Study On Key Technologies Of Three-Phase Three-Wire System And Three-Phase Four-Wire System APF

The use of more and more power electronic devices has caused the grid current and voltage waveforms to be distorted,and the harmonic pollution caused to the power grid has become more and more serious.The decline in power quality has brought great hidden dangers to the power grid and electrical equipment.Therefore,it is extremely urgent to improve power quality and suppress harmonics.Active Power Filter(APF)has precise dynamic compensation performance,fast response capability and wide adaptability,making it an important device for suppressing harmonics.Firstly,this article introduces the topology and system structure of the three-level APF.By analyzing of various three-level topologies,the diode clamp topology is selected as the power topology of the three-level APF,and researched its working principle.Comparison and analysis of a variety of common harmonic current detection methods,I select ip-iq harmonic current detection method.Current tracking control select repeat control and quasi PR.Three-phase three-wire three-level APF use SVPWM modulation based on simplified 60° coordinates System.Because there is a capacitor midpoint on the DC side of the three-level APF and it is necessary to control the voltage balance of the two capacitors,Three-phase four-wire system selects three-bridge four-wire APF structure to cut costs.The three-bridge three-phase four-wire APF selects 3D-SVPWM modulation in the abc coordinate system,and adds phase-locking technology under voltage imbalance and zero-sequence current detection and compensation techniques.Secondly,the simulation model of three-phase three-wire under balanced load and three-phase four-wire under unbalanced load three-level APF system is built with MATLAB/simulink software.The simulation results verify the feasibility and rationality of control algorithms with the SVPWM modulation based on the 60° coordinate system and 3D-SVPWM in the abc coordinate system.At the same time,the causes of midpoint potential fluctuation are analyzed.The feasibility of equalizing the capacitor voltage by software equalization or hardware is verified by simulation.Finally,the main circuit parameters of the diode-clamped three-level APF system with a capacity of 60kVar were calculated.The electrical components were selected according to the calculation results,and the main circuit was built.DSP+FPGA is selected as the main control chip of the system,and other peripheral circuits are designed,including sampling circuit,power supply circuit and drive circuit.According to the control algorithm and simulation model,DSP and FPGA software were written with CCS and Quartus II.After that,the whole system of the three-level APF is built and the system is debugged by hardware and software.The final experimental results and simulation results have been used to further illustrate the feasibility of the three-level APF system designed in this paper.