Research On Shunt Active Power Filter And Its DC Side Voltage Balance Control Method

Active Power Filters can compensate for harmonics and reactive power in real time,so it is widely used in industrial applications.However,when APF is in working,due to its own loss or when it is switched,there is an exchange of energy between the DC side and the AC side.So the DC side bus voltage willfluctuate.In addition,for the three-level Active Power Filter,there will be current flowing into or out of the capacitor midpoint in the DC side,resulting in the midpoint potential imbalance.DC side of the bus voltage fluctuation and the midpoint of the potential imbalance will lead to the output voltage distortion,thus affecting the compensation performance and efficiency of APF system.So,it is important to maintain the stability of the DC-Link voltage for APF.At first,this paper analyses the reason of the DC side voltage fluctuation and the imbalance of the midpoint potential of the T-type three-level APF.Then introduces the principle of the main circuit,and the commutation process is analyzed.At last,researches the PI control method and carrier pulse width modulation strategy used in controlling APF DC side bus voltage and midpoint potential balance.Secondly,in order to solving the problem about DC side bus voltage fluctuation and midpoint potential balance of three-level APF.This paper adopts the PI control and the carrier pulse width method with the zero sequence voltage superimposed on the modulation reference voltage.Then,according to the control requirement of the system,the APF model is built in the software of MATLAB/SIMULINK,and analysis the control method.Finally,on the basis of the theoretical analysis and simulation of APF DC side v oltage control.The experimental platform of T-type three-level active power filter control system of three-phase and three-wire is built.And the DC side bus voltage and the midpoint potential are controlled by the method described above.Then,some experiments are done on the platform,and a large number of experimental waveforms are got.It can be seen from the results that PI controland the neutral point potential balance control method of adding the zero sequence voltage on the modulation reference voltage can effectively control the DC side voltage balance.It can prove the method of the above isreasonable.