Study On Harmonic Current Compensation Controlling Of Shunt Active Power Filter

The extensive use of power electronic devices makes harmonic problem deteriorated increasingly, and harmonic becomes the primary factor influencing power quality; On the other hand, modern electrical equipment are more sensitive to power quality, then it appeals higher requirements on quality of power supply. Active power filter is considered as the most effective method to restrict harmonic, its research and application are widely studied. This paper focuses on the research of harmonic current compensation control for parallel active power filter, and try to reduce the active filter switching loss and improve its compensation effect.The principle, classification and topological structure of active power filter are introduced firstly, then the thesis sets up the mathematic model of the three-phase PWM VSC based on switching function concept, after that the mathematic model is simplified to two-phase dc variables.Several common APF harmonic detection technology are presented, the theise describes three-phase circuit instantaneous reactive power theory, then it explains detection methods base on p-q algorithm and ip-iq algorithm respectively. Emulation using p-q algorithm been done when the system voltage is not distorted.Some common control methods for current compensation are analyzed and compared, especially the hysteresis control and the principle of triangular wave control are highlighted. the thesis proposes a new hysteresis current control method based on optimal voltage vector after In-depth study of the existing home and abroad current control methods. This new method is characterized by combining a group of hysteresis interphase current comparator with a set of stepped interphase current comparator to find the zone of the optimal voltage vector and carry out control measure fast. Computer simulation results on the platform of PSCAD\EMTDC Show that this method can rapidly and accurately determine the optimal electric voltage vector, which can effectively reduce the switching frequency and improve the efficiency of active filters.The hysteresis control has the best control effect. The thesis improves the traditional hysteresis current control method, by adjustting the overall three-phase hysteresis band and hysteresis widths of each phase respectively to achieve the objective of reducing losses.hysteresis width regulation according to the overall size of three-phase current may lead to lower switching losses, in this thesis, the traditional hysteresis current control has been improved to form a new method that combining overall and phase separation regulation. The overall three-phase current size and the size of each phase current are both taken into account so as to find out the optimal hysteresis width that would lower switching losses in maximal degree. Simulation results show the effectiveness of the method.