Research On Sliding Mode Control Of UPQC

Independent distributed power generation system connecting to the grid makes grid structure become more complex and diversified,and power electronic devices and other nonlinear load have become more widespread,resulting that a variety of power quality problems appear in the distribution network system.Therefore,the design of controller solving voltage quality problems and current quality problems at the same time is the key of improving the power quality.Unified Power Quality Conditioner(UPQC)achieves the organic structure combination and function coordination of the series and parallel active power filter,and has the comprehensive compensation capability of voltage and current.UPQC can realize the suppression of voltage distortion,current harmonics and phase imbalance problems,and achieve the function of reactive power compensation.Firstly,the meaning,classification and characteristics of power quality are summarized and analyzed.On the basis of reading a large number of domestic and foreign literatures,topology of UPQC,detection methods and control methods are studied.Secondly,system components and working principle of UPQC are analyzed.According to the system structure of UPQC,mathematical model is established in a-b-c coordinate and synchronously rotating coordinate separately.Compensation detection method without phase-locked loop is adopted in the synchronous rotating coordinate system,improving the shortcoming that phase-locked loop compensation detection method can lead to detection error in the fault condition of voltage distortion and imbalance.Thirdly,although PID control,single-cycle control,deadbeat control,hysteresis control and intelligent control algorithm have made some achievements in the region of UPQC control,they are poor self-adaptive and difficult to achieve coordinated control.Sliding mode control method with strong robustness is adopted to design the UPQC controller.Voltage compensation unit after input-output feedback linearization is a second-order system,so higher order sliding mode control with higher control precision is adopted to design the voltage compensation unit controller;current compensation unit adopts fuzzy sliding mode control based on the index approaching rate sliding mode control,improving the control parameters of the controller.Comparative analysis of simulation results show that combination of two methods achieves the coordinated control of UPQC and weakens the “chattering” problem of sliding mode control,improving robustness and control accuracy.Lastly,hardware design including capacity design and component selection and software design by CCS3.3 are conducted.Experimental platform of UPQC is built and prototype experiment is conducted,verifying that the method can effectively improve power quality.