Research On Control Strategy And Implementation Of UPQC To Improve The Power Quality Of Railway Automatic Blocking And Continuous Transmission Lines

Electrified railway is the mainstay of the transportation system,which is of great significance to the development of society.And the automatic blocking and continuous transmission line is responsible for the power supply task of railway traffic signals,which is an important part of the electrified railway.Owing to the fact that the automatic blocking and continuous transmission line is laid along the railway and the environment is complex and changeable,it will cause various power quality problems,which have serious impact on railway transportation and production.Aiming at the characteristics of power quality problems of 10kV automatic blocking and continuous transmission line,this paper attempted to improve the power quality problems by unified power quality conditioner(UPQC),mainly from the aspects of detection method and control strategy.First of all,this paper introduced the characteristics,existing power quality problems and it's harm of 10kV automatic blocking and continuous transmission line,and expounded the measures to solve the problems of power quality.And then the topology,working principle,power flowing and mathematical model of UPQC were analyzed,which laid the foundation for the detection method and control strategy.Secondly,in the detection process,this paper firstly described the current detection methods,and then discussed the voltage detection methods.Combined with the characteristics of UPQC,the comprehensive detection method based on dq0transform was emphatically analyzed.When the three-phase voltage is distorted and unbalanced,with the combination of dq0 method and i_p-i_q method,this method can quickly and accurately detect the fundamental positive sequence voltage,and provide a phase criterion for the current detection to avoid the errors caused by the phase-locked loop.Finally,simulation comparisons showed that the detection method is correct and feasible.Then,in the control process,this paper firstly discussed the traditional control strategy,and then analyzed the PI controller.Aiming at the problems of PI controller,a direct adaptive control strategy based on command generator tracker(CGT)was proposed.When the input is a time-varying signal,this control strategy enables the output of the controlled object to track the reference model output perfectly,which reduces the tracking errors and achieves the asymptotic tracking effect.This strategy not only optimizes the control algorithm but also simplifies the hardware circuit.Through simulation comparisons,the proposed strategy provides more robustness,flexibility and adaptability in all operating conditions of the power system over PI controller.Finally,the experimental hardware circuit with TMS320F28035 as the core device was built and completed.The related hardware circuits were designed in detail and experiments were conducted.The experimental results showed that the UPQC can effectively improve the voltage and current quality problems of 10kV automatic blocking and continuous transmission line by the direct adaptive control strategy based on CGT.