Research Of Three-phase Four-wire APF Based On Three-level Technique

This paper focuses on the three-level technology, mainly including its application on active power filter in Three-Phase Four-Wire system, and discussing the analysis and design method of the equipment in detail.Firstly, this paper analyzes the structure of three phase four wire system of active power filter based on three-level converter. The topology structure is designed in combination with economic cost and development cycle. At the same time, mathematical model and control structure are established combined with its working status.In addition, the method of designing output grid LCL filter is given.Secondly, the control strategies of Three-Phase Four-Wire system based on Three-level converter are analyzed in the related research. In order to make sure each phase to work independently, the control strategy is studied under the ABC coordinate frame. This paper introduces the method of designing controllers for the current inner loop, the DC-side voltage stable loop and balance loop briefly. Repetitive control is introduced into the current control loop. In addition, an improved method based on second-order low-pass filter is proposed to compare with the traditional PI controller for the voltage loop. Face to the imbalance of DC-side midpoint voltage for three-level converter, different modulation modes of the concrete implementation process are studied in detail. At last, Matlab/Simulink simulation and experimental results verify the correctness and effectiveness of the control strategy.Finally, the design of man-machine communication interface related to the active power filter based on DSP control is discussed. The main parameters of the communication variables about most active power filter, the corresponding development environment, several main operation interface and functions APF are given. It has certain reference value and strong operability in the practical application.