Research On Speed-sensorless Low Speed Performance Of Induction Motor Based On Full Order Flux Observer

Induction motor has the characteristics of low cost,simple structure,high reliability and excellent control performance,which has been widely used in various fields of national production.With the continuous development of economy and society,the accuracy and reliability of AC speed regulation are put forward higher requirements.The speed information as the key to improve the motor control accuracy is more prominent.At present,it is a common method to obtain speed information by installing speed sensor to the motor,but this method destroys the mechanical robustness of the motor,and increases the difficulty of the installation and maintenance of the system.At the same time,it also increases the cost and volume of the system;in addition,in some dusty and humid occasions,the accuracy of the speed sensor will be disturbed,which will affect the performance of the motor control.Compared with this method,it is low cost and high reliability to obtain the speed information by sampling the voltage and current information of the motor and using the motor model.Therefore,speed sensorless technology has been studied and concerned by many scholars.This paper first introduces the mathematical model of three-phase asynchronous motor in threephase static coordinate system,and deduces the mathematical model and state space equation of asynchronous motor in different coordinate systems according to the basic principle of coordinate transformation;then introduces the basic principle of field oriented control of asynchronous motor.According to the state space equation of induction motor,the full order flux observer and speed identification technology are introduced.In this paper,the transformation method of vector control coordinate transformation is briefly introduced,and then coordinate transformation is used as a tool to realize the equivalence from three-phase AC motor to DC motor for the purpose of imitating the control of DC motor,and the motor state equations in three coordinate systems in the transformation process are derived;then three open-loop control methods of direct field oriented control are introduced The characteristics of the three kinds of open-loop observers are compared.Aiming at the problems of the three kinds of open-loop observers,the full order flux observer and speed identification technology are introduced comprehensively.Then,the traditional feedback matrix of the observer is given.On the premise that the system stability is guaranteed by Lyapunov’s second method and Popov’s super stability theorem,the speed adaptive rate without speed sensor is derived.Aiming at the problem of poor performance of the observer with zero feedback matrix and pole multiple assignment in low-speed power generation state,the feedback gain matrix is improved according to the speed stability theorem to improve the stable operation of the motor in low-speed power generation state.This paper introduces three commonly used digital discretization methods,and analyzes the advantages and disadvantages of the three methods from the aspects of calculation amount and operation speed.A piecewise discretization method is proposed to realize the discretization of the observer,while taking into account the speed and amount of discrete computation.Finally,based on the full order flux observer and speed identification principle,with the help of Matlab /Simulink simulation tool,the speed sensorless asynchronous motor is simulated,and the feasibility of the improved error feedback matrix and the new speed adaptive rate at low speed is verified.The motor hardware experiment platform based on DSP + FPGA is built and verified.The experimental results show that the designed error feedback matrix and speed adaptive rate can ensure the stability of the motor at low speed.