Research On Three-phase Four-wire Active Power Filter For Low Voltage Power Distribution System

When a large number of power electronic devices are used in the three-phase four-line low-voltage power distribution system,it is easy to cause unbalance of three-phase load,so that the system produces a large number of harmonic current and neutral current,which seriously affects the power quality of the power grid and threatens the safe operation of the power grid and the electrical equipment.So it is significant to study the problems of harmonic suppression,neutral current elimination and three-phase current balance in the three-phase four-wire system,which will be an urgent problem to be solved in the power system.Therefore,three-phase four-wire active power filter is selected as the main research object to solve the harmonic problems in the low-voltage distribution system.And the specific research content of this article includes the following aspects.?1?According to the characteristics of different topology of active filter,the three-phase four-leg active power filter is used as the main circuit topology,and its mathematical model is established.Aiming at the strong coupling relationship of four-leg active power filter in the dq0 coordinate axis,it is decided to use the cross decoupling control mode to realize the independent control of the three-phase current,and the overall control structure of the system is determined.?2?The key technologies in the design of active power filter are studied.The harmonic current detection is combinedi_p-i_q-₀idetection method with the FBD detection method,and replaces the traditional low-pass filter with a sliding average filter,to achieve the optimization of harmonic current detection algorithm.The current inner loop adopts a combination of PI and repetitive control to compensate the defect of the peak current existing in the PI control.The voltage outer loop introduces the soft-start control method to the DC-side voltage control to cover the shortage of the single PI control.PWM modulation uses the 3D-SVPWM based on the abc coordinate system to realize the purpose of indirect compensation current tracking instruction current.?3?The algorithms of harmonic current detection,current loop control,voltage loop control and SVPWM modulation are determined by the way of simulation and comparison.And based on the overall simulation model,simulation analysis of different load and power distortion of low-voltage distribution system is carried out.Finally,the overall harmonic compensation effects of the system and the correctness of the scheme are verified.?4?The TMS320F28335 chip as the control center of active power filter hardware and software have been designed,and experimental verification is carried out under the experimental prototype.The experimental data is stored in the SD card and the computer can query and analyze historical data.Finally,the correctness and feasibility of the three-phase four-leg active filter in this article is verified by experiments.