Three-phase Four-arm APF Technology Based On Improved Sine Amplitude Integration

Power quality is an important indicator reflecting the economy,safety,reliability and stability of power system operation.China has clear standards for voltage,frequency and waveform quality in power quality.The waveform quality includes three-phase voltage symmetry and distortion rate.With the economic growth in recent years,energy consumption is too large and oil prices are rising.New energy vehicles and clean energy are the direction of future development.However,the AC charging piles of electric vehicles and a large number of photovoltaic wind power are connected to the grid,and the harmonic pollution is becoming more and more serious.Therefore,harmonic suppression is an important research direction.Three-phase four-arm active power filter is a new type of power electronic device that can suppress both harmonic and unbalanced components.In this thesis,the principle and method of harmonic suppression are studied.The main contents are as follows :(1)Firstly,the main equipment of harmonic generation and its main harmonic frequency are described,and the principle,advantages and disadvantages of modern harmonic control methods are analyzed.Finally,the three-phase four-arm structure is selected as the main topology of the active filter,and its working principle,control strategy and harmonic mathematical model with nonlinear load and unbalanced load in abc coordinate system and dq coordinate system are analyzed.(2)Secondly,on the basis of analyzing the principles,advantages and disadvantages of traditional harmonic extraction methods such as ip-iq method and FBD(Fryze Buchholz Dpenbrock)method based on instantaneous reactive power theory,aiming at the problem that SOGI(Second-Order General Integrator)phase-locked loop is greatly affected by grid DC voltage and noise burr,it is improved by using second-order bandpass filter and Kalman filter.The improved SAI(Sine Amplitude Integral)algorithm proposed in this thesis can extract the three-sequence fundamental wave at the same time,and use the multi-stage SAI method to eliminate the interference of higher harmonics and achieve accurate harmonic extraction.The grid-connected model parameters of three-phase fourarm APF(Active Power Filter)are designed.By analyzing and comparing the advantages and disadvantages of common controllers,PR controller is selected as the current tracking controller.The simulation system is constructed in Simulink.The THD(Total Harmonic Distortion)values of three harmonic extraction methods are analyzed and compared to verify the improvement of harmonic suppression performance by the improved SAI method proposed in this thesis.(3)Then,the application of the improved APF in the three-phase four-arm DG inverter is studied to realize the integration of the harmonic suppression function and the power control function,that is,the multi-function of the inverter.Based on the research results of improved APF,this paper analyzes the constant PQ control and algorithm of three-phase four-arm inverter,and puts forward the function switching strategy,harmonic secondary compensation control method and harmonic compensation capacity algorithm.(4)Finally,the RT-Lab real-time simulation platform is used to design the simulation system,which verifies the effectiveness of the improved SAI algorithm proposed in this thesis to compensate harmonics.