Development Of Three-phase Four Wire Active Power Filter Based On Three-level Space Vector

In recent years,with the continuous development of power electronic technology,a large number of power electronic equipment and nonlinear load bring great convenience to human production and life,but also bring serious harmonic pollution to the distribution system.At present,Active Power Filter(APF)is the most effective measure to control power network harmonics.At the same time,due to the development of multilevel technology,three-level APF has become a research hotspot in recent years due to its advantages such as low output voltage distortion,low harmonic content and small switching loss.Therefore,this paper takes three-phase four wire three-level APF as the research object to solve the harmonic problem in three-phase four-wire system.In this paper the concrete research content is as follows:First,mainly expounds the practical significance of this topic from the topology structure,the harmonic current detection and current control technology of three-phase four-wire system research status quo of APF is analyzed.Secondly,this paper briefly describes the working principle and topology of NPC three-phase four wire three-level APF,analyzes the working state of NPC three-level three bridge arm APF,and establishes the mathematical model of APF and LCL filter.Thirdly,the harmonic fractional detection algorithm based on multi-synchronous rotating coordinate system for three-phase four-wire system is analyzed in detail.At the same time,PI control and repetitive control are used to establish a composite controller to track the command current,and the parameters of the control link are designed.In particular,in this paper based on the traditional 60° coordinate space vector pulse width modulation technology Space Vector Pulse Width Modulation(SVPWM),put forward for the neutral voltage balance control,a modified virtual space vector modulation Virtual Space Vector Pulse Width Modulation strategy(VSVPWM).The strategy introduces time factor to adjust the unbalanced direction of neutral point potential,realizes the dynamic control of neutral point voltage,and reduces the influence of DC voltage fluctuation on APF output compensation current.Finally,an experimental prototype of three-phase four-wire three-level APF is developed,including circuit parameter design,device selection,and software program design and compilation.In particular,a production workshop 3#transformer harmonic control site was selected to carry out the field application of the prototype.