Study On Control Methods Of AC Motor Of Torque Response Under High Performance Load In Rolling Process

Over the past 20 years,the mainstream electric drive system in rolling industry has been switched from DC motor control to AC motor control.Large scale wide strip steel hot continuous rolling and cold continuous rolling production line,in particular,are using AC motor drive system mainly because AC motor can be easily maintained,and can be shaped of smaller size and smaller rotation inertia under the same power while having higher power utilization rate,comparing to DC motor.There are three types of AC motor control for large scale wide strip steel continuous rolling line.The first type is the design of synchronous motor driving the main drive system of rolling mill.By doing this,synchronous motor will stay in an excitation working state and the motor would work in a capacitive load state,which is rewarding for the reactive power compensation in factory.This control method is basically using direct torque control based on space vector control.The second type is for the drag system under medium power state like the edge mill,coil rolling,flying shear and so on,aiming at acquiring small rotation inertia by using AC induction motors to easily start and fast respond to the load.The control method is basically using vector field orientation and armature current decoupling.The third type is for the auxiliary drive system with small power and multi-motors,such as the transmission roller table equipments.Normally it adopts the frequency conversion control system of a common direct current system.There is a rather obvious common feature within drag-drive system in the rolling process:the frequent mutation of load,such as the bite steel and cast steel of a main motor,shearing action of a flying shear,roll bite steel of a coiler,so and forth.At the same time,these characteristics also bring us the corresponding shortcomings for AC motor application in the rolling process:the inevitable dynamic speed drop.No matter what control method we use,the speed of dynamic adjustment precision will always be limited.Unfortunately,speed matching and dynamic response of high performance are required for the continuous rolling mill,which requires us solving the stated defect above.According to theory,AC motor control system is a typical nonlinear control system,which means when using the classical control theory to its speed and tension(torque)control,dynamic performance will be greatly restrained and can not be completed to DC motor control system.In order to make full use of the advantages of AC motor drive system and overcome its deficiencies,the presentpaper mainly focuses on the external compensation control method of drive system to meet with the control performance requirement of large-scale wide strip steel continuous rolling mill main drive equipment.The main innovations and work are listed as followed.Soft sensing load observer is proposed and designed,compensation control is given from the perspective of speed.Without the participation of direct load detection device,the dynamic speed landing problem is solved and the accuracy of dynamic speed compensation is improved.Due to the sudden change of rolling load,although there is a direct detection instrument for rolling pressure,the lag response of mechanical and electromagnetic induction principle is still inevitable.Thus external compensation method can not lead to the desired results.The present designed load observer is based on the observed-sudden change of electromagnetic torque of AC motor itself.The change of the electromagnetic torque of the motor appears not only within the load change,also within the normal speed adjustment.Given the fact that the change of torque cannot be obtained by directly detecting the rolling force and they have no direct linear relationship,we designed an soft-intelligent load observer.We try to obtain the accurate rolling load mutations information without any delay so as to give out an exact external compensation value.Coiling tension compensation controller is proposed and designed.Without the direct detection of a tension sensor,the self-adaptive tension tracking control is realized with time-varying parameters of the controller,meanwhile the accuracy and adaptability of the coiling tension control are improved.Given that the tension control accracy of a coiler is quite important in rolling process because it's related to coil shape,shape quality and the direct moving of steel coil.After Reel in the roll biting steel,coil diameter will have a continuous change from small scale to large scale with different specifications of width.The rotation inertia,in the very process,will produce obvious time-varying change which results in the time-varying adjust in tension object mode.If we choose to use the classical fixed parameter linear regulator control method,we can not get the global tension dynamic optimization control,and the accuracy of high-performance tension response will be confined.Therefore we design a coiling tension tracker and an external compensation control method based on the ADRC control principle.We use the tracking performance of this principle and its special tendency to minimize the parameter requirment of an extended state observer to successfully improve the self-adaptability of the controller.A control method about the electric excitation of synchronous motor with the combination of passive control and air-gap magnetic field is proposed,the control quality of speed-controlling system is improved and the capacity of power switch machine is reduced.Firstly,in the directional vector dynamic control process of electric excitation synchronous motor due to the armature-reaction causing by the mutation of charge,the passive control method of directional and none real-time decouple problem is solved,which is generally caused by the decouple of torque and flux-linking,the reduction of dynamic quality of the control for speed-control system and the uplift of the stator voltage,the increase of the voltage and capacity leading by increasing perceptual power.Secondly,the complexity of the non-linear control of alternating current machine is weakened,the combination of passive control and directional air-gap magnitude field is raised aiming at solving the shock of power angle and unsteady problems basing on the electric excitation current,the torque current,the mix of rotator current due to the sudden change of rolling load.Theoretically,the stability of controller is proved,so as the relationship between stability margin and stator resistor.The advantages of passive control are that by directly using the energy relationship of engine machines,the non-linear structure of machine can be preserved,the design of simplified controller can be eliminated and the overall stability of the system can be maintained and no singularity problem will show up.All the methods in the present paper give out detailed theortical analysis and descriptions and their corresponding simulations and results.The summarization,analysis,induction and summarization of the control methods for high performance AC motor are also demonstrated.