Research On Modular Shunt APF Based On Adaptive Theory

With the wide application of non-linear load, the harmonic pollution is becomingincreasingly serious. APF is regarded as the most effective method to improve powerquality. It cannot only make dynamic compensation for harmonic wave and reactivecurrent, but also has the advantages of high reliability and better compensation effect,which allow it to be widely applied in various industrial fields. In this paper, in-depthresearch is conducted on some of the key technologies of two-level shunt APF.Harmonic detection，as one of the most important technologies of APF, is thepremise of its proper functioning. Firstly, the basic principle of adaptive filter andrecursive least squares (RLS) algorithm are analyzed. On this basis, an improvedadaptive harmonic detection method is proposed based on RLS algorithm.Differentfrom traditional method, the reference signals of adaptive filter are generated throughClarke conversion of load current instead of using phase-locked loop. The simulationresults indicate the method proposed has faster transient responding time.As another key technology of APF, current tracking directly affects itscompensation effect. Basic theories of sliding mode control and adaptive exponentialreaching law are elaborated firstly. Based on discrete mathematic model of two-levelAPF, adaptive discrete sliding mode controller is designed.When APF is applied in the large capacity situation, conflict will occur betweenthe device switching frequency and capacity. To solve this problem, modular APF isapplied to enlarge capacity, and each module adopts the same two-level APF topologywith independent DC side. Five commonly used parallel methods of modular APF areanalyzed and an improved parallel method and current sharing strategy amongmodules are proposed in this paper. Besides, the generation process of the mainmodule is also studied.Aiming at the influence of the output inductor on APF, average voltage valuemethod is chosen as the way for inductor selection. In the high voltage fields, APF isusually connected to power grid via transformer. The effect of the transformer leakageinductance on APF is analyzed by mathematical modeling.Finally, Matlab simulation is applied to confirm the reliability and effectivenessof the theories in this paper. And parts of the theories are verified by experiments.