Completely Decoupling Two-Degree-of-Freedom Speed Sesnsorless Control Strategies Of Linear Induction Machine

Linear induction machine(LIM)is one driver machine that can directly generate thrust for linear motion without the intermediate transmission mechanic device.For this reason,the structure of the system could be greatly simplified,and it is also beneficial to reduce the size and mass of system.Owing to these advantanges,LIMs have a wide range of applications in the fields of rail transit,precision instruments,aerospace and automation equipment.Moreover,the speed sensorless control of the LIM eliminates the need for a sophisticated and expensive speed sensor,reduces the cost of the system,and improves the reliability of the system,so it has received extensive attention.However,the speed sensorless control of LIM still has the following problems:(1)The dynamic performance of the LIM with speed sensorless control needs to be improved further,and the system control parameter adjustment is difficult to be performed;(2)The instabe phenomenon of the LIM with speed sensorless control may occur at the low speed regenerate mode;(3)the speed sensorless control of LIM is sensitive to the changes of the motor parameters.This article will study the above issues and give corresponding solutions.Firstly,in order to obtain the basic parameters required for LIM control,the offline parameter identification method of LIM is studied.With the proposed method,sinusoidal with dc bias excitation is applied on the motor to obain the impedances of the motor at the different frequencies,then the motor parameter is obtained according to the acquired impendance information.To relieve the ill-impact of the inverter nonlinearities,the effects of the dead time and delay are analyzied,then the corresponding compensation methods are proposed to improve the accuracy of identified motor parameters.Secondly,to improve the dynamic performance of the speed sensorless control of LIM,the speed observer and speed controller are systematically designed,and a two-degree-offreedom(2DOF)speed sensorless control method is obtained.With this method,the speed tracking performance of the system can be changed by adjusting the speed controller parameters without affecting the load disturbance rejection capability,and changing the parameters of the speed observer can change the load disturbance rejection capability of the system without affecting the speed tracking performance.Owing to this 2DOF characteristic,not only the system parameter commsission is easy,but also the speed tracking performance and load disturbance rejection capability is optiumed simutaneously.Thirdly,based on the 2DOF speed sensorless control method proposed above,the stability of speed sensorless control of LIM is studied.By analyzing the stability and damping characteristics of the method,the reason why the above method is under-damped to the load disturbance response is revealed.At the same time,the necessary conditions for the stability of the method are obtained,and an observer feedback gain design method which can stabilize the system at the regenerative mode is obtained.In order to improve the damping of the system and further improve the load disturbance rejection capability,the structure of the speed observer is further improved,and the parameter design method of the adaptive law is given.With the improved 2DOF speed sensorless control method,the decoupling of speed tracking performance,load disturbance rejection capability and stability is realized,where the stability is assured by the feedback gain of the speed observer,the speed tracking performance can be adjusted by the speed controller parameters,and the load disturbance rejection capability can be adjusted by the adaptive parameters of the speed observer.Lastly,the robustness of the speed sensorless control to the motor parameter is also studied.In order to eliminate the ill-impact of the primary resistance change on the speed sensorless control,the primary resistance online identification method is presented combining with the proposed 2DOF speed sensorless control method.In addition,considering the change of the mutual inductance,the mutual inductance online identification method is also proposed.With these proposed online parameter techniques,the 2DOF speed sensorless control method could preserve a better robustness to the primary resistance and mutual inductance variation.