Research On Speed-sensorless System Based On MRAS For Asynchronous Motor

With the development of power electronics，the technology of Vector control ofasynchronous motor has improved rapidly. Vector control is developed based on the idea thatthe controlling means of induction motor can be equivalent to the DC motor, The inductionmotor mathematic model that is high nonlinear and complex coupling can be separated bycoordinate transformation theory, Stator current can be decomposed into excitation currentcomponent and the torque current component, Then the magnetic field and torque can beseparately controlled by controlling the two current components like separately excited DCmotor. But in actual system, mounting speed sensor will cause a serial of problems such asreducing the system robust, increasing system cost, can’t be used in hot or humid environmentand so on. For the advantage of simple structure, low cost, speed-senseless vector controlsystem is a hotspot aspect in modern AC drive. Among all speed-senseless technologies, theMRAS (Model Reference Adaptive System) technology draw people’s attitude for the highprecision and strong reliability.The theory of vector control is analyzed, and then the transformation principle andasynchronous motor mathematic model is illustrated in detail, the principle of Space VectorPWM are also given. And the Indirect Field Oriented Control System Based on RotorMagnetic Flux is designed. By modifying the speed estimation model, a Back-EMF basedMRAS model without pure integration is gained on the basis of analyzing of basic structureand principle of MRAS. On this basis, the model to estimate speed without sensor usingBEMF Based MRAS is designed. Adding this method in vector control, the speed-senselessvector control system using MRAS of asynchronous motor is designed.The hardware design and software design of the system is designed at first. The hardwaredesign has two parts, the control circuit and the power circuit. The TMS320F2812model DSPis used as the control circuit core, the control circuit includes the electric source circuits, theclock and reset circuits, the D/A circuits and the communication circuits. The power circuitincludes rectification circuits, covariant circuits, separation circuits, sensor circuits andprotective circuits. The software including main program and interrupt program, it is realizedby C language in CCS3.3, every function module of the control system is realized withmodule structural programming. The PWM method has an important effect on theperformance for induction motor vector control system, so the improvement is added to theSVPWM, and its performance is improved, and the SVPWM (Space Vector Pulse Width Modulation) programe using two-phase stationary reference volume as inputs is designed.At last, the simulation and experiment are taken. The emulate modulations of the systemare constituted on Matlab/Simulink, the simulation is highly realistic, and the results provethat the MRAS method can estimate speed efficiently, and the system is feasibility. At last, thesystem is brought about, the system hardware debug is carried, and the system operation isnormal, then the wave is recorded by experiments, wave is recorded by experiment, theresults prove that: the method to estimate speed without sensor using MRAS is feasibility; thesystem is stable, high-accuracy and strong anti interference capable.