Research On Harmonic Suppression Strategy Of Parallel APF Based On Composite Control

Since the 21st century,power electronic devices have been widely used in practical life,bringing tremendous vitality to social and economic development.At the same time,due to their inherent nonlinear characteristics,they will inevitably cause harmonic pollution to the power system when applied to the power grid.As a new type of harmonic suppression device,Active Power Filter(APF)is one of the most effective means to solve the above problems.The parallel APF has been widely used in the field of harmonic control due to its simple structure and convenient control.Therefore,this article conducts research on the three-phase three-wire parallel APF,and the main work done is as follows:(1)Based on the working principle of the parallel APF,the main circuit topology is established,and corresponding mathematical models are derived in three coordinate systems.At the same time,decoupling analysis of the current loop is carried out,providing a theoretical basis for the subsequent research on the detection strategy and control technology of the parallel APF.(2)Research on harmonic detection strategies:In response to the shortcomings of large detection delay and poor filtering effect in the low-pass filter section of traditionali_p-i_q detection methods,an integral mean filter based on the average algorithm is used to replace it.(3)Research on compensation current tracking strategy:In the current control algorithm of parallel APF,Repetitive Control(RC control)is often combined with PI control.This method has obvious advantages in tracking AC signals,but it does not perform well in dynamic performance.In order to solve the above problems,this article weakens the inherent delay of repetitive control by adding a command current feedforward channel,and introduces fuzzy control to adjust the PI controller parameters in real-time to reduce the dynamic response time of the system.(4)Research on DC side voltage control strategy:To solve the problem of slow DC side voltage response speed and large overshoot when parallel APF starts or load suddenly changes,this paper combines traditional PI and fuzzy control to form a dual mode control,which can flexibly switch control strategies according to the size of the error.(5)A parallel APF main circuit model was built in the Matlab/Simulink environment to validate the above research.The simulation results show that the i_p-i_q detection method using an integral mean filter has smaller delay and higher detection accuracy,and the improved composite control system has significant improvements in dynamic time efficiency and disturbance resistance performance.