On Photovoltaic Grid-Connected Power Quality Control Strategy Based On Active Disturbance Rejection

In the 21 st century,with the gradual depletion of fossil energy,the development and utilization of renewable energy has gradually been valued by countries around the world.As an inexhaustible green energy source,photovoltaic power generation is gradually favored by all countries.The conversion of light energy from photovoltaic panels to electrical energy to the grid is also required to go through several complex steps.Different designs and controls in each link will have an impact on power quality.This thesis studies and improves the dynamic performance and steady-state performance of the grid-connected current output under the traditional control strategy.The full thesis is based on MATLAB/Simulink platform for simulation research,the specific work contents are as following:Firstly,the topology structure of the front and rear two-stage photovoltaic grid-connected is designed.The front stage selects the 100 kW photovoltaic array,the maximum power point tracking strategy based on the area difference comparison method and the boosting chopping circuit.Inverter bridge and LCL type filter.Then,reasonable hardware parameters are designed for each module,and the output characteristics of the photovoltaic array under different external conditions are studied.Secondly,the mathematical modeling of the whole photovoltaic grid-connected inverter is carried out.Then,for the problem that the LCL-type grid-connected inverter has a resonance peak at the resonance,the dual current loop active of the capacitor current feedback and the grid-connected current feedback is adopted.Damping method is used to suppress;PI control of voltage outer loop is added for the pre-voltage fluctuation problem.The traditional control strategy represented by PI and Quasi Proportional Resonance(QPR)based on capacitive current feedback is studied.On the basis of analyzing the essence of control,it is found that the dynamic characteristics of PI control are poor and the stability is not good.The PR-controlled grid-connected current has a phase error with the grid voltage and is too dependent on the lack of an accurate model.Then,due to the fast response of the anti-interference control and no overshoot,and the accuracy of the control,the strong anti-interference ability and so on,it is decided to adopt the auto disturbance rejection control.After the nonlinear auto-disturbance rejection is studied in the system,Linear Auto Disturbance Rejection Control(LADRC)is proposed for the problem that the algorithm has many parameters to be fixed and the structure is complex.The third-order auto-disturbance suppression control algorithm is derived and the parameters are studied.Finally,combining the anti-interference control technology with the grid-connected control technology,a third-order ADRC controller for LCL grid-connected control is designed.This strategy is used to simulate on Simulink,and the dynamic characteristics,accuracy and robustness are studied.Then the PI and QPR control strategies under the same conditions are compared,and the superiority of the method is proved.