| The traditional means of harmonic control which can only filter out the harmonic with particular order and occur acceptor resonance with grids will gradually be replaced by other new instruments. Active Power Filter (APF) is widely considered the most effective instrument to solve the problem of harmonic pollutions and improve the power quality. With the development of algorithm and theory and the improvement of power electronic technology, the practical application of the APF is being promoted. In foreign countries, low-power APF has been production. However, harmonic treatment of the high-power APF has not yielded satisfactory results. At home, APF is still in the experimental stage. Therefore, APF is a research focus in the field of power electronics technology at home and abroad.In this paper, the development and application of APF are shown firstly. APF is categorized by the structure of main circuit, the way of access to power grids and the power supply systems and details the configuration and applicable occasion. It is detailed that the framework and working principle of the APF with voltage source inverter (VSI) which is shunt,3-leg 3-wire.Several common methods of harmonic current detecting are introduced and the advantages and disadvantages of these methods are compared. For three-phase three-wire circuits, p-q and ip-iq harmonic current detecting based on the theory of Instantaneous Reactive Power is detailed. Finally, ip-iq harmonic current detecting method which is fast and free from the effects of voltage quality is selected to be achieved in this paper and our projects.The harmonic current detection module is designed and achieved to realize the ip-iq harmonic current detecting method. The harmonic current detection module is composed of analog signal conditioning circuits, AD sampling circuit, zero-crossing detection circuit and PLL circuit. AD7656 with the precision of 16-bit which can sample six signals at the same time acts as A/D conversion chip, which improves sampling precision and reliability of the hardware circuit. AD7656 is controlled by TMS320F2812 when DSP captures rising edge of sample signal. Aiming at the phase difference between the zero-crossing signal and the sinusoidal signal in a grid cycle, this paper proposes a solution to ensure the sampling points and decrease the cumulative error. A math model is set up in this paper to research the Transient characteristics of PLL to find out the Stabilization time and the maximum overshoot. In this paper, we resolves the problem of that the first rising edge of Sample signal is not synchronized with rising edge zero-crossing signal by the software compensation.The main program, A/D conversion program, and calculation program of harmonic detection are designed and their flow charts are drawn. The flows of these programs are also described.With the help of SimCoupler which is a interface module in PSIM, the diction module of APF is simulated by PSIM which is a professional simulation software in the filed of power electronics and Matlab. The model of detection module and part of software model are set up in PSIM. The design of digital low-pass filter is completed with Filter Design & Analysis Tool in Matlab.Some data and diagrams of simulation are got. We get some results of experiment by the harmonic detecting module of APF. The results of simulation are compared with the results of experiment to find out the difference between them and the deficiencies of experiment. We analyze the error in the experiments to have a further improvement in next step. The work have been done is summarized. Some methods to improve the inadequacies of experiment are proposed. |
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