Application Research Of Active Power Filter In Distribution System

Active Power Filter(APF)is a power electronic device which can compensate harmonics,reactive power and unbalanced components.It is an important application of Flexible Alternating Current Transmission Systems(FACTS)in distribution network.When shunt APF is connected with capacitors on the load side,harmonics will be amplified and system will become unstable,which will affect the safe and stable operation of the distribution network.Since the power factor correction capacitor,electromagnetic interference(EMI)suppression capacitor and single-phase motor starting capacitor on the load side will be connected randomly,threatening the stability of the distribution system at all time,it is necessary to study this problem in depth.On the basis of fully analyzing the controller design and the system modeling of the traditional shunt active power filter,this paper first improves the modeling of it.It fills the gap that the traditional closed-loop transfer function model cannot correctly reflect the instability of the system when the load side of the shunt APF is connected with a capacitor.Through the modified model,the harmonic positive feedback amplification path is analyzed,and the mechanism of system instability is well explained.Then,aiming at the hybrid repetitive digital controller with direct current controlling method shunt APF system,using the modified model,the instability problem is decomposed into two aspects: “external circuit instability” and “hybrid repetitive controller instability”.The influence of various electronic parameters and controller parameters on the “two instabilities” is analyzed.The modified model after decomposition is used to guide the optimization of proportional integral path and the optimal design of repetitive controller corrector,so as to realize the system stabilization.The simulation results show that the stability of the direct current control shunt APF system is improved obviously.At the same time,aiming at the multi proportional resonant controller with indirect current controlling method shunt APF system,using the modified model,the stability analysis is carried out,and the imaginary part of the unstable leading pole in the s-domain is corresponded to the resonant frequency of the shunt APF system simulated by MATLAB/Simulink.It accurately reflects the operation of the system.By optimizing the phase compensator of the proportional resonance controller,the phase compensation angle of different frequency band is selected to realize the system stabilization.The simulation results show that the stability of the indirect current control shunt APF system is improved obviously.Finally,the simulation analysis is carried out on MATLAB/Simulation,and the prototype experiment is carried on a 75 kVA active power filter system platform built on the TMS320F28335 digital signal processor(DSP).The phenomenon of harmonic amplification and system instability exists when capacitors are connected on the load side of the shunt APF system is proved through the simulation and prototype experiment.The correctness and validity of the proposed system stabilization strategy are also verified through them.