The Research Of Active Power Filter Based On Three Phase Four Wire System

Electricity as the most widely used energy in modern society, the power quality is one of the important symbol of development level of a country. With the rapid development of power electronic technology, power electronic devices have been widely used. With the rising popularity of office automation and home appliances, single-phase nonlinear loads have been extensively used in the three phase four wire system, such as computer, fluorescent lamp,printers, air conditioning, elevators, TV sets, washing machines, refrigerators, etc. Although the harmonic generation of a single electrical equipment does not cause great influence to the power grid, but due to the use of very large quantity, and work at the same time, the electrical equipments will create a large number of harmonic to cause great influence to the power grid.This paper mainly aimed at the three phase four wire system harmonic problems of the office and residential building, and the causes of harmonic, the significance of the governance,harmonic governance standards, harmonic suppression measures, the research status at home and abroad of active power filter and the basic principle of active power filter were introduced briefly. The harmonic current detection algorithm and compensation current tracking control algorithm of the three phase four wire system were analyzed in detail in this paper. A active power filter model based on the new type of three phase four bridge arm inverter was been designed in the software of MATLAB.This model of active power filter based on the shortage of detection speed and accuracy of the existing linear PI controller of three-phase phase-locked loop harmonic current detection algorithm under asymmetric power distortion, a nonlinear PI controller based on variable gain harmonic current detection algorithm of three-phase phase-locked loop was proposed in this paper. At the same time, a new three phase four bridge arm three level inverter SVPWM control algorithm based on the diode clamping and leap clamping capacitance type of topology structure and the two-dimensional space vector pulse width modulation algorithm of the three-phase hree bridge arms active power filter was put forward.This control algorithm is relatively simple because it does' t need to compute the cosine function and just solve four easy equations when calculating the vector effect time. With the increase number of level, this inverter structure is relatively simple because it does' t need fly across capacitor and clamping diodes and it can be applied to high power applications.In this paper, reference vector of cube orientation and the judgment of the tetrahedron were analyzed in detail, and calculated the action time of each basic space vector. The simulation showed that the harmonic detection algorithm proposed in this paper had good practicability under the condition of power voltage distortion, and this harmonic detection algorithm could well satisfy the real time and high precision of active power filter harmonic detection requirements. The three-phase four wire active power filter could well restrain harmonic and compensate the line current produced by the unbalanced load under asymmetricpower distortion. This new active power filter had high compensation precision and good dynamic response.