Research On Control Strategy Of Three-Phase Three-Wire Shunt Active Power Filter

With the widespread application of modern power electronics technology in fields such as aerospace,rail transit,communication and healthcare,and new energy generation,a large number of nonlinear power electronics devices have caused serious harmonic pollution.Shunt active power filters,as an efficient and flexible equipment for power quality control,can detect and suppress harmonics of different frequencies in the power grid in real-time.This article studies the key control technologies of three-phase three-wire shunt active power filters.Firstly,in response to the problem of traditional i_p-i_q harmonic current detection method not being able to accurately lock phase in three-phase unbalanced power grids,a dual second-order generalized integrator is used to separate the positive and negative sequence components of the power grid voltage.Then,a synchronous rotating coordinate system software phase-locked loop is used to lock phase in the separated positive sequence component signal of the power grid voltage.In order to accelerate the filtering of harmonic components in the load current,an integral mean filtering module was designed to replace the low-pass filter.Secondly,in the aspect of harmonic current control,the control target is converted from the harmonic compensation current to the output voltage of the inverter by using the variable characteristics of the control target of Model predictive control,which leads to the model predictive voltage tracking control based on sector judgment.On this basis,a model predictive voltage tracking control based on the optimal switch state is proposed,which predicts the subset of switch states at the next moment based on the switch states of the previous sampling period,thereby reducing the number of rolling optimizations,effectively improving the harmonic current tracking ability,and reducing the waveform distortion rate of the power grid current and system switch losses.Then,the first-order linear Active disturbance rejection control mathematical model of the DC side voltage of the shunt active power filter is established.Based on fuzzy linear Active disturbance rejection control,a fuzzy linear Active disturbance rejection control with variable universe is proposed.This control can improve the steady-state accuracy of DC side capacitor voltage control without changing the fuzzy rules and membership functions of fuzzy control.The stability of the proposed control method is verified by Mathematical analysis.Finally,the proposed optimization control strategy was validated using MATLAB simulation software and a developed experimental prototype.The simulation and experimental results show that the improved i_p-i_q harmonic current detection method can meet the requirements of harmonic current detection in three-phase unbalanced power grids,with higher steady-state accuracy of the output fundamental active current and faster dynamic response speed under sudden load changes.The proposed model predictive voltage tracking control method based on optimal switch state reduces the total waveform distortion of the power grid current before and after load sudden changes,and effectively reduces the switching frequency of the system.Compared to fuzzy LADRC control,the proposed variable universe fuzzy LADRC control obtains DC side capacitor voltage with advantages of faster response speed,stronger anti-interference ability,and higher steady-state accuracy.