Observer-based Speed Sensorless Induction Motor Direct Torque Control System The Speed Of Recognition

Direct torque control (DTC) system of induction motors has got wideattention with advantages such as novel thoughts, simple control schemeand excellent performance. Based on the DTC theory, a simulation modelof DTC system is built, and then the characteristics of DTC system andthe existing problems are detailedly analyzed.The speed estimation without speed sensor is an important trend ofmodern AC drive, and the speed-adaptive observer is the most commonlyused method in the speed sensorless technology. The speed-adaptiveobserver consists of a state-variable observer augmented with aspeed-adaptation loop. The observer gain and the speed-adaptation lawdetermine the properties of the observer. The observer gain is usuallyselected by using pole placement and ignoring the effect of thespeed-adaptation loop. After studying the existence of unstable regions ofobserver using the pole-placement technique in depth, it is known that thereason which causes instability problems of observer based onpole-placement technique is the system can't satisfy Lyapunov theoremof stability.With respect to the problem of the adaptive observer usingpole-placement technique, the adaptive observer that can enhance thesystem overall stability in full speed range is proposed. The gain matrix Gof the observer and the speed-adaptation law are obtained according tothe Lyapunov stability theory. When defining the Lyapunov function, apositive definite and symmetrical matrix variable P is introduced totransform the Lyapunov inequality into linear matrix inequalities (LMI),and then the matrix G and P can be obtained by using the LMI Toolbox ofMatlab. With the appropriate gain matrix G and speed-adaptation law, theLyapunov matrix inequality of the adaptive observer can hold over fullspeed region, which overcomes the disadvantage of the existence of theunstable regions and the inaccurate speed identification in the traditionalobserver.The proposed scheme is simulated in the Matlab6.5/Simulinkenvironment, and the simulation results indicate that the proposed observer can ensure the speed control system stable in its full speedrange.