Research On Shunt Active Power Filter Based On Variable Saturation Soft Variable Structure Controller

The widespread of a large number of nonlinear loads leads to harmonic and reactive power problems,which reduces the power quality of the power grid and threatens the safety and stability of power system operation.Therefore,the active power filter(APF)has been greatly developed and widely used due to its advantages of dynamic regulation of power quality.In this paper,a shunt APF has been studied as follows.Firstly,this paper introduced the common topology of shunt APF and deduced the mathematical models of three-phase three-wire and three-phase four-wire APF.And laid the foundation for the design of control strategy by decoupling analysis.Secondly,the harmonic detection method of three-phase three-wire APF was studied.On the basis of it,the instantaneous reactive power detection method was extended to the three-phase four-wire APF,and the zero line current separation method and0--p qi i i method are obtained.Several kinds of harmonic detection methods were compared and simulated,and the experimental results were analyzed.Then,the current tracking control method used in shunt APF was studied,and the parameter calculation of the PI control method was discussed.Due to the fact that PI control method has slow tracking speed and steady-state error,and can not adapt to the APF system with the characteristics of multi-input,multi-output and strong coupling,a controller based on the theory of variable saturation soft variable structure control was adopted.In the three-phase three-wire system and the three-phase four-wire APF system,the simulation experiments of the variable saturation soft variable structure controller were carried out,and the effectiveness of the method was proved.Finally,a shunt APF hardware test platform was designed.The hardware design including main circuit,device selection and auxiliary circuit was completed,as well as the software design including main program and subroutine.A three-phase three-wire APF experimental platform was built,and the hardware experiment wascarried out under three-phase uncontrolled rectifier bridge with inductive load and complex loading condition.The experimental results were analyzed.The experimental results showed that the active power filter with variable saturation soft variable structure controller can achieve ideal compensation effect under three-phase non-controlled rectifier bridge with resistive and inductive loads and real complex load,which proved the validity and practicability of variable saturation soft variable structure controller in practical application.