Research On The Sensorless Control Of Induction Motor Based On Z-MRAS And The Problem Of Multiple Convergence Points

Induction motor is the most widely used traction motor in rail transit system.The use of speed sensor brings some problems,such as increased cost,complex structure,difficult maintenance and so on.Application of speed sensor-less control technology can effectively solve the above problems.Speed estimation is the core link of speed sensor-less control.The speed estimation method based on model reference adaptative algorithm has the advantages of simple structure,good low speed performance and fast dynamic response.It is a highly practical sensor-less control method.In this context,a new Z-MRAS speed estimation method is studied and its estimation accuracy,stability and parameter robustness are analyzed.Aiming at the problem of multiple convergence points caused by model nonlinearity,the position of convergence points,the stability of the system and the running state of the system are analyzed.An improved method of mixed speed identification is proposed to solve the problem that the speed cannot be effectively observed in the zero frequency locked state.Firstly,the mathematical model of induction motor is established,and the basic principle of vector control of induction motor with rotor field orientation is analyzed.Then,the basic theory of the model reference adaptive system,the design basis of the adaptive law,and the typical model reference adaptive speed identification method are introduced.Secondly,the control performance of Z-MRAS is studied.The structure of Z-MRAS speed identification system is analyzed and its adaptive law is derived by using Popov hyperstability theory.The closed-loop transfer function of the speed estimation system is obtained by small signal linearization.The stability of the system is analyzed by the root locus and characteristic root under different working conditions.The sensitivity coefficients of estimated speed to stator resistance and rotor resistance are established and the sensitivity of the system to the error of motor parameters at different speeds is analyzed.Thirdly,the influence of model nonlinearity on the speed convergence point is studied.Under the condition of inaccurate observation speed,the position of speed balance point is obtained according to the expression of reference model and adjustable model.Its convergence is preliminarily judged in the four quadrants of motor operation.By establishing the equation of state of the nonlinear system,the speed deviation point,zero-speed rotation speed and flux information are obtained,and the stability and convergence conditions are analyzed using the Lyapunov indirect method.Combined with the running state of asynchronous motor,the relationship between the actual torque output of zero frequency point and speed offset point motor,torque command and actual speed is analyzed.In order to solve the problem of zero frequency lock observation speed clamp,an improved method using direct feedforward compensation is proposed,and the above theory is verified by simulation.Finally,part of the experimental verification of the Z-MRAS speed identification method was completed on the 5.5k W asynchronous motor pair towing platform in the laboratory.