Study Of AC Asynchronous Motor Speed Sensorless Field-Oriented Control Based On DSP

With the application of field-oriented technique, the speed control of ACIM (Alternating Current Induction Motor) is becoming a good competitor of traditional DC (Direct Current) motor speed control system in the aspects of speed control and torque control. By eliminating speed sensor, the sensor-less control system of ACIM is supposed to be simpler, lower-cost and rugged, and accordingly is becoming a hot research subject recently. Under this circumstance, the sensor-less field-oriented system is studied in this paper.Firstly, the state-of-art and development trends of the AC variable speed drive system are introduced, and the concept of sensor-less field-oriented control system is followed. The objectives and main contents of the research are also presented. Secondly, the basic principle of the field-oriented control and coordinate transformations are presented. The mathematic models of induction motor in different reference frames are also covered. Then the field-oriented control principle is discussed.Thirdly, the speed estimation and rotor flux observation methods are studied by utilizing the theory of MRAS (Model Reference Adaptive System), which is based on the theory of superstability. The simulation results of the established model show that the MRAS-based field-oriented control system has good static and dynamic performance.Fourthly, a full-functional digital variable frequency drive system of ACIM is constructed based on DSP 56F8346, which is dedicated to motor control application, plus self-made hardware circuits. And experiments are conducted on the MRAS-based sensor-less control strategy. Software modules are coded for estimation of the rotor speed and flux, and SVPWM (space vector pulse width modulation) algorithm. Good experimental results are reached and it justifies the feasibility of the control strategy.Finally, the research work is concluded, and some suggestions for the next work are put forward.