Research On Tension Control System Of Cold-Rolled Vertical Loop

The final process of cold rolling production line,rewinding and withdrawing unit,directly determines the quality of strip steel.For continuous production,loop is essential equipment.Also,the process of loop is complex.The production efficiency of rewinding and withdrawing-straightening unit depends on looper tension control system.Under the background of the rewinding and withdrawing-straightening unit in stainless steel plant,the thesis analyse the mechanical structure of vertical loop and looper position and tension control system.The thesis illustrates tension control from three equipment.There are Tension roller,winch and helper roller.Based on this,a mathematic model of strip steel tension were built.Then make the final control object model of frequency changer-motor-strip steel tension.Take characteristic of vertical loop into consideration,the mathematic model is nonlinear and time varying system.Although the traditional PID controller can meet the technological requirement,the parameters must be a compromise.If the requirement be enhanced,the controller will not satisfy the requirements.There for,fractional order PID controller was introduced.Compared with traditional PID controller,the fractional order PID controller has wider control range and better control result,because for two more control parameters.As for the question of tension model change,modified differential evolution algorithm was put forward to tune control parameters of fractional order PID controller.The loop filling process are divided into several parts to control.Every part adopt different control parameters.Based on the transfer function of controlled object,a set of parameters for traditional PID controller and a set of parameters for fractional order PID controller were tuned in accordance with expected magnitude margin and phase margin.Building control system model in Simulink,the response curve proved that the fractional order PID controller controlled better.An improved differential evolution algorithm was put forward as the method of tuning control parameters.Implementing the algorithm in MATLAB and using it to tune control parameters.The response curve in Simulink proved that the DE algorithm had better adaptability and the controller had better availability.Because for fast implementation in computer-control system,the improved differential evolution algorithm can tune parameters instantly.As a consequence,the fractional order of PI controller based on differential evolution algorithm are able to control the vertical loop tension control system quickly and efficiently.