Research Of Cascaded H-Bridge Shunt Active Power Filter

With the rapid increase of domestic economy and improvement of living standard, different kinds of power electronic equipments and on-linear loads have been applied. Power quality issues are becoming more complex and integrated. As a new set of power electronic device, active power filter(APF) is now getting attention and obtaining application because of its superior harmonic suppression and reactive power compensation performance. However, the application of APF is restricted in high voltage and large power fields. This dissertation presents the cascaded H-bridge APF with modular combination in order to increase voltage and the number of output level to make up for such deficiencies. In the meantime, to expand the application of cascaded H-bridge topology, applying this topology to shunt capacitor flexible switching technology is studied and experimental verification shows the feasibility.First of all, d_q current detection algorithm is applied to detect harmonic and reactive current. The current tracking control method is studied, and triangular carrier comparison control method is applied. The principle of PI controller and repetitive controller are introduced, and both controllers are designed to apply the object of model. Then, a composite controller made up by PI and repetitive controller is studied. The PI controller can ensure satisfied dynamic response performance, while the repetitive controller is used to improve the compensation precision. The model of IGBT, single filter inductor and DC capacitor is selected.Then, the technology of phase shifting carrier and its application in cascaded H-bridge APF is discussed, and the influence of phase shifting carrier technology on harmonic content is analyzed. As no connection exists between each DC side of H-bridge, the difference of module loss may cause ranges among the DC voltage. In order to remain the equipment capacity at a certain extent, the principle of two-level control strategy is proposed. The upper level is used to stable the total voltage of DC side between phases, while the lower level is applied to make sure that each DC voltage equals to each other.Afterwards, a simulation model of three-cascaded H-bridge APF structure is established by software of PSIM. Based on the simulation model, a experimental platform of cascaded H-bridge 7-level APF is designed. The model consists of main circuit section and the control section, and the implementation in hardware and software is discussed in detail. Experimental studies are conducted in soft start, DC voltage control, reactive and harmonic compensation to verify the control strategies described herein.After analyzing control strategies of cascaded H-Bridge APF, in order to expand the application of cascaded H-bridge topology, applying cascaded H-bridge topology to shunt capacitor flexible switching technology is proposed, which is Based on project relies of Economic and Technical Research Institute of Jiangsu Electric Power Company. A experimental simulation platform of this idea is designed, and main circuit parameters and control method are determined. Dynamic control and flexible switching of compensation capacitor group is analyzed to show the improvement of power quality indicators. Finally, the H-bridge platform is applied in experimental verification of cascaded H-Bridge topology in capacitor flexible switching technology.