Research On DC Voltage Control Strategy Of Three-Phase Four-Wire Three-Level APF

With economic development,a large number of complex and changeable power electronic devices are used in daily life and industrial development to improve the quality of life and production efficiency.At the same time,various power quality problems have also followed.Various non-linear loads are connected to the power system,and the large amount of harmonics and reactive power generated by them seriously damage the power system,reduce the working efficiency and service life of power electronic equipment,cause additional losses,and also cause electronic equipment faults and interference affect the safe operation of power electronic equipment.Active Power Filter(APF)is an important compensation device for improving power quality.It has the advantages of high efficiency,stability,and sensitivity.It is currently a power electronic device that controls the pollution of the power system,improves the efficiency of the power system,and ensures the safety of electricity,this article deeply studies the relevant control strategies of the three-phase four-wire APF.The compensation effect of APF is affected by many factors,among which the accuracy and calculation speed of the harmonic current detection method are important factors.This article introduces the improved i_p-i_q detection method and the improved phase-locked loop,which eliminates the interference of voltage fluctuations on the i_p-i_q detection,compares the phase-locked performance of the traditional phase-locked loop,and verifies the superiority of the dual second-order generalized integral phase-locked loop.The APF equivalent circuit model is simplified,the positive sequence active components are effectively extracted through the improved detection algorithm,and detailed formula derivation and analysis are performed.Regarding the DC side voltage control algorithm of three-phase four-wire three-level active power filter,the most commonly used control algorithm is PI control,but PI control has poor robustness,large overshoot and slower dynamic response.Variable loads often fail to achieve the desired control effect.This paper uses fuzzy PI control combined with a quasi-proportional resonance controller to design a composite controller,which can perform fuzzy inference on the DC side voltage control and realize self-tuning of control parameters.The DC side voltage control parameters are dynamically adjusted to suppress the neutral harmonic current.By improving the quasi-proportional resonance controller to individually control each frequency signal,the influence between adjacent frequency signals is avoided,the control effect is improved,and the compensation quality is guaranteed.A mathematical model is established for the neutral point potential balance,and the reason for the neutral point potential drift is analyzed,and the neutral point potential balance is controlled by injecting the zero sequence component,which is simple and effective,and achieves a better control effect.Through theoretical derivation,a diode midpoint clamp three-level APF simulation model is built in the MATLAB simulation software,compare the current waveforms before and after compensation through different load simulations to verify the design of this article.The effectiveness and superiority of the compound controller.Briefly introduce the hardware circuit of the device designed in this article,and verify the effectiveness and reliability of the control strategy described in this article through experiments.