Research On Voltage Balance Control Strategy Of H-Bridge Three-Phase Four-Wire Low Voltage APF

With the increasing diversity of power loads and the increasing application of power electronic devices,power quality problems such as harmonic pollution,reactive power consumption,and voltage fluctuations have become increasingly prominent,and these problems are particularly obvious in medium-and low-voltage distribution networks.In China,low-voltage power distribution networks and some medium-voltage power distribution networks,such as non-ferrous metal smelters and underground mines,mostly adopt three-phase four-wire systems.Therefore,research on power quality adjustment equipment suitable for three-phase four-wire distribution network is in line with the technological development trend and the needs of the national economy.This paper takes the three-phase four-wire APF(active power filter)as the research object,and has carried out the following work:1.The APF topology suitable for three-phase four-wire system is discussed,and the characteristics of different structures such as diode clamp type,flying capacitor type and H-bridge type are analyzed.Finally,the H-bridge topology is selected according to needs of research;2.This paper analyzes the working process of three-phase four-wire H-bridge APF,and establishes a mathematical model based on instantaneous power theory,and ip-iq theory,and clarify the detection and compensation methods of harmonic current and reactive current;3.This paper focus on the analysis of the change process and influencing factors of the DC side voltage of the three-phase four-wire H-bridge APF,and propose a series of voltage control strategies,including:(1)The control strategy of Two-level voltage based on "global control + phase-to-phase adjustment";(2)The phase-to-phase power distribution algorithm based on negative sequence current injection;(3)The dynamic additional voltage compensation method based on neutral current zeroing;(4)The phase voltage adjustment method based on zero sequence power injection;4.The control strategy of the inverter unit is analyzed.Supported by theory and simulation results,the "current hysteresis control" scheme was selected,and the charging and discharging states of capacitors under different on-off combinations of switching tubes were sorted out,and its correlation with the changes in DC side voltage was summarized.On this basis,a "dynamic bandwidth current hysteresis control method based on DC side voltage balance" is proposed;5.The model was built through Matlab/Simulink,and the aforementioned control strategy was simulated and tested,and the test results proved the effectiveness of the algorithm;6.A three-phase four-wire H-bridge APF experimental platform was built,and it was connected to loads such as fans and uncontrolled rectifiers for reactive power compensation,harmonic control and other experimental research.The experimental results obtained so far have verified some of the aforementioned conclusions.