Research On Three-phase Four-leg Active Power Filter

With the refinement of electronic equipment and the high level of power equipment,the demand for power quality is more and more high,but at the same time,the pollution of power grid is also more and more serious.In order to solve this problem,the research and application of active power filters have been paid much attention by scholars,enterprises and governments.This paper focuses on the shunt active power filter,whose topology structure is three-phase fourleg.It can be applied to three-phase four-wire asymmetric system to solve the harmonic problem caused by nonlinear load.By detecting the load current,the shunt three-phase four-leg active power filter extracts the harmonic current that needs to be compensated,which is used as the instruction signal of the active power filter,so as to achieve the purpose of harmonic control by means of current compensation.Firstly,this paper designed a three-phase four-leg active power filter model which was suitable for the three-phase four-wire system under the topology of asymmetric load,selected the important parameters and components and established the mathematical model of APF.In order to realize harmonic compensation for the central line,this paper selected the main topological structure of the four bridge arms,and calculated the parameters such as the capacitance of the bus on the DC side,the voltage value on the DC side and the inductance on the output side of the filter according to the relevant formulas.In order to realize the control of the four bridge arms,the realization process of 3D-SVPWM modulation algorithm was analyzed in detail according to the mathematical model.In the harmonic detection link,this paper designed the harmonic detection algorithm suitable for the three-phase four-wire system under the asymmetric condition,and integrated the voltage control algorithm into the harmonic detection link,combined the harmonic detection algorithm and the current loop,and finally realized the DC side voltage control.In order to solve the problems of positive sequence current,negative sequence current and zero sequence current under the asymmetric load condition of three-phase four-wire system,the d-q algorithm was applied to the detection of positive sequence fundamental wave and negative sequence fundamental wave current,which effectively avoided the error caused by the grid side voltage involved in the calculation.In addition,based on the α-β construction algorithm,an improvedα-β construction algorithm for zero sequence current detection was derived in detail.After the improvement,the calculation amount was smaller and the detection was more accurate.In addition,this paper took the energy exchange between the capacitor and the active power on the side of the network as the core idea,and increases the active current required for capacitor voltage stabilization on the d-axis to realize voltage stabilization control.In the current tracking link,based on the mathematical model,this paper solved the coupling problem between the three-axis current in the d-q-0 coordinate system,and designed the PI controller,BP neural network PID controller and PI+repetition control controller.Finally,the current tracking effect of the three current controllers was simulated and compared in the MATLAB/Simulink environment.In order to make the active power filter track the instruction harmonic current better,the current loop controller is studied in detail in this paper.After analyzing the commonly used PI controller,because it could not track the high frequency current well,this paper proposed the application of BP neural network PID controller to the current loop,which could effectively solve the problem of PID parameters difficult to set and current burr in the compensation process.In addition,PI+ repetition control was applied to current loop.It made use of the manufacturing of resonance points to enhance the gain of the harmonic current frequency points,and at the same time used the error signal compensation to control the next period to enhance the current tracking ability.Finally,based on the above simulation,this paper build an experimental platform with MT PXIE1071 as the hardware-in-loop simulation case,and transported the Simulink simulation to the hardware-in-loop case.Through the hardware-in-loop experiment,the feasibility and accuracy of the control algorithm mentioned in the paper were verified.This paper through the Simulink environment to build the simulation model of the algorithm,a simulation model and transplanted to the hardware in loop in the case,through the hardware in the loop experiment platform,from the harmonic detection algorithm was proposed in this paper,the control algorithm,model of main circuit design,the compensation effect of active power filter was verified its each link and the whole machine is effective and feasible.