Study On An Active Power Filter Based On A New Three Level Topology

With the popularization and application of various types of power electronicequipment, distribution network harmonic issues are also increasingly serious.Increasingly sophisticated electronic equipment needs more high-quality and cleanenergy. On the contrary, the increasing use of power electronic devices injects moreand more harmonics into the grid. In terms of harmonic suppression, active powerfilter is an efficient, fast, real-time, stable device, valued and applied in many fields.Three-phase four-wire APF has obvious advantages in the distribution networkharmonic governance issues, received more and more attention.In this paper, three-phase four-wire shunt active power filter for the study, fromthe main circuit topology, phase-locked loop to current and voltage closed-loopcontrol strategy and other aspects are conducted in-depth research.Firstly, this paper compares the two typical three-level converters withConergy NPC converter from the structure, the cost, the modulation method and theloss distribution areas. The results showed that the Conergy NPC has the highestcomprehensive cost performance, and has obvious advantages in terms of cost andloss balance. Based on this foundation, establish a mathematical model of the APFbased on the converter.Secondly this paper studies the traditional software PLL based on singlesynchronous reference frame. The result indicates that the software PLL has a longadjustment time and steady-state error in the presence of the three-phase voltageunbalance conditions and other issues. For these shortcomings, this paper improvesthe response rate and the negative sequence voltage component elimination andeffectively improves the dynamic and steady-state performance of PLL and verifiesthe performance by simulation.Because the AC signal for the PI control can not be achieved without staticerror tracking and the long reponse time of repetitive contol, this paper proposes acombination current control strategy and gives a detailed parameter setting method.This control strategy has fast response, high steady-state accuracy and simple.Meanwhile, in order to ensure the stable of the system, both the closed loop of DCside voltage and its balancing loop are analyzed and designed. These current andvoltage control are simulated.Finally, the experimental results of the new three-level APF shows that the newstructure and the current and voltage control strategy are effective and practical.