Research On Shunt Active Power Filter Based On Three-level Topology

Through the fast development during the past half century,the power electronic technology had been widely applied into the industry and civilian field.The development of the power electronic technology brought a great convenience to human’s life,but also introduced serious harmonic pollution to the grid.Therefore,the methods of improving the power quality is becoming the research focus,the active power filter(APF)is widely applied because it could accurately,timely suppress the harmonic pollution.Furthermore,compared to the APF with the two-level structure,the device is the APF with the three-level structure is suffered lower bus voltage,and then the APF with the three-level structure has low total harmonic distortion(THD),small switch loss and high efficiency.The thesis takes the parallel APF of the three-level topology as the research object.In the thesis,the principle of the three-level APF is studied,and different topology structures of the three-level inverter circuit are introduced and compared.Moreover,the diode clamped topology structure is chosen,and the models of the three-level APF in the three-phase abc coordinate and the dq coordinate are developed and analyzed.Then there is the research of key technology,the d-q method which based the instantaneous reactive power theory is chosen as the detection method of analyzing the harmonic current of the three-level APF.And the dual closed-loop control model is designed for the three-level APF,the voltage outer loop keeps the DC-link voltage stable,and the current inner loop controls the output current to track the command current accurately and flexibly.This thesis designs a compound control based on the PI control and the repetitive control to achieve the purpose of tracking the control current.Furthermore,the PMW method of the three-level APF is also researched,and the SVPWM is chosen and analyzed.The reasons of the unavoidable neutral point voltage drift of the three-level APF are analyzed,and the potential solution is proposed.Finally,the simulation model of the three-level APF system based on the MATLAB is developed,and then simulation results indicate that the THD of grid under PI+ repeated composite control is less than that under PI control,and the compensation effect is better,so the feasibility is verified.The hardware system and software system of the three-level APF are introduced.The control unit based on TMS320F28335 is designed for the self-designed three-level APF system.After completing the realization of the control and the writing of the main program,the experiments with low voltage are conducted to validate the effectiveness of proposed method and system.