Study Of Nolinear Control Strategy For Shunt APF Based On Differential Geometry Theory

Electricity is one of the most important energy sources for modern industrial development.With various power electronic devices and a large number of nonlinear load incorporated into the power system,abundant harmonic current is injected into the power system,which is a serious threat to the safety and stability for the power grid.Active power filter(APF),as an efficient device eliminating harmonic pollution,can realize dynamic compensation,which can effectively improve the power quality.Disadvantages of the traditional compensation strategy are that the current is not precise and dynamic performance needs to be improved.In this paper,nonlinear control theory based on differential geometry theory and sliding mode control method are introduced into the study of APF current control strategy.The contents of this paper are as follows:Firstly,this paper focuses on the research for single-phase shunt APF,which is an important branch of APF.Mathematical modeling for this system is a relatively simple single-input single-output system.With the help of the nonlinear mathematical method based on differential geometry,the affine nonlinear model is established,the feasibility of exact feedback linearization is validated,and the linearized model is derived.On this basis,a siliding mode control method based on differential geometry for single-phase APF current is proposed.Also,simulation experiments and engineering prototype verify that the proposed theory is proper and feasible,and possesses obvious advantages compared with the traditional PI control strategy.This part can provide the application example for the following study for three-phase APF.Sencondly,the research for three-phase three-wire shunt APF based on LCL filer is the key point.This system is a relatively complex multi-input multi-output system,which involves more state variables and related parameters in the modeling process.In this paper,the affine nonlinear system model of the system is established in the d-q two-phase rotating referrence frame.Then,the APF's active and reactive components are decoupled with adopting the state feedback linearization method based on differential geometry,resulting in two independent subsystems.And,in order to accurately trace the reference currents,two independent sliding mode controllers are designed,the proposed design scheme can weaken the dependence on accurate mathematical mode and guarantee the rapidity and stability at the same time.Finally,detailed simulation and experimental results are reported,which exhibit the steady-state and transient-state performance of the equipment.