| Traditional cars consume non-renewable petroleum resources and emit harmful gases such as carbon oxides and nitrogen oxides into the air.With the emergence of energy and environment crisis,electric vehicles have become a research hotspot.Electric vehicles are mainly composed of vehicle control system,battery system,and electric drive system.Among them,the electric drive system is a part that directly converts electrical energy into mechanical energy and determines the performance of electric vehicles.This article studies the AC induction motor(ACIM),which is usually used in electric vehicles.In order to achieve closed-loop speed control,it is necessary to measure motor speed as feedback.In order to avoid problems such as reduced reliability,increased cost,difficult maintenance and limited installation caused by the installation of speed sensor,the technology of sensorless vector control has become a research hotspot.The speed estimation methods based on the motor model are affected by motor parameters,especially the rotor resistance that varies greatly during the operation of motor.Therefore,it is necessary to introduce online identification of rotor resistance into the sensorless control technology to reduce the effect of rotor resistance on motor speed identification and increase the accuracy of speed identification.The common methods for the identification of motor speed,offline identification of rotor resistance and online identification of rotor resistance are summarized.The advantages and disadvantages of these methods are analyzed and compared,and the methods to be studied in this paper are determined.The basic principles of vector control and coordinate transformation are studied.And the expressions of coordinate transformation are deduced.The mathematical models of ACIM in three-phase stationary coordinate system,two-phase stationary coordinate system and synchronous rotating coordinate system are deduced,which lay a theoretical foundation for the identification of motor speed and rotor resistance.The rotor resistance identification strategy based on the electromagnetic torque model reference adaptive system(MRAS)is studied.The torque expressions in different coordinate systems are deduced.The adaptive mechanism is determined using Popov hyperstability and the rotor resistance online identification is realized.Considering the influence of stator resistance on identification,a rotor resistance identification strategy based on reactive power MRAS is established.Since the stator resistance is not contained in the expression,its influence on the estimation result is avoided and the accuracy of the estimated rotor resistance at low speed is ensured.The speed identification strategy based on the Extended Kalman Filter(EKF)is studied,and the discrete state equation of ACIM in two-phase stationary coordinate system is deduced.Based on the iterative steps of EKF,a speed identification scheme is built to realize the sensorless vector control of ACIM.Rotor resistance identification is introduced into induction motor speed identification,which reduces the influence of rotor resistance variation on speed identification and improves the accuracy of speed identification.The simulation model is built in Simulink and simulation experiments are designed.The strategies of speed identification,rotor resistance identification and sensorless vector control based on rotor resistance identification are verified in this paper.The experimental platform for motor towing system is built using the development box of Texas Instruments.The effectiveness of the theory and the simulation is verified through experiments. |
