ABSTRACT Dynamic mathematical model of asynchronous motor is a higher order、nonlinear、the strong coupling of multivariable system. Using coordinate transformation to change the three-phase stationary coordinate system into a two-phase synchronous rotating coordinate system, You can implement a decoupling of the stator current , to realize the decoupling control of flux and torque ,so as to achieve the effect of DC motor rotor field oriented control has brought essential advances in AC variable speed drive system. the starting point to solve the problem of sensorless control is to use detection of stator voltage and current easily detected physical quantities to replace the speed sensor . In this way, reducing costs, improving the control system simplicity and robustness. The key o