Research On DC Side Voltage Control Of Three-level APF

Nowadays,power electronic equipment is widely used in the power system,which brings convenience to people's life.But it will also lead to more serious harmonic pollution and lower power quality.Active power filter(APF)can compensate harmonic and reactive power,and it can be used in many applications.Therefore,the use of APF for harmonic governance is now favored by scholars.At present,people's requirements for APF compensation performance have been improved,and multi-level technology has also developed rapidly.Three-level APF has become a research hotspot because of its good compensation effect and low output harmonic content.However,whether the DC-side voltage of three-level APF is stable and whether the neutral-point voltage is balanced will have a certain impact on the compensation effect and reliability of APF.Therefore,this paper takes LCL three-level APF as the research object.This paper mainly studies how to ensure the stability of DC side voltage and neutral-point voltage balanced.In this paper,the working principle and topological structure of APF are explained at first.Analysis and comparison of several commonly used harmonic detection techniques.Thep qi-i detection method can still accurately detect the harmonic component when the voltage is distorted.Therefore,this paper chooses thep qi-i detection method for harmonic detection.Secondly,this paper chooses the fuzzy PI control to control the DC side voltage.This paper introduces the traditional PI control method and its advantages and disadvantages,because it has the shortcomings of slow dynamic response speed.Therefore,this paper integrates the fuzzy control into the traditional PI control,and uses the fuzzy PI control to control the DC side voltage stability.At the same time this paper designs the fuzzy controller used in this paper.Using this method to tune parameters to improve control performance.By comparing the simulation results of these two methods with that of MATLAB/Simulink,It can be concluded that the response speed of the fuzzy PI control method is 0.07 s,while that of the traditional PI control method is 0.15 s.Moreover,this method has good robustness and can control DC side voltage very well when the load changes abruptly.This paper also controls the phenomenon of midpoint imbalance.The space vector pulse width modulation(SVPWM)is analyzed.On this basis,this paper analyses the causes of the neutral-point voltage imbalance,and then explains how several different types of vectors affect the neutral-point voltage.In this paper,adjusting factors are introduced to regulate the action time of positive and negative small vectors to achieve the balance of neutral point charge,and then to complete the balance control of neutral-point position.The method is verified by simulation with MATLAB.The neutral point potential without control is about-20 V,while the neutral point potential with control is about stable near zero.This paper designs hardware circuits such as sampling circuit,and software flow and builtexperimental platform based on DSP TMS320F28335...