Research And Implementation Of Doubly-fed Linear Motor Control System

Compared with ground transportation,rail transportation shares the pressure of ground transportation to a great extent.Not only that,the punctuality and safety of rail transportation are superior to other transportation,then people have favored rail transportation in recent years.The linear motor-driven rail transit overcomes the inherent intermediate transmission mechanism of the rotary motor drive mode,which is environmentally friendly,low noise,economical,and has a minor turning radius.The linear motor is used in subways and maglev trains.At present,the linear motors used in rail transportation are linear induction motors or linear synchronous motors.The doubly-fed linear motor studied in this thesis are the new favorite of linear motors.The unique structure allows it to achieve asynchronous,synchronous and doubly-fed operation.Although it has not been used in practical projects,the unique performance has high potential research value.The thesis firstly introduces the structure characteristics and working principle of the doubly-fed linear motor.According to the evolution process of the doubly fed linear motor and the unified theory of the motor,the mathematical model of the doubly fed linear motor in the three-phase static coordinate system is deduced by analogy with the wound asynchronous motor,based on the principle of coordinate transformation,the mathematical model in the twophase rotating coordinate system is further deduced.Secondly,the stator flux linkage is selected as the orientation vector.The vector control strategy of the doubly-fed linear motor based on the stator flux orientation is introduced.The closed-loop control system is established with speed and reactive power as the outer loop and current as the inner loop.Based on the common voltage stator flux observation model,the improved flux observation model with flux amplitude and phase compensation is introduced.In the MATLAB/Simulink environment,the model is built and simulated.First,the size of the cut-off frequency in the improved flux linkage observation model was determined,then the speed response and reactive power response were simulated and verified.The simulation results indicated that the speed and reactive power response follows the command value and the simulation result is consistent with the theoretical calculation result.In addition,the reactive power response shows that the stator-side excitation current can be indirectly controlled by controlling the mover-side excitation current,thereby improving the stator-side power factor.At the same time,through comparison,the simulation results of the improved flux linkage observation model have smaller amplitude fluctuations,faster response and better observation effect.Finally,a motor experiment platform with DSP28335 as the controller is built,the design schemes of the main circuit,driving circuit,signal detection and conditioning circuit and control circuit are given and the selection basis of important device parameters in the circuit is analyze.The design flow chart of the controller software and the initial positioning method of the rotor are also given.The hardware and software of the experiment platform are tested jointly,and the experimental results verify the feasibility of the designed motor control system.