Study On The Control Scheme Of Three-Phase Four-Wired System Active Power Filters

In this paper, three-leg three-level power filter used in three-phase four-wired system is mainly analyzed。Firstly, the mathematical model of three-level power inverter in three-phase four-wired system is studied in abc frame. Then, through dq0 frame transformation,this model is transformed into dq0 frame. Such study is prepared for the theory basic of next work. About harmonic detection, this paper mainly described a i p- i qdetection based on shunt Active Power theory. After analysis, this measure can be directly used in three-phase four-wired system.Novel deadbeat control strategy is knowned as responsed quickly, and make a relatively strong control for harmonic current caused of nonlinear load. So, this paper has described a novel deadbeat control scheme based on repetitive harmonic predictor, so as to get the predictive harmonic current.Under three-phase four-wired system, two-dimensional (2D) space vector modulation (SVM) methods cannot be used for applying of 0 vector current. That's why this paper has made a research in 3D space vector modulation. At the same time, a direct PWM is applied to the active power filter. Through simulink study, it's analysized and presented that it's useful.In the last part, because of the deadbeat control scheme relied a lot on the system parameters. Based on the least-squares method, a method of on-line parameter identification is applied. Through detecting and changing system parameter, make the control target successful.