Research On Nonlinear Control Strategies For Dynamic Voltage Restorer

With the increasingly rise of industrialisation,electric power load increases sharply, especially the capacity of the impact load and the non-linear load continues to grow,which makes the network appeared a wide range of power quality problems.According to statistics and analysis of the national scholars and the power department,voltage sag is one of the highest probability problem among various power quality problems in power system.Dynamic Voltage Restorer is a DFACTS device,emerging in recent years,concatenating between power and sensitive loads,has good dynamic characteristics.When the voltage sag occurs,it can compensate voltage sag effectively in millisecond.It is an effective device which can inhibit the dynamic voltage disturbances and can inhibit the harmonic interference and voltage flicker in power supply voltage.The control system is the core of the entire DVR.In the control system of DVR,the detection part and the control algorithms design part are the key to the entire DVR controller.In the detection part,types of existing harmonic detection methods are introduced. Integrating the compensating theory of DVR,this article made a theoretical derivation and selected the detecting method of voltage based on Park transformation in theory.Then,some relevant research is done in simulation to testify the validity of the detecting method.In the control part,this article deduced the model of DVR detailedly.Considering that DVR is a coupling nonlinear system in synchronous rotating dq coordinate system,two methods are adopted to design controllers.One is inverse system method with variable structure control theory.The original system model of DVR is linearized and decoupled to be two pseudo-linear systems.Then,this article adopts variable structure control theory,by which the variable structure control laws of the pseudo-linear systems are designed.The other is state feedback exact linearization method with variable structure control theory. The original system model of DVR is linearized and decoupled to be two pseudo-linear systems.Then,the variable structure control laws of the pseudo-linear systems are designed.At last,this article made a simulation on the basis of theoretical analysis,made a comparison and analysis with the state-feedback decouple control method which with PI adjustment.The simulation results verify the feasibility and efficiency of variable structure control method.