Research On Three-phase Four-wire Parallel Type Three-level Active Power Filter

At present, there are a large number of nonlinear loads in the power system, most of them are three-phase and four-wire structure, and the nonlinear loads lead to the generation of harmonics. In order to guarantee the power quality, harmonics must be filtered out. Compared with other filtering equipments, the shunt active power filter(APF) has a lot of advantages such as high efficiency, good stability and so on. Therefore, the three-phase four wire shunt active power filter is studied in this paper..The basic structure and working characteristics of series and shunt active power filter are compared and analyzed, and the deficiencies of series APF in practical application are pointed out. Then this paper studies the basic operation principle of shunt APF and the topology of TNPC. On the basic of this, the main circuit structure of three-phase and four-wire parallel APF is analyzed. Then the article gives the reasons for not choosing the APF which with three-phase three- wire structure and current type. Finally, the parameters of the main circuit of three-phase and four- wire parallel APF are designed.The instantaneous reactive power theory is briefly analyzed, After that, the paper studies two traditional methods of harmonic current detection and does a depth analysis of the(Park transformation) harmonic current detecting method based on instantaneous reactive power theory. Meanwhile, the paper points out the error of this method in the harmonic detection, aiming at these problems, it uses an improved methodThen for the APF of T type three-level, the paper does a study for the three common methods and points out the advantages and disadvantages of each method. At the same time, the three level hysteresis control strategy is studied in detail. According to its’ characteristics, the calculation method of the corresponding hysteresis width is given, and the final simulation shows output waveforms of the three-level hysteresis.Finally, according to the theoretical analysis and simulation experiments, builds simulation model of the whole system, and the simulation studies two different load conditions. On the basis of simulation, we built a three-phase and four-wire shunt APF experimental system, the devices of main circuit and control process of software have been described, according to the experiment, we know that the APF of this study is consistent with the theoretical analysis and the experimental results.