| This study is an important part of the Doctoral Program of Higher Education of the Ministry of Education (NO.20101402120004).It is proposed on account of the more and more low quality of power supply. The wide application of power electronic devices makes the harmonic pollution of the power system serious day by day. Traditional approaches of eliminating harmonics have become incompetent for modern power system. Active power filters (APF), as a novel power electronic device, are considered to be the most promising alternative of harmonic elimination due to their fast response and flexibility. In recent years, digital signal processing technology has been developing rapidly. It is of great practical significance to study on active power filters using DSP-based control.The system configuration and working principle of a three-phase three-wire active power filter is analyzed in this article. Further-more, the harmonic current detection method and control strategy is studied in depth. A testing platform is designed based on the previous work. During the design, how to implement the hardware and software of an experimental device of APF is focused on. Specifically speaking, the following issues are the main contents of this article.The history and current situation of APF is described as well as its classification. The system configuration and working principle of a shunt APF is analyzed emphatically.Highly accurate and real-time harmonic detection method is the premise of the effective elimination of harmonics for APF. Two commonly used approaches are discussed in depth, which are based on the instantaneous reactive power theory. Both the advantages and disadvantages of the two method mentioned above are indicated. In view of the deficiencies, a new harmonic current detection method based on the decomposition of instantaneous current is summed up using the thinking of coordinate transformation in motor analysis. The new method not only inherits the advantages of conventional methods but also conquers the defects well. Meanwhile, the new method is of wider adaptability.It is necessary for APF to introduce proper control, which includes two aspects. For current tracking control, both the hysteresis band current control and triangular wave comparison method are discussed comparatively, and their separate operating characteristics are summarized. The implementation of triangular wave comparison method on DSP is mainly studied. For DC voltage control, the reason for the fluctuation of DC voltage is analyzed in detail from the perspective of energy exchange, and a close-loop control is introduced to stabilize DC voltage.The mathematical model of the power circuit for three-phase three-wire shunt APF is established. Furthermore, how to design the power circuit is discussed. Using Matlab/Simulink power system toolbox, a simulation model is built. The simulation results are presented and analyzed, which demonstrate the accuracy of the control method and selected parameters.Based on theoretical analysis, the power circuit, driving circuit, protection circuit and control circuit are designed. The assembly language program for control system is written and debugged on CCS3.1. A testing platform of hardware and software of shunt APF is established, and experimental studies are carried out. The experiment results show that all parts of the experimental device can work effectively and it can detect the harmonic components in distorted current. All the experiments verify that the design of hardware and software for shunt APF is rational and the proposed method is feasible. The present work lays a foundation for further testing and debugging. |
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