Research On Shunt Active Power Filter Without Harmonic Detection

With the development of modern power electronic technology, more and more electric and electronic equipments apply to industrial production and people's daily life. It creats a huge benefit to society, bringing a huge improvement to people's lives, while also seriously pollutes the grid.Active power filter can effectively suppress harmonics and improve the quality of the grid, but its good performance depends on the excellent control methods. There are already many good control strategies, but most of them are often based on the detection of non-linear load harmonic. The inaccurate and non real-time harmonic detection will seriously affect the performance of active filters.Firstly the paper studies the energy exchange theory between AC and DC side of the active filter; then the paper points out that the detection of harmonic is the detection of non-linear load fundamental component essentially, by analyzing the basic principles of harmonic detection method; finally by analyzing the average model (or the RMS model)of active filter voltage and current double closed-loop control system, the paper points out that harmonic detection in active filter control system is only a feed-forward link, not a necessary link.On the basis of analysis above, a control strategy without harmonic detection is derived. And then the equivalence between this control strategy and the traditional control strategy based on harmonic detection is analyzed. Under the dq coordinate system, control system parameters is designed. Finally phase-locked loop based on zero-crossing detection with hysteresis comparator and phase-locked loop based on dq transformation are studied.In order to verify the effectiveness of the proposed control strategy, simulation is executived on matlab, and an active power filter experimental platform is set up. Then harmonic compensation experiment is carried out on the experiment platform. Experimental results show that active power filter without harmonic detection can effectively eliminate non-linear load harmonics, and improve the quality of grid current significantly.