Active Power Filter Variable Structure Control Strategy

Because of the serious "power pollution" problem, more and more attentions have been paid to "power clean". This paper's purpose is to provide a kind of effective control scheme, analysis and design methods for active power filter by studying on variable structure control.Firstly, the backgrounds, developments and future prospects of active power filter are presented. Because active power filter overcomes the drawbacks of passive power filter and has multi-functions, such as harmonic compensation, reactive power compensation, flicker/imbalance compensation and voltage regulation, it has been considered as one of the most effective methods to suppress the serious "power pollution" problem. However, there are many researches including system structure and control scheme have to be done in order to achieve advanced active power filter.Based on detail studies of variable structure control theory and the drawbacks of instantaneous reactive power theory, the compensation control of active power filter is transformed to motion following control applied with variable structure control theory. In the second chapter, the application method of variable structure control for active power filter is also presented. The comparison between the control schemes based on instantaneous reactive power theory and variable structure control theory manifests that variable structure control theory not only provides the effective control scheme, but also supplies the theoretical references for system analysis, such as parameter design, robustness and stability.Next, the application of variable structure control for active power filter, which are classified into shunt, series and hybrid ones, are studied in detail. Applied with space vector diagram, a novel method for analyzing the control law and current controllability of variable structure control is proposed. The detail discussions of parameter design, robustness and stability analysis are also made. Furthermore, based on modeling the DC capacitor voltage control subsystem, a kind of fuzzy voltage controller is proposed, which results in good control performance.In order to reduce the chattering of variable structure, a novel control scheme----fuzzy variable structure control is proposed in the fifth chapter. In this control scheme the reaching law approach and fuzzy logic arc integrated. When applied to active power filter, this novel control scheme not only reduces the switching frequency and the switching loss, but also has better performance and robustness.On the basis of above researches, a shunt active power filter based on variable structure control is designed and implemented. The implementation technology, including main circuit, digital control system of microprocessor 8098 and software are extensively studied. At last, the significant experimental results verify the effectiveness of variable structure control and validity theoretical analysis for active power filter.