Modeling And Control Strategy Of Three Level Active Power Filter

It is the goal of electric power reform to ensure the high quality of power supply,improve the efficiency of power production and operation,and improve the operation reliability of power systems.Harmonic pollution is one of the important reasons for the high energy consumption in China,and there are a lot of sensitive loads in the modern power grid,and the power quality of terminal user have become increasingly demanding.Harmonic suppression is an effective measure to improve power quality,APF is an important equipment,therefore the study of APF is of practical significance.Firstly,define the APF designing program according to the characteristics of output current harmonics and operation requirements of active power filter,the NPC three-level topology with LC filter is selected and its operating principle is analyzed briefly.Focuses on the accurate design of the controller parameters of active power filter,a small signal model of voltage control in dq rotating coordinate system is established based on the traditional DC side voltage control model,then a PI parameter tuning method based on small signal model is proposed.Using zero pole configuration change the small-signal model with right-half plane zero into the ordinary two order delay system,the selection principle of PI parameters is discussed in detail according to the Routh-Criterion and two-step tuning method,focus on the analysis of the influence of different PI parameters on the system performance.This method is feasible,it is verified by the simulation and experimental results.Secondly,the hardware circuit and software system of active power filter are designed based on the theoretical study.The hardware mainly includes parameter design of inductance and capacitance of main circuit,control system isolated power supply and auxiliary power supply,ADC sampling and signal conditioning circuit,IGBT drive interface circuit,protection circuit,control circuit of a contactor.The software mainly includes the interrupt service routine,the harmonic extraction filter program,the single synchronous coordinate system software phase locked loop program,the positional digital PID program.Finally,based on the research above,the experimental prototype of 6kVA(calculated according to the 25% current distortion rate)three level APF is built,debug the prototype according to the design plan,during the debugging process the system is optimized and upgraded,and the experimental waveforms are measured by the oscilloscope and powerquality analyzer.Analysis of the measured voltage waveform,DC capacitor voltage,grid current and active power filter output current waveform of the experimental results,it is verified that the control strategy and design method used in the system is correct and effective.While ensuring the compensation performance of the system,the DC voltage has a smaller overshoot,which can effectively reduce the current distortion rate of the grid,and the performance of the design is realized.