Research On Unified Power Quality Conditioner Based On Linear Active Disturbance Rejection Control

The increasing consumption of traditional fossil energy makes renewable energy develop rapidly.However,when renewable energy power generation is connected to the grid,it will cause power quality problems such as voltage fluctuations and harmonics.In addition,the use of a large number of nonlinear loads will produce harmonic pollution to the power grid.In order to integrate renewable energy into the grid and solve various power quality problems in the power system,this paper studies a unified power quality conditioner(UPQC)based on linear active disturbance rejection control(LADRC)to improve a variety of power quality problems and ensure the safe and stable operation of the power system.Firstly,a fundamental positive-sequence component extraction method based on tiny time incremental decomposition is proposed,which can quickly extract the fundamental positive sequence components of load voltage and load current.In addition,the control method to generated the reference current of the d-axis in series converter is studied,and the d-axis reference current is calculated by the fundamental positive-sequence component extraction and the instantaneous reactive power theory,which can ensure the power balance of the system and reduce the voltage fluctuation on the DC link.Secondly,the principle of LADRC control method is analyzed,and the mathematical model of UPQC series and parallel converter is established.According to the different performance requirements of UPQC under different working conditions,the LADRC controller of series and parallel converter is designed and improved.An improved second-order LADRC controller was designed for the parallel converter to reduce the effect of grid-connected current on load voltage tracking,and the performance of the improved LADRC controller was analyzed.Then,the mechanism of DC link voltage fluctuation under unbalanced load conditions and the influence on the output current of series converter under the traditional control strategy are analyzed.In addition,the DC link voltage stabilization control method based on super capacitor charging and discharging to the DC link capacitor,and the constant current charging method to the super capacitor are proposed,to reduce the DC voltage fluctuation and the imbalance of the output grid current of the series converter.Finally,the proposed method is simulated and analyzed by MATLAB/Simulink software,under the conditions of voltage source nonlinear load,current source nonlinear load,unbalanced load,load transient,grid voltage transient and high frequency interference to the sensors,and compared with the traditional PI control method,the effectiveness of the proposed method is verified.48 figures,3 tables,75 references...