Research On Control Strategy Of Three-phase Four-wire Three-level Active Power Filter

With the development of science and technology,a large number of non-linear loads are applied in all walks of life.These loads generate a lot of harmonics,and the quality of electrical energy applications caused by them has caused widespread concern.In order to solve the power quality problem,related concepts of active power filters(APF)have been proposed.With the deepening of research,active power filters have gradually become the main means of harmonic control and improvement of power quality,and have been favored by people.The three-phase four-wire system that is widely developed and used in people’s daily life has the problems of harmonics,zerosequence current impact,and three-phase imbalance.Therefore,exploring related governance programs has strong practical significance.This article first introduces the research background and significance of active power filters,and then discusses the working principle and structure of active power filters in detail.In addition,the paper analyzes the theoretical structure and mathematical modeling of the three-level four-wire three-level topology.Based on this,the paper analyzes and studies the APF harmonic extraction algorithm and system control strategy.As for the harmonic detection algorithm,based on the existing algorithms,this paper elaborates the ip-iq harmonic detection algorithm based on the instantaneous reactive power theory.Then,it is used in the APF’s harmonic current instruction extraction.In addition,a related simulation model was established in MATLAB for verification.At the same time,after analyzing different control strategies,this paper applies the feedforward channel,PI control,and repetitive control related technologies to establish a double closed-loop system.The voltage outer loop uses a PI control strategy to control the DC-side voltage.The current inner loop adopts the "PI control + embedded repetitive control" composite control strategy.In addition,the design method of each parameter in the control system is explained in detail,and their frequency characteristics and stability are analyzed.Based on the above research,this paper builds a three-phase four-wire APF simulation model on the MATLAB platform.The model has verified the current inner loop using a single PI control system and a "PI + repetitive" control system,and verified that the composite control system has higher steady-state accuracy and better dynamic performance.Finally,this paper builds the relevant hardware experimental platform,in which the digital core control system adopts a "DSP + FPGA" joint control structure.This structure guarantees the rapid detection,calculation and real-time control of digital systems.The final result shows that the APF system designed in this paper has strong compensation performance and achieves the national standard requirements.