| Active Power Filter(APF) is widely used in various industrial fields based on its good compensation performance and wide applicability. With the increased compensation demand and the rapid development of technology of multilevel, the most powerful practicality is the application in the three-level neutral-point-clamped inverters. Its application does not only improve the installed capacity, but also enhance harmonic compensation performance and system reliability. However, the stability of the DC-bus voltage and accuracy of harmonic current detection directly influence on the power losses and the compensation effect. Therefore, this paper is mainly going to do the research on the two aspects of APF.Firstly, this paper introduces the compensation principle of the APF and the traditional ip-iq harmonic detection method, and discusses the energy exchange mechanism between the dc-side and the ac-side. On this basis, this paper illustrates a new detection method, which does not need phase-locked loop and low pass filter and can avoid the phase detecting error and the delay time. The simulation shows that the detection method has a good effect.This paper also discusses the effect of DC-side voltage on the power loss and compensation performance of APF, and makes a simple analysis on the DC-side voltage fluctuation, then deduces the range of voltage value on the DC-side, and researches one DC-bus voltage controller, combining with the relationship of APF voltage on DC-side, grid voltage and compensation performance. Based on the traditional PI control and the fuzzy control theory, the stability of DC-bus voltage has been realized through the adaptive fuzzy PI controller. This paper also discusses the capacitors in DC-side and AC inductance of APF system. The simulation has been verified that the dc side voltage range can be referenced, and when in power grid voltage fluctuation, the controller can optimize the APF compensation performance, at the same time it can effectively control the DC-side voltage stability.This paper studies a neutral voltage balance control strategy based on fuzzy control, via the analysis on the causes of the neutral-voltage imbalance by SVPWM modulation algorithm and achieves dynamic neutral-point potential balance, modify the action time of positive and negative small vectors simultaneously through the produced balance factor f by fuzzy rules.Finally, the paper introduces the overall structure of experiment platform, and experimentally proves some theories and the effectiveness and reasonability mentioned in the paper. |
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