Research On Harmonic Current Detection And Control Technology In Shunt Active Power Filter

With the electrification level improves continually, the problems of power quality is drawing more and more attention, in which the harmonic pollution problem due to a variety of power electronic devices widely used in all walks of life is especially prominent. Active power filter with its high controllability, rapid response, not influenced by system parameters, etc, occupies an important place in harmonic suppression and reactive power compensation and becomes a research hotspot at home and abroad.The basic principle of shunt active power filter is to add compensation current to the power grid, making grid current ideal sine wave. The key performance indexes of the active power filter are the dynamic response speed and compensation precision of steady state. In order to optimize the compensation effect of it, harmonic current detection and control technology were studied in this paper.Firstly the mathematical model of three-phase three-wire shunt APF was established in the synchronous reference frame, and three-phase digital phase locked loop was designed, which laid a foundation for harmonic detection and current control. Secondly the harmonic detection methods based on instantaneous power theory and Discrete Fourier Transformation were analyzed. Taking advantage of the basic principle that generalized integrator can track sine signal with no steady-state error, multiple sets of generalized integral controller was designed in parallel. Thus any harmonics within50times can be detected. Conventional PI control can only realize no difference tracking of dc signal, while the reference signal of APF is a superposition of periodic signals which have different frequencies. So the PI-repetitive compound control method was adapted and the compensation performance of APF was improved. The parameter design of compound control system was finished. Simulation and experiments were conducted to validate the effectiveness.Combining with the scientific research project that high-power three-phase three-wire shunt active power filter, in which the author has joined, the realization of the whole digital control system was studied according to the requirements of device. Completed Hardware design and software design of the digital control system were completed, including the design of core control circuit of DSP, peripheral circuit and software programming. Based on the LabWindows/CVI virtual instrument development platform, the human-computer interaction interface was realized using an industrial computer. CAN communication protocol was adopted by the upper computer to communicate with DSP to transmit data. The real-time running state of the system was monitored. The upper computer can set control parameters and inquire malfunction, assists the DSP control system.